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BSEE HEAT NETWORKS


Heat networks are a key element in the UK’s commitment to reducing carbon emissions and tackling fuel poverty. Beata Blachut, Technical Manager for CHP and heat networks with SAV Systems, discusses the concept of fourth generaon heat networks


carbon and cutting heating bills. And in December, BEIS also reported that heat network consumers pay, on average, at least £100 a year less for their heating and hot water, compared to non-network consumers. However, for heat networks to fulfil their full potential a more sustainable approach is required to their design and operation. In particular, a new generation of smart networks (4G) that integrate electricity, thermal and gas grids needs to be adopted. Current (third generation or 3G) heat networks are usually limited by their original design – typically an energy centre powered by combined heat and power (CHP) backed by boilers and while there may be an opportunity to add lower carbon energy sources in the future, this would require extensive upgrading of the energy centre and the buildings being served by the network.


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In contrast, a key characteristic of 4G heat network design is the wherewithal to manage the increasing complexity of energy networks, and the intermittent availability of ‘green electricity’, efficiently and cost-effectively. This is essential as the UK’s intermittent renewable electricity production (e.g. wind, tidal, solar) grows. For example, nearly a third (29.8%) of all UK electricity in the second quarter of 2017 came from renewable sources, most of it from wind.


The intermittent nature of these renewable energy sources is driving a move to greater integration of the different energy sectors (electricity, gas, heat) to better co-ordinate energy production with consumption and incorporate stabilisation factors. For example, when the wind isn’t blowing sufficiently to meet power demand, another energy source needs to come into play. Fast-acting gas-fired power stations are currently an important ‘stabilising’ factor, though the heat generated by this process is usually wasted.


A better option is to make wider use of CHP in power stations and more locally in buildings to provide the required stabilisation whilst also


ast September, the Department for Business, Energy and Industrial Strategy (BEIS) highlighted the importance of heat networks in reducing


producing heat for the heat network. Using decentralised CHP very close to the building(s) being served will minimise distribution losses. The increased diversity of energy sources also contributes to complexity, insofar as the traditional heat sources of CHP and boilers will be joined by technologies such as heat pumps, solar thermal, photovoltaics, fuel cells, waste heat etc. Some of these will be incorporated into the buildings, so the latter become both consumers and producers, creating even more complexity.


Energy storage


One of the main challenges posed by intermittent renewable energy is that times of highest generation may not coincide with times of maximum demand. It is therefore essential to have a reliable and cost-effective way to store this energy until it is needed. Batteries are often seen as the obvious way to store electrical power; however studies have shown that storing the energy as hot water is at least 100 times less costly than battery storage.


Thus, 4G heat networks will be able to exploit surplus electrical power by converting it to heat energy for storage – ideally using thermal stores utilising low carbon technologies such as heat pumps; though electric boilers would be another option. To minimise distribution losses, such energy storage should be as local as possible to the building. This has serious implications for building design, as provision must be made for considerably higher volumes of stored heat energy than would traditionally be the case.


In this respect the amount of thermal energy stored is determined by the physical volume of the stored hot water and the temperature differential (T) between the stored hot water (around 80°C) and the return water of the system. Apart from maximising the benefits of the thermal store, low flow and return temperatures (ideally 20°C) also help future integration of low carbon technologies that require low temperatures to operate.


The lower temperatures also help to reduce the heat losses from distribution pipework. Tests in Denmark with residential heat networks have shown that flow/return water


temperatures of 55°C/35°C reduce heat losses from distribution pipework by around 75%, compared to traditional higher temperature systems (e.g. 80°C/55°C).


The holy grail for 4G heat networks is to reduce the flow and return temperatures even further, to 50°C flow/20°C return.


4G heat networks will also need to incorporate intelligent metering not only for billing, but also to provide real-time data on energy consumption in individual


spaces/apartments, as well as across the entire network. This will help to optimise outputs from the energy centre and across the network.


Size maers


Heat networks may be either large district heating schemes or small block heating schemes, and both have potential benefits.


The greatest potential for larger district heating schemes is where there is a low-cost heat source relatively close to the buildings that will be connected to the heat network. Obvious examples include a power station producing waste heat that can be captured and used in the heat network - or surplus heat from industrial processes and/or waste incineration. For such schemes to be viable it is essential they have a source of low cost heat, to balance the cost and disruption of constructing the distribution infrastructure.


Where such low-cost heat sources are not available locally it will generally be more practical to consider smaller schemes – often known as block heating or


communal heating. These are very straightforward and require only the installation of heating and hot water pipes in the building, creation of an energy centre (typically on the same site) and provision of heat interface units in each space being heated. Consequently, block heating schemes are commercially viable and easy to implement, compared to large district heating schemes.


Summary


With an overarching need to reduce carbon emissions, it is essential to plan and manage a transition to 4G heat networks within smart energy systems that combine and co-ordinate production and consumption among heating, electricity, gas and transport systems. Such sustainable systems will focus on wider use of low grade renewable and waste heat sources and have the ability to manage intermittent energy sources efficiently using responsive technologies such as CHP.


www.sav-systems.com


u4G smart energy networks will integrate a range of energy sources with the ability to manage intermient energy sources eciently.


Adversing: 01622 699116 Editorial: 01354 461430 CUT CARBON WITH 4G HEAT NETWORKS


16 BUILDING SERVICES & ENVIRONMENTAL ENGINEER APRIL 2018


VISIT OUR WEBSITE: www.bsee.co.uk


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