Loop-to-Loop Heat Pumps

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I am simulating a building which has three water-cooled centrifugal
chillers and one loop-to-loop heat pump. The baseline building has three
equally sized cent. chillers. I am seeing an increase in cooling energy
for the system of about 18%. eQUEST is also crashing about every third
run even though the only changes I am making are to the capacity ratios.
Any thoughts would be greatly appreciated.

The centrifugal chillers are connected to a condenser water loop with
cooling tower and the chilled water loop with a CHW temp of 44F.
The loop-to-loop heat pump is connected to a lake/well loop with high
and low temps of 110 and 30. It provides heating to a separate lower
temperature hot water loop at 130F and CHW to the main CHW loop at 44F.

The engineer has sized the proposed system for 225 tons on the ground
loop/loop-to-loop heat pumps, and 450 tons split between the other three
chillers. I applied capacity ratios for all four pieces of equipment to
split the loads accordingly.

The loop-to-loop is running for most of the hours between 10 and 30%
part load even if I size the heat pump well below its maximum capacity.

Thanks in advance,

Sam Mason

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Joined: 2011-09-30
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