Unable to insert a Coil:WaterHeating:AirToWaterHeatPump:Wrapped component into a branch

asked 2021-11-14 18:00:54 -0600

RMurray
83 ●4

updated 2021-11-16 10:40:48 -0600

Aaron Boranian

14250 ●86 ●24 http://bigladdersoftware.com/

I was hoping to account for the heat removed from the zone air by the HPWH by modeling the evaporator coil and draw-through fan separately from the compound object WaterHeater:HeatPump:WrappedCondenser. So, I tried to create a branch for airflow that contained Coil:WaterHeating:AirToWaterHeatPump:Wrapped as the first component and the fan as the second one. Any suggestions would be most appreciated!

P.S. I also tried simply adding a Coil:Cooling:DX:SingleSpeed, instead, but this couldn't be added to a branch object either.

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answered 2021-11-16 10:57:06 -0600

Aaron Boranian

14250 ●86 ●24 http://bigladdersoftware.com/

updated 2021-11-19 09:42:09 -0600

TL;DR: You shouldn't assign the wrapped DX coil of a HPWH to a branch -- you should instead assign the compound HPWH system object that contains the wrapped DX coil to a branch.

The Coil:WaterHeating:AirToWaterHeatPump:Wrapped object is meant to be one component of a heat pump water heater (HPWH), specifically the DX air-to-water coil that heats water on the condenser while cooling air on the evaporator. There are multiple other objects that are also needed:

WaterHeater:HeatPump:WrappedCondenser: compound object that represents the entire HPWH system
WaterHeater:Stratified: storage tank
Fan:OnOff, etc.: fan to blow air across the evaporator

So, when defining where the wrapped DX coil is located, it is assigned as an internal component of the WaterHeater:HeatPump:WrappedCondenser object, which is what is actually assigned to a branch. This is why the only nodes to define for the wrapped DX coil object are the evaporator air inlet & outlet nodes.

You can see an example of this wrapped HPWH compound object and it's internal components in the SingleFamilyHouse_HP_Slab.idf example file that comes with your EnergyPlus installation.

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Thanks for your response, Aaron! I should clarify, though, that the WaterHeater:HeatPump:WrappedCondenser compound object can only be used with the WaterHeater:Stratified object, according to 9.5.0 documentation.