Accounting for refrigeration heat exchange in energy performance simulations of large food retail buildings

Abstract

Heat exchange between chilled food storage and conditioned spaces in large food retail stores is not currently required as part of design stage regulatory compliance energy performance models. Existing work has identified that this exchange has a significant impact on store energy demand and subsequently leads to unrealistic assessment of building performance. Research presented in this paper uses whole building dynamic thermal simulation models that are calibrated against real store performance data, quantifying the impact of the refrigeration driven heat exchange. Proxy refrigerated units are used to simulate the impact of these units for the sales floor areas. A methodology is presented that allows these models to be simplified with the aim of calculating a realistic process heat exchange for refrigeration and including this in thermal simulation models; a protocol for the measurement of chilled sales areas and their inclusion in the building models is also proposed. It is intended that this modelling approach and the calculated process heat exchange inputs can be used to improve the dynamic thermal simulation of large food retail stores, reduce gaps between predicted and actual performance and provide more representative inputs for design stage and regulatory compliance energy calculations. Practical applicationThe modelling methodology and research findings presented in the paper are of practical use for building energy modelling engineers using dynamic simulation models to design and/or evaluate the energy performance of large food retail stores. The methodology can be used in the design of new facilities or the evaluation of large scale retrofit projects. It is also of practical interest to energy and facility managers within large food retail organisations as it will aid their understanding of applied energy performance models. Key wordsHeat exchange, refrigeration, supermarkets, food retail, thermal modelling Introduction Large food retail stores (commonly known as supermarkets) are energy intensive, in the UK they account for approximately 3% of electricity demand and are responsible for 1% of greenhouse gas emissions.1 Energy used to refrigerate food in the sales floor area (SFA) and back of house (BOH) storage can account for over 40% of a typical store's total consumption.2 Internal heat gains from refrigeration are nominally accounted for in regulatory compliance energy models but the data inputs currently used to represent these are unrealistic as will be demonstrated in this paper.

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