It's essentially a reversible air conditioner.
In summer, it functions like a normal air conditioner cooling inside your home. In winter, the refrigerant reverses and instead of cooling, the heat pump warms your interior spaces. There are two main types, 'air source' and 'geothermal' heat pumps.
It's designed and optimized for operation in freezing cold weather.
Until recently, most air source heat pumps worked poorly below freezing. If they worked at all. However, technological advancements now allow them to operate in weather as cold as -30C and beyond!
Cold climate heat pumps utilize a few different systems to sustain cold weather operation:
DC Inverter Compressor (Variable Frequency Drive): DC compressors are more efficient than AC compressors, allowing them to draw heat from colder outside temperatures. Additionally, the variable frequency drive reduces cycling which prolongs compressor life.
Enhanced Vapor Injection (EVI): Typically used in cold climate air-to-water heat pumps, EVI diverts some hot refrigerant back into the compressor before it reaches the indoor coil. This reduces the temperature differential on the compressor, increasing its efficiency and ability to operate in cold weather.
Auto-Defrost: In order to extract heat from sub-zero outside air, the outdoor coil must get colder than the surrounding air. This causes frost to naturally build up. Remember how we said a cold weather heat pump is basically a reversible air conditioner? That's exactly how a defrost cycle works.
When frost builds up, the system reverses and heat is temporarily pulled from the house like in air conditioner mode. This melts the outdoor coil. Once defrost is complete, the system reverses and continues heating the house.
Base Pan Heater: Water from defrosted coils has to go somewhere, and some ends up in the base pan of the outdoor unit. To prevent ice from building in the pan, an element heater at the base of the pan is added so water exits the unit freely.
Compressor Heating Belt: To aide cold weather operation and increase efficiency, some heat pumps will have a heating belt installed around the compressor. This allows the heat pump to operate in colder winter conditions.
Absolutely they do!
The long standing myth is "heat pumps don't work in the cold". After all, what's the point of a heating device, if it doesn't work the one time you need it; in the cold!
Even the HVAC industry (installers, suppliers, etc) is guilty of dismissing heat pumps as not being cold weather capable. Old product offerings and a lack of mainstream commercial availability have allowed this stigma to live on. In fact, many of the above cold weather adaptations have only become commercially available in the last 5-10yrs.
But make no mistake: Air source heat pumps can function in cold Canadian winters.
Until the improvements in cold climate air source heat pumps, geothermal was the only reliable cold weather option.
While the heat pump concept is similar between a geothermal and an air-source system, the difference lies in the heating source (air vs geo, or ground/earth).
A geothermal system draws heat from the ground instead of the air. To do so, water loops spanning hundreds of feet long are buried into the ground, below the frost line. In some cases this means 6-10 feet or deeper, where ground temperatures stay nearly constant through the entire winter and summer season.
A geothermal heat pump system operates with impressive efficiency rates which keeps energy costs low. However, the massive upfront cost to bury ground loops can offset any energy efficiency gains. Calling feasibility into question.
Since cold weather air source heat pumps are 5-20% the installed cost of a geothermal system, they are far more feasible.
They're extremely efficient at heating, which means cheaper heating bills.
Logically, we would think that perfect heating efficiency ends at 100%, right? Wrong!
At 100% efficiency, 1 watt of energy consumed produces 1 watt of heat. Electric resistance heat is an example of 100% efficiency.
However a heat pump operates at higher than 100% efficiency. Yes, it's true!
In fact, depending on the temperature differential, heat pumps can operate above 300% efficiency and beyond. This means for 1 watt of energy consumed, 3 watts of heat are produced.
Energy efficiency all depends on the differential between the outside and inside environment. The GREATER the temperature spread, the LOWER the efficiency of the heat pump.
Yes, nearly always.
The real value proposition occurs in dwellings without natural gas access. When electric is the only heating option, a cold climate heat pump is the easiest way to slash electric heating costs by more than 50%. It's cheaper, and it's greener.
Also note, if the dwelling requires air conditioning, the upfront install costs of a heat pump may be cheaper than a natural gas furnace with a combined AC condenser.
Energy efficiency ratings for cold weather heat pumps are a nightmare. They're confusing, there's many different ratios, and they're riddled with sneaky marketing tactics.
The single most important efficiency rating is the Coefficient Of Performance.
Remember how we said cold climate heat pumps can operate above 300% efficiency? This is what the COP measures. A 300% efficiency is represented as a COP of 3. A 280% efficiency is a COP of 2.8. So a COP rating is simply the percent efficiency, displayed in decimal number form. It would be easier to understand if they just stuck with percent efficiency, right?
Coefficient of performance is calculated as watts produced, divided by watts consumed. So 1w of electricity consumed, producing 3.4w of heat, means a COP of 3.4.
The coefficient of performance is NOT a static number. Ever!
The COP of any cold climate heat pump fluctuates based on the current outside temperature. The hotter it is outside, the higher the heating efficiency due to a lower temperature differential. The colder it is at the outside coil, the lower the efficiency due to a higher temperature differential.
The COP of a cold climate heat pump is represented as a chart.
This chart is the single most important efficiency metric in calculating seasonal energy costs. If you're shopping for a cold climate heat pump and the manufacturer does not provide a COP chart, run! Without a COP chart, heating costs can NOT be estimated in cold weather areas. Any claims made will be purely marketing babble.
An easy way to use COP to calculate energy costs is to take the average winter temperature of the area in question and then use the corresponding COP rating of the cold climate mini split heat pump to be used.
For example: Say the average winter temperature is -15C and the COP of the cold climate mini-split is 2.4 at -15C. You can simply take an electric resistance heating bill, and divide it by 2.4 to estimate the energy costs if you switch to a cold weather mini split. Simple, right?
It's worth noting, the coefficient of performance can also be used to demonstrate cooling efficiency on a simple apples to apples basis. Since the same units (watts) are used for input and output numbers, cooling COP produces an easy energy efficiency ratio to use for energy cost calculations. Unfortunately very few manufacturers provide COP for cooling.
Get ready to be confused. Here are some less useful ratings you may see on a cold weather heat pump. We recommend you skip this section, but the info is here to chew on if you so desire. Note, these ratings are virtually useless for estimating cold weather heating costs, but do give vague indication on unit performance.
Energy Efficiency Ratio (EER): Typically used for air conditioning efficiency (which a heat pump has built in), the EER is calculated as BTU of heat transferred, divided by watts of energy consumed. Wait what? BTU to watts, isn't that apples to oranges? Yes it is.
Since 1 watt is 3.4 BTU, one way to convert from EER to COP cooling is dividing the EER number by 3.4. So an EER of 9 would be an air conditioning COP of 2.65. But bigger numbers look better for marketing, right?
As with any heat pump or air conditioner, efficiency is not static. It depends on temperature differential. So the EER of an air conditioner with an exterior temperature of 20 Celsius will be higher than at 40 Celsius. So a static EER rating is only a glimpse at the true efficiency, but cannot be used for true energy consumption calculations.
An EER rating is typically calculated using a 95F exterior temperature and an 80F return air temperature at 50% humidity.
As is the theme with heat pumps, raising or lowering either of these temperature will affect the energy consumption and efficiency of the unit. So if you live in Phoenix AZ, the real efficiency of your air conditioning heat pump will be much lower than the EER rating on the sticker.
Seasonal Energy Efficiency Ratio (SEER): Like EER, the SEER is measured as BTU produced, divided by watts consumed. Apples to oranges.
The difference is the SEER attempts to average the rating over a spread of temperatures. This creates great misrepresentation due to the varying climates across North America. Like EER, the SEER uses 80F interior temperature. However it uses a range of exterior temperatures from 65F to 104F. Typically EER works out to be 87.5% of SEER, making SEER a higher number.
As with all non COP ratings, SEER can NOT be used for calculating energy consumption. Actual heat pump efficiency will differ dramatically between a Victoria, BC summer and the scorching heat of Death Valley, Nevada.
While SEER is only used to demonstrate the cooling efficiency of a heat pump, it is one of the most commonly used efficiency ratings for a heat pump. So as a general rule, look for a higher number to represent higher efficiency.
Heating Seasonal Performance Factor (HSPF): Is basically SEER, only for heating instead of cooling.
Since SEER is seasonal cooling performance in watts to BTU, HSPF is seasonal HEATING performance in watts to BTU. That is, BTU of heat produced, divided by watts of electricity consumed, and averaged across a basket of temperatures.
The problem is, this basket is usually calculated in climate zone 4 in the Southern United States. Who needs heat in the southern states, right?! If you're looking for high quality cold climate heat pumps for Northern Canada, using the HSPF formula is pointless since Canadian winter efficiency will be far less.
For accurate efficiency of Canadian heat pumps, forget HSPF and use the coefficient of performance rating.
Energy Star: Energy Star is a government efficiency agency which stamps any electronic equipment meeting a certain standard for energy consumption. In the case of cold climate air source heat pumps, this standard is HSPF 8.5+, SEER 15+, and EER 12.5+. So any system with an energy star sticker will have efficiency ratings exceeding these values across these metrics.
Are you confused yet? Take our advice, stick to COP for measuring efficiency. The key thing to remember is the greater the temperature differential the lower the efficiency.
That is, the greater you're trying to change the interior temperature from the exterior temperature, the less efficient the mini-split will be. This applies to both cooling and heating operations on a heat pump. Greater temperature differential means more work. Makes sense, right?
It's important to note HOW efficiency changes with temperature differential changes. As efficiency changes, BTU output changes.
When seeing a Canadian heat pump with 12,000btu stamped on the side, a buyer may think "this will put out 12,000btu max across all working temperatures", but this isn't true.
In heating mode at 5C outside temperature, this unit can put out more than its rated value, maybe even 15,000-18,000btu at max heat.
However, as outside temperatures drop the heat pump has less heat available to extract. So even though the compressor is consuming the same amount of electricity in maximum heating mode, the amount of heating BTU it can send inside drops.
At -30C this means the same unit may only produce 8,000btu or less, even though the unit is stamped 12,000btu on the side.
Whereas an electric resistance heater puts out a constant amount of heat, regardless of interior or exterior temperatures. This is the main difference between electric resistance heating and a heat pump.
There are 3 main types of heat pumps, mini splits, central ducted, and air to water. Each are suited to certain applications.
Mini splits are the most popular heat pump type. They are comprised of 2 main parts, an ductless interior coil and exterior coil. Of course these two coils are connected by refrigerant lines which is a highly efficient method of transferring heat to its desired area.
Cold climate mini split heat pumps are popular for many reasons:
Sizes: Typically ranging from 9,000btu to 36,000btu, mini splits also have the ability to run multiple indoor heads from a single exterior coil.
Cost: Winter rated mini split heat pumps usually range from $1,000 to $5,000 depending on the size, efficiency and quality.
Application: Best suited to space and area heating. Great for areas where central HVAC is not possible. However, the scalability of mini-splits allows them to be an effective solution for nearly any space or situation.
Central heat pumps are paired with an interior air handler which is connected to a central air duct system. To provide a reliable heating solution, a backup resistance element is usually installed for extreme cold operation and system redundancy.
Central air heat pumps are less readily available in many cold weather markets, but are the ultimate whole house solution. They are also an excellent retrofit option for existing ducted houses.
It should be noted that as with any centrally ducted system, some heat is lost in the ducts.
Air-to-water heat pumps are designed for radiant in floor heating, or for hot water applications.
One of the greatest advantages of a cold climate air to water heat pump, is the ability to use thermal mass to balance heating production. By heating a radiant concrete slab or large quantity of water, the heat is "stored" in this thermal mass for a much longer time than it would be with and air to air system.
This makes an air to water heat pump a great candidate for use with solar power. Since the thermal mass can retain heat produced during daytime hours and release it during hours without sunlight, heating loads are balanced better. Think of it like a heat battery.
Let's not forget that smooth, toasty warm release of a radiant system. Mmm, comfy!