_ _ April 1981 RAIN Page 19 Heat Pumps In principle, a heat pump water heater is a pretty simple machine, utilizing refrigeration technologies that have been around for over a hundred years. By manipulating the pressure and temperature of a fluid with a low boiling point, such as freon, heat can be moved from the ambient air into a hot water tank, using much less energy than it would take to heat the water directly with a resistance heater. Most of the energy that a heat pump uses goes to run a compressor and a fan. The fan blows air over a heat exchanger, which is called an evaporator. The liquid freon inside the evaporator is converted into a vapor as it draws heat from the air. The warm vapor then goes through a compressor, which increases the pressure and temperature of the freon. The hot pressurized vapor goes into another heat exchanger, called a condenser, where the freon is condensed back into a liquid as it releases its heat to the water in the tank. The cool liquid then flows through an expansion valve, lowering the pressure and temperature of the freon as it flows through the evaporator to repeat the cycle. Heat pump efficiency is measured by what is called the Coefficient of Performance (COP), which is simply the amount of energy _ to hoi wal.... I·... clrie I ,...1. •.........,•••,..... 1Jj .... lftOIor-clrMn~III!!I!.....!i~ii~~ Iff c~ret.......nI ... cOiftpreUOr ...... w:""" ~ -.... . re1nwrran. - I ....blenl.ir 8s I.. Cool ••"-".11 • < uN ........ . ~ ._.- _.uHl c>:<:::J w.... ,of...., ••' & 2 ... 1 - - - C'lrcua.' in9 E-Tech pump that ends up getting put into the hot water tank divided by the amount of energy it takes to run the heat pump. A COP of 2, for example, means that the heat pump is over twice as efficient as a resistance water heater, which means that it uses only half as much electrici ty . HeatPump Water Heaters Goodbye to Active Solar? by Kevin Bell Heat pumps for residential and commercial water heating have recently crashed onto the energy scene, and their appearance has provoked a lively debate among many solar advocates. Some manufacturers are predicting that heat pump water heaters will completely displace active solar hot water systems in most parts of the country. Some solar proponents agree. Others are exhibiting violent tenden . cies whenever heat pump water heaters are mentioned. It turns out that despite the confident assertions being made by both sides, a number of questions about how much of a threat heat pumps really pose to active solar have yet to be answered. Unlike similar appliances such as refrigerators and air conditioners, heat pumps are expected to operate over a wide range of temperatures and conditions. Several companies that tried to market heat pumps for both space and water heating during the 1950s made the mistake of assuming that a heat pump is simply a backwards air conditioner. They discovered, much to their dismay, that the technology is not as simple as it looks. The resulting failures left heat pumps with a stigma that has only recently begun to fade. Heat pump technology has improved considerably since that time, and despite a number of early problems, it is clear that heat pump water heaters have reached a point where they are both reliable and effective, within certain limitations. However, those limitations pose some interesting problems. For example, the evaporaThere are cheaper and easier ways to utiIize that "waste heat" than putting what amounts to a large air conditioner in your house in the dead of winter. tor tends to freeze if the air temperature drops below 45°F (i"'C), and the compressor has a hard time handling temperatures above 100°F (3i"'C) or so. Most heat pump water heaters can be seriously cont.-"
RkJQdWJsaXNoZXIy NTc4NTAz