fan speed vs flow - indoor VRF units
fan speed vs flow - indoor VRF units
(OP)
Dear all,
I would kindly ask for an information please.
While reading indoor VRF cutsheet e.g. slim duct unit , I have noticed that external static pressure rises while air flow drops?! I was expecting to see increase in flow when fan speed is increased (and thus, static pressure). E.g. 46Pa corresponds to 450m3/h while 16Pa corresponds to 600m3/h. Does not make sense to me.
Please see the link below...
http://www.ahi-toshiba.com/catalog/index.php?SECTI...
What seems to be the problem?
Cheers
I would kindly ask for an information please.
While reading indoor VRF cutsheet e.g. slim duct unit , I have noticed that external static pressure rises while air flow drops?! I was expecting to see increase in flow when fan speed is increased (and thus, static pressure). E.g. 46Pa corresponds to 450m3/h while 16Pa corresponds to 600m3/h. Does not make sense to me.
Please see the link below...
http://www.ahi-toshiba.com/catalog/index.php?SECTI...
What seems to be the problem?
Cheers





RE: fan speed vs flow - indoor VRF units
+
The fan capabilities are fixed, but the duct size and outside pressures are not. These outside influences are going to dictate how much air the fan can push through. For example, the smaller the duct size or the larger the outside air pressure, the less air flow you will get with your fan. This is the criteria they are stating here. So, for the same unit, you will get 450 m3/h @ 46 Pa and 600 m3/h @ 16 Pa. You are getting less flow at 46 Pa than 16 Pa external pressure is what it is saying. Hopefully this makes sense. This cut sheet is strictly talking about what the fan 'sees' as far as static pressure, which is dependent on velocity, duct size, and external pressure.
I hope this makes sense.
RE: fan speed vs flow - indoor VRF units
RE: fan speed vs flow - indoor VRF units
learn the basics about fans, different types of fans have different system curves.
RE: fan speed vs flow - indoor VRF units
RE: fan speed vs flow - indoor VRF units
>>>>>These fora should not be used to bypass your own in-depth research on the issues that affect you, nor is it intended to be a substitute for appropriate professional assistance within your field or geographical region.
RE: fan speed vs flow - indoor VRF units
your question simply reflects lack of very basic knowledge, and the best you can do is to attain it before attempting anything else in hvac field. there is no shortcut for such things!
this is what i got when googling for "basic fan curves"
https://www.google.hr/search?q=basic+fan+curves&am...
i think that i can reasonably assume that you are at least as good as myself in using google.
if you feel somewhat pushed, that's with best intetions...
RE: fan speed vs flow - indoor VRF units
BIPVguy: I think you mixed up ESP and the pressure drop of the unit.
the data of the VRF mso tlikley show the pressure of the (external) ductwork, which you need to design and know the pressure drop for that the design flowrate. So the more dP, the less flow.
I think what you were thinking you read is that is what flow you get out of the units with how much pressure,, like with an external fan. Then it would be the pressure drop of the unit, which indeed should increase with flow. Those units have an internal fan (like an AHU), so the data you see assumes what I described all above and the more pressure drop your ductwork has, the less flow.
For devices with their own fan, we typically don't see nor care about their itnernal pressuredrop (coil etc.). We only care about the external data... that specific unit manufacturer already takes into account his fan , and all the itnernal parts.