need help calculating ventilation needs

[jlinzmaier]

I'm in the process of setting up a 420 gal DT. The tank will be 8ft long and 3ft wide. I'll have four 400w MH as lighting and 3 dart pumps below the tank (and possibly the ballasts for the lights). I don't want heat and evaporation to be a problem so I intended to use some exhast fans set on a cycle so that they turn on when the lights are on.

The only trouble is, I have no idea how much air flow I need. I was at mendards today and saw some ultra quiet fans that I really liked. They were something like this. Exhaust fan

This fan is rated for 80 CFM and I have no idea what that means. I also saw some that were 100 CFM. I'm wondering if two of these fans above the tank running while the lights are on will be enough?? I could easily install four but I don't want to waste the electicity or fork out the extra expense if I don't have to.


Any suggestions would be very much appreciated!!

Jeremy

 

[jlinzmaier]

Few more details I forgot to mention.

There will be several 4in holes beneath the tank so that these exhast fans will be sucking up cool fresh air from the basement.

The tank itsself will be enclosed in a relatively air tight column. There will be no opening to the attic or out and around the tank. There will be a bit of air escape from the edges of the cabinet doors but essentially there will only be air flow from the basement being sucked up by the fans and blown out through the sophet.

Jeremy

 

[Mr.Biggs]

CFM = cubic feet/min that is the amount of air they will move at a specific pressure rating.

It is best to set the air to be pulled out of a space then to try and push it in.

 

[Mr.Biggs]

A Good rule of thumb is to move the given air space one time in 1-5 min.

So 8'*3'*3' tank stand volume would be = 72 ft3 the 80 CFM fan should be ok

you say there is no opening to the attic, but you will be blowing it out the sophet? I thought the two are connected??

living in WI you will have to make sure that the air gets outside and not in the attic in the winter or you will create a wet mess in the attic.

you may want to recover some of the heat in the winter time as long as humidity is not a problem.

 

[jlinzmaier]

<a href=showthread.php?s=&postid=14357275#post14357275 target=_blank>Originally posted</a> by Mr.Biggs
A Good rule of thumb is to move the given air space one time in 1-5 min.

So 8'*3'*3' tank stand volume would be = 72 ft3 the 80 CFM fan should be ok

you say there is no opening to the attic, but you will be blowing it out the sophet? I thought the two are connected??

living in WI you will have to make sure that the air gets outside and not in the attic in the winter or you will create a wet mess in the attic.

you may want to recover some of the heat in the winter time as long as humidity is not a problem.

After I thought about it for a minute I figured out the CFM.

There is no opening to the attic. The exhaust fans have ductwork that connect to an exit out of the sophet just like how a bathroom fan works.

It would be great to use the heat in some way, but I have no idea on how to use the heat without the humidity. Granted, the air gets dry indoors in the wintertime, but I'm predicting 8-10 gallons evap per day so I think that might be a bit much to recirculate into the house.

Where did you get the calculation for moving the given air space in 1-5 minutes??

I'll have a total air space of 8.5ft X 3ft X 3.5ft (89.25 cu ft) below the tank and 8.5 ft X 3ft X 3ft (76.5 cu ft) above the tank. The total air space needed to be moved is 165.75 cu ft. Two exhast fans that move 80 CFM will move that entire space in barely over a minute. That sounds adequate to me, maybe overkill. I could save money by installing just one which would move the entire air space in just over two minutes and still be within your range of 1-5 minutes.

Yes the air will be pulled instead of pushed. The fans will be above the tank pulling air from the basement moving it up and around the tank then pushing it out through a vent in the sophet.

Really appreciate your input Mr. Biggs!

Can anyone else confirm that calculating the recirculation of the entire air space over 1-5 minutes is adequate/appropriate??

Jeremy

 

[Mr.Biggs]

I made the calculation based on tank foot print and the fact that most stands are 3' or less.

Best results will be with fan high up in the space on one end and the cold air coming from down low on the other end.

Make sure that the hose in the attic is the insolated type or it will get condensation on both sides of it in the winter.

 

[jlinzmaier]

Thanks Mr. Biggs!!

Jeremy

 

[jlinzmaier]

<a href=showthread.php?s=&postid=14358492#post14358492 target=_blank>Originally posted</a> by Mr.Biggs
I made the calculation based on tank foot print and the fact that most stands are 3' or less.

Should have clarified better. What I meant to ask was why a turnover of the entire volume 1-5 minutes (vs 10 or 15 minutes).

Jeremy

 

[Mr.Biggs]

I'm sorry I don't remember where I picked it up from, I think it was a HVAC book. The calculation is based on a continuous hot humid environment. The air exchange rate for an intermittent environment like your bath room would be less.

 

[jlinzmaier]

Really appreciate your help Mr. Biggs!
Thanks.

Jeremy