Going cool on district heating
Heat networks: as demand for heating falls, is district heating all it’s cracked up to be, asks Rory Bergin
The introduction of heat networks, otherwise known as district heating systems, into new building projects on urban sites has become a de facto standard in London. Greater London Authority guidance is very clear: Policy 4A.5 states that ‘Boroughs… should maximise the opportunities for providing new networks that are supplied by decentralised energy [and] ensure that all new development is designed to connect to the heating and cooling network.’ The accepted truth is that heat networks are a cost-effective way of meeting carbon reduction targets but is this really the case? Some issues to consider are outlined below.
Heat networks cost about £1,000 per metre, so using them to link bungalows doesn’t make sense, using them to link multi-storey urban buildings does.
Heat networks cost more than individual installations, but they last much longer, so over a 25-year period where boilers will be replaced twice, a heat network is cheaper to install. In most cases, the heat network is installed by a developer and the building tenant or eventual owner is not part of the discussion.
Like any heating system, heat networks have to be well designed to work at their best and there are not that many people in the UK who have experience of designing and installing them. Consequently there have been a number of problems reported by building owners. Overheating in common areas is a particular issue caused by poor insulation of pipework and over-circulation of hot water.
Heat networks need a system for delivering directly into dwellings. This is usually a heat exchanger about the size of a combi boiler and needs to be sited close to the network for easy access to maintenance.
Many housing associations are put off by heat networks because of concern about maintaining an unfamiliar system. Many of the companies that design and install these systems can also maintain them and manage the complex billing systems that are required to ensure that residents only pay for the heat that they use. A reason that many of these heat networks were removed from housing estates in the 1980s is that they were poorly managed by local authorities and usually did not meter the heat to individual users.
Costs to users
This is one of the trickiest areas. When heat networks are installed, someone needs to pay for it. This is usually dealt with by adding a service charge to bills of the users of the system. This is a relatively small amount but pays back the installer over a long period. The heat user pays no upfront cost, but the final bill will be larger.
This is even trickier. Heat networks can lose as much as 50 per cent of their heat through the network, so calculations of CO2 emissions must take this into account. Compared to individual boilers there is no reason to use communal systems for CO2 reductions unless part of the heat is going to be supplied by a CHP engine. CHP uses the spare heat produced by generating electricity to boost the efficiency above what can be achieved with a boiler-only model. A typical CHP system saves about 60 per cent of CO2 compared to a conventional boiler. If the CHP can be fuelled by renewable fuel then the savings are over 100 per cent, as the electricity offsets electricity produced from the grid. But renewably fuelled CHP systems are barely a glint in the eye of system manufacturers, so treat this idea with caution.
The big issue
A strategic problem with heat networks is that there is a plan to reduce their business case by about 50 per cent over the next 30 years, known as the Green Deal. We need to reduce our heating demand by this much if we are to have any chance at reducing our CO2 emissions from heating systems. Heat networks provide a flexible mechanism for delivering heat, but if they don’t need to deliver so much heat, are they worth the effort and would our investment be better directed elsewhere?
Rory Bergin is head of sustainability and innovation at HTA