Governments and utility companies are struggling to educate the public and industry to conserve non-renewable energy. They are now talking about deleting or restricting the use of incandescent light bulbs. Savings to the individual homeowner may not be significant, but countrywide it can make a substancial reduction in power usage. One area that hasnt been pursued as much as it should be is heating with heat pumps, or heat pumps combined with other sources of non-renewable energy. Homeowners will see a much larger savings using heat pumps than changing light bulbs. However it does take a bigger investment. Residential heat pumps, as part of a new home or added to gas or oil furnaces, perform best in areas where the average winter temperatures are between 28?F (-2C) and 45?F (7C). Heat pumps sized for heat losses down to an outdoor ambient of 18?F to 20?F (-7C) will provide fuel cost savings of $500 to $600 a year.
Sizing
Sizing heat pumps to meet heating loads for temperatures below 15?F is not cost effective, but when combined with supplementary heating to meet heating load that falls below 15?F a few weeks a year can be very effective in reducing the average home heating bill. Manufacturers show heating ratings for heat pumps down to 15F (9.5C) with COP rating of up to 2.56. Providing heat outputs up to 30,000 BTUs while consuming, on average, 3.4 kW. (Electric heat at 3.4 kW would only provide 11560 BTU/h.) Heat pumps extract heat from outdoor air at all temperatures above and below freezing by removing heat from the outdoor air compressing it and delivering it as superheated refrigerant gas to the indoor heat transfer coil. Heat is extracted from outdoor air even below freezing temperatures. Frost, however, builds up on outdoor coils during freezing weather and this is done automatically whenever temperatures are below freezing. Defrosting switches the heat pump to cooling for a few minutes and then returns to heating again.
Controls
Controlling heat pumps in conjunction with a gas, oil or electric furnace (as a backup) is best done with a single stage cool and two-stage heat pump thermostat interconnected with a changeover relay to switch the operation from heating with heat pump to supplementary heat whenever the heat pump is not able to maintain the setpoint of the thermostat. In some areas heat pumps will do the job during the day but may fall short overnight. There is little savings in setting the temperature back at night. Setback as recovery of more than 1 degree will bring on auxiliary heat and consume any savings made overnight. When outdoor temperatures are below 18?F (-7C) for prolonged periods, a thermostat with outdoor temperature sensors that lock out the heat pump when alternating between the heat pump and backup heat isnt practical. Builders of new homes have to be convinced that lowering the heating cost by reducing heat losses and installing high efficient heating equipment, including heat pumps, is just as important as three-car garages, hot tubs and multiple bathrooms.
