Baseline Building Summary. Baseline building systems 7 and 8 have one or more cooling towers. One tower is assumed to be matched to each baseline building chiller. The number of baseline building chillers is determined in 6.8.2. Each baseline building chiller has its own condenser water pump that operates when the chiller is brought into service. The range between the condenser water return (CWR) and condenser water supply (CWS) is 10 F so the condenser water flow is a constant 2.5 gpm per cooling ton1 when the chiller is in service. The baseline building pumping energy is assumed to be 19 W/gpm. The baseline building cooling tower is assumed to have a twospeed fan that is controlled to provide a CWS of 70 F when weather permits. The tower fan cycles to onespeed or off to maintain a CWS of 70 F at low wetbulb conditions. Under cooling conditions closer to design conditions, the CWS floats up to a maximum of 85 F (the design condition).
Cooling Tower Name  
Applicability  All cooling towers 

Definition  A unique descriptor for each cooling tower 
Units  Text, unique 
Input Restrictions  User entry. Where applicable, this should match the tags that are used on the plans. 
Baseline Rules  Descriptive name that keys the baseline building plant 
Cooling Tower Type  
Applicability  All cooling towers 

Definition  The type of cooling tower employed. The choices are:

Units  List (see above) 
Input Restrictions  As designed 
Baseline Rules  The baseline cooling tower is an open tower axial fan device with a twospeed fan (See PRM G3.1.3.11) 
Cooling Tower Capacity  
Applicability  All cooling towers 

Definition  The tower thermal capacity per cell adjusted to CTI (Cooling Technology Institute) rated conditions of 95 F condenser water return, 85 F condenser water supply, and 78 F wetbulb with a 3 gpm/nominal ton water flow. The default cooling tower curves below are at unity at these conditions. 
Units  Btu/h 
Input Restrictions  As designed 
Baseline Rules  The baseline building chiller is autosized and increased by 15%. The tower is sized to deliver 85 F condenser water supply at design conditions for the oversized chiller. 
Cooling Tower Number of Cells  
Applicability  All cooling towers 

Definition  The number of cells in the cooling tower. Each cell will be modeled as equal size. Cells are subdivisions in cooling towers into individual cells, each with their own fan and water flow, and allow the cooling system to respond more efficiently to lower load conditions. 
Units  Numeric: integer 
Input Restrictions  As designed 
Baseline Rules  One cell per tower and one tower per chiller. 
Cooling Tower Total Fan Horse Power  
Applicability  All cooling towers 

Definition  The sum of the nameplate rated horsepower (hp) of all fan motors on the cooling tower. Pony motors should not be included. 
Units  Horsepower (hp) 
Input Restrictions  As designed. For minimum compliance with ASHRAE Standard 90.12007, must be at least 38.2 gpm/hp for an axial fan cooling tower and at least 20.0 gpm/hp for a centrifugal fan cooling tower. (Table 6.8.1G) 
Baseline Rules  Not applicable since pump power is specified as 19 watts/gpm. 
Cooling Tower Design WetBulb  
Applicability  All cooling towers 

Definition  The design wetbulb temperature that was used for selection and sizing of the cooling tower. 
Units  Degrees Fahrenheit (°F) 
Input Restrictions  As designed. 
Baseline Rules  Same as proposed design 
Cooling Tower Design Entering Water Temperature  
Applicability  All cooling towers 

Definition  The design condenser water supply temperature (leaving tower) that was used for selection and sizing of the cooling tower. 
Units  Degrees Fahrenheit (°F) 
Input Restrictions  As designed. Default to 85°F. 
Baseline Rules  85°F or 10°F above the design wetbulb temperature, whichever is lower (Table 6.8.1G) 
Cooling Tower Design Return Water Temperature  
Applicability  All cooling towers 

Definition  The design condenser water return temperature (entering tower) that was used for selection and sizing of the cooling tower. 
Units  Degrees Fahrenheit (°F) 
Input Restrictions  As designed. Default to 95°F. 
Baseline Rules  Set to 95°F for a range of 10 F. (Table 6.8.1G) 
Cooling Tower Capacity Adjustment Curve(s)  
Applicability  All cooling towers  

Definition 
A curve or group of curves that represent the available total cooling capacity as a function of outdoor air wetbulb, condenser water supply and condenser water return temperatures. The default curves are given as follows: (6.8.31) $$ t_R = t_{cwr}  t_{cws}$$ $$ t_A = t_{cws}  t_{owb}$$ $$ t_A = a + b \times t_R + c \times \left. t_R\right. ^2 + d \times FRA + e \times FRA^2 + f \times t_R \times FRA$$ $$ FRA = \frac{ d  f \times t_R + \sqrt{\left ( d+ f \times t_R \right )^2  4 \times e \times \left ( a + b \times t_R + c \times \left. t_R \right. ^2  t_A\right )}}{2 \times e} $$ $$FW\!B = a + b \times FRA + c \times FRA^2 + d \times t_{owb} + e \times \left. t_{owb} \right. ^2 + f \times FRA \times t_{owb}$$ $$ Q_{available} = Q_{rated} \times FW\!B \times \left ( \frac{t_R}{10} \right )$$ where
[table title="Default Capacity Coefficients – Cooling Towers" id="defaultcapacitycoefficients–coolingtowers"]


Units  Data structure  
Input Restrictions  User may input curves or use default curves. If defaults are overridden, the rating software must indicate that supporting documentation is required on the output forms.  
Baseline Rules  Use default curves. 
Cooling Tower Set Point Control  
Applicability  All cooling towers  

Definition  The type of control for the condenser water supply. The choices are:
A fixed control will modulate the tower to provide the design supply water temperature at all times. A wetbulb reset control will reset according to the following control scheme: (6.8.32) $$ t_{cws} = t_{owb} + t_A + RR \times \left ( t_{dwb}  t_{owb}\right )$$ where
A reset ratio (RR) of 0 will force the tower to always attempt a fixed approach to the outdoor wetbulb temperature. A reset ratio (RR) of 1 will cause the system to perform as if it had fixed condenser water controls. 

Units  List (see above)  
Input Restrictions  As designed. If the user does not use the default curve, supporting documentation is required.  
Baseline Rules  Fixed at 70°F 
Cooling Tower Capacity Control  
Applicability  All cooling towers 

Definition  Describes the modulation control employed in the cooling tower. Choices include:

Units  List (see above) 
Input Restrictions  As designed. 
Baseline Rules  Twospeed fan 
Cooling Tower LowSpeed Airflow Ratio  
Applicability  All cooling towers with twospeed or pony motors 

Definition  The percentage full load airflow that the tower has at low speed or with the pony motor operating. This is equivalent to the percentage full load capacity when operating at low speed. 
Units  Ratio 
Input Restrictions  As designed. 
Baseline Rules  0.50 
Cooling Tower LowSpeed kW Ratio  
Applicability  All cooling towers 

Definition  The percentage full load power that the tower fans draw at low speed or with the pony motor operating 
Units  Ratio 
Input Restrictions  As designed. 
Baseline Rules  0.30 
Cooling Tower Power Adjustment Curve  
Applicability  All cooling towers with VSD control  

Definition 
A curve that varies the cooling tower fan energy usage as a function of partload ratio for cooling towers with variable speed fan control. The default curve is given as follows: (6.8.33) $$ PLR = \frac{Q_{operating}}{Q_{available}\left ( t_R, t_A, t_{OW\!B}\right )}$$ $$ TW\!R\!\_F\!AN\!\_F\!P\!L\!R = a + b \times PLR + c \times PLR^2$$ $$ P_{operating} = P_{rated} \times TW\!R\!\_F\!AN\!\_F\!P\!L\!R $$ where
[table title="Default Efficiency TWRFANFPLR Coefficients – VSD on Cooling Tower Fan" id="defaultefficiencyTWRFANFPLRcoefficients–VSDoncoolingtowerfan"]


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 from DOE 2, given above. 
Cooling Tower Minimum Speed  
Applicability  All cooling towers with a VSD control 

Definition  The minimum fan speed setting of a VSD controlling a cooling tower fan expressed as a ratio of full load speed. 
Units  Ratio 
Input Restrictions  As designed. The default is 0.40. 
Baseline Rules  Not applicable 
 1. Cooling capacity is related to flow and deltaT through the equation Q = 500 * GPM * DeltaT. When Q is one ton (12,000 Btu/h), GPM = 24 / DeltaT and DeltaT = 24 / GPM
Baseline HVAC Tower Characteristics
Baseline building systems 7, 8, 11, 12, and 13 have one or more cooling towers.
The baseline heat rejection device shall be an axialfan opencircuit cooling tower with variablespeed fan control and shall have an efficiency of 38.2 gpm/hp at the conditions specified in Table 6.8.17 of Standard 90.121016.
Condenser water design supply temperature shall be calculated using the cooling tower approach to the 0.4% evaporation design wetbulb temperature as generated by the formula below, with a design temperature rise of 10°F.
$$Approach\ 10°F\ Range = 25.72  (0.24 \times WB)$$
where
WB is the 0.4% evaporation design wetbulb temperature in °F; valid for wet bulbs from 55°F to 90°F.
The tower shall be controlled to maintain a leaving water temperature based on climate zone (see below), floating up to the design leaving water temperature for the cooling tower.
Climate Zone 
Leaving Water Temperature 
5B, 5C, 6B, 8 
65°F 
0B, 1B, 2B, 3B, 3C, 4B, 4C, 5A, 6A, 7 
70°F 
3A,4A 
75°F 
0A, 1A, 2A 
80°F 
The baseline building design condenserwater pump power shall be 19 W/gpm and modeled as constant volume. For computer room systems using System 11 with an integrated waterside economizer, the baseline building design condenser waterpump power shall be increased by 3 W/gpm for flow associated with the waterside economizer. Each chiller shall be modeled with separate condenser water and chilledwater pumps interlocked to operate with the associated chiller.
Cooling Tower Name 


Applicability 
All cooling towers 
Definition 
A unique descriptor for each cooling tower 
Units 
Text, unique 
Input Restrictions 
User entry. Where applicable, this should match the tags that are used on the plans. 
Baseline Rules 
Descriptive name that keys the baseline building plant 
Cooling Tower Type 


Applicability 
All cooling towers 
Definition 
The type of cooling tower employed. The choices are:
Open cooling towers collect the cooled water from the tower and pump it directly back to the cooling system. Closed towers circulate the evaporated water over a heat exchanger to indirectly cool the system fluid. 
Units 
List (see above) 
Input Restrictions 
As designed 
Baseline Rules 
The baseline cooling tower is an open tower axial fan device with a variable speed drive. 
Cooling Tower Capacity1 


Applicability 
All cooling towers 
Definition 
The tower thermal capacity per cell adjusted to CTI (Cooling Technology Institute) rated conditions of 95 °F condenser water return, 85 °F condenser water supply, and 78 °F wetbulb with a 3 gpm/nominal ton water flow. The default cooling tower curves below are at unity at these conditions. 
Units 
Btu/h 
Input Restrictions 
As designed 
Baseline Rules 
The baseline building chiller is autosized and increased by 15%. The tower is sized to supply 85 °F condenser water or 10 °F approach to wet bulb, whichever is lower, at design conditions for the oversized chiller. 
Cooling Tower Number of Cells 


Applicability 
All cooling towers 
Definition 
The number of cells in the cooling tower. Each cell will be modeled as equal size. Cells are subdivisions in cooling towers into individual cells, each with their own fan and water flow, and allow the cooling system to respond more efficiently to lower load conditions. 
Units 
Numeric: integer 
Input Restrictions 
As designed 
Baseline Rules 
One cell per tower and one tower per chiller. 
Cooling Tower Total Fan Horse Power 


Applicability 
All cooling towers 
Definition 
The sum of the nameplate rated horsepower (hp) of all fan motors on the cooling tower. Pony motors should not be included. 
Units 
Gpm/hp or unitless if energy input ratio (EIR) is specified (If the nominal tons but not the condenser water flow is specified, the condenser design water flow shall be 2.4 gpm per nominal cooling ton.) 
Input Restrictions 
As designed, but the cooling towers shall meet minimum performance requirements in Table 6.8.1G of Standard 90.12016 and must be at least 38.2 gpm/hp for an axial fan cooling tower and at least 20 gpm/hp for a centrifugal fan cooling tower. 
Baseline Rules 
38.2 gpm/hp 
Cooling Tower Design WetBulb 


Applicability 
All cooling towers 
Definition 
The design wetbulb temperature that was used for selection and sizing of the cooling tower. 
Units 
Degrees Fahrenheit (°F) 
Input Restrictions 
As designed. 
Baseline Rules 
1% wetbulb design conditions if the baseline systemhas a cooling tower 
Cooling Tower Design Leaving Water Temperature 


Applicability 
All cooling towers 
Definition 
The design condenser water supply temperature (leaving tower) that was used for selection and sizing of the cooling tower. 
Units 
Degrees Fahrenheit (°F) 
Input Restrictions 
As designed. Default to 85°F. 
Baseline Rules 
85°F or 10°F above the design wetbulb temperature, whichever is lower 
Cooling Tower Design Entering Water Temperature 


Applicability 
All cooling towers 
Definition 
The design condenser water return temperature (entering tower) that was used for selection and sizing of the cooling tower. 
Units 
Degrees Fahrenheit (°F) 
Input Restrictions 
As designed. Default to 95°F. 
Baseline Rules 
Set to 10 °F above the cooling tower design leaving water temperature. 
Cooling Tower Capacity Adjustment Curve(s) 


Applicability 
All cooling towers 

Definition 
A curve or group of curves that represent the available total cooling capacity as a function of outdoor air wetbulb, condenser water supply and condenser water return temperatures. The default curves are given as follows: (Equation 3.8.31) $$t_{R} = t_{cwr}  t_{cws}$$ $$t_{A} = t_{cws}  t_{owb}$$ $$t_{A} = a + b \cdot t_{R} + c \cdot t_{R}^{2} + d \cdot FRA + e \cdot FRA^{2} + f \cdot t_{R} \cdot FRA$$ $$FRA = \frac{d f \cdot t_{R} + \sqrt{(d + f +t_{R})^{2}  4 \cdot e \cdot \left ( a+b \cdot t_{R} + c \cdot t_{R}^{2}  t_{A} \right )}}{2 \times e}$$ $$FWB = a + b \cdot FRA + c \cdot FRA^{2} + d \cdot t_{OWB} + e \cdot t_{OWB}^{2} + f \cdot t_{OWB} \cdot FRA$$ $$Q_{available} = Q_{rated} \cdot FWB \cdot \left ( \frac{t_{R}}{10} \right )$$ Where


Units 
Data structure 

Input Restrictions 
User may input curves or use default curves. If defaults are overridden, the rating software must indicate that supporting documentation is required on the output forms. 

Baseline Rules 
Use default curves. 
Cooling Tower Set Point Control 


Applicability 
All cooling towers 

Definition 
The type of control for the condenser water supply. The choices are:
A fixed control will modulate the tower to provide the design supply water temperature at all times. A wetbulb reset control will reset according to the following control scheme: (Equation 3.8.32) $$t_{cws} = t_{owb} + t_{A} + RR \cdot \left ( t_{dwb} + t_{owb} \right )$$ where
A reset ratio (RR) of 0 will force the tower to always attempt a fixed approach to the outdoor wetbulb temperature. A reset ratio (RR) of 1 will cause the system to perform as if it had fixed condenser water controls. 

Units 
List (see above) 

Input Restrictions 
As designed. If the user does not use the default curve, supporting documentation is required. 

Baseline Rules 
Controlled to 70°F when weather permits, floating up to leaving water temperature at design conditions 
Cooling Tower Capacity Control 


Applicability 
All cooling towers 
Definition 
Describes the modulation control employed in the cooling tower. Choices include:

Units 
List (see above) 
Input Restrictions 
As designed. 
Baseline Rules 
Variable speed fan 
Cooling Tower LowSpeed Airflow Ratio 


Applicability 
All cooling towers with twospeed or pony motors 
Definition 
The percentage full load airflow that the tower has at low speed or with the pony motor operating. This is equivalent to the percentage full load capacity when operating at low speed. 
Units 
Ratio between 0 and 1.0 
Input Restrictions 
As designed. 
Baseline Rules 
0.50 
Cooling Tower LowSpeed kW Ratio 


Applicability 
All cooling towers 
Definition 
The percentage full load power that the tower fans draw at low speed or with the pony motor operating 
Units 
Ratio between 0 and 1.0 
Input Restrictions 
As designed. 
Baseline Rules 
0.30 
Cooling Tower Fan Power Adjustment Curve 


Applicability 
All cooling towers with VSD control 

Definition 
A curve that varies the cooling tower fan energy usage as a function of partload ratio for cooling towers with variable speed fan control. The default curve is given as follows: (Equation 3.8.33) $$PLR = \frac{Q_{operating}}{Q_{available}(t_{R},t_{A}, t_{owb})}$$ $$TWR\_FAN\_FPLR = a + b \cdot PLR + c \cdot PLR^{2} + d \cdot PLR^{3}$$ $$P_{operating} = P_{rated} \cdot TWR\_FAN\_FPLR$$
where


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 and coefficients, given above. 
Cooling Tower Minimum Speed 


Applicability 
All cooling towers with a VSD control 
Definition 
The minimum fan speed setting of a VSD controlling a cooling tower fan expressed as a ratio of full load speed 
Units 
Ratio between 0 and 1.0 
Input Restrictions 
As designed. The default is 0.40. 
Baseline Rules 
Not applicable 
 1. Cooling capacity is related to flow and deltaT through the equation Q = 500 * GPM * DeltaT. When Q is one ton (12,000 Btu/h), GPM = 24 / DeltaT and DeltaT = 24 / GPM
Cooling Tower Name  
Applicability  All cooling towers 

Definition  A unique descriptor for each cooling tower 
Units  Text, unique 
Input Restrictions  User entry. Where applicable, this should match the tags that are used on the plans. 
Cooling Tower Type  
Applicability  All cooling towers 

Definition  The type of cooling tower employed. The choices are:

Units  List (see above) 
Input Restrictions  As designed 
Cooling Tower Capacity  
Applicability  All cooling towers 

Definition  The tower thermal capacity per cell adjusted to CTI (Cooling Technology Institute) rated conditions of 95 F condenser water return, 85 F condenser water supply, and 78 F wetbulb with a 3 gpm/nominal ton water flow. The default cooling tower curves below are at unity at these conditions. 
Units  Btu/h 
Input Restrictions  As designed 
Cooling Tower Number of Cells  
Applicability  All cooling towers 

Definition  The number of cells in the cooling tower. Each cell will be modeled as equal size. Cells are subdivisions in cooling towers into individual cells, each with their own fan and water flow, and allow the cooling system to respond more efficiently to lower load conditions. 
Units  Numeric: integer 
Input Restrictions  As designed 
Cooling Tower Total Fan Horse Power  
Applicability  All cooling towers 

Definition  The sum of the nameplate rated horsepower (hp) of all fan motors on the cooling tower. Pony motors should not be included. 
Units  Horsepower (hp) 
Input Restrictions  As designed. 
Cooling Tower Design WetBulb  
Applicability  All cooling towers 

Definition  The design wetbulb temperature that was used for selection and sizing of the cooling tower. 
Units  Degrees Fahrenheit (°F) 
Input Restrictions  As designed. 
Cooling Tower Design Entering Water Temperature  
Applicability  All cooling towers 

Definition  The design condenser water supply temperature (leaving tower) that was used for selection and sizing of the cooling tower. 
Units  Degrees Fahrenheit (°F) 
Input Restrictions  As designed. Default to 85°F. 
Cooling Tower Design Return Water Temperature  
Applicability  All cooling towers 

Definition  The design condenser water return temperature (entering tower) that was used for selection and sizing of the cooling tower. 
Units  Degrees Fahrenheit (°F) 
Input Restrictions  As designed. Default to 95°F. 
Cooling Tower Capacity Adjustment Curve(s)  
Applicability  All cooling towers  

Definition 
A curve or group of curves that represent the available total cooling capacity as a function of outdoor air wetbulb, condenser water supply and condenser water return temperatures. The default curves are given as follows: (6.8.31) $$ t_R = t_{cwr}  t_{cws}$$ $$ t_A = t_{cws}  t_{owb}$$ $$ t_A = a + b \times t_R + c \times \left. t_R\right. ^2 + d \times FRA + e \times FRA^2 + f \times t_R \times FRA$$ $$ FRA = \frac{ d  f \times t_R + \sqrt{\left ( d+ f \times t_R \right )^2  4 \times e \times \left ( a + b \times t_R + c \times \left. t_R \right. ^2  t_A\right )}}{2 \times e} $$ $$FW\!B = a + b \times FRA + c \times FRA^2 + d \times t_{owb} + e \times \left. t_{owb} \right. ^2 + f \times FRA \times t_{owb}$$ $$ Q_{available} = Q_{rated} \times FW\!B \times \left ( \frac{t_R}{10} \right )$$ where
[table title="Default Capacity Coefficients – Cooling Towers" id="defaultcapacitycoefficients–coolingtowers"]


Units  Data structure  
Input Restrictions  User may input curves or use default curves. If defaults are overridden, the rating software must indicate that supporting documentation is required on the output forms. 
Cooling Tower Set Point Control  
Applicability  All cooling towers  

Definition  The type of control for the condenser water supply. The choices are:
A fixed control will modulate the tower to provide the design supply water temperature at all times. A wetbulb reset control will reset according to the following control scheme: (6.8.32) $$ t_{cws} = t_{owb} + t_A + RR \times \left ( t_{dwb}  t_{owb}\right )$$ where
A reset ratio (RR) of 0 will force the tower to always attempt a fixed approach to the outdoor wetbulb temperature. A reset ratio (RR) of 1 will cause the system to perform as if it had fixed condenser water controls. 

Units  List (see above)  
Input Restrictions  As designed. If the user does not use the default curve, supporting documentation is required. 
Cooling Tower Capacity Control  
Applicability  All cooling towers 

Definition  Describes the modulation control employed in the cooling tower. Choices include:

Units  List (see above) 
Input Restrictions  As designed. 
Cooling Tower LowSpeed Airflow Ratio  
Applicability  All cooling towers with twospeed or pony motors 

Definition  The percentage full load airflow that the tower has at low speed or with the pony motor operating. This is equivalent to the percentage full load capacity when operating at low speed. 
Units  Ratio 
Input Restrictions  As designed. 
Cooling Tower LowSpeed kW Ratio  
Applicability  All cooling towers 

Definition  The percentage full load power that the tower fans draw at low speed or with the pony motor operating 
Units  Ratio 
Input Restrictions  As designed. 
Cooling Tower Power Adjustment Curve  
Applicability  All cooling towers with VSD control  

Definition 
A curve that varies the cooling tower fan energy usage as a function of partload ratio for cooling towers with variable speed fan control. The default curve is given as follows: (6.8.33) $$ PLR = \frac{Q_{operating}}{Q_{available}\left ( t_R, t_A, t_{OW\!B}\right )}$$ $$ TW\!R\!\_F\!AN\!\_F\!P\!L\!R = a + b \times PLR + c \times PLR^2$$ $$ P_{operating} = P_{rated} \times TW\!R\!\_F\!AN\!\_F\!P\!L\!R $$ where
[table title="Default Efficiency TWRFANFPLR Coefficients – VSD on Cooling Tower Fan" id="defaultefficiencyTWRFANFPLRcoefficients–VSDoncoolingtowerfan"]


Units  Data structure  
Input Restrictions  User may input curves or use default curves. If defaults are overridden, supporting documentation is required. 
Cooling Tower Minimum Speed  
Applicability  All cooling towers with a VSD control 

Definition  The minimum fan speed setting of a VSD controlling a cooling tower fan expressed as a ratio of full load speed. 
Units  Ratio 
Input Restrictions  As designed. The default is 0.40. 
Cooling Tower Name  
Applicability  All cooling towers 

Definition  A unique descriptor for each cooling tower 
Units  Text, unique 
Input Restrictions  User entry. Where applicable, this should match the tags that are used on the plans. 
Cooling Tower Type  
Applicability  All cooling towers 

Definition  The type of cooling tower employed. The choices are:

Units  List (see above) 
Input Restrictions  As designed 
Cooling Tower Capacity  
Applicability  All cooling towers 

Definition  The tower thermal capacity per cell adjusted to CTI (Cooling Technology Institute) rated conditions of 95 F condenser water return, 85 F condenser water supply, and 78 F wetbulb with a 3 gpm/nominal ton water flow. The default cooling tower curves below are at unity at these conditions. 
Units  Btu/h 
Input Restrictions  As designed 
Cooling Tower Number of Cells  
Applicability  All cooling towers 

Definition  The number of cells in the cooling tower. Each cell will be modeled as equal size. Cells are subdivisions in cooling towers into individual cells, each with their own fan and water flow, and allow the cooling system to respond more efficiently to lower load conditions. 
Units  Numeric: integer 
Input Restrictions  As designed 
Cooling Tower Total Fan Horse Power  
Applicability  All cooling towers 

Definition  The sum of the nameplate rated horsepower (hp) of all fan motors on the cooling tower. Pony motors should not be included. 
Units  Horsepower (hp) 
Input Restrictions  As designed. 
Cooling Tower Design WetBulb  
Applicability  All cooling towers 

Definition  The design wetbulb temperature that was used for selection and sizing of the cooling tower. 
Units  Degrees Fahrenheit (°F) 
Input Restrictions  As designed. 
Cooling Tower Design Entering Water Temperature  
Applicability  All cooling towers 

Definition  The design condenser water supply temperature (leaving tower) that was used for selection and sizing of the cooling tower. 
Units  Degrees Fahrenheit (°F) 
Input Restrictions  As designed. Default to 85°F. 
Cooling Tower Design Return Water Temperature  
Applicability  All cooling towers 

Definition  The design condenser water return temperature (entering tower) that was used for selection and sizing of the cooling tower. 
Units  Degrees Fahrenheit (°F) 
Input Restrictions  As designed. Default to 95°F. 
Cooling Tower Capacity Adjustment Curve(s)  
Applicability  All cooling towers  

Definition 
A curve or group of curves that represent the available total cooling capacity as a function of outdoor air wetbulb, condenser water supply and condenser water return temperatures. The default curves are given as follows: (6.8.31) $$ t_R = t_{cwr}  t_{cws}$$ $$ t_A = t_{cws}  t_{owb}$$ $$ t_A = a + b \times t_R + c \times \left. t_R\right. ^2 + d \times FRA + e \times FRA^2 + f \times t_R \times FRA$$ $$ FRA = \frac{ d  f \times t_R + \sqrt{\left ( d+ f \times t_R \right )^2  4 \times e \times \left ( a + b \times t_R + c \times \left. t_R \right. ^2  t_A\right )}}{2 \times e} $$ $$FW\!B = a + b \times FRA + c \times FRA^2 + d \times t_{owb} + e \times \left. t_{owb} \right. ^2 + f \times FRA \times t_{owb}$$ $$ Q_{available} = Q_{rated} \times FW\!B \times \left ( \frac{t_R}{10} \right )$$ where
[table title="Default Capacity Coefficients – Cooling Towers" id="defaultcapacitycoefficients–coolingtowers"]


Units  Data structure  
Input Restrictions  User may input curves or use default curves. If defaults are overridden, the rating software must indicate that supporting documentation is required on the output forms. 
Cooling Tower Set Point Control  
Applicability  All cooling towers  

Definition  The type of control for the condenser water supply. The choices are:
A fixed control will modulate the tower to provide the design supply water temperature at all times. A wetbulb reset control will reset according to the following control scheme: (6.8.32) $$ t_{cws} = t_{owb} + t_A + RR \times \left ( t_{dwb}  t_{owb}\right )$$ where
A reset ratio (RR) of 0 will force the tower to always attempt a fixed approach to the outdoor wetbulb temperature. A reset ratio (RR) of 1 will cause the system to perform as if it had fixed condenser water controls. 

Units  List (see above)  
Input Restrictions  As designed. If the user does not use the default curve, supporting documentation is required. 
Cooling Tower Capacity Control  
Applicability  All cooling towers 

Definition  Describes the modulation control employed in the cooling tower. Choices include:

Units  List (see above) 
Input Restrictions  As designed. 
Cooling Tower LowSpeed Airflow Ratio  
Applicability  All cooling towers with twospeed or pony motors 

Definition  The percentage full load airflow that the tower has at low speed or with the pony motor operating. This is equivalent to the percentage full load capacity when operating at low speed. 
Units  Ratio 
Input Restrictions  As designed. 
Cooling Tower LowSpeed kW Ratio  
Applicability  All cooling towers 

Definition  The percentage full load power that the tower fans draw at low speed or with the pony motor operating 
Units  Ratio 
Input Restrictions  As designed. 
Cooling Tower Power Adjustment Curve  
Applicability  All cooling towers with VSD control  

Definition 
A curve that varies the cooling tower fan energy usage as a function of partload ratio for cooling towers with variable speed fan control. The default curve is given as follows: (6.8.33) $$ PLR = \frac{Q_{operating}}{Q_{available}\left ( t_R, t_A, t_{OW\!B}\right )}$$ $$ TW\!R\!\_F\!AN\!\_F\!P\!L\!R = a + b \times PLR + c \times PLR^2$$ $$ P_{operating} = P_{rated} \times TW\!R\!\_F\!AN\!\_F\!P\!L\!R $$ where
[table title="Default Efficiency TWRFANFPLR Coefficients – VSD on Cooling Tower Fan" id="defaultefficiencyTWRFANFPLRcoefficients–VSDoncoolingtowerfan"]


Units  Data structure  
Input Restrictions  User may input curves or use default curves. If defaults are overridden, supporting documentation is required. 
Cooling Tower Minimum Speed  
Applicability  All cooling towers with a VSD control 

Definition  The minimum fan speed setting of a VSD controlling a cooling tower fan expressed as a ratio of full load speed. 
Units  Ratio 
Input Restrictions  As designed. The default is 0.40. 