Heat pumps have been around for many years so the idea is not new. What's new are the improvements that have been made in the construction, design and efficiency of the products on the market today. Electronic controls have improved not only the efficiency, but also the amount of heat that can be extracted at a lower temperature. This means that in almost all weather regions of Canada a heat pump is a viable heat source.

Heating efficiency of air source heat pumps can be referred to in two ways. The first is COP or Coefficient of Performance. This is simply an operational efficiency of the unit in heating mode at any point in time. As an example, if you have a unit that is rated with a COP of 3.0 the unit can be said to be 300 percent efficient. That is, for every dollar of energy you put in, you get $3 out. The technical definition is the total heating capacity at any point in time in BTUs divided by the total electrical input in watts x 3.12. The COP rating of any equipment will change with outdoor temperature. The colder it gets outside the less heat can be extracted from the air and the lower the COP rating.

The second term used to describe efficiency in the heating mode is HSPF or the Heating Seasonal Performance Factor. The higher the HSPF rating, the more efficient a heat pump is. As the term indicates this is a seasonal rating. The definition is the total heating output of a heat pump during its normal usage period for heating divided by the total electric power input in watt-hours during the same time period.

Air conditioning or cooling efficiency is rated the same as with any air conditioner. The term for cooling efficiency is SEER (Seasonal Energy Efficiency Rating). The higher the SEER rating, the more energy efficient the unit is. The technical definition is the total cooling of an air conditioner or heat pump in BTUs during normal annual usage period for cooling divided by the total electric energy input in watt-hours during the same period. The current minimum SEER rating in North America for air conditioning is 13.

What makes a heat pump a good economic choice is its excellent heating efficiency ratings. A typical basic air source heat pump will have a HSPF rating over 7 and a COP rating between 2.5 and 3. This means a heat pump is 200-300 percent efficient.

How does a heat pump give heating efficiencies in excess of 200 percent? Using the power of the refrigeration cycle, heat is extracted from the air, which in turn has absorbed solar energy. The refrigeration cycle takes that heat and amplifies to give us usable heat. As a heat pump is just an air conditioner in reverse, it stands to reason that with a heat pump you also get air conditioning.

The refrigeration cycle for a heat pump in heating mode works in the following manner. Hot discharge gas (refrigerant) leaves the compressor through a reversing valve to the outdoor coil, which is acting as a condenser. Air from the conditioned space passes over the coil, picking up heat from the refrigerant. The refrigerant, in losing its heat, is changed from a gas to a liquid. The liquid refrigerant then goes through the expansion device of the outdoor coil where it is reduced to a low temperature liquid. The refrigerant now passes through the outdoor coil, and the outside air gives up some of its heat to the refrigerant. This low pressure and temperature gas is now drawn to the compressor to become high pressure and temperature gas and the cycle starts again.

A typical air source heat pump will operate effectively to outdoor temperatures of 17 F. As the outdoor temperature drops, less heat can be extracted. For this reason an air source heat pump must be installed with a back-up heat source. This back-up heat source must be designed to handle 100 percent of the heat load. Typical temperature increases using a heat pump are 15-20 F.

So, to sum it all up, installing a heat pump will provide you savings on your heating costs and provide the bonus of air conditioning in the summer months. As in all systems it is critical not to undersize the ductwork or problems will occur.