HOW HEAT PUMPS WORK
A heat pump is an efficient form of electrically based heating and cooling. Unlike other heating and cooling systems, which convert fuel or electricity directly into heat, a heat pump moves heat from one place to another, in the same manner as an air conditioner.
Heat pumps can provide efficient heating and cooling
Even at relatively cold temperatures, the heat pump can extract heat from outside air (air source heat pump) or from the ground or ground water (ground source heat pump) to heat your home, though efficiencies diminish as temperatures cool. During warm summer days it will function in reverse and provide cooling.
In almost any part of Canada, it is not economical to use a heat pump as the only source of heat in your home. A heat pump large enough to meet your heating needs would work inefficiently in summer. Combining a heat pump with an existing furnace or other supplemental heater can reduce home energy expenses, but initial costs and additional electricity costs should be factored in.
Remember that your house is a system. If you are planning to draftproof and upgrade insulation, your heating needs will likely decrease. A home energy audit can help you figure out where to begin making energy efficient changes.
In some areas of B.C., using a heat pump as part of your year-round heating and cooling system can significantly cut your heating costs. Savings will vary depending on the fuel and efficiency of your current system. If you use the cooling function of a heat pump where you didn't previously use air conditioners or other mechanized cooling, it will lead to increased energy use and costs.
Health & comfort
Choosing the right kind and size of heat pump for your region and your needs can make your home temperature easy to keep comfortable all year round. Air source heat pumps aren't likely to work effectively in areas where temperatures often go below -7°C. In northern B.C., ground source (also called earth source, geothermal or geoexchange) heat pumps can be a more effective option.
Heat pumps are much like refrigerators, which means they contain chemical refrigerants that are used to transfer heat in or out of your home. Some of these coolants contribute to depleting the ozone layer. There are models and manufacturers that use less harmful coolants. Choose a heat pump that minimizes pollution and maximizes energy efficiency.
Heat pumps and voltage fluctuations
BC Hydro has received inquiries from customers in some areas relating to the operation of heat pumps. With the “cycling” of heat pumps there is the potential for voltage fluctuations and momentary interruptions of electricity supply, which can affect adjoining properties.
The precise causes of these disturbances are still under investigation. Additional loads associated with heat pumps can also affect BC Hydro’s ability to safely deliver your entire household electricity requirements.
For these reasons, prior to making a final decision to install a heat pump we recommend that you consult with the heat pump contractor to ensure that the system has soft start capability. We also advise that you contact BC Hydro’s Electric Service Coordination Centre at 1 877 520 1355 to discuss your planned installation.
What you need to know
General heat pump information
- The efficiency of any heating system will be limited if your home has leaks or poor insulation. It generally makes sense to upgrade insulation and draftproof your home before upgrading your heating system.
- A heat pump installer will assess if the existing duct work needs to be changed. A heat pump requires larger duct work because there is a higher volume of air at a lower temperature. If this duct work isn't sufficient for the load, then the overall efficiency (and comfort) of the system decreases.
- Do not use the cooling cycle of a heat pump when it's not essential. Use the cooling cycle only to replace air conditioning, not instead of using other lower energy cooling practices. Passive cooling techniques, such as increasing insulation and shading windows, are more energy-efficient ways to cool your home.
- The outdoor coil of the heat pump absorbs heat from the outside air and transfers it to your home. In hot weather, the heat pump operates in reverse, transferring heat from inside your home to the outdoors.
- In B.C., where heating requirements are far greater than cooling, consider only the heating performance when selecting a heat pump.
- Select a heat pump with "soft start" capabilities. This allows the heat pump to slowly come up to operating levels to prevent brown outs or voltage fluctuations.
Air source heat pump
- An Air Source Heat Pump (ASHP) functions by taking the heat from the outside air and moving it indoors rather than using a fuel to warm up the air indoors. Even at low temperatures there is enough ambient heat in the outside air to allow the heat pump to efficiently perform this transfer.
- There are ASHPs that function at extremely low temperatures but for the most part they operate most effectively down to -7°C. In regions where the temperature is below -7°C. In extended periods the secondary heating system will be providing the majority of the heating, thus reducing or eliminating the efficiencies gained by installing an ASHP.
- An air source heat pump is less efficient at cold temperatures. An ASHP is actually the most effective for heating in a mild climate. If the temperature drops a lot in the winter then in most cases a backup system has to work.
- The efficiency of an ASHP is directly dependant on the outside temperature. When selecting an ASHP model, ensure it is optimal for your climate region.
- In areas requiring mechanized cooling as well as heating, it's important to find the size of heat pump that will maximize both heating and cooling efficiencies. Selecting an ASHP large enough to provide the home's entire heating requirement could function poorly for cooling, thus reducing any potential annual savings. Discuss the various options with your contractor.
Ground source heat pump
- A ground source heat pump (GSHP) functions much like an ASHP, but instead of exchanging the heat from the outside air it uses a fluid, pumped down through piping into the ground, to recover or reject the heat. Using the ground as the heat source is beneficial because, unlike the air, the temperature is very constant throughout the year, typically in the range of 7°C to 13°C.
- GSHPs can provide very high efficiencies in optimal situations. Unfortunately, it requires a much higher up-front cost to install piping in the ground. Installation of a GSHP is not ideal for all situations, factors like the soil conditions and the balancing of heating and cooling requirements (close to equal amounts of cool and heating throughout the year) must be considered.
- A qualified heat pump designer will be able to discuss this with you and make recommendations on the suitability of your location. When considering a GSHP it is important that the contractor be certified to perform the design and installation. In addition, the GSHP system should be CSA-C448 certified.
- For more information on earth energy systems including a current list of eco-energy rebate accredited installers, designers, and drillers, please contact the Canadian GeoExchange Coalition or call 514 807 7559.
Heat pump operation
Follow these guidelines to ensure efficient, comfortable operation of heat pumps:
- In the heating mode, do not set the temperature back at night or when you are out, unless you are using a "smart" programmable heat pump thermostat. Setting back a standard heat pump thermostat can increase energy consumption.
- Replace filters regularly. Vacuum dirt and dust from the indoor coil once a year to prevent restricted airflow. Adequate airflow 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 airflow and reduce system efficiency as well as the life of the compressor.
- Keep the coil in the outdoor unit clear of snow, leaves and other debris so that airflow is not restricted.
- In belt-driven indoor units, check belt tension once a year and adjust if loose. Have the system adjusted annually by a trained professional.
- Natural Resources Canada's Office of Energy Efficiency suggests that you select a unit with demand-defrost control to minimize defrost cycles (system reversals are hard on the machine). This in turn reduces the energy needed to run both the heat pump and the supplementary heat source.
- Have the system serviced annually by a qualified technician.
Heat pump efficiency improvements
In heat pump efficiency has increased in the past few years due to the incorporation of the following improvements:
- Variable speed blowers, compressors and motors provide variable speeds of operation to optimize performance and efficiency. Heat pumps with multi-speed components will typically start in the first stage or low speed. If comfort levels or settings cannot be satisfied at that speed, the second stage or high speed activates. Some heat pump systems have more than two stages or speeds of operation.
- Larger coil surface areas provide maximum heat transfer efficiency.
- Time delays vary the on and off cycles of compressors, motors and, in winter, supplemental heat packages, thus maximizing the pump's operating efficiency.
- Expansion valves allow the heat pump to control the flow of the refrigerant more efficiently.
- "Soft start" capabilities allow the heat pump to slowly come up to operating levels to avoid putting a sudden big load on the electrical system and can cause lights to flicker.
I have heard that some heat pumps can be noisy. Is this true? How can I ensure the model I get is quiet?
Natural Resources of Canada's Office of Energy Efficiency has some information on the sound rating of heat pumps: sound rating is a tone-corrected, A-weighted sound power level, expressed in bels. Select a heat pump with an outdoor sound rating in the vicinity of 7.6 bels or lower if possible. The sound rating is an indicator of the sound power level of the heat pump outdoor unit. The lower the value, the lower the sound power emitted by the outdoor unit. These ratings are available from the manufacturer, and are published by the Air-Conditioning and Refrigeration Institute (ARI), 4301 North Fairfax Drive, Arlington, Virginia 22203, U.S.A.
Our heating system is fine right now, but we are looking to get air conditioning for the summer. Would a heat pump be a good way to go?
That depends on your existing system, and your needs. For year-round comfort and efficiency, you can use a heat pump to augment your existing home heating system and to replace an air conditioner. However, it would be inefficient – and expensive – to have a heat pump installed to use only as an air conditioner. Most parts of B.C. do not require the use of summer air conditioning on very many days in a year, and even in the hot parts of Southern B.C., a heat pump is not a good investment solely for air conditioning.
I've installed a heat pump, but why is my electricity bill higher?
When this happens, it's usually for one of two reasons. The first is when it's a gas furnace to heat pump install. With a heat pump, your main heating energy source is now electric instead of gas, so that will increase your electricity bill, while reducing your gas one.
Another reason can be in situations where the heat pump is being used for cooling in a home that didn't use air conditioning before. In this situation, using a heat pump is actually increasing overall energy use instead of helping reduce power use. Instead of using the heat pump for air conditioning, use passive measures first to keep your home cool, like shading windows and minimizing indoor heat generation.