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Water Cooled Evaporative Air Conditioning

Numerous advantages over air-cooled units

Image of evaporative cooled condensing unit.

Although water is used to assist with cooling, this technology is not related to the conventional Evaporative Air Coolers often called swamp coolers. Water is used to remove heat from the refrigerant and at the same time reduce the work of the compressor. The Water Cooled Evaporative Air Conditioner is a residential application of a technology already in use in commercial buildings for split system air conditioners known as chillers. Think of this technology as a mini-chiller for residential use.

Evaporative cooled condensing units for split system air conditioners have a number of advantages over air-cooled units. This is why most commercial air conditioners larger than about 250 tons typically rely on cooling towers to cool water and remove heat generated from the compression cycle of the chiller. The key elements of the unit include multiple low-pressure water nozzles that spray a mist of water over the condenser coils to remove heat after the refrigerant is compressed. Water temperature can be maintained at about 10° F over wet bulb via heat absorbed through evaporation, which is then removed via a fan on top of the unit.

Unlike air cooled units, which lose in the range of 25 percent of their rated efficiency at temperatures exceeding 100° F relative to their SEER rating, the efficiency of an evaporative water cooled unit has a minimal drop.

In the past, evaporative cooled condenser units were used only in commercial applications. Now one manufacturer has a model that is designed specifically for the residential market.

Freus Inc. has developed a water cooled evaporative condenser unit. A "scroll" compressor compresses the R-22 refrigerant. A small water pump continually sprays water over the condenser coil, which cools the coil primarily via conduction from the copper coil to the water, sprayed on the coil. The coil is solid copper; approximately three times the thickness (i.e. 0.032" vs. 0.012") of that used in air-cooled condensers, and the copper is coated to prevent corrosion. Magnesium anodes are included to treat the water and reduce coil corrosion.

A float maintains approximately 3.5 inches of water in the bottom of the condenser. Every 8 hours of run time, a timer causes a purge pump to pump all water from the bottom of the unit (approximately 5-8 gallons). The float valve then causes more water to flow until a level of about 3.5 inches is restored.

Water removes heat from the condenser coils far more efficiently than air. The heat transfer and evaporative process is increased via a fan on top of the condenser.

Above 95° F, a typical air cooled condenser draws approximately an additional 10% power for each 10° F increase in temperature. In contrast, an evaporative cooled condenser draws about the same power over a wide range of outdoor temperatures.

Residential and small commercial models are available from 2 to 12 tons. The dimensions of the evaporator unit are comparable to a 3-5 ton conventional condenser unit.


Energy Efficiency

In dry climates, evaporative air conditioners use much less energy than standard, vapor-compression air conditioners.


Easy

Units are widely available throughout the sunbelt and in Hawaii. Significant numbers of units have been installed in California, Florida, Nevada and Texas.

In areas where there are hard freezes, the owner must ensure water is drained from both the condenser unit and the copper water supply line.


Most of the initial cost differential is due to the cost of the unit. However, an added cost of assuring a water supply to the outdoor condensing unit is required. The cost of the unit is best characterized as similar to upgrading the SEER of a standard air conditioner to higher grade equipment with higher SEERs.


These units will have lower operational costs compared to other air conditioners manufactured to meet minimumFederal-mandated SEER ratings.


Units are required to meet all local mechanical codes.


Not Applicable


Installation procedures are identical to an air cooled condenser with the following exceptions: 1) A 1/4" copper water line must be installed--typically connected to a nearby outside water faucet with an included connection kit; 2) A water flush line must be run to vegetation or a drain; 3) A condensate recovery drain from the evaporator coil to the condenser can reduce net water consumption approximately 50 percent.

Condenser units may be placed either on a roof or on a pad adjacent to a structure. Just as with air-cooled units, locations not subject to direct sunlight are preferred. Semi-annual maintenance is recommended.


The warranty for this equipment resembles the warranty for conventional split-system air conditioner systems. Most split-system units have a 1-year parts warranty, 5-year on the compressor, and sometimes a longer period for the outside cabinet. The Evaporative cooled condensing unit essentially has a single manufacturer as of this date. The warranty offered is a limited 5-year compressor warranty, an optional limited 10-year warrant on copper parts, and a limited 15-year warranty on the fiberglass cabinet.


The primary benefit of an evaporative water cooled condenser unit is a 25 to 40 percent reduction of overall power consumption relative to a SEER 10, and a 40 to 50 percent reduction in peak power consumption (i.e. temperatures exceeding 95° F) relative to a SEER 10, according to the manufacturer.

The cost of a Freus condenser is comparable to a SEER 14. Payback on the incremental cost relative to a SEER 10 is typically in the range of three years in hot, arid climates.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.