3.7.5.3 Evaporative Cooler

This is equipment that pre-cools the outside air that is brought into the building. It may be used with any type of cooling system that brings in outside air. This equipment is not applicable for the baseline building.

Evaporative Cooling Type
Applicability	Systems with evaporative pre-cooling
Definition	The type of evaporative pre-cooler, including: None Non-Integrated Indirect Non-Integrated Direct/Indirect Integrated Indirect Integrated Direct/Indirect An integrated pre-cooler can operate together with the compression or CHW cooling. A non-integrated pre-cooler will shut down the evaporative cooling whenever it is unable to provide 100% of the cooling required. In all cases, the evaporative pre-cooler must be modeled with 100% of the outside air routed through the pre-cooler.
Units	None
Input Restrictions	As designed
Baseline Rules	Not applicable

Direct Stage Effectiveness

Applicability

Systems with evaporative pre-cooling

Definition

The effectiveness of the direct stage of an evaporative cooling system. Effectiveness is defined as follows:

(Equation 3.7.5.3-1)

$$DirectEFF=\frac{T_{db}-T_{direct}}{T_{db}-T_{wb}}$$

Where

DirectEFF	The direct stage effectiveness
Tdb	The entering air dry-bulb temperature
Twb	The entering air wet-bulb temperature
Tdirect	The direct stage leaving dry-bulb temperature

Units

Numeric

Input Restrictions

As designed

Baseline Rules

Not applicable

Indirect Stage Effectiveness

Applicability

Systems with evaporative pre-cooling

Definition

The effectiveness of the indirect stage of an evaporative cooling system. Effectiveness is defined as follows:

(Equation 3.7.5.3-2)

$$IndEFF=\frac{T_{db}-T_{ind}}{T_{db}-T_{wb}}$$

where

IndEFF	The indirect stage effectiveness
Tdb	The entering air dry-bulb temperature of the supply air
Twb	The entering air wet-bulb temperature of the “scavenger air”
Tind	The supply air leaving dry-bulb temperature

Units

Numeric, a value between zero and one

Input Restrictions

As designed

Baseline Rules

Not applicable

Evaporative Cooling Performance Curves

Applicability

Systems with evaporative cooling

Definition

A curve that varies the evaporative cooling effectiveness as a function of primary air stream airflow. The default curves are given as follows:

(Equation 3.7.5.3-3)

$$PLR=\frac{CFM_{operating}}{CFM_{design}}$$

$$EFF\_FFLOW=a+b\cdot PLR+ c \cdot PLR^{2}$$

where

PLR	Part load ratio of airflow based on design airflow
EFF-FFLOW	A multiplier on the evaporative cooler effectiveness to account for variations in part load
CFMoperating	Operating primary air stream airflow (cfm)
CFMdesign	Design primary air stream airflow (cfm)
a, b, c	Coefficients from Appendix H

Units

Data structure

Input Restrictions

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

Baseline Rules

Not appliable

Auxiliary Evaporative Cooling Power
Applicability	Systems with evaporative cooling
Definition	The auxiliary energy of the indirect evaporative cooler fan, and the pumps for both direct and indirect stages
Units	kW or kW/cfm
Input Restrictions	As designed
Baseline Rules	Not applicable

Evaporative Cooling Scavenger Air Source
Applicability	Systems with evaporative cooling
Definition	The source of scavenger air for an indirect section of an evaporative cooler. Options include: Return Air Outside Air
Units	List (see above)
Input Restrictions	As designed
Baseline Rules	Not applicable

This is equipment that pre-cools the outside air that is brought into the building. It may be used with any type of cooling system that brings in outside air. This equipment is not applicable for the baseline building. The analyst must be careful to input evaporative cooler and outside air controls, as allowed by the software that reasonably reflect anticipated operation as indicated in sequences of operation, and review the simulation outputs, particularly zone or return air relative humidity, to ensure that the simulated sensible cooling from the evaporative cooler is realistic.

Evaporative Cooling Type
Applicability	Systems with evaporative pre-cooling
Definition	The type of evaporative pre-cooler, including: None Non-integrated indirect Non-integrated direct/indirect Integrated indirect Integrated direct/indirect An integrated pre-cooler can operate together with the compression or CHW cooling. A non-integrated pre-cooler will shut down the evaporative cooling whenever it is unable to provide 100% of the cooling required. In all cases, the evaporative pre-cooler must be modeled with 100% of the outside air routed through the pre-cooler.
Units	None
Input Restrictions	As designed
Baseline Building	Not applicable

Evaporative Cooling System Capacity
Applicability	Systems with evaporative cooling
Definition	The total sensible cooling capacity of the evaporative cooling system at design outdoor dry-bulb conditions. This value may be derived from other inputs of supply fan design air rated capacity (5.7.3), direct stage effectiveness, indirect stage effectiveness, and design outdoor conditions.
Units	None
Input Restrictions	Not applicable. This is a derived input. If there are excessive UMLH in any zone served by the evaporative cooling system, a supplementary DX cooling unit must be defined by the user. See Section 3.7.5.2 of this document for descriptors related to DX cooling units.
Baseline Building	Not applicable

Direct Stage Effectiveness

Applicability

Systems with evaporative pre-cooling

Definition

The effectiveness of the direct stage of an evaporative cooling system. Effectiveness is defined as follows:

$$DirectEFF=\frac{T_{db}-T_{direct}}{T_{db}-T_{wb}}$$

(27)

Where:

DirectEFF = The direct stage effectiveness

T_db = The entering air dry-bulb temperature

T_wb = The entering air wet-bulb temperature

T_direct = The direct stage leaving dry-bulb temperature

Units

Numeric (0 <= eff <=1)

Input Restrictions

As designed

Baseline Building

Not applicable

Indirect Stage Effectiveness

Applicability

Systems with evaporative pre-cooling

Definition

The effectiveness of the indirect stage of an evaporative cooling system. Effectiveness is defined as follows:

$$IndEFF=\frac{T_{db}-T_{ind}}{T_{db}-T_{wb}}$$

(28)

Where:

IndEFF = The indirect stage effectiveness

Tdb = The entering air dry-bulb temperature of the supply air

Twb = The entering air wet-bulb temperature of the “scavenger air”

Tind = The supply air leaving dry-bulb temperature

Units

Numeric (0 <= eff <=1)

Input Restrictions

As designed

Baseline Building

Not applicable

Evaporative Cooling Performance Curves

Applicability

Systems with evaporative cooling

Definition

A curve that varies the evaporative cooling effectiveness as a function of primary air stream airflow. The default curves are given as follows:

$$PLR=\frac{CFM_{operating}}{CFM_{design}}$$

$$EFF\_FFLOW=a+b\times PLR+c\times PLR^2$$

(29)

Where:

PLR = Part load ratio of airflow based on design airflow

EFF-FFLOW = A multiplier on the evaporative cooler effectiveness to account for variations in part load

CFM_operating = Operating primary air stream airflow (cfm)

CFM_design = Design primary air stream airflow (cfm)

Table 71. Part Load Curve Coefficients – Evaporative Cooler Effectiveness

Coefficient	Direct	Indirect
a	1.1833000	1.0970000
b	-0.2575300	-0.1650600
c	0.0742450	0.0680690
Source: COMNET 2017

Units

Data structure

Input Restrictions

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

Baseline Building

Not used

*Auxiliary Evaporative Cooling Power*
Applicability	Systems with evaporative cooling
Definition	The auxiliary energy of the indirect evaporative cooler fan, and the pumps for both direct and indirect stages
Units	Watts
Input Restrictions	As designed
Baseline Building	Not applicable

*Evaporative Cooling Scavenger Air Source*
Applicability	Systems with evaporative cooling
Definition	The source of scavenger air for an indirect section of an evaporative cooler. Options include: Return air Outside air
Units	List (see above)
Input Restrictions	As designed
Baseline Building	Not applicable

This is equipment that pre-cools the outside air that is brought into the building. It may be used with any type of cooling system that brings in outside air. The analyst must be careful to input evaporative cooler and outside air controls, as allowed by the software that reasonably reflect anticipated operation as indicated in sequences of operation, and review the simulation outputs, particularly zone or return air relative humidity, to ensure that the simulated sensible cooling from the evaporative cooler is realistic. This equipment is not applicable for the baseline building for projects subject to Standard 90.1-2022 Section G3.2.

Evaporative Cooling Type
Applicability	Systems with evaporative pre-cooling
Definition	The type of evaporative pre-cooler, including: None Non-integrated indirect Non-integrated direct/indirect Integrated indirect Integrated direct/indirect An integrated pre-cooler can operate together with the compressor or CHW cooling. A non-integrated pre-cooler will shut down the evaporative cooling whenever it is unable to provide 100% of the cooling required. In all cases, the evaporative pre-cooler must be modeled with 100% of the outside air routed through the pre-cooler.
Units	None
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations Not applicable G3.3 Minor Alterations Same as proposed.

Evaporative Cooling System Capacity
Applicability	Systems with evaporative cooling
Definition	The total sensible cooling capacity of the evaporative cooling system at design outdoor dry-bulb conditions. This value may be derived from other inputs of supply fan design air rated capacity (5.7.3), direct stage effectiveness, indirect stage effectiveness, and design outdoor conditions.
Units	None
Input Restrictions	Not applicable. This is a derived input. If there are excessive UMLH in any zone served by the evaporative cooling system, a supplementary DX cooling unit must be defined by the user. See Section 3.7.5.2 of this document for descriptors related to DX cooling units.
Baseline Building	G3.2 New Construction/Major Alterations Not applicable G3.3 Minor Alterations Same as proposed.

Direct Stage Effectiveness

Applicability

Systems with evaporative pre-cooling

Definition

The effectiveness of the direct stage of an evaporative cooling system. Effectiveness is defined as follows:

$$DirectEFF=\frac{T_{db}-T_{direct}}{T_{db}-T_{wb}}$$

(28)

Where:

DirectEFF = The direct stage effectiveness

T_db = The entering air dry-bulb temperature

T_wb = The entering air wet-bulb temperature

T_direct = The direct stage leaving dry-bulb temperature

Units

Numeric (0 <= eff <=1)

Input Restrictions

As designed

Baseline Building

G3.2 New Construction/Major Alterations

Not applicable

G3.3 Minor Alterations

Same as the proposed design.

Indirect Stage Effectiveness

Applicability

Systems with evaporative pre-cooling

Definition

The effectiveness of the indirect stage of an evaporative cooling system. Effectiveness is defined as follows:

$$IndEFF=\frac{T_{db}-T_{ind}}{T_{db}-T_{wb}}$$

(29)

Where:

IndEFF = The indirect stage effectiveness

Tdb = The entering air dry-bulb temperature of the supply air

Twb = The entering air wet-bulb temperature of the “scavenger air”

Tind = The supply air leaving dry-bulb temperature

Units

Numeric (0 <= eff <=1)

Input Restrictions

As designed

Baseline Building

G3.2 New Construction/Major Alterations

Not applicable

G3.3 Minor Alterations

Same as the proposed design.

Evaporative Cooling Performance Curves

Applicability

Systems with evaporative cooling

Definition

A curve that varies the evaporative cooling effectiveness as a function of primary air stream airflow. The default curves are given as follows:

$$PLR=\frac{CFM_{operating}}{CFM_{design}}$$

$$EFF\_FFLOW=a+b\times PLR+c\times PLR^2$$

(30)

Where:

PLR = Part load ratio of airflow based on design airflow

EFF-FFLOW = A multiplier on the evaporative cooler effectiveness to account for variations in part load

CFM_operating = Operating primary air stream airflow (cfm)

CFM_design = Design primary air stream airflow (cfm)

Table 78. Part Load Curve Coefficients – Evaporative Cooler Effectiveness

Coefficient	Direct	Indirect
a	1.1833000	1.0970000
b	-0.2575300	-0.1650600
c	0.0742450	0.0680690
Source: COMNET 2017

Units

Data structure

Input Restrictions

Where publicly accessible performance curves are available for as-designed equipment they may be used for the proposed design otherwise the default equations and coefficients given above should be used. If default curves are not used, supporting documentation is required.

Baseline Building

G3.2 New Construction/Major Alterations

Not used

G3.3 Minor Alterations

Default curves.

Auxiliary Evaporative Cooling Power
Applicability	Systems with evaporative cooling
Definition	The auxiliary energy of the indirect evaporative cooler fan, and the pumps for both direct and indirect stages
Units	Watts
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations Not used G3.3 Minor Alterations Same as proposed except for evaporative cooling system auxiliary fan and pumping systems included in the scope of the retrofit, motor efficiency should be modeled with the minimum efficiency requirement of Standard 90.1-2022 Section 10.4.1 as applicable. Fractional horsepower fan motors (motors 1/12 hp or greater and less than 1 hp) shall be modeled with a motor efficiency of 70%. If any of the exceptions apply, then it shall be modeled the same in the baseline and proposed.

Evaporative Cooling Scavenger Air Source
Applicability	Systems with evaporative cooling
Definition	The source of scavenger air for an indirect section of an evaporative cooler. Options include: Return air Outside air
Units	List (see above)
Input Restrictions	As designed
Baseline Building	G3.2 New Construction/Major Alterations Not used G3.3 Minor Alterations Same as proposed.