Fan Calculation
Fan Calculation
(OP)
Hi
I am trying to calculate if the fan I have installed at a particular site is to large. The dimensions of the room are 4.7m x 3.0m x 3.1m that gives me a total volume of 43.71m^3 the inlet size of a single louvre vent into the room is 0.500m x 0.400m that gives me an inlet area of 0.2m^2 the amount of air changes required per hour is 1.9 the outlet size of the exhaust fan is 0.398m in diameter . The fan would draw air form the external atmosphere through the single louvre inlet vent into the room and expel it through the exhaust outlet where the fan is mounted to the external atmosphere. At 1.9 air changes per hour I calculated the required velocity using 43.71m^3 x (1.9/60) to be 1.3845 m^3/s the current fan uses the 1440 rpm curve but I see the value of 1.385 falls quite close to the origin of the chart. Furthermore ploting this value will omly give me an equivalent static pressure value in Pa, once I have this value what do I use it for or how do I use it to verify adequate fan sizing
I am trying to calculate if the fan I have installed at a particular site is to large. The dimensions of the room are 4.7m x 3.0m x 3.1m that gives me a total volume of 43.71m^3 the inlet size of a single louvre vent into the room is 0.500m x 0.400m that gives me an inlet area of 0.2m^2 the amount of air changes required per hour is 1.9 the outlet size of the exhaust fan is 0.398m in diameter . The fan would draw air form the external atmosphere through the single louvre inlet vent into the room and expel it through the exhaust outlet where the fan is mounted to the external atmosphere. At 1.9 air changes per hour I calculated the required velocity using 43.71m^3 x (1.9/60) to be 1.3845 m^3/s the current fan uses the 1440 rpm curve but I see the value of 1.385 falls quite close to the origin of the chart. Furthermore ploting this value will omly give me an equivalent static pressure value in Pa, once I have this value what do I use it for or how do I use it to verify adequate fan sizing





RE: Fan Calculation
Errr, I think you'll find converting 1.9 changes per HOUR to m3/SECOND requires you to divide by 3600, not 60.
Some common sense should apply here. At an area of 0.2m2, this implies a velocity of 7 m/sec / 15 mph - That's a pretty strong breeze - gale force 4 (moderate wind)
Pressure will relate then to how much flow you can get out of your vent with that pressure. ASHRAE guidelines maybe?
Where does 1.9/hr come from? Seems very low according to this guide http://www.engineeringtoolbox.com/air-change-rate-...
Equally 1.9 per minute or 114 per hour sounds rather big.
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RE: Fan Calculation
The application is for a battery room and the 1.9 comes from a calculation used to determined the changes per hour required in the room to keep the H2 (Hydrogen) concentration to below 0.8% this is when the battery's are gassing.
So on correcting my previous error the 43.71m^3 x (1.9/3600) will be 0.0231 m^3/s this falls even lower on the chart so this would give a velocity of 0.115 m/sec
But this in only considering the velocity flow through the inlet vent based on air change requirements and room size. Once I have this how would I select an adequate fan size ? would I opt for the 960rpm or 1440rpm fan. Given that this value is rather small 0.0231 m^3/s I would think both fans on the curve data sheet are to large
RE: Fan Calculation
At 0.115m/sec your area is far too big - you won't find a fan to fit that and do that sort of flowrate / velocity
You need something like this https://www.tlc-direct.co.uk/Main_Index/Ventilatio...
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Fan Calculation
So essentially the fan size can be reduced dramatically. I looked at a the link you posted and plotted the 0.115 m/s on the curve it gives me a static pressure rating what would I use this for. The fan is venting into the open atmosphere essentially extracting the gas contents of the room and drawing in fresh air through the louvre inlet.
RE: Fan Calculation
RE: Fan Calculation
RE: Fan Calculation