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

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?

( 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.

( 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%.

( 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.

( 2023-09-29 14:05:23 -0500 )edit