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Split type Inverted heat pump model with multiple indoor units

asked 2015-07-01 08:26:16 -0500

Waseem's avatar

updated 2020-01-24 10:13:37 -0500

Is there a way to model split inverted heat pump unit (ductless) with multiple indoor units? I know the PTHP is a single zone system but what if it is connected to multiple indoor units, how to model this scenario then?

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answered 2015-07-01 09:37:58 -0500

kwalkerman's avatar

To connect one outdoor unit to multiple indoor units, take a look at the Variable Refrigerant Flow Equipment objects. You will need to use the following:

AirConditioner:VariableRefrigerantFlow - this is the outdoor unit

ZoneTerminalUnitList - this is a list of indoor units. The outdoor unit will reference this list so that it knows which indoor units it is connected to.

ZoneHVAC:TerminalUnit:VariableRefrigerantFlow - this is the indoor unit, and is used instead of the PTHP.

Coil:Cooling:DX:VariableRefrigerantFlow and Coil:Heating:DX:VariableRefrigerantFlow - these are the variable refrigerant cooling and heating coils. Each ZoneHVAC:TerminalUnit:VariableRefrigerantFlow will need one cooling and one heating coil.

The example file: "DOASDXCOIL_wADPBFMethod.idf" shows an implementation of these objects.

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@kwalkerman: Thanks for your answer but in PTHP we only have ZoneHVAC:PackagedTerminalHeatPump, which accommodates coils, fans etc. and we don't have specifically indoor and outdoor units. If I replace ZoneHVAC:TerminalUnit:VariableRefrigerantFlow with ZoneHVAC:PackagedTerminalHeatPump, then what will be outdoor unit for PTHP?

Waseem's avatar Waseem  ( 2015-07-01 10:17:33 -0500 )edit

with ZoneHVAC:PackagedTerminalHeatPump, the performance of the outdoor unit is integrated into directly into the ZoneHVAC unit. There is no separate outdoor unit.

kwalkerman's avatar kwalkerman  ( 2015-07-01 11:37:38 -0500 )edit

@kwalkerman: Sorry if I misunderstood it. Are you suggesting that I should use VRF system and then using multiple terminal units instead of PTHP (as PTHP is limited to one indoor unit i.e. ZoneHVAC:PackagedTerminalHeatPump)?

Waseem's avatar Waseem  ( 2015-07-02 07:43:40 -0500 )edit

@Waseem: yes. Use the VRF system with multiple ZoneHVAC:TerminalUnit:VariableRefrigerantFlow units.

kwalkerman's avatar kwalkerman  ( 2015-07-02 11:50:58 -0500 )edit

@kwalkerman: Thanks :)

Waseem's avatar Waseem  ( 2015-07-02 12:28:56 -0500 )edit

answered 2015-07-01 16:42:11 -0500

Archmage's avatar

I think it depends if the muliple indoor units are all in the same thermal zone or not. If they are in different zones, then this is VRF. If they are all in the same zone then it is just one big PTHP and you would just ignore the fact that there are really multiple indoor units. You can also model with just a single zone terminal unit using the VRF system, as for a mini-split.

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@Archmage: Yes, they are serving the same zone and it makes more sense to just represent them as one big PTHP, but how you will add their capacities etc.?

Waseem's avatar Waseem  ( 2015-07-01 17:31:51 -0500 )edit

It is hard to say, but I would think the compressor/condenser section would determine the cooling and heating capacities, while the strait sum of indoor units would determine the zone air flow. Time to apply some engineering judgement.

Archmage's avatar Archmage  ( 2015-07-02 06:15:38 -0500 )edit

answered 2015-07-01 11:18:14 -0500

I think you can just put your heat pumps in an AHU and then connect them up to the zones with a VAVnoreheat or singleductuncontrolled, depending on whether it is a variable air flow or constant air flow system.


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this would still be one indoor unit and one outdoor unit, but you would be able to supply multiple zones with the one unit.

kwalkerman's avatar kwalkerman  ( 2015-07-01 11:59:39 -0500 )edit

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Asked: 2015-07-01 08:26:16 -0500

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Last updated: Jul 01 '15