For the end user

From ITSAC (Sept. 95) - San Diego - CA :

"Modern cool storage systems can save up to 10 % or more of electricity consumption for A/C".

From Harp Brewery - Dundalk - Ireland :

From these remarks, it is easy to understand that there is no general rule to evaluate the COP reduction factor in relation to the observed reduced capacity.

Indeed, the COP factor depends on :

• the nature of the chiller : hermetic, semi-hermetic (can be aggravated by the quality of the compressor / motor coupling)
• the technology of the evaporator : sealed, tubular and grid, plates and also on the number of passing (2 is more tricky, whereas 4 is less sensitive)
• the quality of the constructor, in particular the coupling of the compressor / evaporator.

Note on the variation of the chiller efficiency with its reduced capacity

It is well known that a cooling system usually runs on reduced capacity. This means that :

• for the compressor, there is a by-pass of the gas at the end of the compressor circuit leading to an unproductive work.

• for the evaporator, the running conditions are outside the normal conditions and then its efficiency decreases.

In conclusion, taking into account the experience of the chiller’s constructors, it seems to be reasonable to keep in mind the following hypotheses 

25 % reduction capacity à +10 % electricity consumption

50 % reduction capacity à +20 % electricity consumption

75 % reduction capacity à +40 % electricity consumption

For the country

 It is well known that to provide electricity 

the power plant needs :

 ~2 300 Kcal / kWh elec. night

~2 500 - 3 000 Kcal / kWh elec. day

~3 500 - 4 000 Kcal / kWh elec. peak hours

i.e. 40 % more during the peak time than during the night.