How Do Heat Pumps Work?
Heat pumps have been around for quite a while. Probably the simplest way to describe them is that they are an air conditioner that worksbackward. Whereas the air conditioner blows cold air into the house and exhausts hot air into the atmosphere, the heat pump does the opposite. Heat pumps and air conditioners work the same way. A simplistic picture of a heat pump would be two pieces of tubing, each formed into a coil.The function of each coil is to be a heat exchanger. The bottom of each coil is connected to a compressor. One coil connected to the intake port of the compressor and the other coil connected to thedischarge port. Each of the other ends of the coils is connected to an expansion valve. The coil that is connected to the intake port of the compressor isconnected to the discharge port of the expansion valve and the other coil is connected the intake port. A fluid, which when under pressure becomes a gas, is put into the system. It is called a refrigerant. OK, so now we have a totally enclosedsystem containing the refrigerant. Here's how it all works to pump heat or cold, depending upon your needs. p> 
The refrigerant, in its gaseous state, is pressurized and circulated through the system by the compressor. On the discharge side of the compressor, the now hot and highly pressurized gas is cooled ina coil/heat exchanger, called a condenser, until it condenses into a high pressure, moderate temperature liquid. The resulting heat on this coil/heat exchanger is blown into the houseThe condensed refrigerant then passes through an expansion valve where the pressure is lowered. The expansion valve then passes the low pressure, (almost) liquid refrigerant to another coil/heatexchanger, the evaporator. There the refrigerant evaporates into a gas, and the coil/heat exchanger becomes cold. The refrigerant then returns to the compressor and the cycle is repeated. Evaporation and condensation are flip sides of the same coin. One cools, the other heats. Compressing a gas back into a liquid requires a mechanical crushing force, but the result is that the gasturns hot. The difference between an air conditioner and a heat pump is that the heat pump is reversible. It will heat or cool, depending upon which way the valve is thrown. What distinguishes a heat pump from an air conditioner is that a heat pump is by definition reversible, meaning the process can move in either direction. Although the underlying physics are thesame, you get mirror image effects depending on which way the valve is thrown. Heat pumps are most efficient in the South. Most of the heat generated by a heat pump comes from the atmosphere. In frigid temperatures below around 15 degrees Fahrenheit, a heat pump will nolonger do an adequate job of heating your home. Those heat pumps sold in areas where the temperature takes limited dips to 20 degrees and lower will have electric heating strips to provide heat whenthe heat pump can't. As you look into the market for heat pumps, you'll notice there are many designs available. In addition to the typical air-to-air heat pumps, there are ground source heat pumps as well as newtechnologies that make use of magnetism. The market for heat pumps is forever making strides in efficiency. A basic knowledge of the way heat pumps work can help you make a more informed choice asyou invest for your home. | 
