How many fans should i put on my new hood? Modifications?

[justin-branam]

i just finished building my template hood to test it out. you can see the way it will function. the middle board with the square holes in it will actually have a piece of glass in it so i dont get any water splash up. I am also going to paint any part that may come in contact with water with some marine paint.

the stars are where i am thinking of putting fans. two on the back to push air across the water, and i will have two vents on the side for the air to escape. i am also going to put 2 fans on one side of the light pushing air, and 2 on the other side pulling air so i can get a nice flow throught the lighting to coll the MH's down. i dont need to worry about pulling humid air since the lights will sealed from the water. does this seem like nough fans. i am probably going to use fans somewhere in the 80cfm range.

So does anyone see any way i could improve the top other than putting it on hinges so i can open it (thats the next step).

[GaryP]

Remember if you are pulling air with the fans that they are going to be exposed to very humid salt saturated air that is going to cause corrosion on the fans. Its better to blow the air in and allow some place for the air to escape.

My strategy is to put more fans then you need so that you have excess cooling for certain times of the year when you need more help like when the windows are open and its humid in the house (like now). You can always cut down on cooling but its hard to increase on cooling capacity if you don't have the fans for it.

[justin-branam]

Remember if you are pulling air with the fans that they are going to be exposed to very humid salt saturated air that is going to cause corrosion on the fans. Its better to blow the air in and allow some place for the air to escape.

" i dont need to worry about pulling humid air since the lights will sealed from the water."

on the bottom half, air will only be pushed in. on the top half with the lights, that will be sealed fromt he bottom section via pieces of glass, the air will be pushed through one side and pulled out the other side. the air will be no more humid thatn room air, and may actually be drier from the heat of the MH's.
I may go ahead and get a few extra fans, just in case. thanks.

[GaryP]

Three things to keep in mind in your design. 1. Glass gets dirty. 2. Glass will need to be cleaned when it gets dirty. 3. Glass will absorb some of your light before it gets to the water, even if its clean. Glass is never 100% transparent. Depending on the type of glass, it may abosorb light in certain spectra you would rather not be removing before it gets to the tank. That's why most reefers don't use glass covers on their tanks, besides the seperate heat issue.

[justin-branam]

Three things to keep in mind in your design. 1. Glass gets dirty. 2. Glass will need to be cleaned when it gets dirty. 3. Glass will absorb some of your light before it gets to the water, even if its clean. Glass is never 100% transparent. Depending on the type of glass, it may abosorb light in certain spectra you would rather not be removing before it gets to the tank. That's why most reefers don't use glass covers on their tanks, besides the seperate heat issue.

i do realize i will have to clean it. i plan on doing that with my weekly water changes. lucky for me my neighbor works at a glass cutting shop. i asked him to get me some glass that would not absorb any type of UV rays or anything, and that is as clear as possible. i think he said the clearest he has is 96% (of light passing through). i figure this will be fine. Should there be anything else to add to this?

anything else i should be aware of? Thanks for the help!

[AlexKilpatrick]

One thing I was thinking is that you could easily measure whether you have enough fans or not. Get a couple of inexpensive indoor/outdoor thermometers. (Radio Shack sells them). Put one temperature probe in your hood, but not directly under your MH. Put another one someone in the room, but reasonably close by. If the two temperatures are within a couple of degrees of each other, then you don't need any more fans because the fans are equalising the temperature. The thermometers are only accurate to +/- 2 degrees, in my experience, so that is about as close as you are going to get.

I have never tried this myself, but it should work. Personally, I would not want to have more fans than I really needed. That's just extra noise.

[GaryP]

i do realize i will have to clean it. i plan on doing that with my weekly water changes. lucky for me my neighbor works at a glass cutting shop. i asked him to get me some glass that would not absorb any type of UV rays or anything, and that is as clear as possible. i think he said the clearest he has is 96% (of light passing through). i figure this will be fine. Should there be anything else to add to this?

anything else i should be aware of? Thanks for the help!

The glass on SE bulbs and covering pendants on DE bulbs is designed to absorb UV light. UV is not good, it kills stuff. The near UV light wavelenght such as the 420 nm spectrum (actinic) is good. That is what is thought to promote color pigment production in corals. Its a defensive strategy of shallow water corals to prevent them from being damaged by UV light. You are basically tricking the corals into thinking they are being blasted by UV by using the light close to UV but without damaging them with actual UV light. Remember that UV light is the light that causes sunburn and skin cancer. It is what is called "ioninizing radiation" and does the same thing to corals as it does to your skin. 96% transmission is pretty good. You just need to make sure the 4% you are losing isn't at one particular wavelength that you reall need. The glass you are mentioning is probably similar to the low iron, low phosphorus glass that is used in some of the high end aquariums. It is close to the clarity you get with acrylic.