Q: Dear Jim: When my air conditioner is running during the summer, I can feel hot air coming from it outdoors. Are there any devices that capture this heat for my hot water? Also, is there anything to make it dehumidify better? - Kyle L.

A: Dear Kyle: It is a common misconception that air conditioners actually cool the air. What an air conditioner does is just move the heat from indoors to outdoors. Your refrigerator is a good analogy to an air conditioner.

There are several devices that you can install that will use the air conditioner's waste heat to warm your hot water. It's free energy. Why waste it? These devices are called desuperheaters and heat pump water heaters (HPWH). There are also devices to change the ratio of cooling/ dehumidification in your central air conditioner to make it operate more efficiently, improve your comfort, and reduce allergies.

Desuperheaters are devices that connect your central air conditioner hot condenser coils to the water heater tank. Instead of the condenser coils giving off the heat to the outdoor air blowing past them, they heat the water inside the water heater tank.

One common method uses a sealed coil inside the water heater through which the hot air conditioner refrigerant flows.

Heat water with free energy as house cools

Another design uses a separate heat exchanger to heat the water. Some simple models have the heat exchanger built into a circular base upon which your water heater rests. Built-in desuperheaters are common on geothermal heat pumps and can be used with standard heat pumps.

Add-on or integral heat pump water heaters (HPWH) are efficient devices that both heat your water and also cool and dehumidify whenever they are heating the water. This reduces the amount of time your central air conditioner has to operate so you save electricity overall.

HPWHs operate in a similar fashion to a window air conditioner. They draw their heat for the hot water from the air in

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your utility room or basement. Instead of having the hot condenser coils outdoors, the HPWH has a built-in heat exchanger that is connected to your existing water heater. When the HPWH is running, your house is being cooled and dehumidified for free as a byproduct of heating your water. I have a small add-on model in my own basement.

Overall, a HPWH operates two to three times more efficiently than a standard electric water heater so your water heating costs are reduced by about half. With the added advantage of its dehumidification, you can set your central air conditioner thermostat higher without sacrificing comfort.

Several of the add-on HPWHs are easy to install yourself. A valve is attached to the standard drain valve near the base of your existing water heater. The HPWH can be placed on the floor or mounted on the wall. My HPWH is only 9 x 16 x 23-inches. If you want the cool, dehumidified air in another room, you can duct the output air to an adjacent room in your home.

Another add-on HPWH style is circular and designed to mount on top of your existing electric water heater. This generally requires professional installation, but it saves floor space. Complete integral HPWH models that include the entire electric water heater tank are also available if your current tank is leaking and needs replacement.

There are also some devices that are effective for improving comfort while lowering your air-conditioning bills. If you have an old central air conditioner and you have made your home more efficient over the years, it is probably oversized now. This results in a cool, clammy feeling inside your home because it does not run long enough to adequately dehumidify the air.

Installing a dehumidifying heat pipe can cure this problem. Using simple heat pipe technology (no moving parts and no electricity) developed by NASA, the coil super cools the return air to increase dehumidification. This heat energy is re introduced into the air on the other end of the heat pipe. The final output air is slightly warmer, but much drier for better comfort, less mold, and allergies.

New super-efficient whole-house dehumidifiers are also money-savers. They can be attached to the duct system and bring in filtered fresh outdoor air during the summer. If the air is drier, you can set the thermostat higher.

Write for (instantly download - www.dulley.com) Utility Bills Update No. 458 - buyer's guide of nine heat pump water heater, desuperheater, dehumidifying heat pipes and dehumidifier manufacturers, and cooling/ comfort and water heating efficiency tips. Please include $3 and a business-size SASE. James Dulley, Illinois Country Living, 6906 Royalgreen Dr., Cincinnati, OH 45244.

James Dulley is a mechanical engineer who writes on a wide variety of energy and utility topics. His column appears in a large number of daily newspapers.

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