Understanding Air-Source Heat Pumps

There are two main types of heat pumps connected by ductwork: air-to-air and ground-source (or geothermal). These systems collect heat from the air or ground outside your home and concentrate it for use inside. Absorption heat pumps (or gas-fired heat pumps) use heat or thermal energy as their energy source. The most common type of heat pump is the air-source heat pump, which transfers heat between your house and the outside air.

Air-source heat pumps are electrical appliances that sit outside and are used to extract heat from the outside air for indoor heating, and for domestic hot water if required; they deliver heat in the winter and air conditioning in the summer. They are a competitive option to a traditional furnace and central air conditioning system and provide you with all-season comfort.

How They Work
Air-source heat pumps use electricity to transfer energy between indoor and outdoor air. Because they move heat rather than generate heat, these systems consume far less electricity than electric furnaces, baseboard heaters or space heaters.

In cooling mode, the heat pump functions like an air conditioner, moving heat from inside to outside the home. In heating mode, the refrigerant flow is reversed to extract low-temperature heat from outdoors and deliver concentrated high-temperature heat to the home.

An air-source heat pump consists of three main components: an outdoor unit, an indoor unit and a refrigerant.

1. The outdoor unit contains a fan that draws in air from the surroundings.
2. The air passes over an evaporator coil containing a refrigerant, which absorbs the heat from the air and evaporates becoming a gas.
3. The evaporated refrigerant is then compressed by a compressor, which increases its temperature.
4. The hot gas then passes through a heat exchanger where it transfers its heat to water that circulates throughout a building via piping and ductwork, releasing the heat into your home.
5. The cooled gas then passes through another heat exchanger where it absorbs heat from the indoor circulating ductwork returning to the evaporator coil where the cycle repeats.

Maximizing Efficiency and Performance

Air-source heat pumps are highly efficient heating systems, capable of producing more energy than they consume. Their efficiency can be measured by its Coefficient of Performance (COP), which is the ratio of heat output to electrical input. A higher COP indicates a more efficient system. Depending on conditions, they can achieve COPs of 2 to 4, meaning they produce 2 to 4 units of heat for every unit of electricity consumed. This high efficiency is because most of the heat generated comes from the ambient air, a free and renewable energy source.

While the COP will be set by the manufacturer and model of the air-source heat pump through its design in efficiency, there are a few things that can be done to help ensure that a heat pump is running as efficiently as possible:

Insulate your home

This helps heat to remain inside for a long as possible, therefore helping to reduce the demand on a heat pump to provide the desired indoor temperatures and using less energy.

Use a programmable thermostat

A programmable thermostat can help improve the COP. A thermostat can be used to set heating times and temperatures so that a heat pump doesn’t have to work as hard to meet high user demand, such as when you’re away from home or asleep.

Regular maintenance

It’s important to have your air-source heat pump serviced by a qualified technician, typically once a year. This will help ensure that it runs at peak efficiency and does not use more energy than necessary. Contact your local Lennox Dealer to schedule your yearly service.

More efficient heating system

The indoor heating setup can be just as important as the heat pump. Since air-source heat pump systems work at lower heating temperatures than other heating systems, more importance is placed on the internal heating equipment to release the heat as effectively as possible. For air to water heat pumps, the use of large surface area equipment such as underfloor heating and modern radiators can help improve overall efficiency.

Types of Air-source Heat Pumps

• Ducted systems take heat from the air and send it to a central indoor unit, then distribute it throughout your home via a system of ducts. For cooling, the heat is taken from indoors and moved through the ducts and back outside.
• Ductless systems work by moving hot air from the outside into your home to provide heat. For cooling purposes, they take the hot air out of your home and move it outside. They blow the heated or cooled air directly into the room through line sets that connect the heat pump to the indoor air handlers.
• Single-stage systems are the most basic. They have two settings: on or off, where they operate at full capacity or not at all. Single-stage systems are usually the most expensive to operate and often installed when trying to heat and cool a specific area of the home, such as add-on rooms, that weren’t ducted.
• Two-stage systems have two speeds. During moderate temperatures it runs on the lower speed, avoiding the short cycle condition and providing better overall comfort and more efficient operation.
• Variable-speed systems run almost continuously, and since they don’t go through the startup phase as often, variable speed units lower your utility costs.

With advancements in technology, heat pumps are now suitable for a variety of climates and applications. A few relatively new innovations are improving their performance, such as being equipped with a desuperheater, scroll compressor and back-up burner.

• A desuperheater recovers waste heat from the heat pump’s cooling mode and uses it to heat water and can heat water two to three times more efficiently than an ordinary electric water heater.
• A scroll compressor consists of two spiral-shaped scrolls. One is stationary while the other orbits around it, compressing the refrigerant by forcing it into increasingly smaller areas. Compared to the typical piston compressors, scroll compressors have a longer operating life and are quieter.
• Back-up burners help solve the problem of the heat pump delivering relatively cool air during cold weather and reduces its use of electricity by providing supplemental heat.

There are many factors to consider, such as the size of your home, the climate of your area, your budget and your personal preferences. Lennox provides many heat pump solutions for your needs. If you’re upgrading your home with a new air-source heat pump, you may be eligible for a tax credit or rebate.

Benefits of Air-source Heat Pumps

Comfort
Air-source heat pumps provide extremely consistent temperature, avoiding the hot and cold spikes common in traditional heating and cooling systems. They don’t turn on and off at certain temperatures. Instead, they continuously run to maintain the desired temperature. In addition, they help improve air quality through air filtration and reduce allergens in the air as well as help to dehumidify your environment, making your living spaces more comfortable.

Quiet Operation
Because heat pumps deliver a steady supply of temperature-controlled air, noise caused by the expansion and contraction of heat ducts is eliminated. In addition, both the indoor and outdoor air-source heat pump components are whisper quiet, mainly if you're using ductless mini-splits.

Cost Savings
Switching from propane, fuel oil, an electric furnace or electric baseboard heating will result in significant savings every year. An efficient heat pump consumes less electricity, resulting in lower energy bills. The higher the COP, the more energy efficient the system, leading to significant cost savings over time.

Energy Efficiency
Can provide significant energy savings compared to traditional heating and cooling systems by transferring heat rather than generating it. To choose an electric air-source heat pump, look for the ENERGY STAR® label, which is independently certified to save energy, save money and protect the climate. In warmer climates, SEER is more important than HSPF. In colder climates, focus on getting the highest HSPF feasible. Lennox provides many ENERGY STAR® heat pumps.

Flexible

In existing homes, an air-source heat pump is an easy upgrade because there are systems designed to work in almost any application, with or without air ducts. In a new home, heat pumps provide additional flexibility by eliminating the need for both ductwork and a furnace exhaust vent.

Simplicity
Having one system for heating and cooling simplifies your maintenance regimen when compared to a traditional system.

Reduced Carbon Emissions

Air-source heat pumps are a low-carbon heating technology, and their efficiency contributes to further reducing carbon emissions. By utilizing renewable energy from the air, air-source heat pumps help combat climate change and reduce environmental impact.

Now that you have more information about the differences among single-stage, two-stage and variable-speed systems, you can choose the right system for your home. As you have learned, climate, energy efficiency, your geographic location and budget can all play a role in helping you determine which system best fits your unique needs. A local Lennox pro can provide a professional consultation to help in your decision.

This article has been reviewed by Nick Orth, Director of Outdoor Cooling, for accuracy. Nick brings 20 years of expertise in the HVAC space.