I am trying to model 2 325-ton water cooled chillers that connect to a cooling tower on the roof. After running the two chillers each with the cooling tower assigned in the heat rejection field we ended up using more energy for heat rejection than for the total cooling of the building. This didn't make sense at all, so we tried removing the cooling towers from the chillers and assigning a cooling tower to the cooling plant at the plant level. Oddly enough, this ended up nearly doubling the heat rejection energy.
Am I missing something here? Is there some way to model two chillers sharing a tower that I am missing?
Alternately, this whole issue stemmed from splitting my plant into two 325 ton chillers. Initially, we had a single 650 ton chiller with a cooling tower assigned to it and our numbers for space cooling and heat rejection seemed to make sense. As soon as I split the chiller into two, we ended up with this issue.
How are the chillers set up in real life? Lead/lag?
How do you have them sequenced in TRACE?
Have you assigned the same type of cooling tower to each chiller? This may not be the same as wanting them to go to one cooling tower but rather each with its own of that type. Such that you have two cooling towers capable of rejecting 650-tons, and if they are constant speed fans, they would each run for their respective chiller, effectively doubling the heat rejection consumption.
A screen shot of the plant tab may help...