How to model Adiabatic Humidifier

asked 2022-09-25 07:47:54 -0500

Keigo
3699 ●1 ●43 ●21 https://www.linkedin.c...

updated 2022-10-01 14:54:51 -0500

I want to model adiabatic humidifier. According to this post, EvaporativeCooler:Direct:ResearchSpecial seems to be the most appropriate.

For ASHRAE90.1 Appendix G compliance, if the proposed design includes humidification then the baseline building design shall use adiabatic humidification, but the problem is that the proposed case and the baseline case have different HVAC systems.

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My proposed case has DOAS. The adiabatic humidifier is installed after the heating coil of the DOAS. I can model it as per design. The indoor setpoint in heating is 22ºCDB, 40%RH (or more). The outdoor air is humidified only when heating.

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The HVAC sytem of my baseline case is System 8—VAV with PFP Boxes. I'm going to add EvaporativeCooler:Direct:ResearchSpecial after AirTerminal:SingleDuct:ParallelPIU:Reheat. Is this correct?

Besides, I need to calculate Cooler Design Effectiveness for the baseline case. I thought about Step 1 to 5 below to calculate it. Is this approach correct?

Could you correct me if I'm wrong?

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Cooler Design Effectiveness = (DBin - DBout)/(DBin - WB), according to Engineering Reference. The proposed case and the baseline case should have different Cooler Design Effectiveness to meet the same indoor setpoint.

The original PDF is here in case the text in the above psychrometric charts is too small to read.

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answered 2022-09-29 05:41:38 -0500

Keigo
3699 ●1 ●43 ●21 https://www.linkedin.c...

updated 2022-10-02 06:39:51 -0500

For the Baseline case (System 8—VAV with PFP Boxes), I could not add EvaporativeCooler:Direct:ResearchSpecial after AirTerminal:SingleDuct:ParallelPIU:Reheat due to Node connection constraint. It seems that AirTerminal object must be directly connected to Zone Air Inlet Node. I got a severe error, and the simulation terminated.

The only other option I can think of is adding EvaporativeCooler:Direct:ResearchSpecial before OutdoorAir:Mixer, but in this option, I also need to add a reheat coil to ensure sufficient humidification. I'm not sure if this option is allowed in terms of ASHRAE90.1 compliance.

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For LEED certification which is based on ASHRAE90.1 Appendix G, I found a LEED Interpretation although it's very old. Acording to the Interpretation, Humidity control requirements in the baseline building should be the same as in the proposed building, even if that requires reheat to be modeled with that system type. So, using the same humidity control is a priority, and it seems that minor changes to the Baseline HVAC system are allowed for that.

P.S.

Revised psychrometic charts are as follows.

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