Phase Change Material (PCM) Eutectic Solutions Used For Passive Cooling

Thermal Energy Storage (TES) may be considered as a useful tool to reduce the cooling load requirement by means of spreading day time loads over 24 hour period utilising the naturally occurring ambient temperature difference.

The night-time cooler ambient can be used to charge the latent heat capacity of various Positive Temperature Eutectic also called Phase Change Material (PCM) solutions between +4°C ( 39°F) and +117 °C (243°F) without using any refrigeration machinery by simply allowing the surrounding air to freeze these solutions. Later the stored energy by the Positive Eutectic, PCM Thermal Energy Storage can be released back to the occupied space during day-time to handle the heat gains.

This technique is generally called Passive Cooling and it may enable the charging process to take place by means of free cooling, i.e. without running the chillers and as a result becomes a very economical and environmentally friendly system. Furthermore, PCM energy storage opens new opportunities to explore heat balance for the existing and new systems, which could offer significant overall system efficiency improvements.

Alternatively, the sun energy during day-time is stored and later utilised during colder night-time to heat the space for a free heating as well as storing heat in the hot water circuits.

Privatisation has created a new kind of energy market whereby the period of energy usage and the type of energy used is becoming the main criteria for price structuring rather than overall energy consumption. Hence, cooling systems must be designed to provide sufficient flexibility for load shifting and a PCM Thermal Energy Storage technique can be considered as a useful tool to achieve this aim.

Building services must be designed to provide sufficient flexibility for load shifting and energy usage control in order to achieve the most economical operation. A PCM Thermal Energy Storage technique whereby "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.

Passive Cooling PCM Thermal Energy Storage (TES) benefits can also be applied for electronic chamber, shelter, telecom shelters, remote pump and electric control cabinet cooling for remote location whereby the lack of electricity eliminated the mechanical air conditioning or alternatively mechanical cooling free applications around the World.

These Passive Shelter Cooling systems can even operate in hot countries like the Middle East due to higher space temperature (45ºC / 113°F) requirements in comparison with Office Cooling. A PCM solution of 32ºC (89.6°F) is sufficient to maintain the room temperature below 45°C (113°F) by simply using the temperature swing between day and night time.

The same concept has also been successfully applied for cold storage transport applications using Eutectic beams. The majority of the perishable food must be chilled during transport but the cost of refrigerated truck restricts the use of transport cooling in particular in the third world where the biggest waste occurs. A PCM, Eutectic filled high ceiling beams can be simply charged using standard cold storage can keep the product temperature under control at a very attractive lower cost to install and run.

These passive cooling units can be supplemented using a very small refrigeration compressor or a chilled water circuit for lower temperatures but products like chocolate, bakery products and flowers can be easily maintained under control by simply charging these beams / containers over-night and utilising the stored energy during day-time transport. Furthermore, this concept enables the owners utilise their standard Lorries to be used as refrigerated trucks during harvest / peak season at a fraction of the cost for a conventional refrigerated truck.

HVAC / Air Conditioning PCM passive cooling concept offers mechanical refrigeration free passive-cooling by simply storing the night cool energy and releasing the stored cold latent heat capacity during day-time to keep the space temperatures under control. Low ambient temperatures coupled with free cooling offer a significant reduction of energy consumption relating to the cooling operation, which is in the region of 16-46 % depending on the type of passive cooling unit and location.

Based on the applied projects, ambient profiles in many parts of the world and associated feasibility studies indicates that PCM assisted Passive Cooling concept offers economical and very environmentally friendly cooling options. In any country whereby the night ambient does not allow being sufficiently low enough to charge PCM Thermal Energy Storage (TES) cells over-night, a supplementary dry cooler and / or small chiller can be added to top up the difference between the ambient and PCM temperature for an economical solution.

Modern society's reliance on refrigeration and air conditioning indicates that refrigeration and the associated environmental issues will be with us for a considerable time and therefore one has to utilise existing and available alternative technologies with minimum usage of energy.

A Positive Temperature Eutectic " PETES " Thermal Energy Storage not only provides the end user with an Environmentally Friendly design but also the following additional benefits can be obtained:

• Reduced and No Refrigeration Equipment

• Capital Cost Saving

• Reduced Maintenance.

• Energy Cost Saving

• Reduced CO2 Emission

• Environmentally Friendly Installation

• Improved System Operation / Reliability

• Flexibility for the Future Capacities Changes

The temperature ranges offered by the proposed Phase Change Materials solutions utilise free ambient cooling, conventional chilled water temperature ranges for both the charging and discharging sides of the system. Hence, they can be applied to any new or retrofit application with minimal technical and economical impacts.

Finally, the possibility of Free Cooling Cycle TES system offer new horizons for designers to control the energy balance to match the load and electricity demand / consumption of the system as a whole.

Zafer Ure, M.Sc., C.Eng., MCIBSE., MASHRAE., MInstR., is the Managing Director of Environmental Process Systems Ltd. and has 25 years experience in the HVAC industry and has writen many papers for industry conferences and magazines. Details of PCM Products can be found ay www.pcmproducts.net  and Zafer can be contacted on +44 1733 243400 or at z.ure@epsltd.co.uk