Does Blower Position in System Make any Difference?
Does Blower Position in System Make any Difference?
(OP)
Hi:
I'm building a swamp cooler for my attic, and I'm considering where to position the blower. I could position it as the first thing in the system before the heat exchanger, the pads and the ducts. Or I can position it after the heat exchanger and the pads, so it sucks air through them, then pushes the air through the ducts.
Does it make a difference if the blower is pushing air from the front, or pulling it from the back?
Thanks,
Eric
I'm building a swamp cooler for my attic, and I'm considering where to position the blower. I could position it as the first thing in the system before the heat exchanger, the pads and the ducts. Or I can position it after the heat exchanger and the pads, so it sucks air through them, then pushes the air through the ducts.
Does it make a difference if the blower is pushing air from the front, or pulling it from the back?
Thanks,
Eric





RE: Does Blower Position in System Make any Difference?
However, draw through results in better air distribution over the cooling pad...
RE: Does Blower Position in System Make any Difference?
So if I understand you correctly, I will get exactly the same flow rate regardless of where I position the blower?
The whole reason I'm trying to move the blower to the front is because the motor may be adding about 300 watts of heat to the system AFTER the air is humidified. 300 watts = about 1000 btu.
I'm building a 2 stage cooler, so the air will travel through a heat exchanger first, so by the time the air gets to the pads the pressure should be very even.
My main concern is the flow rate. Any sacrifice in flow rate will cost more than the small energy gain from moving the blower.
Is it a scientific fact that flow will not be affected?
RE: Does Blower Position in System Make any Difference?
RE: Does Blower Position in System Make any Difference?
Thanks.
RE: Does Blower Position in System Make any Difference?
The heat exchanger in particular is causing a noticable pressure drop.
RE: Does Blower Position in System Make any Difference?
http://www.wonderquest.com/swamp-coolers.jpg
RE: Does Blower Position in System Make any Difference?
"Fans are much more efficient at PULLING air than at PUSHING air"
How would the fan know what it is doing?
What I mean is that a fan simply provides/causes a pressure difference in the airflow going through it.
To put this in numbers, let's say the fan creates a 1000Pascal pressure-difference.
Then, the fan does not know if this is from 7000Pa downstream of the fan to 8000Pa after the fan, or from 2000Pa for the fan to 3000Pa after the fan.
Atmosperic pressure is 100.000Pa so the several 100Pa's we are talking about in HVAC-fans do not matter.
On the choice of push or pull in this case:
I would say the heat added by the fan is of little consequence. I am sure it will be less than 1K. (We are talking about cooling by evaporation, right? In that case the heat from the motor might be benificial because it will help evaporation and you will get the heat from the motor into the airstream anyway, no matter where it is placed.)
I think I would place the fan in the cleanest and dryest air, so blow through.
RE: Does Blower Position in System Make any Difference?
Perhaps temperature change is negligible, perhaps not. Just be sure.
RE: Does Blower Position in System Make any Difference?
RE: Does Blower Position in System Make any Difference?
I decided to put the blower after the heat exchanger and pads so it goes like this:
heat exchanger -> pads -> blower -> ducts
I decided that it was best to err on the side of caution, so I did it the traditional way. I included a few pics so you can see what I'm talking about.
Now I have to decide how to do the ducts. Evaporative cooling requires much more air flow than air conditioning. In fact, I think you'd always want the maximum amount you can get. I'm hoping to get 4000-5000 cfm, which my blower can handle.
I looked at home depot for the biggest ducts and vents I can find. The biggest vent I can find is a 14 X 14 box that fits between the studs and accepts a 10 inch duct. I'm thinking of using 5-6 vents. You can see the layout of my house in the attached pic.
Will 5 or 6 of these 10 inch insulated ducts allow plenty of air to flow without much friction? Should I try to use 12 or 14 inch? I don't have any feel for this because I've never done any HVAC before.
Also, will I have a problem running a duct approx 25 feet to my kitchen? I suppose there will be less flow there, but I can live with that.
ducts:
ht
Am I on the right track?
Thanks in advance.
RE: Does Blower Position in System Make any Difference?
RE: Does Blower Position in System Make any Difference?