GSHPs in District Heating
DECC published Heat Pumps in District Heating in February 2016 which recognises the value of using heat pumps in district heating to lower carbon emissions, in place of central gas boilers or gas-based CHP.
The full report Heat Pumps in District Heating runs to 135 pages. The following is an extract of some of the key findings:
- Alongside a decarbonising grid, integrating heat pumps into district heating offers large CO2 emissions reduction potential.
- The analysis showed that incorporating heat pumps into district heating schemes has the potential, in the context of a rapidly decarbonising electricity grid, to offer large CO2 savings relative to district heating based on either gas-CHP (for large schemes) or gas boilers (for small schemes). Assuming the current trajectory towards low carbon electricity generation, we found CO2 savings versus gas burning schemes in the range 48-84%.
As may be expected from simple thermodynamic arguments, we showed that the CO2 savings are greater where the following scheme characteristics are combined:
- Heat pumps provide a larger fraction of the heating
- Heat pumps operate with a lower source-sink temperature difference, leading to increased efficiency
- Network thermal losses are lower, especially for lower temperature distribution networks with building integrated heat pumps
Networks based on heat pumps offer the greatest CO2 savings
As a result, we found that, of the various configurations studied, low or medium- temperature networks based entirely on heat pumps offer the greatest CO2 savings potential.
It is important to note that heat pumps bring potential additional benefits that may shift the economic balance in their favour compared to the alternatives. In particular, the ability to provide cooling as well as heating has been found to be a key driver for the use of heat pumps in heat networks.
The speed of replacement of gas with Heat Pumps in District Heating will depend on financial support
The extent to which heat pumps replace conventional heating plant will depend on the balance between environmental and economic objectives.
In the four core scenarios modelled, we found the cost of CO2 savings for heat pump schemes versus their counterfactuals (gas based systems) to lie in the range £133-£227/tCO2. This suggests that if the large CO2 savings on offer are to be achieved, there will need to be a continuation of financial support for renewable heat or interventions to ensure a high effective price of carbon emissions.
Further cost savings are obtained when both heating and cooling required
However, further cost savings could be achieved by using heat pumps in schemes where both heating and cooling are required.
Cooling demand is often a driver for the installation of heat pumps over other technologies in heat networks. Using heat pumps for both heating and cooling can help increase the thermodynamic efficiency of a system if heating and cooling loads are balanced, either instantaneously or seasonally.