why the ventilation load calculation results in energy plus and HAP are different?

asked 2023-09-06 11:52:37 -0500

payam's avatar

updated 2023-09-07 09:41:46 -0500

Hello Everyone, I made same models in HAP and E+(Openstudio) with exactly the same inputs, in E+ I used Ideal HVAC system and in HAP i used CAV single zone system, but the ventilation load (sensible heating load) in HAP is way higher than E+ results. I am using the ASHRAE 62.1 number for ventilation, and the way that I calculate by hand, HAP results are fine. Does the energy plus Ideal system mixes the inside air with outdoor air? I saw in engineering reference that EnergyPlus uses the infiltration air for the ventilation too. But the difference is way higher. Also I made model in IES in IES I was about 18 % higher in heating loads, and it was again because of ventilation load. if anyone knows the answer or has the same issue i will appreciate if you could share that with me. Thank you

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are you taking the same outdoor ventilation air flow, temperature and relative humidity?

obuchely's avatar obuchely  ( 2023-09-06 17:09:34 -0500 )edit

I think HAP uses this formula, which is equal to number of cfm that i calculate by excel. Vou = all zones(Rp × Pz) + all zones(Ra × Az) But for E+ I am not sure how it works. For the outdoor air features, II checked they are pretty similar.

payam's avatar payam  ( 2023-09-09 19:47:39 -0500 )edit

Are you ussing schedules for ventilation? I recently also had to compare a HAP model with an EP model and I realized that to calculate the demand, HAP always considers the loads at 100%.

DPalma's avatar DPalma  ( 2023-09-18 04:55:39 -0500 )edit

interesting , how is your result ? are they close ? no i use the maximum amount for each objects, also there is a methode in OpenStudio, import DDY (design days) which calculate the HVAC size automatically, with sizing factor. in this methode i read the zone sensible cooling and heating sensible output which shows the calculated design load ,its good on cooling, but its not close with HAP results in heating.

payam's avatar payam  ( 2023-09-29 14:05:23 -0500 )edit