need help on tracking cost of c hillers

[nitrousbaby]

I take care of the HVAC for my church in michigan and I am trying to find ways to figure out if it is cheaper to build ice with our 600 ton york chiller and burn it to cool the building or to just use the 550 york centrifical chiller to cool the building. I would like to hear your guys opinion in this matter, we do get a energy cost break between 10pm a 8am so thats when we build the ice.

 

[RossABQ]

Off hand, most people who have ice storage do it to shave demand charges at peak cooling periods. Those demand charges are usually more than the break between off-peak and nighttime rates. Are you using ice to meet 100% of daytime demand? Depending on the efficiency of your icemaking and storage system, it might make sense but I'd be skeptical. Is the icemaker an ammonia system?

 

[ChrisConley]

A 600 ton chiller for a church? Seems large to me.... but I guess I don't know how large the church is.

Regardless, you'd have to do an energy simulation and cost analysis to get a true picture. One of the things to keep in mind is that a chiller that produces ice is less efficient that a standard chiller, and more expensive.

You also need a place for a lot of ice.

 

[NCDesign]

You also need a place for a lot of ice.

From Wikipedia

1 "ton of cooling" ... is 12,000 BTU/h. It is the amount of power needed to melt one short ton of ice in 24 hours.

If i've done my math and conversions correctly.
A physical ton of ice can give you 288,000 BTU of cooling. A block of ice that weighs a ton will be about 34 cubic Ft. Your chiller is capable of 7200000 btu/h. So over 24 hours your chiller is capable of 172800000 BTU. If your building load is such that you only use a 1/3 of that capacity through out the day (57600000 BTUh) you would need 200 tons of ice. The ice would require 6,800 cubic feet of storage space.
That is why, like RossABQ said, you usually see ice storage only for a means of shaving peak electrical demand.

 

[nitrousbaby]

thanks guys your response helped and Ive done some research and yeah this setup is only good to shave peak times, and the church is 350,000 sq ft.

 

[marcoh]

Unless you are paying significant maximum demand charges it is unlikely that that a thermal energy storage system would financially stack up, especially as a retrofit.