Dan Ludgate, Group Development Director, talks about the role of heat pumps in district heating and stand-alone applications.
Cenergist is an energy and water services company that provides turnkey district heating and heat pump solutions for both residential and commercial applications. It is one of the leading providers of ground source heat pumps utilising ambient loop shared ground arrays.
District Heating
Communal and district heating works on the principle of several properties utilising heat and hot water generated in a central energy centre. Compared to individual systems, this offers operational cost savings and reduced CO2 emissions through diversified heat and hot water usage.
Currently in the UK there are approximately 600,000 properties supplied through communal or district heating systems. They represent just over 1% of total heat demand. The government’s target is by 2050 to increase this to 17% of heat demand in homes and 24% for industrial and public sector buildings. This growth is supported through grants and also planning regulations that encourage district heating for new residential developments and energy from waste (EfW) schemes.
Air and ground source heat pumps refer to the medium from which useful heat is extracted. Air source-heat pumps (ASHP) utilise technology similar to your fridge but in reverse, with outside air blown over a heat exchanger filled with a refrigerant that extracts heat down to temperatures of minus 10-15C. Typically for each kWh of electricity used to pump the refrigerant around the system, 2-3kWth of heat are generated.
Ground source heat pumps (GSHPs) circulate a water-glycol mixture through underground pipes to extract latent heat in the ground. These can be laid horizontally underneath an open area such as a field or car park, or alternatively vertically down a borehole to depths of typically 150m. GSHPs are more efficient that ASHPs as the heat in the ground is more even throughout the year. For each kWh of electricity used, the GSHP will generate 3-4 kWth of heat.
Heat pumps can be used to provide heat directly to buildings or they can be combined into wider district heating systems. While they can increase the cost of heat generated, heat pumps can substantially reduce carbon emissions. With ASHPs, these savings can be upto 50% of emissions, rising to over 60% with GSHPs. An example of this type of integration is the Bunhill district heating system in Islington, London. The gas CHP system supplies 1,350 homes and utilises heat from a 1MW ASHP that extracts heat from a London Underground ventilation shaft. The carbon intensity of Bunhill is less than 0.12 kg/kWh.
Pure Ground Source Heat Pump Systems
For urban apartment blocks, it is also possible to use solely GSHP systems to supply heating and hot water for residents. Rather than the traditional dedicated borehole for each house, shared ground loop arrays allow heat from the whole borefield to be utilised across a number of properties with a dedicated heat pump in each home. This approach offers several advantages:
- Each unit is self-contained so the resident is in direct control of the running cost of their system as it relies on their individual electricity supply
- Maintenance costs are substantially reduced compared to individual gas/electric systems or district heating networks
- Compared to electric storage systems, resident bills are reduced by up to 50%
The largest GSHP programme currently in the UK is at Leeds. Across the next 3 years, Leeds City Council plans to replace electric storage heating in over 1,400 properties with new GSHP systems. This is part of Leeds’s goal to reach net zero carbon by 2030.
The main risk area with GSHP systems is where the borefield or distribution grid has been incorrectly designed. The lack of heat in the system can lead to individual units freezing, leaving residents without heating or hot water. Boreholes can be used in both urban and suburban settings subject to detailed ground surveys.
Air Source Heat Pump Systems
Large commercial ASHP systems are used in commercial and industrial applications as well as incorporated into district heating systems such as Bunhill. For residential applications, they are generally used as individual ASHPs for each property. For well insulated homes, ASHPs can offer cost effective low carbon heating and hot water solutions.
The main risks with ASHPs concern the need for well insulated properties and correct sizing to meet heat demand. They offer a very cost effective solution for rural properties that are reliant on oil or LPG and also in the new build sector.
Obstacles to Growth
There is strong public interest in the net zero agenda with widespread recognition of the challenge of climate change. The key to growing the take up of district heating and heat pump systems is therefore ensuring that the decision to adopt such solutions does not entail significant financial cost to the individual compared to a traditional gas-fired or electric storage heating system.
The natural gas network was built through public subsidies in the post-war era. Gas-fired systems can usually access the network without the need to contribute towards the actual capital cost of the network, rather paying an access and maintenance charge.
For district heating and GSHP systems, the cost of installing the heat grid or borefield represents a major investment cost that has to be met by the end user in a relatively short period of time. To create a level-playing field, it is therefore important for Government to provide sufficient subsidy support for such systems.
The Government has responded through a series of subsidy schemes such as the Renewable Heat Initiative, Heat Networks Investment Project funds, Clean Heat Grant or Green Homes Grant. While these have provided financial support, the constant changes in funding levels and eligibility rules has hampered private sector investment and confused end users.
To meet the 2030 and 2050 targets, it is important that government moves to a stable, long-term incentive scheme such as the ROC regime for offshore wind. If this is introduced then private investment can be attracted to drive forward the goal of net zero.
