3.7.5.1 General

This group of building descriptors applies to all cooling systems.

Cooling Source
Applicability	All systems
Definition	The source of cooling for the system. The choices are: Chilled water Direct expansion (DX) Other
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	The baseline building cooling source is direct expansion for systems 1-6 and chilled water for systems 7-8 and 11-13. Systems 9 and 10 have no cooling capability. See Table 3.7-2.

Total Cooling Capacity

Applicability

All cooling systems

Definition

The total cooling capacity (both sensible and latent) of a cooling coil or packaged DX system at AHRI test conditions. The building descriptors defined in this chapter assume that the fan is modeled separately, including any heat it adds to the air stream. The cooling capacity specified by this building descriptor should not consider the heat of the fan.

Units

kBtu/h

Input Restrictions

As designed. Fan energy shall be modeled separately from cooling, unless the fan cycles, so for packaged equipment that has the fan motor in the air stream the Total Cooling Capacity shall be adjusted for the heat generated by the fan using the following procedure .

(Equation 3.7.5.1-1)

$$Q_{Net} = Q_{Rated} - Q_{Fan}$$

(Equation 3.7.5.1-2)

$$Q_{Fan}=\frac{Q_{Rated}}{COP_{cooling}}-\frac{Q_{Rated}}{COP_{nfcooling}}$$

where

Q_Net	The net cooling capacity of the packaged equipment without consideration of the fan (Btu/h)
Q_Rated	The total cooling capacity of the packaged equipment including the impact of the fan, as rated by AHRI (Btu/h)
Q_fan	The heat generated by the fan and fan motor (if fan motor is in airstream), at AHRI rated conditions (Btu/h)
COP_cooling	The coefficient of performance (COP) of the packaged equipment with consideration of the fan, where COP_Rated = EER_Rated / 3.412
COP_nfcooling	The coefficient of performance (COP) of the packaged equipment without consideration of the fan, as determined from equations 3.7.5.2-1 and 3.7.5.2-2

Baseline Rules

The total cooling capacity of the baseline building system is oversized by 15%. Sizing calculations shall be based on 1% dry-bulb and 1% wet-bulb design conditions.

Sensible Cooling Capacity

Applicability

All cooling systems

Definition

The sensible heat cooling capacity of the coil or packaged equipment at ARI conditions. The building descriptors defined in this chapter assume that the fan is modeled separately, including any heat it adds to the air stream. The cooling capacity specified by this building descriptor should not consider the heat of the fan.

Units

kBtu/h

Input Restrictions

As designed. For packaged equipment that has the fan motor located in the air stream such that it adds heat to the cooled air, the software shall adjust the sensible cooling capacity as follows:

(Equation 3.7.5.1-3)

$$Q_{s.adj} = Q_{s,rated} + BHP_{supply} \times 2.545$$

==Where

Q_s,adj	The adjusted sensible cooling capacity of a packaged unit (kBtu/h)
Q_s,rated	The ARI rated sensible cooling capacity of a packaged unit (kBtu/h)
BHP_supply	The supply fan brake horsepower (bhp).

Baseline Rules

The sensible cooling capacity of the baseline building is oversized by 15%. Sizing calculations shall be based on 1% dry-bulb and 1% wet-bulb design conditions.

Cooling Capacity Adjustment Curves

Applicability

All cooling systems

Definition

A curve that represents the available total cooling capacity as a function of cooling coil and/or condenser conditions. The common form of these curves is given as follows:

(Equation 3.7.5.1-4)

$$Q_{t,available}=CAP\_FT \times Q_{t,adj}$$

For air cooled direct expansion

(Equation 3.7.5.1-5)

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

For water cooled direct expansion

(Equation 3.7.5.1-6)

$$CAP\_FT=a + b \cdot t_{wb}+ c \cdot t_{wb}^{2}+ d \cdot t_{wt}+ d \cdot t_{wt}^{2}+f\cdot t_{wb}\cdot t_{wt}$$

For chilled water coils

(Equation 3.7.5.1-7)

$$CAP\_FT=a + b \cdot t_{wb}+ c \cdot t_{wb}^{2}+ d \cdot t_{db}+ d \cdot t_{db}^{2}+f\cdot t_{wb}\cdot t_{db}$$

Where

Q_t,available	Available cooling capacity at specified evaporator and/or condenser conditions (MBH)
Q_t,adj	Adjusted capacity at ARI conditions (Btu/h), from equation 3.7.5.1-3
CAP_FT	A multiplier to adjust Q_t,adj
T_wb	The entering coil wet-bulb temperature (°F)
T_db	The entering coil dry-bulb temperature (°F)
T_wt	The water supply temperature (°F)
T_odb	The outside-air dry-bulb temperature (°F)
a, b, c, d, e, f	Cooling capacity curve coefficients taken from Appendix H for each cooling system type.

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.
Software may represent the relationship between cooling capacity and temperature in ways other than the equations given above.

Units

Data structure

Input Restrictions

As designed. The equations and coefficients given above are the default.

Baseline Rules

The default curves shall be used for the baseline HVAC system.

Coil Bypass Factor

Applicability

All cooling systems

Definition

The ratio of air that bypasses the cooling coil at design conditions to the total system airflow.

Units

Ratio

Input Restrictions

The rated building shall use the factors given below.

Table 3.7.5.1-1: Default Coil Bypass Factors

System Type	Default Bypass Factor
Packaged Terminal Air-conditioners and Heat Pumps	0.241
Other Packaged Equipment	0.190
Multi-Zone Systems	0.078
All Other	0.037

Baseline Rules

Same as the rated building

Coil Bypass Factor Adjustment Curves

Applicability

All DX cooling systems (optional input)

Definition

Adjustments for the amount of coil bypass due to the following factors:

Coil airflow rate as a percentage of rated system airflow
Entering air wet-bulb temperature
Entering air dry-bulb temperature
Part load ratio

Units

Data structure

Input Restrictions

Where applicable, the following default values shall be used for the coil bypass factor adjustment curve:

(Equation 3.7.5.1-8)

$$CBF_{adj}=CBF_{Rated} \times COIL\_BF\_FFLOW \times COIL\_BF\_FT \times COIL\_BF\_FPLR$$

(Equation 3.7.5.1-9)

$$COIL\_BF\_FFLOW = a + b\cdot CFMR + c \cdot CFMR^{2} + d \cdot CFMR^{3}$$

(Equation 3.7.5.1-10)

$$COIL\_BF\_FT = a + b\cdot T_{wb} + c \cdot T_{wb}^{2} + b\cdot T_{db} + c \cdot T_{db}^{2} +f\cdot T_{wb} \cdot T_{db}$$

Equation 3.7.5.1-11)

$$COIL\_BF\_FPLR = a + b\cdot PLR$$

Where

CBF_rated	The coil bypass factor at ARI rating conditions
CBF_adj	The coil bypass factor adjusted for airflow and coil conditions
CFMR	The ratio of airflow to design airflow
COIL-BF-FFLOW	A multiplier on the rated coil bypass factor to account for variation in air flow across the coil (take coefficients from Appendix H)
COIL-BF-FT	A multiplier on the rated coil bypass factor to account for a variation in coil entering conditions (take coefficients from Appendix H)
COIL-BF-FPLR	A multiplier on the rated coil bypass factor to account for the part load ratio (take coefficients from Appendix H)
T_wb	The entering coil wet-bulb temperature (°F)
T_dba	The entering coil dry-bulb temperature (°F)
PLR	Part load ratio
a,b,c,d,e,f	Separate coefficients from Appendix H for COIL_BF_FT and COIL_BF_FFLOW

Baseline Rules

The above default values shall be used when applicable.

90.1-2019

This group of building descriptors applies to all cooling systems.

Cooling Source

Applicability

All systems

Definition

The source of cooling for the system. The choices are:

Chilled water
DX
Other

Units

List (see above)

Input Restrictions

As designed

Baseline Building

The baseline building cooling source is shown in Table 58. See Section 3.1.2 of this document for HVAC system mapping.

Table 58. Cooling Source for Baseline Building System

Baseline Building System	Cooling Type
1 – PTAC	Direct expansion
2 – PTHP	Direct expansion
3 – PSZ AC	Direct expansion
4 – PSZ HP	Direct expansion
5 – Packaged VAV with Reheat	Direct expansion
6 – Packaged VAV with PFP Boxes	Direct expansion
7 – VAV with Reheat	Chilled water
8 – VAV with PFP Boxes	Chilled water
9 – Heating and Ventilation	None
10 – Heating and Ventilation	None
11- Single Zone VAV	Chilled Water
12- Single Zone CAV HW	Chilled Water
13- Single Zone CAV ER	Chilled Water

Total Cooling Capacity

Applicability

All cooling systems

Definition

The total cooling capacity (both sensible and latent) of a cooling coil or packaged DX system at Air-Conditioning, Heating and Refrigeration Institute (AHRI) conditions. The building descriptors defined in this chapter assume that the fan is modeled separately, including any heat it adds to the air stream. The cooling capacity specified by this building descriptor should not consider the heat of the fan.

Note that most CHW coils, and coils in custom DX equipment, particularly those serving high outside air fractions, will have capacities provided in HVAC schedules and submittals at entering air conditions very different from AHRI conditions. For these units, when entered in software using the following simulation methods, custom performance curves will generally be needed, or the capacities and efficiencies recalculated at the AHRI conditions.

Units

kBtu/h

Input Restrictions

As designed. For packaged equipment that has the fan motor in the air stream such that it adds heat to the cooled air, the software shall adjust the total cooling capacity as follows:

Q_t,net,rated=Q_{t,gross,rated}-Q_fan,rated

(11)

Where:

Q_t,net,rated = The net total cooling capacity of a packaged unit as rated by AHRI (Btu/h)

Q_{t,gross,rated} = The AHRI rated total cooling capacity of a packaged unit (Btu/h)

Q_{t,fan, rated}₌The heat generated by the fan and fan motor (if fan motor is in airstream) at AHRI rated conditions

If the gross and net total cooling capacities at AHRI conditions are known, the fan heat at rated conditions is the difference between the two values. If the either the gross or net total cooling capacity is unknown, the fan heat at rated conditions shall be accounted for by using equation below :

W_fan= Q_{t.gross.rated} - Q_t.net.rated 3.412 [Btuh)/W]

Source: Standard 90.1-2019 User’s Manual (unpublished)

Baseline Building

The total cooling capacity of the systems in the baseline building is oversized by 15%. Sizing calculations shall be based on the heating design day and cooling design day conditions, as defined in Section 3.2.3 of this document. Oversizing would be carried out at zone level where the sizing parameters would be applied to the zone design cooling coil loads, but not the airflow rates.

Sensible Cooling Capacity

Applicability

All cooling systems

Definition

The sensible cooling capacity of the coil or packaged equipment at Air-conditioning and Refrigeration Institute (ARI) conditions. The building descriptors defined in this chapter assume that the fan is modeled separately, including any heat it adds to the air stream. The cooling capacity specified by this building descriptor should not consider the heat of the fan.

Note that the sensible heat ratio (SHR) used by some energy simulation tools can be calculated from the sensible cooling capacity and total cooling capacity:

SHR = Sensible Cooling Capacity / Total Cooling Capacity

Units

kBtu/h

Input Restrictions

As designed. For packaged equipment that has the fan motor located in the air stream such that it adds heat to the cooled air, the software shall adjust the sensible cooling capacity as follows:

Q_s,adj=Q_s,rated+BHP_supply×2.545

(12)

Where:

Q_s,adj = The adjusted sensible cooling capacity of a packaged unit (kBtu/h)

Q_s,rated = The ARI rated sensible cooling capacity of a packaged unit (kBtu/h)

BHP_supply = The supply fan brake horsepower (bhp) in the proposed building design.

If the number of UMLH in the proposed design exceeds 300, the software shall warn the user to resize the equipment.

Baseline Building

The sensible cooling capacity of the systems serving baseline building is oversized by 15%. Sizing calculations shall be based on the heating design day and cooling design day conditions, as defined in Section 3.2.3 of this document

Cooling Capacity Adjustment Curves

Applicability

All cooling systems

Definition

The sensible cooling capacity of the coil or packaged equipment at ARI conditions. The building descriptors defined in this chapter assume that the fan is modeled separately, including any heat it adds to the air stream. The cooling capacity specified by this building descriptor should not consider the heat of the fan.

Note that the SHR used by some energy simulation tools can be calculated from the sensible cooling capacity and total cooling capacity:

SHR = Sensible Cooling Capacity / Total Cooling Capacity

A curve that represents the available total cooling capacity as a function of rated cooling coil capacity and/or condenser conditions. The common form of these curves is given as follows:

Q_t,available=CAP_FT×Q_t,adj

(13)

For air-cooled DX

CAP_FT=a+b×t_wb+c×t_wb²+d×t_odb+e×t_odb²+f×t_wb×t_odb

(14)

For water-cooled DX

CAP_FT=a+b×t_wb+c×t_wb²+d×t_wt+e×t_wt²+f×t_wb×t_wt

(15)

For chilled water coils

CAP_FT=a+b×t_wb+c×t_wb²+d×t_db+e×t_db²+f×t_wb×t_db

(16)

Where:

Qt,available = Available cooling capacity at specified evaporator and/or condenser conditions (thousand British thermal units per hour [MBH])

Qt,adj = Adjusted capacity at ARI conditions (Btu/h) (see Equation 5)

CAP_FT = A multiplier to adjust Qt,adj

twb = The entering coil wet-bulb temperature (°F)

tdb = The entering coil dry-bulb temperature (°F)

twt = The water supply temperature (°F)

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

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.

Software may represent the relationship between cooling capacity and temperature in ways other than the equations given above.

Table 59. Cooling Capacity Curve Coefficients

Coefficient	Air Cooled DX		Water Cooled DX		Chilled Water Coils
Coefficient	Air-Source (PTAC)	Air-Source (Other DX)	Water-Source (Heat Pump)	Water-Source (Other DX)	Fan-Coil	Other Chilled Water
a	1.1839345	0.8740302	-0.2780377	0.9452633	0.5038866	2.5882585
b	-0.0081087	-0.0011416	0.0248307	-0.0094199	-0.0869176	-0.2305879
c	0.0002110	0.0001711	-0.0000095	0.0002270	0.0016847	0.0038359
d	-0.0061435	-0.0029570	-0.0032731	0.0004805	0.0336304	0.1025812
e	0.0000016	0.0000102	0.0000070	-0.0000045	0.0002478	0.0005984
f	-0.0000030	-0.0000592	-0.0000272	-0.0000599	-0.0010297	-0.0028721
Note: These curves are the DOE-2.1E defaults, except for Water-Source (Other DX), which is taken from the ECB Compliance Supplement, public review draft prepared by the SSPC 90.1 ECB Panel, Version 1.2, March 1996.

Units

Data structure

Input Restrictions

As designed. The equations and coefficients given above are the defaults.

Baseline Building

Default curves will be used for baseline building

*Coil Latent Modeling Method*
Applicability	All DX cooling systems
Definition	The method of modeling coil latent performance at part-load conditions
Units	List
Input Restrictions	One of the following values: Bypass factor – used by DOE-2 based programs NTU-effectiveness – used by EnergyPlus
Baseline Building	Same as proposed

Coil Bypass Factor

Applicability

All DX cooling systems (optional input)

Definition

The ratio of air that bypasses the cooling coil at design conditions to the total system airflow

Units

Ratio

Input Restrictions

Prescribed values as shown in Table 60

Table 60. Default Coil Bypass Factors

System Type	Default Bypass Factor
Packaged Terminal Air-conditioners and Heat Pumps	0.241
Other Packaged Equipment	0.190
Multi-Zone Systems	0.078
All Other	0.037

Baseline Building

Defaults

Coil Bypass Factor Adjustment Curve

Applicability

All DX cooling systems (optional input)

Definition

Adjustments for the amount of coil bypass due to the following factors:

Coil airflow rate as a percentage of rated system airflow
Entering air wet-bulb temperature
Entering air dry-bulb temperature
Part load ratio

Units

Data structure

Input Restrictions

Where applicable, prescribed (fixed) simulation engine defaults based on HVAC system type. The following default values shall be used for the adjustment curves:

CBF_adj=CBF_rated×COIL-BF-FFLOW×COIL-BF-FT×COIL-BF-FPLR

(17)

COIL-BF-FFLOW=a+b×CFMR+c×CFMR²+d×CFMR³

(18)

COIL-BF-FT=a+b×T_wb+c×T_wb²+d×T_db+e×T_db²+f×T_wb×T_db

(19)

COIL-BF-FPLR=a+b×PLR

(20)

Where:

CBF_rated = The coil bypass factor at ARI rating conditions

CBF_adj = The coil bypass factor adjusted for airflow and coil conditions

CFMR = The ratio of airflow to design airflow

COIL-BF-FFLOW = A multiplier on the rated coil bypass factor to account for variation in airflow across the coil (take coefficients from Table 61)

COIL-BF-FT = A multiplier on the rated coil bypass factor to account for a variation in coil entering conditions (take coefficients from Table 62)

COIL-BF-FPLR = A multiplier on the rated coil bypass factor to account for the part load ratio (take coefficients from Table 63)

T_wb = The entering coil wet-bulb temperature (°F)

T_db = The entering coil dry-bulb temperature (°F)

PLR = Part load ratio

And the coefficients are listed in the tables below.

Table 61. Coil Bypass Factor Airflow Adjustment Factor

Coefficient	COIL-BF-FFLOW (PTAC)	COIL-BF-FFLOW (HP)	COIL-BF-FFLOW (PSZ/other)
a	-2.277	-0.8281602	-0.2542341
b	5.21140	14.3179150	1.2182558
c	-1.93440	-21.8894405	0.0359784
d		9.3996897

Table 62. Coil Bypass Factor Temperature Adjustment Factor

Coefficient	COIL-BF-FT (PTAC)	COIL-BF-FT (HP)	COIL-BF-FT (PSZ, other)
a	-1.5713691	-29.9391098	1.0660053
b	0.0469633	0.8753455	-0.0005170
c	0.0003125	-0.0057055	0.0000567
d	-0.0065347	0.1614450	-0.0129181
e	0.0001105	0.0002907	-0.0000017
f	-0.0003719	-0.0031523	0.0001503

Table 63. Coil Bypass Factor Part Load Adjustment Factor

Coefficient	COIL-BF-FPLR (All Systems)
a	0.00
b	1.00

Source: (CEC 2013)

Baseline Building

Use defaults as described above