Heat Pumps - Are they really more efficient than traditional means?

HVAC represents 38% of an average building’s energy consumption. In a world where preserving the planet is becoming a priority, scientists are looking for alternative, more ecological solutions, particularly in the heating/cooling sector which is highly energy-intensive. Today we are going to focus on heat pumps that offer a more environmentally friendly alternative to traditional means of heating and cooling.

Heat pump is a central heating system, based on the circulation of a refrigerant in a closed circuit, that can be reserved for heating and cooling. This refrigerant is a fluid that can be compressed and expanded.

This technology can either capture the heat in the outside air and transfer it inside to heat a room or capture the heat in the room and release it outside to cool it. To cool a room, the process is similar except that the heat is taken from the inside instead of the outside.

How a Heat Pump Works?

A heat pump is composed by 4 main elements:

• An evaporator whose purpose is to extract calories (calorie is a term used to refer to heat) from the ambient air outside. Indeed, thanks to a contact between the evaporator and the outside, the refrigerant (liquid) will capture the calories of the outside air, which is hotter than the refrigerant. This temperature difference causes the heat to flow spontaneously from the warmer source to the colder source. The refrigerant will then boil and evaporate as it recovers these calories.

• A compressor in which the gaseous refrigerant enters and is compressed to raise its temperature. Indeed, compressing the gas raise its pressure and thus its temperature.

• A condenser that transmits the calories contained in the refrigerant to the air in the house. In fact, the refrigerant, at high pressure and charged with calories, transfers this heat to the air inside the house: the interior room is heated. At the same time, the temperature of the refrigerant drops and it returns to the liquid state: this is condensation.

• An expansion valve which, once the refrigerant has returned to the liquid state, will lower its pressure. At the outlet of the expansion valve, the refrigerant must have returned to a temperature lower than the outside air, so the liquid passes from a high pressure to a low pressure. This decrease in pressure and therefore in temperature is necessary to capture heat during a new operating cycle.

Currently, there are three types of heat pumps: air-to-air, water source, and geothermal, which are differentiated by the fluid that gives and that receives the calories. Air to air heat pumps use calories from the air to heat or cool the air of a building. Geothermal heat pumps transfer heat from the ground to the buildings and water source heat pumps extract calories from water.

Are Heat Pumps Energy Efficient?

Energy efficiency in HVAC systems is measured by a factor called Coefficient of Performance or COP or Energy Efficiency Ratio (EER). Efficient heat pumps have a COP of at least 3 and air conditioners a EER of at least 12. With a COP of 3, a heat pump that consumes 1 kWh of electricity produces 3 kWh of heating. In comparison, a gas boiler would have a maximum efficiency around 0.9 and air conditioner has an average EER of 8.5.