With many people spending more time than usual in their homes this year, how can the environmental cost of heating them be reduced?
When it comes to heating, retiree Lucy Craig’s bungalow in north London is high tech. A self-professed gadget lover, when she refurbished eight years ago, she was keen to find the most carbon friendly methods for keeping her home warm. She settled on heat pumps.
Outside her house, all that can be seen of the pump is an innocuous metal box. Inside the machine is a closed circuit of liquid that cycles in a pipe running from the box outdoors to a water tank indoors. This liquid is a refrigerant with a very low boiling temperature, so even winter air has enough energy to vaporise it. At the outdoor box, the heat pump fans air over the refrigerant, helping it to absorb heat, which it then transfers to the water tank inside the house.
Craig has one of these pumps to generate hot water for an underfloor heating system and another that generates hot water that runs from the taps. On her countertop, an owl-shaped monitor on the tells her how much she is using. It’s usually good news. Heat pumps use only around a quarter of the energy needed for a traditional gas boiler and Craig is able to get the electricity needed to keep the system running from solar panels she has had installed on her roof.
What makes heat pumps so efficient is the refrigerant gas inside the network of pipes. It flows through a cycle of evaporation and condensation as it absorbs heat from the air, turns to vapour and is then compressed with an electric-powered pump. This compression step helps to concentrate the energy stored in the refrigerant. When it gets inside, the refrigerant cools and condenses as it transfers its heat to the water in the inside tank.