Chiller Allocation

Yes, that will work. Just do the math.

I would... measure the output of the chiller going to each of the three buildings and then determine the share of the operating cost from that. You could even do it real time and then apportion the cost as need be.

I think you're looking for something like this:

http://www.kep.com/catalog/flow/tutorials/pdfs/chilledmeteringf049.pdf

There are others, it's a common concept in Europe where tenants are billed for their chilled water, heat and hot water usage just like electricity and potable water.

Your question implies that you know the power cost of running the chiller and wish to allocate it among a number of users based on individual space area and required temperature. Unless all other factors are equal, which they rarely are, this can result in an inequitable division of energy costs.

For example, when a user requires cooling at nights and weekends when others do not, your actual power cost for him may be higher due to low efficiency of the chiller operating at part load. Or, a user with windows facing west can use more cooling energy and at different times than a user with windows facing north.

Here are two ways for you to work this out:

1. Run an hour-by-hour simulation for an entire cooling season using hourly weather data for your area together with models of chiller performance and individual user space cooling energy requirements. EnergyPro
2. Install electric power meter for chiller system including pumps, etc., plus chilled water energy meter for each user. Connect all meters to computer programmed to calculate hourly power cost as per your electric utility's rate schedule and to allocate the cost among the individual users based on their hourly share of the cooling energy used.

Thanks for your comment ,

Is there any methods to find theoretical solution for this question ??

My no. 1 suggestion, doing an hour-by-hour simulation, is in fact a theoretical solution. It requires you to make a number of assumptions concerning occupation levels, internal loads, building materials, heat transmission, solar radiation, chiller efficiency, weather conditions, etc.

There are many software simulation programs available ranging from quite simple to very complex, depending on the degree of accuracy you wish.

An allocation of the cost of electrical energy used by the chiller system between the various users based on space area alone would be a first order theoretical solution. It may or may not be very accurate.

I suggest that you study the link EnergyPro I included in my first reply. If you feel you can do it, this program can solve your problem and supply you with the documentation to justify the cost allocation you finally decide to make.

fix Btu meters in the main chilled water pipe line enters to each building. take the chiller kWh value proposioally for 3 building based on the cooling load in each building.

with these..