Evaporator Capacity according TD

[georgedvf]

Hello!

I've always used Heatcraft Evaporators and I select them according the BTUH's in the catalog, wich is the capacity when 10ºF TD.

Today I got a project where there's a low humidity requirement (35-50%), so I was thinking I could use a higher TD, maybe 22ºF so humidity will be lower and they won't have to buy such a big dehumidifier system.

The guy who helps me recommended me a Evaporator that using 10ºF TD is 14,000BTUH, but using 22ºF TD is 30,270BTUH.

The question is, the capacity of an Evaporator can be increased such like this when using TD??? Is there a limit to increase Evaporator capacity using TD???

Please correct me if you don't understand me well!
Thanks in advanced!

[mad fridgie]

In simple terms you can use TD to determine capacity.
For example the evap you selected has a duty of 1400 BTUH per F.
As the TD increases there are other factors that come into play (slightly de rates) these are normally very specific to each evap.
You can achieve your original duty, by slowing the fan speed (reduced air flow) and having a bigger TD

[lana]

Hi there,

What is the room temerature ?

If low RH is required then you can not do it with one cooling process.
You either have to use some kind of de-humidifier or you have to do the process in two or four stages.

If you are familliar with psychrometric chart then you will see what I mean.
Have a look at the charts.
Cheers

[georgedvf]

Thanks mad_fridgie, lana.

lana:
The rom will be 40ºF, but the low humidity will be achieved by using de-humidifier as I said in the first post.

The thing is that they're telling me to use smaller evaporator using bigger TD so it "helps" to low humidity.

I'm surprised because I've never used TD to modify in such a big difference the capacity of an evaporator.

Greetings!

[Romanicus]

Hi, I've done a project like this for a movie archive room (40 % RH), but i chose the dt of 8 K. This low RH leves can't be reach by condensation dehumidifying. You can reach them by absorbtion dehumidifiers. Anyhow, I sent to the dehumidifier manufacturer the air quality according to the selection software of the evaporator and they gave me the right equipment.

[Tesla]

I also worked on a film archive which used variable speed fans, high TD and reheat elements. This worked fine.