Hot afternoons cause real problems for both users and suppliers of electricity. The efficiency of a standard air conditioning system depends inversely on the difference between the indoor and outdoor temperatures, so the hotter the day the less efficiently the system runs, pushing up the cost of cooling for the user.


And the impact of all the air conditioners coming on during the same part of the day is to push peak loads up – this means that the electricity generators need to have a large amount of ‘spare’ capacity available, requiring them to build and maintain power stations that may only be needed intermittently. These power stations, which only come on at peak times, tend to be the least efficient and the most polluting.


Thermal energy storage can ease this problem for both users and suppliers. By cooling down a thermal reservoir during off peak hours, the users benefit from cheaper electricity (on a time-of-use tariff) which they will use less of because their chiller will be working more efficiently in the cooler temperatures. The suppliers will benefit from the evening out of demand.


Thermal energy storage systems come in many forms. Large commercial buildings with concrete slab floors can use the floor as storage by burying pipes in it and circulating chilled water at night. Smaller buildings can use an icemaker at night, using the latent heat of melting to cool the building during the day. Chilled water can also be used, stored in large tanks – chilled water storage systems are technically easier than ice system, but have a lower energy density.


Single family homes have generally not used thermal storage due to high initial costs. We are working on a project to combine chilled water storage with a radiant cooling system to bring thermal storage to the residential market. The main question that we hope to answer with our research is:


  • Do the advantages of thermal storage outweigh the cost of building the storage?