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How to disable Parallel PIU Fan during cooling

asked 2022-08-19 01:02:33 -0600

Keigo's avatar

updated 2022-08-19 08:53:08 -0600

I believe most of you guys know the answer to my question since VAV with PFP Boxes is very popular HVAC system a.k.a. Baseline System 8 in ASHRAE90.1.

I want to run Parallel PIU (Powered Induction Unit) Fan only during heating. When no heating, I want to turn it off, which is the correct PIU fan operation (see my previous post), but I don't know how to do it.

I tested with a slightly modified ExampleFile: HVACTemplate-5ZoneVAVFanPowered.idf. I changed the terminal unit of SPACE5-1 from HVACTemplate:Zone:VAV to HVACTemplate:VAV:FanPowered (All the terminal units became VAV:FanPowered). Flow Type of HVACTemplate:VAV:FanPowered was changed to Parallel. I also changed the cooling/heating setpoints slightly (Cooling: 26degC, Heating:20degC) to make a clear difference between cooling and heating. After running the modified idf file, I opend the expidf file and edited AvailabilityManager:NightCycle as follows.

    VAV Sys 1 Availability,  !- Name
    HVACTemplate-Always 1,   !- Applicability Schedule Name
    FanAvailSched,           !- Fan Schedule Name
    CycleOnAnyZoneFansOnly,  !- Control Type
    0.2,                     !- Thermostat Tolerance {deltaC}
    Thermostat;              !- Cycling Run Time Control Type

I referred to the section of AirTerminal:SingleDuct:ParallelPIU:Reheat in I/O Reference. I thought AvailabilityManager:NightCycle overrides the PIU fan schedule.

image description

The chart below is the simulation result on one winter day and one summer day. The weather file is Chicago.

image description

There are 1 system supply fan and 5 PIU fans (5 zones). As you can see, PIU fans operate on 7th July, although the heating load is exactly 0W in all zones throught the day. I thought there was something wrong with my AvailabilityManager:NightCycle setting. I tried other Control Type, other Cycling Run Time Control Type and adding Zonelist, but all in vain. How can I disable the Parallel PIU Fans when there is no heating?

All the relevant files are here. The EnergyPlus version is V9-6-0.

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answered 2022-08-22 22:31:19 -0600

ngkhanh's avatar

updated 2022-08-23 01:32:46 -0600

Check this modified_idf which I change Fan On Flow Fraction from autosize to 0.0 to get summer sizing day with zero PIU fan flowrate. As schematic, Fan PIU is secondary while VAV damper is primary so if you don't want to turn on the fan during cooling mode you need to get Fan On Flow Fraction at zero

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Perfect! Parallel PIU Fans turned Off only during cooling and remain On during heating. Thank you so much!

Keigo's avatar Keigo  ( 2022-08-22 23:03:14 -0600 )edit

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Asked: 2022-08-19 01:02:33 -0600

Seen: 237 times

Last updated: Aug 26 '22