Dehumidifying Heat Pipes

In order to make a room comfortable in hot, humid climates, an air conditioner must lower the indoor humidity level as well as the air temperature. If an air conditioner fails to lower the humidity adequately, the air will be cool, but will feel uncomfortably damp. Inappropriately sized air conditioners are prone to this problem; large units quickly cool the air, but cycle off before they can properly dehumidify it. In extremely humid climates, even correctly sized air conditioning equipment could fail to maintain a home at a comfortable humidity level.

One technology that addresses this problem is the dehumidifying heat pipe, a device that enables an air conditioner to dehumidify better and still efficiently cool the air. The heat pipe is ideal for hot, humid environments.

A dehumidifying heat pipe resembles two heat exchangers, located on either side of the air conditioner's evaporator coil. Several tubes connect the two sections. A refrigerant (usually an HCFC) inside the tubes pre-cools the incoming supply air by absorbing the heat from it. This causes the refrigerant in the tube to evaporate. The air conditioner evaporator cools it further, extracting up to 91% more water vapor than a conventional evaporator would. After the refrigerant in the tubes changes into a vapor, it flows to the condensing section at the other end of the system. There, it releases its heat into the air stream and returns to its liquid state again. Gravity then causes the refrigerant to flow to the evaporator end of the pipe to begin the cycle again.

Most models of heat pumps and central air conditioners can be retrofitted with dehumidifying heat pipes. You can choose either a replacement cooling coil that incorporates the heat pipe, or add-on heat pipes for the unit's ventilation system. You may also want to consider a complete air-conditioner unit that incorporates the heat pipe.

Although the heat pipes don't use any electricity directly, they cause the conditioned air to leave the system slightly warmer than it would have in the absence of the heat pipe, so it takes more energy to cool your home. The system also consumes more fan power to blow air past the heat pipe. However, the manufacturer claims that your thermostat can be set higher with the low humidity air, allowing a net energy savings.