3.8.2 Chillers

Chiller Name
Applicability	All chillers
Definition	A unique descriptor for each chiller
Units	Text, unique
Input Restrictions	User entry. Where applicable, this should match the tags that are used on the plans.
Baseline Rules	Chillers are only designated when the baseline system is of type 7 (VAV with reheat) or 8 (VAV with PFP Boxes) (see Table G3.1.1B).

Chiller Type

Applicability

All chillers

Definition

The type of chiller, either a vapor-compression chiller or an absorption chiller.

Vapor compression chillers operate on the reverse-Rankine cycle, using mechanical energy to compress the refrigerant, and include:

Reciprocating – uses pistons for compression
Screw – uses two counter rotating screws for compression
Scroll – uses two interlocking spirals or scrolls to perform the compression
Centrifugal – uses rotating impeller blades to compress the air
Absorption chillers – use heat to vaporize a working fluid (usually either ammonia or lithium bromide)
Single Effect Absorption – use a single generator & condenser
Double Effect Absorption – use two generators/concentrators and condensers, one at a lower temperature and the other at a higher temperature. It is more efficient than the single effect, but it must use a higher temperature heat source.

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

The baseline building chiller is based on the design capacity of the proposed design as follows from ASHRAE 90.1 Appendix G:
[table title="Type and Number of Chillers" id="type-and-number-of-chillers"]

Building Peak Cooling Load	Number and Type of Chillers (s)
$\leq$300 tons	1 water-cooled screw chiller
>300 tons, <600 tons	2 water-cooled screw chillers sized equally
$\geq$600 tons	2 water-cooled centrigugal chillers minimum with chillers added so that no chiller is larger than 800 tons, all sized equally

Number of Identical Chiller Units
Applicability	All chillers
Definition	The number of identical units for staging.
Units	None
Input Restrictions	As designed. Default is 1.
Baseline Rules	From [bookref id="type-and-number-of-chillers"] above, there is one chiller if the cooling load is 300 tons or less and two equally sized chillers for loads between 300 and 600 tons. For loads above 600 tons, two or more chillers of equal size are used, with no chiller larger than 800 tons.

Chiller Fuel
Applicability	All chillers
Definition	The fuel source for the chiller. The choices are: Electricity (for all vapor-compression chillers) Gas (Absorption units only, designated as direct-fired units) Oil (Absorption units only, designated as direct-fired units) Hot Water (Absorption units only, designated as indirect-fired units) Steam (Absorption units only, designated as indirect-fired units)
Units	List (see above)
Input Restrictions	As designed.
Baseline Rules	Electricity

Chiller Rated Capacity
Applicability	All chillers
Definition	The cooling capacity of a piece of heating equipment at rated conditions.
Units	Btu/h or tons
Input Restrictions	As designed. If unmet load hours are greater than 300, the chiller may have to be made larger.
Baseline Rules	Determine loads for baseline building and oversize by 15%.

Chiller Rated Efficiency
Applicability	All chillers
Definition	The Coefficient of Performance (COP) at ARI rated conditions.
Units	Ratio
Input Restrictions	As designed
Baseline Rules	With the ASHRAE Standard 90.1-2007 baseline, use the minimum values of efficiency from either Table 6.8.1C for various types of chillers or the values from Tables 6.8.1H, 6.8.1I or 6.8.1J for centrifugal chillers. With the ASHRAE Standard 90.1-2001 baseline, use the minimum values of efficiency from either Table 6.2.1C for various types of chillers, or the values from Tables 6.2.1H, 6. 2.1I or 6. 2.1J for centrifugal chillers.

Chiller Minimum Unloading Ratio

Applicability

All chillers

Definition

The minimum unloading capacity of a chiller expressed as a fraction of the rated capacity. Below this level the chiller must cycle to meet the load.

[table title="Default Minimum Unloading Ratios" id="default-minimum-unloading-ratios"]

Chiller Type	Default Unloading Ratio
Reciprocating	25%
Screw	15%
Centrifugal	10%
Scroll	25%
Single Effect Absorption	10%
Double Effect Absorption	10%

Units

Percent (%)

Input Restrictions

As designed. If the user does not employ the default values, supporting documentation is required.

Baseline Rules

Use defaults listed above.

Chiller Cooling Capacity Adjustment Curve

Applicability

All chillers

Definition

A curve or group of curves or other functions that represent the available total cooling capacity as a function of evaporator and condenser conditions and perhaps other operating conditions. The default curves are given as follows:

(6.8.2-1)

$$ Q_{available} = CAP \_ FT \times Q_{rated}$$

For air-cooled chillers:

(6.8.2-2)

$$ CAP \_FT = a + b \times t_{chws} + c \times \left. t_{chws}\right. ^2 + d \times t_{odb} + e \times \left. t_{odb}\right. ^2 + f \times t_{chws} \times t_{odb}$$

For water-cooled chillers:

(6.8.2-3)

$$ CAP \_FT = a + b \times t_{chws} + c \times \left. t_{chws} \right. ^2 + d \times t_{cws} + e \times \left. t_{cws} \right. ^2 + f \times t_{chws} \times t_{cws}$$

where

Q_available	Available cooling capacity at present evaporator and condenser conditions (MBH)
t_chws	The chilled water supply temperature (°F)
t_cws	The condenser water supply temperature (°F)
t_odb	The outside air dry-bulb temperature (°F)
Q_rated	Rated capacity at ARI conditions (MBH)

Note: If an air-cooled unit employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

[table title="Default Capacity Coefficients – Electric Air-Cooled Chillers" id="default-capacity-coefficients-–-electric-air---cooled-chillers"]

Coefficient	Scroll	Recip	Screw	Centrifugal
a	0.40070684	0.57617295	-0.09464899	N/A
b	0.01861548	0.02063133	0.03834070	N/A
c	0.00007199	0.00007769	-0.00009205	N/A
d	0.00177296	-0.00351183	0.00378007	N/A
e	-0.00002014	0.00000312	-0.00001375	N/A
f	-0.00008273	-0.00007865	-0.00015464	N/A

[table title="Default Capacity Coefficients – Electric Water-Cooled Chillers" id="default-capacity-coefficients-–-electric-water---cooled-chillers"]

Coefficient	Scroll	Recip	Screw	Centrifugal
a	0.36131454	0.58531422	0.33269598	-0.29861976
b	0.01855477	0.01539593	0.00729116	0.02996076
c	0.00003011	0.00007296	-0.00049938	-0.00080125
d	0.00093592	-0.00212462	0.01598983	0.01736268
e	-0.00001518	-0.00000715	-0.00028254	-0.00032606
f	-0.00005481	-0.00004597	0.00052346	0.00063139

[table title="Default Capacity Coefficients – Fuel- & Steam-Source Water-Cooled Chillers" id="default-capacity-coefficients-–-fuel--&-steam---source-water---cooled-chillers"]

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption	Engine Driven Chiller
a	0.723412	-0.816039	1.000000	0.573597
b	0.079006	-0.038707	0.000000	0.0186802
c	-0.000897	0.000450	0.000000	0.000000
d	-0.025285	0.071491	0.000000	-0.00465325
e	-0.000048	-0.000636	0.000000	0.000000
f	0.000276	0.000312	0.000000	0.000000

Units

Data structure

Input Restrictions

User may input curves, other appropriate functions, or use default curves. If the default curves are overridden, supporting documentation is required.

Baseline Rules

Use default curves.

Electric Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of an electric chiller as a function of evaporator conditions, condenser conditions and part-load ratio. The default curves are given as follows:

(6.8.2-4)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ EIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ air-cooled \enspace EIR\_FT = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 + \ d \times t_{odb} + \ e \times \left. t_{odb}\right. ^2+ \ f \times t_{chws} \times t_{odb}$$ $$ water-cooled \enspace EIR\_FT = a + b \times t_{chws}+ c \times \left. t_{chws}\right. ^2 + d \times t_{cws} + e \times \left. t_{cws}\right. ^2+ f \times t_{chws} \times t_{cws}$$ $$P_{operating} = P_{rated} \times EIR\_FPLR \times EIR\_FT \times CAP\_FT $$

where

PLR	Part load ratio based on available capacity (not rated capacity)
Q_operating	Present load on chiller (Btu/h)
Q_available	Chiller available capacity at present evaporator and condenser conditions (Btu/h)
t_chws	The chilled water supply temperature (°F)
t_cws	The condenser water supply temperature (°F)
t_odb	The outside air dry-bulb temperature (°F)
P_rated	Rated power draw at ARI conditions (kW)
P_operating	Power draw at specified operating conditions (kW)

Note: If an air-cooled chiller employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

[table title="Default Efficiency EIR-FT Coefficients – Air-Cooled Chillers" id="default-efficiency-eir---ft-coefficients-–-air---cooled-chillers"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.99006553	0.66534403	0.13545636	N/A
b	-0.00584144	-0.01383821	0.02292946	N/A
c	0.00016454	0.00014736	-0.00016107	N/A
d	-0.00661136	0.00712808	-0.00235396	N/A
e	0.00016808	0.00004571	0.00012991	N/A
f	-0.00022501	-0.00010326	-0.00018685	N/A

[table title="Default Efficiency EIR-FT Coefficients – Water-Cooled Chiller" id="default-efficiency-eir--ft-coefficients-–-water---cooled-chiller"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	1.00121431	0.46140041	0.66625403	0.51777196
b	-0.01026981	-0.00882156	0.00068584	-0.00400363
c	0.00016703	0.00008223	0.00028498	0.00002028
d	-0.00128136	0.00926607	-0.00341677	0.00698793
e	0.00014613	0.00005722	0.00025484	0.00008290
f	-0.00021959	-0.00011594	-0.00048195	-0.00015467

[table title="Default Efficiency EIR-FPLR Coefficients – Air-Cooled Chillers" id="default-efficiency-eir---fplr-coefficients-–-air---cooled-chillers"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.06369119	0.11443742	0.03648722	N/A
b	0.58488832	0.54593340	0.73474298	N/A
c	0.35280274	0.34229861	0.21994748	N/A

[table title="Default Efficiency EIR-FPLR Coefficients – Water-Cooled Chillers" id="default-efficiency-eir---fplr-coefficients-–-water---cooled-chillers"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.04411957	0.08144133	0.33018833	0.17149273
b	0.64036703	0.41927141	0.23554291	0.58820208
c	0.31955532	0.49939604	0.46070828	0.23737257

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation is required.

Baseline Rules

Use default curves.

Fuel and Steam Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of a fuel-fired or steam chiller as a function of evaporator conditions, condenser conditions, and part-load ratio. The default curves are given as follows:
Default Curves for Steam-Driven Single and Double Effect Absorption Chillers

(6.8.2-5)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ FIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ FIR\_FT = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 + \ d \times t_{cws} + \ e \times \left. t_{cws}\right. ^2+ \ f \times t_{chws} \times t_{cws}$$ $$Fuel_{partload} = Fuel_{rated} \times FIR\_FPLR \times FIR\_FT \times CAP\_FT $$

Default Curves for Direct-Fired Double Effect Absorption Chillers

(6.8.2-6)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ FIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ FIR\_FT1 = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 $$ $$ FIR\_FT2 = d + e \times t_{cws} + \ f \times \left. t_{cws}\right. ^2 $$ $$Fuel_{partload} = Fuel_{rated} \times FIR\_FPLR \times FIR\_FT1 \times FIR\_FT2 \times CAP\_FT $$

The default curves for engine driven chillers are the same format as those for the Steam-Driven Single and Double Effect Absorption Chillers but there are three sets of curves for different ranges of operation based on the engine speed.

where

PLR	Part load ratio based on available capacity (not rated capacity)
FIR-FPLR	A multiplier on the fuel input ratio (FIR) to account for part load conditions
FIR-FT	A multiplier on the fuel input ratio (FIR) to account for the chiller water supply temperature and the condenser water temperature
FIR-FT1	A multiplier on the fuel input ratio (FIR) to account for chilled water supply temperature
FIR-FT2	A multiplier on the fuel input ratio (FIR) to account for condenser water supply temperature
CAP-FT	A multiplier on the capacity of the chiller (see Equation (6.8.2-2))
Q_operating	Present load on chiller (in Btu/h)
Q_available	Chiller available capacity at present evaporator and condenser conditions (in Btu/h)
t_chws	The chilled water supply temperature (in °F)
t_cws	The condenser water supply temperature (in °F)
t_odb	The outside air dry-bulb temperature (°F)
Fuel_rated	Rated fuel consumption at ARI conditions (in Btu/h)
Fuel_partload	Fuel consumption at specified operating conditions (in Btu/h)

[table title="Default FIR-FPLR coefficients – Fuel- & Steam-Source Water-Cooled Absorption Chillers" id="default-fir---fplr-coefficients-–-fuel---&-steam---source-water---cooled-absorption-chillers"]

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption
a	0.098585	0.013994	0.13551150
b	0.583850	1.240449	0.61798084
c	0.560658	-0.914883	0.24651277
d	-0.243093	0.660441	0.00000000

[table title="Default FIR-FPLR coefficients – Engine Driven Chillers" id="default-fir---fplr-coefficients-–-engine-driven-chillers"]

Coefficient	%Speed$\leq$Min.	%Speed>Min. %Speed<60%	%Speed>60%
a	0.3802	1.14336	1.38861
b	2.3609	0.022889	-0.388614
c	0.0000	0.0000	0.0000
d	0.0000	0.0000	0.000

[table title="Default FIR-FT coefficients – Fuel- & Steam-Source Water-Cooled Absorption Chillers" id="default-fir---ft-coefficients-–-fuel---&-steam---source-water---cooled-absorption-chillers"]

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption
a	0.652273	1.658750	4.42871284
b	0.000000	0.000000	-0.13298607
c	0.000000	0.000000	0.00125331
d	-0.000545	-0.290000	0.86173749
e	0.000055	0.000250	-0.00708917
f	0.000000	0.000000	0.0010251

[table title="Default FIR-FT coefficients – Engine Driven Chillers" id="default-fir---ft-coefficients-–-engine-driven-chillers"]

Coefficient	%Speed$\leq$Min.	%Speed>Min. %Speed<60%	%Speed>60%
a	1.0881500	1.2362400	1.2362400
b	0.0141064	0.0168923	0.0168923
c	0.0000000	0.0000000	0.0000000
d	-0.00833912	-0.0115235	-0.0115235
e	0.0000000	0.0000000	0.0000000
f	0.0000000	0.0000000	0.0000000

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation is required.

Baseline Rules

Use default curves.

Chilled Water Supply Temperature
Applicability	All chillers
Definition	The chilled water supply temperature of the chiller at design conditions
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	The baseline chilled water supply temperature is set to 44°F.

Chilled Water Return Temperature
Applicability	All chillers
Definition	The chilled water return temperature setpoint
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	The baseline chilled water return temperature is set to 56°F.

Chilled Water Supply Temperature Reset
Applicability	All chillers
Definition	The reset schedule for the chilled water supply temperature. The chilled water setpoint may be reset based on demand or outdoor air temperature.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed. The default is [bookref id="chilled-water-supply-temperature-reset-schedule"].
Baseline Rules	The baseline chilled water supply temperature is reset from 44°F to 54°F based on outdoor air temperature as shown in the figure below. [figure title="Chilled Water Supply Temperature Reset Schedule" id="chilled-water-supply-temperature-reset-schedule"][/figure]

Condenser Type
Applicability	All chillers
Definition	The type of condenser for a chiller. The choices are: Air-Cooled Water-Cooled Evaporatively-Cooled Air-cooled chillers use air to cool the condenser coils. Water-cooled chillers use cold water to cool the condenser and additionally need either a cooling tower or a local source of cold water. Evaporatively-cooled chillers are similar to air-cooled chillers, except they use a water mist to cool the condenser coil which makes them more efficient.
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	The baseline chiller is always assumed to have a water-cooled condenser, although the chiller type will change depending on the design capacity. If the chiller size is less than 600 tons, the baseline chiller is a water-cooled screw; if the capacity is greater than or equal to 600 tons, the baseline chiller is a water-cooled centrifugal chiller.

Air-Cooled Condenser Power
Applicability	All chillers
Definition	The energy usage of the condenser fan(s) at design conditions on an air-cooled chiller. This unit should only be used for chillers composed of separate evaporator and condenser sections where the fan energy is not part of the chiller COP.
Units	Kilowatts (kW)
Input Restrictions	As designed. The user must enter data for remote air-cooled condensing units.
Baseline Rules	Not applicable, since all baseline chillers have water-cooled condensers.

90.1-2007

Chiller Name
Applicability	All chillers
Definition	A unique descriptor for each chiller
Units	Text, unique
Input Restrictions	User entry. Where applicable, this should match the tags that are used on the plans.
Baseline Rules	Chillers are only designated when the baseline system is of type 7 (VAV with reheat) or 8 (VAV with PFP Boxes) (see Table G3.1.1B).

Chiller Type

Applicability

All chillers

Definition

The type of chiller, either a vapor-compression chiller or an absorption chiller.

Vapor compression chillers operate on the reverse-Rankine cycle, using mechanical energy to compress the refrigerant, and include:

Reciprocating – uses pistons for compression
Screw – uses two counter rotating screws for compression
Scroll – uses two interlocking spirals or scrolls to perform the compression
Centrifugal – uses rotating impeller blades to compress the air
Absorption chillers – use heat to vaporize a working fluid (usually either ammonia or lithium bromide)
Single Effect Absorption – use a single generator & condenser
Double Effect Absorption – use two generators/concentrators and condensers, one at a lower temperature and the other at a higher temperature. It is more efficient than the single effect, but it must use a higher temperature heat source.

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

The baseline building chiller is based on the design capacity of the proposed design as follows from ASHRAE 90.1 Appendix G:
[table title="Type and Number of Chillers" id="type-and-number-of-chillers"]

Building Peak Cooling Load	Number and Type of Chillers (s)
$\leq$300 tons	1 water-cooled screw chiller
>300 tons, <600 tons	2 water-cooled screw chillers sized equally
$\geq$600 tons	2 water-cooled centrigugal chillers minimum with chillers added so that no chiller is larger than 800 tons, all sized equally

Number of Identical Chiller Units
Applicability	All chillers
Definition	The number of identical units for staging.
Units	None
Input Restrictions	As designed. Default is 1.
Baseline Rules	From [bookref id="type-and-number-of-chillers"] above, there is one chiller if the cooling load is 300 tons or less and two equally sized chillers for loads between 300 and 600 tons. For loads above 600 tons, two or more chillers of equal size are used, with no chiller larger than 800 tons.

Chiller Fuel
Applicability	All chillers
Definition	The fuel source for the chiller. The choices are: Electricity (for all vapor-compression chillers) Gas (Absorption units only, designated as direct-fired units) Oil (Absorption units only, designated as direct-fired units) Hot Water (Absorption units only, designated as indirect-fired units) Steam (Absorption units only, designated as indirect-fired units)
Units	List (see above)
Input Restrictions	As designed.
Baseline Rules	Electricity

Chiller Rated Capacity
Applicability	All chillers
Definition	The cooling capacity of a piece of heating equipment at rated conditions.
Units	Btu/h or tons
Input Restrictions	As designed. If unmet load hours are greater than 300, the chiller may have to be made larger.
Baseline Rules	Determine loads for baseline building and oversize by 15%.

Chiller Rated Efficiency
Applicability	All chillers
Definition	The Coefficient of Performance (COP) at ARI rated conditions.
Units	Ratio
Input Restrictions	As designed
Baseline Rules	With the ASHRAE Standard 90.1-2007 baseline, use the minimum values of efficiency from either Table 6.8.1C for various types of chillers or the values from Tables 6.8.1H, 6.8.1I or 6.8.1J for centrifugal chillers.

Chiller Minimum Unloading Ratio

Applicability

All chillers

Definition

The minimum unloading capacity of a chiller expressed as a fraction of the rated capacity. Below this level the chiller must cycle to meet the load.

[table title="Default Minimum Unloading Ratios" id="default-minimum-unloading-ratios"]

Chiller Type	Default Unloading Ratio
Reciprocating	25%
Screw	15%
Centrifugal	10%
Scroll	25%
Single Effect Absorption	10%
Double Effect Absorption	10%

Units

Percent (%)

Input Restrictions

As designed. If the user does not employ the default values, supporting documentation is required.

Baseline Rules

Use defaults listed above.

Chiller Cooling Capacity Adjustment Curve

Applicability

All chillers

Definition

A curve or group of curves or other functions that represent the available total cooling capacity as a function of evaporator and condenser conditions and perhaps other operating conditions. The default curves are given as follows:

(6.8.2-1)

$$ Q_{available} = CAP \_ FT \times Q_{rated}$$

For air-cooled chillers:

(6.8.2-2)

$$ CAP \_FT = a + b \times t_{chws} + c \times \left. t_{chws}\right. ^2 + d \times t_{odb} + e \times \left. t_{odb}\right. ^2 + f \times t_{chws} \times t_{odb}$$

For water-cooled chillers:

(6.8.2-3)

$$ CAP \_FT = a + b \times t_{chws} + c \times \left. t_{chws} \right. ^2 + d \times t_{cws} + e \times \left. t_{cws} \right. ^2 + f \times t_{chws} \times t_{cws}$$

where

Q_available	Available cooling capacity at present evaporator and condenser conditions (MBH)
t_chws	The chilled water supply temperature (°F)
t_cws	The condenser water supply temperature (°F)
t_odb	The outside air dry-bulb temperature (°F)
Q_rated	Rated capacity at ARI conditions (MBH)

Note: If an air-cooled unit employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

[table title="Default Capacity Coefficients – Electric Air-Cooled Chillers" id="default-capacity-coefficients-–-electric-air---cooled-chillers"]

Coefficient	Scroll	Recip	Screw	Centrifugal
a	0.40070684	0.57617295	-0.09464899	N/A
b	0.01861548	0.02063133	0.03834070	N/A
c	0.00007199	0.00007769	-0.00009205	N/A
d	0.00177296	-0.00351183	0.00378007	N/A
e	-0.00002014	0.00000312	-0.00001375	N/A
f	-0.00008273	-0.00007865	-0.00015464	N/A

[table title="Default Capacity Coefficients – Electric Water-Cooled Chillers" id="default-capacity-coefficients-–-electric-water---cooled-chillers"]

Coefficient	Scroll	Recip	Screw	Centrifugal
a	0.36131454	0.58531422	0.33269598	-0.29861976
b	0.01855477	0.01539593	0.00729116	0.02996076
c	0.00003011	0.00007296	-0.00049938	-0.00080125
d	0.00093592	-0.00212462	0.01598983	0.01736268
e	-0.00001518	-0.00000715	-0.00028254	-0.00032606
f	-0.00005481	-0.00004597	0.00052346	0.00063139

[table title="Default Capacity Coefficients – Fuel- & Steam-Source Water-Cooled Chillers" id="default-capacity-coefficients-–-fuel--&-steam---source-water---cooled-chillers"]

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption	Engine Driven Chiller
a	0.723412	-0.816039	1.000000	0.573597
b	0.079006	-0.038707	0.000000	0.0186802
c	-0.000897	0.000450	0.000000	0.000000
d	-0.025285	0.071491	0.000000	-0.00465325
e	-0.000048	-0.000636	0.000000	0.000000
f	0.000276	0.000312	0.000000	0.000000

Units

Data structure

Input Restrictions

User may input curves, other appropriate functions, or use default curves. If the default curves are overridden, supporting documentation is required.

Baseline Rules

Use default curves.

Electric Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of an electric chiller as a function of evaporator conditions, condenser conditions and part-load ratio. The default curves are given as follows:

(6.8.2-4)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ EIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ air-cooled \enspace EIR\_FT = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 + \ d \times t_{odb} + \ e \times \left. t_{odb}\right. ^2+ \ f \times t_{chws} \times t_{odb}$$ $$ water-cooled \enspace EIR\_FT = a + b \times t_{chws}+ c \times \left. t_{chws}\right. ^2 + d \times t_{cws} + e \times \left. t_{cws}\right. ^2+ f \times t_{chws} \times t_{cws}$$ $$P_{operating} = P_{rated} \times EIR\_FPLR \times EIR\_FT \times CAP\_FT $$

where

PLR	Part load ratio based on available capacity (not rated capacity)
Q_operating	Present load on chiller (Btu/h)
Q_available	Chiller available capacity at present evaporator and condenser conditions (Btu/h)
t_chws	The chilled water supply temperature (°F)
t_cws	The condenser water supply temperature (°F)
t_odb	The outside air dry-bulb temperature (°F)
P_rated	Rated power draw at ARI conditions (kW)
P_operating	Power draw at specified operating conditions (kW)

Note: If an air-cooled chiller employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

[table title="Default Efficiency EIR-FT Coefficients – Air-Cooled Chillers" id="default-efficiency-eir---ft-coefficients-–-air---cooled-chillers"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.99006553	0.66534403	0.13545636	N/A
b	-0.00584144	-0.01383821	0.02292946	N/A
c	0.00016454	0.00014736	-0.00016107	N/A
d	-0.00661136	0.00712808	-0.00235396	N/A
e	0.00016808	0.00004571	0.00012991	N/A
f	-0.00022501	-0.00010326	-0.00018685	N/A

[table title="Default Efficiency EIR-FT Coefficients – Water-Cooled Chiller" id="default-efficiency-eir--ft-coefficients-–-water---cooled-chiller"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	1.00121431	0.46140041	0.66625403	0.51777196
b	-0.01026981	-0.00882156	0.00068584	-0.00400363
c	0.00016703	0.00008223	0.00028498	0.00002028
d	-0.00128136	0.00926607	-0.00341677	0.00698793
e	0.00014613	0.00005722	0.00025484	0.00008290
f	-0.00021959	-0.00011594	-0.00048195	-0.00015467

[table title="Default Efficiency EIR-FPLR Coefficients – Air-Cooled Chillers" id="default-efficiency-eir---fplr-coefficients-–-air---cooled-chillers"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.06369119	0.11443742	0.03648722	N/A
b	0.58488832	0.54593340	0.73474298	N/A
c	0.35280274	0.34229861	0.21994748	N/A

[table title="Default Efficiency EIR-FPLR Coefficients – Water-Cooled Chillers" id="default-efficiency-eir---fplr-coefficients-–-water---cooled-chillers"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.04411957	0.08144133	0.33018833	0.17149273
b	0.64036703	0.41927141	0.23554291	0.58820208
c	0.31955532	0.49939604	0.46070828	0.23737257

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation is required.

Baseline Rules

Use default curves.

Fuel and Steam Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of a fuel-fired or steam chiller as a function of evaporator conditions, condenser conditions, and part-load ratio. The default curves are given as follows:
Default Curves for Steam-Driven Single and Double Effect Absorption Chillers

(6.8.2-5)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ FIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ FIR\_FT = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 + \ d \times t_{cws} + \ e \times \left. t_{cws}\right. ^2+ \ f \times t_{chws} \times t_{cws}$$ $$Fuel_{partload} = Fuel_{rated} \times FIR\_FPLR \times FIR\_FT \times CAP\_FT $$

Default Curves for Direct-Fired Double Effect Absorption Chillers

(6.8.2-6)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ FIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ FIR\_FT1 = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 $$ $$ FIR\_FT2 = d + e \times t_{cws} + \ f \times \left. t_{cws}\right. ^2 $$ $$Fuel_{partload} = Fuel_{rated} \times FIR\_FPLR \times FIR\_FT1 \times FIR\_FT2 \times CAP\_FT $$

The default curves for engine driven chillers are the same format as those for the Steam-Driven Single and Double Effect Absorption Chillers but there are three sets of curves for different ranges of operation based on the engine speed.

where

PLR	Part load ratio based on available capacity (not rated capacity)
FIR-FPLR	A multiplier on the fuel input ratio (FIR) to account for part load conditions
FIR-FT	A multiplier on the fuel input ratio (FIR) to account for the chiller water supply temperature and the condenser water temperature
FIR-FT1	A multiplier on the fuel input ratio (FIR) to account for chilled water supply temperature
FIR-FT2	A multiplier on the fuel input ratio (FIR) to account for condenser water supply temperature
CAP-FT	A multiplier on the capacity of the chiller (see Equation (6.8.2-2))
Q_operating	Present load on chiller (in Btu/h)
Q_available	Chiller available capacity at present evaporator and condenser conditions (in Btu/h)
t_chws	The chilled water supply temperature (in °F)
t_cws	The condenser water supply temperature (in °F)
t_odb	The outside air dry-bulb temperature (°F)
Fuel_rated	Rated fuel consumption at ARI conditions (in Btu/h)
Fuel_partload	Fuel consumption at specified operating conditions (in Btu/h)

[table title="Default FIR-FPLR coefficients – Fuel- & Steam-Source Water-Cooled Absorption Chillers" id="default-fir---fplr-coefficients-–-fuel---&-steam---source-water---cooled-absorption-chillers"]

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption
a	0.098585	0.013994	0.13551150
b	0.583850	1.240449	0.61798084
c	0.560658	-0.914883	0.24651277
d	-0.243093	0.660441	0.00000000

[table title="Default FIR-FPLR coefficients – Engine Driven Chillers" id="default-fir---fplr-coefficients-–-engine-driven-chillers"]

Coefficient	%Speed$\leq$Min.	%Speed>Min. %Speed<60%	%Speed>60%
a	0.3802	1.14336	1.38861
b	2.3609	0.022889	-0.388614
c	0.0000	0.0000	0.0000
d	0.0000	0.0000	0.000

[table title="Default FIR-FT coefficients – Fuel- & Steam-Source Water-Cooled Absorption Chillers" id="default-fir---ft-coefficients-–-fuel---&-steam---source-water---cooled-absorption-chillers"]

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption
a	0.652273	1.658750	4.42871284
b	0.000000	0.000000	-0.13298607
c	0.000000	0.000000	0.00125331
d	-0.000545	-0.290000	0.86173749
e	0.000055	0.000250	-0.00708917
f	0.000000	0.000000	0.0010251

[table title="Default FIR-FT coefficients – Engine Driven Chillers" id="default-fir---ft-coefficients-–-engine-driven-chillers"]

Coefficient	%Speed$\leq$Min.	%Speed>Min. %Speed<60%	%Speed>60%
a	1.0881500	1.2362400	1.2362400
b	0.0141064	0.0168923	0.0168923
c	0.0000000	0.0000000	0.0000000
d	-0.00833912	-0.0115235	-0.0115235
e	0.0000000	0.0000000	0.0000000
f	0.0000000	0.0000000	0.0000000

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation is required.

Baseline Rules

Use default curves.

Chilled Water Supply Temperature
Applicability	All chillers
Definition	The chilled water supply temperature of the chiller at design conditions
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	The baseline chilled water supply temperature is set to 44°F.

Chilled Water Return Temperature
Applicability	All chillers
Definition	The chilled water return temperature setpoint
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	The baseline chilled water return temperature is set to 56°F.

Chilled Water Supply Temperature Reset
Applicability	All chillers
Definition	The reset schedule for the chilled water supply temperature. The chilled water setpoint may be reset based on demand or outdoor air temperature.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed. The default is [bookref id="chilled-water-supply-temperature-reset-schedule"].
Baseline Rules	The baseline chilled water supply temperature is reset from 44°F to 54°F based on outdoor air temperature as shown in the figure below. [figure title="Chilled Water Supply Temperature Reset Schedule" id="chilled-water-supply-temperature-reset-schedule"][/figure]

Condenser Type
Applicability	All chillers
Definition	The type of condenser for a chiller. The choices are: Air-Cooled Water-Cooled Evaporatively-Cooled Air-cooled chillers use air to cool the condenser coils. Water-cooled chillers use cold water to cool the condenser and additionally need either a cooling tower or a local source of cold water. Evaporatively-cooled chillers are similar to air-cooled chillers, except they use a water mist to cool the condenser coil which makes them more efficient.
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	The baseline chiller is always assumed to have a water-cooled condenser, although the chiller type will change depending on the design capacity. If the chiller size is less than 600 tons, the baseline chiller is a water-cooled screw; if the capacity is greater than or equal to 600 tons, the baseline chiller is a water-cooled centrifugal chiller.

Air-Cooled Condenser Power
Applicability	All chillers
Definition	The energy usage of the condenser fan(s) at design conditions on an air-cooled chiller. This unit should only be used for chillers composed of separate evaporator and condenser sections where the fan energy is not part of the chiller COP.
Units	Kilowatts (kW)
Input Restrictions	As designed. The user must enter data for remote air-cooled condensing units.
Baseline Rules	Not applicable, since all baseline chillers have water-cooled condensers.

Chiller Name
Applicability	All chillers
Definition	A unique descriptor for each chiller
Units	Text, unique
Input Restrictions	User entry. Where applicable, this should match the tags that are used on the plans.
Baseline Rules	Chillers are only designated when the baseline system is of type 7 (VAV with reheat) or 8 (VAV with PFP Boxes) (see Table G3.1.1B).

Chiller Type

Applicability

All chillers

Definition

The type of chiller, either a vapor-compression chiller or an absorption chiller.

Vapor compression chillers operate on the reverse-Rankine cycle, using mechanical energy to compress the refrigerant, and include:

Reciprocating – uses pistons for compression
Screw – uses two counter rotating screws for compression
Scroll – uses two interlocking spirals or scrolls to perform the compression
Centrifugal – uses rotating impeller blades to compress the air
Absorption chillers – use heat to vaporize a working fluid (usually either ammonia or lithium bromide)
Single Effect Absorption – use a single generator & condenser
Double Effect Absorption – use two generators/concentrators and condensers, one at a lower temperature and the other at a higher temperature. It is more efficient than the single effect, but it must use a higher temperature heat source.

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

The baseline building chiller is based on the design capacity of the proposed design as follows from ASHRAE 90.1 Appendix G:

Table 6.8.2-1: Type and Number of Chillers

Building Peak Cooling Load	Number and Type of Chillers (s)
$\leq$300 tons	1 water-cooled screw chiller
>300 tons, <600 tons	2 water-cooled screw chillers sized equally
$\geq$600 tons	2 water-cooled centrigugal chillers minimum with chillers added so that no chiller is larger than 800 tons, all sized equally

Number of Identical Chiller Units
Applicability	All chillers
Definition	The number of identical units for staging.
Units	None
Input Restrictions	As designed. Default is 1.
Baseline Rules	From Table 7.8.2-1 above, there is one chiller if the cooling load is 300 tons or less and two equally sized chillers for loads between 300 and 600 tons. For loads above 600 tons, two or more chillers of equal size are used, with no chiller larger than 800 tons.

Chiller Fuel
Applicability	All chillers
Definition	The fuel source for the chiller. The choices are: Electricity (for all vapor-compression chillers) Gas (Absorption units only, designated as direct-fired units) Oil (Absorption units only, designated as direct-fired units) Hot Water (Absorption units only, designated as indirect-fired units) Steam (Absorption units only, designated as indirect-fired units)
Units	List (see above)
Input Restrictions	As designed.
Baseline Rules	Electricity

Chiller Rated Capacity
Applicability	All chillers
Definition	The cooling capacity of a piece of heating equipment at rated conditions.
Units	Btu/h or tons
Input Restrictions	As designed. If unmet load hours are greater than 300, the chiller may have to be made larger.
Baseline Rules	Determine loads for baseline building and oversize by 15%.

Chiller Rated Efficiency
Applicability	All chillers
Definition	The Coefficient of Performance (COP) at ARI rated conditions.
Units	Ratio
Input Restrictions	As designed
Baseline Rules	With the ASHRAE Standard 90.1-2007 baseline, use the minimum values of efficiency from either Table 6.8.1C for various types of chillers or the values from Tables 6.8.1H, 6.8.1I or 6.8.1J for centrifugal chillers.

Chiller Minimum Unloading Ratio

Applicability

All chillers

Definition

The minimum unloading capacity of a chiller expressed as a fraction of the rated capacity. Below this level the chiller must cycle to meet the load.

Table 6.8.2-2: Default Minimum Unloading Ratios

Chiller Type	Default Unloading Ratio
Reciprocating	25%
Screw	15%
Centrifugal	10%
Scroll	25%
Single Effect Absorption	10%
Double Effect Absorption	10%

Units

Percent (%)

Input Restrictions

As designed. If the user does not employ the default values, supporting documentation is required.

Baseline Rules

Use defaults listed above.

Chiller Cooling Capacity Adjustment Curve

Applicability

All chillers

Definition

A curve or group of curves or other functions that represent the available total cooling capacity as a function of evaporator and condenser conditions and perhaps other operating conditions. The default curves are given as follows:

(6.8.2-1)

$$ Q_{available} = CAP \_ FT \times Q_{rated}$$

For air-cooled chillers:

(6.8.2-2)

$$ CAP \_FT = a + b \times t_{chws} + c \times \left. t_{chws}\right. ^2 + d \times t_{odb} + e \times \left. t_{odb}\right. ^2 + f \times t_{chws} \times t_{odb}$$

For water-cooled chillers:

(6.8.2-3)

$$ CAP \_FT = a + b \times t_{chws} + c \times \left. t_{chws} \right. ^2 + d \times t_{cws} + e \times \left. t_{cws} \right. ^2 + f \times t_{chws} \times t_{cws}$$

where

Q_available	Available cooling capacity at present evaporator and condenser conditions (MBH)
t_chws	The chilled water supply temperature (°F)
t_cws	The condenser water supply temperature (°F)
t_odb	The outside air dry-bulb temperature (°F)
Q_rated	Rated capacity at ARI conditions (MBH)

Note: If an air-cooled unit employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

Table 6.8.2-3: Default Capacity Coefficients – Electric Air-Cooled Chillers

Coefficient	Scroll	Recip	Screw	Centrifugal
a	0.40070684	0.57617295	-0.09464899	N/A
b	0.01861548	0.02063133	0.03834070	N/A
c	0.00007199	0.00007769	-0.00009205	N/A
d	0.00177296	-0.00351183	0.00378007	N/A
e	-0.00002014	0.00000312	-0.00001375	N/A
f	-0.00008273	-0.00007865	-0.00015464	N/A

Table 6.8.2-4: Default Capacity Coefficients – Electric Water-Cooled Chillers

Coefficient	Scroll	Recip	Screw	Centrifugal
a	0.36131454	0.58531422	0.33269598	-0.29861976
b	0.01855477	0.01539593	0.00729116	0.02996076
c	0.00003011	0.00007296	-0.00049938	-0.00080125
d	0.00093592	-0.00212462	0.01598983	0.01736268
e	-0.00001518	-0.00000715	-0.00028254	-0.00032606
f	-0.00005481	-0.00004597	0.00052346	0.00063139

Table 6.8.2-5: Default Capacity Coefficients – Fuel- & Steam-Source Water-Cooled Chillers

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption	Engine Driven Chiller
a	0.723412	-0.816039	1.000000	0.573597
b	0.079006	-0.038707	0.000000	0.0186802
c	-0.000897	0.000450	0.000000	0.000000
d	-0.025285	0.071491	0.000000	-0.00465325
e	-0.000048	-0.000636	0.000000	0.000000
f	0.000276	0.000312	0.000000	0.000000

Units

Data structure

Input Restrictions

User may input curves, other appropriate functions, or use default curves. If the default curves are overridden, supporting documentation is required.

Baseline Rules

Use default curves.

Electric Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of an electric chiller as a function of evaporator conditions, condenser conditions and part-load ratio. The default curves are given as follows:

(6.8.2-4)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ EIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ air-cooled \enspace EIR\_FT = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 + \ d \times t_{odb} + \ e \times \left. t_{odb}\right. ^2+ \ f \times t_{chws} \times t_{odb}$$ $$ water-cooled \enspace EIR\_FT = a + b \times t_{chws}+ c \times \left. t_{chws}\right. ^2 + d \times t_{cws} + e \times \left. t_{cws}\right. ^2+ f \times t_{chws} \times t_{cws}$$ $$P_{operating} = P_{rated} \times EIR\_FPLR \times EIR\_FT \times CAP\_FT $$

where

PLR	Part load ratio based on available capacity (not rated capacity)
Q_operating	Present load on chiller (Btu/h)
Q_available	Chiller available capacity at present evaporator and condenser conditions (Btu/h)
t_chws	The chilled water supply temperature (°F)
t_cws	The condenser water supply temperature (°F)
t_odb	The outside air dry-bulb temperature (°F)
P_rated	Rated power draw at ARI conditions (kW)
P_operating	Power draw at specified operating conditions (kW)

Note: If an air-cooled chiller employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

Table 6.8.2-6: Default Efficiency EIR-FT Coefficients – Air-Cooled Chillers

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.99006553	0.66534403	0.13545636	N/A
b	-0.00584144	-0.01383821	0.02292946	N/A
c	0.00016454	0.00014736	-0.00016107	N/A
d	-0.00661136	0.00712808	-0.00235396	N/A
e	0.00016808	0.00004571	0.00012991	N/A
f	-0.00022501	-0.00010326	-0.00018685	N/A

Table 6.8.2-7: Default Efficiency EIR-FT Coefficients – Water-Cooled Chiller

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	1.00121431	0.46140041	0.66625403	0.51777196
b	-0.01026981	-0.00882156	0.00068584	-0.00400363
c	0.00016703	0.00008223	0.00028498	0.00002028
d	-0.00128136	0.00926607	-0.00341677	0.00698793
e	0.00014613	0.00005722	0.00025484	0.00008290
f	-0.00021959	-0.00011594	-0.00048195	-0.00015467

Table 6.8.2-8: Default Efficiency EIR-FPLR Coefficients – Air-Cooled Chillers

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.06369119	0.11443742	0.03648722	N/A
b	0.58488832	0.54593340	0.73474298	N/A
c	0.35280274	0.34229861	0.21994748	N/A

Table 6.8.2-9: Default Efficiency EIR-FPLR Coefficients – Water-Cooled Chillers

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.04411957	0.08144133	0.33018833	0.17149273
b	0.64036703	0.41927141	0.23554291	0.58820208
c	0.31955532	0.49939604	0.46070828	0.23737257

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation is required.

Baseline Rules

Use default curves.

Fuel and Steam Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of a fuel-fired or steam chiller as a function of evaporator conditions, condenser conditions, and part-load ratio. The default curves are given as follows:
Default Curves for Steam-Driven Single and Double Effect Absorption Chillers

(6.8.2-5)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ FIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ FIR\_FT = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 + \ d \times t_{cws} + \ e \times \left. t_{cws}\right. ^2+ \ f \times t_{chws} \times t_{cws}$$ $$Fuel_{partload} = Fuel_{rated} \times FIR\_FPLR \times FIR\_FT \times CAP\_FT $$

Default Curves for Direct-Fired Double Effect Absorption Chillers

(6.8.2-6)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ FIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ FIR\_FT1 = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 $$ $$ FIR\_FT2 = d + e \times t_{cws} + \ f \times \left. t_{cws}\right. ^2 $$ $$Fuel_{partload} = Fuel_{rated} \times FIR\_FPLR \times FIR\_FT1 \times FIR\_FT2 \times CAP\_FT $$

The default curves for engine driven chillers are the same format as those for the Steam-Driven Single and Double Effect Absorption Chillers but there are three sets of curves for different ranges of operation based on the engine speed.

where

PLR	Part load ratio based on available capacity (not rated capacity)
FIR-FPLR	A multiplier on the fuel input ratio (FIR) to account for part load conditions
FIR-FT	A multiplier on the fuel input ratio (FIR) to account for the chiller water supply temperature and the condenser water temperature
FIR-FT1	A multiplier on the fuel input ratio (FIR) to account for chilled water supply temperature
FIR-FT2	A multiplier on the fuel input ratio (FIR) to account for condenser water supply temperature
CAP-FT	A multiplier on the capacity of the chiller (see Equation (6.8.2-2))
Q_operating	Present load on chiller (in Btu/h)
Q_available	Chiller available capacity at present evaporator and condenser conditions (in Btu/h)
t_chws	The chilled water supply temperature (in °F)
t_cws	The condenser water supply temperature (in °F)
t_odb	The outside air dry-bulb temperature (°F)
Fuel_rated	Rated fuel consumption at ARI conditions (in Btu/h)
Fuel_partload	Fuel consumption at specified operating conditions (in Btu/h)

Table 6.8.2-10: Default FIR-FPLR coefficients – Fuel- & Steam-Source Water-Cooled Absorption Chillers

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption
a	0.098585	0.013994	0.13551150
b	0.583850	1.240449	0.61798084
c	0.560658	-0.914883	0.24651277
d	-0.243093	0.660441	0.00000000

Table 6.8.2-11: Default FIR-FPLR coefficients – Engine Driven Chillers

Coefficient	%Speed$\leq$Min.	%Speed>Min. %Speed<60%	%Speed>60%
a	0.3802	1.14336	1.38861
b	2.3609	0.022889	-0.388614
c	0.0000	0.0000	0.0000
d	0.0000	0.0000	0.000

Table 6.8.2-12: Default FIR-FT coefficients – Fuel- & Steam-Source Water-Cooled Absorption Chillers

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption
a	0.652273	1.658750	4.42871284
b	0.000000	0.000000	-0.13298607
c	0.000000	0.000000	0.00125331
d	-0.000545	-0.290000	0.86173749
e	0.000055	0.000250	-0.00708917
f	0.000000	0.000000	0.0010251

Table 6.8.2-13: Default FIR-FT coefficients – Engine Driven Chillers

Coefficient	%Speed$\leq$Min.	%Speed>Min. %Speed<60%	%Speed>60%
a	1.0881500	1.2362400	1.2362400
b	0.0141064	0.0168923	0.0168923
c	0.0000000	0.0000000	0.0000000
d	-0.00833912	-0.0115235	-0.0115235
e	0.0000000	0.0000000	0.0000000
f	0.0000000	0.0000000	0.0000000

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation is required.

Baseline Rules

Use default curves.

Chilled Water Supply Temperature
Applicability	All chillers
Definition	The chilled water supply temperature of the chiller at design conditions
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	The baseline chilled water supply temperature is set to 44°F.

Chilled Water Return Temperature
Applicability	All chillers
Definition	The chilled water return temperature setpoint
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	The baseline chilled water return temperature is set to 56°F.

Chilled Water Supply Temperature Reset
Applicability	All chillers
Definition	The reset schedule for the chilled water supply temperature. The chilled water setpoint may be reset based on demand or outdoor air temperature.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed. The default is Figure 6.8.2-1.
Baseline Rules	The baseline chilled water supply temperature is reset from 44°F to 54°F based on outdoor air temperature as shown in the figure below. Figure 6.8.2-1: Chilled Water Supply Temperature Reset Schedule

Condenser Type
Applicability	All chillers
Definition	The type of condenser for a chiller. The choices are: Air-Cooled Water-Cooled Evaporatively-Cooled Air-cooled chillers use air to cool the condenser coils. Water-cooled chillers use cold water to cool the condenser and additionally need either a cooling tower or a local source of cold water. Evaporatively-cooled chillers are similar to air-cooled chillers, except they use a water mist to cool the condenser coil which makes them more efficient.
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	The baseline chiller is always assumed to have a water-cooled condenser, although the chiller type will change depending on the design capacity. If the chiller size is less than 600 tons, the baseline chiller is a water-cooled screw; if the capacity is greater than or equal to 600 tons, the baseline chiller is a water-cooled centrifugal chiller.

Air-Cooled Condenser Power
Applicability	All chillers
Definition	The energy usage of the condenser fan(s) at design conditions on an air-cooled chiller. This unit should only be used for chillers composed of separate evaporator and condenser sections where the fan energy is not part of the chiller COP.
Units	Kilowatts (kW)
Input Restrictions	As designed. The user must enter data for remote air-cooled condensing units.
Baseline Rules	Not applicable, since all baseline chillers have water-cooled condensers.

Chiller Name
Applicability	All chillers
Definition	A unique descriptor for each chiller
Units	Text, unique
Input Restrictions	User entry. Where applicable, this should match the tags that are used on the plans.
Baseline Rules	Baseline HVAC systems 7, 8, 11, 12, and 13 have chillers.

Chiller Type

Applicability

All chillers

Definition

The type of chiller, either a vapor-compression chiller or an absorption chiller.

Vapor compression chillers operate on the reverse-Rankine cycle, using mechanical energy to compress the refrigerant, and include:

Positive displacement – includes reciprocating (piston-style), scroll and screw compressors
Centrifugal – uses rotating impeller blades to compress the refrigerant and impart velocity
Single Effect Absorption – use a single generator & condenser
Double Effect Absorption – use two generators/concentrators and condensers, one at a lower temperature and the other at a higher temperature. It is more efficient than the single effect, but it must use a higher temperature heat source.
Double Effect Absorption, Indirect-Fired
Gas Engine Driven Chiller

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

The baseline building chiller is based on the baseline building peak cooling load, as follows:

Table 3.8.2-1: Chiller Type

Building Peak Cooling Load	Number and Type of Chillers (s)
≤300 tons	One water-cooled screw chiller
>300 tons, <600 tons	Two water-cooled screw chillers sized equally
≥600 tons	A minimum of two (2) water-cooled centrifugal chillers minimum with chillers added so that no chiller is larger than 800 tons, all sized equally

Number of Identical Chiller Units
Applicability	All chillers
Definition	The number of identical units for staging.
Units	Unitless integer
Input Restrictions	As designed. Default is 1.
Baseline Rules	There is one chiller if the cooling load is 300 tons or less and two equally sized chillers for loads between 300 and 600 tons. For loads above 600 tons, two or more chillers of equal size are used, with no chiller larger than 800 tons. See Table 3.8.2-1.

Chiller Fuel

Applicability

All chillers

Definition

The fuel source for the chiller. The choices are:

Electricity (for all vapor-compression chillers)
Gas (absorption units only, designated as direct-fired units)
Oil (absorption units only, designated as direct-fired units)
Hot Water (absorption units only, designated as indirect-fired units)
Steam (Absorption units only, designated as indirect-fired units)

Units

List (see above)

This input is restricted, based on the choice of Chiller Type, according to the following rules:

Table 3.8.2-2: Chiller Fuel

	Electricity [SG1]	Gas/Oil	Hot Water	Steam
Reciprocating	Allowed
Scroll	Allowed
Screw	Allowed
Centrifugal	Allowed
Single Effect Absorption		Allowed	Allowed	Allowed
Direct Fired Double Effect Absorption		Allowed	Allowed	Allowed
Indirect Fired Absorption		Allowed	Allowed	Allowed

Input Restrictions

As designed.

Baseline Rules

Electricity

Chiller Rated Capacity
Applicability	All chillers
Definition	The cooling capacity of a piece of heating equipment at rated conditions.
Units	Btu/h or tons
Input Restrictions	As designed. If unmet load hours are greater than 300, the chiller may have to be made larger.
Baseline Rules	Determine loads for baseline building and oversize by 15%.

Chiller Rated Efficiency

Applicability

All chillers

Definition

The efficiency of the chiller expressed as EER for air cooled chillers, kW/ton for water cooled, positive displacement chillers, and COP for fuel-fired and heat driven chillers. COP is also sometimes used for electric chillers. The applicable test procedure is AHRI Standard 550/590. The test conditions for the full load (FL) rating are summarized below:

44°F leaving chilled-fluid temperature
2.4 gpm/ton evaporator fluid flow
85°F entering condenser-fluid temperature
3.0 gpm/ton condenser-fluid flow

Chillers are also rated at part load conditions known as IPLV (integrated part load value). The IPLV is the weighted average of the chiller efficiency at 100%, 75%, 50% and 25%. The corresponding weights for these part-load conditions are are 17%, 39%, 33%, and 11%.

Units

kW/ton, EER or COP, depending on chiller type

Input Restrictions

As designed, but chillers must meet minimum efficiency standards

Baseline Rules

The baseline chiller efficiencies are as follows:

Table 3.8.2-3: Baseline Chiller Rated Efficiency

Type	Size	FL	IPLV	Test Procedure
Screw	< 75 tons	≤ 0.75	≤ 0.60	ARI 550/590
	≥ 75 tons and < 150 tons	≤ 0.72	≤ 0.56
	≥ 150 tons and < 300 tons	≤ 0.66	≤ 0.54
	≥ 300 tons and < 600 tons	≤ 0.61	≤ 0.52
	≥ 600 tons	≤ 0.56	≤ 0.50
Centrifugal	< 150 tons	≤ 0.61	≤ 0.55
	≥ 150 tons and < 300 tons	≤ 0.61	≤ 0.55
	≥ 300 tons and < 400 tons	≤ 0.56	≤ 0.52
	≥ 400 tons and < 600 tons	≤ 0.56	≤ 0.50
	≥ 600 tons	≤ 0.56	≤ 0.50
FL = Full Load IPLV = Integrated Part Load Value

Chiller Minimum Unloading Ratio

Applicability

All chillers

Definition

The minimum unloading capacity of a chiller expressed as a fraction of the rated capacity. Below this level the chiller must cycle to meet the load. The following are default values for various types of chillers

Table 3.8.2-4: Baseline Chiller Minimum Unloading Ratio

Chiller Type	Default Unloading Ratio
Reciprocating	25%
Screw	15%
Centrifugal	10%
Scroll	25%
Single Effect Absorption	10%
Double Effect Absorption	10%

Units

Percent (%)

Input Restrictions

As designed. If the user does not employ the default values, supporting documentation is required.

Baseline Rules

The baseline HVAC chiller will be either a screw or centrifugal. Use the defaults for these chiller types from the above table: 15% for screw and 10% for centrifugal.

Chiller Cooling Capacity Adjustment Curve

Applicability

All chillers

Definition

A curve or group of curves or other functions that represent the available total cooling capacity as a function of evaporator and condenser conditions and perhaps other operating conditions. The default curves are given as follows:

(Equation 3.8.2-1)

$$Q_{available} = CAP\_FT \times Q_{rated}$$

For air-cooled chillers:

(Equation 3.8.2-2)

$$CAP\_FT = a + b \cdot t_{chws} + c \cdot t_{chws}^{2} + d \cdot t_{odb} + e \cdot t_{odb}^{2} +f \cdot t_{chws} \cdot t_{odb}$$

For water-cooled chillers:

(Equation 3.8.2-3)

$$CAP\_FT = a + b \cdot t_{chws} + c \cdot t_{chws}^{2} + d \cdot t_{cws} + e \cdot t_{cws}^{2} +f \cdot t_{chws} \cdot t_{cws}$$

where

Q_available	Available cooling capacity at present evaporator and condenser conditions (MBH)
t_chws	The chilled water supply temperature (°F)
t_cws	The condenser water supply temperature (°F)
t_odb	The outside air dry-bulb temperature (°F)
Q_rated	Rated capacity at ARI conditions (MBH)
a, b, c, d, e, f	Default coefficients are selected from Appendix H

Note: If an air-cooled unit employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

Units

Data structure

Input Restrictions

User may input curves, other appropriate functions, or use default curves. If the default curves are overridden, supporting documentation is required.

Baseline Rules

Use default equations and coefficients for the baseline chillers..

Electric Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of an electric chiller as a function of evaporator conditions, condenser conditions and part-load ratio. Note that for variable-speed chillers, the part-load cooling efficiency curve is a function of both part-load ratio and leaving condenser water temperature. The default curves are given as follows:

(Equation 3.8.2-4)

$$PLR = \frac{Q_{operating}}{Q_{available}(t_{chws},t_{cws/odb})}$$

$$EIR\_FPLR = a + b \cdot PLR + c \cdot PLR^{2}$$

Variable speed

$$EIR\_FPLR = a + b \cdot PLR + c \cdot PLR^{2} + d \cdot t_{cws} + e \cdot t_{cws}^{2} + f \cdot PLR \cdot t_{cws} + g \cdot PLR^{3} + h \cdot t_{cws}^{3} + i \cdot PLR^{2} \cdot t_{cws} + j \cdot PLR \cdot t_{cws}^{2}$$

Air cooled

$$EIR\_FT = a + b \cdot t_{chws} + c \cdot t_{chws}^{2} + d \cdot t_{odb} + e \cdot t_{odb}^{2} + f \cdot t_{chws}\cdot t_{odb} $$

Water cooled

$$EIR\_FT = a + b \cdot t_{chws} + c \cdot t_{chws}^{2} + d \cdot t_{cws} + e \cdot t_{cws}^{2} + f \cdot t_{chws}\cdot t_{cws} $$

Where

PLR	Part load ratio based on available capacity (not rated capacity)
Q_operating	Present load on chiller (Btu/h)
Q_available	Chiller available capacity at present evaporator and condenser conditions (Btu/h)
t_chws	The chilled water supply temperature (°F)
t_cws	The condenser water supply temperature (°F)
t_odb	The outside air dry-bulb temperature (°F)
P_rated	Rated power draw at ARI conditions (kW)
P_operating	Power draw at specified operating conditions (kW)
a, b, c, d, e, f	Coefficients selected from Appendix H

Note: If an air-cooled chiller employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation is required.

Baseline Rules

Use default equations and coefficients for the baseline HVAC chillers.

Fuel and Steam Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of a fuel-fired or steam chiller as a function of evaporator conditions, condenser conditions, and part-load ratio. The default curves are given as follows:

Default Curves for Steam-Driven Single and Double Effect Absorption Chillers

(Equation 3.8.2-5)

$$PLR = \frac{Q_{operating}}{Q_{available}(t_{chws},t_{cws/odb})}$$

$$FIR\_FPLR = a + b \cdot PLR + c \cdot PLR^{2}$$

$$FIR\_FT = a + b \cdot t_{chws} + c \cdot t_{chws}^{2} + d \cdot t_{cws} + e \cdot t_{cws}^{2} + f \cdot t_{chws} \cdot t_{cws}$$

Default Curves for Direct-Fired Double Effect Absorption Chillers

(Equation 3.8.2-6)

$$PLR = \frac{Q_{operating}}{Q_{available}(t_{chws},t_{cws/odb})}$$

$$FIR\_FPLR = a + b \cdot PLR + c \cdot PLR^{2}$$

$$FIR\_FT1 = a + b \cdot t_{chws} + c \cdot t_{chws}^{2}$$

$$FIR\_FT2 = d + e \cdot t_{cws} + f \cdot t_{cws}^{2}$$

$$Fuel_{partload} = Fuel_{rated} \cdot FIR\_FPLR \cdot FIR1\_FT1 \cdot FIR1\_FT2 \cdot CAP\_FT$$

The default curves for engine driven chillers are the same format as those for the Steam-Driven Single and Double Effect Absorption Chillers but there are three sets of curves for different ranges of operation based on the engine speed.

where

PLR	Part load ratio based on available capacity (not rated capacity)
FIR-FPLR	A multiplier on the fuel input ratio (FIR) to account for part load conditions
FIR-FT	A multiplier on the fuel input ratio (FIR) to account for the chiller water supply temperature and the condenser water temperature
FIR-FT1	A multiplier on the fuel input ratio (FIR) to account for chilled water supply temperature
FIR-FT2	A multiplier on the fuel input ratio (FIR) to account for condenser water supply temperature
CAP-FT	A multiplier on the capacity of the chiller (see Equation (Equation 3.8.2-2))
Q_operating	Present load on chiller (in Btu/h)
Q_available	Chiller available capacity at present evaporator and condenser conditions (in Btu/h)
t_chws	The chilled water supply temperature (in °F) (For air cooled chillers, the permitted range is 40 °F to 54 °F.)
t_cws	The condenser water supply temperature (in °F)
t_odb	The outside air dry-bulb temperature (°F) (For air cooled chillers, the permitted range is 40 °F to 115 °F.)
Fuel_rated	Rated fuel consumption at ARI conditions (in Btu/h)
Fuel_partload	Fuel consumption at specified operating conditions (in Btu/h)
a, b, c, d, e, f	Default coefficients are selected from Appendix H

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation is required.

Baseline Rules

Not applicable. The baseline HVAC system has electric chillers.

Chilled Water Supply Temperature
Applicability	All chillers
Definition	The chilled water supply temperature of the chiller at design conditions
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	The baseline chilled water supply temperature is set to 44°F.

Chilled Water Return Temperature
Applicability	All chillers
Definition	The chilled water return temperature setpoint
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Rules	The baseline chilled water return temperature is set to 56°F.

Chilled Supply Temperature Control Type
Applicability	All chillers
Definition	The method by which the chilled water setpoint temperature is reset. The chilled water setpoint may be reset based on demand or outdoor air temperature.
Units	List: demand or outdoor air temperature
Input Restrictions	As designed
Baseline Rules	Outdoor air temperature

Chilled Water Supply Temperature Reset
Applicability	All chillers
Definition	The reset schedule for the chilled water supply temperature. The chilled water setpoint may be reset based on demand or outdoor air temperature.
Units	Data structure
Input Restrictions	As designed. The default to reset based on outdoor air temperature as follows: 44°F at OAT 80°F and above 54°F at OAT 60°F and below Ramped linearly between 44°F and 54°F at temperatures between 80°F and 60°F
Baseline Rules	The baseline chilled water supply temperature reset uses the defaults. However, if the baseline chilled-water system serves a computer room HVAC system, the supply chilled-water temperature shall be reset higher based on the HVAC system requiring the most cooling; i.e., the chilled-water setpoint is reset higher until one cooling coil valve is nearly wide open. The maximum reset chilled-water supply temperature shall be 54°F. Temperature reset is not required for systems served by purchased chilled water.

Condenser Type
Applicability	All chillers
Definition	The type of condenser for a chiller. The choices are: Air-Cooled Water-Cooled Evaporatively-Cooled Air-cooled chillers use air to cool the condenser coils. Water-cooled chillers use cold water to cool the condenser and additionally need either a cooling tower or a local source of cold water. Evaporatively-cooled chillers are similar to air-cooled chillers, except they use a water mist to cool the condenser coil which makes them more efficient.
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	The baseline chiller is always assumed to have a water-cooled condenser, although the chiller type will change depending on the design capacity.

Air-Cooled Condenser Power
Applicability	All chillers with air-cooled condensers where fan energy is not part of the COP.
Definition	The energy usage of the condenser fan(s) at design conditions on an air-cooled chiller. This unit should only be used for chillers composed of separate evaporator and condenser sections where the fan energy is not part of the chiller COP.
Units	Kilowatts (kW)
Input Restrictions	As designed. The user must enter data for remote air-cooled condensing units.
Baseline Rules	Not applicable, since all baseline chillers have water-cooled condensers.

90.1-2019

Chiller Name
Applicability	All chillers
Definition	Unique descriptor for each chiller
Units	Text, unique
Input Restrictions	User entry. Where applicable, this should match the tags that are used on the plans.
Baseline Building	Chillers are only designated when the baseline system is of type 7 (VAV with reheat), 8 (VAV with PFP boxes) 11, 12, and 13

Chiller Type

Applicability

All chillers

Definition

The type of chiller, either a vapor-compression chiller or an absorption chiller.

Vapor compression chillers operate on the reverse-Rankine cycle, using mechanical energy to compress the refrigerant, and include:

· Positive displacement: Includes reciprocating (piston-style), scroll and screw compressors.

· Centrifugal: Uses rotating impeller blades to compress the refrigerant and impart velocity.

· Single effect absorption: Uses a single generator and condenser.

· Double effect absorption: Uses two generators/concentrators and condensers, one at a lower temperature and the other at a higher temperature. It is more efficient than the single effect, but it must use a higher temperature heat source.

· Double effect absorption, indirect-fired.

· Gas engine driven chiller.

· Positive displacement: Includes reciprocating (piston-style), scroll and screw compressors.

Units

List (see above)

Input Restrictions

As designed

Baseline Building

The baseline building will use electric chillers regardless of the cooling energy source. The baseline building chiller is based on the baseline building peak cooling load, as follows:

Table 81. Type and Number Chillers

Building Peak Cooling Load	Number and Type of Chiller(s)
<= 300 tons	1 water cooled screw chiller
>300 tons, < 600 tons	2 water cooled screw chillers, sized equally
>= 600 tons	A minimum of two (2) water cooled centrifugal chillers, sized to keep the unit size below 800 tons, all sized equally.

Number of Identical Chiller Units
Applicability	All chillers
Definition	The number of identical units for staging
Units	None
Input Restrictions	As designed. Default is 1
Baseline Building	From Table 81 above, there is one chiller if the baseline system cooling load is 300 tons or less and two equally sized chillers for baseline system loads between 300 and 600 tons. For loads above 600 tons, two or more chillers of equal size are used, with no chiller larger than 800 tons.

Chiller Fuel

Applicability

All chillers

Definition

The fuel source for the chiller. The choices are:

· Electricity (for all vapor-compression chillers)

· Gas (absorption units only, designated as direct-fired units)

· Oil (absorption units only, designated as direct-fired units)

· Hot Water (absorption units only, designated as indirect-fired units)

· Steam (absorption units only, designated as indirect-fired units)

Units

List (see above)

Input Restrictions

As designed.

This input is restricted, based on the choice of chiller type, according to the following rules:

	Electricity	Gas	Hot Water	Steam
Reciprocating	Allowed
Scroll	Allowed
Screw	Allowed
Centrifugal	Allowed
Single effect absorption		Allowed	Allowed	Allowed
Direct fired double effect absorption		Allowed	Allowed	Allowed
Indirect fired absorption		Allowed	Allowed	Allowed

Baseline Building

Electricity

Chiller Capacity
Applicability	All chillers
Definition	The cooling capacity of a chiller at rated conditions
Units	Btu/h or tons
Input Restrictions	As designed. If UMLH are greater than 300, the chiller may have to be made larger.
Baseline Building	The zone loads and airflow rates are oversized by 15% and the chiller is sized to the sum of the individual oversized zone peak loads. The zones shall be sized using weather files containing 1% dry-bulb and 1% wet-bulb cooling design temperatures. Section 3.1.5 has more details regarding design day data to be used for equipment sizing.

Chiller Rated Efficiency

Applicability

All chillers

Definition

The efficiency of the chiller: EER for air cooled chillers, kW/ton for water cooled, positive displacement chillers, and COP for fuel-fired and heat driven chillers at ARI 550/590 rated full-load conditions. The test conditions for the full load (FL) rating are summarized below:

· 44°F leaving chilled-fluid temperature

· 2.4 gpm/ton evaporator fluid flow

· 85°F entering condenser-fluid temperature

· 3.0 gpm/ton condenser-fluid flow

Units

Ratio (kW/ton, EER, or COP based on chiller type and condenser type)

Input Restrictions

As designed. Must meet the minimum requirements of Table 6.8.1C of Standard 90.1-2019.

Baseline Building

Use the minimum efficiency requirements EER or kW/ton values from Table 82 (Standard 90.1-2019 Table G3.5.3).

Table 82. Minimum Efficiency Requirements for Water Chilling Packages

Size Category

Sub Category

Minimum Efficiency

Test Procedure

Water cooled, Electrically Operated, Positive Displacement (rotary screw and scroll)

<150 tons

>150 tons and <300 tons

>300 tons

Allowed

kW/ton

0.790 FL 0.676 IPLV.IP

0.718 FL 0.629 IPLV.IP

0.639 FL 0.572 IPLV.IP

ARI 550/590

Water cooled, Electrically Operated, Centrifugal

<150 tons

>150 tons and <300 tons

>300 tons

kW/ton

0.703 FL 0.670 IPLV.IP

0.634 FL 0.596 IPLV.IP

0.576 FL 0.549 IPLV.IP

ARI 550/590

FL= Full Load; IPLV = Integrated Part Load Value

Integrated Part Load Value
Applicability	All chillers
Definition	The part-load efficiency of a chiller developed from a weighted average of four rating conditions, according to AHRI Standard 550
Units	Ratio (kW/ton, COP, or EER, depending on chiller type and condenser type) Water cooled electric chiller: kW/ton Air cooled or evaporatively cooled electric chiller: EER All non-electric chillers: COP
Input Restrictions	As designed. Must meet the minimum requirements of Table 6.8.1C of Standard 90.1-2019.
Baseline Building	The baseline building is analyzed with the minimum full load efficiency as specified in Table 82. The IPLV is calculated by the simulation software according to ANSI/AHRI Standard 550/590 based on the full load efficiency and the performance curves.

Chiller Minimum Unloading Ratio

Applicability

All chillers

Definition

The minimum unloading capacity of a chiller expressed as a fraction of the rated capacity. Below this level the chiller must cycle to meet the load.

Table 83. Default Minimum Unloading Ratios

Chiller Type	Default Unloading Ratio
Reciprocating	25%
Screw	15%
Centrifugal	10%
Scroll	25%
Single Effect Absorption	10%
Double Effect Absorption	10%

Units

Percent (%)

Input Restrictions

As designed. If the user does not employ the default values, supporting documentation is required.

Baseline Building

Same as proposed (if the proposed includes a chiller). Else, use defaults listed above.

Chiller Minimum Part Load Ratio
Applicability	All chillers
Definition	The minimum unloading capacity of a chiller expressed as a fraction of the rated capacity. Below this level the chiller must cycle to meet the load. If the chiller minimum part-load ratio (PLR) is less than the chiller minimum unloading ratio, then the software shall assume hot-gas bypass operation between the minimum PLR and the minimum unloading ratio. Standard 90.1-2019 Section 6.5.9 specifies a limit for maximum hot-gas bypass as a percentage of the total cooling capacity of the cooling system. The difference between the maximum unloading ratio and minimum part load ratio cannot exceed this limit for hot gas bypass operation.
Units	Percent (%)
Input Restrictions	As designed, but constrained to a minimum value of 10%. If the user does not employ the default values, supporting documentation is required.
Baseline Building	When the baseline design has a screw chiller, the minimum part load ratio is 15%. When the baseline design has a centrifugal chiller, the minimum part load ratio is 10%.

Chiller Cooling Capacity Adjustment Curve

Applicability

All chillers

Definition

A curve or group of curves or other functions that represent the available total cooling capacity as a function of evaporator and condenser conditions and perhaps other operating conditions. The default curves are given as follows:

??????????=???_??×?????? (52)

For air cooled chillers:

???_??=?+?×??ℎ??+?×??ℎ??2+?×????+?×????2+ (53)

?×??ℎ??×????

For water cooled chillers:

???_??=?+?×??ℎ??+?×??ℎ??2+?×????+?×????2+ (54)

?×??ℎ??×????

Where:

Qavailable = Available cooling capacity at present evaporator and condenser conditions (MBH)

tchws = The chilled water supply temperature (°F)

tcws = The condenser water supply temperature (°F)

todb = The outside air dry-bulb temperature (°F)

Qrated = Rated capacity at ARI conditions (MBH)

Note: If an air cooled unit employs an evaporative condenser, todb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

Separate curves are provided for Path A and Path B chillers in COMNET Appendix H (COMNET 2017).

Table 84. Default Capacity Coefficients – Electric Air Cooled Chillers

Coefficient	Scroll	Recip	Screw	Centrifugal
a	0.40070684	0.57617295	-0.09464899	N/A
b	0.01861548	0.02063133	0.03834070	N/A
c	0.00007199	0.00007769	-0.00009205	N/A
d	0.00177296	-0.00351183	0.00378007	N/A
e	-0.00002014	0.00000312	-0.00001375	N/A
f	-0.00008273	-0.00007865	-0.00015464	N/A
Tchws	Min = 40°F, Max = 54°F	Min = 40°F, Max = 54°F	Min = 40°F, Max = 54°F	NA
Todb	Min = 40°F, Max = 115°F	Min = 40°F, Max = 115°F	Min = 40°F, Max = 115°F	NA

Table 85. Default Capacity Coefficients – Electric Water Cooled Chillers

Coefficient	Recip	Screw	Scroll	Centrifugal
a	0.36131454	0.58531422	0.33269598	-0.29861976
b	0.01855477	0.01539593	0.00729116	0.02996076
c	0.00003011	0.00007296	-0.00049938	-0.00080125
d	0.0000301	0.00007296	-0.00049938	-0.00080125
e	-0.00001518	-0.00000715	-0.00028254	-0.00032606
f	-0.00005481	-0.00004597	0.00052346	0.00063139
Tchws	Min = 40°F, Max = 54°F	Min = 40°F, Max = 54°F	Min = 40°F, Max = 54°F	Min = 40°F, Max = 54°F
Todb	Min = 60°F, Max = 85°F	Min = 60°F, Max = 85°F	Min = 60°F, Max = 85°F	Min = 60°F, Max = 85°F

Table 86. Default Capacity Coefficients – Fuel- and Steam-Source Water Cooled Chillers

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption	Engine Driven Chiller
A	0.723412	-0.816039	1.000000	0.573597
B	0.079006	-0.038707	0.000000	0.0186802
C	-0.000897	0.000450	0.000000	0.000000
D	-0.025285	0.071491	0.000000	-0.00465325
E	-0.000048	-0.000636	0.000000	0.000000
F	0.000276	0.000312	0.000000	0.000000

Units

Data structure

Input Restrictions

The user may input curves or use default curves. If the default curves are overridden, supporting documentation is required.

Baseline Building

Use default curve

Electric Chiller Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of an electric chiller as a function of evaporator conditions, condenser conditions, and part-load ratio. Note that for variable-speed chillers, the part-load cooling efficiency curve is a function of both part-load ratio and leaving condenser water temperature. The default curves are given as follows:

Table 87. Default Efficiency EIR-FT Coefficients – Air Cooled Chillers

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.99006553	0.66534403	0.13545636	N/A
b	-0.00584144	-0.01383821	0.02292946	N/A
c	0.00016454	0.00014736	-0.00016107	N/A
d	-0.00661136	0.00712808	-0.00235396	N/A
e	0.00016808	0.00004571	0.00012991	N/A
f	-0.00022501	-0.00010326	-0.00018685	N/A
Tchws	Min = 40°F, Max = 54°F	Min = 40°F, Max = 54°F	Min = 40°F, Max = 54°F	N/A
Todb	Min = 40°F, Max = 115°F	Min = 40°F, Max = 115°F	Min = 40°F, Max = 115°F	N/A

Table 88. Default Efficiency EIR-FT Coefficients – Water Cooled Chillers

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	1.00121431	0.46140041	0.66625403	0.51777196
b	-0.01026981	-0.00882156	0.00068584	-0.00400363
c	0.00016703	0.00008223	0.00028498	0.00002028
d	-0.00128136	0.00926607	-0.00341677	0.00698793
e	0.00014613	0.00005722	0.00025484	0.00008290
f	-0.00021959	-0.00011594	-0.00048195	-0.00015467

Table 89. Default Efficiency EIR-FPLR Coefficients – Air Cooled Chillers

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.06369119	0.11443742	0.03648722	N/A
b	0.58488832	0.54593340	0.73474298	N/A
c	0.35280274	0.34229861	0.21994748	N/A

Table 90. Default Efficiency EIR-FPLR Coefficients – Water Cooled Chillers

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.04411957	0.08144133	0.33018833	0.17149273
b	0.64036703	0.41927141	0.23554291	0.58820208
c	0.31955532	0.49939604	0.46070828	0.23737257

Chilled Water Supply Temperature
Applicability	All chillers
Definition	The chilled water supply temperature of the chiller at design conditions
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Building	The baseline chilled water supply temperature is set to 44°F

Chilled Water ReturnTemperature
Applicability	All chillers
Definition	The chilled water return temperature setpoint
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed
Baseline Building	The baseline chilled water supply temperature is set to 56°F

Chilled Water Supply Temp. Control Type
Applicability	All chillers
Definition	The method by which the chilled water setpoint temperature is reset. The chilled water setpoint may be reset based on demand or OAT.
Units	List
Input Restrictions	None, can be either “outside air-based reset” or “demand-based reset”
Baseline Building	Outside air based reset

Chilled Water Supply Temp. Reset
Applicability	All chillers
Definition	The reset schedule for the chilled water supply temperature. The chilled water setpoint may be reset based on demand or OAT.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed. The default is as shown in the figure below.
Baseline Building	The baseline chilled water supply temperature is reset from 44°F to 54°F based on OAT as shown in the figure below. The figure depicts a linear reset schedule that represents the chilled water setpoint as a function of outdoor air dry-bulb temperature. This schedule is defined by the following data points: · 44°F at OAT 80°F and above · 54°F at OAT 60°F and below · Ramped linearly between 44°F and 54°F at temperatures between 80°F and 60°F

Air Cooled Condenser Power
Applicability	All chillers with air cooled condensers where fan energy is not part of the COP
Definition	The energy usage of the condenser fan(s) at design conditions on an air cooled chiller. This unit should only be used for chillers composed of separate evaporator and condenser sections where the fan energy is not part of the chiller COP.
Units	Kilowatts (kW)
Input Restrictions	As designed. The user must enter data for remote air cooled condensing units.
Baseline Building	Not applicable, since all baseline chillers have water cooled condensers

Chiller Name
Applicability	All chillers
Definition	A unique descriptor for each chiller
Units	Text, unique
Input Restrictions	User entry. Where applicable, this should match the tags that are used on the plans.

Chiller Type

Applicability

All chillers

Definition

The type of chiller, either a vapor-compression chiller or an absorption chiller.

Vapor compression chillers operate on the reverse-Rankine cycle, using mechanical energy to compress the refrigerant, and include:

Reciprocating – uses pistons for compression
Screw – uses two counter rotating screws for compression
Scroll – uses two interlocking spirals or scrolls to perform the compression
Centrifugal – uses rotating impeller blades to compress the air
Absorption chillers – use heat to vaporize a working fluid (usually either ammonia or lithium bromide)
Single Effect Absorption – use a single generator & condenser
Double Effect Absorption – use two generators/concentrators and condensers, one at a lower temperature and the other at a higher temperature. It is more efficient than the single effect, but it must use a higher temperature heat source.

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

The baseline building chiller is based on the design capacity of the proposed design as follows from ASHRAE 90.1 Appendix G:
[table title="Type and Number of Chillers" id="type-and-number-of-chillers"]

Building Peak Cooling Load	Number and Type of Chillers (s)
$\leq$300 tons	1 water-cooled screw chiller
>300 tons, <600 tons	2 water-cooled screw chillers sized equally
$\geq$600 tons	2 water-cooled centrigugal chillers minimum with chillers added so that no chiller is larger than 800 tons, all sized equally

Number of Identical Chiller Units
Applicability	All chillers
Definition	The number of identical units for staging.
Units	None
Input Restrictions	As designed. Default is 1.

Chiller Fuel
Applicability	All chillers
Definition	The fuel source for the chiller. The choices are: Electricity (for all vapor-compression chillers) Gas (Absorption units only, designated as direct-fired units) Oil (Absorption units only, designated as direct-fired units) Hot Water (Absorption units only, designated as indirect-fired units) Steam (Absorption units only, designated as indirect-fired units)
Units	List (see above)
Input Restrictions	As designed.

Chiller Rated Capacity
Applicability	All chillers
Definition	The cooling capacity of a piece of heating equipment at rated conditions.
Units	Btu/h or tons
Input Restrictions	As designed. If unmet load hours are greater than 300, the chiller may have to be made larger.

Chiller Rated Efficiency
Applicability	All chillers
Definition	The Coefficient of Performance (COP) at ARI rated conditions.
Units	Ratio
Input Restrictions	As designed

Chiller Minimum Unloading Ratio

Applicability

All chillers

Definition

The minimum unloading capacity of a chiller expressed as a fraction of the rated capacity. Below this level the chiller must cycle to meet the load.

[table title="Default Minimum Unloading Ratios" id="default-minimum-unloading-ratios"]

Chiller Type	Default Unloading Ratio
Reciprocating	25%
Screw	15%
Centrifugal	10%
Scroll	25%
Single Effect Absorption	10%
Double Effect Absorption	10%

Units

Percent (%)

Input Restrictions

As designed. If the user does not employ the default values, supporting documentation is required.

Chiller Cooling Capacity Adjustment Curve

Applicability

All chillers

Definition

A curve or group of curves or other functions that represent the available total cooling capacity as a function of evaporator and condenser conditions and perhaps other operating conditions. The default curves are given as follows:

(6.8.2-1)

$$ Q_{available} = CAP \_ FT \times Q_{rated}$$

For air-cooled chillers:

(6.8.2-2)

$$ CAP \_FT = a + b \times t_{chws} + c \times \left. t_{chws}\right. ^2 + d \times t_{odb} + e \times \left. t_{odb}\right. ^2 + f \times t_{chws} \times t_{odb}$$

For water-cooled chillers:

(6.8.2-3)

$$ CAP \_FT = a + b \times t_{chws} + c \times \left. t_{chws} \right. ^2 + d \times t_{cws} + e \times \left. t_{cws} \right. ^2 + f \times t_{chws} \times t_{cws}$$

where

Q_available	Available cooling capacity at present evaporator and condenser conditions (MBH)
t_chws	The chilled water supply temperature (°F)
t_cws	The condenser water supply temperature (°F)
t_odb	The outside air dry-bulb temperature (°F)
Q_rated	Rated capacity at ARI conditions (MBH)

Note: If an air-cooled unit employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

[table title="Default Capacity Coefficients – Electric Air-Cooled Chillers" id="default-capacity-coefficients-–-electric-air---cooled-chillers"]

Coefficient	Scroll	Recip	Screw	Centrifugal
a	0.40070684	0.57617295	-0.09464899	N/A
b	0.01861548	0.02063133	0.03834070	N/A
c	0.00007199	0.00007769	-0.00009205	N/A
d	0.00177296	-0.00351183	0.00378007	N/A
e	-0.00002014	0.00000312	-0.00001375	N/A
f	-0.00008273	-0.00007865	-0.00015464	N/A

[table title="Default Capacity Coefficients – Electric Water-Cooled Chillers" id="default-capacity-coefficients-–-electric-water---cooled-chillers"]

Coefficient	Scroll	Recip	Screw	Centrifugal
a	0.36131454	0.58531422	0.33269598	-0.29861976
b	0.01855477	0.01539593	0.00729116	0.02996076
c	0.00003011	0.00007296	-0.00049938	-0.00080125
d	0.00093592	-0.00212462	0.01598983	0.01736268
e	-0.00001518	-0.00000715	-0.00028254	-0.00032606
f	-0.00005481	-0.00004597	0.00052346	0.00063139

[table title="Default Capacity Coefficients – Fuel- & Steam-Source Water-Cooled Chillers" id="default-capacity-coefficients-–-fuel--&-steam---source-water---cooled-chillers"]

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption	Engine Driven Chiller
a	0.723412	-0.816039	1.000000	0.573597
b	0.079006	-0.038707	0.000000	0.0186802
c	-0.000897	0.000450	0.000000	0.000000
d	-0.025285	0.071491	0.000000	-0.00465325
e	-0.000048	-0.000636	0.000000	0.000000
f	0.000276	0.000312	0.000000	0.000000

Units

Data structure

Input Restrictions

User may input curves, other appropriate functions, or use default curves. If the default curves are overridden, supporting documentation is required.

Electric Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of an electric chiller as a function of evaporator conditions, condenser conditions and part-load ratio. The default curves are given as follows:

(6.8.2-4)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ EIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ air-cooled \enspace EIR\_FT = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 + \ d \times t_{odb} + \ e \times \left. t_{odb}\right. ^2+ \ f \times t_{chws} \times t_{odb}$$ $$ water-cooled \enspace EIR\_FT = a + b \times t_{chws}+ c \times \left. t_{chws}\right. ^2 + d \times t_{cws} + e \times \left. t_{cws}\right. ^2+ f \times t_{chws} \times t_{cws}$$ $$P_{operating} = P_{rated} \times EIR\_FPLR \times EIR\_FT \times CAP\_FT $$

where

PLR	Part load ratio based on available capacity (not rated capacity)
Q_operating	Present load on chiller (Btu/h)
Q_available	Chiller available capacity at present evaporator and condenser conditions (Btu/h)
t_chws	The chilled water supply temperature (°F)
t_cws	The condenser water supply temperature (°F)
t_odb	The outside air dry-bulb temperature (°F)
P_rated	Rated power draw at ARI conditions (kW)
P_operating	Power draw at specified operating conditions (kW)

Note: If an air-cooled chiller employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

[table title="Default Efficiency EIR-FT Coefficients – Air-Cooled Chillers" id="default-efficiency-eir---ft-coefficients-–-air---cooled-chillers"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.99006553	0.66534403	0.13545636	N/A
b	-0.00584144	-0.01383821	0.02292946	N/A
c	0.00016454	0.00014736	-0.00016107	N/A
d	-0.00661136	0.00712808	-0.00235396	N/A
e	0.00016808	0.00004571	0.00012991	N/A
f	-0.00022501	-0.00010326	-0.00018685	N/A

[table title="Default Efficiency EIR-FT Coefficients – Water-Cooled Chiller" id="default-efficiency-eir--ft-coefficients-–-water---cooled-chiller"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	1.00121431	0.46140041	0.66625403	0.51777196
b	-0.01026981	-0.00882156	0.00068584	-0.00400363
c	0.00016703	0.00008223	0.00028498	0.00002028
d	-0.00128136	0.00926607	-0.00341677	0.00698793
e	0.00014613	0.00005722	0.00025484	0.00008290
f	-0.00021959	-0.00011594	-0.00048195	-0.00015467

[table title="Default Efficiency EIR-FPLR Coefficients – Air-Cooled Chillers" id="default-efficiency-eir---fplr-coefficients-–-air---cooled-chillers"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.06369119	0.11443742	0.03648722	N/A
b	0.58488832	0.54593340	0.73474298	N/A
c	0.35280274	0.34229861	0.21994748	N/A

[table title="Default Efficiency EIR-FPLR Coefficients – Water-Cooled Chillers" id="default-efficiency-eir---fplr-coefficients-–-water---cooled-chillers"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.04411957	0.08144133	0.33018833	0.17149273
b	0.64036703	0.41927141	0.23554291	0.58820208
c	0.31955532	0.49939604	0.46070828	0.23737257

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation is required.

Fuel and Steam Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of a fuel-fired or steam chiller as a function of evaporator conditions, condenser conditions, and part-load ratio. The default curves are given as follows:
Default Curves for Steam-Driven Single and Double Effect Absorption Chillers

(6.8.2-5)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ FIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ FIR\_FT = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 + \ d \times t_{cws} + \ e \times \left. t_{cws}\right. ^2+ \ f \times t_{chws} \times t_{cws}$$ $$Fuel_{partload} = Fuel_{rated} \times FIR\_FPLR \times FIR\_FT \times CAP\_FT $$

Default Curves for Direct-Fired Double Effect Absorption Chillers

(6.8.2-6)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ FIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ FIR\_FT1 = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 $$ $$ FIR\_FT2 = d + e \times t_{cws} + \ f \times \left. t_{cws}\right. ^2 $$ $$Fuel_{partload} = Fuel_{rated} \times FIR\_FPLR \times FIR\_FT1 \times FIR\_FT2 \times CAP\_FT $$

The default curves for engine driven chillers are the same format as those for the Steam-Driven Single and Double Effect Absorption Chillers but there are three sets of curves for different ranges of operation based on the engine speed.

where

PLR	Part load ratio based on available capacity (not rated capacity)
FIR-FPLR	A multiplier on the fuel input ratio (FIR) to account for part load conditions
FIR-FT	A multiplier on the fuel input ratio (FIR) to account for the chiller water supply temperature and the condenser water temperature
FIR-FT1	A multiplier on the fuel input ratio (FIR) to account for chilled water supply temperature
FIR-FT2	A multiplier on the fuel input ratio (FIR) to account for condenser water supply temperature
CAP-FT	A multiplier on the capacity of the chiller (see Equation (6.8.2-2))
Q_operating	Present load on chiller (in Btu/h)
Q_available	Chiller available capacity at present evaporator and condenser conditions (in Btu/h)
t_chws	The chilled water supply temperature (in °F)
t_cws	The condenser water supply temperature (in °F)
t_odb	The outside air dry-bulb temperature (°F)
Fuel_rated	Rated fuel consumption at ARI conditions (in Btu/h)
Fuel_partload	Fuel consumption at specified operating conditions (in Btu/h)

[table title="Default FIR-FPLR coefficients – Fuel- & Steam-Source Water-Cooled Absorption Chillers" id="default-fir---fplr-coefficients-–-fuel---&-steam---source-water---cooled-absorption-chillers"]

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption
a	0.098585	0.013994	0.13551150
b	0.583850	1.240449	0.61798084
c	0.560658	-0.914883	0.24651277
d	-0.243093	0.660441	0.00000000

[table title="Default FIR-FPLR coefficients – Engine Driven Chillers" id="default-fir---fplr-coefficients-–-engine-driven-chillers"]

Coefficient	%Speed$\leq$Min.	%Speed>Min. %Speed<60%	%Speed>60%
a	0.3802	1.14336	1.38861
b	2.3609	0.022889	-0.388614
c	0.0000	0.0000	0.0000
d	0.0000	0.0000	0.000

[table title="Default FIR-FT coefficients – Fuel- & Steam-Source Water-Cooled Absorption Chillers" id="default-fir---ft-coefficients-–-fuel---&-steam---source-water---cooled-absorption-chillers"]

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption
a	0.652273	1.658750	4.42871284
b	0.000000	0.000000	-0.13298607
c	0.000000	0.000000	0.00125331
d	-0.000545	-0.290000	0.86173749
e	0.000055	0.000250	-0.00708917
f	0.000000	0.000000	0.0010251

[table title="Default FIR-FT coefficients – Engine Driven Chillers" id="default-fir---ft-coefficients-–-engine-driven-chillers"]

Coefficient	%Speed$\leq$Min.	%Speed>Min. %Speed<60%	%Speed>60%
a	1.0881500	1.2362400	1.2362400
b	0.0141064	0.0168923	0.0168923
c	0.0000000	0.0000000	0.0000000
d	-0.00833912	-0.0115235	-0.0115235
e	0.0000000	0.0000000	0.0000000
f	0.0000000	0.0000000	0.0000000

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation is required.

Chilled Water Supply Temperature
Applicability	All chillers
Definition	The chilled water supply temperature of the chiller at design conditions
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed

Chilled Water Return Temperature
Applicability	All chillers
Definition	The chilled water return temperature setpoint
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed

Chilled Water Supply Temperature Reset
Applicability	All chillers
Definition	The reset schedule for the chilled water supply temperature. The chilled water setpoint may be reset based on demand or outdoor air temperature.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed. The default is [bookref id="chilled-water-supply-temperature-reset-schedule"]. [figure title="Chilled Water Supply Temperature Reset Schedule" id="chilled-water-supply-temperature-reset-schedule"][/figure]

Condenser Type
Applicability	All chillers
Definition	The type of condenser for a chiller. The choices are: Air-Cooled Water-Cooled Evaporatively-Cooled Air-cooled chillers use air to cool the condenser coils. Water-cooled chillers use cold water to cool the condenser and additionally need either a cooling tower or a local source of cold water. Evaporatively-cooled chillers are similar to air-cooled chillers, except they use a water mist to cool the condenser coil which makes them more efficient.
Units	List (see above)
Input Restrictions	As designed

Air-Cooled Condenser Power
Applicability	All chillers
Definition	The energy usage of the condenser fan(s) at design conditions on an air-cooled chiller. This unit should only be used for chillers composed of separate evaporator and condenser sections where the fan energy is not part of the chiller COP.
Units	Kilowatts (kW)
Input Restrictions	As designed. The user must enter data for remote air-cooled condensing units.

Chiller Name
Applicability	All chillers
Definition	A unique descriptor for each chiller
Units	Text, unique
Input Restrictions	User entry. Where applicable, this should match the tags that are used on the plans.

Chiller Type

Applicability

All chillers

Definition

The type of chiller, either a vapor-compression chiller or an absorption chiller.

Vapor compression chillers operate on the reverse-Rankine cycle, using mechanical energy to compress the refrigerant, and include:

Reciprocating – uses pistons for compression
Screw – uses two counter rotating screws for compression
Scroll – uses two interlocking spirals or scrolls to perform the compression
Centrifugal – uses rotating impeller blades to compress the air
Absorption chillers – use heat to vaporize a working fluid (usually either ammonia or lithium bromide)
Single Effect Absorption – use a single generator & condenser
Double Effect Absorption – use two generators/concentrators and condensers, one at a lower temperature and the other at a higher temperature. It is more efficient than the single effect, but it must use a higher temperature heat source.

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

The baseline building chiller is based on the design capacity of the proposed design as follows from ASHRAE 90.1 Appendix G:
[table title="Type and Number of Chillers" id="type-and-number-of-chillers"]

Building Peak Cooling Load	Number and Type of Chillers (s)
$\leq$300 tons	1 water-cooled screw chiller
>300 tons, <600 tons	2 water-cooled screw chillers sized equally
$\geq$600 tons	2 water-cooled centrigugal chillers minimum with chillers added so that no chiller is larger than 800 tons, all sized equally

Number of Identical Chiller Units
Applicability	All chillers
Definition	The number of identical units for staging.
Units	None
Input Restrictions	As designed. Default is 1.

Chiller Fuel
Applicability	All chillers
Definition	The fuel source for the chiller. The choices are: Electricity (for all vapor-compression chillers) Gas (Absorption units only, designated as direct-fired units) Oil (Absorption units only, designated as direct-fired units) Hot Water (Absorption units only, designated as indirect-fired units) Steam (Absorption units only, designated as indirect-fired units)
Units	List (see above)
Input Restrictions	As designed.

Chiller Rated Capacity
Applicability	All chillers
Definition	The cooling capacity of a piece of heating equipment at rated conditions.
Units	Btu/h or tons
Input Restrictions	As designed. If unmet load hours are greater than 300, the chiller may have to be made larger.

Chiller Rated Efficiency
Applicability	All chillers
Definition	The Coefficient of Performance (COP) at ARI rated conditions.
Units	Ratio
Input Restrictions	As designed

Chiller Minimum Unloading Ratio

Applicability

All chillers

Definition

The minimum unloading capacity of a chiller expressed as a fraction of the rated capacity. Below this level the chiller must cycle to meet the load.

[table title="Default Minimum Unloading Ratios" id="default-minimum-unloading-ratios"]

Chiller Type	Default Unloading Ratio
Reciprocating	25%
Screw	15%
Centrifugal	10%
Scroll	25%
Single Effect Absorption	10%
Double Effect Absorption	10%

Units

Percent (%)

Input Restrictions

As designed. If the user does not employ the default values, supporting documentation is required.

Chiller Cooling Capacity Adjustment Curve

Applicability

All chillers

Definition

A curve or group of curves or other functions that represent the available total cooling capacity as a function of evaporator and condenser conditions and perhaps other operating conditions. The default curves are given as follows:

(6.8.2-1)

$$ Q_{available} = CAP \_ FT \times Q_{rated}$$

For air-cooled chillers:

(6.8.2-2)

$$ CAP \_FT = a + b \times t_{chws} + c \times \left. t_{chws}\right. ^2 + d \times t_{odb} + e \times \left. t_{odb}\right. ^2 + f \times t_{chws} \times t_{odb}$$

For water-cooled chillers:

(6.8.2-3)

$$ CAP \_FT = a + b \times t_{chws} + c \times \left. t_{chws} \right. ^2 + d \times t_{cws} + e \times \left. t_{cws} \right. ^2 + f \times t_{chws} \times t_{cws}$$

where

Q_available	Available cooling capacity at present evaporator and condenser conditions (MBH)
t_chws	The chilled water supply temperature (°F)
t_cws	The condenser water supply temperature (°F)
t_odb	The outside air dry-bulb temperature (°F)
Q_rated	Rated capacity at ARI conditions (MBH)

Note: If an air-cooled unit employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

[table title="Default Capacity Coefficients – Electric Air-Cooled Chillers" id="default-capacity-coefficients-–-electric-air---cooled-chillers"]

Coefficient	Scroll	Recip	Screw	Centrifugal
a	0.40070684	0.57617295	-0.09464899	N/A
b	0.01861548	0.02063133	0.03834070	N/A
c	0.00007199	0.00007769	-0.00009205	N/A
d	0.00177296	-0.00351183	0.00378007	N/A
e	-0.00002014	0.00000312	-0.00001375	N/A
f	-0.00008273	-0.00007865	-0.00015464	N/A

[table title="Default Capacity Coefficients – Electric Water-Cooled Chillers" id="default-capacity-coefficients-–-electric-water---cooled-chillers"]

Coefficient	Scroll	Recip	Screw	Centrifugal
a	0.36131454	0.58531422	0.33269598	-0.29861976
b	0.01855477	0.01539593	0.00729116	0.02996076
c	0.00003011	0.00007296	-0.00049938	-0.00080125
d	0.00093592	-0.00212462	0.01598983	0.01736268
e	-0.00001518	-0.00000715	-0.00028254	-0.00032606
f	-0.00005481	-0.00004597	0.00052346	0.00063139

[table title="Default Capacity Coefficients – Fuel- & Steam-Source Water-Cooled Chillers" id="default-capacity-coefficients-–-fuel--&-steam---source-water---cooled-chillers"]

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption	Engine Driven Chiller
a	0.723412	-0.816039	1.000000	0.573597
b	0.079006	-0.038707	0.000000	0.0186802
c	-0.000897	0.000450	0.000000	0.000000
d	-0.025285	0.071491	0.000000	-0.00465325
e	-0.000048	-0.000636	0.000000	0.000000
f	0.000276	0.000312	0.000000	0.000000

Units

Data structure

Input Restrictions

User may input curves, other appropriate functions, or use default curves. If the default curves are overridden, supporting documentation is required.

Electric Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of an electric chiller as a function of evaporator conditions, condenser conditions and part-load ratio. The default curves are given as follows:

(6.8.2-4)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ EIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ air-cooled \enspace EIR\_FT = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 + \ d \times t_{odb} + \ e \times \left. t_{odb}\right. ^2+ \ f \times t_{chws} \times t_{odb}$$ $$ water-cooled \enspace EIR\_FT = a + b \times t_{chws}+ c \times \left. t_{chws}\right. ^2 + d \times t_{cws} + e \times \left. t_{cws}\right. ^2+ f \times t_{chws} \times t_{cws}$$ $$P_{operating} = P_{rated} \times EIR\_FPLR \times EIR\_FT \times CAP\_FT $$

where

PLR	Part load ratio based on available capacity (not rated capacity)
Q_operating	Present load on chiller (Btu/h)
Q_available	Chiller available capacity at present evaporator and condenser conditions (Btu/h)
t_chws	The chilled water supply temperature (°F)
t_cws	The condenser water supply temperature (°F)
t_odb	The outside air dry-bulb temperature (°F)
P_rated	Rated power draw at ARI conditions (kW)
P_operating	Power draw at specified operating conditions (kW)

Note: If an air-cooled chiller employs an evaporative condenser, t_odb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit.

[table title="Default Efficiency EIR-FT Coefficients – Air-Cooled Chillers" id="default-efficiency-eir---ft-coefficients-–-air---cooled-chillers"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.99006553	0.66534403	0.13545636	N/A
b	-0.00584144	-0.01383821	0.02292946	N/A
c	0.00016454	0.00014736	-0.00016107	N/A
d	-0.00661136	0.00712808	-0.00235396	N/A
e	0.00016808	0.00004571	0.00012991	N/A
f	-0.00022501	-0.00010326	-0.00018685	N/A

[table title="Default Efficiency EIR-FT Coefficients – Water-Cooled Chiller" id="default-efficiency-eir--ft-coefficients-–-water---cooled-chiller"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	1.00121431	0.46140041	0.66625403	0.51777196
b	-0.01026981	-0.00882156	0.00068584	-0.00400363
c	0.00016703	0.00008223	0.00028498	0.00002028
d	-0.00128136	0.00926607	-0.00341677	0.00698793
e	0.00014613	0.00005722	0.00025484	0.00008290
f	-0.00021959	-0.00011594	-0.00048195	-0.00015467

[table title="Default Efficiency EIR-FPLR Coefficients – Air-Cooled Chillers" id="default-efficiency-eir---fplr-coefficients-–-air---cooled-chillers"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.06369119	0.11443742	0.03648722	N/A
b	0.58488832	0.54593340	0.73474298	N/A
c	0.35280274	0.34229861	0.21994748	N/A

[table title="Default Efficiency EIR-FPLR Coefficients – Water-Cooled Chillers" id="default-efficiency-eir---fplr-coefficients-–-water---cooled-chillers"]

Coefficient	Scroll	Reciprocating	Screw	Centrifugal
a	0.04411957	0.08144133	0.33018833	0.17149273
b	0.64036703	0.41927141	0.23554291	0.58820208
c	0.31955532	0.49939604	0.46070828	0.23737257

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation is required.

Fuel and Steam Chiller Cooling Efficiency Adjustment Curves

Applicability

All chillers

Definition

A curve or group of curves that varies the cooling efficiency of a fuel-fired or steam chiller as a function of evaporator conditions, condenser conditions, and part-load ratio. The default curves are given as follows:
Default Curves for Steam-Driven Single and Double Effect Absorption Chillers

(6.8.2-5)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ FIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ FIR\_FT = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 + \ d \times t_{cws} + \ e \times \left. t_{cws}\right. ^2+ \ f \times t_{chws} \times t_{cws}$$ $$Fuel_{partload} = Fuel_{rated} \times FIR\_FPLR \times FIR\_FT \times CAP\_FT $$

Default Curves for Direct-Fired Double Effect Absorption Chillers

(6.8.2-6)

$$ PLR = \frac {Q_{operating}}{Q_{available}\left ( t_{chws} , t_{cws/odb}\right )}$$ $$ FIR\_FPLR = a + b \times PLR + c \times PLR^2$$ $$ FIR\_FT1 = a + \ b \times t_{chws}+ \ c \times \left. t_{chws}\right. ^2 $$ $$ FIR\_FT2 = d + e \times t_{cws} + \ f \times \left. t_{cws}\right. ^2 $$ $$Fuel_{partload} = Fuel_{rated} \times FIR\_FPLR \times FIR\_FT1 \times FIR\_FT2 \times CAP\_FT $$

The default curves for engine driven chillers are the same format as those for the Steam-Driven Single and Double Effect Absorption Chillers but there are three sets of curves for different ranges of operation based on the engine speed.

where

PLR	Part load ratio based on available capacity (not rated capacity)
FIR-FPLR	A multiplier on the fuel input ratio (FIR) to account for part load conditions
FIR-FT	A multiplier on the fuel input ratio (FIR) to account for the chiller water supply temperature and the condenser water temperature
FIR-FT1	A multiplier on the fuel input ratio (FIR) to account for chilled water supply temperature
FIR-FT2	A multiplier on the fuel input ratio (FIR) to account for condenser water supply temperature
CAP-FT	A multiplier on the capacity of the chiller (see Equation (6.8.2-2))
Q_operating	Present load on chiller (in Btu/h)
Q_available	Chiller available capacity at present evaporator and condenser conditions (in Btu/h)
t_chws	The chilled water supply temperature (in °F)
t_cws	The condenser water supply temperature (in °F)
t_odb	The outside air dry-bulb temperature (°F)
Fuel_rated	Rated fuel consumption at ARI conditions (in Btu/h)
Fuel_partload	Fuel consumption at specified operating conditions (in Btu/h)

[table title="Default FIR-FPLR coefficients – Fuel- & Steam-Source Water-Cooled Absorption Chillers" id="default-fir---fplr-coefficients-–-fuel---&-steam---source-water---cooled-absorption-chillers"]

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption
a	0.098585	0.013994	0.13551150
b	0.583850	1.240449	0.61798084
c	0.560658	-0.914883	0.24651277
d	-0.243093	0.660441	0.00000000

[table title="Default FIR-FPLR coefficients – Engine Driven Chillers" id="default-fir---fplr-coefficients-–-engine-driven-chillers"]

Coefficient	%Speed$\leq$Min.	%Speed>Min. %Speed<60%	%Speed>60%
a	0.3802	1.14336	1.38861
b	2.3609	0.022889	-0.388614
c	0.0000	0.0000	0.0000
d	0.0000	0.0000	0.000

[table title="Default FIR-FT coefficients – Fuel- & Steam-Source Water-Cooled Absorption Chillers" id="default-fir---ft-coefficients-–-fuel---&-steam---source-water---cooled-absorption-chillers"]

Coefficient	Single Stage Absorption	Double Stage Absorption	Direct-Fired Absorption
a	0.652273	1.658750	4.42871284
b	0.000000	0.000000	-0.13298607
c	0.000000	0.000000	0.00125331
d	-0.000545	-0.290000	0.86173749
e	0.000055	0.000250	-0.00708917
f	0.000000	0.000000	0.0010251

[table title="Default FIR-FT coefficients – Engine Driven Chillers" id="default-fir---ft-coefficients-–-engine-driven-chillers"]

Coefficient	%Speed$\leq$Min.	%Speed>Min. %Speed<60%	%Speed>60%
a	1.0881500	1.2362400	1.2362400
b	0.0141064	0.0168923	0.0168923
c	0.0000000	0.0000000	0.0000000
d	-0.00833912	-0.0115235	-0.0115235
e	0.0000000	0.0000000	0.0000000
f	0.0000000	0.0000000	0.0000000

Units

Data structure

Input Restrictions

User may input curves or use default curves. If defaults are overridden, supporting documentation is required.

Chilled Water Supply Temperature
Applicability	All chillers
Definition	The chilled water supply temperature of the chiller at design conditions
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed

Chilled Water Return Temperature
Applicability	All chillers
Definition	The chilled water return temperature setpoint
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed

Chilled Water Supply Temperature Reset
Applicability	All chillers
Definition	The reset schedule for the chilled water supply temperature. The chilled water setpoint may be reset based on demand or outdoor air temperature.
Units	Degrees Fahrenheit (°F)
Input Restrictions	As designed. The default is [bookref id="chilled-water-supply-temperature-reset-schedule"]. [figure title="Chilled Water Supply Temperature Reset Schedule" id="chilled-water-supply-temperature-reset-schedule"][/figure]

Condenser Type
Applicability	All chillers
Definition	The type of condenser for a chiller. The choices are: Air-Cooled Water-Cooled Evaporatively-Cooled Air-cooled chillers use air to cool the condenser coils. Water-cooled chillers use cold water to cool the condenser and additionally need either a cooling tower or a local source of cold water. Evaporatively-cooled chillers are similar to air-cooled chillers, except they use a water mist to cool the condenser coil which makes them more efficient.
Units	List (see above)
Input Restrictions	As designed

Air-Cooled Condenser Power
Applicability	All chillers
Definition	The energy usage of the condenser fan(s) at design conditions on an air-cooled chiller. This unit should only be used for chillers composed of separate evaporator and condenser sections where the fan energy is not part of the chiller COP.
Units	Kilowatts (kW)
Input Restrictions	As designed. The user must enter data for remote air-cooled condensing units.