Opportunities and challenges for waste heat in energy systems - from sustainable cooling to heat recovery.

This paper tracks a research journey over a number of years from sustainable cooling to heat recovery. It includes an investigation of the decarbonisation of heating and cooling by working across commercial boundaries as part of a smart energy system. Many cooling applications exist close to a demand for heat and by sharing energy between applications can deliver near zero carbon heating and cooling in a cost effective way. The paper describes the evolution of research at London South Bank University in sustainable cooling and heating. It starts with describing the challenges associated with decarbonisation of the UK energy system and then links this with the need to develop more sustainable cooling concepts. Research carried out on sustainable cooling of London Underground is described including the challenges associated with heat exchange, followed by the evolution of a heat recovery scheme for connection to the Bunhill Heat Network which bivalently cooled the Tube and delivered heating to local housing. The paper then describes the development of smart local energy systems, using a case study called GreenSCIES which integrates heating and cooling with mobility (Electric Vehicles) and power to create a smart local energy system. Wider opportunities for integration of heating and cooling are then described with some specific case studies. The paper concludes by looking ahead to future policy opportunities

Waste heat from the London Underground: an investigation of the potential benefits of integrating heating and cooling

Waste or recoverable heat is a resource that could be cost-effectively exploited by district heating (DH) systems to increase the efficiency of heat supply in buildings. This paper introduces the Bunhill waste heat recovery (WHR) system, a novel scheme that recovers waste energy from a ventilation shaft of the London Underground (LU) transport network. The system is based upon the installation of a heat recovery heat exchanger consisting of cooling coils and a reversible fan; the coils are connected to a heat pump that supplies low-carbon thermal energy to the Bunhill DH network in central London. One particularly important aspect of the Bunhill WHR system is its ability to operate in a way that not only provides heating to the local heat network, but can also simultaneously supply cooled air to the LU tunnels depending on the operation of the reversible fan. The current paper presents the results from an investigation into the benefits of integrating heating and cooling from the perspective of reducing carbon emissions and the levelised costs of energy from the WHR system, whilst also alleviating peak temperatures at nearby LU stations through the cooling provided. The findings of the investigation are presented together with recommendations for further development and future deployment of WHR systems, which not only apply to underground railways but also to other sources of recoverable heat

Potential of treated wastewater as an energy source for district heating: incorporating social elements into a multi-factorial comparative assessment for cities.

Recovering waste heat from urban infrastructures is gaining greater importance in the context of decarbonisation. However, evaluating the feasibility of waste heat recovery projects requires a holistic analysis of potential impacts, which includes social elements that are often overlooked. This paper introduces a novel methodology for assessing the competitiveness of waste heat integration into district heating, based on a multi-factorial decision support tool that incorporates energy poverty as a key performance indicator, in addition to energy, environmental and economic factors. The comparative assessment is based on the implementation of large-scale heat pumps recovering wastewater heat, a resource of great potential that is still underutilised in Europe. The methodology is tested in the cities of London and Riga, which are in countries with significantly different stages of DH development. In London, an emerging market with high growth potential, and in Riga, where there is a well-established DH system. The study has shown that waste heat can significantly reduce consumers' bills for heating, which was observed in all analysed scenarios. The social benefit decreases when the replaced technology involves biomass heat-only boilers or combined heat and power. The methodology presented is generic and can be applied to other locations and heat sources

Project SHOES: Secondary heat opportunities from electrical substations

Through the mechanism of stepping up and stepping down voltages with electrical power transformers, losses in the form of heat occur and are dissipated to the atmosphere. These losses have the opportunity to be recovered and upgraded to help support the thermal demands of buildings as allow carbon secondary heat source. The electrification of heat facilitates the uptake of electrically driven heat pumps that are efficient means of upgrading low temperature heat sources to commonly used temperatures and the employment of district heating networks enables the transition of these alternative heat sources into the economy. This paper describes the results discovered from an initial investigation on the contribution available from a transformer energy recovery scheme using the Southampton Bulk Supply Point substation and District Heating Scheme as a case study. Benefits to the heat sector and asset owner are analysed from the results considering the techno-economic, environmental and social performance with the aim to provide guidance to the engineering community for further in-depth feasibility studies on this waste energy recovery concep

Investigation of a Solar Assisted Heating System

Low emissivity transpired solar collectors (low-ε TSCs) consist of metal solar absorber, collector plates, with a spectrally sensitive surface, perforated with holes. Ambient air is drawn through the holes and heated by convection from the solar collector plate, increasing the air temperature by up to 25 K. The heated air can be used for e.g. space heating or pre-heating hot water, in buildings. The performance of low-ε TSCs combined with heat pumps in various configurations, to deliver heat to buildings, has been investigated using computational models and compared with conventional heating systems to determine the potential energy, carbon and cost savings available. The results showed that using low-ε TSCs incorporated into a heat pump based ventilation air system produced annual savings in energy, CO2e and costs of up to 14%, compared to similar systems where the TSC was not used. The greatest savings were achieved when using an exhaust air heat pump. Recommendations for further development of this novel technology are also presented

Study of novel solar assisted heating system

The potential for energy, carbon dioxide equivalent (CO2e) and cost savings when using low emissivity (low-ε) transpired solar collectors (TSCs), combined with heat pumps in a range of configurations, has been investigated using computer modelling. Low-ε TSCs consist of metal solar collector plates with a spectrally sensitive surface, perforated with holes. Ambient air is drawn through the holes and heated by convection from the solar collector plate, increasing the air temperature by up to 25 K. The heated air can be used for e.g. space heating, or pre-heating water in buildings. The models developed have been used to compare the performance of low-ε TSC/heat pump heating systems in small and large buildings, at a range of locations. The model results showed savings in energy, CO2e and costs of up to 16.4% when using low-ε TSCs combined with an exhaust air heat pump compared with using the exhaust air heat pump alone. Practical application: If the UK is to meet its target of reaching net zero greenhouse gas emissions by 2050, it will be necessary to adopt low or zero carbon heating technologies. The novel low emissivity transpired solar collector device investigated can contribute to this. Its advantages include: (i) utilising solar radiation; (ii) readily integrated with existing heating systems e.g. heat pumps; (iii) significant energy, CO2e emissions and cost savings; (iv) low cost device; (v) minimal energy input i.e. one small fan; (vi) can be retrofitted to existing buildings; (vii) its benefits were applicable at all of the (wide range of) locations tested

The Impact of Policy Changes: The Opportunities of Community Renewable Energy Projects in the UK and the Barriers they Face

The UK’s energy system is predominantly centralised with a major reliance on fossil fuels. The trilemma of successfully delivering energy security, equity, and environmental sustainability, whilst dealing with an ageing energy infrastructure, demands change within the entire energy system. In recent years, Community Renewable Energy (CRE) projects have played a significant role in the transition of the UK’s energy system, but since 2016 government support for them has been less robust. This paper reports a web-based survey and semi-structured interviews of the UK’s community energy groups undertaken between August 2016 and March 2017. The results indicate that huge problems have arisen due to the changes in government policy, particularly for solar photovoltaic schemes. The majority of CRE organisations have chosen to focus on managing their existing assets rather than plan further growth. Additionally, this paper highlights the key challenges facing CRE projects that wish to develop innovative business models under the new policy conditions. Keywords: Community Renewable Energy (CRE); Business model; Feed -in-Tariff (FIT

Causes, Consequences and Prevention of Refrigeration Fires in Residential Dwellings

There are around 300 residential dwelling fires in Great Britain each year where a fridge or freezer is cited as the cause. A number of these incidents have resulted in injuries/fatalities and produced significant levels of property damage. This paper examines the causes and consequences of refrigeration fires in residential dwelling fires in Great Britain (London and England) and the evidence collected via fire investigation of residential dwelling fires involving fridges or freezers. Analysis of the data collected from these fires suggests that, once ignition occurs, fires started by faults in fridge/freezers are more likely to spread beyond both the appliance and the room of origin, and tend to cause more damage than fires started by the other types of white goods appliance (washing machine, dishwasher or tumble dryer). A number of common failure modes leading to ignition in domestic refrigeration fires, along with specific fire escalation and spread mechanism are identified. Based upon the information obtained from fire investigations and a comparison between the design and construction of refrigeration appliances used in Great Britain and USA, a number of recommendations are suggested which could be used to help reduce the risk of domestic refrigeration fires

Relationship between specific energy consumption and size of supermarket stores

© 2019 International Institute of Refrigeration. All rights reserved. Energy consumption data for 2017 were analysed for 190 retail (supermarket) stores from one retailer in the UK. The relationship between energy consumption and store size was investigated. The mean energy intensity defined by the ratio of electrical energy consumption across the sales floor area was 866 kWh.m-2.yr-1 for an average sales floor area of 469 m2. Plotting energy intensity against store size showed that smaller stores had a higher energy intensity. Measuring energy intensity using electrical energy consumption, total energy consumption, sales or gross floor area, perimeter area of the store and store volume all showed a similar trend. Electrical energy consumption is well correlated with refrigeration capacity (r2 = 0.779), however, it is has a slightly better correlation with sales floor area (r2 = 0.883). . When including these data with other data from previous studies, it can be seen that large stores (supermarkets) had an approximately constant energy intensity (decreasing slightly with increased floor area) and smaller stores (convenience) had a much higher energy intensity which increases strongly with decreasing floor area. Therefore to represent stores ranging from small to large a power law relationship is required

Application of Phase Change Materials to Domestic Refrigerators

The paper investigates the performance improvement provided by a phase change material associated with the evaporator in a domestic refrigerator. The heat release and storage rate of encapsulated ice, used as the thermal energy storage material, has been investigated numerically. The mathematical model for phase change is based on the enthalpy method and the governing equations were discretized on a fixed grid using the finite difference method. The influence of PCM thickness (2, 3 and 4 × 10-3 m slabs), ambient temperature (20°C, 25°C, 30°C and 43°C) and evaporating temperature (-15°C and -10°C) have been investigated. The results showed that the melting and freezing time increased proportionally with PCM thickness. The refrigerator autonomy was reduced by 47% when the ambient temperature was increased from 20°C to 43°C and the freezing time increased by 27% when the evaporating temperature was reduced from -10°C to -15°C. Overall, the model provides a useful tool for evaluating the design and operation of a thermal storage refrigerator