Ice thermal storage in air-con

Klaus Grandegger and Aslan Al-Barazi.

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Klaus Grandegger from Fafco SA of Biel/Bienne, Switzerland and Aslan Al-Barazi from IMEC Electromechanical Engineering of Sharjah look at the key factors involved in making ice thermal storage a success.

Ice thermal storage units can be the solution to possible problems in modern refrigeration and air-conditioning. In certain cases they are even the most economical investment. Over and above which new research has shown that certain refrigeration systems with ice storage units need even less electrical energy than conventional systems. Ice storage units today represent a popular method to provide refrigeration.

Although there is a wide choice of different ice storage systems on the market, the predominant system for air-con applications is the so-called indirect brine system using plastic tube heat exchangers. The advantages of this system are obvious, which makes it the first choice when ice storage is considered.

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FEATURED COMMENT This is interesting and I intend to work on this idea. No doubt water (having highest heat capacity) if good for heating   6 Comments Read more comments »

Why use ice storage?

At an ice melting heat of 333 kJ/kg and sole utilisation of the latent energy, there is theoretical storable energy of 84.5 kWh/m3 water as ice available. This is about twelve-fold the storable energy in comparison to direct use of the sensible energy from water – or, looked at differently – the required storage size is only 1/12. In practical use it can be assumed that there is a 50-60 kWh ice storage capacity latent per m3 vessel volume, depending on design and melting method.

The ice melting point of 0°C means that typical applications for ice storage units are in the temperature range between +2…+6°C. Ice storage units have the advantage of simple plant technology, the use of an inexpensive and ecologically harmless storage medium and, in many cases, can today be employed economically. The wide range of ice storage unit application opportunities in the temperature range mentioned above is unbeatable. The following aspects are generally pivotal for the cost-effectiveness of ice storage systems:

•Basically anywhere where high refrigeration capacity is required;
•Where there is a requirement for high refrigeration capacity but short operating times;
•Where water-saving, modern, dry cooler systems are used;
•Where the annual operating periods are generally short (purely comfort air-con, low plant utilisation);
•Where there is a difference between day/night tariff for power and where there is demand charge for electricity;
•Where an existing plant is to be extended;
•Where an outdated plant is being renewed;
•Where there are layout constraints;
•Where part loads predominate;
•Where there are frequent refrigeration machine cycles (here there is a distinct improvement in efficiency);
•Where there are irregular cooling demands (shopping malls, office buildings, universities, exhibitions, stadiums, theatres, museums);
•For emergency refrigeration applications, where emergency refrigeration is only required for short periods; and
•Where substitution/replacement of absorption refrigeration machines is required, particularly where the transformer station cannot be enlarged or the power source is limited.

The use of the latent energy of ice in the form of melting heat thus represents a simple possibility to store cooling energy and to keep the storage space and therefore also the investment cost as low as possible.