Choosing the Right Heat Pump

AERMEC – Geothermal heat pump

Heat pumps extract heat from exterior air, water, or the ground and transfer it to the building’s heating system. While the initial installation cost might be high for certain types of heat pumps, the long-term gains can be worthwhile. Many heat pumps can currently produce up to three or four times the energy they consume in electricity. Reversible systems can also be used for building cooling.

Here are the main points to consider when making your choice:

• How it works
• Types available
• Heat pump sizes
• Technical features
• Options and trends

Heat pumps function similarly to refrigerators and air conditioners, using the same principles.
They are made up of four main elements: an evaporator, a compressor, a condenser, and an expansion valve.

• An evaporator works as a heat exchanger to extract the heat from the exterior source and evaporate the refrigerant.
• A compressor increases the pressure and circulates the refrigerant.
• A condenser works as a heat exchanger to transfer the heat from the refrigerant to the interior heating system, so the refrigerant loses heat and condenses.
• An expansion valve is used so that the refrigerant returns to its liquid state, completing the cycle so that it can evaporate again.

Reversible heat pumps work in reverse to cool an interior space in the same way as air conditioners: The interior heat exchanger becomes the “evaporator”, extracting the heat from the room. The exterior heat exchanger becomes the “condenser” and transfers the heat to the exterior.

FRISQUET Air_water heat pump

Heat pumps can be split into three main types: air source, ground source (geothermal), and water source. The type you choose will depend on factors such as the heat source(s) and installation space available, the existing heating systems, and your budget.

Air source heat pumps extract heat from outdoor ambient air and transfer it indoors. They can be air-to-air or air-to-water.

Air/air heat pumps transfer the heat to interior air handling units, which blow the air directly into one room, or into different spaces via a ducted system. They can be used in reverse as air conditioners. They are an economical and easy-to-install choice for small homes, apartments, and commercial spaces but cannot be used for hot water heating.

Air/water heat pumps transfer the heat from the air to a wet central heating system such as hot water radiators or underfloor heating. Some models can also be used to heat domestic hot water. Although air-to-water heat pumps tend to be more expensive than air-to-air, they are a popular choice for buildings with existing central heating systems because they can be easily installed and do not require ducting or air-handling units. Be sure to choose a heat pump that is compatible with the existing heating installation. For example, check whether it is a high-temperature or low-temperature system.

ROTH water-to-water heat pump system

Geothermal heat pumps use a heat transfer fluid such as antifreeze and buried pipes to extract heat from the ground. The heat transfer fluid is then compressed through the heat exchanger to transfer the heat to the heat pump. They tend to be very efficient because the ground temperature stays more stable than the air temperature throughout the year. However, installation can be costly and the depth and surface area of the ground required for it will depend on the heating and cooling needs of your space. It is best to get professionals to calculate this. For ground/water systems, the heat is transferred from the heat pump to the heating system and/or domestic hot water system.

Water source heat pumps work in a similar way to geothermal systems, except the pipes are submerged in a body of water such as a lake, river, or pond. If the water is close to your property, this might be easier to install than a buried geothermal system. For water/water systems the heat pump transfers the heat to the central heating system and/or domestic hot water system. Water source heat pumps tend to be more efficient than air source heat pumps because heat transfers better through water and large bodies of water tend to hold a more stable temperature throughout the year.

While some heat pump manufacturers provide general guidelines on sizing, the best solution is to work with an experienced contractor or get an energy audit. Factors such as how well the building is insulated will influence the type of heat pump and heating system you’ll need to choose. The output of most heat pumps falls in the range of 4 to 16kW.

Consider the following technical points when choosing your heat pump:

• Noise level (in dB): Think about the noise level of the exterior unit (and interior unit depending on the system).
• For heating efficiency, check the coefficient of performance (COP) which is the power output (W) / the power input (W) measured at certain temperature conditions. The higher the rating the better. For example, a heat pump with a COP of 3 produces three times the amount of energy than the electricity it consumes.
• For cooling efficiency, check the energy efficiency ratio (EER) which is the cooling capacity (in BTU/h) / power input (W) measured at certain temperature conditions. As with the COP, the higher the rating the better.
• Check the seasonal energy efficiency ratio (SEER) for cooling systems and the seasonal coefficient of performance (SCOP) for heating systems, which take into account performance at different temperatures over a season and the energy consumed in watt-hours.
• Energy certifications: Consider whether the appliance has a performance certification such as an Energy Star rating (used in the US) or the EU Ecolabel, as they often take into account multiple performance factors such as power output, energy consumption, and noise level and provide a classification based on these criteria, making it easier to compare units.

KERMI Hybrid heat pump

Discovering current options and trends can help you keep up with evolving regulations, such as those created to reduce energy consumption. Here are the current heat pump options and trends to consider:

• Hybrid heat pumps connect a second source of energy (such as solar collectors, gas, or pellet boilers) to ensure optimal energy use and comfort in cases where the heat pump might lose efficiency, such as in extreme cold.
• Inverter heat pumps have variable-speed compressors that can save energy compared to fixed-speed ones. They regulate the room temperature by varying the speed of the compressor motor, adjusting the output to the required level rather than stopping and starting.
• WiFi-connected heat pumps allow the heating and cooling to be monitored and controlled at a distance.