Mechanical ventilation problem

Hello everyone,

I’m running a basic energy simulation for a small room using LBT. I have noticed that there are no mechanical ventilation loads in the results. Could anyone please tell me what the problem might be?
Thank you for your help. (157.0 KB)

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You have to use an ideal air system if you want to get the mechanical ventilation load, @Nikou . Detailed HVAC systems often have the ventilation load taken care of in one central air loop so it’s not possible to get a room-by-room breakdown of ventilation loads.

Hello community, I reopen this post because in 1.3.0 Versión, if I use a HB Ideal Air system and I apply a HB Ventilation schedule (With flow by room) the natural/mechanical ventilation load is null or empty. How can I fixed it?

I see a strange result in the simulation process and I need to confirm the impact of ventilation.


I update more info of the problem, If i set Custom output: Zone Ideal Loads Supply Air Standard Density Volume Flow Rate. The results show the m3/s of supply air I set.

So it might be correct, How can I see the energy impact of the HB Ventilation without heat recovery ?

Update 2: I tried also setting “all” in load type, and it says null (See No Mechanical Ventilation in Ideal Air Loads results).

Finally, as I see, the cooling and heating output change if I change the ventilation values, so Its work. As a result, I decide to do this to see the ventilation loads, creating two simulations: One with ventilation and other without ventilation, and the difference between cooling and heating result (with and without ventilation) is the ventilation loads.

This is almost always an issue with requesting the right outputs from the simulation. As you can see from the change in heating/cooling, the ventilation schedule will be used if it is specified. If setting up the simulation parameters to request the right outputs is taking too long, the HB Annual Loads component ensures that you are always requesting the correct outputs to get all terms of the load balance (including mechanical ventilation).

Thanks @chris ! I used Annual Loads and Peak loads and it show the impact of ventilation in ventilation program schedule. This result is useful for me.

I will check why doest register the mechanical o natural of room energy output.


I finally found the problem!!

If you set in SIM output the hvac energy use as true, the Room energy result mech vent load is null (I dont know why).

But if you set the hvac energy use off, you get the load of mechanical ventilation that you set in program schedule.



Hey @gonchotorena ,

I wasn’t able to recreate this situation in LBT 1.4 so I assume that whatever had caused this weirdness with the hvac_energy_use_ in version 1.3 has since been fixed.