Connecting AHU system to VRF Outdoor Unit in Energy Plus Model

asked 2019-01-16 21:32:10 -0600

zahro
373 ●1 ●9

updated 2019-02-02 13:52:26 -0600

My system will be using a central AHU system as the fresh air supply, and it will be connected to the VRF outdoor unit. I am trying to calculate the annual electricity consumption of my system. I am using DOAS system to model my AHU, but what I understand from energy plus is that the DOAS system has their own outdoor unit, and will not be included as the load for VRF outdoor unit. Is that correct?

Is it possible for me to connect the DOAS system to VRF outdoor unit, to have good estimate of electricity consumption, considering the performance curve of VRF system? If it's not possible, what possibly could I do for this situation?

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answered 2019-01-17 09:23:32 -0600

rraustad

13834 ●79 ●12 http://www.fsec.ucf.edu/

You can connect an AirTerminal:SingleDuct:Mixer directly to the VRF indoor unit to provide outdoor air. This may not be available directly in OpenStudio or via measures. However, this component is available in EnergyPlus. Each version of EnergyPlus has an ExampleFiles-ObjectsLink.html file in the ExampleFiles folder. This file shows that the example files DOASToFanCoilInlet.idf, DOASToFanCoilSupply.idf and DOASToPTAC.idf each show how to connect the mixer to these equipment types. Connecting the mixer to VRF indoor units will be similar or identical. Also see documentation to learn about the mixer component.

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If I understand correctly, by that means, the fresh air cooling load would be handled by VRF indoor unit instead of the DOAS cooling coil? For now, I use HVAC Template of VRF and DOAS in Energy Plus so probably it might not work for my current model, how do you think if I subtract the cooling capacity of the AHU from the actual outdoor unit capacity, and put those number instead in my model? Would it provide a good estimate of electric consumption of both AHU and Outdoor Unit?

zahro ( 2019-01-17 19:56:38 -0600 )edit

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Subtracting DOAS capacity from VRF probably won't change things much. If modeling DOAS connected to zone equipment then the best course of action would be to set things up that way.

rraustad ( 2019-01-22 07:54:35 -0600 )edit

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answered 2019-01-17 08:43:20 -0600

pow_skier

290 ●2 ●6

It is possible. DOAS will supply fresh (tempered) air to the space and then in the space - thermal zone - will be a indoor VRF therminal which is connected to it's own outdoor unit. On the Building Component Library are some measures that may do what you are looking for in an automated fashion.

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I am sorry but I could not understand your explanation, so what do you mean is that you can set the DOAS to bring the fresh air directly to the zone, and those load would be handled by the VRF indoor unit? I am defining all my system in Energy Plus, and up until now I have not understood Ruby yet, that's why I am avoiding using Open Studio measure this time. Do you have any alternative method in defining the system?

zahro ( 2019-01-17 20:07:15 -0600 )edit

@pow_skier

I have tried all alternatives on OS and had no sucess.

I guess I will have to define everything on E+ as well.

If anyone have a better idea, it will be appreciated.