Trying to model an office building with fresh air heat recovery. What I mean by that is that the fresh air is brought in from outside passes through a paper heat exchanger (Mitsubishi Lossnay type unit) which picks up heat from the air being exhausted and then supplied to the space , simply for fresh air this does not act as the main heating or cooling method.
So the supply air to the space won't be the sample as the external temperature, as it will be slightly heated or cooled from the air extracted from the space. I have used the BTM , air exchanges tabs to set up an AHU supply with a set point previously, but I just wonder is there an accurate way to set it up for this type of system? This is for a 24 hour building so that external temperature will vary a lot.
Regards
John
fresh air heat recovery
-
Complex Potential
- VE Expert
- Posts: 467
- Joined: Wed Jan 09, 2013 11:57 am
- Location: Bristol, UK
Re: fresh air heat recovery
You can specify the condition of the air underneath where you set the usage profile. If you create the following absolute profile you can apply it as the air condition:
to+0.6*(ta-to)
where,
0.6 is the assumed heat recovery efficiency (you can change it to whatever you like, remembering to adjust if you have an unbalanced flow rate).
to is the outdoor air temperature
ta is the indoor air temperature (ie the return temperature)
That should then result in the correct supply temperature being applied and the correct aux vent room load appearing in the space. The only thing you need to be careful of is that it will create a phantom system side load on the fresh air which you will need to ignore. If you stick to Vista room variables it should not be an issue but if you are pulling out system loads then you will need to be careful.
I think you can remove the system side air load issue by setting the aux vent system to none in the system tab under templates but you may need to experiment to be sure.
CP
to+0.6*(ta-to)
where,
0.6 is the assumed heat recovery efficiency (you can change it to whatever you like, remembering to adjust if you have an unbalanced flow rate).
to is the outdoor air temperature
ta is the indoor air temperature (ie the return temperature)
That should then result in the correct supply temperature being applied and the correct aux vent room load appearing in the space. The only thing you need to be careful of is that it will create a phantom system side load on the fresh air which you will need to ignore. If you stick to Vista room variables it should not be an issue but if you are pulling out system loads then you will need to be careful.
I think you can remove the system side air load issue by setting the aux vent system to none in the system tab under templates but you may need to experiment to be sure.
CP