By Patrick O’Donnell
for East Penn Energy Solutions
Is a heat pump the right choice for you?
They’re a masterpiece of technical wizardry, pulling warmth like magic from the ground or air and transporting it into your home — or, during warmer months, acting as an air conditioner by pulling it from your house.
There are two types of heat pumps generally in use by consumers. The first is an air-source; the second, a ground-source. While they work on similar principles, their methods and efficiencies are vastly different.
We’re going to explain how they work and the benefits and drawbacks of each in a two-part series. We’ll start with the air-source model.
In general, an air-source heat pump’s system is similar to your refrigerator. There’s a compressor and coils made of copper tubing covered in aluminum fins. The fins help to transfer heat to or from the liquid. In a split-system unit – the most common type of system – one of the copper tubes is outside the home. The other one is inside. In what’s called a packaged system, both coils and the fan are located outdoors. Heated or cooled air is sent into the house through ductwork.
During heating season, a liquid refrigerant that’s flowing in the outside coils pulls heat from the air. As it absorbs the heat, it evaporates into a gas. The gas is transferred to the copper coils inside the home, where it condenses back into a liquid — releasing heat in the process.
Air-source heat pumps work very well in warmer climates, but when you live in an area where the temperature regularly drops below 40°F, they need a backup system. Each time the mercury drops to 39°F and below, a supplementary heating system must be activated.
Most of the units rely on an electric heat (resistance coils) back-up system, which is one of the least efficient heating methods available. More likely than not, this electric heat system will negate any benefits — and savings — gained by using a heat pump.
There are, however, newer models that use natural-gas furnaces as a backup. These are much more efficient — and much less expensive — to power.
If you have an older heat pump, it could pay to replace it with a newer model. They’re more efficient and keep your home more comfortable, due in part to better control of the heat transfer process, improvements in motor and compressor design, and — a biggie — variable speed blowers.
Older models used a single-speed blower — or fan — to move the air throughout your HVAC system. It’s an inefficient method, because the fan is always blasting out air on high, causing drafts, putting strain on the system, and making a lot of noise.
Variable-speed blowers start out on a low speed and ramp up as needed. If a only a minor change in temperature is needed, the blower will run on low, using less electricity and increasing the life of your heat pump.
If you’re looking to install a heat pump, one of the things you need to consider is its EnergyGuide label, which details its efficiency. The label is explained quite well by the folks at energy.gov.:
“Heating efficiency for air-source electric heat pumps is indicated by the heating season performance factor (HSPF), which is the total space heating required during the heating season, expressed in Btu, divided by the total electrical energy consumed by the heat pump system during the same season, expressed in watt-hours.
Cooling efficiency is indicated by the seasonal energy efficiency ratio (SEER), which is the total heat removed from the conditioned space during the annual cooling season, expressed in Btu, divided by the total electrical energy consumed by the heat pump during the same season, expressed in watt-hours.
The HSPF rates both the efficiency of the compressor and the electric-resistance elements. The most efficient heat pumps have an HSPF of between 8 and 10.
The SEER rates a heat pump’s cooling efficiency. In general, the higher the SEER, the higher the cost. However, the energy savings can return the higher initial investment several times during the heat pump’s life. A new central heat pump (SEER=12) replacing a 1970s vintage unit (SEER=6) will use half the energy to provide the same amount of cooling, cutting air-conditioning costs in half. The most efficient heat pumps have SEERs of between 14 and 18.
To choose an air-source electric heat pump, look for the ENERGY STAR® label. To qualify for the label, units must have SEERs of 12 or greater and HSPFs of 7 or greater. For units with comparable HSPF ratings, check their steady-state rating at -8.3 degrees C, the low temperature setting. The unit with the higher rating will be more efficient. In warmer climates, SEER is more important than HSPF. In colder climates, focus on getting the highest HSPF feasible.”
If you have any questions about heat pumps, heating and cooling in general, or energy efficiency, please contact us. We’ll be happy to help! In the meantime, keep checking our blog for the next installment on heat pumps.