HOT|COOL NO. 4/2017 "Technical Innovation and Optimization"


By Michele Tunzi, Miaomiao He, David Allinson and Kevin Lomas - Loughborough University, UK. Mark Gillott and Lucelia Taranto Rodrigues - University of Nottingham, UK. Svend Svendsen, Technical University of

Denmark Kgs. Lyngby, Denmark, Charles Bradshaw-Smith, SmartKlub Ltd, Oxon, UK. Nick Ebbs, Blueprint, Nottingham, UK. John Lindup, A.T. Kearney Limited, London, UK.

The large price drop in solar PV and electrical batteries offers new opportunities for optimizing district energy plants, but requires a more complex daily operation of these plants. Solar PV production used locally by a ground source heat pump (GSHP) with a minimal use of the national grid is one opportunity. Even if, for the benefit of the GSHP, the share of electricity for boosting the temperatures of district heating water goes up when lowering forward temperatures in the network down to as low as 45 °C, the overall operational income is improved.

TRENT BASIN AND PROJECT SCENE The work presented in this article illustrates the optimal operation of a multi-vector district energy system, assessing the main techno-economic parameters and different scenarios for a community energy system. It is based on a new housing development in Nottinghamwhich is part of a large regeneration of the ex-industrial areas alongside the River Trent. Project SCENe (Sustainable Communities Energy Networks) is an initiative supported by Innovate UK and the Energy Research Accelerator (ERA). It looks to accelerate the adoption of Community Energy Systems (CES). This approach represents a different way of generating and supplying heat and electricity to homes and commercial buildings where locally produced energy is used locally with minimal use of the national grid. The benefits are, potentially, reduced cost and more efficient use of distributed renewables to reduce the overall carbon emissions from the energy system. The investigation described here focused on 33 new low-energy buildings assuming their connection to a low temperature district heating (LTDH) network, fuelled by a ground source heat pump (GSHP) with a maximum heat capacity of 350 kW. The energy system will also embed 20 m3 of thermal storage, 450 kWp of solar PV and a battery bank of 2.1 MWh, representing the largest domestic application in North Europe and the first of its kind in the UK. As presented in the schematic view of Figure 1, a local Energy Service Company (ESCO) will manage and operate the multi- vector district energy system, supplying heat to the end-users, whereas the electricity demand will be covered through a typical domestic contract with the local energy supplier. As this will not affect the operation of the CES, the domestic electricity demand was disregarded in the analysis presented. The multi-vector energy system was simulated using energyPRO, an advanced energy software that allows for the simulation and optimisation of complex energy systems.

Despite its actual share of less than 2 % of the entire UK heat market, district heating (DH), due to its flexibility and capacity to integrate low-grade heat sources, has been recognised as a key technology in the transition towards a low carbon society. In fact, heat networks will play an important role in the future UK energy market to help securing energy supply and reducing CO2 emissions. It was estimated by the Department of Energy and Climate Change (DECC) – now restructured as the Department of Business, Energy and Industrial Strategy (BEIS) – that DH could supply in a cost-effective way up to 14 % and 43 % of the total UK heat demand in buildings by 2030 and 2050 respectively. This would be quite significant in the decarbonisation of the UK economy as heating and cooling consume nearly half of national primary energy. In a mature DH market such as Denmark’s, typical yearly average supply/return temperatures experienced in the network are 80/40 °C and real-time operations of four existing DH networks in Denmark can be found at system-consultancy/online-presentations. Aiming to integrate alternative low-grade heat sources and reduce the distribution losses, their current efforts are seeking to achieve a load dependent supply/return temperatures of 50/20 °C, defined in literature as the 4th generation DH (4GDH) concept. The challenge is to ensure the same levels of space heating (SH) and domestic hot water (DHW) in existing buildings, as well as for new low-energy ones, with these lower operating temperatures. The design conditions used to size heating systems rarely occur during normal winters; hence, lower operating temperatures, even in existing heating systems, can be adequate to maintain the same indoor comfort for the majority of the time. In low- energy buildings, with low temperature, heat emitters such as underfloor heating (UFH) or low temperature radiators (LTR), inlet temperatures in the range of 35/45 °C can be appropriate to guarantee indoor comfort. In practice, regulations on legionella bacterium limit the lower temperature for DHW. In the UK, water must be heated to 60 °C in storage tanks or 50 °C if heated instantaneously.

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