Help with energy calcs

[Graham Eady]

I am using an 'air load' calculator which gives me a total cooling load in kBtu for an installation based on the cfm for different locations around the US.
The figure that I get is the cooling required to bring the air temp down to the required set point but I want to be able to convert this figure to the required electrical load for the whole cooling plant.
What I am looking for are some 'rules of thumb' for coming up with the calculation.
The air supply that is being cooled will be provided via an AHU ( air handling unit ) and the systems are 'full fresh air' ( no re-circulated air ) and I assume that it will have a dx coil or a cooling coil operating on chilled water.
I have looked at packaged chillers on the web and have a good idea of the general power input to cooling load output --
what I need now is an idea of the efficiency of a cooling coil and the associated pipe work.
I have a methodology for different heating systems e.g. if we have a gas fired boiler providing low pressure hot water to a coil in an AHU I assume an efficiency of 80% for the boiler and an efficiency of 66% for the heat tranfer to the air ( includes pipe heat losses and heat tranfer in the coil to the air )
Can I assume a similar 66% for a chilled water circuit through a cooling coil ?
If we are using a dx coil in the air stream -- what is the efficiency of the cooling ?

As you have probably guessed, am an electrical engineer not a refridgeration engineer.

HELP

[nike123]

Efficiency of chiller is about 250-300%!

[Graham Eady]

Efficiency of chiller is about 250-300%!

Thanks for the reply.
Do you have any figures for the efficiency of the application -- for example the chiller will produce chilled water according to it's efficiency but then this water is passed through a coil in an AHU -- how much is typically lost in the pipework and efficiency of the cooling transfered to the air passing through the AHU -- in other words the 'application efficiency'

[Greengrocer]

For a typical chilled water A/C application you would expect to gain approx. 1c from the chiller to the AHU inlet & another 1c on the way back. So for a chiller leaving water temp of 7c it would arrive at the AHU at 8c + the AHU DT (normally 5c) sub total 13c +1c for the return & back to the chiller at 14c or so.
Pipe run lengths, insulation, type of coil in AHU and ambient temps will determine actual overall system efficiency. Pumps might also have a small effect.
A Dx system will be more efficient than a chilled water but harder to control to match fluctuations in fresh air.