Abstract
In this article we present and validate a novel methodology for estimating the temperature development and heat extraction demand of closed refrigerated display cabinets (RDCs) in operating conditions, for near-future prediction and optimisation in smart grids. The approach is based on an in-house developed hygro-thermal model of an RDC, in which the conditions in each of the three main calculation domains, representing the internal air, heat exchanger and interior, are estimated at a temporal scale of seconds. The interior air temperature, heat extraction rate and run-off condensate were validated towards experimental data with good conformity. Moreover, for demand response purposes, in this article, we provide examples of how the model can be used to evaluate the temporal flexibility in heat extraction demand of RDCs. In a hypothetical supermarket with 11 RDCs exposed to various thermal loads and customer interactions, it is estimated that the heat extraction demand could be reduced to 0 for up to 83∕127 s during opening/non-opening hours respectively. With a strategic pre-cooling, the latter time could be extended to 322 s. For the case of a demand response signal requesting the supermarket to absorb excess energy, all RDCs would be able to run at full power for up to 17∕29 s, and approximately half of them for additional 20 s during opening hours. These findings are based on a total of 44 five-minutes-ahead simulations of possible scenarios for the 11 RDCs, all calculated by the presented model in approximately 10 s. In conclusion, the model provides fast and reliable results for real-time predictions in refrigeration control systems either for the benefit of the electrical grid by demand response or for energy efficiency purposes.
Highlights
By the year 2050, the European Union (EU) aims to reduce its release of greenhouse gases (GHG) by 80% − 95% compared with the levels in 1990 [1]
By applying the four scenarios, namely S1–S4 mentioned above, we can estimate the number of refrigerated display cabinets (RDCs) that would require active cooling at a given time after a demand response signal to turn off the refrigeration system; or, alternatively, for what duration the compressors could be operated at increased power
For the case of a demand response signal requesting the supermarket to absorb energy, all RDCs could be activated and would be able to run at full power for 17 s at idle state, S3, or 29 s as in the case of doors being operated as in S4, before the coldest would have reached the lower limit of 4 ◦C
Summary
By the year 2050, the European Union (EU) aims to reduce its release of greenhouse gases (GHG) by 80% − 95% compared with the levels in 1990 [1]. To enable supermarkets to engage and use their full potential for demand response purposes, smart grid communication possibilities together with detailed insights in the current and future temperature and heat extraction demand of the RDCs and their content must be predicted and controlled carefully [19,25]. This requires certain investments in updating the current control equipment [26]. To evaluate and enable the demand response potential in RDCs in supermarkets and support further development of energy-efficient supermarkets, we have developed a validated, accurate and computationally affordable model that predicts the temperature development of three main domains within the RDC with a temporal resolution of seconds
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