COLD STORES
Load shifting using thermal energy storage
Thermal energy storage is the temporary storage of high or low temperature energy for later use. It bridges the time gap between energy requirement and energy use, and Zafer Ure of Ecomesh discusses its uses in cold stores here.
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or HVAC and refrigeration application purposes, water and water ice constitute the principal storage media. Water has the advantage of universal availability and low cost, but it off ers just 0°C (32°F) water ice which restrict its applications. If it is applied purely for sensible energy storage capacity it requires large storage tanks.
Phase Change Materials (PCM) between -100°C (-148°F) and 90°C (242°F) overcome the water disadvantages by combining the latent and sensible energy storage capacities into a single storage unit and therefore off er designers new horizons and practical application options. PCM latent heat cool energy storage can be provided by utilising conventional water chillers for new and retrofi t applications without the need for any modifi cations, as well as having the
possibility of free cooling. By storing day-time warm energy for evening periods and over-night cool energy for day-time cooling requirements, a PCM system can simply bridge the gap between energy availability and energy use and therefore has the potential to achieve considerable environmental as well as economical benefi ts for many heating and cooling applications. Energy usage, economical and environmental issues are becoming a focal point for both end users and the public at large. Current trends towards privatisation and an open market approach for utility companies has created a new kind of energy market whereby the period of energy usage and type of energy used is becoming the main criteria for price structuring rather than overall energy consumption.
Hence, current cold storage must be designed to provide suffi cient fl exibility for load shifting and energy usage control in order to achieve the most economical operation. A thermal energy storage (TES) technique of storing high or low temperature energy for later use, in order to bridge the time gap between energy availability and energy use, can be considered as a useful tool to achieve this aim.
Unfortunately, HVAC and refrigeration TES applications utilise water ice. However, PCMs freeze and melt above or below 0°C (32°F) off ering new opportunities for environmentally friendly and economical systems for both new and retrofi t process, cooling or heating load shifting applications.
Thermal Energy Storage bridges the time gap between energy requirement and energy use. A thermal storage application may involve a 24-hour or alternatively weekly or seasonal storage cycles depending on the system design requirements. Whilst the output is always thermal, the input energy may be either thermal
44 May 2018
www.acr-news.com
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