What Is An Air Source Heat Pump (ASHP)? Your Go-To Guide

October 14, 2021
 | 
Evan
 
Montilla

Whether you’re dealing with constant HVAC repairs or you’re looking for an eco-friendly upgrade, air source heat pumps make sense. At BlocPower, we help building owners find systems that meet their unique energy needs, and heat pump technology offers numerous advantages over boilers, furnaces, and other combustion systems. 

In the United States, adoption of air source pumps has been relatively slow, partially because of misunderstandings about the technology. At one point, combustion heating systems offered more dependable operation in cold climates. That’s no longer the case, and for the vast majority of buildings, air source heat pump retrofits are a superior option.

So, what is an air source heat pump—and is it an appropriate solution for your building? In this article, we’ll explain the basic functionality and clear up some common misconceptions.


Ready to upgrade to an eco-friendly heating and cooling system? BlocPower’s experts can help you install an efficient system while taking advantage of incentives. See if BlocPower is available in your area.

What is an air source heat pump?

An air source heat pump (also called an ASHP or an air-to-air heat pump) is a complete heating and cooling system that doesn’t depend on fossil fuel combustion. In many Asian and European countries, air source heat pumps are the standard technology—they offer excellent efficiency with few drawbacks. 

Essentially, the technology uses ambient air from outside the building as either a heat source or heat sink. The method of operation is similar to a refrigerator, although heat pumps are significantly more complex technology.

Basic heat pump system components include:

  • Outdoor Condenser and Evaporator Unit - A fan collects ambient air and moves that air over a coil, creating a heat exchange.
  • Indoor Air Handler Unit - The indoor unit also contains a coil. Air moves across the coil, and then a fan blows the hot or cold air into the room (or through the building’s ductwork). 
  • Compressors - As with traditional AC units, a heat pump contains a compressor, which pressurizes the refrigerant to allow it to move throughout the system. The system reuses the refrigerant for the entire life cycle of the pump. 
  • Reversing and Expansion Valves - The reversing valve changes the flow of the refrigerant, which allows the pump to provide both heating and cooling. An expansion valve reduces the pressure and temperature of the refrigerant, regulating its flow to meet the required temperature.

These components function in the same basic manner, regardless of whether the pump provides cold or hot air—the reversing valve determines whether the ASHP is heating or cooling the building. 

How does air source heating work? 

Heat pumps move heat, but they don’t generate heat. That’s a major difference between ASHP technology and traditional options like furnaces and boilers: A heat pump draws heat energy from ambient air, even in cold climates. A refrigerant allows the system to move the energy into (or out from) a building.

In heating mode, the ambient air from outside the building acts as the heat source. This is possible even when the ambient air is cold; the heat pump’s refrigerant can extract heat even in cold climates. 

So, how do air source heat pump systems work? Here’s an overview of the process:

  1. Ambient air moves across the indoor coil, heating the refrigerant into a gas. 
  2. The outdoor unit applies pressure to this gas, which creates a hotter gas.
  3. The indoor unit acts as the condenser. The refrigerant condenses back into a liquid, releasing its heat. This stored heat is transferred throughout the building through ductwork or other heating delivery systems. 
  4. The refrigerant moves to the outdoor unit, which relieves the pressure. The refrigerant turns cold, which restarts the cycle.

Excess heat can be used to generate hot water. Many large residential buildings maintain separate water heating systems, but in some instances, a properly sized heat pump system can provide most (or all) of the building’s hot water.

How does air source heat pump cooling work?

For air source heat pump cooling, the basic process is reversed. The indoor unit acts as the evaporator, and the outdoor unit acts as the condenser. Air from inside the building moves across the coils, and the refrigerant absorbs the heat energy. 

This process evaporates the refrigerant, creating a gas. The gas moves to the outdoor unit, which releases the pressure, returning the refrigerant to liquid form. The reversing valve determines whether the outdoor or indoor unit acts as the evaporator or condenser.  

Types Of Air Source Pumps

While air source pumps use similar technology, different systems are available to meet the needs of different types of buildings. In new installations, air source systems are often ductless. However, if a building has an existing ventilation system, installers can connect the outdoor condenser to the ductwork. Passing air through the ductwork diminishes the efficiency of the heat transfer, but ducted ASHP systems are still much more efficient than combustion systems.

Common heat pump options include:

  • Mini-Split Heat Pumps - Mini-split systems have one indoor unit and one outdoor unit. All zones covered by a mini-split system must have the same set temperature; building managers may install separate mini-split systems for each room to get around this limitation.

  • Multi-Split Heat Pumps - Multi-split systems allow individual rooms to set different temperatures. Multiple indoor units connect to one (or several) outdoor units. However, the system can only provide one type of temperature control at a time—the system is either heating or cooling.

  • Variable Refrigerant Flow (VRF) Heat Pumps - VRF systems have an outdoor unit and multiple evaporators, similar to multi-split systems. They can change the flow of refrigerant while operating, which allows them to provide heating or cooling to each indoor unit. 

Most residential, commercial, and multi-use properties use mini-split or multi-split systems. VRF systems have significant advantages for larger commercial and residential buildings, and when properly installed, VRF technology can provide numerous benefits for both residents and building owners.

Common Myths About Air Source Heat Pumps

Air source heat pumps are an energy-efficient, ecologically friendly technology. Nevertheless, North American adoption has been slow, partially due to misunderstandings about limitations. Here’s a look at some of the most common misconceptions.


“Air source heat pumps can’t operate in colder climates.”

At one time, this was partially true; at temperatures of 15°F or below, heat pumps became less efficient (and more expensive) than traditional gas combustion systems. Many building owners maintained secondary heating sources after installing heat pumps—when the ambient air dropped past a certain temperature, they would allow the boiler to fill in the gaps. 

BlocPower specializes in cold-climate air source heat pump installation. Cold-climate ASHPs feature improved thermostatic expansion valves and coil designs, along with other innovations that allow them to operate reliably at up to -15°F. They’re 100% efficient down to 5°F, and even at colder temperatures, cold-climate ASHPs lose little efficiency.

“Retrofitting isn’t possible for some older heating systems."

In older buildings, air source heat pumps are an efficient option for heating and cooling. Installers can use the building’s ductwork to deliver heating and cooling to residents. We’ve handled retrofits for older houses of worship and other like-commercial buildings that have extensive heating and cooling needs; heat pumps are always preferable to combustion technologies.

“Air source heat pumps are too expensive.”

Eco-friendly heating technologies can be expensive, but state and municipal energy programs can bring down the cost substantially. Heat pumps also save money over time by improving efficiency: Per the Northeast Energy Efficiency Partnership (NEEP), single-residence cold-climate heat pumps deliver an annual savings of around $459 on average as compared to oil systems. NEEP’s analysis focused on homes in the Northeast and Mid-Atlantic regions.

For larger buildings, the annual savings can be even greater—provided that the system is appropriately designed and professionally installed. At BlocPower, we work with our clients to find options that are affordable and optimally suited for the local climate.

“Air source heat pumps are noisy."

The outdoor units of air source heat pump systems typically operate around 50-60 decibels (dB), which is equivalent to the noise level of light rainfall. Indoor units can be even quieter, with decibel ratings of around 25 dB.

In cities like New York, noise isn’t a significant consideration—especially when accounting for the fact that some traditional air conditioning units can reach noise levels over 80 dB. Proper installation helps to decrease noise levels, and low-noise exterior units with an output of around 35 dB are available for applications that require them.


Air Source Heat Pumps: Many Advantages, Few Drawbacks

When right-sized to a building, heat pumps can cut heating and cooling bills drastically immediately after installation. They require limited maintenance—BlocPower offers bi-annual and annual maintenance services—and they’re more versatile than boilers, furnaces, and other fossil fuel infrastructures.

For optimal benefit, air source systems need to take advantage of recent technologies. Metrics like seasonal energy efficiency ratio (SEER) and heating seasonal performance factor (HSPF) can provide useful insights when selecting systems. Professional right-sizing and installation can help to improve efficiency. Our clients report energy bill savings of up to 40%.

BlocPower's expertise enables building owners to take advantage of energy incentives, and with flexible financing options, we’re ready to help you install a modern electric system. Get started by answering a few quick questions about your building.

Back to Blog Posts