Heat Trajectory

There are a number of potential pathways to decarbonise heat. At present, according to CCC analysis presented in Net Zero the UK Contribution to solving Global Warming . less than 5% of energy used for heating homes and buildings comes from low-carbon sources While we think that this might be a little pessimistic (as many commercial buildings are already all electric and the use of electricity for heating is not a statistic that is centrally collected) there is no doubt that decarbonising heat is a a major challenge.

Heat Pumps

Heat pumps are one of the key pathways for decarbonising heat. See Heatpumps. These devices can be used for heating, cooling and heat sharing. As explained in the section on heat pumps, the energy gain in heating mode depends on the temperature of the heat source. A higher co-efficient of performance is obtained when the delivery temperature is closer to the temperature of the heat source.

Carbon savings from heat pumps are therefore based on two parameters. The first is the carbon intensity of the electricity used to run it. If this comes from the UK electricity grid this will be the grid intensity. The second is the COP of the heat pump. This in turn primarily depends on the temperature of heat source and the temperature of the delivered heat. There are many other considerations (including electrical and mechanical efficiency of the actual plant and the seasonal variation in source temperatures) and but for determination of the carbon trajectory of heat pump based heating systems these are the key parameters.

The diagram on the left shows the carbon trajectory for heat supplied by heat pumps at various COP’s. The diagram also show a reference line for heat supplied by gas boiler fed by natural gas. A COP of 1 can be thought of as direct electrical resistance heating (such as an electrical heater element). The diagram shows that direct resistance heating is at a lower carbon intensity than gas as early as 2021.

Taking a typical COP of 3.5 for a good Heat pump installation we can show the savings over gas as the difference between the reference line for gas and the carbon intensity of the Heat pump at that COP.

The diagram shows the trajectory as kg CO2e / kWh of heat delivered, carbon savings from switching to heat pump from gas boilers. This illustrates that the heat trajectory delivers increased savings with time as the electricity grid intensity falls.