Different indoor air temperatures between unconditioned and conditioned zone

Hi, I am a new user. I am working on a Gh script using LB+HB for my Master Degree thesis. I am experiencing a weird issue. When comparing air temperatures in the zone without any system and with Ideal Air Loads conditioning, it happens that temperatures in the free-running zone are way higher (nearly unrealistic) with respect to the ones calculated when adding an HVAC system.
I can’t figure out the problem, so I’m asking support to the community.
I am not able to attach any file as I am new here.
Thanks to anybody who will help me

Hi @eleonora98,

That sounds quite feasible to me - thinking about the heat balance of the room, if there’s gains inside a space and no conditioning or ventilation, the room will increase in temperature until the external conduction loss equals the internal gains.

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Hi @charlie.brooker
thanks for your reply. I should point out that natural ventilation is allowed into the zone when indoor temperature exceeds 23°C and outdoor temperature is higher than 10°. The problem is that, when the zone experiences T>23°C in free-running mode, outdoor temperature is way under 10°C, so windows are not opened. Should I change NV constraints?
Maybe, as you said, since ventilation is not allowed due to the constraints I established, indoor temperatures without mechanical systems are higher. Instead, when the zone is conditioned, mechanical ventilation is on and mitigates indoor temperatures, as outdoor air is cold. Is my thought correct?
Thank you very much


I’ve just set up a quick test to check and I’m pretty happy with the results at a glance.
Energy_VentVsConditioned.gh (115.1 KB)

I have got the cross vent option turned on to enable wind driven ventilation despite it being one sided vent. In my opinion, without much further thought to it, I’ve done this as I would still expect there to be some wind driven vent and I’m not familiar with the details of nat vent modelling in HB.

I just tested turning off the wind cross vent and it doesn’t make any noticeable impact on the results


Sorry I’ve just re read your last comment. It’s -10C outside and your minimum external temperature for natural ventilation is 10C. That suggests that your internal gains are either very high, or your constructions are highly insulating. If the temperature is still rising inside. It may also be worth adding some infiltration to your model, which with that delta T should have a fairly big impact even if the infiltration rate is relatively low.

Big ladder sets out the logic of the Ideal Air System really well

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I figured out the problem. When running the EP simulation of the conditioned zone, mechanical ventilation is added. The ventilation rate per area that I manually plugged into the setEPzoneLoads was very high for a school classroom (0.0038 m3/sm2, which is higher than the rate suggested by HB for laboratories and cleanrooms). This outdoor air supply drastically decreased indoor temperature in this simulation with respect to the other one without HVAC system.
To decrease indoor temperatures in the free-running simulation, the solution is letting the windows open even when outdoor temperatures are low (e.g. 2°C), in order to dissipate the heat deriving from high internal gains. This can be done changing the minimum outdoor temperature for natural ventilation from the component setEPNatVent.

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