Cooling the Nutrient Solution

[omerizm]

I need to cool down my NS. It peakes at 30 degrees celcius in very hot days. I grow lettuce and recommended temp is 24 C.

I'm thinking about using the return water from the cooling pads, which runs at 20 degrees.

The idea is, put a pump in the cooler tank, pump it through some tubing insterted in the nutrient tank, return heated water back to cooler tank. Use a thermostat to maintain temp. What do you think?

And, can I use copper tubing? Will it do any harm to the plants? If yes, what else can I use?

Thanks in advance.

[GpsFrontier]

I am not sure what the cooling pads are, or how much liquid it circulates. But coils in the solution or visa versa may work. To be honest I am not sure if copper coils would react with the nutrients at all, although it might add excess copper to the nutrient solution. You can also use stainless steel tuning (very expensive), or any poly tubing (the smaller diameter the better). Although metal will give much better heat transfer. If using poly tubing you may need as much as 3 times as much as metal tubing for the same results.


P.S. If you had a link to the coiling pads that you were planing to use, and a simple diagram how you plan to use it, I could possibly help with refining it.

[omerizm]

Its the water coming out of the evaporative cooler pad. The circulated water that wets the pads is always cool, about 20 C. Theres as much cool water as the nutrient solution so it will be enough.

Here's an example of an evaporative cooler pad: http://www.rotorsource.com/images/evapcooling/illus.jpg

I'm sure it will work with enough tubing but I have worries about copper. As you said plastic is very bad for conducting heat. And stainless steel is very hard to bend into a coil shape like this:

http://www.advancedtubular.com/wiki/...il_65pitch.jpg

[omerizm]

Or maybe aluminum tubing?

[GpsFrontier]

I saw the link for the what you call the cooling pad. It looks like nothing more than a filter/pad for a swamp cooler. The pad/filter does not cool the the water, it actually heat's it up. If you run it through your coils before it gets to the top of the pad and drips down through the filter you may have a chance. But I'm not sure how much volume it can do. At 20C, 68F you will need a large set of coils as well as volume of liquid going through it to even help. Keep in mind, if it's in an enclosed system the coils will heat it up as well, further reducing it's effectiveness.

I'm not sure where you have your system but I would use a geothermal heat exchange system, if I can at all run the pipe/tubing outside. Either as a closed loop, or open loop system. Although I think a open loop would be the most cost effective even in the long run.

As for aluminum I am not sure if it reacts any different to the nutrients than copper. Stainless steel is the only metal that I would be sure of. I don't remember what department it was in but they do have them already formed in coils, they were just too expensive for me to consider.

[omerizm]

Yes you are right, its the kind of pad that is used in swamp coolers. They are commonly used in greenhouse cooling.

http://www.igcusa.com/greenhouse_coo...nformation.htm

The water dripping down the cooling pads is cool, actually it is equal to the exit temp. of the air.

For example, right now the outside temperature is 33, the temp of the air leaving the pads is 22, water in the cooling tanks is 22 as well, and the temp in the middle of the greenhouse is 26. The nutrient solution is 27. (all in celcius)

This is a 15 meter square hobby greenhouse in my terrace, I am not on the ground. I am in Europe, so don't worry about the name of the department, we probably don't have it here anyway.

It is true that since the temperature diff. is small, I need a lot of tubing and flow rate.

I will look for steel tubing formed in coils.

Thank you for your help.