Heat Exchange Units

[kkhyuen]

I'm using a heat exchanger to preheat my incoming air for a typical FCU HVAC system.. I've set the HX at 90% efficiency for sensible heat transfer.

After I run the apachesim, I go and query the tempeature of the airstream immediately after the HX unit and I dont see it gain or drop in temp as expected. It's basically the same as ambient air temp. Is there something i'm missing?

Thanks

[JosephG]

Did you put in a controller for the heat recovery?

[kkhyuen]

Ok i missed that one. Didnt realise you had to define the temperature of the conditioned air.

I find it strange that you're telling the heat exchanger to attain a certain temperature when in reality it depends on the two entering air stream conditions and the heat exchange should transfer what ever it can do based on the efficiency rate.

oh well.. as long it works.

Thanks

[JosephG]

I find it strange that you're telling the heat exchanger to attain a certain temperature when in reality it depends on the two entering air stream conditions and the heat exchange should transfer what ever it can do based on the efficiency rate.

While what you're saying is correct in that it depends on the two entering air streams, you don't always want to do heat recovery, for example, when you're wanting to cool the air you don't necessarily want to heat it some more (unless you are cooling / dehumidifying then reheating). You also wouldn't want to do heat recovery if you're recovering less heat than the energy input required to recover that heat. The controller for heat recovery just gives it a target to reach, however that target temperature isn't necessarily reached.

I don't know, it makes perfect sense to me, everything that 'can' be controlled should be controlled.