Fresh air loads

[agoyal]

Hi, I'm looking to clarify how to best model the fresh air loads in a building. There is the auxiliary ventilation under the 'air exchanges' tab in the thermal templates. Also under the 'systems' tab there is the 'building outside air supply'. Which one is telling IES how much fresh air is required in each space?

[Complex Potential]

If you are just dealing with a standard thermal model then I'd go with the aux vent option although they both work. If you specify the air to come into the room at outside condition then it will simply show as a room side load within Vista. If you set the air to be supplied at a certain temperature then the central fresh air sensible and latent heating and cooling loads will show up at the building level within Vista (although you may still be left with a small room side component if the supply temperature differs from the room temperature).

A word of warning; setting heat recovery within the systems will only impact the central fresh air sensible heating and not the cooling which doesn't make much sense but that's just the way IES works.

CP

[agoyal]

Thanks for the clarification, that makes more sense now. If I want to completely separate fresh air loads then I guess it's better to set it as a building load rather than room load.

[RossThompson87]

A word of warning; setting heat recovery within the systems will only impact the central fresh air sensible heating and not the cooling which doesn't make much sense but that's just the way IES works.

Would this mean the only way to model cooling recovery is by adding in the HVAC module link?

I'm guessing this also means cooling recovery is also excluded from the Part L compliance models?

Ross

[Complex Potential]

A word of warning; setting heat recovery within the systems will only impact the central fresh air sensible heating and not the cooling which doesn't make much sense but that's just the way IES works.

Would this mean the only way to model cooling recovery is by adding in the HVAC module link?

I'm guessing this also means cooling recovery is also excluded from the Part L compliance models?

Ross

You might be able to do it by using some clever absolute profile assigned to the supply air temperature within the air exchanges but otherwise, yes, I think HVAC is the only way.

And yes, by extension this means that heat recovery does nothing on the cooling side within IES Part L models. I asked about this and was told that it's not a major problem because Part L is UK based and UK buildings are always heavily weighted in terms of heating so any impact of heat recovery on cooling should be small.

Of course, sometimes you are only looking for a small improvement to get over the line, but, yeah... hmm