BSEE COMMUNAL LIVING
As we move towards a lower carbon future, CHP communal heat networks oer an important opportunity to change the way we heat our buildings and homes, says Mike Heord, Remeha CHP’s general manager
One means of using energy more efficiently in multiple occupant buildings is to adopt heat networks, where centrally generated heat is distributed in the form of steam, hot water or chilled liquids to multiple buildings to provide heating, cooling or hot water with reduced waste. There are two main types of heat networks: district heating, where networks may vary in size and can cover an entire city, and smaller communal heat networks, where heat is supplied to multiple occupants from a central energy store.
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The government has stated its aim to connect 14 to 20 per cent of all homes to a heat network by 2030 and has launched a £320m scheme to help accelerate the adoption of low carbon heat networks across the UK’s public, private and domestic sectors. Of the 17,000 heat networks in 2017, 11,500 are communal heat networks. So smaller communal heating/heat networks will be an important element as we head towards our 2050 target to reduce greenhouse gas emissions by at least 80 per cent from 1990 levels. Although electrification of heat is one approach to decarbonising heat in buildings, highly efficient gas appliances, such as combined heat and power (CHP), will continue to play an important role as a bridge to full decarbonisation. CHP brings a number of key benefits within a heat network: greater security, grid independence, lower transmission costs, and lower costs.
Greater security
CHP units generate electricity and heat simultaneously on-site in a highly efficient process. This on-site generation process means that smaller scale CHP communal heating schemes can balance the peaks and troughs in electricity supply. According to the ADE, CHP communal heating schemes can help provide enough capacity to keep the lights on, enable second by second matching of power use and demand, and the ability to expand and adapt power use and demand.
uOnsite generaon means that smaller scale CHP communal heang schemes can balance the peaks and troughs in electricity supply
Grid independence and lower costs
The electrical grid is evolving fast to prepare for the additional demand for electricity and higher peak loads from
ccording to the Association of
Decentralised Energy, 54 per cent of energy in the UK is wasted, mainly through heat.
Adversing: 01622 699116 Editorial: 01622 687031 Energy saving heat networks
electric vehicles. There are, however, issues concerning marginal generation and the seasonal nature of heat demand. For this reason, installing synchronous CHP units can offer real benefits, mitigating spikes in demand and bridging any gap in energy supply. CHP is highly efficient at producing both heat and electricity close to where it needs to be. Given the inherent efficiency losses of centralised generation and distribution, CHP can be up to 30 per cent more efficient when both the heat and electricity are used at the point of generation. The financial argument for CHP is equally compelling. Energy costs are lower, as CHP produces site electricity requirements at gas prices, which are typically a third cheaper per kW/h than buying directly from the grid. According to a 2016 ‘spark spread’ projection from BEIS comparing electricity and gas costs, these savings are set to continue into 2025.
Maximising system eciency
So what are the considerations when using CHP in communal heat networks? Firstly, the sizing. It’s important to consider both thermal and electrical demand when sizing the CHP within the communal heating scheme to determine if CHP is feasible for the application.
To ensure that the customer can claim Enhanced Capital Allowance (ECA) on the equipment, the thermal capacity should be matched to the thermal demand base load of the system. CIBSE AM12 suggests that CHP is sized at 10-15 per cent of the peak demand for both heating and hot water applications. Our experience has led us to recommend sizing to the thermal and electrical base load. This will maximise the efficiency of the system as the CHP can run constantly and the building can use all the heat and electricity generated.
For hot water only applications, a cold water pre-heat system can be employed. However, a demand profile and buffering are key elements to ensure respectable financial payback.
Electrical design
Good suppliers will be able to advise on both the hydraulic and electrical design as they will likely have seen a similar application before – and the end result. As a result, they will often be able to provide useful, time-saving schematics and exemplar drawings. In terms of electrical design, while this doesn’t need to be complicated, your supplier can help with a number of considerations. Areas of consideration include the size of the cables (to reduce the maximum volt drop), controls (to stop units from exporting to the grid), and the interfacing of the building management system (BMS). Early consultation with your distribution network operator (DNO) is advisable to make sure that embedded generation equipment can be added to the grid system. If sized correctly, however, then exporting back to the grid will simply not occur.
A G59 application process – soon to be a G99 application – will also need to be made. Again, ask your supplier for assistance.
26 BUILDING SERVICES & ENVIRONMENTAL ENGINEER DECEMBER 2018 Hydraulic design
A modern heat network is designed on a 70/40°C flow return system which allows the CHP to condense, running at full output for longer, and minimises heat loss on the distributed pipework. Water treatment and magnetic filters make sure that the system is fully compliant and, operationally, as efficient as possible.
Hydraulic commissioning is the final critical step as it will ensure that operational performance matches the design.
Integraon
How the BMS is integrated is of paramount importance to ensure that the vessel is loaded and uploaded as efficiently as possible. When integrating CHP with condensing boilers, the boilers must operate without influence from the CHP unit for maximum results. Where the design of a communal heat network calls for heat interface units (HIUs), designing the return temperature to 30°C or 40°C will ensure that the CHP continues to run at full output.
Future heang
As the UK transitions to a low carbon world, CHP communal heating schemes present an exciting opportunity to transform the way we heat our buildings and homes. Environmental and economic benefits, improved energy security and better energy management are just some of the advantages. And with experienced suppliers like Remeha providing total solutions and expert support to ensure maximum results, there’s no better time to consider new ways of heating.
remeha.co.uk VISIT OUR WEBSITE:
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To ensure that the customer can claim
Enhanced Capital Allowance (ECA) on the
equipment, the thermal capacity should be matched to the thermal demand base load of the system.
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uCHP is highly ecient at producing both heat and electricity close to where it needs to be
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