Measure Guideline: 

Evaporative Condensers

A. German, B. Dakin, and M. Hoeschele

Alliance for Residential Building Innovation (ARBI)

March 2012
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iii

Measure Guideline: Evaporative Condensers

Prepared for: 

Building America

Building Technologies Program

Office of Energy Efficiency and Renewable Energy 

U.S. Department of Energy 

Prepared by: 

A. German, B. Dakin, M. Hoeschele

Alliance for Residential Building Innovation (ARBI)

Davis Energy Group, Team Lead

123 C Street

Davis, California 95616

NREL Technical Monitor: Michael Gestwick

Prepared under Subcontract No. KNDJ-0-40340-00

March, 2012
iv

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v 

Contents 

List of Figures ............................................................................................................................................ vi

List of Tables ............................................................................................................................................. vii

Definitions ................................................................................................................................................. viii

Executive Summary ................................................................................................................................... ix

Acknowledgements .................................................................................................................. ix

Section 1: Introduction ....................................................................................................................... 1

Section 2: Measure Selection Criteria ............................................................................................... 3

2.1 Technology Description .......................................................................................................3

2.2 Measure Tradeoffs and Non-Energy Benefits .....................................................................4

2.3 System Interactions ..............................................................................................................5

2.4 Performance Characterization ..............................................................................................5

2.5 Appliance Design .................................................................................................................7

2.6 Costs ..................................................................................................................................8

2.7 Energy Savings and Cost Effectiveness .............................................................................10

Section 3: Measure Implementation Details ................................................................................... 18

3.1 Field Inspection ..................................................................................................................18

3.2 System Design and Site Preparation ..................................................................................19

3.3 Installation Prodecure ........................................................................................................19

3.4 Verification Procedures and Tests .....................................................................................21

3.5 Operation and Maintenance ...............................................................................................22

Attachment A: Prescriptive Measure Checklist for Contractors .......................................................... 24

Attachment B: Modeling Methodology and Detail ................................................................................. 25

Attachment C: Additional Modeling Results .......................................................................................... 27

References ................................................................................................................................................. 29
vi

List of Figures

Figure 1: Evaporative condenser operation schematic.......................................................................... 3

Figure 2: Performance characterization of air-cooled and evaporative cooled condensers over a 

range of outdoor dry bulb temperatures............................................................................................ 7

Figure 3: Example of condenser coil configuration to allow for adequate drainage of liquid 

refrigerant.............................................................................................................................................. 7

Figure 4: Condenser coil before (left) and after (right) prolonged operation without any water 

management strategies ....................................................................................................................... 9

Figure 5: Building America and IECC climate zone reference map..................................................... 11

Figure 6: Annual cooling energy comparison of air-cooled and evaporative cooled condensers 

over a range of rated EER in a hot-dry climate ............................................................................... 13

Figure 7: Full load condenser EER (Btu/wh) (no indoor fan energy) versus both outdoor and 

entering wet-bulb temperatures (WB°F)........................................................................................... 17

Figure 8: Float to adjust water sump level ............................................................................................. 20

Figure 9: Gauges connected to operating evaporative condenser to verify correct charge ............ 21

Figure 10: Water sump and pump filter basket during operation........................................................ 23

Unless otherwise noted, all figures were created by the ARBI team.
vii

List of Tables

Table 1: Annual Cooling Energy Savings Compared to a SEER 13 Air Conditioner......................... 12

Table 2: Annual Cooling Energy Savings Compared to a SEER 15 Air Conditioner......................... 12

Table 3: Incremental Cost Justified by Energy Modeling Savings Compared to a SEER 13 Air 

Conditioner for Various Interest Rate Financing Scenarios .......................................................... 14

Table 4: Incremental Cost Justified by Energy Modeling Savings Compared to a SEER 15 Air 

Conditioner for Various Interest Rate Financing Scenarios .......................................................... 14

Table 5: Minimum Annual Cooling UtilityBill to Justify Evaporative Condensers under Various 

Payback Scenarios Based on a Mature Market Incremental Cost of $750 over a SEER 13 Air 

Conditioner.......................................................................................................................................... 15

Table 6: Minimum Annual Cooling Utility Bill to Justify Evaporative Condensers under Various 

Payback Scenarios Based on a Mature Market Incremental Cost of $350 over a SEER 15 Air 

Conditioner.......................................................................................................................................... 15

Table 7: New Construction Assumptions by Climate Zone.................................................................. 25

Table 8: Existing Home Assumptions by Building Vintage.................................................................. 26

Table 9: Annual Cooling Energy Savings Compared to an Existing Home Circa 1980 with a SEER 

13 Air Conditioner............................................................................................................................... 27

Table 10: Annual Cooling Energy Savings Compared to an Existing Home Circa 1980 with a SEER 

15 Air Conditioner............................................................................................................................... 27

Table 11: Annual Water Operating Costs for Evaporative Condenser Assuming National Average 

Water Rates......................................................................................................................................... 28

Table 12: Incremental Cost Justified by Energy Modeling Savings Compared to a SEER 13 Air 

Conditioner for Various Interest Rate Financing Scenarios – Includes Both Energy Utility 

Savings and Additional Water Costs................................................................................................ 28

Table 13: Incremental Cost Justified by Energy Modeling Savings Compared to a SEER 15 Air 

Conditioner for Various Interest Rate Financing Scenarios – Includes Both Energy Utility 

Savings and Additional Water Costs................................................................................................ 28

Unless otherwise noted, all tables were created by the ARBI team.
viii

Definitions

AC

ACCA

Air conditioner

Air Conditioning Contractors of America

AFUE Annual Fuel Utilization Efficiency – Seasonal efficiency for 

residential gas furnaces

AHRI

ARBI

Air-Conditioning, Heating, and Refrigeration Institute

Alliance for Residential Building Innovation

Btu British thermal unit

CARB

CEC

Consortium for Advanced Residential Buildings

California Energy Commission

cfm Cubic feet per minute

DEG Davis Energy Group

o

F

EC

Degrees Fahrenheit

Evaporative condenser

EER Energy Efficiency Ratio

EIR

HSP

HVAC

Electric input ratio

House Simulation Protocols

Heating, ventilation, and air conditioning

kW Kilowatt

kWh 

SHGC

Kilowatt-hour

Solar heat gain coefficient

SMUD

PG&E

Sacramento Municipal Utility District

Pacific Gas and Electric Company

RECS

SCE

Residential Energy Consumption Survey

Southern California Edison

SEER

TXV

Seasonal Energy Efficiency Ratio

Thermostatic expansion valve

W

ZNE

Watt

Zero net energy
ix

Executive Summary

The purpose of this measure guideline on evaporative condensers is to provide information on a 

cost-effective solution for energy and demand savings in homes with cooling loads. This is a 

prescriptive approach that outlines selection criteria, design and installation procedures, and 

operation and maintenance best practices. This document has been prepared to provide a process 

for properly designing, installing, and maintaining evaporative condenser systems as well as 

understanding the benefits, costs, and tradeoffs. The primary audience for this document includes 

the following: 

• HVAC contractors

• Builders

• Remodelers.

As a secondary audience, homeowners who have a basic understanding of HVAC systems will 

also benefit from the information contained within. 

Evaporative cooling has been used successfully throughout history to provide cooling and is 

especially effective in hot-dry climates. The use of evaporative processes to improve cooling 

efficiency is an important vehicle for reducing energy use and peak demand in hot-dry climates. 

Direct space cooling through evaporative cooling does not provide the same quality of comfort 

as compressor-based processes in that for most technologies moisture is added rather than 

removed from the air. While this may be acceptable in dry climates it is not in humid climates 

where air conditioning is relied upon not only for sensible cooling but for dehumidification. 

Evaporative condensers utilize the high efficiency of evaporative cooling at the condensing unit, 

while also providing dehumidification identical to a conventional air conditioning system. 

Evaporative condensers may play a key role in meeting Building America performance goals in 

new homes, and also in existing homes that have high loads due to sub-standard wall insulation 

and windows, that are much more costly to upgrade. 

Acknowledgements

Davis Energy Group would like to acknowledge the United States Department of Energy 

Building America program and their funding and support of development of this guideline as 

well as research that informed it. We also thank Western Cooling Efficiency Center at the 

University of California, Davis for their research and contribution to this measure guideline. In 

addition, we would like to acknowledge Pacific Gas and Electric, Southern California Edison 

and the Sacramento Municipal Utility District for their previous research efforts that have 

contributed to the large body of information on evaporative condensers and have supported 

product development.
1

Section 1: Introduction

Residential air conditioning has become increasingly common throughout the United States over 

the past 30 years as comfort demands have increased and market demands have pushed 

compressor-based cooling into climates not previously seen. Increasingly, air conditioners are 

being installed in milder, transitional climates to compensate for these increased comfort 

demands, as well as increased building loads seen from the trend towards larger homes and 

greater window areas. The 2009 Residential Energy Consumption Survey (RECS) shows that 

61% of residential homes have central air conditioning. This is up significantly from 47% in 

1997 and only 23% in 19781

.

Evaporative cooling has been used successfully throughout history to provide cooling and is 

especially effective in hot-dry climates. The use of evaporative processes to improve cooling 

efficiency is an important vehicle for reducing energy use and peak demand in hot-dry climates. 

Direct space cooling through evaporative cooling does not provide the same quality of comfort 

as compressor-based processes in that for most technologies, moisture is added rather than 

removed from the air. While this may be acceptable in dry climates, it is not in humid climates 

where air conditioning is relied upon not only for sensible cooling but for dehumidification. 

Evaporative condensers (ECs) utilize the efficiency of evaporative cooling to cool entering 

condenser air at the condensing unit, while also providing dehumidification identical to a 

conventional air conditioning system. Evaporative condensers may play a key role in meeting 

Building America performance goals in new homes, and also in existing homes that have high 

loads due to sub-standard wall insulation and windows, that are much more costly to upgrade.

The purpose of this measure guideline on evaporative condensers is to provide information on a 

cost-effective solution for energy and demand savings in homes with cooling loads. This 

document outlines system tradeoffs including a discussion of selection criteria, system 

performance, energy and cost savings, design and installation procedures, and operation and 

maintenance best practices. The primary audience for this document includes contractors, 

builders, and remodelers with certain information also applicable to homeowners.

Previous research has demonstrated the efficiency benefits of evaporative condensers. Davis 

Energy Group (DEG) has completed simulations and laboratory and field testing of a variety of 

evaporative condensers. With Building America support, a Freus unit was field tested in the 

Southern California desert town of Borrego Springs in 2006 and 2007 (Springer et al, 2008). 

Performance results showed significant energy savings over standard air-cooled condensing 

equipment. During 2009, DEG worked with Beutler Corporation (manufacturer of the AquaChill 

evaporative condenser) to assess AquaChill design and performance, and help set up their inhouse test facility. Potential enhancements were identified with the help of a refrigeration 

engineer and design variations were tested. Condenser coil and other design improvements were 

incorporated into the “second generation” system and lab testing of this design showed improved 

performance over the previous version, with a 15 EER rating at AHRI conditions (75°F outdoor 

wet bulb temperature). These results are also summarized in The Consortium of Advanced 

Residential Buildings’ (CARB) Building America 2009 annual report (CARB, 2009). Lab testing 

of a production AquaChill unit was also completed by Southern California Edison (SCE, 2009) 

 1 http://www.eia.gov/emeu/consumptionbriefs/recs/actrends/recs_ac_trends.html
2

and reported an EER of 13.5 at AHRI conditions, but applied actual fan energy use instead of a 

default value.

In December 1998, Davis Energy Group (DEG, 1998) completed an evaluation of residential 

evaporative condensers that involved evaluation of two EC designs including: evaluating test 

data from Pacific Gas & Electric’s (PG&E) Technical and Ecological Services (TES) laboratory, 

developing DOE-2 performance curves based on the lab test data, estimating EC savings using 

DOE-2 and the developed curves, and field testing of ECs. In the summer of 2007, Davis Energy 

Group evaluated two residential Freus installations for a PG&E technology evaluation report 

(DEG, 2008). Monitoring data from the sites were used to develop a performance algorithm 

using MicroPas hourly loads. Simulation projections suggest 21%-33% annual cooling energy 

savings and 22%-35% coincident peak cooling demand savings in typical Central Valley 

applications. 

During the summer of 2009, the Sacramento Municipal Utility District (SMUD) worked with 

ADM Associates to complete monitoring and field evaluation of 26 AquaChill units (Keesee et 

al, 2010). The data was analyzed and compared to usage data for typical residential homes in 

SMUD territory. Findings from the study include that air conditioning energy use can be reduced 

by 29% for a typical single family home in SMUD territory and peak power can be potentially 

reduced 23% compared to a typical single family 4-ton unit.

The improved “second generation” AquaChill was installed and instrumented at an existing, 

occupied home in Davis, California, in September, 2010, and was monitored through the 2011 

summer (ARBI, 2011). Results showed an average measured condenser EER of 17. In 2010, 

DEG conducted a study for PG&E to evaluate evaporatively cooled condensers as a potential 

component of a Zero Net Energy (ZNE) strategy for new and existing homes (DEG, 2010). The 

results of the study showed that evaporative condensers have significant benefits and can be cost 

effective in hot-dry climates where cooling energy use is significant. 
3

Evaporative Cooler vs. 

Evaporative Condenser ________________________________________________

An evaporative cooler works by 

cooling the supply air stream 

through evaporation of water, which 

generally results in increased

relative humidity inside the home. 

Evaporative condensers use the 

same principle but to cool the 

refrigerant at the outdoor 

condensing unit by cooling entering 

condenser air. Since the refrigerant 

is part of a closed loop this strategy 

does not result in the addition of 

moisture into the home.

Section 2: Measure Selection Criteria

2.1 Technology Description

Evaporative condensers (ECs) operate by rejecting condenser 

heat to a water sump that is cooled by the evaporation of 

water. They replace the fin-tube air-cooled condenser coil with 

a refrigerant-to-water copper heat exchanger that is 

evaporatively cooled. ECs cool the refrigerant by spraying 

water on the condenser coils during operation, resulting in 

lower condensing temperatures, reducing demand, and 

potentially improving utility load factor because the increased 

efficiency is most pronounced during peak demand periods 

that correspond with the hottest days of the summer. The 

temperatures seen by the refrigerant in the condensing unit 

more closely follow the outdoor wet bulb temperature than the 

outdoor dry bulb temperature. This allows for higher operating 

efficiencies than their high efficiency air-cooled counterparts

due to the fact that wet bulb temperatures can be as much as 

40°F lower than peak summer dry bulb temperatures, 

especially in dry Southwestern climates.

Earlier EC designs consisted of a conventional air-cooled condenser with evaporative media 

wrapped around the outside to evaporatively pre-cool the air entering the condensing unit. The 

first true residential evaporative condenser was 

introduced into the market in 1997 by Bacchus Industries. 

This design immersed the refrigerant coils in the sump of 

evaporatively cooled water providing significant 

performance benefits due to both the improved heat 

transfer effectiveness and to the impact of lower 

condensing temperatures. It also eliminated the issue of 

condenser coil fin degradation associated with moisture 

drift in the earlier designs.

Modern designs operate by spraying a continuous flow of 

water on to the refrigerant lines while the condenser inlet 

air passes up through the water covered refrigerant lines 

(see Figure 1). Upward-flowing condenser inlet air 

absorbs moisture from the water spray and becomes 

cooler, conducting heat away from the tube surfaces in 

the process. The cooled inlet air continues to absorb 

moisture as it evaporates the water film on the refrigerant 

tube surfaces. This evaporation of water results in further 

cooling of the refrigerant lines.

Evaporative condensers require water to provide the 

evaporative cooling effect. Water is consumed both by Figure 1: Evaporative condenser operation 

schematic
4

evaporation and the replacement of cooling water to avoid excessive mineral build-up in the 

sump water. This can be accomplished either by periodically purging the sump or through a 

bleed line where water is continually bled off the high pressure side of the circulating pump 

during operation. 

2.2 Measure Tradeoffs and Non-Energy Benefits

The following subsections describe the non-energy benefits and tradeoffs unique to residential 

evaporative condensers.

Occupant Comfort, Health, and Safety

Evaporative condensers operate on a similar principle as evaporative coolers, but without the 

side effects of reduced occupant comfort due to humidification of the airstream. Indoor air 

quality and perceived comfort are the same as with a conventional air-cooled condenser.

Evaporative condensers meet all performance and prescriptive-based safety, health, and building 

code requirements for use in both new and existing homes.

Legionnaire’s Disease

Evaporative condensers afford an environment that is potentially favorable to the growth of 

Legionnaires' disease bacteria, or Legionella. Legionella infections have been traced to 

commercial cooling towers, and it is possible that given the sump water temperatures, Legionella

could be present in evaporative condensers. However, the system enclosures and drift eliminators 

in residential evaporative condensers appear to be effective at eliminating the aerosols which are 

commonly given off by larger cooling towers. There are no reports of health risks in the 

literature stemming from the use of these products. 

Equipment Maintenance

Evaporative condensers require more maintenance than air-cooled condensers. If the water is not 

replaced regularly through a purge cycle or continuous bleed, hardness minerals will build up on 

the system components, reducing equipment performance, and ultimately leading to potential 

component failure. The units require semi-annual maintenance at the beginning and the end of 

each cooling season. At the end of each cooling season, the condensing unit needs to be 

disconnected, the water supply turned off and the sump drained, leaving the drain plug off during 

winter. At the beginning of each cooling season, the intake screens and base pan need to be 

hosed off and cleaned of any debris, the drain plug reinstalled, water valve opened and power 

restored to the unit.

Water Usage

Water is consumed through both the evaporation process and through water removed during the 

purge cycles. Most of the water consumption is due to evaporation and the rate of use is 

dependent upon outdoor climate conditions, with evaporation rates increasing with hotter and 

dryer operating conditions (SCE, 2009). Some water districts have sensitivity to the use of 

evaporative cooling equipment due to the issue of increased water use. The California Energy 

Commission (CEC) under the Title-24 state energy code requires that evaporative condensers do 

not use more than 5.0 gallons per ton-hour of capacity at AHRI rating conditions (CEC, 2010). 

While the current cost of water is sufficiently low as to present no operating cost barriers, 

increasing water rates and local restrictions on water use could have a negative impact on the 
5

Borrego Springs Field 

Monitoring

________________________________________________

Under Building America, Davis 

Energy Group monitored 

evaporative condenser and aircooled condenser performance in 

four test homes located in the desert 

climate of Borrego Springs, 

California, for 15 months in 2006 

and 2007 (Springer et al, 2008). 

Overall steady state efficiency of 

the evaporative condenser was 

almost twice as high as that of the 

13 SEER unit (12 EER vs. 7 EER) 

and about the same as the 21 SEER 

unit operating in 2nd stage. 

proliferation of evaporative condensers. However, “purge” or “bleed” water can be used for 

irrigation and in most cases can be easily routed from the unit to an appropriate use site.

Climate Considerations

Evaporative condensers offer the greatest benefit in hot-dry climates where cooling loads are 

high and dry outdoor temperatures allow for higher operating efficiencies than a comparable aircooled condenser under the same condition. While evaporative condensers will provide some 

performance advantage over air-cooled condensers under humid conditions, they may not offer 

sufficient savings to justify any additional costs and water usage.

Durability and Reliability

It is difficult to assess long term durability of current 

evaporative condenser technologies because they have been 

available in their current form for less than ten years. 

However, current evaporative condensers have achieved a 

measure of reliability and durability over the relatively short 

length of time they have been on the market. DEG installed a 

Freus unit to provide cooling for their offices in 2006 and has 

intentionally avoided periodic maintenance to determine the 

consequences. The only maintenance that has been required to 

keep it operating is cleaning leaves and debris from the 

strainer around the pump. Another Freus unit was installed on 

a home in Borrego Springs as part of an earlier Building 

America study (Springer et al, 2008). There have been no 

reports of failure from the owner since it was installed in 2007. 

Pump failure has been an issue in certain applications. Water 

pumps may require more frequent replacement than other 

components.

2.3 System Interactions

Often, the most cost-effective energy-savings measures that can be implemented are those that 

reduce the cooling and heating loads. Savings can be enhanced through a whole-building 

performance-based approach of optimizing building orientation, and building envelope design 

that includes proper window management through the use of high performance windows and 

reducing glazing area, high insulation levels, and good building construction practices that result 

in reducing building heating and cooling loads. 

Proper design and commissioning of other components within the HVAC system is also crucial 

for optimal system performance. Airflow and the ductwork should be sized according to the 

building and system requirements. Undersized ductwork and returns along with high pressure 

drop air filters will increase system static pressure resulting in lower airflows across the cooling 

coil and subsequently reduced cooling capacity with PSC fan systems, or increased fan energy 

with ECM fan systems, causing reduced system performance and comfort.

2.4 Performance Characterization

The performance of air-cooled vapor compression equipment degrades with increasing outdoor 

temperatures. As refrigerant condensing temperatures rise with increasing condenser inlet air 
6

EER vs. SEER

________________________________________________

Similar to air-cooled condensers, 

evaporative condensers are rated 

according to EER which is tested at 

outdoor conditions of 95o

F dry bulb and 

75o

F wet bulb. There is currently no 

official AHRI SEER testing procedure 

for evaporative condensers. California’s 

Title-24 code uses two EER ratings, 

EERa and EERb, to calculate the 

seasonal efficiency used for modeling 

purposes. EERa is the AHRI listed EER. 

EERb is tested at conditions similar to 

those used in the SEER test for aircooled condensers, 82o

F/65oF outdoor 

dry bulb and web bulb, respectively, and 

is required to be tested and published by 

the manufacturer according to AHRI 

guidelines.

temperatures, electrical demands for air-cooled equipment increase and cooling capacity drops 

resulting in lower equipment efficiencies. Typically, air-cooled equipment condenses at 

temperatures 15°F-25°F higher than the outdoor dry bulb temperature. However, evaporative 

condenser condensing temperatures are based on the coincident outdoor wet bulb temperature. 

With evaporative condensers, the refrigerant condensing temperature is based on the coincident 

outdoor wet bulb temperature at any outdoor dry bulb condition. During peak cooling periods in 

hot dry climates, this is 20°F to 40°F lower than the condensing temperatures seen by air-cooled 

condensers. The lower condensing temperature allows for more efficient compressor operation 

and increased capacity. Since evaporative condenser efficiency is tied to outdoor wet bulb 

temperature, both capacity and efficiency degradation are lower as outdoor temperature 

increases. Both the cooling capacity and efficiency of evaporative condensers are relatively 

constant in dry climates because wet bulb temperatures vary 

much less than dry bulb temperatures. This characteristic 

promises a performance advantage over air-cooled equipment

in hot-dry climates, and allows for cooling system downsizing 

in many applications.

Figure 2 shows air conditioner efficiency over a range of 

outdoor dry bulb temperatures for a hot-dry climate assuming 

AHRI rating conditions2

. The AHRI rated efficiency for the 

Beutler AquaChill of 14.7 EER was used for this comparison. 

It can be seen that the evaporative condenser performs better 

than a similarly rated air-cooled condenser at dry bulb 

temperatures above 95o

F (the temperature at which the AHRI 

EER rating test is conducted), which usually coincides with 

times of peak load during the afternoon. It is also the case that 

dry climates are often dryer than the AHRI assumptions which 

would move the evaporative condenser curve up resulting in 

high efficiencies at even higher temperatures. A typical highefficiency air-cooled unit is rated at 12.5 EER and under most 

cooling operating conditions (>80oF), the evaporative 

condenser operates more efficiently. This graph is based on performance curves of normalized 

EIR (electric input ratio) and capacity as a function of entering wetbulb and outdoor drybulb as 

developed for the DOE2.2 energy model. The BEopt v1.1 default curves for a SEER 13 

residential air conditioner were used for the three air-cooled units and the eQUEST default curve 

for evaporatively cooled condensers (EvapCond-EIR-fEWB andOWB) was used for the 

evaporative condenser. 

 2 Assumes constant entering wet bulb temperature of 67o

F and fan output of 400 cfm/watt at 0.365 W/cfm based on 

AHRI EER test rating conditions and constant humidity ratio of 0.14 lb water / lb dry air.
7

Figure 2: Performance characterization of air-cooled and evaporative-cooled condensers over a 

range of outdoor dry bulb temperatures

2.5 Appliance Design

Evaporative condenser coils are typically configured in a 

horizontal orientation to increase surface area for contact 

with the evaporating water. However, this can cause 

problems with proper liquid refrigerant drainage during 

operation. The condenser coil should be configured in 

such a way that it has maximum surface area on the 

horizontal plane and a slight downward slope to the coils. 

Figure 3 shows a method of this by coiling the refrigerant 

tubes in a sort of “inverted beehive” to facilitate drainage. 

Build-up of mineral deposits on the condenser coils, in the 

water sump and on the water system components can be a 

concern, especially in areas with hard water or water with 

high levels of dissolved solids. The use of wide spray 

nozzles reduces the risk of clogging, and the use of 

sacrificial anodes enhances the life of the other components. 

These anodes may periodically need to be replaced, 

5

7

9

11

13

15

17

19

21

65 75 85 95 105 115

EER

Outdoor Drybulb Temperature (°F)

Evaporatively Cooled EER 14.7

Air Cooled EER 14.7

Air Cooled EER 12.5

Air Cooled EER 11

Figure 3: Example of condenser coil 

configuration to allow for adequate 

drainage of liquid refrigerant
8

depending on water conditions. Proper flushing of water in the water sump is also important. 

Periodic purge or a continuous bleed are both acceptable strategies. Systems that use a purge 

strategy must incorporate a second pump which results in additional cost and electricity use.

Due to the constant exposure to water, it is important to isolate the compressor and controls from

water spray. Plastic, fiberglass, stainless, or galvanized materials with corrosion resistance 

should be used in construction.

Safety switches should be installed that turn off the system and initiate a service call in the case 

of low water levels in the sump. Many systems use a basket-type filter for the water circulation 

pump. In these cases, the low limit sensor should be installed inside the basket to adequately 

measure the water levels adjacent to the pump. In the case of extreme clogging of the filter 

basket, water levels may differ between inside and outside the basket.

2.6 Costs

Currently, evaporative condensers are only available through select manufacturers and are

produced at very low volumes resulting in relatively high incremental costs. According to 

conversations with manufacturers, assuming volume pricing there are two system components 

that represent an additional cost over an air-cooled condenser. One is the water system including 

the pump and spray device. The other is the corrosion-resistant housing, typically either plastic 

or fiberglass. These materials are more expensive than standard painted sheet metal and often 

require a more expensive manufacturing process such as injection molding. Assuming volume 

production similar to that of air-cooled condensers, manufacturers predict a 30% system price 

increase over a high efficiency (SEER 15) air-cooled unit, or roughly $350. Estimated mature 

market incremental cost over a SEER 13 unit is $750. Currently, costs are significantly higher 

with incremental equipment costs to the homeowner over a SEER 15 condensing unit between 

$1,000 and $1,350. The relative performance of systems that these costs are based on is 

representative of the 14.7 EER evaporative condenser and the 12.5 EER air-cooled condenser in 

Figure 2. Incremental costs may be reduced in some cases by equipment downsizing by 1⁄2 ton 

due to the reduced capacity degradation of evaporative condensers at high outdoor air design 

conditions.

Labor costs are assumed to be similar. While additional plumbing is required during installation, 

it is minimal and contractors who are familiar with evaporative condenser installations do not 

typically charge for additional labor. Maintenance costs are negligible when maintenance is 

performed by the homeowner. Homeowners may elect to enter into a maintenance contract with 

the HVAC contractor. This typically includes semi-annual maintenance with costs around $175 

annually.

Most high efficiency evaporative condensers require R-410A refrigerant and a thermostatic 

expansion valve (TXV) installed at the evaporator coil. Replacement costs depend on whether 

these components are present in the existing unit. The price estimates presented above do not 

include any additional costs associated with the addition of a TXV or change-out of an 

evaporator coil. If a TXV is necessary, additional costs are typically around $150. There may 

also be additional labor costs associated with plumbing water source and drain lines to the 

condenser location.
9

Evaporative condensers consume water both through the evaporation process and through 

replacement of cooling water to keep mineral content down. Water consumption rates are highly 

dependent on local climate conditions and have been seen to vary quite a bit based on prior 

studies of both field and laboratory testing, with a range between 1.3 to 3.5 gallons per ton-hr 

(DEG, 2008; Keesee et al, 2010; SCE, 2009). Water rates across the country also vary 

drastically; average rates in 2009 were $3.90 per 1,000 gallons (Global Water Intelligence, 

2009).3 Assuming 400 hours of summer operation on a 3-ton system in a hot-dry climate4 and an 

average consumption rate of 2.5 gallons per ton-hr, this results in an average annual cost of about 

$12.00 for evaporative condenser water usage.

 3 Global Water Intelligence, Vol 10, Issue 9 (September 2009). 

http://www.globalwaterintel.com/archive/10/9/market-insight/no-let-pressure-water-tariffs.html 4 This is a conservative estimate based on monitoring in the hot-dry climate of Davis, California, on an existing 

home over a relatively mild summer. A total of 316 operating hours were monitored.

Supporting Research

The UC Davis Western Cooling Efficiency Center is currently conducting accelerated aging 

tests on an AquaChill evaporative condenser by operating the unit continuously without 

removing any dissolved solids (no pump down or bleed off). This testing assesses the effect 

of mineral deposits on performance degradation. Makeup water is supplied to maintain 

proper sump level. The water supply is Davis, California, city water which is very hard (303 

ppm) and high in total dissolved solids (520 ppm). Currently the unit has been operating for a 

6-month period with over 1,700 hours of operation (60 minutes on followed by 30 minutes 

off). This is the equivalent of four to six summers of operation in a hot-dry climate (based on 

300-400 total annual hours of operation identified from monitoring studies). Significant 

scaling of the condenser coils (see pictures below), water sump, pump, and spray nozzles has 

been observed; however, condenser performance degradation has only been on the order of 

20%. Results are preliminary and will be reported on in 2012 under a project funded by 

Southern California Edison.

Figure 4: Condenser coil before (left) and after (right) prolonged operation without any water 

management strategies
10

PG&E ZNE Technology 

Evaluation

________________________________________________

In 2010 DEG evaluated evaporative 

condensers (ECs) as a potential 

component of a Zero Net Energy 

(ZNE) strategy in PG&E service 

territory (DEG, 2010). eQUEST

software was used to estimate 

energy use, EC performance and 

savings. Assuming a rated EER of 

12.7, in hot-dry climates ECs were 

projected to reduce annual air 

conditioning source energy by about 

20% compared to a SEER 13 aircooled condenser and by 3% 

compared to a SEER 15 unit. Peak 

demand savings were estimated at 

31% and 14% compared to standard 

and high efficiency equipment.

2.7 Energy Savings and Cost Effectiveness

Energy Savings

An evaluation of energy savings was completed using BEopt 

v1.1 which has the capability of modeling evaporatively

cooled condensers. The AHRI rated efficiency for the Beutler 

AquaChill of 14.7 EER was used for modeling purposes. 

Recent monitoring in hot-dry climates has shown operational 

efficiencies above this with an estimated EER at rated 

conditions of 16.2. There are effectively two base cases against 

which an evaporative condenser may be compared. One is a 

SEER 13, EER 11 air-cooled condenser. SEER 13 is the 

minimum efficiency for air conditioners according to federal 

appliance standards. The other is a high efficiency air-cooled 

condenser, which are increasingly installed throughout the 

country, especially in areas where residential energy codes are 

stricter. A commonly installed high efficiency air conditioner 

has efficiency ratings of SEER 15 and EER 12.5. Table 1 and 

Table 2 show example cooling energy and demand savings 

compared to a SEER 13 and a SEER 15 base case, 

respectively. Savings are representative of new construction 

assuming a 2,400 ft2 house built to Building America 

Benchmark specifications. Construction assumptions in the model are based on the House 

Simulation Protocols (Hendron et al, 2010). See Attachment B for a detailed account of the 

modeling assumptions. Savings percentages are similar for existing homes since the assumption 

is that air conditioner replacement would occur when the air conditioner reaches the end of its 

useful life and the base case effectively becomes the unit that would be installed in the absence 

of an evaporative condenser option. However, absolute annual kWh savings would be expected 

to increase for existing homes. Utility dollar savings include savings from the reduction of 

electricity only and do not include water costs. See Attachment C for modeling results for 

existing homes and for analysis that includes water costs. 

Specific climates were selected for evaluation to cover the major climate regions nationally. 

Figure 5 shows nationally where both the Building America and IECC climate zones are located.
11

Figure 5: Building America and IECC climate zone reference map
12

Savings are most significant in hot climates (hot-dry, hot-humid, and mixed-humid) with percent 

cooling savings at 17% in humid climates and 27% in dry climates compared to a SEER 13 unit. 

While percent savings are still high for cold and marine climates, the reduced cooling load 

results in relatively small annual kWh savings. The peak demand benefits are substantial, which 

is especially valuable for summer-peaking electric utilities. Compared to SEER 13 base case, 

peak load is reduced by over 1 kW (>27%) for both the hot-dry and hot-humid climates. These 

savings values are reduced between 40% and 70% when compared to a SEER 15 air conditioner. 

While modeling does show decent improvement in humid climates, field studies are necessary to 

quantify any benefits under humid conditions. The 17% savings are primarily due to the higher 

EER over the air-cooled base case. In humid climates it would be more beneficial to invest in an 

air-cooled unit with higher EER and SEER ratings than the high efficiency base case used in this 

model instead of an evaporative condenser.

Proper maintenance is important to ensure continued savings over time. Savings may be reduced 

if maintenance is neglected by the development of water scale on the condenser coils, water 

nozzles or other components in areas with hard water or water with high levels of dissolved 

solids.

Table 1: Annual Cooling Energy Savings Compared to a SEER 13 Air Conditioner

Building 

America

Climate Zone

IECC 

Climate 

Zone

Sample City

Annual Cooling 

Energy Use (kWh) Annual 

kWh 

Savings

%

kWh 

Savings

Annual 

kW 

Savings

%

kW 

Savings

Annual 

Utility 

Savings Base 5

Case 

Evap 

Condenser

Hot-Dry 3B Fresno, CA 2,373 1,728 644 27% 1.27 31% $73 

Hot-Humid 2A Houston, TX 3,259 2,710 549 17% 1.19 27% $62 

Mixed-Humid 2A Atlanta, GA 1,712 1,421 291 17% 0.72 21% $33 

Marine 3C Santa Rosa, CA 73 57 16 22% 0.23 9% $2 

Cold 5B Denver, CO 488 360 127 26% 1.00 33% $14 

Table 2: Annual Cooling Energy Savings Compared to a SEER 15 Air Conditioner

Building 

America

Climate Zone

IECC 

Climate 

Zone

Sample City

Annual Cooling 

Energy Use (kWh) Annual 

kWh 

Savings

%

kWh 

Savings

Annual 

kW 

Savings

%

kW 

Savings

Annual 

Utility 

Savings Base 6

Case 

Evap 

Condenser

Hot-Dry 3B Fresno, CA 2,094 1,728 366 17% 0.87 24% $41 

Hot-Humid 2A Houston, TX 2,874 2,710 164 6% 0.75 19% $18 

Mixed-Humid 2A Atlanta, GA 1,511 1,421 91 6% 0.40 13% $10 

Marine 3C Santa Rosa, CA 64 57 7 11% 0.03 1% $1 

Cold 5B Denver, CO 432 360 71 17% 0.73 27% $8 

Figure 6 shows a comparison of cooling energy use generated through BEopt modeling in a hotdry climate for an air-cooled condenser and evaporative condenser relative to rated EER. The 

 5

 National average utility rate of $0.1126 / kWh 6

 National average utility rate of $0.1126 / kWh 
13

single data point for the evaporative condenser is representative of the 14.7 EER based on the 

AquaChill. Considering energy use only, an evaporative condenser rated at 14.7 EER will 

perform better than an air-cooled condenser that is rated 15 EER or below. As rated EER 

increases, the difference between the two system types becomes less disparate until they cross 

around 16 EER.

Figure 6: Annual cooling energy comparison of air-cooled and evaporative cooled condensers 

over a range of rated EER in a hot-dry climate

Savings and cost effectiveness ultimately depends on the building cooling load and air 

conditioner energy use within the home. Analysis using BEopt was conducted to identify the 

sensitivity of savings to building cooling load. Within a given climate zone, percent cooling 

savings is relatively consistent across both existing and new buildings with various building 

characteristics and cooling loads.

Cost Effectiveness – New Construction

Incremental costs for energy efficiency in new construction are typically passed on to the 

homeowner and financed through the home mortgage. Assuming a 30-year mortgage term Table 

3 and Table 4 show the incremental cost over the SEER 13 and SEER 15 base cases, 

respectively, that would result in a positive annual cash flow to the homeowner based on utility 

electricity savings and mortgage payments. 

1,000

1,100

1,200

1,300

1,400

1,500

1,600

1,700

1,800

1,900

2,000

10 11 12 13 14 15 16 17 18 19 20

Annual Cooling Energy (kWh)

EER (Btu/Wh)

Air Cooled Condenser

Evaporative Condenser
14

SCE Lab Testing

________________________________________________

In 2009, SCE conducted laboratory 

testing of the first generation 

AquaChill to determine system 

capacity and efficiency under 

various climate conditions (SCE, 

2009). Performance degradation 

was found to be much less than aircooled equipment at high outdoor 

temperatures. Operational EERs, 

which include indoor fan energy 

use, ranged between 14.2 in mild 

conditions down to 13 in hot-dry 

conditions (115o

F outdoor dry bulb, 

74o

F wet bulb).

Evaporative condensers are recommended in hot-dry climates where the advantage over aircooled condensers is most significant. Assuming mature 

market incremental costs of $750 and $350 over a SEER 13 

and SEER 15 air conditioner, respectively, it can be seen that 

the evaporative condenser is cost effective under all reasonable 

financing scenarios in a hot-dry climate. Cost effectiveness in 

hot-humid climates also looks favorable; however, further field 

testing of this technology in humid climates is necessary to 

better qualify modeling results. Cost effectiveness is reduced in 

milder climates where lower cooling loads diminish the 

savings potential. Areas with higher electricity rates or houses 

with higher cooling loads will benefit from increased cost 

effectiveness.

Given the high variability of water rates, costs associated with 

water use are not included in this analysis. A similar analysis 

that includes water costs based on national averages is 

available in Attachment C. Additional maintenance costs have 

also not been included. When the homeowner signs a 

maintenance contract it assumes this replaces a similar contract for the base case air conditioner. 

While there may be an incremental cost above that for an air-cooled unit, this is not expected to 

be significant. 

Table 3: Incremental Cost Justified by Energy Modeling Savings Compared to a SEER 13 Air 

Conditioner for Various Interest Rate Financing Scenarios

Climate Zone 3% 4% 5% 6% 7%

Hot-Dry $1,434 $1,266 $1,126 $1,008 $909 

Hot-Humid $1,222 $1,079 $960 $859 $774 

Mixed-Humid $648 $572 $509 $456 $411 

Marine $36 $32 $28 $25 $23 

Cold $283 $250 $223 $199 $180 

Table 4: Incremental Cost Justified by Energy Modeling Savings Compared to a SEER 15 Air 

Conditioner for Various Interest Rate Financing Scenarios

Climate Zone 3% 4% 5% 6% 7%

Hot-Dry $814 $719 $640 $573 $516 

Hot-Humid $365 $322 $287 $257 $231 

Mixed-Humid $202 $178 $158 $142 $128 

Marine $16 $14 $12 $11 $10 

Cold $159 $140 $125 $112 $101 
15

Cost Effectiveness – Retrofit

Financing scenarios are more variable in retrofit applications than in new construction. The 

homeowner may pay for the upgrade out of pocket or he may finance it through a variety of 

mechanisms including a second mortgage, low interest energy upgrade loans, or high interest 

credit cards. Cost effectiveness will depend on interest rates, inflation, and utility rate escalation. 

Additional modeling was conducted in BEopt to estimate typical energy use for an old air 

conditioner in an existing home (see Attachments B and C). Modeling inputs assumed an 

existing air conditioner that has reached the end of its useful life with a degraded operating EER 

of 8. Due to age and maintenance neglect, many existing air conditioners operate at efficiencies 

much lower than this. Table 5 and Table 6 shows the minimum annual cooling utility bill for an 

existing home that justifies the incremental cost of an evaporative condenser for three payback 

term scenarios over a SEER 13 and SEER 15 air conditioner, respectively. Assumptions include 

average percent cooling savings7 and a mature market cost of $750 over a SEER 13 base case 

and $350 over a SEER 15 base case. The cost effectiveness of evaporative condensers improves 

as cooling energy use increases. Therefore, homes with cooling utility bills larger than those in 

the tables with benefit from a quicker payback period. In dry climates, because of the minimal 

mature market cost increase for the evaporative condenser above a SEER 15 air-cooled unit, the 

cost effectiveness is better compared to the SEER 15 than the SEER 13. 

Table 5: Minimum Annual Cooling Utility Bill to Justify Evaporative Condensers under Various 

Payback Scenarios Based on a Mature Market Incremental Cost of $750 over a SEER 13 Air 

Conditioner

Climate Zone 5-year 

payback

10-year 

payback

15-year 

payback

Hot-Dry $820 $410 $270 

Hot-Humid $1,430 $720 $480 

Mixed-Humid $1,330 $670 $440 

Marine $1,140 $570 $380 

Cold $780 $390 $260 

Table 6: Minimum Annual Cooling Utility Bill to Justify Evaporative Condensers under Various 

Payback Scenarios Based on a Mature Market Incremental Cost of $350 over a SEER 15 Air 

Conditioner

Climate Zone 5-year 

payback

10-year 

payback

15-year 

payback

Hot-Dry $670 $340 $220 

Hot-Humid $2,740 $1,370 $910 

Mixed-Humid $2,120 $1,060 $710 

Marine $1,310 $650 $440 

Cold $620 $310 $210 

Incremental costs for evaporative condensers will vary based on many factors, especially in 

retrofit applications where site factors will affect the implementation costs. Equipment make and 

 7 26% and 16% cooling energy use savings were used for the SEER 13 and SEER 15 base cases, respectively. These 

values reflect average percent savings based on results from modeling of several different building types.
16

SMUD Field Testing

________________________________________________

During the summer of 2009, 

SMUD worked with ADM 

Associates to complete monitoring 

and field evaluation of 26 

AquaChill evaporative condenser

units (Keesee et al, 2010). Their 

findings concluded that cooling 

energy use could be reduced in a 

hot-dry climate by 29% and peak 

load by 23% (4-ton unit) for a 

typical single family home.

model, product pricing through distribution channels, contractor familiarity with the technology, 

changes in production volume, local incentives, and site factors (existing conditions, proximity 

to water plumbing, etc) are a few of the factors that will influence final project costs. It is highly 

recommended that current bids along with local utility rates are used in lieu of the default costs, 

if possible.

Annual utility savings, annual water cost, and simple payback 

in years can be calculated according to the following 

equations. Annual cooling electricity use can be estimated by 

looking at monthly utility bills. Subtract average electricity 

usage (kWh) in the winter months from average use in the 

summer months to determine the portion of the bill that can be 

attributed to air conditioning. If there are other highly seasonal 

electrical loads, such as electric heating or a pool pump, this 

methodology will not be accurate. Percent cooling kWh 

savings can be estimated from values in column 6 of Table 1 or 

Table 2 depending on the climate zone and base case to be 

evaluated. FOld_AC is a factor which represents the reduction in 

energy usage between an existing 8 EER air conditioner and 

the base case. For evaluating savings compared to a SEER 13 

base case, use 0.72 for FOld_AC and for the SEER 15 base case 

use 0.44. These three values along with the local electricity rate ($/kWh) can be used in Equation 

1 to estimate annual utility savings. Use Equation 2 to calculate annual water costs associated 

with operating the evaporative condenser. Annual savings and water costs and the incremental 

cost are then plugged into Equation 3 to calculate an estimated simple payback. If incentives are 

available subtract those from the incremental cost before calculating payback.

Equation 1

Annual Utility Savings 

= Annual Cooling Energy Use * FOld_AC * % kWh Savings

100 * Local Utility Rate ($ / kWh)

Equation 2

Annual Water Costs

= Annual Cooling Energy Use * FOld_AC * ( 1- % kWh Savings

100 ) * 1.3 (ton∙hr / kWh) * 

2.5 (gallon / ton∙hr) * Local Water Rate ($ / gallon)

Equation 3

Payback (yrs) = 

Incremental Cost - Incentives

Annual Utility Savings - Annual Water Costs
17 

Supporting Research 

A second generation AquaChill was installed in an existing home in 2010 and detailed 

monitoring was conducted throughout the 2011 cooling season (ARBI, 2011). Average 

operating efficiency of the unit has been 12.6 EER. The 12.6 EER includes monitored fan 

energy of an old PSC motor operating in existing ducts at high static pressures. Average 

condenser efficiency (shown in Figure 7 below) without fan energy is roughly 17 EER. 

Efficiency and system capacity appear to be most sensitive to changes in indoor conditions 

(Entering WB) and do not appear to vary much with outdoor wet bulb. Linear regression 

analysis was used to estimate the condenser only EER at rated conditions (75o

F outdoor wet 

bulb and 67oF entering wet bulb) at an EER of 20.2. Building in standard AHRI assumptions 

for fan energy (0.365 W/cfm and 400 cfm/ton), system EER was calculated at 16.2. 

Figure 7: Full load condenser EER (Btu/wh) (no indoor fan energy) versus both outdoor and 

entering wet-bulb temperatures (WB°F) 
18

Section 3: Measure Implementation Details

3.1 Field Inspection 

All installation work must follow local and national code. Installers should familiarize 

themselves with their local jurisdiction and identify any requirements that may be specific to the 

project. Special attention should be paid whenever retrofit work is to be conducted as existing 

homes may pose unique safety concerns. 

Evaporative condenser system installation criteria should be reviewed and compared to site 

conditions. A pre-installation inspection should determine the following information for the 

equipment under consideration:

• Are there local water use limitations on evaporative cooling systems that may preclude 

use of the system?

• Is there adequate access to supply water at the proposed location for the condensing unit?

• What are the local requirements for disposing of purged water? Is there adequate 

capability for purge water drainage at the proposed location for the condensing unit? 

• For retrofits, is the proposed equipment compatible with existing systems, specifically the 

evaporator coil and refrigerant type? If not, the scope of work may be greater than 

replacing the condensing unit only. 

¡CAUTION – Installing and servicing air conditioning systems can be 

hazardous!

________________________________________________________________________________________________________________________________________

• Technicians with proper training are necessary. Licensed HVAC professionals 

should hold appropriate contractor and refrigerant handling licenses.

• Always make sure there is an electrical disconnect installed with all outdoor 

condensers and turn off the electrical disconnect before installing or servicing air 

conditioning equipment. There may exist more than one disconnect.

• Wear appropriate protective clothing and gear including safety glasses and gloves.

• All equipment used for refrigerant charging, evacuation, and charge measurements 

should be certified and properly maintained. Follow EPA guidelines for proper 

handling and disposal of refrigerant. Refrigerant venting is prohibited by law.
19

Important!

________________________________________________

Installation and servicing of air 

conditioning systems can be 

hazardous and technicians with 

proper training are necessary. 

Always turn off the electrical 

disconnect when servicing the unit.

3.2 System Design and Site Preparation

Sizing an Air Conditioner

Accurately estimating the cooling load on a home is important to select an appropriately sized air 

conditioner. Undersized units are unable to cool the house sufficiently and oversized units cycle 

excessively, reducing air conditioner efficiency, humidity control, and occupant comfort. Air 

conditioners should be sized and selected in accordance with ACCA Manuals J and S. The 

Manual J sizing procedure takes into account house characteristics including orientation, 

insulation levels, windows, and internal gains, as well as duct location and quality to estimate the 

cooling capacity and system airflow necessary on a “design” summer day. Manual S outlines a 

procedure for selecting an air conditioner based on manufacturer data and Manual J results.

For hot-dry climates, refer to EC manufacturer’s engineering tables for rated capacities at design 

conditions. Because evaporative condensers maintain their capacity at higher design conditions, 

it may be possible to specify a smaller capacity EC than a standard air-cooled condensing unit, 

especially in severe cooling climates like Phoenix or Las Vegas. In a retrofit situation, it may be 

possible to downsize the condensing unit by a half ton or more and still provide the same cooling 

capacity.

Duct Design

Proper sizing of the ductwork is also essential to ensure expected performance from any air 

conditioner. Undersized ducts create high pressure losses, resulting in reduced airflows and high 

fan energy use. ACCA Manual D duct sizing procedures should be followed to ensure correct 

duct sizing. In retrofit applications replacement or repair of the duct system may be warranted. 

The designer should try to minimize system pressure drop as much as possible by shortening 

duct runs, properly size return and supply ducts, avoid overly restrictive filters, and limiting duct 

bends and connections.

TXV Selection

When possible, all systems should be installed with a variable refrigerant metering device. 

Evaporative condensers tend to have a lower pressure difference between the high and low sides 

than do air-cooled systems. Most TXVs are not designed for such low pressure differentials. 

Subsequently, an oversized TXV should be used or one that is specifically designed for lowpressure applications. Check with the manufacturer for their recommendations.

3.3 Installation Prodecure

The following instructions outline the general installation steps 

that are specific for evaporative condensers and are not meant 

to be a step-by-step installation procedure. It is important to 

follow manufacturer-supplied installation instructions as 

requirements vary by product. Contractor training in the 

particular product being installed is highly recommended. 

Where information is omitted, refer to standard air-cooled 

residential condenser installation practices. Refer to 

Attachment A for a checklist to follow for installations.

Step 1 - Condenser location and installation: Identify an appropriate location prior to installation. 

The condenser must be located where there is access to electricity and water and with adequate 
20

capability to drain bleed or purge water. Condensing units should be properly located outdoors 

on a level concrete pad, preferably positioned to avoid direct sun. The installation should 

conform with minimum clearance requirements to ensure adequate condenser airflow and access 

to service panels. The concrete pad on which the condensing unit is installed must be level to 

ensure proper water distribution over the condenser coils. Always ensure there is an electrical 

disconnect which is disconnected whenever servicing or replacing a condensing unit.

Step 2 - Supply water: Connect the water supply 

to the water fitting on the condenser. While the 

supply water need not be from a potable source,

this is the most straightforward solution in most 

instances. Always check with manufacturer’s 

literature regarding use of non-potable water. 

Turn the water supply on and fill the water sump 

to the appropriate level by adjusting the float 

(Figure 8). The pump may need to be running to 

accurately set the float level. Water treatment is 

generally not necessary, since chlorine added to 

city water supplies along with the flushing cycle 

of the evaporative condenser are adequate as 

biocide treatment of water for residential 

applications. If chemical water treatment is used, 

check with manufacturer, local codes and water 

authorities for permissible products and requirements for proper disposal of chemical water 

treatments.

Step 3 - Purge water: Connect a hose to the drain line and route to the desired location. Drain 

water must be routed away from the condensing unit and the house foundation to minimize 

erosion but is safe to be used for a number of purposes including landscaping. Check local 

requirements because in hard water areas some landscaping may not tolerate the higher salt and 

mineral content of the purge water. The line may be directed to vegetation nearby or captured in 

a reservoir for use elsewhere. Units with a continuous bleed strategy utilize gravity to expel the 

water from the sump. These systems require that the drain hose lie lower than the elevation of the 

condenser for the system to function correctly. Units with a purge pump provide more flexibility 

in options for disposing of the purge water. If chemical water treatment is used, the purge line 

may need to be routed to an appropriate drain.

If the unit has a purge control, adjust it based on local conditions. Preferably, water hardness and 

alkalinity is measured onsite; otherwise, local or regional water reports may be referenced. Refer 

to manufacturer specifications for setting based on water quality.

Figure 8: Float to adjust water sump level
21

Step 4 - Evacuation and Charging: 

Refer to manufacturer’s installation 

instructions for refrigerant line 

evacuation and charging procedures. 

All work must be performed by 

licensed and trained personnel with 

proper equipment. Follow the current 

EPA guidelines for refrigerant 

handling. Federal law prohibits 

refrigerant venting. For systems with 

a TXV installed at the indoor coil, 

refrigerant charging must be 

accomplished using the sub-cooling 

method according to sub-cooling 

targets provided by the manufacturer. 

Follow best practices regarding 

under what outdoor conditions 

charging should be conducted. 

3.4 Verification Procedures and Tests

System Start-up

Once installation is complete, the manufacturer start-up procedures should be followed and the 

system tested for correct operation. Before starting the system, verify the following:

• All panels and doors are in place and secure

• The sump drain cap is in place and secure

• The water supply valve is turned on and the sump is filled to the required level

• A clean air filter is installed upstream of the indoor fan

• The electrical disconnect is in the ON position.

At the indoor thermostat turn the system into cooling mode and lower the temperature setpoint to 

initiate air conditioner operation. Verify that the following systems are functioning correctly:

• Indoor fan is supplying air to the supply registers and exhausting from the return 

• Outdoor compressor turns on

• Water circulation system: verify the water is circulating from the sump to the spray 

nozzles and that the spray nozzles are emitting a continuous spray and are not clogged. 

• Water sump level; verify that the float switch and fill valve are both functioning and that 

the level in the sump is at the desired level and remaining constant.

• Water bleed or purge system: with bleed systems verify that bleed is continuous and there 

doesn’t appear to be any restrictions in the line. With periodic purge systems operate the 

Figure 9: Gauges connected to operating evaporative 

condenser to verify correct charge
22

system long enough to verify that the purge pump activates and purges the sump to the 

required level. Ensure the purge level is set appropriately. For all systems, make sure 

water is being bled or purged to the proper location.

System Commissioning

System commissioning is an important component of any installation to ensure that the system 

operates per design expectations. This is especially true in retrofit applications where improper 

existing conditions may negate the benefits from implementation of this measure. Recommended 

tests include the following (while some of these tests do not specifically address the condensing 

units they are imperative to achieve optimal unit capacities and efficiencies.):

• Cooling coil airflow: It is recommended that airflow be tested preferably using an airflow 

metering plate or fan assisted duct blaster, although a good flow hood will suffice. Due to 

system restrictions imposed by the ductwork and other components, relying on the tap 

setting specifications is not an accurate way of verifying correct airflow. A minimum of 

350 cfm per installed ton of capacity is recommended. In dry climates, where the need for 

latent cooling is minimal, higher airflow (up to 500 cfm per ton) is desirable. In humid 

climates where the latent component of cooling is more pronounced, lower airflows are 

suggested, around 350 cfm/ton.

• Fan watt draw: Ductwork restrictions can result in both reduced airflow and increased fan 

energy use. AHRI rating procedures assume an optimistic fan efficacy of 0.365 W/cfm. 

However, field studies have shown that fans can use as much as 1.2 W/cfm. Verify that 

fan power is equal to or less than 0.58 W/cfm8

.

• Duct leakage testing: Duct leakage can represent a significant portion of energy use for 

space conditioning and reduces cooling system performance. Verify that duct leakage to 

outdoors in new ductwork is less than 4 cfm at 25 Pascals per 100 square feet of 

conditioned floor area or 6% of total system airflow, whichever is lower. For existing 

ducts diagnose and repair leaks to the extent possible. The goal is to minimize duct 

leakage as much as possible; attempts should be made to reduce leakage to at least 15% 

of total system airflow. In some cases, replacement of the duct system may be warranted. 

Third-party Testing

Third-party testing is always recommended to verify correct installation and ensure expected 

performance. Recommended tests include verification of refrigerant charge, cooling coil airflow, 

fan watt draw, and duct leakage.

3.5 Operation and Maintenance

Evaporative condensers require semi-annual maintenance at the beginning and the end of each 

cooling season. In addition, standard maintenance practices associated with air-cooled systems 

should also be followed including regular air filter replacement, cleaning of condenser coils, etc.

Bi-annual Start-up: 

1. Remove the front door and clear the sump area of debris. Wash it out with water. 

 8 California’s Title-24 energy code includes a prescriptive requirement for system fan power of 0.58 W/cfm based 

on field results from California research in new construction homes.
23

2. If present, inspect the sacrificial 

anode(s) to determine if replacement is 

necessary. If there is heavy mineral 

deposits on the sump floor, consult the 

manufacturer regarding alternative 

methods for water treatment.

3. Remove and clean the circulation 

pump intake screen. Replace the screen 

when clean. (Figure 10)

4. Rinse out sump of debris and minerals 

as needed.

5. Ensure the drain cap is in place and 

secure.

6. Remove and clean the screen at the 

water supply valve. Replace the screen 

when clean.

7. Turn on the water valve and fill the 

sump to the appropriate level according to manufacturer instructions. Verify that the float 

is adjusted properly.

8. Remove the top access panel and inspect the condenser coils and spray nozzles. If 

excessive mineral deposits are visible, cleaning may be necessary. Follow manufacturerspecific details for cleaning as improper handling of the condenser coils may invalidate 

the warranty.

9. Clean access doors and panels as appropriate if coated with mineral deposits

10. Turn the electrical disconnect to the on position.

11. At the indoor thermostat turn the temperature setpoint down to initiate air conditioner 

operation.

12. Confirm that the outdoor compressor and pump are operating and that water is circulating 

correctly.

13. Replace and secure the front door and any other panels that were removed.

Bi-annual Shut-down: 

1. Turn off the thermostat, electrical disconnect and the supply water valve.

2. Remove the drain cap and drain the sump entirely. Rinse off intake screens, flush the 

sump pan and pump screens. 

3. Once sump is empty, leave the drain cap removed so that the sump drains through winter. 

Store drain cap in a safe place for use the following summer.

4. Replace and secure any panels that may have been removed.

Figure 10: Water sump and pump filter basket during 

operation
24

Attachment A: Prescriptive Measure Checklist for Contractors

Installation Procedure Guidelines for 

Evaporative Condensers Completed?

1. Field Inspection

1.1 Is the proposed equipment compatible with existing or planned mechanical systems? 

1.2 Is there adequate access to supply water at the proposed location for the condenser? 

1.3 Is there capability for purge water drainage at the proposed location for the condenser? 

2. System Design

2.1 Condenser sizing

2.1.1 Manual J and S completed Cooling Load:_________ A/C Size:_________ 

2.2 Ductwork design

2.2.1 Manual D completed 

3. Installation

3.1 Unit location

3.1.1 Unit is level for proper water distribution over the condenser coils 

3.2 Supply water

3.2.1 Water supply connected to the fitting at the unit 

3.2.2 Sump filled to the proper level and water supply valve turned on 

3.2.3 Float level is set appropriately 

3.2.4 If required, water treatment system properly installed or applied 

3.2.4 Drain cap in place and secure 

3.3 Purge water

3.3.1 Hose properly routed to drain location 

3.3.2 Purge control adjusted and set 

3.4 Evacuation and charging

3.4.1 System was completely evacuated before initiating charge 

3.4.2 Proper charge has been set and verified 

3.5 Electrical connections at the condenser 

3.5.1 Communication between condenser and thermostat 

3.5.2 Electrical disconnect installed 

3.6 Clean air filter installed upstream of the indoor fan 

4. Verification and Operation

4.1 Visual verification of correct operation

4.1.1 System responds properly to user input to thermostat 

4.1.2 Water circulation system functions correctly and spray nozzles aren't clogged 

4.1.3 Water sump level is correct and self-maintains and the fill valve functions correctly 

4.1.4 Water purge functions correctly 

4.2 System airflow tested Airflow (cfm):_________ 

4.3 System fan power on maximum cooling Power (W):_________ 

4.3 Duct leakage Leakage (cfm):_________ Leakage (% of airflow): _________ 

4.3 O&M manual provided to occupant – Maintenance service contract should be set up with the 

installer or the occupant made familiar of all maintenance procedures.


25

Attachment B: Modeling Methodology and Detail

BEopt modeling evaluated both new construction and existing homes in a variety of climates. 

The new construction model was based on a standard 2,400 ft2 B10 Benchmark house which was 

assumed to be square, with equal wall area and equal window area on all four cardinal 

orientations. Construction assumptions are based on the House Simulation Protocols (HSP) 

(NREL, 2010) and the insulation and window values were tailored to each climate zone. The 

foundation was assumed to be slab for all climate zones. 

Table 7: New Construction Assumptions by Climate Zone

BA Climate Zone Hot-Dry HotHumidMixedHumidMarine Cold

IECC Climate Zone CZ 3B CZ 2A CZ 2A CZ 3C CZ 5B

Representative City Sacramento, 

CA

Houston,

TX

Atlanta, 

GA

Santa 

Rosa, CA

Denver, 

CO

Wall Insulation R-13 R-13 R-13 R-13 R-13+R-5

Window U-value/SHGC 0.4/0.3 0.4/0.3 0.4/0.3 0.4/0.3 0.35/0.35

Slab Insulation R-Value 

and Depth

R-0 R-0 R-0 R-0 10, 2 ft

Ceiling Insulation R-30 R-30 R-30 R-30 R-38

For existing homes, building geometry and configuration were determined based on research and 

review of the 2010 DOE Buildings Energy Data Book (BEDB) (DOE, 2011) and the 2009 

California Residential Appliance Saturation Study (RASS) (KEMA, 2010) and include the 

following:

• Single story 1,800 square foot home with three bedrooms. This is consistent with RASS 

and BEDB averages. RASS average for single family homes is 1,882 ft2 for California 

building stock. BEDB estimates characteristics of a typical single-family home from the 

mid 1970s with a heated average floor space of 1,934sqft and a cooled average floor 

space of 1,495 ft2

. Average conditioned floor area of homes constructed between 1980 

and 1989 is 1,806 ft2

.

• 16% glass as a percentage of conditioned floor area, based on RASS averages. The 

BEDB reports window areas for a typical 1970s era home of between 11% and 15% of 

conditioned floor area.

• Glass is equally distributed on all four sides to eliminate orientation effects

• Wall area and slab perimeter based on an aspect ratio of 2.0. This is consistent with a 

sampling of actual homes. To maintain equal wall and glazing areas distribution on all 

orientations, an L-shape building model was used.

Three eras of existing homes were evaluated according to the distinctions made in the HSP (pre 

1980, 1980s era, and 1990s era). Building characteristic assumptions are based on the HSP as 

well as California’s Title 24 vintage assumptions where appropriate. U-factor and SHGC values 
26

for the single metal-pane windows were taken from the default values in Tables 116-A and 116-

B in California’s 2008 Building Energy Efficiency Standards (CEC, 2010).

Table 8: Existing Home Assumptions by Building Vintage

Pre 1980 1980-1989 Post 1989

Wall Insulation R-0 R-11 R-13

Window U-value/SHGC Single metal 

1.28/0.80

Single metal 

1.28/0.80

Single metal 

1.28/0.80

Slab Insulation R-Value 

and Depth

R-0 R-0 R-0

Ceiling Insulation R-0 R-9 R-13

The furnace and water heater are assumed to have been seldom or never maintained. Base 

efficiency specifications and Maintenance Factors (MFs) were taken from Table 30 and Table 33 

in the HSP. The furnace was assumed to have a rated efficiency of 78 AFUE and the water 

heater 0.54 EF. Equations 19 and 21 in the HSP were used to degrade the efficiency according to 

age and MF. Ductwork was assumed to be located in the attic with R-2.1 insulation and 30% 

leakage.

Appliance, lighting, and plug energy end-uses are all based on Building America assumptions. 

Appliances are assumed to be standard efficiency and five years old. 10% fluorescent lighting is 

assumed for existing homes. 
27

Attachment C: Additional Modeling Results

Table 9 and Table 10 show the cooling energy savings for an existing home that was built 

between 1980 and 1989 for the SEER 13 and SEER 15 base cases, respectively. 

Table 9: Annual Cooling Energy Savings Compared to an Existing Home Circa 1980 with a SEER 

13 Air Conditioner

Building 

America

Climate Zone

IECC 

Climate 

Zone

Sample City

Annual Cooling 

Energy Use (kWh) Annual 

kWh 

Savings

%

kWh 

Savings

Annual 

kW 

Savings

%

kW 

Savings

Annual 

Utility 

Savings Base 9

Case 

Evap 

Condenser

Hot-Dry 3B Fresno, CA 5,534 4,120 1,414 26% 1.94 30% $159 

Hot-Humid 2A Houston, TX 6,409 5,478 931 15% 1.51 24% $105 

Mixed-Humid 2A Atlanta, GA 4,004 3,380 624 16% 1.41 23% $70 

Marine 3C Santa Rosa, CA 894 730 164 18% 0.83 14% $18 

Cold 5B Denver, CO 2,073 1,515 558 27% 2.08 34% $63 

Table 10: Annual Cooling Energy Savings Compared to an Existing Home Circa 1980 with a SEER 

15 Air Conditioner

Building 

America

Climate Zone

IECC 

Climate 

Zone

Sample City

Annual Cooling 

Energy Use (kWh) Annual 

kWh 

Savings

%

kWh 

Savings

Annual 

kW 

Savings

%

kW 

Savings

Annual 

Utility 

Savings 10 Base 

Case 

Evap 

Condenser

Hot-Dry 3B Fresno, CA 4,924 4,120 804 16% 1.29 22% $90 

Hot-Humid 2A Houston, TX 5,705 5,478 227 4% 0.88 15% $26 

Mixed-Humid 2A Atlanta, GA 3,563 3,380 183 5% 0.81 15% $21 

Marine 3C Santa Rosa, CA 796 730 67 8% 0.25 5% $7 

Cold 5B Denver, CO 1,839 1,515 325 18% 1.45 26% $37 

Annual cost for water usage was calculated for each climate zone based on seasonal ton-hours of 

cooling output from BEopt modeling and an average consumption rate of 2.5 gallons per ton-hr 

based on prior studies of both field and laboratory testing (DEG, 2008; Keesee et al, 2010; SCE, 

2009). Water consumption rates will vary based on local climate conditions. A national average 

water rate of $3.90 per 1,000 gallons was used (Global Water Intelligence, 2009). Results are 

shown in Table 11.

 9

 National average utility rate of $0.1126 / kWh 10 National average utility rate of $0.1126 / kWh 
28

Table 11: Annual Water Operating Costs for Evaporative Condenser Assuming National Average 

Water Rates

Climate Zone Annual 

Water Costs

Hot-Dry $22

Hot-Humid $34

Mixed-Humid $18

Marine $1

Cold $5

Table 12 and Table 13 show the incremental cost over the SEER 13 and SEER 15 base cases, 

respectively, that would result in a positive annual cash flow to the homeowner based on 

estimated utility electricity savings, increased water costs, and mortgage payments. The 

assumptions are the same as in the similar analysis based on electricity savings only (Table 3 and 

Table 4) and include a 30-year mortgage term.

Table 12: Incremental Cost Justified by Energy Modeling Savings Compared to a SEER 13 Air 

Conditioner for Various Interest Rate Financing Scenarios – Includes Both Energy Utility Savings 

and Additional Water Costs

Climate Zone 3% 4% 5% 6% 7%

Hot-Dry $1,007 $889 $791 $708 $638 

Hot-Humid $559 $494 $439 $393 $354 

Mixed-Humid $294 $260 $231 $207 $186 

Marine $21 $19 $17 $15 $13 

Cold $190 $167 $149 $133 $120 

Table 13: Incremental Cost Justified by Energy Modeling Savings Compared to a SEER 15 Air 

Conditioner for Various Interest Rate Financing Scenarios – Includes Both Energy Utility Savings 

and Additional Water Costs

Climate Zone 3% 4% 5% 6% 7%

Hot-Dry $387 $342 $304 $272 $246 

Hot-Humid $0 $0 $0 $0 $0 

Mixed-Humid $0 $0 $0 $0 $0 

Marine $1 $1 $1 $1 $1 

Cold $65 $58 $51 $46 $41 
29

References

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America.

ACCA. Manual S Residential Equipment Selection. Air Conditioning Contractors of America.

ARBI (2011). “Test Plan: Evaporative Condenser Performance.” Prepared for Building America 

by the Alliance for Residential Building Innovation (ARBI). August, 2011.

CARB (2009). “2009 Annual Progress Report Budget Period 2 (BP2) – Attachment BB: Second 

Generation Evaporative Condenser Summary Report.” Prepared for the Department of Energy by 

The Consortium for Advanced Residential Buildings. December, 2009.

CEC (2010). “2008 Building Energy Efficiency Standards – Residential Compliance Manual.” 

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DEG (1998). “Evaluation of Residential Evaporative Condensers in PG&E Service Territory.” 

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30

SCE (2009). “Performance Evaluation of an Evaporatively-Cooled Split-System Air 

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DOE/GO-102012-3531 ▪ March 2012

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