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Preheat SHW water with HX on Condenser loop

asked 2015-04-10 18:13:58 -0600

pflaumingo gravatar image

updated 2015-06-25 20:09:49 -0600

I have a building design with a large condenser water loop and the DHW design uses a heat exchanger with the condenser loop (60F-80F deadband) to preheat the incoming mains water before reaching the water heater inlet. Is there a way to model this natively in OpenStudio? Could I just add an HX in series before the Water Heater on the DHW supply side and then place that HX on the demand side of the condenser loop?

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answered 2015-04-10 21:15:13 -0600

updated 2015-04-10 21:19:56 -0600

I recently used the following configuration for a large hotel project with a similar design. The design called for a condenser loop providing HHW and CCW from boilers and fluid coolers to terminal WSHPs. The service hot water was heated by the condenser loop through a HX and storage tank system.

I added a HX to the demand side of the condenser loop (not shown) and then added the same HX to the supply side of the SHW loop. I also ended up simplifying the model by removing the WaterHeater:Mixed object. However, I did test the HX and WaterHeater:Mixed configuration and it also worked.

WSHP Loop (HX is on the supply side off the screen)

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SHW Loop

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Matthew, thanks for the response. I have pretty much an identical WSHP system along with a water-to-water HP for a radiant system and a self-contained PVAV on the same condenser loop. What sort of temperatures you were able to get leaving the heat exchanger as I imagine that condenser loop is only at about 80F-85F maximum, right? I would think that typically water leaving a water heater would be at about 120F and then mix with the mains water for the desired temperature. Or is that the simplification you are referring to because the target DHW temperature, on average, is much lower?

pflaumingo gravatar image pflaumingo  ( 2015-04-11 16:03:01 -0600 )edit

I didn't output the HX node temps to check, but the condenser loop had a 50-95F range with a 70-75F deadband per the sequence of operations and I wasn't concerned with the SHW use because it was already at an acceptable level for the building type.

MatthewSteen gravatar image MatthewSteen  ( 2015-04-14 19:11:03 -0600 )edit

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Asked: 2015-04-10 18:13:58 -0600

Seen: 450 times

Last updated: Jun 25 '15