BE SURE TO ALWAYS COMPARE THE SAME VALUES BETWEEN MODELS
When you are talking to salespeople or looking at the literature, you may feel inundated with acronyms and technical vocabulary. This section is meant to be a reference when you encounter these terms and may provide guidance on what values are appropriate for homes in Waterloo Region.
Operational temperature range
The temperature range of a heat pump is the range over which it is designed to operate efficiently. The operational range will indicate whether or not you need a separate backup heating system (eg dual fuel). In Waterloo Region, average temperatures range between -11 °C and 26 °C but can reach lows of -20 °C and highs of 30 °C. The range is a function of both a heat pump’s design and its size. Design factors such as variable speed compressors, defrost capability, and inclusion of a built-in resistance heater affect the temperature range over which a heat pump is effective and efficient.
Heating/cooling load and capacity
British thermal units (Btu) are a measure of heating/cooling load.
Heating/cooling load is the amount of heating/cooling that a home requires to maintain the desired temperature. This value is needed to determine the correct size of the heat pump: too small and it will not supply all of the heating/cooling required and too big and the system will be less energy efficient. The load is affected by the insulation levels in the home, how airtight the building is, its size and the local climate. Your contractor should do a heat loss calculation based on the actual or modeled heat load of the home. The heating/cooling load is reported as Btu.
British thermal units per hour (Btu/h) and kW are measures of heating/cooling power or capacity.
Cooling capacity/power is typically measured in refrigeration tons. 1 ton = 12,000 Btu/h
Heating/cooling power or capacity is the amount of heating/cooling that a heat pump can provide: it should match or be slightly higher than the heating/cooling load. A home in Waterloo Region’s climate will require more heating capacity than cooling capacity so a heat pump system that is used for winter heating will be sized based on the heating load.
The number of heating degree days (HDD)/cooling degree days (CDD) is sometimes used to estimate the energy needed to heat or cool a building. For a season, it is the sum of the number of degrees Celsius that each daily mean temperature is below (or above) 18’C over the season.
The number of heating degree days determine a region’s climate zone. Waterloo Region falls in climate zone 5, as it has an average of 4200 HDD per season. Since heat pump efficiency varies non-linearly with temperature, this value can only give a very rough estimate of seasonal energy use.
Most of the energy used for heating over a Waterloo Region winter will occur in the range of -5 °C to 0 °C. While colder temperatures cause a building to require more heat, these temperatures are less frequent in Waterloo Region. This is shown in the following graph.
The efficiency of conventional furnaces is reported as a percentage (e.g. 80% efficient), and is a measure of the percentage of the energy going into the system that becomes heat that is released into the home. The value remains relatively constant over all outside temperatures.
Heat pumps however, have to work harder to extract heat from the outdoors when temperatures are lower: their efficiency changes with outdoor temperature. These changes in efficiency can be hard to model and are further complicated by energy use for defrosting and variable speed compressors. Consequently, there are many terms used to describe the efficiency of heat pumps, and none of them tell the whole story.
COP is the coefficient of performance for heating or cooling. It is a calculated value that is similar to efficiency as it is the ratio of kW of heat energy released to the kW of energy going into the system and is calculated for set indoor/outdoor temperatures. It is meant to be used to compare the general efficiency of different systems under controlled conditions. Heat pumps are tremendously energy efficient because they are moving heat, not generating heat: COP values of 2-4 (200%-400% efficient) are common. These terms are meant to be used for comparison purposes.
SCOP is the seasonal coefficient of performance for heating. It is a ratio of the heat energy released into the home over a heating season to the energy going into a system over that season (usually for climate zone IV). This value is specific to a particular climate and will typically be lower than the COP. In Europe, this term is referred to as the seasonal performance factor (SPF). These terms are meant to be used for comparison purposes.
HSPF, the heating seasonal performance factor is another measure of heating efficiency but using different units. It is the seasonal ratio of heat energy released into the home to electrical energy used by the system. Unless noted otherwise, HSPF factors are usually given for climate region IV. Waterloo Region is in climate region VI, and HSPF factors will be lower here. 1 HSPF = 3.41 SCOP. These terms are meant to be used for comparison purposes.
EER is the energy efficiency ratio. It is calculated by dividing the cooling output by the electrical power input for set indoor/outdoor temperatures and expressed as Btu/kWh. Just like the COP, it is meant to be used for comparison purposes and is commonly used for window air conditioners as well as heat pumps.
SEER is the seasonal energy efficiency ratio. It is the total cooling output over the cooling season divided by the total energy used by the system over that time and is expressed with units of Btu/Wh. SEER values are based on a climate with an average summer temperature of 28 °C. SEER values will be higher in Waterloo Region, which has an average summer temperature of 25 °C. These terms are meant to be used for comparison purposes.
Sound ratings are published for the outdoor units of heat pump systems. These are tone-corrected, A-weighted sound power levels, expressed in decibels – dB(A). Most quality heat pumps operate at 60dB or lower, which is more than a bird chirp (44dB), but less than a conversation (60dB).
Airflow through a home’s ducts is measured in cubic feet per minute (CFM or SCFM under standardized conditions) or litres per second (L/s). Generally, there should be 44 to 67 litres per second (L/s) per kilowatt, or 350 to 500 CFM. The correct flow will be specified by the manufacturer.
All heat pumps need a thermostat to control indoor air temperature. The installer will typically recommend a thermostat that is compatible with the chosen heat pump (some heat pumps accept standard thermostats while others only work with those that come from the manufacturer). Since heat pump systems are more efficient when temperatures are stable, a programmable thermostat is not generally recommended.
Most heat pump systems have an auxiliary heating system, either an electric heating coil or a fuel powered furnace, boiler or other heating system. This will come on when temperatures fall below the point where the heat pump can efficiently extract heat from the outdoors.
The compressor may be single-, dual, or variable stage. The compressor is the engine that makes the heat pump work. A single stage compressor is either off or full power, a dual stage compressor can operate at less than full power and is more efficient. A variable stage compressor has many power levels and is the most energy efficient. Variable stage compressors may also provide better temperature and humidity control, and are often quieter.