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Electric Heat Pumps

Key Points

  • A heat pump is like a conventional air conditioner except it also can run in reverse.
  • Heat pump efficiency often exceeds 200%.
  • Heat pumps do not emit indoor products of combustion.

Heat Pump Advantages

An electric heat pump has numerous advantages compared to a natural gas-fired furnace, an oilfired furnace, or an electric resistance baseboard heating system.

Electric Heat Pumps
  • Higher efficiency ratings
  • Lower operating costs
  • Lower initial capital cost (all electric)
  • Electricity is available everywhere
  • Heats and cools
  • No indoor products of combustion (including carbon monoxide)
  • No venting required
  • No open flame
  • Extended equipment life
  • How a Heat Pump Works

Background

A heat pump is like a conventional air conditioner except it also can run in reverse and provide indoor heat in the winter. Both the air-source heat pump and the air conditioner contain two sets of coils, a compressor, and fans to circulate the conditioned air. However, a heat pump also contains a valve that enables it to switch between "air conditioner" and "furnace." When the valve is switched one way, the heat pump acts like an air conditioner, and when it is switched the other way it reverses the flow of the refrigerant and acts like a heater. It does this by extracting available heat from the outside air and transferring or ''pumping'' it inside a home. During the summer, the heat pump reverses this operation, extracting heat from the air inside a home and pumping it outside.

Geothermal heat pumps (ground-source) are more versatile than air source heat pumps because they have a lower setpoint temperature and can also provide hot water. The backup or supplemental heating needs are not as great. Geothermal heat pumps exchange heat with the earth through a system of buried plastic pipes called a ground heat exchanger. In the winter, fluid in the pipes extracts heat from the earth and carries it through the system and into the building. In the summer, heat is pulled from the building, carried through the system, and conducted into the cool earth.

The following is a more in-depth discussion of some of the top three key advantages.

Higher Efficiency Ratings

The heat pump moves heat without a flame of combustion. It very efficiently pumps the heat to and from the conditioned areas to achieve comfort. In fact, because the heat pump does not create heat, but merely "moves" it from one place to another, its efficiency often exceeds 200%. It moves more energy than it takes to operate the compressor and fans. Electric resistance baseboard heating systems are 100% efficient and new natural gas-fired and oil-fired furnaces are 80-90% efficient at best.

There are, however, preferred operating temperature ranges where heat pumps operate most efficiently. For example, an air source heat pump works best when the outdoor temperature is above freezing (a setpoint of 32°F). When the temperature drops below freezing, an air source heat pump often requires supplemental heating such as 100% efficient electric resistance coils. The heat pump efficiency that might be 200% above 45°F, drops to 150% at 25°F and 100% at 0°F. It is still more than 100% efficient at low temperatures, it just loses its heating capacity. A geothermal or water source heat pump can operate efficiently and at higher capacity at even lower temperatures, in most cases down to 0°F.

The Seasonal Energy Efficiency Ratio (SEER), Energy Efficiency Ratio (EER), and Coefficient of Performance (COP) are all cooling efficiency measurements for heat pumps and air conditioners. SEER is primarily used to rate equipment because it calculates cooling system performance based on average temperature conditions over a cooling season. This measurement is more useful than the EER or COP, which calculate energy performance based on a single outdoor operating temperature. SEER takes into consideration the seasonal cooling requirements, so it can vary from region-to-region based on local climate.

Essentially, SEER and EER measure the number of cooling British thermal units (Btu) provided per watt-hour of energy consumed. A rating of 12 EER delivers 12 Btus of cooling for every watt-hour of energy consumed. A 12 EER heat pump requires 1 kW of electricity to produce 1 ton of air conditioning capacity, since 1 ton of air conditioning capacity is equivalent to 12,000 Btu/hr of cooling. Current standards call for SEER ratings of 13 or higher.

As a matter of practice, EER and COP are generally used for geothermal heat pumps and SEER and HSPF are used for residential heat pumps. COP is defined as the ratio of the heating effect produced (usually expressed in kBtu/hr) divided by the energy input expressed on the same basis. It is a dimensionless number and a bigger COP number is more efficient. A COP of 1.0 is basically 100% efficient, meaning that 1 unit of heat is produced for each unit of energy consumed. A 3.0 COP rating means 3 units of heat are produced for each unit of energy consumed.

Heating efficiencies are often measured by a term called Heating System Performance Factor (HSPF). HSPF is rendered as Btu/Watthour so that typical HSPF are nominally on the order of 6.8-10 Btu/Wh. An HSPF of 3.4 is essentially equivalent to 100% efficiency. Over the last 10 years, there has been increased interest in the development of heat pumps that operate more efficiently at low temperatures (below 32°F). Commonly called Low Temperature Heat Pumps (LTHPs), they differ from conventional heat pumps through the addition of a second “booster” compressor and a “subcooling economizer,” which is a heat exchanger. With everything running, a LTHP keeps up with heating load until 0°F (with a COP of 2.23), while conventional heat pumps bottom out at 25°F. At 0°F, the LTHP makes twice as much heat per unit of electricity input as the conventional heat pump (COP of 1). To read more about low temperature heat pumps, see "How Low Can You Go? Heat Pumps for Cold Climates."

Lower Operating Cost

Because of their high efficiencies, heat pumps can have substantially lower operating costs compared to natural gas furnaces and other heating systems. The Heating System Comparison calculator allows homebuilders in different climate zones to show potential buyers a quick comparison of the operating cost.

For a 2,000 ft² home in Norfolk, VA, the annual heating cost with a heat pump is $685 (assuming 8.0 HSPF efficiency rating and $0.10/kWh) compared to $863 for an 80% efficient natural gas furnace ($1.30/ccf), or $1,653 for a hot water oil boiler (assuming 80% efficient and $3.50/gal heating oil).

2,000 ft² Home in Norfolk, VA

Heat Pump (8.0 HSPF, 235% efficient)

Heat Pump (9.0 HSPF, 265% efficient)

Natural Gas Furnace (80% efficient)

Natural Gas Furnace (90% efficient)

Hot Water Oil Boiler (80% efficient)

Electricity Use for Heating System (kWh) 6,851 6,158 579 (blower fan) 579 (blower fan) 579 (blower fan)
Natural Gas Use (ccf) or Oil (gallons) n/a n/a 619 ccf 551 ccf 456 gal.
Annual Heating Cost $685 $616 $863 $774 $1,653

Note that the above calculation assumes $0.10/kWh and $1.30/ccf natural gas cost. It is also possible to enter other scenarios into the calculator if they are needed to more accurately reflect home energy use. A Cooling System Comparison calculator is also available for air conditioning options.

Lower Initial Capital Cost

If a home will be using electric resistance backup heat, then an electric heat pump will have a significantly lower capital cost than the cost of an air conditioner plus a gas/oil-fired furnace.

Considering the installation of a heat pump? Contact us or call 1-800-879-4056 for more information.

White River Valley Power Factor has been prepared solely for the purpose of providing helpful information to users of this service. The information has been compiled by Tech Resources, a contractor to White River Valley Electric; however, no representation is made by either Tech Resources or White River Valley Electric as to the completeness or accuracy of the information contained therein. In particular, some information may be incomplete, may contain errors or may be out of date. In addition, neither Tech Resources nor White River Valley Electric endorses any product or service mentioned therein.