How Does A Heat Pump Work?

A heat pump works like a air conditioner in reverse. Where an air conditioner takes heat from the warm interior of a house in the summer time and pumps that heat to the warmer outside, a heat pump draws heat from the cool to cold outside (even down to - 20 C) and pumps that free environmental heat to the house interior (see the explanation below). In a central heat pump system the indoor heat exchanger (coil) is in the furnace. In a split system the indoor heat exchanger (coil) is on one or more wall units.

The free environmental heat that the heat pump gathers makes a heat pump very efficient. Some energy is required to pump the outdoor heat but typical seasonal heating efficiencies for populated Canadian locations (i.e. not the far north) are around 2.3:1 or in other words for every 1 kWh of electric energy that is used operate the heat pump, the house receives 2.3 kWh of heat over the heating season.

This image shows a "split" or ductless heat pump system. It's used to assist heating a space within a house without a forced air duct supply like the kitchen/living room or the master bedroom area of an electrically heated townhouse.

How does it work?

The heat pump's exterior unit consists of a housing with a compressor, heat exchange coils and a fan. The interior unit consists of a wall mounted housing with a coil and fan. In addition refrigerant lines provide "tubes" for the refrigerant to conduct the energy from the outdoor to indoor in winter and vice versa in summer. In winter the compressor takes outdoor temperature refrigerant and compresses (squeezes) it down in volume which raises it's temperature. 

Insulated tubes (lines) conduct this high temperature refrigerant to the indoor coil where it's heat is released and the compressed gas actually condenses (like steam to water) as it releases it's heat. The return refrigerant lines conducts the liquid refrigerant back to the outdoor unit still under pressure to an expansion valve where the refrigerant expands (like air at the nozzle of a compressed air gun) into the outdoor coils. The expanded refrigerant in the outdoor coils is much cooler than the outdoor air and receives heat from the outdoor air that is passed over it by the outdoor fan. This received heat from the outside air is the "free" environmental heat. The compressor then again compresses this "warmed" refrigerant and sends it around for the next cycle.

Heat Pumps Typically Lower GHG Emissions

Electric utilities with relatively clean (low GHG emissions) electrical supply can reduce a house's GHG emissions by replacing the high GHG emission fossil fuels (natural gas, fuel oil or propane) furnace or boiler with a heat pump. Primarily the clean environmental heat that is gathered by the heat pump is emissions free and secondly the clean (low GHG emission) electricity supplied by the utility is much less polluting than using fossil fuels.

We do studies to advise on if this system significantly lowers your GHG emissions and is economical too. See our fees webpage for the Space Heating Fuel Transition to Heat Pump Study fees.

© 2020 by the Building Science Trust inc. Design by Ben