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District heating puts communities in control

The Department of Energy and Climate Change's latest initiative, the Community Energy Strategy, is a sign of recognition of the significant role district heating systems can play in the UK, says Chris Davies of Kensa Heat Pumps
On 27th January 2014, the Department of Energy and Climate Change launched its latest initiative, the Community Energy Strategy. Aiming to provide support to the more than 5,000 community energy groups which already exist across the country, the long-term vision is to kickstart a decentralised power and heat revolution in the UK, similar to that seen in Denmark and Germany.

According to DECC, putting communities in control can help generate energy, reduce energy use, manage energy demand and help with more effective energy procurement, as well as often being able to tackle energy challenges at a local level more effectively than central Government is able to.

All lofty and well-meaning objectives, I'm sure. Whether the entire strategy will prove to be quite as 'ruthlessly pragmatic' as Ed Davey promises, time will tell.

However from a renewable heat perspective the strategy does for the first time begin to finally recognise the significant role district heating systems can play in the UK. Among the initiatives announced is a new DECC Heat Networks Delivery Unit (HNDU), which aims to transform district heating in the UK and provide financial support, guidance and expertise to local authorities wishing to consider the potential for district heat.

And with the non-domestic stream of the RHI and (in the case of existing buildings) the Energy Company Obligation both supporting district heating solutions, the case for communal heating is strengthening.

Challenging perceptions
District heating currently provides less than two per cent of the UK's heat demand, but given the intentions of the Community Energy Strategy, this is clearly an area DECC is keen to see increase.

The generally accepted definition of a district heating system of course is large, centralised biomass or CHP plant housed in a plant room and servicing multiple dwellings. This is becoming increasingly common at reasonably small scale for apartment blocks.

Indeed we have probably all heard the fabled tales of biomass boilers being installed in new build developments alongside 'back up' gas boilers in order to meet local authority renewable contribution planning requirements, only never to be switched on; while those which are operational require constant maintenance and regular biomass fuel deliveries, bringing with it associated management and service costs.

This traditional approach to district heating has further drawbacks, particularly in small to medium scale residential schemes. Firstly, heat losses through the central distribution pipework can be significant; hardly energy efficient.

Control over such systems can also be problematic and of course the space needed for plant rooms to house such systems is not insignificant - in the case of new build often taking up real-estate that could otherwise have been made available for another dwelling or apartment. Billing of course also becomes problematic, with the landlord needing to find a way to either meter or apportion the cost of heat usage between occupants.

Then, in the case of biomass, there is the ongoing question of reliability, fuel sustainability and quality. Biomass boilers are fussy creatures, one commentator recently describing them as akin to a new-born baby: always crying for attention - and heaven help if you put the wrong food in!

Quality of the wood chips or pellets is the single most important factor in the operation and efficiency of a biomass system, with commentators suggesting that the wrong choice of fuel can affect performance by as much as 50 per cent, of course impacting on the real life running costs and carbon emissions significantly from what was originally predicted. Indeed, experts will tell you that you actually have to 'tune' the boiler to the fuel being used - based on the moisture content of the particular batch delivery - in order to optimise operation.

So when it comes to district renewable heat, are there other alternative approaches out there which mitigate all of these issues? I think so.

Of course heat pumps can also be applied in a 'central plant room' type approach in the same way as biomass boilers. The recently announced uplifts to the non-domestic RHI tariffs for ground source heat pumps begin to make this look like an interesting proposition. However this approach still has issues as it does not address the problem of heat loss through the central distribution pipework. Additionally, because the heating water flow temperatures need to be kept low to retain the efficiency of the system (generally 50°C or lower), it becomes prohibitive to use Heat Interface Units, meaning in turn that to provide domestic hot water becomes complex and expensive to achieve.

Innovative solution
Kensa however is pioneering an innovative district ground source heat pump system architecture which directly resolves all of these problems, removing the efficiency losses through central distribution pipework and allowing each apartment or dwelling to have complete control over its own heating and hot water production, while also removing the need for centralised billing. The benefits of this solution lend themselves well to new build developments or retro-fit schemes looking to adopt a community energy / district heating approach.

This solution utilises the concept of a District Vertical Array - essentially a communal borehole ground collector array - linked to a central flow / return circuit which in turn serves compact and extremely quiet ground source heat pumps installed within each individual dwelling.

There are three fundamental elements to the Kensa system architecture:

· The District Vertical Array - the array of vertical boreholes used to provide the renewable energy source to the building

· The central distribution pipework - crucially, this circulates the relatively cold water (<10°C) returned from the ground array, so there are no associated system losses to consider

· The small, quiet Kensa Shoebox heat pump (pictured above) - installed within in the curtilage of each dwelling and using the central distribution pipework as its heat source.

This approach overcomes all of the drawbacks of traditional 'central plant' district heating systems and crucially DECC and Ofgem have confirmed that individual ground source heat pumps linked to a communal ground array in this way satisfies the definitions of district heating, thus making it eligible for payments over 20 years under the non-domestic RHI.

The solution is also completely scalable in that a district heating system may be as small as two dwellings - perhaps a pair of semi-detached houses - sharing a common borehole. This flexibility therefore allows developers to employ an innovative technical solution while retaining ownership of the system and benefit from the RHI, or for social housing providers and other owners of multiple dwellings such as holiday let providers to adopt a scalable district heating system approach across their off-gas grid housing stock.

Adopting a communal ground array approach also provides other advantages, for example a reduction in the overall number of boreholes required as a diversity factor can be applied, decreasing the average borehole depth per property and lowering costs as well as enhancing the productivity of the drilling operation.

// The author is the commercial director of Kensa Heat Pumps //
2 April 2014


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