How to Buy, Use and Maintain Heat Pumps for Greater Heat Pump Efficiency. Comparison of the Major Types of Heat Pumps.
Is a Heat Pump Right for You?
How Do Heat Pumps Work?
Split-System Heat Pumps
Split-Ductless Heat Pumps
Portable Heat Pumps
Water-Source and Ground-Source Heat Pump Systems
Tips for Buying and Using Heat Pumps for High Energy Efficiency
Create a Zoned HVAC System for Improved Energy Savings
Maintenance You Can Do Yourself to Improve the Efficiency of a Whole House Heat Pump
How to Build a Roof for a Heat Pump Condenser Unit
Heat pumps heat the home by transferring heat from the outside air into the home, and cool the home by transferring heat from inside the home to the outside. This is how air conditioners cool the home, and heat pumps use the same technology as air conditioners. To heat the home they operate in reverse, Freon is pumped in one direction when cooling and in the opposite direction when heating. They can heat the home at a lower cost than a central heating system on days that are not too hot. They normally cool the home at a cost similar to central air conditioning. They are normally a good investment in moderate climates.
There are heat pump systems that transfer heat to and from a body of water such as a pond, and systems that transfer heat from the ground. Some heat pumps can dehumidify the home. The main disadvantage to heat pumps is that they can only be used on days when the outdoor temperature is not too cold and not too hot. See, How Do Heat Pumps Work?
Your yearly energy cost for heating the home or just one room will depend on how many energy-saving features are on the model and whether you know how to use a heat pump efficiently. Some of these features are explained in Tips for Buying an Energy Efficient Heat Pump. Heat pumps don’t burn fuel to create heat, so there is no risk of carbon monoxide poisoning and there is no flame to worry about.
If you must replace both your air conditioning and your heating equipment, buying a whole house split-system heat pump or a split-ductless heat pump system is much less expensive than buying conventional air conditioning and heating systems. A split-ductless system has all of the heating/cooling units mounted to exterior walls, with no HVAC ducts. They can be used to heat and cool a small house or a section of a house, as explained in Split-Ductless Heat Pumps
When heating a home on days that are not very cold, transferring heat energy from outside to inside costs less than generating energy in a furnace or other heating unit by burning fuel or using resistance electric heat. In climates that are occasionally too cold for a heat pump, whole house heat pump systems have supplemental electric heaters. In the summer, using a heat pump can cost about the same as using an air conditioner because their components are similar and they both use the refrigeration cycle.
Conventional heat pumps, as described above, are called “air-source heat pumps” because they transfer energy with the outside air. “Water-source” and “ground-source” heat pumps, which are described below in the section Water-Source and Ground-Source Heat Pump Systems transfer heat energy with the earth or a with a nearby body of water. Inside the home they are the same as air-source heat pumps.
Is A Heat Pump Right For You?
If your climate is moderate and you heat your home more days than you cool it, a heat pump is probably a good investment. You are much less likely to have high heat pump efficiency if you live in a very hot or very cold climate. Also, if your climate is warm and you must replace your central heating system and whole house air conditioner, you can heat and cool your home with a heat pump to avoid buying both sets of equipment. There are, however too many factors to estimate how much you would save. Twelve of the factors are given below. Also, heat pumps have a few problems of their own. See Problems that Heat Pumps Have and Air Conditioners Don’t Have.
Whole house heat pumps normally heat a home more economically than other types of central heating systems down to temperatures of around 25 to 30 degrees, depending on the model. At that point, either a gas furnace or an air handler with supplemental electric heat must kick in to create the heat. In winter, heat pumps use electricity to transfer heat from outside to inside your home, so the colder it is outside the less heat is in the air and the more electricity it takes to make your home warm. This is also true in cooling the home in the summer but air conditioners are similar to heat pumps operating in their cooling mode, and will probably use a similar amount of electricity.
Many factors determine how much it would cost to buy, install and use a heat pump. They are true for all types of heat pumps:
- How efficient is the heat pump you would buy? See topic below, Tips for Buying an Energy Efficient Heat Pump
- Is your climate moderate, relatively hot or relatively cold?
- Heat pumps cool at a similar cost as air conditioners, but they heat for less on days that are not too cold. Thus, the colder it is the more electricity they use to create heat.
- If you have a high efficiency gas furnace, a heat pump will probably not yield a high enough return on investment to offset the cost of replacing it with a heat pump. You can install an air conditioner for much less than a split-system heat pump.
- Installing a whole-house heat pump with HVAC ducts (a split-system heat pump) would not be a good investment if you must install all new HVAC ducts. The cost is high and the ducts must be installed along the ceilings in some rooms, which harms the appearance of your home and thus its market value. You must use existing HVAC ducts.
- If your home is small you can cool it with split-ductless heat pumps. These have units mounted into walls and use no HVAC ducts. One outside unit provides the conditioned air for all four. See, Split-Ductless Heat Pumps If these are used, one or more can be turned off to save energy.
- A whole-house split system heat pump can be a good investment in colder climates if you use your furnace heating system as backup heating for cold days.
- Is your home well-insulated, with thermal windows, and your attic well-insulated? Using a heat pump will cost less than in a well-insulated home.
- Are the electricity rates high or low where you live?
- If you heat your home with gas, is the cost of gas relatively high or low in your region? The costs vary by about 100% from state to state in the continental United States.
- Were your HVAC ducts installed for heating or for heating and air conditioning? Ducts installed for heating are smaller, causing heat pump cooling to be less efficient.
- If you have a “zoned HVAC system” or will convert your system to zoned by installing dampers, a whole-house split system heat pump can be used more efficiently. A damper controls the airflow to a zone of the house, such as the second floor. A separate thermostat in each zone controls the damper to shut off the airflow or keep it at a set temperature. See Create a Zoned HVAC System for Improved Energy Savings
Problems That Heat Pumps Have and Air Conditioners Do Not Have
- In some parts of the country, some models can ice up in winter on snowy days. Also, water dripping off of gutters can turn to ice. They are inefficient when covered by ice and can suffer damage. They normally go into defrost mode to melt the ice, but this may not always be sufficient.
- On very cold and windy days they may not heat the home sufficiently because they may have little or no extra heating capacity for strong wind.
- They can become buried in snow during snow storms. See How to Build a Roof for a Heat Pump Condenser Unit
- Basically, they are probably not as reliable as gas furnaces at heating the home, because their condenser unit is outdoors so there are more possible problems.
How Do Heat Pumps Work?
“How does a heat pump transfer heat from outdoors to indoors on a cold day to heat a home?” Explained simply, Freon transfers heat by being pumped through tubes from inside the home to outside and back to the inside. Freon, like water, is a gas at higher temperatures and lower pressures and a liquid at lower temperatures and higher pressures. In winter, it is pumped outside in liquid form. The tube expands, causing the pressure to become lower so the Freon becomes a gas. As the tube becomes wider the pressure becomes very low so the gas becomes very cold, colder than the surrounding air. Since heat flows from hot to cold, heat energy from the outside air flows into the Freon.
The Freon is pumped through the compressor which compresses it to make it a hot liquid, which is pumped into the house. In the house it expands to become a hot gas, which flows through coils. Air is blown past the coils, which heats it, and it is then blown into every room of the house.
To cool the home in summer, a heat pump transfers heat energy from inside the house to the outside by pumping the Freon through the same tubes but in the opposite direction. All of the same components are used. This is called the “refrigeration cycle” which air conditioners use.
Split-System Heat Pumps
Conventional whole house heat pump systems are called “split-system heat pumps”. These are “air-source” because they transfer heat between the house and the outside air. They are called “split-system” because some of their components are outside in the yard or on the roof and some are inside. The compressor, fan and outdoor coil is outside and the indoor coil and blower is inside. They transfer heated or cooled air directly to rooms through HVAC ducts with a register in the wall or ceiling of each room.
New whole house heat pumps can reduce your heating costs greatly over electric furnaces and baseboard heaters and they dehumidify better than standard central air conditioners, so your home will be more comfortable in warmer, muggier months.
In the past, air-source heat pumps were more appropriate for warmer climates, but in recent years the technology has improved. They’re now cost-effective in some colder regions, such as the upper parts of the Northeast and Midwest. However, an auxiliary heating system is necessary where temperatures drop below 10 degrees F to 25 degrees F, depending on your system’s size.
Since they draw energy from the outdoor air to heat the home, the warmer the outdoor temperature the more energy efficient they are. Also, they cannot heat the home when the outside air temperature is below about 35°F. Most have electric resistance heating strips to heat your home on very cold days. When cooling the home, they release energy into the outdoor air so the hotter it is outside the more energy they use to cool the home.
Split-system heat pumps can reduce your heating costs by up to 50 percent if you heat your home electrically and your climate is moderate. Also, they dehumidify better than standard central air conditioners. They are steadily improving, and the range of temperatures for which they can heat the home efficiently has been increasing. They are now used in relatively cold regions with back-up heat for times when the temperature is too cold.
Whole house heat pumps can have a significant problem. If they are not equipped with ultraviolet C (UVC) lights, the heat pumps often emit odors. The residents may not realize that the odors come from fungus, mold, and bacteria on the coils of the heat pump. When not controlled by UVC, the fungus, mold, and bacteria can spread throughout HVAC ducts. In addition to emitting unpleasant smells, they can create health problems and cause a reduction in heat pump efficiency.
Split-Ductless Heat Pumps
Split-ductless heat pumps, also called “mini-split heat pumps” have the basic components of whole house split system heat pumps but do not use heating ducts. An outdoor unit, normally resting on the ground, contains a compressor/condenser which produces and pumps heated or cooled refrigerant to from one to four inside units, which are mounted to walls in different rooms. Each inside unit produces warm air in winter and cool air in summer to heat or cool the room it is in. They are sometimes chosen because not all of the rooms need to be cooled or because they can be turned off in rooms that are not being used. Since they have no ductwork, they do not have the energy loss associated with HVAC ducts, which has several causes. This loss is very significant in some homes, especially if the ductwork was designed for forced air heat. They must be mounted high on walls, and some homeowners don’t like their appearance.
The cost of installing a split-ductless heat pump with multiple indoor units can be higher than other systems that heat and cool individual rooms, but there may be federal and state tax credits to offset the initial installation cost.
Like conventional whole house heat pumps, they use energy taken from the outdoor air to heat the home, so the warmer the outdoor temperature the more energy efficient they are. Also, they cannot heat the home when the outside air temperature is below about 35°F. Most have electric resistance heating strips for very cold days. When cooling the home, they release energy into the outdoor air, so the hotter it is outdoors, the more electricity they use to cool the home.
Their outside unit contains a fan, a compressor, and an outdoor coil, as do conventional heat pumps. Refrigerant is heated or cooled in the outdoor unit and pumped through small tubes to small, indoor units, which produce heated and cooled air and pump it into the rooms they are in. The indoor units are normally mounted on walls near the top so the condensation water can drain out of the house. There can be from one to four indoor units. They can be installed on a ceiling when they must be located in the center of the house.
Mini-split heat pump systems are growing in popularity, mainly in homes with no HVAC ducts. They can heat or cool an entire house if the house is not large and the climate is moderate. Each indoor unit has its own thermostat, so different rooms can be set at different temperatures and the units can be turned off for periods of the day to save energy. A possible problem is that in some places there are no qualified installers or repair persons.
Mini-split heat pump systems do not heat and cool as efficiently as split-system heat pumps with HVAC ducts because they do not use ducts. They do not always heat or cool all parts of the satisfactorily. Their energy efficiency ratings for cooling (SEER, Seasonal Energy Efficiency Rating) and heating (HSPF) can be as high as those of split-system heat pumps, but these values are misleading. They only indicate the ratio of output heating or cooling to the electrical power used, i.e., how much hot or cold air is created for how many kilowatt-hrs of electricity. This is explained below.
To install a mini-split heat pump system, the installer must cut at least a 3” diameter hole through the wall of the house for the conduit. The conduit houses a power cable, refrigerant tubing, suction tubing, and a condensate drain tube. A separate hole for each inside unit may be necessary so that each unit can drain.
Most models require that a 240v circuit be installed, which may be expensive to install. A cable must be run from the main circuit panel to the outdoor unit, with an outdoor disconnect box, so the cost depends on the distance from the circuit panel to the outdoor unit. Also, if your home does not have 200 amps, you may need to do a “heavy-up” to increase the capacity to 200 amps. Models that operate on a 120v circuit are available but these are less efficient.
The best models have various energy-saving features, such as a remote control for each unit and higher efficiencies. The most efficient models have an “inverter”, which controls how much refrigerant flows at all times. With this, more is delivered when more hot air or cold air is needed in the house, which is more efficient than the heat pump being turned on and shut off throughout the day, controlled by a thermostat. The most efficient models have ENERGYSTAR designations.
You can compare their cooling efficiencies by comparing their SEER ratings. The heating efficiency, HSPF, is normally not given for heat pumps because the SEER is sufficient to describe the efficiency of the equipment. Also, the HSPF is more complicated than the SEER rating because it takes into account supplemental heating needs and the energy used to defrost the unit, which depends on how often there is freezing temperature. The SEER is the ratio of output cooling (in Btu/hr) to input electrical power (in watts) for a typical year’s weather (temperatures and humidities) in a typical location. ENERYSTAR designations and SEER ratings vary with the climate in which the product is used, so they are not accurate comparisons. See www.energystar.gov.
Split-ductless heat pumps are often used in room additions because they can cost much less to operate in the heating season than electric space heaters if the climate is moderate. They may cost about the same as window unit air conditioners to operate in the cooling season, but they don’t block the view through a window as do window air conditioners. Also, they don’t provide an entrance for intruders, as do window unit air conditioners.
For maximum efficiency. they should be installed by a professional heating and cooling technician who can determine the proper size and right product for your home and climate.
Split-Ductless Heat Pumps Compared to Conventional Whole House Split-System Heat Pumps
If your home is small and you are considering installing a split heat pump system with all new HVAC ducts, installing a split-ductless system may be better for you. It’s cost could be lower and you will have no ducts taking up space all over the house. If your home has HVAC ducts, a split-ductless system would cost more to buy and install than a split heat pump system because a split-ductless system has four expensive inside units. This system would cost much less to operate if you have each room in a separate zone and the thermostats shut off some of the units much of the time.
If you are considering installing a split heat pump system with all new HVAC ducts and ducts would run through your attic, ask the contractor to estimate how much energy you would lose through the attic ducts in the cooling season. This could be a significant expense if you live in a hot climate, and tip the scale in favor of installing a split-ductless system. Another factor that could tip the scale is that there may be no qualified split-ductless installers or repair persons in your area.
Portable Heat Pumps
Portable heat pumps have the basic components of split-system heat pumps in a unit that can be moved around the house. They rest on the floor on wheels and draw in and exhaust air through the lower sash of a double-hung window or through a horizontally sliding window. The largest models are designed to heat and cool one large room. Some models have dehumidifier and fan functions. They begin heating the room quickly, unlike oil-filled electric space heaters, and cool as quickly as window air conditioners. Unlike window air conditioners, they allow an open view through the window. At least one brand can be used as an HEPA Air Purifier instead of a heat pump, which is useful when the pollen count is high.
The most efficient portable heat pumps are similar in their cooling efficiencies to the most efficient window unit air conditioners. This is because a heat pump operating in the cooling mode is mechanically similar to an air conditioner. Heat pumps cost much more to buy than window unit air conditioners, so they are only a good investment if they will be used mainly for heating, and only if your outdoor temperature is moderate, so they can be energy efficient.
Their costs range from about $300 to about $1000. Some portable heat pumps are called, “heat pump portable air conditioners”, but these are the same. Heating efficiencies are not often given because a model’s heating efficiency is similar to its cooling efficiency. One high capacity portable heat pump with a dehumidifier function has these technical specifications:
TECHNICAL SPECIFICATIONS FOR A HIGH CAPACITY PORTABLE HEAT PUMP
|Cooling Capacity||13,000 Btu|
|Heating Capacity||12,500 Btu|
|Power Supply||115v (60 Hz)|
|Cooling Input||12A (1350W)|
|Heating Input||11A (1180W)|
|Sound Level||46 dB (A) Max|
|Product Size||18.875" wide x 17.125" deep x 32" high|
Before buying a portable heat pump, determine if the electrical circuit it will be using has enough extra capacity; most circuits do not. An electrical circuit is the wiring that provides power for all of the outlets and lights protected by one circuit breaker or fuse. To check which outlets and lights are on a circuit, turn off its circuit breaker or remove its fuse. The lights and outlets that don’t operate are on that circuit. Normally, all of the lights and outlets on a circuit are relatively close together on the same floor, but there is an exception. A basement outlet may be on almost any circuit in the house because it was added by tapping into a cable that runs through the basement to another part of the house.
A typical portable heat pump requires about 12 amps, and most of the circuits in your home are probably 15-amp circuits, so they would not have enough extra capacity unless they are used for almost nothing else. Most kitchens have outlets on 20-amp circuits, so you could use a 14 gage extension cord from a kitchen circuit. If an outside circuit is a 20-amp circuit you could run a 14 gage extension cord out the window to it. It is best to hire an electrician to install a 20 amp circuit with an outlet near the window where the heat pump will be used.
A portable heat pump’s efficiency may be given either as an EER value or an SEER value. The EER (Energy Efficiency Ratio) is the ratio of cooling (in Btu/hr) to electrical power (in watts), at 95° outside and 80° inside, with 50% relative humidity. The SEER (Seasonal Energy Efficiency Ratio) is similar except it is calculated for a typical year’s weather (temperatures and humidities) in a typical location. The EER for a heat pump is about 87% of it’s SEER. Do not compare the estimated cost of operating a portable heat pump with that of operating a mini-split heat pump by comparing their EER’s or SEER’s because mini-split heat pumps have larger fans. Their fans blow the heated and cooled air farther into the room. The EPA does not rate portable heat pumps for efficiency or award them an ENERGY STAR® designation.
To help you to buy a model of the right size, to operate the portable heat pump with maximum efficiency, there may be a “sizing guide” printed on the box or in the user’s manual on the website. One manufacturer gives the sizing guide shown below for its products. It is for a room with an average number of sun-exposed windows. If a room has few windows or no sun-exposed windows you could buy a heat pump with a lower cooling capacity.
A SIZING GUIDE FOR PORTABLE HEAT PUMPS
|Room Size (sq. ft.)||Cooling Capacity (Btu/hr)|
Dual Hose Models Compared with Single Hose Models
All portable heat pumps are either “single hose” or “dual hose”. In a dual hose heat pump, air is drawn into the house through one hose, passed through a heat exchanger and blown out of the house through the other hose. In the winter, this outside air heats cold refrigerant flowing through the heat exchanger. In the summer, it cools hot refrigerant.
In a single hose heat pump, air is forced from inside the house, past a heat exchanger to outside the house in all seasons of the year. It is air which has leaked into the house through doors and windows. In summer the air transfers heat from the heat exchanger to the outside air. In winter the air leaves the house as cold air after transferring its heat to air that passes through the heat pump into the house. A single hose heat pump is much less effective and much less efficient.
Dual hose models have cooling efficiencies in the range of 9 to 10 EER, according to their manufacturers. This is about 10.5 to 11.5 SEER. Dual hose and single hose models are compared below. The best portable heat pumps have several energy-saving features: self-evaporation technology; dual hose design; 3-speed fans; energy-saving thermostats; and dual motor design.
For a portable heat pump to operate efficiently you must change its filters regularly. Also, vacuum it inside, following the instructions given in the Use and Care manual. A dual hose portable heat pump can be used at a conventional double hung window or at a window with sliding sashes.
Water-Source and Ground-Source Heat Pump Systems
Water-source and ground-source heat pump systems are called “geothermal” heat pump systems. They can reduce your home’s energy use and control humidity, and they are quiet, long lasting and require little maintenance. A ground-source system has long loops of piping buried in the ground through which refrigerant is pumped. The temperature deep in the ground is between 50º and 60º depending on the season and region of the country.
In these systems, the refrigerant is pumped through the piping and enters the evaporator of the heat pump in the house at the temperature under the ground. The refrigerant in the piping absorbs heat in the winter and releases heat in the summer. The technology is similar to that of conventional air-source heat pump systems but it uses much less electricity to deliver the same heating and cooling because the ground holds more energy per cubic ft. and energy transfers more easily from the ground to coolant than from air to coolant. Since their installation requires much digging, the cost is very high and is seldom used in homes. However, their high efficiency can make ground-source heat pump systems suitable for very large homes.
A water-source heat pump system can be a “lake loop system” or a “well system” (open loop system). A lake loop system has long loops of piping that run along the bottom of a lake or pond and have refrigerant pumped through them. In a well system, water is pumped from a well or lake through a heat exchanger to absorb energy or add energy to it, then discharges it into a different well or lake. The temperature at the bottom of a deep lake or pond is much cooler than the outside air in the summer and is warmer than the outside air in the winter, so the refrigerant in the piping absorbs heat in the winter and releases heat in the summer.
As with ground source heat pumps, the technology used in water-source heat pump systems is similar to that of conventional air-source heat pump systems but uses much less electricity to deliver the same heating and cooling because heat transfers more easily from water to coolant than from air to coolant. Both types of water-source systems can be good investments if a body of water is close to your house and the climate is moderate.
Geothermal is not practical for small lots and certain soil conditions, and installation is costly, especially for ground-source systems. However, federal and local incentives can drop the initial cost considerably, and the maintenance and repair costs are much lower than conventional air-source systems.
Tips for Buying and Using Whole House Heat Pumps for High Energy Efficiency
How to Buy an Energy Efficient Heat Pump
If you plan to buy a heat pump, there are too many factors for you to estimate how much electricity you would save. Many of the factors are listed above in Is a Heat Pump Right for You? Some heat pump manufacturers have a “Savings Estimator” on their websites, but this may give exaggerated savings. A split heat pump or mini-split heat pump would probably be a good investment if your heating bills are high and your climate is moderate because your air conditioning costs may remain about the same with a heat pump. Your savings from buying a mini-split heat pump would of course be high if you turn off the units in rooms when they are not occupied.
- Heat pump manufacturers and retailers give descriptions such as, “12,000 BTU, 13-SEER mini-split ductless heat pump”, and “One ton, 18-SEER mini-split heat pump”. A ton is 12,000 BTU’s/hr. Describing its capacity in BTU’s is incorrect because it is actually BTU’s/hr. Normally, the Btu’s/hr for cooling is given but not the Btu’s/hr for heating because they are close. The specification table will give them both. The SEER, which is the cooling efficiency, is given but not the heating efficiency, the HSPF, because the SEER is sufficient to describe the efficiency of the equipment.
Also, the HSPF is more complicated than the SEER rating because it takes into account supplemental heating needs, i.e., using electric heat when the temperature is too cold for the heat pump, and the energy used to defrost the unit, which depends on how often there is freezing temperature. A rule of thumb is, in warmer climates, a higher SEER is more important, and in colder climates, a higher HSPF is better.
- For better energy efficiency in the heating season, choose a heat pump with a high HSPF. For units with comparable HSPF ratings, check their steady-state rating at -8.3°C, the low temperature setting. The unit with the higher rating will be more efficient.The cooling efficiency may be given as the SEER or EER. The EER (Energy Efficiency Ratio) is the ratio of output cooling (in Btu/hr) to input electrical power (in watts), at 95° outside and 80° inside, with 50% relative humidity. The SEER (Seasonal Energy Efficiency Ratio) is similar except it is calculated for a typical year’s weather (temperatures and humidities) in a typical location. The EER for a heat pump (or any other cooling device) is about 87% of it’s SEER.
- A heat pump system must be sized and installed properly for maximum energy efficiency, so hire a well-qualified HVAC contractor. Heat pumps are sized for either the heating demand or the cooling demand, depending on which is greater. If it is too large it will cycle on and off more than necessary, wasting energy, and this may shorten it’s life by putting more stress on the equipment. If it is too small, it will cost slightly less to operate on most days but on the coldest days the supplemental electric heat will be used more often, wasting electricity.
An HVAC professional is trained to determine the home’s heating and cooling requirements, but these are difficult to estimate accurately, so many HVAC contractors tend to size the system larger than necessary to be safe. You may tell the contractor that it is better to install a unit that is too small than too large, to avoid any chance of installing a system that is too large.
- Heat pump systems require larger duct sizes than other central heating systems to obtain their maximum efficiency. If you are installing a heat pump system, it would not be cost effective to replace your ductwork, but the efficiency claimed by the manufacturer could only be achieved if the ducts were larger than those in your home.
- If your climate is relatively cold for a heat pump, the electric heat would be used often, so consider using some other type of auxiliary heat source than electric resistance heating. Electric resistance heat is used in the large majority of heat pump systems because the equipment costs much less to buy. It is simply large heating coils in the HVAC supply duct.
You may be able to adapt your gas or oil furnace that you were planning to remove, for auxiliary heat, to lower your heating bills. You can call your local utility company for information on how to do this. Some manufacturers of heat pumps offer a “hybrid” system; a conventional gas or oil furnace heats the home on colder days and the home is heated by the heat pump on moderate days. An intelligent controller determines which is most energy efficient from hour to hour. This system is expensive to buy, but may be a good investment for a large house in a cold climate. The combustion fuel could be propane, natural gas, oil, or even coal and wood.
- As mentioned above, whole house heat pumps that do not have ultraviolet C (UVC) lights often emit odors due to fungus, mold, and bacteria on the coils. This can create health problems and cause a reduction in heat pump efficiency. Thus, buy a heat pump with ultraviolet C lights.
- Fans and compressors can be noisy, so they should not be located near bedroom windows if possible, especially if you have single-pane windows. You can reduce this noise by choosing relatively quiet equipment or by mounting the unit on a noise-absorbing base.
- Heat pumps have many feature options which are designed for increased energy efficiency. The efficiencies, HSPF and SEER, basically reflect how many energy-saving options the heat pump has. These include:
- A desuperheater coil that heats water in the water heater by recycling waste heat. It greatly reduces the cost of heating water in homes that have electric water heaters.
- Dual-mode (two-stage) compressors and motors that save energy by adjusting up or down according to the level of heating or cooling needed.
- Scroll compressors which are quieter, more energy efficient and last longer than other compressors.
- Two-speed and variable-speed blowers. The control system determines when less air than normal should cross the coils, to use only the energy that is needed. The least expensive heat pumps have only one speed.
- Defrost Mode. Frost can form on the outdoor coils, which is insulation, making the heat pump less efficient. Heat pumps with defrost mode have sensors that determine when there is frost. Heat is then sent back outdoors to melt the ice. Conventional heat pumps do this on a time and temperature basis, wasting energy.
Tips for Using Heat Pumps for High Energy Efficiency
- If you are heating and cooling your home with a central heat pump, hire an HVAC contractor to do a tune-up and inspection every one or two years. The key components of your system are checked and adjustments are made to keep the system operating efficiently and extend its life. A very thorough tune-up and inspection will include:
- Checking carbon monoxide emission
- Inspecting tubes for refrigerant leaks
- Checking if the system has lost refrigerant. If refrigerant is lost the heat pump will be less efficient.
- Inspecting visible ductwork and flue pipe for air leaks. Air leaks in the ductwork reduce the unit’s efficiency.
- Checking the unit for peak efficiency and adjust if necessary
- Inspecting the indoor blower wheel and motor and recording amp draw (how much electricity it uses). If amp draw is too high it is wasting electricity.
- Checking for noise that indicates that the motor bearings are worn.
- Inspecting unit wiring and electrical disconnect
- Calibrating the thermostat.
- To improve the efficiency of your heat pump you can do some annual maintenance procedures yourself. The annual maintenance procedures that owners can do are given in the owner’s manual. If you don’t have the manual, try to find it on the manufacturer’s website or order it from the manufacturer. Some of the procedures that may be listed are given below in Maintenance You Can Do Yourself to Improve the Efficiency of Whole House Heat Pump
- Change the filter the first week of each month. A dirty filter reduces the airflow through the system, decreasing its efficiency and can lead to compressor damage if it continues for an extended period.
- Do not set back the temperature at night in the heating season unless you have a thermostat designed for heat pump set-back, the electric resistance backup heat would engage when the thermostat is raised in the morning, resulting in higher energy consumption.
- If the outdoor unit is closely surrounded by shrubbery, replant the shrubbery 2 to 3 feet away. Shrubbery traps heat, decreasing the coils’ ability to dissipate heat in the cooling season. Also, leaves could be drawn into the unit by the fan. This could cause the fan to create a vacuum back pressure that could shorten the life of the unit.
- Check that the outdoor unit is level. It must be level for maximum efficiency. If not, there could be problems with drainage and premature wear. If the concrete slab is very old, one side may have sunk into the ground. If not level, adjust the leveling feet or shim the feet with slate shingles or cedar shims.
- If high winds are common, plant shrubbery to block the unit from wind. High winds can reduce efficiency by allowing frost to form because the defrost cycles may be unable to melt it in high winds.
- Check if your heat pump cycles too often in the cooling season. If it cycles too often it is wasting energy. They normally cycle about three times per hour when the outdoor temperature is 95° to 105°. If yours cycles more than this your thermostat may not be working correctly or the filter is clogged or the blower is malfunctioning. Replace the filter, and if this doesn’t help you should call an HVAC technician.
- Buy a programmable thermostat designed for heat pumps and use it to set back the temperature when heating (not cooling). All other programmable thermostats can cause the unit to operate inefficiently, canceling out any savings achieved by lowering the temperature setting. Programmable thermostats designed for heat pumps are available at home centers.
- Do not allow run-off from the roof to fall on the outdoor unit. This could cause ice buildup.
- Never use a weather cover over the outdoor unit. This will trap moisture, causing rust and damage to electrical parts.
- If the outdoor unit is exposed to summer sun, build a plywood roof for it to give it shade and increase its efficiency at cooling. The refrigerant releases its heat energy at the coils through radiation, allowing it to condense from hot gas to liquid. When radiation from the sun heats the coils, the refrigerant enters the house at a higher temperature, making the heat pump less efficient. See How to Build a Roof for a Heat Pump Condenser Unit
- If a room or section of your home has no HVAC ducts leading to it for heating and cooling and you use electric space heaters and window unit air conditioners to heat and cool it, you could lower your energy costs by using a mini-split heat pump. See Split-Ductless Heat Pumps It could be a poor investment to buy and operate if you use it while heating and cooling the rest of the home, but it would allow you to turn off the central heating and air conditioning when using only that room. The investment would include the cost of mounting it and installing a new circuit for it.
- If you have freezing weather, do not install a condenser unit under a gutter that overflows when it isn’t cleaned. If water drips onto the unit and freezes, the coils could become covered with ice.
- Post this list of energy tips on the wall next to the heat pump:
- Change the filter the first week of each month.
- (if your thermostat is not designed for heat pump set-back) Do not set back the temperature in the heating season.
- If you do not have a variable-speed fan, do not run the fan continuously, except on “auto” fan setting on thermostat. This can degrade heat pump performance.
- Call a service technician if you see excess ice buildup or hear excess noise.
- Call a service technician if the indicator light shows that resistance heat is being used.
Create a Zoned HVAC System for Greater Energy Savings
To save energy using a heat pump you could hire an HVAC contractor to install flow control valves, called “dampers” in some of the HVAC ducts. These allow you to reduce or shut off the heated or cooled air to individual rooms or areas of your house. For example, you could shut off the hot or cold air to the second floor during the day and to the first floor at night.
To install dampers throughout your house will probably cost from $2000 to $3000, but you can of course spend much less by installing them only in ducts leading to rooms or zones where you don’t need as much heating or cooling.
There is a major challenge in creating a zoned system, so you must hire a well-qualified contractor. The HVAC duct system in a home has two or three branches. If a duct that feeds air to a single room is partially or completely closed by a damper, more air flows out of the other registers on that branch, so the same volume of air is blown into the house. Closing a damper only saves energy if the thermostat is in a location where it receives the extra heated and cooled air, keeping the temperature the same there when the damper is closed.
For example, if the flow of cooled air to a second floor bedroom is shut off by a damper, the other second floor bedrooms will become cooler if the thermostat is on the first floor. If the thermostat is on the second floor hallway, the temperature will not change for the second floor, so less cold air will be delivered in the house and your costs will be reduced. A common way to zone a system is to put the first floor on one zone with a thermostat and the second floor on another zone with its own thermostat. You could, for example set the downstairs thermostat to receive much less heated or cooled air at night when nobody is normally there.
Maintenance You Can Do Yourself to Improve the Efficiency of a Whole House Heat Pump
You can save energy using heat pump if you do some simple maintenance that is often recommended for home owners to do.
- Clean the outdoor coil. Dirty coils reduce the heat pump’s efficiency. They are in the outdoor unit in the yard or on the roof.
- You must first shut off the power to the heat pump at its electrical disconnect switch. This is outside in a weatherproof metal box located near the heat pump. Also, turn off the circuit breaker for the unit in the main electrical service panel. Then, wait a few minutes to allow any stored electrical charge in the unit’s capacitors to dissipate.
- Remove the cover on top of the and the protective side grille. Be careful not to break any wires.
- Remove any leaves or pieces of debris from the outside of the coils. Vacuum the coils, being careful not to bend them. Spraying it with a garden hose could bend the coils.
- From inside the outdoor unit, spray water through the coils through to the outside to remove debris.
- If your owner’s manual recommends that you oil the fan motor bearings, do this also.
- While the cover and side grille are removed, straighten any bent fins inthe outdoor unit. Bent fins restrict air flow, causing the unit run harder, decreasing its energy efficiency so it uses more electricity. Fins are made from delicate thin metal and can be damaged by sticks falling from a tree, hail, or power washing. A fin comb is used to straighten bent fins of a condensing unit for an air conditioning or heat pump system. These tools may come with single, multiple or interchangeable heads that have different fin comb sizes and counts to best match the coil fin size of the repaired unit. Some six sided head models will work for 8, 9, 10, 12, 14 and 15 fins per inch coils. The comb is carefully drawn across the bent coil fins straightening them out in the process. They are sold at plumbing stores and can be ordered at some home centers.
- Inside your home, periodically clean or replace the filter in the duct. Do this every 6 months, or more frequently if it becomes clogged with dust in less than 6 months. The filter is located where the return duct meets the heat pump, in the duct or in the heat pump. The filter will be either disposable or washable—this should be marked on the filter’s edge, along with directions for cleaning. If the filter is washable, it is good to have a spare so you can wash it and leave it out all day to dry. There are a wide variety of HVAC filters. The disposable filters designed to remove the most particles cause the most resistance to airflow, causing the system to be less energy efficient. The least expensive disposable filters trap only large particles and may allow the components of your system to become too dirty.
- Inside your home, clean and lubricate the fan motor, but only if your owner’s manual includes this among the maintenance procedures that homeowners can do. Check for a loose fan belt.
- Inside the home, adjust the blower unit and the drive belts if instructions for this are given in the manufacturer’s instruction booklet. This will improve the efficiency of the heat pump.
How to Build a Roof for a Heat Pump Condenser Unit
- Sledge Hammer
- Framing Square
- Tape Measure
- 1/2” thick plywood or 1” thick boards
- (7) 8’ 2×4’s
- 12d nails or 3” deck screws
- Package of shingles
- ¾” roofing nails
- 8d nails or 2” screws
- 4’ of ½” EMT pipe (sold in the electrical dept. of home centers)
- Cut the pieces of the frame from 2×4’s. The top should have a slight slope, be a foot above the condenser (so heat isn’t trapped), and be large enough to shade the condenser throughout the day. If the condenser is east or west of the house, the roof should be large enough to shade the condenser when the sun is low.
- Using 3” deck screws or 12d nails, build the top of the frame and mount the legs. Nail or screw on a piece of 2×4 as a diagonal (not shown on dwg). Place it over the condenser. Drill two ¾” holes through each piece of the frame that rests on the ground, and nail or screw these to the legs (see drawing).
- Cut ½” EMT pipe into four 12” pieces to use as stakes, with one end of each cut to 45º to penetrate the ground. Flatten 1” of the other end with a sledgehammer and bend it over. This end will hold down the board. Pound the stakes through the holes until the ends rest on the boards.
- Using 1/2” plywood or 1” boards, cut the wood for the roof. Fasten it to the frame using 8d nails or 2” screws.
- Cut the shingles with a utility knife and nail them to the roof with ¾” roofing nails.
I hope you will consider all of these types of heat pumps before choosing one, and try my suggestions for improved heat pump efficiency, and enjoy much lower electric bills!