IES-VE User Forum

Hi all

This is bugging me.

It appears that apache only applies the heat recovery value defined within Apache Systems to the heating component of the supply air but not the cooling component.

I have air being supplied via the aux vent tab with a supply temperature of 20C and heat recovery works fine for the heating component but does squat for the cooling side. The heat recovery only gets entered under the "heating" tab of Apache Systems so I suspect this is just the way IES works, which would be annoying because I cant find anything similar for the cooling side.

Also, I thought that entering the fresh air via "system air" instead of aux vent might work but for the life of me I cannot find the dialogue box for specifying the supply temperature of the system air at either system level or room level.

I really hope I'm missing something here because, if I'm not, IES essentially only has a half-implemented, simplified heat recovery modelling capability (obviously I know ApacheHVAC could do it but that would be huge overkill in this case).

All comments and advice welcome.

CP

Yes that’s correct, the heat recovery in Apache Systems will apply to the heating side only, this is true whether using auxiliary ventilation or system outside air. Best approach would be to use Apache HVAC, sometimes it can be surprising how quick Apache HVAC can be when you just need to represent a simple concept.

Alternatively you could ape the performance of the heat recovery in Apache Systems via a formula profile, again this can be as simple or as complicated as it needs to be. As a simplistic version something like the following would base the supply condition off the heat recovery efficiency, room air temperature, and outside air condition. Imagining 70% heat recovery we could use: (0.7*ta) + (0.3*to)

One consideration however would be that there will be some “energy” required to maintain the supply condition returned by the formula profile. Obviously in reality this energy is just the recovered heat but it will represent itself as a ventilation heating/cooling load in the model. Setting the Auxiliary Ventilation system in Apache Systems to a unique “dummy system” will help prevent this energy being included with the space conditioning energy.

With regard to setting the System Outside Air supply condition, this can be set in Apache Systems under the “Air Supply” tab.

Thanks Terence

That's a bit disappointing...

Correct me if I'm wrong, but aping the heat recovery effect via such a formula will only work in cases where the supply temperature is equal to the room setpoint since you would be taking the room side aux vent variable as the air side load.

In my case the supply condition is lower than the cooling setpoint and so I don't think I can do as you suggest without messing up the room side cooling load. I'm currently pulling the air side from the systems loads tab in vista.

I was hoping to get a nice simple divide between central fresh air load and room side FCU load requirements without having to model it all up in HVAC because the model is quite large.

I guess I'll just post process the numbers on a spreadsheet but I would ask that this functionaility get added to the list of things to do down the line please because, let's be fair, the way Apache System currently models heat recovery is simply wrong and it's a pretty simple change given everything's already in place, right?

As an aside, since VE Compliance uses apache as it's backbone, am I right in assuming that Part L models also dont see any cooling benefit from the inclusion of heat recovery?

If you use HVAC then with multiplexing and “Assign From Room Group” it shouldn’t take you too long, even for a large model

To answer your question, yes same rules will apply in Compliance, heat recovery will be applied to the heating side only. As a percentage of the whole year I can’t imagine there are too many hours though when the air temperatures in the CIBSE TRY files exceed the room cooling set-point (24°C) so the effect will be minimal.

Thanks Terence

I appreciate you taking the time to respond to this.

CP

Hi

I know it has been a while since this conversation but could you please explain what do you mean by the "dummy system"? how do I prevent the energy which is actually the recoverd heat to be calculated in the heat load? thanks a lot!