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BUILDING HEAT NETWORKS A low temperature approach


Mark Deeney, Contracng Director for Glen Dimplex Heang & Venlaon, examines common issues faced by tradional building heat networks and the advantages of a low temperature approach.


here are many building design challenges that we currently face in the industry, especially when developing projects in our crowded and busy cities. Our Building Regulations have been continuously updated over recent years to reflect our need for heat efficient dwellings, and this has gone some way to creating a more energy efficient society.


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This development was a change that needed to happen. However, by increasing the performance of the building envelope to satisfy Part L requirements, this has resulted in inefficiencies and other issues elsewhere in building design, predominately in the area of heating.


Traditionally, a high temperature network is used to ensure continuous availability of heating and hot water to multiple apartments, circulating water between 70º-40ºC and higher. However, the heat loss from these system types is now getting trapped inside our buildings.


This is causing over heating issues in multi-residential apartments, which is having an effect on operating costs and creating comfort and health issues. To counteract this, many developments have adopted the introduction of a separate cooling system, but this is an added cost which treats the symptoms rather than addressing the cause of the issues.


A low temperature soluon


The industry – including CIBSE’s ‘Heat Networks: Code of Practice for the UK’ – recognises the importance of low temperature heat networks as an alternative to high temperature networks, to maximise efficiency and minimise heat losses. Achieving it, however, remains one of the biggest challenges for engineers.


‘ Swapping HIUs


for a low temperature distribuon system combined with an air source heat pump could reduce that Carbon Tax payment from £873 to £475 per apartment, a potenal 45% saving. It will also reduce plant room space, whilst enabling a two – rather than four – pipe network and revised insulaon specificaon for addional cost savings.


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uLow temperature building heat networks can deliver a number of benefits.


10 BUILDING SERVICES & ENVIRONMENTAL ENGINEER SEPTEMBER 2018


The most effective way to counteract issues of energy efficiencies and overheating, is to reduce the flow temperature of the internal network from as high as 80ºC to an optimal 21ºC, which is the exact approach used by Glen Dimplex Heating & Ventilation’s unique Zeroth Energy System. Using a system of individual heat pumps situated within each dwelling, instead of Heat Interface Units (HIUs) using continuous high temperature water, offers an innovative new approach for providing heating, cooling and hot water in city apartments.


For a typical heat network design of 70º-40ºC, we calculate the energy loss in reality to vary between 7.38 and 5.38 kW across the network. In an energy distribution system with an operating temperature of 15º-25ºC the losses would vary between 0.75 and 0.38 kW – a reduction of 90 per cent by comparison and limiting annual energy losses to only five per cent over the year.


Using this approach, low temperature water flows around the building’s main energy loop to individual apartments, where a heat pump provides heating, cooling and hot water at the


desired temperature. The heat pump connects to a choice of emitters within the apartment, such fan coils, which deliver warm air into a room through vents in the ceiling or wall, underfloor heating or smart electric fan-assisted wet radiators. The central plant only needs to fill the balance of energy for the entire building, rather than servicing the total heating and cooling requirements of every resident at once. This system allows for lower corridor temperatures and improved thermal comfort, without necessitating a traditional chiller system to overcome internal gains, not to mention a more sustainable solution, as less total energy is required to heat and cool the entire building. This in turn can lower OPEX bills for the operator.


Carbon tax savings


There is another significant advantage for developers in London, where an energy distribution system can provide significant savings on carbon tax.


As part of the London Environment Strategy, which sets the target of making London zero carbon by 2050, the Greater London Authority (GLA) operates a carbon tax on new developments in the capital.


In essence, developers must reduce the Dwelling Emission Rate (DER) of a dwelling to 35 per cent below the Target Emission Rate (TER) required to secure a pass in Part L of the England and Wales Building Regulations – the Nearly Zero Energy Building (NZEB) standard. The remaining carbon, expressed in tonnes, must then be offset in the form of an abatement payment which is set by each individual borough. The GLA recommends a price of £60 per tonne paid for 30 years, or £1,800 per tonne remaining. For a typical development of 125 dwellings including a mix of apartment sizes, this is an abatement payment of £109,106 for the whole building, or £873 per apartment.


Swapping HIUs for a low temperature distribution system combined with an air source heat pump could reduce that Carbon Tax payment from £873 to £475 per apartment, a potential 45% saving. It will also reduce plant room space, whilst enabling a two – rather than four – pipe network and revised insulation specification for additional cost savings. Whilst the exact figures will vary by project due to the mix of dwelling types and differences in carbon payments required by boroughs, it is clear there are benefits to this new approach for heating and cooling using heat pumps in multi- dwelling buildings. With other major cities expected to follow London’s lead, the opportunity is only set to increase.


www.gdhv.com ‘


The industry – including CIBSE’s ‘Heat Networks: Code of Pracce for the UK’ – recognises the importance of low temperature heat networks as an alternave to high temperature networks, to maximise eciency and minimise heat losses. Achieving it, however, remains one of the biggest challenges for engineers.


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uThe most eecve way to counteract issues of energy eciencies and overheang, is to reduce the flow temperature of the internal network from as high as 80C to an opmal 21C, which is the approach used by Glen Dimplex Heang & Venlaon’s Zeroth Energy System.


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