Having your air conditioner and low peak demand too

Thermal Energy Storage

Suppose you run an air conditioner that uses 4 kilowatt-hours electrical energy in peak periods and it moves 20 kWh of heat energy from inside your home to outside.

This result can also be achieved if the same air-conditioner "freezes" a liquid at, say, 15 degrees Celsius overnight and in peak period you melt the frozen chemical with 20 kWh of heat energy from inside our home. (eg. By using about 140 kg of potassium fluoride converted to 214 litres of potassium fluoride tetrahydrate.)

ABC TV's Catalyst aired a program in 2007 "Council House Two" on similar Phase Change Material (PCM) technology that is installed in an office building in Melbourne.

Extract from Transcript of a guided tour of this amazing building with the host of Catalyst, Dr. Graham Phillips:

Dr Graham Phillips: The air conditioning in this building is very different. We’ve all seen radiators, of course, that radiate heat. Well these things on the ceiling essentially do the opposite of that. Through the copper piping there runs chilled water cooled down to about 15 degrees Celsius and as that circulates around it essentially sucks the heat out of the room.
...
The system they use to chill the water for the air conditioning is ingenious. They’ve got three giant tanks like this filled with 10,000 stainless steel balls.

Here’s one of the balls. They’re normally sealed and inside there’s a special substance. They wouldn’t tell me what it was – a trade secret apparently. But it’s some sort of salt mixture that freezes at 15 degrees Celsius not zero like water ice. That means these balls are very easy to freeze: they require a very small amount of energy. So, on a hot day, water is flushed through the tanks, as the balls melt, they chill the water and that’s used in the air conditioning system.

Do "Time Of Use" (TOU) tariffs work?

Industry and business have had TOU tariffs for several years. A peak period cost of 26 cents per kWh can be cut by 20 cents per kWh to just 6 cents per kWh by moving the peak load required by air conditioning and refrigeration to off-peak periods.

The option for saving 20 cents per kWh, a whopping 75 percent of peak period energy costs, has not created any discernible action let alone excitement among Australia's business managers to date.

Example of Commercially Available Energy-Storage Air Conditioner System

The following animation is from the web site of Phase Change Products Pty Ltd (PCP).

What is Thermal Energy Storage (TES)?

TES is a simple technology based on storing thermal energy in a liquid, solid or phase change material (PCM). Stored energy in PCMs can come from a variety of sources: waste heat, excess refrigeration capacity, night-time refrigeration or co-generation facilities.
Energy is released when needed for air conditioning, process cooling, or process/space heating.

PCMs solidify inside a PCM-filled vessel with a heat exchanger, or PCM-filled spheres or cylinders contained installed in large tanks.

Thermal Energy Storage systems generate energy cost savings and environmental benefits by using low cost off-peak electrical energy. TES vessels can be installed in schools, hospitals, airports, office buildings, churches, sport facilities, government offices and industrial plants.

Thermal Energy Storage with Phase Change Material

A volume of material is used to store thermal energy while it changes from the solid phase to the liquid phase at a specific temperature. The phase change material (PCM) stores heat during the melting process and stores cold during the solidification process. A thermo fluid transfers the energy from the storage tank to a load (process, HVAC unit, etc.). The phase change Thermal Energy Storage unit may charge and discharge at the same time: the melting and solidification processes of the material may happen simultaneously.