Electric Air Source Heat Pumps

A heat pump is one of the most energy-efficient heating and cooling systems available today. Unlike other types of heating systems, which convert fuel or electricity directly to heat, a heat pump is designed to move heat from one place to another. Even at temperatures as cold as -18° C (0° F) or below, the heat pump is able to extract heat from outside air to use in heating your home.

How It Works

A heat pump is designed to move heat from one place to another. The outdoor coil of the heat pump absorbs heat from the outside air, even at relatively low temperatures, and transfers it to your home. In hot weather the heat pump operates in reverse to provide cooling. It transfers heat from within your home to the outdoors.

The outdoor unit of a heat pump contains coils filled with refrigerant, which absorb heat from the outside air. Even though the outdoor air temperature may be as low as -18° C (0° F) , the refrigerant is much cooler and is able to absorb heat. As it begins to absorb heat, the refrigerant evaporates, absorbing even greater quantities of heat. The heated refrigerant vapour passes through coils and then on to the compressor, where it is pressurized. This process increases the temperature and condensing point of the refrigerant so that it is now hotter than the inside air. The heated refrigerant travels to the indoor coil. As a fan blows air across the coils, the refrigerant releases heat into the surrounding air. Heated air is circulated throughout the house.

The heat pump also cools your house in the same manner. Simply switching the heat pump from a heating mode to a cooling mode reverses the valves that control the refrigerant cycle. So instead of extracting heat from the outdoors, the heat pump will remove heat and moisture from the indoors.

Saving Energy With Heat Pumps

When purchasing a new heat pump, be sure to check the efficiency rating of the proposed unit. A higher efficiency rating will result in lower operating costs. Heat Pump efficiency is generally designated by the term "SEER" (Seasonal Energy Efficiency Ratio) for cooling performance and the term "HSPF" for heating performance. New units have SEERs ranging from 10.0 to over 16.0 and "HSPF" from 8.0 to over 10.0. In B.C. where heating requirements are far greater than cooling, only the heating performance should be considered when selecting a heat pump. Higher the HSPF, lower the heating energy cost.

For split systems with an outdoor unit and an indoor coil, the efficiency varies with the match between the indoor cooling coil and outdoor condensing unit. The manufacturer should be consulted to determine the combined efficiency. The American Refrigeration Institute (ARI) publishes an annual directory listing various combinations of outdoor units and indoor coils with their HSPF and SEER rating. Most major manufacturers' product lines are included in this directory. All units must meet Canadian Standards Association (CSA) standard C273.3

Over the past several years, efficiency has increased due to the incorporation of the following improvements:

• Variable speed blowers, compressors, and motors - This equipment provides variable speeds of operation to optimize performance and efficiency. Heat pumps utilizing multi-speed components will typically start in the first stage or low speed. If comfort levels or control settings cannot be satisfied with the first stage, the second stage or high speed will activate. Some heat pump systems have more than two stages or speeds of operation.
• Larger Coil Surface Areas - Large surface coils provide maximum heat transfer efficiency.
• Time Delays - Time delays vary the on and off cycles of compressors, motors, and supplemental heat packages.
• Expansion Valves - Expansion valves control the flow of refrigerant in proportion to the load on the evaporator. Compared with other types of fixed metering devices, expansion valves are able to exercise control over a much wider range of operating conditions.

Other Energy Efficiency Features

Besides a unit's HSPF, there are additional energy saving features to look for when selecting a heat pump for your home.

• Dual fuel back-up- Dual fuel heat pump systems are supplemented by a fossil fuel furnace or boiler instead of the traditional electric resistance coils. When outdoor temperatures are moderate, the building heat requirements can be satisfied by the heat pump alone. When outdoor temperatures are below the economic balance point, the heat pump is switched off and the furnace or boiler supplies heat at close to its peak efficiency.
• Programmable setback thermostats - Programmable thermostats with adaptive-recovery or "ramping" are designed specifically for use with heat pumps. They allow the thermostat to be programmed for one or more "setback" periods per day. Their microprocessor unit senses the temperature differential to be overcome when bringing the space temperature back up, and brings the temperature up gradually over a longer period of time. This allows the heat pump alone to provide the temperature increase and minimizes the use of electric resistance auxiliary heat.

Operation & Maintenance

The following are some guidelines that should be followed to ensure efficient, comfortable operation of heat pumps.

• In the heating mode, do not set the temperature back at night or when you are at work unless a "smart" programmable heat pump thermostat is used. Since heat pumps operate differently than fossil fuel heating systems, setback of a standard heat pump thermostat can actually increase energy consumption: Although it would still be less than conventional resistance heating system. This is due to the use of supplemental heaters to bring the house temperature back to the desired setpoint. Use of supplemental heaters will reduce the efficiency of the heat pump system and result in higher energy costs.
• Keep the temperature setpoint consistent. A standard heat pump thermostat has two controls, one for the heat pump and one for the supplemental heat. If the temperature difference between the room and thermostat setpoint is more than -17° C or -16° C (2° or 3° F), the supplemental heat will be activated. Manually adjusting the thermostat will result in greater reliance on the supplemental heaters and will reduce the efficiency of the heat pump system and increase operating costs.
• Replace filters regularly. Vacuum dirt and dust from the indoor coil once a year to prevent restricted airflow. Adequate air flow through a heat pump system is critical to ensure efficient and comfortable operation.
• Keep supply vents open and free from obstruction. Closing off supply vents will restrict air flow and reduce system efficiency as well as reduce the life of the compressor.
• Keep the coil in the outdoor unit clear of snow, leaves and other debris so that air flow is not restricted.
• In belt-driven indoor units, check this tension in belt once a year and adjust if loose