Why Doesn't DOAS Output Temperature Affect HVAC Input?

Hi, Community!

I am working on a model using the HB DOAS HVAC component in Ladybug Tools. I’ve configured the heat recovery efficiency for the DOAS to 70% for sensible heat and 62% for latent heat. However, when I checked the EnergyPlus results, specifically the “Outdoor Air Drybulb at Ideal Loads Peak [C]” variable, I noticed that the air temperature entering the air conditioning equipment is the same as the outdoor temperature (30°C in my case), even though the DOAS is operating.

I was expecting the air to enter the air conditioning equipment at the DOAS output temperature, which should be around 14°C, considering the configured heat recovery efficiency. This doesn’t seem to be happening, and I feel like the HVAC system is being overestimated since the load handled by the DOAS is not properly reflected in the report.

My questions are:

  1. Why doesn’t EnergyPlus consider the DOAS output temperature for the air entering the air conditioning equipment?
  2. Is there an additional adjustment or configuration needed in the model to ensure the air treated by the DOAS is properly accounted for?
  3. Should I manually recalculate the VRF system load to subtract the load treated by the DOAS, or is this supposed to happen automatically with the current configuration?

I’d appreciate any insights into the expected behavior of the DOAS component in Ladybug Tools and how to align the results with the configured heat recovery logic.

Attached is the model:
TEST_HVAC_DOAS_R02.gh (164.6 KB)

Thank you in advance for your help!

Hi @LuizHVAC

I guess your simulation is correct

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Yes, the simulation is correct, but the air outlet from the DOAS at 14.56 °C should be the external air inlet into the VRF Equipment. However, the External Air is entering the VRF Equipment at 30.10°C, this temperature being different from the DOAS outlet. Reduced temperature outdoor air coming from DOAS should reduce the capacity of the VRF equipment, but it is increasing.

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The below picture is the HVAC system (DOAS+VRF) you selected on HB, represented by OpenStudio app.

I check the configuration of this specific HVAC from HB with the IronBug system as below:

The setpoints and everything I check is matched.

Please find the below picture as well from the produced HTML from your simulation

from 1 in the picture that is DOAS, the air with 30.10 [C] enters and leaves with 14.56. Then if you exclude the cooling coil, and from the heating coil in the 4, the air enters the VRF at 13.05 and leaves the VRF to the your zone at 40. at 5.

I hope this help.

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Thank you very much @behnammmohseni, this helped a lot to understand the behavior of my system.

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