The Department of Energy & Climate Change (DECC)’s Heat Strategy, published in 2013, firmly placed district heating as the preferable source of sustainable heating in urban areas by 2050.
This was followed in 2014 by the government forming a Heat Delivery Unit within DECC, which in turn has funded more than 180 district heating feasibility studies for local government boroughs to the tune of over £9m.
Most recently the government’s Clean Growth Strategy, issued in October, reaffirmed its commitment to build and extend heat networks underpinned with public funds (£330m had been allocated in the 2015 Spending Review) until 2021. It also predicted that, by 2050, 17-24% of UK heating will be supplied via district heating.
What is district heating?
District heating (DH) has been defined by the Building Research Establishment (BRE) as “a pipe network that allows centralised heat sources to be connected to many heat consumers”.
Typically a DH network has three main components: one or more energy centres, the pipe network itself, and connections to customers. It allows heat to be used from sources that would not normally be possible within individual dwellings or buildings.
The key advantages that DH systems have over individual gas-fired boilers (the more common approach to heating dwellings in the UK) is that they can deliver heat in a more efficient manner, more cheaply and with lower carbon emissions.
It does this by capturing thermal energy or heat that would otherwise be wasted. Specifically these sources of heat include combined heat and power (CHP) plants, waste to energy (EfW) refuse incinerator plants, waste heat from industrial sources, geothermal heat, and plants using renewable fuels that are more easily burnt centrally such as biomass, waste wood or straw.
New low-carbon sources of heat can be connected to thermal networks as technology and waste heat sources become available."
Depending on the exact nature of the district heating system and its heat source, the cost of delivering heat to an individual customer can be as little as 6p/kWh. This is compared with an equivalent figure of 10p/kWh for gas heating (which includes fuel cost and the cost of replacing and installing the necessary capital equipment).
Similarly, the CO2 emissions from heat generated in a DH system can be as little as 60kg/mWh, compared with the equivalent figure of 240kg/mWh for a gas heating system using individual boilers.
A further benefit of district heating is that it can use heat from a number of different sources. In this way, as we progressively move towards a low or zero-carbon future, new low-carbon sources of heat can be connected to these thermal networks as technology and waste heat sources become available.
The main barrier to district heating is its capital cost. This includes the cost of extracting or upgrading the heat from the central CHP plan or waste heat source, installing the pipework network within the ground (usually DH pipes are run under roads alongside other utilities) and connecting into individual buildings.
Again, costs vary from scheme to scheme, but typically the cost of running DH pipework in an urban area can be £1,000/m, with a typical connection cost to a two-bedroom flat approximately £1,000.
The key to realising a successful DH scheme is to minimise the capital cost but maximise the number of customers connecting to the network.
A further barrier is the cost of operating the DH system, which needs to be kept to a minimum.
This is mainly down to the effective design of the system hydraulics, keeping the volume of water circulated around the system to a minimum to satisfy the actual (as opposed to the maximum) heating demand.
Variable speed pumps linked to multiple heat sources, which are only bought when the overall system demand requires them, are key components in a successful DH system design.
The other big consideration is to minimise the heat loss from the pipework distribution. This is most effectively done by the use of high-quality bespoke district heating pipework with integral thermal insulation.
Ramboll has been as the forefront of designing and delivering DH networks for more than 40 years. We are one of the lead designers of the District Heating system in Copenhagen, which extends to over 30km in length with four large CHP plants and four waste-to-energy incinerator plants feeding into it.
This network is continually being upgraded and extended, most recently with the addition of the eye-catching Amager Bakke waste-to-energy plant, which has been designed in the shape of a dry ski slope.
In the UK, Ramboll has completed more than 50 individual DH network studies at national, regional and city level, as well as completing the detailed design and delivery of schemes in London and Scotland.
Currently just 2% of the UK's houses are connected to district heating."
One of our most recent projects is in the London Borough of Islington, which has one of the highest concentrations of public and affordable housing in the UK at approximately 50% of total number of residences.
Working with Islington, Ramboll has designed the second phase of its Bunhill DH network adjacent to the City of London.
The scheme takes low-grade heat (15-20°C) from a London Underground extract ventilation shaft and, via a 1MWh heat pump, upgrades this to 75°C.
At this higher temperature the heat can be supplied to the extended district heating network to feed 800 additional social housing apartments.
Not only does this system save CO2 emissions, it crucially also provides heat at a lower cost than the current solution of gas-fired boilers or direct electric heating.
District heating schemes such as Bunhill have the ability to enable local authorities to save carbon and fuel as well as generating revenue streams from the sale of heat and electricity.
This is of particular benefit to boroughs such as Islington where public housing fuel poverty is a major issue. DH enables them to deliver real value by making significant savings and improving the quality of urban life.
In Scandinavia, district heating networks are a key component in their drive to reduce CO2 emissions. Denmark currently has over 60% of its houses connected to a district heating network, and this rises to 98% in cities such as Copenhagen.
In the UK, the comparable figure is currently only 2%, but with UK government support we believe district heating networks will dramatically increase in the next few years.
By Ramboll's Crispin Matison.
This article first appeared on recyclingwasteworld.co.uk in February 2018.