Modeling a Central Heat Pump Chiller (not geothermal)

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I'm aware of TRACE's ability to model geothermal chiller-heaters using bi-directional cascade effects, but how can I get TRACE to do this without a ground loop?  All I have is the evaporater side of the chiller producing chilled water and then rejecting the heat to the condenser side where it supplements the fossil fuel boilers. 

Can I just set the heat rejection type from "ground loop" to "heating plant" and then specify my backup boiler?  If I do this, I loose the ability to select "bi-directional cascade." Is this okay?

Finally, if this chiller is one of several chillers in a chiller plant, should it be sequenced in a "side-car" or "base load" arrangement?

Thanks!

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Anonymous

I suppose you could do this, though I think it would be better to specify that you switch to thermal storage for the heat rejection type (the water in the loop has significant heat capacity that would otherwise be ignored).

If this is the ONLY heat pump chiller in a plant, then you may want to specify it as side car, otherwise parallel should be kept.

The real "magic" of these new chillers is their unloading curves, as seen in the Library. The bidirectional cascade effects simply allow them to operate at higher/lower temperatures (and share energy) when BOTH chillers are on.

 

So if you only have 1 chiller heater, bidirectional cascade doesn't need to be selected anyway.  1 of these is capable of both heating and/or cooling, so I believe you are on the right track, just select thermal storage to account for the water in the pipes.

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