Evaporative cooling - Surface fan efficiency?

[Punchanello]

I'm in the middle of a tank build. All up it's a 700 litre system with an in-cabinet sump and no hood. It will have 3 x GHL Mitras LX7s for lighting and a single return pump (apart from the skimmer no other pumps). So not too much heat generation.

Our house is old and hot. We are renovating so new insulation and A/C are coming but not until after summer (which is December-Jan-Feb here). I don't really want to pay for a chiller for one summer so I'm trying to work out how effective surface fans could be at cooling the system.

If ambient temperatures are reaching the mid-30's is there really any hope in hell of keeping the tank 25 degrees Celsius without the aid of a chiller?

I guess my options are as follows:

1. rely on surface fans which (hopefully?)maintain my tank at 25 degrees (most preferred)
2. delay cycling and livestock until March 2018 (not preferred)
2. fans, lights off and bottles of frozen water all summer long (equal least preferred)
3. Spend $1500 (equal least preferred) on a chiller I will use for one summer.

Anybody had experience with surface fans and evaporative cooling and can help me with some realistic expectations of what they can do?

 

[scuzy]

Evaporative cooling - Surface fan efficiency?

I bought 2x ghl 4 fan units these are 140 cfm on each side of my tank this should cool it down 4-5 degree C

 

[Punchanello]

I bought 2x ghl 4 fan units these are 140 cfm on each side of my tank this should cool it down 4-5 degree C

Yeah, I Was thinking about 2 of those for the DT and one for the sump. Everything GHL make is so damn sexy.

 

[Ron Reefman]

Just how hot does it get in Jan/Feb where you are? And I assume that means it gets about the same inside the house?

 

[ca1ore]

Getting 10 degrees C of cooling from fans is asking a lot. Also, efficiency of evaporative cooling varies significantly based on humidity.

 

[mcgyvr]

If ambient temperatures are reaching the mid-30's is there really any hope in hell of keeping the tank 25 degrees Celsius without the aid of a chiller?

Assuming thats ambient temperatures inside your home where the tank will be located then absolutely not...

But I hope thats not inside home temperatures.. If so.. yuck.. I'd get on that insulation/AC as soon as possible and wouldn't be thinking about a tank at all...

 

[Punchanello]

Mid thirties inside is probably worst case scenario (we do on occassion get a 40 degree day outside) but because this is our first full summer here I'm thinking worst case scenario. It will definitely be hitting 30 degrees inside on the worst days....but hey, it's a dry heat .

Waiting a little longer to get the tank wet won't kill me but you can't blame me for dreaming.





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[krazysvede]

With your ambient temperature inside the house getting so I don't think its possible.

Heres my experience, with a fan on my current 320 gallon tank Im able to keep the temp within 1.5* F. It was 110* (43c) here yesterday. I keep the house at 77* (25) my tank has 4x 80w T5 and 3x 250w halides. With the fan on the DT Im able to keep the tank from from going over 78.5 (26). T5s run 8 hours and Halides run for 6. However, lights come on at night and run from 4pm to midnight after the hottest part of the day. The hottest day this year was 122* (50) and tank got to 80 (26.5) cuz we bumped the AC up a couple degrees so it wasn't running quite so hard.

A few years ago I had 4x 80w T5 and 5x AI Sol LEDs over a 220 gallon and I ran heaters all summer because the tank got a some air on it from one of the AC vents near it and always cooled.

 

[bobafet1]

I've been running a surface fan on my reef for years. In fact, I don't remember the last time I even had a chiller nor would I ever want to add one.

 

[der_wille_zur_macht]

Evaporative cooling is much more powerful than it gets credit for.

Water needs 1 Joule to change 1 gram (or one ml) by one degree. The enthalpy of evaporation (amount of energy required to evaporate) one gram of water is 2257 joules.

Let's assume your tank cools off at night time such that it "resets" itself. During the day, it goes from your target of 25 C to the max of 35 C over a 6 hour period (and then presumably stays at 35 C for the next 6 hours until night starts and it cools back off). Based on this, we know the environment is adding 7,000,000 Joules during that first 6 hours, and there is a total of 12 hours of heating each day. That's 14,000,000 Joules over 12 hours.

To keep the system at 25 C, you need to match that energy rate via evaporation. 14,000,000 Joules per 12 hours is 1,166,666 Joules per hour. At 2257 Joules per gram, we need to evaporate 517 grams of water per hour, for the 12 hour day.

Basically that means you need to evaporate about 6.2 liters of water over 12 hours. That seems well within the realm of possibility for a 700 liter system. For us Americans, we're talking about evaporating 1.6 gallons from a 185 gallon system in 12 hours. Not really an impossible task.

If you're trying to do this in super high humidity, yes - it will be a challenge. But if you were serious when you said it was a "dry heat" then this should be easy with good fans.

Another benefit to evaporative cooling is that it's cheap and easy to try. A few fans pointed at the water might set you back $20 and 10 minutes of effort.

 

[scuzy]

Since adding these my chiller hadn't kicked on as much from the last heat wave.

 

[ca1ore]

When I lived in Phoenix in the late '90's the humidity was often low enough that a swamp cooler worked really well. At higher humidities (much over 50%) it worked much less well. Here in CT, I don't find fans to do all that much (though I'm not much of an AC guy myself; makes my kids soft). Also depends how much cooler it gets at night. Also, you can buy a used chiller for much less than $1,500 and then flip it after you get your AC system.

 

[bobafet1]

........Another benefit to evaporative cooling is that it's cheap and easy to try. A few fans pointed at the water might set you back $20 and 10 minutes of effort.

This is exactly why I won't consider any other method. A decent fan will set you back $20-$40 from Home Depot, it doesn't consume that much electricity, and when it gets too rusty in a few years you can easily buy another one.

 

[Punchanello]

Thanks for all the feedback on this. I've been reading your views with interest and weighing up my options.

I've decided a two pronged approach. I'm not in a position at this stage to get air conditioning because installation will have to happen after some other work is done on the house.

So I'll be topping up my insulation both under the house and in the ceiling which will give me up to a 10 degree buffer on the most extreme days and I'll also be using surface fans. It's pretty dry here so I'm reasonably confident.

My plan is to have the cash on hand anyway to buy a chiller if early summer temperatures start to really heat the tank up. If that happens there's no way it will survive February and I'll buy a chiller, lesson learnt. If it doesn't and the surface fans do the job, hooray for me.