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Modeling DHW recirculation loop in EnergyPlus

asked 2023-11-11 10:28:20 -0600

Afshin's avatar

updated 2023-11-12 13:42:38 -0600

Hi Community,

I am trying to model a domestic hot water re-circulation loop with a water heater and a pump in EnergyPlus and I was wondering if anyone has any experience with modeling that. Any document and sample IDF file would be very helpful.


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answered 2023-11-13 00:40:55 -0600

Keigo's avatar

As long as I know, EnergyPlus cannot model DHW recirculation loop, but there is a workaround.

Let me take the ExampleFile WaterHeaterDHWPlantLoop.idf to explain. The schematic is as shown below.

image description

The schematic looks like a Loop at a glance, but actually, DHW is not recirculated.

The water flow rate in the DHW Loop is equal to the flow rate of hot water (Vh) which is actually consumed at water fixtures (WaterUse:Equipment).

In my MEP experience, DHW recirculation pump is to maintain the water temperature in the DHW recirculation pipe, and it is constant speed. The pump flow rate is different from the actual hot water demand which changes from time to time. However, EnergyPlus cannot model the constant-flow recirculation pump.

Design Pump Head in the ExampleFile is set to 0Pa, which indicates the pump is a "virtual" pump which is only used to drive water flow.

I think you should keep the Design Pump Head 0Pa, and the workaround to model a DHW recirculation pump is that you can add the pump power [W] of the recirculation pump (you can hand-calculate it as it should be constant) to On Cycle Parastic Fuel Consumption Rate [W] and/or Off Cycle Parastic Fuel Consumption Rate [W] in WaterHeater:Stratified or WaterHeater:Mixed. On/Off Cycle Parastic Fuel Type should be Electricity. On/Off Cycle Parastic Heat Fraction to Tank should be 1 if you want to account for the water temperature rise by the pump heat.

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Thanks @Keigo for your response. I really appreciate your visual presentation of the concept. It makes sense to me. I will try your suggestion and will let you know if I face any issues.

Afshin's avatar Afshin  ( 2023-12-03 11:42:21 -0600 )edit

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Asked: 2023-11-11 10:28:20 -0600

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Last updated: Nov 13