Heat Pumps / Air Handlers

Tips for Buying a New Heat Pump

• Heat pumps must be sized and installed properly to work efficiently. Heat pumps are sized for either the heating demand or cooling demand, depending on which implies the larger unit (almost always cooling). However, heat pumps do not perform well over extended periods of sub-freezing temperature and it may not be cost effective to meet all your heating needs with an air-source heat pump.
• Ground source heat pumps (GSHPs) are more efficient and less noisy than conventional air-source heat pumps. Though GSHPs are more expensive to install, the dramatic improvement in efficiency can yield attractive life cycle cost savings. However, the appropriateness of a GSHP depends on the size of your lot, the conditions of the subsoil and landscape, and sometimes the relative magnitudes of summer cooling and winter heating requirements.
• Select a heat pump with a higher HSPF. For units with comparable HSPF ratings, check their steady-state rating at -8.3°C, the low temperature setting. The unit with the higher rating will be more efficient.
• Select a heat pump with a demand-defrost control. This will minimize the defrost cycles thereby reducing supplementary and heat pump energy use.
• Select a heat pump with an outdoor sound rating of 7.6 bels or lower. The lower the value, the less noisy the outdoor unit.
• If installing a heat pump in an existing home without an existing heat pump or air conditioner, ductwork may need to be enlarged. Heat pump systems generally require larger duct sizes than other central heating systems. For proper heat pump operation, air flow should be 50 to 60 liters per second per kilowatt-hour or 400 to 500 cubic foot per minute per ton of cooling capacity.
• If a heat pump is added to an electric furnace, the heat pump coil can usually be placed on the cold (upstream) side of the furnace for greatest efficiency.
• Fans and compressors make noise. Locate the outdoor unit away from windows and adjacent buildings. Some units also make noise when they vibrate. You can reduce this noise by selecting quiet equipment or by mounting the unit on a noise-absorbing base.

Advanced Features to Look for in a Heat Pump

A number of relatively new innovations are improving the performance of heat pumps.

Unlike standard compressors that can only operate at full capacity, two-speed compressors allow heat pumps to operate close to the heating or cooling capacity that is needed at any particular moment. This saves large amounts of electrical energy and reduces compressor wear. Two-speed heat pumps also work well with zone control systems. Zone control systems, often found in larger homes, use automatic dampers to allow the heat pump to keep different rooms at different temperatures.

Some models of heat pumps are equipped with variable-speed or dual-speed motors on their indoor fans (blowers), outdoor fans, or both. The variable-speed controls for these fans attempt to keep the air moving at a comfortable velocity, minimizing cool drafts and maximizing electrical savings. It also minimizes the noise from the blower running at full speed.

Many high-efficiency heat pumps are equipped with a desuperheater, which recovers waste heat from the heat pump’s cooling mode and uses it to heat water. A desuperheater-equipped heat pump can heat water 2 to 3 times more efficiently than an ordinary electric water heater.

Another advance in heat pump technology is the scroll compressor, which consists of two spiral-shaped scrolls. One remains stationary, while the other orbits around it, compressing the refrigerant by forcing it into increasingly smaller areas. Compared to the typical piston compressors, scroll compressors have a longer operating life and are quieter. According to some reports, heat pumps with scroll compressors provide 10°–15°F (5.6°–8.3°C) warmer air when in the heating mode, compared to existing heat pumps with piston compressors.

Although most heat pumps use electric resistance heaters as a backup for cold weather, heat pumps can also be equipped with burners to supplement the heat pump. Back-up burners help solve the problem of the heat pump delivering relatively cool air during cold weather and reduces its use of electricity. Since there are few heat pump manufacturers that incorporate both types of heat supply in one box, these configurations are often two smaller, side-by-side, standard systems sharing the same ductwork. The combustion fuel half of the system could be propane, natural gas, oil, or even coal and wood.

In comparison with a combustion fuel-fired furnace or standard heat pump alone, this type of system is also economical. Actual energy savings depend on the relative costs of the combustion fuel relative to electricity.