Table of Contents
Introduction
If you are exploring options to heat and cool your home or reduce your energy bills, you might want to consider a heat pump system. Heat pumps are a proven and reliable technology in Canada, capable of providing year-round comfort control for your home by supplying heat in the winter, cooling in the summer, and in some cases, heating hot water for your home.
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Heat pumps can be an excellent choice in a variety of applications, and for both new homes and retrofits of existing heating and cooling systems. They are also an option when replacing existing air conditioning systems, as the incremental cost to move from a cooling-only system to a heat pump is often quite low. Given the wealth of different system types and options, it can often be difficult to determine if a heat pump is the right option for your home.
If you are considering a heat pump, you likely have a number of questions, including:
- What types of heat pumps are available?
- How much of my annual heating and cooling needs can a heat pump provide?
- What size of heat pump do I need for my home and application?
- How much do heat pumps cost compared with other systems, and how much could I save on my energy bill?
- Will I need to make additional modifications to my home?
- How much servicing will the system require?
This booklet provides important facts on heat pumps to help you be more informed, supporting you to make the right choice for your home. Using these questions as a guide, this booklet describes the most common types of heat pumps, and discusses the factors involved in choosing, installing, operating, and maintaining a heat pump.
Intended Audience
This booklet is intended for homeowners looking for background information on heat pump technologies in order to support informed decision making regarding system selection and integration, operation and maintenance. The information provided here is general, and specific details may vary depending on your installation and system type. This booklet should not replace working with a contractor or energy advisor, who will ensure that your installation meets your needs and desired objectives.
A Note on Energy Management in the Home
Heat pumps are very efficient heating and cooling systems and can significantly reduce your energy costs. In thinking of the home as a system, it is recommended that heat losses from your home be minimized from areas such as air leakage (through cracks, holes), poorly insulated walls, ceilings, windows and doors.
Tackling these issues first can allow you to use a smaller heat pump size, thereby reducing heat pump equipment costs and allowing your system to operate more efficiently.
A number of publications explaining how to do this are available from Natural Resources Canada.
What Is a Heat Pump, and How Does It Work?
Heat pumps are a proven technology that have been used for decades, both in Canada and globally, to efficiently provide heating, cooling, and in some cases, hot water to buildings. In fact, it is likely that you interact with heat pump technology on a daily basis: refrigerators and air conditioners operate using the same principles and technology. This section presents the basics of how a heat pump works, and introduces different system types.
Heat Pump Basic Concepts
A heat pump is an electrically driven device that extracts heat from a low temperature place (a source), and delivers it to a higher temperature place (a sink).
To understand this process, think about a bicycle ride over a hill: No effort is required to go from the top of the hill to the bottom, as the bike and rider will move naturally from a high place to a lower one. However, going up the hill requires a lot more work, as the bike is moving against the natural direction of motion.
In a similar manner, heat naturally flows from places with higher temperature to locations with lower temperatures (e.g., in the winter, heat from inside the building is lost to the outside). A heat pump uses additional electrical energy to counter the natural flow of heat, and pump the energy available in a colder place to a warmer one.
So how does a heat pump heat or cool your home? As energy is extracted from a source, the temperature of the source is reduced. If the home is used as the source, thermal energy will be removed, cooling this space. This is how a heat pump operates in cooling mode, and is the same principle used by air conditioners and refrigerators. Similarly, as energy is added to a sink, its temperature increases. If the home is used as a sink, thermal energy will be added, heating the space. A heat pump is fully reversible, meaning that it can both heat and cool your home, providing year-round comfort.
Sources and Sinks for Heat Pumps
Selecting the source and sink for your heat pump system goes a long way in determining the performance, capital costs and operating costs of your system. This section provides a brief overview of common sources and sinks for residential applications in Canada.
Sources: Two sources of thermal energy are most commonly used for heating homes with heat pumps in Canada:
- Air-Source: The heat pump draws heat from the outside air during the heating season and rejects heat outside during the summer cooling season.
It may be surprising to know that even when outdoor temperatures are cold, a good deal of energy is still available that can be extracted and delivered to the building. For example, the heat content of air at -18°C equates to 85% of the heat contained at 21°C. This allows the heat pump to provide a good deal of heating, even during colder weather.
Air-source systems are the most common on the Canadian market, with over 700,000 installed units across Canada.
This type of system is discussed in more detail in the Air-Source Heat Pumps section.
- Ground-Source: A ground-source heat pump uses the earth, ground water, or both as the source of heat in the winter, and as a reservoir to reject heat removed from the home in the summer.
These heat pumps are less common than air-source units, but are becoming more widely used in all provinces of Canada. Their primary advantage is that they are not subject to extreme temperature fluctuations, using the ground as a constant temperature source, resulting in the most energy efficient type of heat pump system.
This type of system is discussed in more detail in the Ground-Source Heat Pumps section.
Sinks: Two sinks for thermal energy are most commonly used for heating homes with heat pumps in Canada:
- Indoor air is heated by the heat pump. This can be done through:
- A centrally ducted system or
- A ductless indoor unit, such as a wall mounted unit.
- Water inside the building is heated. This water can then be used to serve terminal systems like radiators, a radiant floor, or fan coil units via a hydronic system.
An Introduction to Heat Pump Efficiency
Furnaces and boilers provide space heating by adding heat to the air through the combustion of a fuel such as natural gas or heating oil. While efficiencies have continually improved, they still remain below 100%, meaning that not all the available energy from combustion is used to heat the air.
Heat pumps operate on a different principle. The electricity input into the heat pump is used to transfer thermal energy between two locations. This allows the heat pump to operate more efficiently, with typical efficiencies well over
100%, i.e. more thermal energy is produced than the amount of electric energy used to pump it.
It is important to note that the efficiency of the heat pump depends greatly on the temperatures of the source and sink. Just like a steeper hill requires more effort to climb on a bike, greater temperature differences between the source and sink of the heat pump require it to work harder, and can reduce efficiency. Determining the right size of heat pump to maximize seasonal efficiencies is critical. These aspects are discussed in more detail in the Air-Source Heat Pumps and Ground-Source Heat Pumps sections.
Efficiency Terminology
A variety of efficiency metrics are used in manufacturer catalogues, which can make understanding system performance somewhat confusing for a first time buyer. Below is a breakdown of some commonly used efficiency terms:
Steady-State Metrics: These measures describe heat pump efficiency in a &#;steady-state,&#; i.e., without real-life fluctuations in season and temperature. As such, their value can change significantly as source and sink temperatures, and other operational parameters, change. Steady state metrics include:
Coefficient of Performance (COP): The COP is a ratio between the rate at which the heat pump transfers thermal energy (in kW), and the amount of electrical power required to do the pumping (in kW). For example, if a heat pump used 1kW of electrical energy to transfer 3 kW of heat, the COP would be 3.
Energy Efficiency Ratio (EER): The EER is similar to the COP, and describes the steady-state cooling efficiency of a heat pump. It is determined by dividing the cooling capacity of the heat pump in Btu/h by the electrical energy input in Watts (W) at a specific temperature. EER is strictly associated with describing the steady-state cooling efficiency, unlike COP which can be used to express the efficiency of a heat pump in heating as well as cooling.
Seasonal Performance Metrics: These measures are designed to give a better estimate of performance over a heating or cooling season, by incorporating &#;real life&#; variations in temperatures across the season.
Seasonal metrics include:
- Heating Seasonal Performance Factor (HSPF): HSPF is a ratio of how much energy the heat pump delivers to the building over the full heating season (in Btu), to the total energy (in Watthours) it uses over the same period.
Weather data characteristics of long-term climate conditions are used to represent the heating season in calculating the HSPF. However, this calculation is typically limited to a single region, and may not fully represent performance across Canada. Some manufacturers can provide an HSPF for another climate region upon request; however typically HSPFs are reported for Region 4, representing climates similar to the Midwestern US. Region 5 would cover most of the southern half of the provinces in Canada, from the B.C interior through New BrunswickFootnote 1.
- Seasonal Energy Efficiency Ratio (SEER): SEER measures the cooling efficiency of the heat pump over the entire cooling season. It is determined by dividing the total cooling provided over the cooling season (in Btu) by the total energy used by the heat pump during that time (in Watt-hours). The SEER is based on a climate with an average summer temperature of 28°C.
Important Terminology for Heat Pump Systems
Here are some common terms you may come across while investigating heat pumps.
Heat Pump System Components
The refrigerant is the fluid that circulates through the heat pump, alternately absorbing, transporting and releasing heat. Depending on its location, the fluid may be liquid, gaseous, or a gas/vapour mixture
The reversing valve controls the direction of flow of the refrigerant in the heat pump and changes the heat pump from heating to cooling mode or vice versa.
A coil is a loop, or loops, of tubing where heat transfer between the source/sink and refrigerant takes place. The tubing may have fins to increase the surface area available for heat exchange.
The evaporator is a coil in which the refrigerant absorbs heat from its surroundings and boils to become a low-temperature vapour. As the refrigerant passes from the reversing valve to the compressor, the accumulator collects any excess liquid that did not vaporize into a gas. Not all heat pumps, however, have an accumulator.
The compressor squeezes the molecules of the refrigerant gas together, increasing the temperature of the refrigerant. This device helps to transfer thermal energy between the source and sink.
The condenser is a coil in which the refrigerant gives off heat to its surroundings and becomes a liquid.
The expansion device lowers the pressure created by the compressor. This causes the temperature to drop, and the refrigerant becomes a low-temperature vapour/liquid mixture.
The outdoor unit is where heat is transferred to/from the outdoor air in an air-source heat pump. This unit generally contains a heat exchanger coil, the compressor, and the expansion valve. It looks and operates in the same manner as the outdoor portion of an air-conditioner.
The indoor coil is where heat is transferred to/from indoor air in certain types of air-source heat pumps. Generally, the indoor unit contains a heat exchanger coil, and may also include an additional fan to circulate heated or cooled air to the occupied space.
The plenum , only seen in ducted installations, is part of the air distribution network. The plenum is an air compartment that forms part of the system for distributing heated or cooled air through the house. It is generally a large compartment immediately above or around the heat exchanger.
Other Terms
Units of measurement for capacity, or power use:
- A Btu/h, or British thermal unit per hour, is a unit used to measure the heat output of a heating system. One Btu is the amount of heat energy given off by a typical birthday candle. If this heat energy were released over the course of one hour, it would be the equivalent of one Btu/h.
- A kW, or kilowatt, is equal to watts. This is the amount of power required by ten 100-watt light bulbs.
- A ton is a measure of heat pump capacity. It is equivalent to 3.5 kW or 12 000 Btu/h.
Air-Source Heat Pumps
Air-source heat pumps use the outdoor air as a source of thermal energy in heating mode, and as a sink to reject energy when in cooling mode. These types of systems can generally be classified into two categories:
Air-Air Heat Pumps. These units heat or cool the air inside your home, and represent the vast majority of air-source heat pump integrations in Canada. They can be further classified according to the type of installation:
- Ducted: The indoor coil of the heat pump is located in a duct. Air is heated or cooled by passing over the coil, before being distributed via the ductwork to different locations in the home.
- Ductless: The indoor coil of the heat pump is located in an indoor unit. These indoor units are generally located on the floor or wall of an occupied space, and heat or cool the air in that space directly. Among these units, you may see the terms mini- and multi-split:
- Mini-Split: A single indoor unit is located inside the home, served by a single outdoor unit.
- Multi-Split: Multiple indoor units are located in the home, and are served by a single outdoor unit.
Air-air systems are more efficient when the temperature difference between inside and outside is smaller. Because of this, air-air heat pumps generally try to optimize their efficiency by providing a higher volume of warm air, and heating that air to a lower temperature (normally between 25 and 45°C). This contrasts with furnace systems, which deliver a smaller volume of air, but heat that air to higher temperatures (between 55°C and 60°C). If you are switching to a heat pump from a furnace, you may notice this when you begin using your new heat pump.
Air-Water Heat Pumps: Less common in Canada, air-water heat pumps heat or cool water, and are used in homes with hydronic (water-based) distribution systems such as low temperature radiators, radiant floors, or fan coil units. In heating mode, the heat pump provides thermal energy to the hydronic system. This process is reversed in cooling mode, and thermal energy is extracted from the hydronic system and rejected to the outdoor air.
Operating temperatures in the hydronic system are critical when evaluating air-water heat pumps. Air-water heat pumps operate more efficiently when heating the water to lower temperatures, i.e., below 45 to 50°C, and as such are a better match for radiant floors or fan coil systems. Care should be taken if considering their use with high temperature radiators that require water temperatures above 60°C, as these temperatures generally exceed the limits of most residential heat pumps.
Major Benefits of Air-Source Heat Pumps
Installing an air-source heat pump can offer you a number of benefits. This section explores how air-source heat pumps can benefit your household energy footprint.
Efficiency
The major benefit of using an air-source heat pump is the high efficiency it can provide in heating compared to typical systems like furnaces, boilers and electric baseboards. At 8°C, the coefficient of performance (COP) of air-source heat pumps typically ranges from between 2.0 and 5.4. This means that, for units with a COP of 5, 5 kilowatt hours (kWh) of heat are transferred for every kWh of electricity supplied to the heat pump. As the outdoor air temperature drops, COPs are lower, as the heat pump must work across a greater temperature difference between the indoor and outdoor space. At &#;8°C, COPs can range from 1.1 to 3.7.
On a seasonal basis, the heating seasonal performance factor (HSPF) of market available units can vary from 7.1 to 13.2 (Region V). It is important to note that these HSPF estimates are for an area with a climate similar to Ottawa. Actual savings are highly dependant on the location of your heat pump installation.
Energy Savings
The higher efficiency of the heat pump can translate into significant energy use reductions. Actual savings in your house will depend on a number of factors, including your local climate, efficiency of your current system, size and type of heat pump, and the control strategy. Many online calculators are available to provide a quick estimation of how much energy savings you can expect for your particular application. NRCan&#;s ASHP-Eval tool is freely available and could be used by installers and mechanical designers to help advise on your situation.
How Does an Air-Source Heat Pump Work?
The Heating Cycle
The Cooling Cycle
The Defrost Cycle
If the outdoor temperature falls to near or below freezing when the heat pump is operating in the heating mode, moisture in the air passing over the outside coil will condense and freeze on it. The amount of frost buildup depends on the outdoor temperature and the amount of moisture in the air.
This frost buildup decreases the efficiency of the coil by reducing its ability to transfer heat to the refrigerant. At some point, the frost must be removed. To do this, the heat pump switches into defrost mode. The most common approach is:
- First, the reversing valve switches the device to the cooling mode. This sends hot gas to the outdoor coil to melt the frost. At the same time the outdoor fan, which normally blows cold air over the coil, is shut off in order to reduce the amount of heat needed to melt the frost.
- While this is happening, the heat pump is cooling the air in the ductwork. The heating system would normally warm this air as it is distributed throughout the house.
One of two methods is used to determine when the unit goes into defrost mode:
- Demand-frost controls monitor airflow, refrigerant pressure, air or coil temperature and pressure differential across the outdoor coil to detect frost accumulation.
- Time-temperature defrost is started and ended by a pre-set interval timer or a temperature sensor located on the outside coil. The cycle can be initiated every 30, 60 or 90 minutes, depending on the climate and the design of the system.
Unnecessary defrost cycles reduce the seasonal performance of the heat pump. As a result, the demand-frost method is generally more efficient since it starts the defrost cycle only when it is required.
Supplementary Heat Sources
Since air-source heat pumps have a minimum outdoor operating temperature (between -15°C to -25°C) and reduced heating capacity at very cold temperatures, it is important to consider a supplemental heating source for air-source heat pump operations. Supplementary heating may also be required when the heat pump is defrosting. Different options are available:
- All Electric: In this configuration, heat pump operations are supplemented with electric resistance elements located in the ductwork or with electric baseboards. These resistance elements are less efficient than the heat pump, but their ability to provide heating is independent of outdoor temperature.
- Hybrid System: In a hybrid system, the air-source heat pump uses a supplemental system such as a furnace or boiler. This option can be used in new installations, and is also a good option where a heat pump is added to an existing system, for example, when a heat pump is installed as a replacement for a central air-conditioner.
See the final section of this booklet, Related Equipment, for more information on systems that use supplementary heating sources. There, you can find discussion of options for how to program your system to transition between heat pump use and supplementary heat source use.
Energy Efficiency Considerations
To support understanding of this section, refer to the earlier section called An introduction to Heat Pump Efficiency for an explanation of what HSPFs and SEERs represent.
In Canada, energy efficiency regulations prescribe a minimum seasonal efficiency in heating and cooling that must be achieved for the product to be sold in the Canadian market. In addition to these regulations, your province or territory may have more stringent requirements.
Minimum performance for Canada as a whole, and typical ranges for market-available products, are summarized below for heating and cooling. It is important to also check to see whether any additional regulations are in place in your region before selecting your system.
Cooling Seasonal Performance, SEER:
- Minimum SEER (Canada): 14
- Range, SEER in Market Available Products: 14 to 42
Heating Seasonal Performance, HSPF
- Minimum HSPF (Canada): 7.1 (for Region V)
- Range, HSPF in Market Available Products: 7.1 to 13.2 (for Region V)
Note: HSPF factors are provided for AHRI Climate Zone V, which has a similar climate to Ottawa. Actual seasonal efficiencies may vary depending on your region. A new performance standard that aims to better represent performance of these systems in Canadian regions is currently under development.
The actual SEER or HSPF values depend on a variety of factors primarily related to heat pump design. Current performance has evolved significantly over the last 15 years, driven by new developments in compressor technology, heat exchanger design, and improved refrigerant flow and control.
Single Speed and Variable Speed Heat Pumps
Of particular importance when considering efficiency is the role of new compressor designs in improving seasonal performance. Typically, units operating at the minimum prescribed SEER and HSPF are characterized by single speed heat pumps. Variable speed air-source heat pumps are now available that are designed to vary the capacity of the system to more closely match the heating/cooling demand of the house at a given moment. This helps to maintain peak efficiency at all times, including during milder conditions when there is lower-demand on the system.
More recently, air-source heat pumps that are better adapted to operating in the cold Canadian climate have been introduced to the market. These systems, often called cold climate heat pumps, combine variable capacity compressors with improved heat exchanger designs and controls to maximize heating capacity at colder air temperatures, while maintaining high efficiencies during milder conditions. These types of systems typically have higher SEER and HSPF values, with some systems reaching SEERs up to 42, and HSPFs approaching 13.
Certification, Standards, and Rating Scales
The Canadian Standards Association (CSA) currently verifies all heat pumps for electrical safety. A performance standard specifies tests and test conditions at which heat pump heating and cooling capacities and efficiency are determined. The performance testing standards for air-source heat pumps are CSA C656, which (as of ) has been harmonised with ANSI/AHRI 210/240-, Performance Rating of Unitary Air-Conditioning & Air-Source Heat Pump Equipment. It also replaces CAN/CSA-C273.3-M91, Performance Standard for Split-System Central Air-Conditioners and Heat Pumps.
Sizing Considerations
To appropriately size your heat pump system, it is important to understand the heating and cooling needs for your home. It is recommended that a heating and cooling professional be retained to undertake the required calculations. Heating and cooling loads should be determined by using a recognized sizing method such as CSA F280-12, "Determining the Required Capacity of Residential Space Heating and Cooling Appliances."
The sizing of your heat pump system should be done according to your climate, heating and cooling building loads, and the objectives of your installation (e.g., maximizing heating energy savings vs. displacing an existing system during certain periods of the year). To help with this process, NRCan has developed an Air-Source Heat Pump Sizing and Selection Guide. This guide, along with a companion software tool, is intended for energy advisors and mechanical designers, and is freely available to provide guidance on appropriate sizing.
If a heat pump is undersized, you will notice that the supplemental heating system will be used more frequently. While an undersized system will still operate efficiently, you may not get the anticipated energy savings due to a high use of a supplemental heating system.
Likewise, if a heat pump is oversized, the desired energy savings may not be realized due to inefficient operation during milder conditions. While the supplemental heating system operates less frequently, under warmer ambient conditions, the heat pump produces too much heat and the unit cycles on and off leading to discomfort, wear on the heat pump, and stand-by electric power draw. It is therefore important to have a good understanding of your heating load and what the heat pump operating characteristics are to achieve optimal energy savings.
Other Selection Criteria
Apart from sizing, several additional performance factors should be considered:
- HSPF: Select a unit with as high an HSPF as practical. For units with comparable HSPF ratings, check their steady-state ratings at &#;8.3°C, the low temperature rating. The unit with the higher value will be the most efficient one in most regions of Canada.
- Defrost: Select a unit with demand-defrost control. This minimizes defrost cycles, which reduces supplementary and heat pump energy use.
- Sound Rating: Sound is measured in units called decibels (dB). The lower the value, the lower the sound power emitted by the outdoor unit. The higher the decibel level, the louder the noise. Most heat pumps have a sound rating of 76 dB or lower.
Installation Considerations
Air-source heat pumps should be installed by a qualified contractor. Consult a local heating and cooling professional to size, install, and maintain your equipment to ensure efficient and reliable operations. If you are looking to implement a heat pump to replace or supplement your central furnace, you should be aware that heat pumps generally operate at higher airflows than furnace systems. Depending on the size of your new heat pump, some modifications may be needed to your ductwork to avoid added noise and fan energy use. Your contractor will be able to give you guidance on your specific case.
The cost of installing an air-source heat pump depends on the type of system, your design objectives, and any existing heating equipment and ductwork in your home. In some cases, additional modifications to the ductwork or electrical services may be required to support your new heat pump installation.
Operation Considerations
You should note several important things when operating your heat pump:
- Optimize Heat Pump and Supplemental System Set-points. If you have an electric supplemental system (e.g., baseboards or resistance elements in duct), be sure to use a lower temperature set-point for your supplemental system. This will help to maximize the amount of heating the heat pump provides to your home, lowering your energy use and utility bills. A set-point of 2°C to 3°C below the heat pump heating temperature set-point is recommended. Consult your installation contractor on the optimal set-point for your system.
- Set Up for an Efficient Defrost. You can reduce energy use by having your system set up to turn off the indoor fan during defrost cycles. This can be performed by your installer. However, it is important to note that defrost may take a little longer with this set up.
- Minimize Temperature Setbacks. Heat pumps have a slower response than furnace systems, so they have more difficultly responding to deep temperature setbacks. Moderated setbacks of not more than 2°C should be employed or a &#;smart&#; thermostat that switches the system on early, in anticipation of a recovery from setback, should be used. Again, consult your installation contractor on the optimal setback temperature for your system.
- Optimize Your Airflow Direction. If you have a wall mounted indoor unit, consider adjusting the airflow direction to maximize your comfort. Most manufacturers recommend directing airflow downwards when heating, and towards occupants when in cooling.
- Optimize fan settings. Also, be sure to adjust fan settings to maximize comfort. To maximize the heat delivered of the heat pump, it is recommended to set the fan speed to high or &#;Auto&#;. Under cooling, to also improve dehumidification, the &#;low&#; fan speed is recommended.
Maintenance Considerations
Proper maintenance is critical to ensure your heat pump operates efficiently, reliably, and has a long service life. You should have a qualified contractor do annual maintenance on your unit to ensure everything is in good working order.
Aside from annual maintenance, there are a few simple things you can do to ensure reliable and efficient operations. Be sure to change or clean your air filter every 3 months, as clogged filters will decrease airflow and reduce the efficiency of your system. Also, be sure that vents and air registers in your home are not blocked by furniture or carpeting, as inadequate airflow to or from your unit can shorten equipment lifespans and reduce efficiency of the system.
Operating Costs
The energy savings from installing a heat pump can help to reduce your monthly energy bills. Achieving a reduction in your energy bills greatly depends on the price of electricity in relation to other fuels such as natural gas or heating oil, and, in retrofit applications, what type of system is being replaced.
Heat pumps in general come at a higher cost compared to other systems such as furnaces or electric baseboards due the number of components in the system. In some regions and cases, this added cost can be recouped in a relatively short time period through the utility cost savings. However, in other regions, varying utility rates can extend this period. It is important to work with your contractor or energy advisor to get an estimate of the economics of heat pumps in your area, and the potential savings you can achieve.
Life Expectancy and Warranties
Air-source heat pumps have a service life of between 15 and 20 years. The compressor is the critical component of the system.
Most heat pumps are covered by a one-year warranty on parts and labour, and an additional five- to ten-year warranty on the compressor (for parts only). However, warranties vary between manufacturers, so check the fine print.
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Ground-Source Heat Pumps
Ground-source heat pumps use the earth or ground water as a source of thermal energy in heating mode, and as a sink to reject energy when in cooling mode. These types of systems contain two key components:
- Ground Heat Exchanger: This is the heat exchanger used to add or remove thermal energy from the earth or ground. Various heat exchanger configurations are possible, and are explained later in this section.
- Heat Pump: Instead of air, ground-source heat pumps use a fluid flowing through the ground heat exchanger as their source (in heating) or sink (in cooling).
On the building side, both air and hydronic (water) systems are possible. Operating temperatures on the building side are very important in hydronic applications. Heat pumps operate more efficiently when heating at lower temperatures of below 45 to 50°C, making them a better match for radiant floors or fan coil systems. Care should be taken if considering their use with high temperature radiators that require water temperatures above 60°C, as these temperatures generally exceed the limits of most residential heat pumps.
Depending on how the heat pump and ground heat exchanger interact, two different system classifications are possible:
- Secondary Loop: A liquid (ground water or anti-freeze) is used in the ground heat exchanger. The thermal energy transferred from the ground to the liquid is delivered to the heat pump via a heat exchanger.
- Direct Expansion (DX): A refrigerant is used as the fluid in the ground heat exchanger. The thermal energy extracted by the refrigerant from the ground is used directly by the heat pump - no additional heat exchanger is needed.
In these systems, the ground heat exchanger is a part of the heat pump itself, acting as the evaporator in heating mode and condenser in cooling mode.
Ground-source heat pumps can serve a suite of comfort needs in your home, including:
- Heating only: The heat pump is used only in heating. This can include both space heating and hot water production.
- Heating with &#;active cooling&#;: The heat pump is used in both heating and cooling
- Heating with &#;passive cooling&#;: The heat pump is used in heating, and bypassed in cooling. In cooling, fluid from the building is cooled directly in the ground heat exchanger.
Heating and &#;active cooling&#; operations are described in the following section.
Major Benefits of Ground-Source Heat Pump Systems
Efficiency
In Canada, where air temperatures can go below &#;30°C, ground-source systems are able to operate more efficiently because they take advantage of warmer and more stable ground temperatures. Typical water temperatures entering the ground-source heat pump are generally above 0°C, yielding a COP of around 3 for most systems during the coldest winter months.
Energy Savings
Ground-source systems will reduce your heating and cooling costs substantially. Heating energy cost savings compared with electric furnaces are around 65%.
On average, a well designed ground-source system will yield savings that are about 10-20% more than would be provided by a best in class, cold climate air-source heat pump sized to cover most of the building heating load. This is due to the fact that underground temperatures are higher in winter than air temperatures. As a result, a ground-source heat pump can provide more heat over the course of the winter than an air-source heat pump.
Actual energy savings will vary depending on the local climate, the efficiency of the existing heating system, the costs of fuel and electricity, the size of the heat pump installed, borefield configuration and the seasonal energy balance, and the heat pump efficiency performance at CSA rating conditions.
How Does a Ground-Source System Work?
Ground-source heat pumps consist of two main parts: A ground heat exchanger, and a heat pump. Unlike air-source heat pumps, where one heat exchanger is located outside, in ground-source systems, the heat pump unit is located inside the home.
Ground heat exchanger designs can be classified as either:
- Closed Loop: Closed-loop systems collect heat from the ground by means of a continuous loop of piping buried underground. An antifreeze solution (or refrigerant in the case of a DX ground-source system), which has been chilled by the heat pump's refrigeration system to several degrees colder than the outside soil, circulates through the piping and absorbs heat from the soil.
Common piping arrangements in closed loop systems include horizontal, vertical, diagonal and pond/lake ground systems (these arrangements are discussed below, under Design Considerations).
- Open Loop: Open systems take advantage of the heat retained in an underground body of water. The water is drawn up through a well directly to the heat exchanger, where its heat is extracted. The water is then discharged either to an above-ground body of water, such as a stream or pond, or back to the same underground water body through a separate well.
The selection of outdoor piping system depends on the climate, soil conditions, available land, local installation costs at the site as well as municipal and provincial regulations. For instance, open loop systems are permitted in Ontario, but are not permitted in Quebec. Some municipalities have banned DX systems because the municipal water source is the aquifer.
The Heating Cycle
The Cooling Cycle
The &#;active cooling&#; cycle is basically the reverse of the heating cycle. The direction of the refrigerant flow is changed by the reversing valve. The refrigerant picks up heat from the house air and transfers it directly, in DX systems, or to the ground water or antifreeze mixture. The heat is then pumped outside, into a water body or return well (in an open system) or into the underground piping (in a closed-loop system). Some of this excess heat can be used to preheat domestic hot water.
Unlike air-source heat pumps, ground-source systems do not require a defrost cycle. Temperatures underground are much more stable than air temperatures, and the heat pump unit itself is located inside; therefore, the problems with frost do not arise.
Parts of the System
Ground-source heat pump systems have three main components: the heat pump unit itself, the liquid heat exchange medium (open system or closed loop), and a distribution system (either air-based or hydronic) that distributes the thermal energy from the heat pump to the building.
Ground-source heat pumps are designed in different ways. For air-based systems, self-contained units combine the blower, compressor, heat exchanger, and condenser coil in a single cabinet. Split systems allow the coil to be added to a forced-air furnace, and use the existing blower and furnace. For hydronic systems, both the source and sink heat exchangers and compressor are in a single cabinet.
Energy Efficiency Considerations
As with air-source heat pumps, ground-source heat pump systems are available in a range of different efficiencies. See the earlier section called An introduction to Heat Pump Efficiency for an explanation of what COPs and EERs represent. Ranges of COPs and EERs for market available units are provided below.
Ground water or Open-Loop Applications
Heating
- Minimum Heating COP: 3.6
- Range, Heating COP in Market Available Products: 3.8 to 5.0
Cooling
- Minimum EER: 16.2
- Range, EER in Market Available Products: 19.1 to 27.5
Closed Loop Applications
Heating
- Minimum Heating COP: 3.1
- Range, Heating COP in Market Available Products: 3.2 to 4.2
Cooling
- Minimum EER: 13.4
- Range, EER in Market Available Products: 14.6 to 20.4
The minimum efficiency for each type is regulated at the federal level as well as in some provincial jurisdictions. There has been a dramatic improvement in the efficiency of ground-source systems. The same developments in compressors, motors and controls that are available to air-source heat pump manufacturers are resulting in higher levels of efficiency for ground-source systems.
Lower-end systems typically employ two stage compressors, relatively standard size refrigerant-to-air heat exchangers, and oversized enhanced-surface refrigerant-to-water heat exchangers. Units in the high efficiency range tend to use multi-or variable speed compressors, variable speed indoor fans, or both. Find an explanation of single speed and variable speed heat pumps in the Air-Source Heat Pump section.
Certification, Standards, and Rating Scales
The Canadian Standards Association (CSA) currently verifies all heat pumps for electrical safety. A performance standard specifies tests and test conditions at which heat pump heating and cooling capacities and efficiency are determined. The performance testing standards for ground-source systems are CSA C (for secondary loop systems) and CSA C748 (for DX systems).
Sizing Considerations
It is important that the ground heat exchanger be well matched to the heat pump capacity. Systems that are not balanced and unable to replenish the energy drawn from the borefield will continuously perform worse over time until the heat pump can no longer extract heat.
As with air-source heat pump systems, it is generally not a good idea to size a ground-source system to provide all of the heat required by a house. For cost-effectiveness, the system should generally be sized to cover the majority of the household&#;s annual heating energy requirement. The occasional peak heating load during severe weather conditions can be met by a supplementary heating system.
Systems are now available with variable speed fans and compressors. This type of system can meet all cooling loads and most heating loads on low speed, with high speed required only for high heating loads. Find an explanation of single speed and variable speed heat pumps in the Air-Source Heat Pump section.
A variety of sizes of systems are available to suit the Canadian climate. Residential units range in rated size (closed loop cooling) of 1.8 kW to 21.1 kW (6 000 to 72 000 Btu/h), and include domestic hot water (DHW) options.
Design Considerations
Unlike air-source heat pumps, ground-source heat pumps require a ground heat exchanger to collect and dissipate heat underground.
Open Loop Systems
Closed-Loop Systems
Installation Considerations
As with air-source heat pump systems, ground-source heat pumps must be designed and installed by qualified contractors. Consult a local heat pump contractor to design, install and service your equipment to ensure efficient and reliable operation. Also, be sure that all manufacturers' instructions are followed carefully. All installations should meet the requirements of CSA C448 Series 16, an installation standard set by the Canadian Standards Association.
The total installed cost of ground-source systems varies according to site-specific conditions. Installation costs vary depending on the type of ground collector and the equipment specifications. The incremental cost of such a system can be recovered through energy cost savings over a period as low as 5 years. Payback period is dependent on a variety of factors such as soil conditions, heating and cooling loads, the complexity of HVAC retrofits, local utility rates, and the heating fuel source being replaced. Check with your electric utility to assess the benefits of investing in a ground-source system. Sometimes a low-cost financing plan or incentive is offered for approved installations. It is important to work with your contractor or energy advisor to get an estimate of the economics of heat pumps in your area, and the potential savings you can achieve.
Operation Considerations
You should note several important things when operating your heat pump:
- Optimize Heat Pump and Supplemental System Set-points. If you have an electric supplemental system (e.g., baseboards or resistance elements in duct), be sure to use a lower temperature set-point for your supplemental system. This will help to maximize the amount of heating the heat pump provides to your home, lowering your energy use and utility bills. A set-point of 2°C to 3°C below the heat pump heating temperature set-point is recommended. Consult your installation contractor on the optimal set-point for your system.
- Minimize Temperature Setbacks. Heat pumps have a slower response than furnace systems, so they have more difficultly responding to deep temperature setbacks. Moderated setbacks of not more than 2°C should be employed or a &#;smart&#; thermostat that switches the system on early, in anticipation of a recovery from setback, should be used. Again, consult your installation contractor on the optimal setback temperature for your system.
Maintenance Considerations
You should have a qualified contractor perform annual maintenance once per year to ensure your system remains efficient and reliable.
If you have an air-based distribution system, you can also support more efficient operations by replacing or cleaning your filter every 3 months. You should also ensure that your air vents and registers are not blocked by any furniture, carpeting or other items that would impede airflow.
Operating Costs
The operating costs of a ground-source system are usually considerably lower than those of other heating systems, because of the savings in fuel. Qualified heat pump installers should be able to give you information on how much electricity a particular ground-source system would use.
Relative savings will depend on whether you are currently using electricity, oil or natural gas, and on the relative costs of different energy sources in your area. By running a heat pump, you will use less gas or oil, but more electricity. If you live in an area where electricity is expensive, your operating costs may be higher.
Life Expectancy and Warranties
Ground-source heat pumps generally have a life expectancy of about 20 to 25 years. This is higher than for air-source heat pumps because the compressor has less thermal and mechanical stress, and is protected from the environment. The lifespan of the ground loop itself approaches 75 years.
Most ground-source heat pump units are covered by a one-year warranty on parts and labour, and some manufacturers offer extended warranty programs. However, warranties vary between manufacturers, so be sure to check the fine print.
Related Equipment
Upgrading the Electrical Service
Generally speaking, it is not necessary to upgrade the electrical service when installing an air-source add-on heat pump. However, the age of the service and the total electrical load of the house may make it necessary to upgrade.
A 200 ampere electrical service is normally required for the installation of either an all-electric air-source heat pump or a ground-source heat pump. If transitioning from a natural gas or fuel oil based heating system, it may be necessary to upgrade your electrical panel.
Supplementary Heating Systems
Air-Source Heat Pump Systems
Air-source heat pumps have a minimum outdoor operating temperature, and may lose some of their ability to heat at very cold temperatures. Because of this, most air-source installations require a supplementary heating source to maintain indoor temperatures during the coldest days. Supplementary heating may also be required when the heat pump is defrosting.
Most air-source systems shut off at one of three temperatures, which can be set by your installation contractor:
- Thermal Balance Point: The temperature below which the heat pump does not have enough capacity to meet the heating needs of the building on its own.
- Economic Balance Point: The temperature below which the ratio of electricity to a supplemental fuel (e.g., natural gas) means that using the supplementary system is more cost effective.
- Cut-Off Temperature: The minimum operating temperature for the heat pump.
Most supplementary systems can be classed into two categories:
- Hybrid Systems: In a hybrid system, the air-source heat pump uses a supplemental system such as a furnace or boiler. This option can be used in new installations, and is also a good option where a heat pump is added to an existing system, for example, when a heat pump is installed as a replacement for a central air-conditioner.
These types of systems support switching between heat pump and supplementary operations according to the thermal or economic balance point.
These systems cannot be run simultaneously with the heat pump &#; either the heat pump operates or the gas/oil furnace operates.
- All Electric Systems: In this configuration, heat pump operations are supplemented with electric resistance elements located in the ductwork or with electric baseboards.
These systems can be run simultaneously with the heat pump, and can therefore be used in balance point or cut-off temperature control strategies.
An outdoor temperature sensor shuts the heat pump off when the temperature falls below the pre-set limit. Below this temperature, only the supplementary heating system operates. The sensor is usually set to shut off at the temperature corresponding to the economic balance point, or at the outdoor temperature below which it is cheaper to heat with the supplementary heating system instead of the heat pump.
Ground-Source Heat Pump Systems
Ground-source systems continue to operate regardless of the outdoor temperature, and as such are not subject to the same sort of operating restrictions. The supplementary heating system only provides heat that is beyond the rated capacity of the ground-source unit.
Thermostats
Conventional Thermostats
Most ducted residential single-speed heat pump systems are installed with a "two-stage heat/one-stage cool" indoor thermostat. Stage one calls for heat from the heat pump if the temperature falls below the pre-set level. Stage two calls for heat from the supplementary heating system if the indoor temperature continues to fall below the desired temperature. Ductless residential air-source heat pumps are typically installed with a single stage heating/cooling thermostat or in many instances a built in thermostat set by a remote that comes with the unit.
The most common type of thermostat used is the "set and forget" type. The installer consults with you prior to setting the desired temperature. Once this is done, you can forget about the thermostat; it will automatically switch the system from heating to cooling mode or vice versa.
There are two types of outdoor thermostats used with these systems. The first type controls the operation of the electric resistance supplementary heating system. This is the same type of thermostat that is used with an electric furnace. It turns on various stages of heaters as the outdoor temperature drops progressively lower. This ensures that the correct amount of supplementary heat is provided in response to outdoor conditions, which maximizes efficiency and saves you money. The second type simply shuts off the air-source heat pump when the outdoor temperature falls below a specified level.
Thermostat setbacks may not yield the same kind of benefits with heat pump systems as with more conventional heating systems. Depending upon the amount of the setback and temperature drop, the heat pump may not be able to supply all of the heat required to bring the temperature back up to the desired level on short notice. This may mean that the supplementary heating system operates until the heat pump "catches up." This will reduce the savings that you might have expected to achieve by installing the heat pump. See discussion in previous sections on minimizing temperature setbacks.
Programmable Thermostats
Programmable heat pump thermostats are available today from most heat pump manufacturers and their representatives. Unlike conventional thermostats, these thermostats achieve savings from temperature setback during unoccupied periods, or overnight. Although this is accomplished in different ways by different manufacturers, the heat pump brings the house back to the desired temperature level with or without minimal supplementary heating. For those accustomed to thermostat setback and programmable thermostats, this may be a worthwhile investment. Other features available with some of these electronic thermostats include the following:
- Programmable control to allow for user selection of automatic heat pump or fan-only operation, by time of day and day of the week.
- Improved temperature control, as compared to conventional thermostats.
- No need for outdoor thermostats, as the electronic thermostat calls for supplementary heat only when needed.
- No need for an outdoor thermostat control on add-on heat pumps.
Savings from programmable thermostats are highly dependant on the type and sizing of your heat pump system. For variable speed systems, setbacks may allow the system to operate at a lower speed, reducing wear on the compressor and helping to increase system efficiency.
Heat Distribution Systems
Heat pump systems generally supply a greater volume of airflow at lower temperature compared to furnace systems. As such, it is very important to examine the supply airflow of your system, and how it may compare to the airflow capacity of your existing ducts. If the heat pump airflow exceeds the capacity of your existing ducting, you may have noise issues or increased fan energy use.
New heat pump systems should be designed according to established practice. If the installation is a retrofit, the existing duct system should be carefully examined to ensure that it is adequate.
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