Canopy Q's

[mnreefgeek]

I'm making a canopy for my 20H this weekend and I think I pretty much know what I want the finished product to look like. But, as usual, I've got a question.
Do I need any type of spacer between the reflector and the wood? If so how much?

Since this is going on such a small tank, I want to keep the profile as low as possible. I was thinking 11 to 12" max. With the 1 1/2 overhandg on the tank and 2" drop on the halide socket this would put the lights about 8" off the surface. Does this sound about right? Or do I need to add another 1" to the total height for a spacer between the reflector and the top of the hood?

Thanks in advance for the help.

[yardboy]

I bought a 250W spiderlight reflector retrokit and attached it to my wooden canopy and it came with some spacers, about 1/2" high. Being paranoid, I mounted a fan directly over the reflector to draw off heat. Not sure if I needed it though.

[Geoff]

i do not have a spacer on mine. i have 400w'ers. and my reflector is really small. i do not think it is a problem unless you do not have any ventilation in the hood. with a smallish tank, heat buildup should be your first concern. a lot of air flow is a good idea.

what wattage is the mh?

G~

[mnreefgeek]

I think I'm going to go with 2x150. I do have a 250, but I can control the 150's with seperate switches to regulate how long I've actually got 300wt hitting the tank.

I was planning on 2x 4" fans. Do you think this is enough?

[Geoff]

what other kinds of cooling do you have for the tank? do you have a sump? blowing air across that will help a lot.

2 fans may be a little low on the ventilation side. that is right on the border. i could see it being enough if the house is kept cool enough, and the hood has some clearance below the ceiling.

hth,

G~

[Reefer Addict]

I think I replied to you in another thread and suggested you do the canopy fans in a push-pull configuration. After further thought, I take back that recommendation.
What I would do is put the two 4" fans in the top rear center of the canopy blowing outward (side-by-side).
Leave an opening low on each side of the canopy, preferably as close to the waterline as you can get them. Make sure the openings are large enough to let the 4" fans 'breathe'.
This design will allow you to cool the water and the bulbs at the same time.
Since heat tends to rise, it will naturally want to exit the fan openings (which will be forcing the air out anyway), while cooler air is drawn in near water level giving good evaporation characteristics.
I designed my canopy this way and I have good cooling results with a 250w halide, 240w of PC's, and a single 4" computer fan (throttled down to about 80cfm) running on an AC Adapter.
You'll still have to watch the tank temperature and adjust the lighting or extra cooling accordingly, but this system will give the best airflow without creating a lot of turbulance within the canopy.
On my canopy sidepanels I used a small (11-1/2"x4") floor grate used for central heating/ac to cover the openings. The floor grates also have the adjustable flow damper in them so you can slow down the airflow a bit if you need to (like during wintertime).

Otherwise it sounds like you're well on your way.
I want to see it when you're finished.

P.S. I should mention that my canopy is fully sealed... it's not an open back.

[mnreefgeek]

OK, so I think I need to rethink my design. I was going to go generally square for approximately 8" and then have a about 5" cap that was similar in shape to a spider light reflector. I thought that would be nicer to look at then just a box.

Now I'm thinking I may just go with the standard square canopy and make it about 14" to keep the lights off of the water. I will mount 2 4" fans high in the rear center, 1 low on the side blowing across the water surface with a few vent holes on the other side for air escape and then I was thinking that I could drop the reflectors a couple of inches off the top via 2x2's and insert a couple of vents in the top for the heat to escape.

Do you think a fan mounted in the top blowing out would draw alot of the heat out or would just a few vents in the top do the job?

[Geoff]

i like blowing out. i have 2 on my hood blowing out. it just give it a boost.

G~

[Reefer Addict]

I've attached a 'model' showing the airflow patterns between what I suggested and what you are considering.

The main problem with having a fan blow 'into' the canopy is that it creates a lot of turbulence and inhibits the flow of air. What you want to do is use the fans to create a vacuum inside the canopy so that air is drawn in through the vents rather than blown in by a fan.
If you notice in the second example, since there is only 1 fan blowing in, and 2 blowing out, the airflow doesn't exit the top vents as you'd expect, but is actually either 'dead' or slightly drawn in.
Also, the turbulence actually puts the heat from the bulbs 'closer' to the water because it mixes all the air up within the canopy rather than drawing off the hottest air from the top of the canopy.

I did these examples from my own knowledge of aerodynamics, but it should be correct enough to give you an idea of what to expect.

Hope that helps.

[mnreefgeek]

Wow, thanks for the pics. It totally makes sence now. I'll go with that design. One last question, I know not another one....

Since this is a 20, I've got a HOT skimmer. I notice in your diagrams that the back is pretty well closed up. How much will the extra space I need to take out of the back wall to accomidate the skimmer going to affect the air flow if at all?

[Reefer Addict]

Heheh... go ahead and ask as many questions as you like... that's what we're here for.

I'd just cut enough out of the canopy so that the skimmer can hook over the lip of the tank, and so that you can remove the collection cup for cleaning.

The way my tank is constructed... ah well, it's probably easier to use a picture rather than explain it...
Basically, I put some little doors on the back of the canopy with cutouts for the equipment that runs through the back. The exhaust fan sits right between the two doors (one on the overflow side, one on the return side.)
That way it gives me room to do what I need to while closing back up to keep the airflow going in the right direction.
You should be alright with a small gap around the skimmer... it'll just act as an extra vent toward the bottom of the canopy.

My diagram was pretty simplified, but as long as the cool air is entering at the bottom and the hot air escaping through the top you'll get better airflow since the air (through convection) naturally wants to do this anyway.

HTH.

Oh, here's the pic.

[Reefer Addict]

I thought I'd also throw in a picture of the grate I'm using for both my side vents.

[mnreefgeek]

Thanks for the pics. What is your tank temp usually at with this set up? How warm /cool is the house generally?

One more thing, did you paint those vents with anything to deter rust?

[Reefer Addict]

Right now the internal house temperature is about 79 degrees (it's 95 outside), and the tank temp is 82.2 degrees (I have it elevated since I'm battling a slight ich problem).
It tends to level off at about 82.5 degrees with a small fan blowing on the water in the sump, though I also use frozen water bottles in my sump to take the temperature down more toward 80 degrees. I intend to get a small chiller sometime soon to keep the water a constant 80 during the day rather than having it fluctuate back and forth.

The grates came with a nice thick powder-coating on them so rust isn't too much of a problem... there's a couple of minor spots from where saltwater had splashed onto them, but under normal circumstances there's dry(er) air coming in so humidity/salt don't build up on them.
The ones I used may be too large for your tank (I gave the dimensions in a post above) but they work well on mine since I have a side width of about 16". I mainly posted it as an example of what you could do.

You'll probably be able to keep your water a bit cooler since you'll have quite a bit more air volume travelling through a smaller space than I do... but you'll still have to keep an eye on the tank temp and adjust accordingly.

HTH.