Heat pumps are becoming a more frequent choice for families replacing an old, inefficient heating and cooling system. This is because a heat pump can heat, as well as cool, your home efficiently. The cost of electricity for heating and cooling a house – although it gradually increases over time, as most prices do – is much less volatile than the cost of natural gas, oil or propane.
A geothermal heat pump is one of the most energy-efficient heating and cooling systems for any climate. Even though it provides a good long-term payback during its lifetime, the initial installation cost is considerably higher than it is for a standard air-source heat pump. Also, depending upon your yard and soil type, a geothermal system may not be appropriate for your house.
An air-source heat pump is basically a central air conditioner with a few extra parts. It’s called a heat pump, because it literally pumps heat out of your house (cooling mode) to – or into your house (heating mode) from – the outdoor air around the compressor/ condenser unit.
In the cooling mode, a heat pump draws heat from the indoor air as it passes through the indoor evaporator coils. Through a refrigeration cycle identical to that of an air conditioner, the heat pump expels this heat outdoors.
The cooling efficiency of a heat pump is rated by its SEER, or seasonal energy efficiency ratio. A heat pump’s cooling efficiency is only slightly less than for a similarly sized conventional central air conditioner.
During the winter, a reversing valve inside the heat pump’s outdoor unit reverses the flow of refrigerant. Instead of running the cool refrigerant through the indoor coil, it runs the hot refrigerant indoors.
The cold refrigerant is run outdoors where it draws heat from the surrounding air. Since the refrigerant is colder than the outdoor air, it absorbs heat, even though the outdoor air may feel cold to you. Heating efficiency is rated by HSPF, or heating seasonal performance factor.
As the temperature gets colder outside and the heating needs of your home increase, the heat pump has a harder time drawing heat from the cold outdoor air. At a certain point, the heat pump no longer can provide enough heat to keep your house warm, and a backup heating source comes on. Your heating and cooling contractor can set the temperature at which the backup comes into play.
Many recent developments in airsource heat pumps have made them very efficient. For example, a heat pump with a modulating, multistage output rotary compressor design, which first was introduced in central air conditioners, is now available in heat pumps and produces extremely high efficiencies for both heating and cooling (HSPF 10 and SEER 22). That means you can get around $2 to $3 worth of heat for each $1 on your utility bill.
This type of heat pump uses its rotary compressor to vary the heating or cooling output from about one-third to full capacity. The result is lower electricity consumption, plus great comfort, quiet operation and even room temperatures.
Another new two-stage heat pump design couples a solar panel with the outdoor unit. On a sunny day, this solar panel produces enough electricity to operate the condenser fan for up to 8 percent electricity savings. When it’s not sunny (or at night), the outdoor condenser fan runs on electricity like any other heat pump.
No matter what type of new heat pump you select, make sure your duct system is compatible with it. There typically should be from 400 to 500 CFM (cubic feet per minute) of airflow per ton of cooling through the unit for the best efficiency. Your old duct system may need to be modified.
