Mitigation potential of horizontal Ground Coupled Heat Pumps for current and future climatic conditions: UK environmental modelling studies

Completed

Energy Efficiency(Other)

Basic and strategic applied research

ENVIRONMENTAL SCIENCES (Earth Systems and Environmental Sciences)

Not Cross-cutting

Dr A Hughes
Groundwater Resources
British Geological Survey (BGS) - NERC

R&D

NERC

01 September 2008

31 August 2011

36 months

£66,940

Power

East Midlands

Dr A Hughes, Groundwater Resources, British Geological Survey (BGS) - NERC

The overall aim of the proposed project is to assess and give recommendations on how to optimise the mitigation potential of horizontal GCHPs in the UK, taking account of changing environmental conditions. Individual measurable objectives are: * To improve an existing mechanistic land surface model (JULES) by incorporating previously omitted soil physical processes (such as water vapour flow) andby coupling a groundwater model to it; * To incorporate equations into this model that describe the interactions between horizontal GCHP heat exchangers and the soil, allowing for a number of GCHP configurations (pipes, coiled systems etc.); * To tailor an existing database of high resolution (1 km) gridded meteorological/soil physical/land cover data over the entire UK-domain to drive and parameterise this model. Meteorological data will consist of both historical and projected data; * To conduct detailed modelling studies with the composite model in 1-D model mode. This will include sensitivity and verification simulations driven with medium-term historical data and data to be collected during the project (near GCHP installations); * To conduct long-term UK-wide simulations, includin g warming scenarios, with the distributed version of the model, using the gridded dataset; * To predict performance indicators, such as the coefficient of performance, COP, both in the heating and cooling mode, as well as the Seasonal Performance Factor (average of COP over heating and cooling season) for combinations of soil type/vegetation type/GCHP system (looking at inter-annual variability a nd long-term projected efficiency); * To quantify the CO2 mitigation potential for this technology over the UK based on the above modelling studies; * To make recommendations to relevant (government) bodies concerning the optimal configuration of future installations of GCHPs at UK domestic, institutional, commercial and agricultural developments.

the key priorities for policymakers in order to decrease combustion of fossil carbon, thereby slowing the increase of CO2 concentration in the Earth's atmosphere. A considerable amount of UK effort has gone into investigating renewable energy sources such as wind, marine and solar power, as well as into bio-energy. However, relatively little work has been undertaken on the topic of ground coupledheat pump systems (GCHP), a relatively underusedtechnology in the UK, in contrast to other countries such as USA, Switzerland and Sweden. To put it simply, GCHPs use temperature differences (between soil and air) to provide space heating An increased uptake of alternative low- or non-CO2 emitting energy sources is one of in the winter and cooling in the summer. This is achieved by placing plasticpipes (filled with fluid containing anti-freeze) in the ground so that they can exchange heat with the soil, so called heat exchangers. This heat is 'upgraded' by a heat pump to heat homes or other buildings, thereby providing a sustainable, renewable and reliable source of energy. The performance of these GCHPs depends on the design and configuration of the heat exchangers (e.g. length of pipes, depth of installation, spacing between pipes). However, the performance of horizontally installed systems, as opposed to the more expensivevertical borehole ones, is also affected, in a rather complex way, by the environment. With this we mean soil, vegetation and atmospheric conditions, which will significantly differ over the UK and over time (diurnal, seasonal and inter-annual variation). The research described in this proposal aims to investigate how the long-term (~50 years, the average lifespan of GCHP systems) performance of these systems varies throughout the UK. Our findings would form the basis of recommendations to local governments (and users) on the location-dependent economic viability of these systems and their potential to reduce carbon emissions, whileexplicitly taking into account that our climate is changing at a significant rate. Also, depending on the balance between how much heat is taken away from and returned to the ground, the soil temperature in the neighbourhood of the heat exchangers may fall or rise; related to this is the movement of soil moisture away from or towards the heat exchanger. These processes will also affect the performance of the system during its life span. These intricate interactions between soil and GCHP can be mimicked by computer model simulations and various packages are available for use by GCHP designers and installers. However, these types of software have been developed to work on a site-by-site basis and moreover they simplify the effect of the environment. Also, they address short time spans only(~1-3 years).Inthis proposal we will use a detailed land surface model, such as the one used by the UK Meteorological Office to predict the weather. First we will improve it to ensure that all important interactions between the below-ground heat exchangers and the soil (heat and moisture flow, including groundwater) are taken into account. Wewill then test it and subsequently drive the model with long-term data, generated to represent the climate, soil type, and vegetation (and related properties) throughout the UK. Only then can we obtain reliable estimates about the UK-wide long-term performance of GCHP systems and their effectiveness in reducing CO2 emissions. This allows us to recommend increased uptake in specific UK areas as well as indicate how specific changes to the designand configurationofGCHP systems (e.g. type of tube and installation depth) can improve performance and hence increase its potential for reduction in CO2 emission.

05/09/08