July, 2014
Feature
Inspection News and Views from the American Society of Home Inspectors



Water Cooled Condenser Coil

ALAN CARSON

WATER-COOLED CONDENSER COIL

Function

In a water-cooled air conditioner, the heat in the refrigerant that has been collected from the house is not discharged into the air outside, but is discharged into water. This water may be from the city supply, from a river, lake, stream or well. In a commercial application, the water might be continuously cycled through a cooling tower. In single-family residential applications, the water just passes by the condenser coil once and is discarded.

Indoor Condenser

The condenser coil is usually located near the evaporator coil, since it does not have to be outdoors or in the attic to discharge heat into the outside air. The condenser sees a more predictable, uniform and dryer climate, and some say this leads to a longer life expectancy. On the downside, the heat given off by the compressor motor ends up inside the house. Obviously this doesn’t help with air conditioning.

Double Pipe Condenser

Water-cooled coils do not employ fins, since we are not passing air over the coil. It is typically a jacketed system with the refrigerant lines inside the water tubing. Usually the water and refrigerant flow in opposite directions.


Looking inside a water-cooled condenser coil, we can see the smaller refrigerant coils enter into the larger water-filled coils

Uses Lots Of Water

Where city water is used, many consider this an expensive and inefficient air conditioning system. Some municipalities won’t let you use this kind of system because it wastes so much water. The water often simply goes down the drain after it has picked up heat from the condenser coil. In some applications, the water can be diverted to be used in watering the lawn or filling a swimming pool. The supply water to the coil should never be from the pool, however. The chlorine in the pool water will corrode the coil quickly.

Common water-cooled coil problems include the following:

1. Leakage

2. Coil cooled by pool water

3. No backflow preventer

4. Low plumbing water pressure

LEAKAGE

Causes

• Leaks may occur in the water-cooled coils because of chemical reactions between the cooling water and the jacket material.

• Leaks may also be the result of mechanical damage, including vibration. In some cases, the coils are enclosed in a metal cabinet, but in others the coils are exposed.

• Corrosion as a result of chemicals in the home may also cause leakage. Paint stripping, for example, can create a very corrosive environment. Swimming pool chemicals in poorly sealed containers can have a similar effect.

Implications

Non-performance of the air conditioning is one implication, and if the leakage goes undetected, extensive water damage can result.

Strategy

Look for evidence of leakage, including stains, moisture trails or wetness. If the leak is downstream of a solenoid valve that is activated when the air conditioner is working, there may be no moisture apparent when the unit is at rest. Before starting the unit, ensure that any supply water isolating valve is open. Water must be flowing for the system to run. A system operating properly will have discharge water that is 15°F to 20°F warmer than the inlet water


Leak occuring just below the oulet pipe

COIL COOLED BY POOL WATER

Some installations circulate water from the swimming pool through the cooling jacket and back to the swimming pool. This strategy uses heat from the house to help warm the swimming pool water. The consensus is that this is a bad idea because the chemicals common in swimming pool water may attack the cooling jacket and cause premature failure.

Causes

The decision to recirculate pool water through this jacket is a design and installation issue.

Implications Corrosion, leakage and premature replacement of the cooling coil are the implications.

Strategy Trace the supply and discharge water lines from the jacket, if possible, to determine where the source water is from. If it is from the pool or you suspect it is from the pool, recommend further investigation by a specialist and let the client know that an alternate arrangement may be recommended. Don’t be fooled by water discharging to the pool. Bringing fresh water from the municipal supply, for example, and discharging the heated water to the swimming pool does not expose the jacket to water that contains pool chemicals.

NO BACKFLOW PREVENTER (ANTI-SIPHON DEVICE)

Where the cooling jacket is fed by the house water supply, an anti-siphon device such as a backflow preventer may be required by the local plumbing authority so that water cannot go back into the drinking supply after passing through the cooling jacket. Where this backflow preventer is not in place, a cross connection exists. This is a dangerous situation in which the drinking water may be contaminated. Water cooled condensers that pull water from isolated wells, ponds or lakes, or work off closed loops are unlikely to require a backflow preventer. Check in your area to see whether or not a backflow preventer is required.


Causes The omission of a backflow preventer may be an installation mistake.

Implications Possible contamination of potable (drinking) water is the implication.

Strategy Look for a backflow preventer on the supply inlet to the air conditioner, when the supply is from the house drinking water.


LOW PLUMBING WATER PRESSURE

Cause

Water-cooled units can use so much water, they may reduce house water pressure drastically. Water-cooled air conditioners typically need about 3 gallons per minute (gpm) flow for every ton. A three-ton unit may need 9 gpm! This doesn’t leave much for taking showers.

Implication

The water pressure for the house plumbing system may not be adequate when the air conditioning is running.

Strategy

If possible, do your plumbing system flow tests with the air conditioner running.

AIR CONDITIONING

We have introduced water-cooled condenser coils as part of an a split air conditioning system, and outlined some of the common conditions. We have also discussed cause, implication and strategy for these conditions. More information on water-cooled air conditioning systems can be found in the ASHI@HOME training program.