Cooling the Nutrient Solution
 

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.

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.

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

Or maybe aluminum tubing?

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.

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.

I use ice sometimes. I also have the reservoirs insulated some. Not much, though. I put a half gallon plastic jug of water in the freezer overnight and put it in the reservoir in the morning. Unfortunately, this is not an ideal way to do things. It is obviously not going to be constant and takes up freezer space. But, it may help while you are looking for a more permanent solution.

Thanks Joe, as you said it is not a permanent solution but it will help till I find one.

cooling and parts
 

I have used copper back in the day in my nute system and never had issues. it turns green and oxidizes but no issues i have ever saw.

i build nute coolers. i buy used wall shaker air conditioner on Craig's list for cheap that work. Then on ebay i buy stainless plate heat exchangers. you get order them in what ever pipe size you want. i cut the evaporator and condenser off the units and install the plate exchangers in there place and recharge with a cheap can of r134. it only takes a smidge of the bottle and a a/c shop should be able to charge it for you for cheap.

I then take a poly 55 gallon drum and install a small pond pump in it and fill it with water then flow that through one plate exchanger and the nutes through the other and you have what would be a very expensive chiller for $200 bucks. the drum has enough surface area if its in the shade outside it will work perfectly. i had two 20 btu wall shakers heating a hot tub for a few years with a pond pump circulating it and it maintained 120f in freezing weather and super hot in the summer we had to install a car radiator on it with a fan and therm o fan switch. so surface area is what the tank is all about.

if you only install a exchanger o the nute side for cooling you will be able to still use the fan and a/c system as a air to water and if your real care full pull the temp prope off teh front and un coil it to stick it in your nut tank or tape it to the input line of the nutes and wrap it with insulation and the unit will turn on and off at the temp you set it at just like it was doing a room and you can install it right in a window just like it should be.

Or a extreme igloo cooler from wall mart and make your blocks of ice to keep the cost down and run lots of copper line in it and just let your current system flow through it. i've been there before. ice is always your hydro buddy. 1 for your hydro system and 2 cubes for your margarita while you sit and watch over the grow in that awful heat. 5 ft of copper in ice water is amazing on a small pond pump. also find a car heater core thats is aluminum and plastic and install a couple or one large PC fan on it and leave it running. every btu counts or makes your ice last longer.

aquarium chiller
 

I have had many people recommend burying your reservoir and or creating some form of "geothermal cooling" by using buried coils with a pump.

I myself found a used aquarium chiller from someone breaking down an aquarium and bought it for 150 bucks. I can manually control my 55 gallon reservoir to seemingly any temperature from 55 degrees upward. I keep my tomato nutrient res. at 67 degrees.

It may be more expensive than other methods but the reliability and programmable nature of the chiller has been great for me. I am a new grower however, and others surely have better/cheaper alternatives.

If you can find a used (cheep) aquarium chiller that could defiantly be a possibility. The new aquarium chillers that I found on-line last summer started at around $300 (if I remember correctly), and were only designed for 15 gallons, they just went up in price from there. I have no experience using them so I wouldn't be able to tell how well they work outside in temperatures like the 120 degree days we have here. I image a rooftop or terrace could reach that temp as well.

P.S. I designed a cooling box a while back that will help keep the heat from the reservoir. It's basically just a large ice chest. I have yet to build it, but plan to hopefully this summer. I attached some pictures, but I have complete directions in a pdf file. I designed it for two 32 gallon trash cans for reservoirs, but it can be built to any shape or size. The inside needs to be kept cool, I can think of a few ways to do that, including an aquarium chiller. It may give you some ideas.

Thank you all for the ideas & suggestions.

I had mixed comments about using copper and today I decided and bought stainless steel tube. 7.5 mm diameter, 0.40 mm thickness, 6 meter long. I guess it shouldn't be hard to bend since it is very thin. It cost... let me convert... 6.7 USD. Is life getting any better than this? :)

As I mentioned earlier, I am planning to use the water from the evaporative cooling unit to cool down the nutrient solution, since it is a source readily available. If I did not have that, then I would consider using some sort of vapor compression refrigiration unit such as a 2nd hand aquarium cooler. Note that this would cost a lot more to buy and operate, since it would consume much more energy.

Now I need to bend the steel tube into a coil form. Also I need a small pond pump to circulate the cold water through the tube. I will use a thermostat that I already have to keep the solution at 22-24 degrees celcius. I will post the results.

If you found 18 feet of stainless steel tubing for $7 USD, I am impressed. Even if you still need to bend it, for that price I will buy the tool to bend it (I have a tool, but only for bends, not coils). What I found was around $40 USD and I doubt it was any more than about 8 feet stretched out. I can get 700 feet of 1/2 inch poly tubing for $40 ($39.95+tax).

Just a note on the water temp of the evaporation cooler. I had bought a large portable one to cool my room with, I sold it because it just drove up the humidity in the house, but that was not my point. When I first bought it and brought it home I also got 20 lbs of ice. The cooler held about 5 gallons of water, I dumped all 20 lbs of ice in the water reservoir, then filled the rest with cool tap water. It felt just like an air conditioner (as I imagined it would). That lasted for 20-30 minutes before the ice had all melted and the water was almost at room temp (about 75 degrees F). It cost about $3 USD for the 20 lbs of ice, I quickly found it would be cheaper to run the AC. But that was just my experience. If the water line going in is directly from the the household pipes the temp might be because of the geothermal effects of the underground lines (sounds like the right temp). But you know your system, and how it's set up.

P.S. Pictures would be nice also.

Bending the tube turned out to be difficult without proper tools, so I asked a friend to do it in his toolshop. I hope to have it by tomorrow. I will post pictures.

Let me explain how I have cool water with this evaporative cooler setup. (I find this difficult because English is a second language to me, please forgive me if it does not make sense to you.)

I think you know the concept of evapotative cooling, but I will start with that anyway. Evaporation process requires energy. So as the water evaporates, It takes energy from what is nearby. As a result what is nearby cools down.

So, you want to cool the air. In order to do that, you force air through a pad. You keep the pad wet, so as the air passes by, some water evaporates and draws heat from the air. To wet the pad, you pump water from a reservoir and let it drip on to the pad. The excess water drips down the pad. You collect that water and return it to the reservoir to use it again. So it is a closed system. I don't use the water from the household pipes.

Now this water that is circulated through the pad gets cold in time. It gets down to the exit temp. of the air. Because energy is drawn from the water itself as well as the air passing by. I'm gonna use that water to cool down the nutrient solution. And It will be always cool as long as the evap. cooler oparates, It won't get heated up.

The evap. cooler should always draw fresh air from the outside and that air should have a low relative humidity. If the relative humidity of the incoming air is high, very little or no water will evaporize and thus, no cooling. If you can not get cool air without putting ice in the water, than you are evaporizing no air. Maybe your incoming air is too humid already?

Here is a chart. For example, let incoming air be at 90F. If RH is 10 percent, the air leaving the pad is 67F. And the continuously circulating water will be at 67F as well. But if the RH is 70 percent, than air leaving the pad is 84F, only 6 degrees cooler:

http://www.alloutcool.com/image-file...art458x298.gif

Love to see the pictures when you get it done, I'm also interested in how well it works for you. Ya I am familiar with evaporative coolers, although I commonly call them swamp coolers. That's an interesting chart, and I have not done extensive testing on them, I'm just going by my real life experiences. This is the portable cooler that I mentioned I had (before I sold it) although I only paid $299 USD at the time.

Master cool

Although technically it's a closed loop system, they still lose water. It evaporates and becomes humidity in the room. As I mentioned it held 5 gallons, but the water level would get to low for the pump if you ran it full blast for 3-4 hours. I didn't want the pump to run dry while I was sleeping so I hooked up the water line to the float valve (it came with) to a faucet (for the toilet tank fill line) in the bathroom and ran it along the baseboards into the bedroom. Now I know it is not suppose to work well in closed spaces, but I was not about to open the windows and allow the 120+ degree heat (fresh air) into a room that was 80 degrees without the cooler even being on.

Of coarse it felt cool if you were right in front of it, but the humidity in the room kept rising (because the water evaporates) to over 60% (from less than 10%). That's why I sold it. At my place of work we had two roof mounted swamp coolers in the shop, and from my experience they still weren't any good unless you were standing directly under the air duct. If you were 10 feet away it did no good for me. I don't know what the water temp was in those systems, but being mounted on the roof and the water lined needing to run up there, it was not any 72 degrees. But all that being said, I can easily build a swamp cooler myself. I have no idea what the books say the temps should be, but I do have real world experience with how they function, work, and cooling ability's (in my area).

I also planed to build something similar, but an actual closed loop design that's more like an AC, than swamp cooler. Because the water does not flow down a filter that the air passes through providing humidity. Instead the water is pumped through a radiator (refurbished, and clean), and the air passes through the radiator. The water would be pumped from an ice chest full of ice water to cool the radiator.

No humidity and cool air. But I have never tested it, and don't know how long the ice water would stay ice cold. As you mentioned it takes energy to cool with a swamp cooler, as it would in this system. That energy is heat transfer (same principal as geothermal energy). But the key is "transfer" not "elimination", so the heat does not disappear, it's just transferred to the water. I know that's slightly different than how a swamp cooler cools, as anyone who has walked under a mister on a hot day knows. But that's because technically it's not a completely closed loop, and the air passes through the water on the filter.

If the air temp and water temp are the same or close then there is not much transfer, but in my area when the outside temp is 120+ degrees there is plenty of transfer. We even leave the hot water heater off all summer because the heat in the garage is hot enough to heat the water in the hot water heater, and that's insulated. We even need to let the shower run (cold water) for about 10 minutes before getting in it because the water is to hot. After about 10 minutes the water that was in the underground pipes (and cooled by geothermal energy) begins to flow out, then you don't get burned when getting in it.

P.S. Sorry English is my only language, but I believe I am able to understand you fine, for what it's worth.

Here is the coil. I put a pencil too so you can compare the size.

http://img139.imageshack.us/img139/7182/img0220l.jpg

I will post pictures when I complete the setup.

He did a nice job getting the coils close and even.

How about coils and a small drink refrigerator
 

I've been thinking about running some water or other cooling solution in coils in my reservoir and pumping it through a small Dorm Room size refrigerator, like something I could pick up on ebay or craigs list. Not sure how I would control the temp to keep it from getting too cold though .

I think a real cheap A/C window unit made into a "window" in the side of the box might work well for cooling the box and contents, plus it has a thermostat control, who knows, you might even find one with a remote ;>)

PC

Here are some photos of my setup:

http://img411.imageshack.us/img411/9131/img0239kr.jpg
Water tank of the evap. cooler.
There is a float valve attached, orange ball.
Two pumps inside.
Black pipe runs water to the evap cooler.
White pipe is the return from the evap. cooler.
Blue pipes are used to circulate cold water through the coil, which is inserted in the nutrient solution tank.


http://img69.imageshack.us/img69/1794/img0246w.jpg
The fans, NFT channels and a small raft system for the seedlings.


http://img196.imageshack.us/img196/5126/img0241ot.jpg
The evap. cooler.
Black pipe runs water from the cooler tank.
White pipe below returns excess water to the cooler tank.


http://img690.imageshack.us/img690/151/img0243ux.jpg
http://img685.imageshack.us/img685/5623/img0244ju.jpg
Nutrient solution cooling setup.
Blue pipes are used to circulate cold water through the coil, which is inserted in the nutrient solution tank.
A thermostate is used to stop the pump when NS colls down to 25 degrees celcius.

Very Nice setup, gives me something to work towards.

Can you give me some details on the thermostat, I've been trying to figure out how to do that part?

Yes this just one of my possible's, Although I would probably run it through some ducting into the box, rather than just building it in the side. I also have an idea of running a duct line directly from the household AC ventilation into the box. Both of these options would require an some exit for the air pressure in the box, otherwise the pressure wont allow the cool air to enter the box very well. Also on the list is dry ice, or ice blocks. I am also considering a thermoelectric electric possibility, like in the electric ice-chests you plug into a cigarette lighter of your car.

omerizm
Thanks for the pictures, it looks like quite a setup you have going. I'm wondering how the humidity is in the greenhouse, is it high? As well as how well the swamp cooler is working, do you know what the difference is between the actual inside and outside temps? How hot is it outside? Also looking forward to hearing how the nutrient cooling coils are working out.

pec0054,

What I use is an ordinary digital thermostat. It has a sensor to measure the temperature. Also it has an electrically controlled switch, which is called a "relay". The controller can be set for heating or cooling, as you prefer. In this case it is used for cooling. When the measured temperature is higher than the set temperature, the switch passes current, and when is is lower, it cuts the current. That is how I run the pump on and off.

GpsFrontier,

The temp. inside the greenhouse is anywhere between 4-11 degrees lower than outside temp. When the outside air is hotter and drier, the cooling efficiency is better. For example, right now outside temp is 36 and inside temp is 28. Yesterday when it hit 40 outside, it was 30 inside. The inside temp. is measured in the middle of the greenhouse, so it represents the average temp. Actually it is a bit cooler near the cooling pad and a bit warmer near the fans, as you can imagine.

Relative humidity inside the greenhouse is usually about 70 percent, which is ok for lettuce.

The coils work but not as good as I want. It lowers the temp. of the NS by about 3 degrees only. The ideal temp. of the NS is 24 degrees but most of the time that does not happen during the day. So basically the pump runs all the time during the day and shuts off only at night. But still, it is helpful because It can keep the temp. below 30 degrees, which is high but not very bad.

I need a longer coil and a more powerful pump to further cool down the NS. But I won't upgrade, It is too much trouble.

PS: All temp. is given in CELCIUS, not FAHRENHEIT.

cooling nutrient solution
 

This is a link to an aquarium chiller. Although it's pricey I wonder if this would be a solution. Any comments?

Oceanic Aquarium Chiller - 1/10 HP - up to 55 gallon


http://www.oceanicsystems.com/assets/008/15829.pdf (Detail)

I use one
 

I don't have that brand, and I use a larger one that I purchased off of Craigslist, I think 1/6 hp. It worked great all summer long keeping the nutrient temp at around 68 degrees.

Be aware, you also will need a pump to push the water through the chiller.

Look around on craigslist for people selling old aquarium equipment and you might find yourself a deal like I did.

Nothing on Craig's list I could afford.

Here's one for $275 and it will cool "one gallon per hour". From what to what and how fast it doesn't say but not much more than buying a compact frig and making one. ?????????

Amazon.com: COOL WATER CHILLER WASTE KING: Home & Garden

İf you can find a cheap, used small fridge (like the ones used in dorms) you can build your own easily.

take out the freezer compartment if there is any, put about 25 meters of thin walled hose inside the fridge, drill two holes on the top for inlet and outlet and take out the two ends of the hose through them. You can use a small aquarium pump to circulate the nutrient solution through the tubing inside the fridge. Don't forget to seal any gaps around the holes for efficient cooling.

This should be a pretty efficient cooler and it costs practically nothing besides the fridge. There are used dorm fridges on ebay under $50. If the thermostat is intact you can control the solution temperature automatically.

omerizm
Although for my situation I would be concerned with amount of electricity a refrigerator uses (even a small one). I am wondering if you built one like that, and if so how well it worked. How big the reservoir was, what the temp was before and after using it etc.. I have considered using such a refrigerator to cool nutrients, but modifying it in a different way. But as I mentioned the cost to run another refrigerator was the factor that led to me not even trying it. Especially the used older models that are most likely not even energy efficient.

Hello GPSFrontier,

No, to be honest I did not built this one, the only cooler I built and used was the one described in this thread, that I posted pictures of. And it was successful, I mean it did the job.

As you know I used the cool water coming from the evaporative cooling pads, circulating it through a coil that I inserted in the nutrient tank. Running costs are cheap with this setup, just an additional small aq. pump running. Now there is no apparent reason for a "modified dorm fridge cooler" not to work, it most certainly will, but as you said it will be much more expensive to run. Actually I guess "modified dorm fridge coolers" will be more effective than most commercial chillers because they use more powerful compressors. What really matters here is the power of the compressor.

If you are concerned about the running costs, I would suggest that you stay away from all kinds of vapor compression refrigeration units. The most efficient refrigiration cycles in the world are about 60% efficient. (cooling power/electricity used). And most commercially available units are between 40%-50% efficient.

To raise the temperature of 1gr of water by 1 degrees, you need 1 calorie. 1 calorie = 4.18 joules and 1 watt = 1 joules per second. Now if you know how many liters of water you need to cool in a certain amount of time and the temperature difference required, you can easily calculate the cooling power. Divide this by 0.6 and there you have the power of the most efficient cooler that will get the job done. If this is too much for you, than no vapor compression refrigeration unit is suitable.

I suggest you try to use some kind of evaporative cooling, or even better, use some kind of heat sink such as the earth and run your solution through it. Or as I did you can use an already available source of cool water and run it in your reservoir.

Evaporative cooling requires much less power than compressive ref. coolers. I guess a counterflow chiller of closed type will be suitable for NS cooling.

Cheers

Hello omerizm,
If you have not built it before that is fine, I was just hoping for come first hand information on how efficient it was. I have thought about modifying it that way myself, but think I can make it more efficient. I would need to do some disassembling of the refrigerator to see how I could make it work best. I don't have a spare one to work with.

To be honest I have never been impressed with formulas. Especially in cases like this where the needed cooling can change from day to day. Not to mention all the variables in it's design. Not all tubing will conduct heat exactly the same, metal tubing will be much more efficient than plastic, and different types of metal will conduct differently. It's not only about the total output of the compressor and the temp drop needed. Not all of that energy (cooling power) will make it to the liquid in the reservoir. So any formula will be flawed. The formula wont be able to take into consideration all the materials used and design, therefore the efficacy of the design.

Like you mentioned using 25 meters of tubing, but it will be more efficient if you used 50 or 75 meters. But no mater what length of tubing you use, plastic tubing wont be as efficient as metal tubing. The formula cant adjust for that, nor can it take into consideration the diameter of the tubing or even thickness. If it did it wouldn't matter what type or size it was, you would be able to use just 1 meter of tubing and receive the same results. All those variables will affect how efficient it is in the end. It may be useful as a guideline, if you have a working model to compare to. But I'm more interested in working practicality of any design.

Also I wouldn't be building it to use in only one system. I wouldn't even want to build it unless it was capable of functioning well for reservoirs of different sizes, and/or where different temperature drops will be needed. It is a lot hotter here in July than it is in May. But I have come to the conclusion that so far compressor based cooling units will probably be more expensive to run than it's worth. I cant justify spending $100 a month in electric bills to grow $50 worth of produce.

I have considered using heat sinks, I even contacted some company's about it. The same type used in portable coolers, I got some good information, but conflicting theories on how efficient it would be on the size I would need to build them, compared to using a compressor unit. But That could be because the company that said it would be too expensive to run only sold completed units. The other company only sold one part and gave me links to places where I could get the rest of them. Any witch way you look at it, I would need to build at least one working model of these and measure the cooling ability's as well as the electrical cost.

Not sure if you know but I have already built a geothermal reservoir, not to mention that I have designs for using geothermal energy to cool the nutrients. So far that's the most cost effective option, even if it's the most inconvenient method. I do have plans to build a sort of revers swamp cooler to cool the nutrient solution. I don't have any experience on how efficient it is but I'm told it works well in our claimant. From the design I can see ways to make it better, but until I have a working model who knows if it will be useful.

Hello Gpsfrontier,

Well I am a mechanical engineer, and I am "impressed with" formulas eheh :) You need to consider the max amount of cooling you need in the hottest season, and the max. reservoir size. Your cooler should be able to work at that extreme design point and you can use a thermostat to adjust to more favorable conditions by simply turning the cooler on and off, keeping your NS temp. at the desired level automatically.

You do approximations and put efficiency factors in your formula to simulate real life conditions. You don't need to consider every single physical effect and all the details for that. It will give you a basic idea to start your design. My point is, a vapor compression refrigerator can be 60% efficient tops, so you calculate how many calories you need per second (for the extreme condition) and divide it by 0.6, and you know the least amount of power you need. It is reasonable to expect that your cooler will be even less efficient than that so expect to use more power.

If you calculate this, you will know the minimum cost you can realistically expect and then maybe you will eliminate the option of vapor compression cycles.

The length, wall thickness and thermal conductivity of the tubing has no effect on efficiency. That only effects the heat removal rate from the NS passing through the tubing. Efficiency is all about the percentage of energy you waste. By using a shorter tube you don't waste anything, you only draw heat slower and it will take a longer time to cool down the same amount of solution but you will use the same amount of energy to do that.

Major energy waste is in the compressor and heat absorbtion of the fridge from the surrounding medium, that is air. So what effects your power consumption is mainly how efficient your compressor is and how well your fridge is insulated. It is also important to insulate the tubing between the reservoir and the fridge.

Hello omerizm,
I think you misinterpret what I'm talking about when I use the term "efficiency". I'm speaking of how cool the nutrient solution gets, not how efficient the compressor is. I know that adding any amount of tubing to the inside of the frig is not going to change how well the compressor works. I'm only concerned with how cool I can get the nutrient solution, and how much it costs to get it there. The key to making it efficient (cooling the nutrient solution) is in getting the warm nutrient solution to transfer as much heat with the cool air inside the frig as possible. Then it will depend on the size (volume of water) of the reservoir and the outside temperature (I grow outside) weather it can cool down the entire volume of water (nutrient solution) to a sufficient temperature, and be able to maintain that water temp all day long. That is what it takes to be efficient to me. Of coarse another factor in how efficient it will be in cooling the nutrient solution is how well insulated the reservoir and outside tubing will be. I didn't really mention that because it's easily enough to do, and I already have planed on doing that regardless.

And although the thermostat can help adjust the water temp, I can assure you my water temp in my reservoir will be no ware near the temp on the thermostat in the fridge (unless it's winter, maybe early spring). The thermostat will need to be set to its coldest setting and remain there all summer. Considering that the fridge will be outside during the hottest parts of the summer that will be 120-125 degrees fahrenheit during the day, and between 100-110 at night. There is no way to bring it inside and just run the lines outside, there is simply no place to put it inside, other than the garage and it's hotter in there than it is outside. Also I have no set plan of what I will be growing this summer, but suffice it to say as many things as I can. That would include more than one reservoir needed. With the amount of money I have for materials being the largest deciding factor in how much I will be able to grow. With reusing as much as I already have, but I want to try some new setups.

Like I said the key to making it efficient is getting as much heat out of the nutrient solution as possible. I have already designed a cooling box witch is pretty much just like a large ice chest. With the reservoir inside here and ducting the cold air from a small refrigerator or window AC unit, that will make the heat transfer more efficient. And kind of like keeping the entire reservoir inside the refrigerator, instead of only running some coils through it.

I designed this cooling box to work with the heat sinks that I was working on as the cooling source, but it's very adaptable and functional. It will even be able to work with the geothermal coil trench design I have as the cooling source. How well and how efficient it works with that cooling source at cooling the nutrients depends mostly on how deep the trench is, how long the coiling tube is, volume of the reservoir, and how well the tube transfers heat. I even have another cooling device design that I'm planing to test this summer, with or without using the cooling box. I'm looking forward to seeing how efficient that will be. Building on what the original person built I can make some improvements, but it's supposed to work well as is in our climate.

P.S. Also another thing to consider is using air stones in the solution. Obviously pumping hot air into the reservoir is not going to be beneficial. So the placement of the air pump, lines and how long the lines are is all going to make a difference.

Is there any such thing as a thermostat with a probe that can be placed in the reservoir and be set for say 72 degrees and only run the pump until it cools?
I don't suppose running the solution thru a fan cooled radiator (like on a auto only smaller) would work ?
If I could find a thermosat like that the pump and the fan would'nt be running constantly.
Idunno, just asking

Hello one800fish,

Of course there is. The one I use to control my cooler works exactly as you described. Here it is:

Enda

And this is the sensor that I connect to it:

Enda

Don't worry about the brand and model. These type of devices are pretty much all the same so you can search and find a manufacturer in your country and purchase one. You don't need to buy it and have it shipped from accross the world because it will probably be more expensive and you will find it hard to get it fixed in case it brakes.

These devices work basically like this: You put the sensor in the medium you want to control, in this case you dip it in the nutrient solution inside the tank. Beware that there are different types of sensors for liquids and gases and also for different temperature ranges. You need to get one suitable for water. My controller works between -60 to 150 degrees Celsius and my sensor measures up to 150 degrees Celsius and it is for measuring liquid temp, so its good for me. By the way, some thermostats are used for cooling and some for heating but nowadays almost all digital thermostats can be used for both. You have a power input in the thermostat, connect it to your power source with a cable. And you have an output, there you want to connect the device you want to control, in this case a pump or fan or whatever you like. There should be a manual that comes with the device that explains the connections. Also from that manual you can learn how to set the controller to a desired temperature and adjust hysteresis and stuff like that. In cooling mode, it basically powers up the fan or pump or whatever when the temperature exceeds a certain point and it cuts the power when it drops below a certain point.

Say that your set temperature is 72F and hysteresis is se to 3F. it will power up the pump when temp exceeds 72+3=75F and it will stop the pump when temp. drops to 72-3=69F. You want a few degrees of hysteresis because you don't want to turn your device on when temp hits 72 and off when it drops to 71, in which case your pump would break from a non stop on/off abuse.

Cheers