First effort drip bucket system 14 headed to 20!

[MontyJ]

GpsFrontier,

While I like your enthusiasm, I'm from Missouri (not really!) and it takes a 2x4 whack upside the head sometimes for me to "get past the numbers", LoL.

Example. I sent my heat transfer problem to TE Technology, those guys who make those really nice Peltier cooling plates, etc. Here is the reply I got back:
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Monty,

The Peltier cooler would need to remove approximately 8 kW of heat in order to cool the water from 100 F to 70 F at 100 gph in a single pass through the cooler. Peltier coolers are generally best used in applications where the heat load is less than 200 W. Your application really requires a compressor system.

Regards,

Paul Lau
Engineering & Sales
TE Technology, Inc. | 1590 Keane Dr. | Traverse City, MI 49696-8257
TEL: 231-929-3966 ext. 107 | FAX: 231-929-4163 | WEB: Home » TE Tech Products
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Now I realize this is worse case; no insulation, realtime flow cooling, not a reservoir application, etc. But it does confirm my guess that the heat load is severe, as these numbers are "real" as far as current conditions.

I know you "know what will work" despite the numbers, but do you really believe your approach, using only 100W can withdraw 8KW of heat?

And you are right I was not clear on your "reverse swamp cooler", and still am not. But until I can get a heck of a lot more insulation on the buckets, lines and reservoir, I am not going to do anything else about the cooling.

Perhaps when I get a better insulated system and larger reservoir, I can get with you on details of your idea. I certainly am a proponent of DIY and simple solutions over complicated ones, but I also don't like to jump into projects that may be just a stab in the dark.

I did communicate with you via your website back around the first of the year and you were very helpful and quick to reply to my query, tho I have forgotten what it was about other than a drip bucket system setup issue.

You do have a ton of helpful info there and I hope people appreciate your efforts!

[Edit] I don't have any way to go with the geothermal approach, unfortunately. I am very limited on what I can do as far as the rental property is concerned. The hot patio cement area is it...

Monty

[GpsFrontier]

Hello MontyJ,
Ya, I would agree the first thing to focus on is insulating the buckets and tubing for sure. But the second part is to cool down the inside of them, otherwise the insulation will only hold in the heat.

I know you "know what will work" despite the numbers, but do you really believe your approach, using only 100W can withdraw 8KW of heat?

I guess your not really familiar with swamp coolers. Find someone that is running one, and ask them if you can feel how cool the water in it is. I have already built two swamp coolers from scratch for my greenhouse, and the way they work is simple. The last one I ran last summer had a 40 gallon reservoir. That reservoir was nothing but a 45 gallon storage tote I got at wal-mart for about $15. It sat in full sun all day with no insulation or lid, and when the swamp cooler was running, the water temp was in the low 60's Fahrenheit, even when the daytime highs were in the 115 to 120 range.

Granted I was using a larger fan, a 20 inch fan. But that was because I was trying to cool the air inside the greenhouse (not the water), so I wanted a lot of air volume. In the case of the reverse swamp cooler, the focus is on a large "water volume" of cool water, not cooling the air. So you don't need as much airflow. Most Swamp coolers only have a small reservoir, but you can make it as large as you want (when you build it yourself). That cold water is what you'll use to cool the nutrient solution with. But even if you wanted to use the same 20 inch high velocity fan I used (like the one in the attached picture), it only uses 30 more watts (162) than the 10 inch inline duct fan.

While I like your enthusiasm, I'm from Missouri (not really!) and it takes a 2x4 whack upside the head sometimes for me to "get past the numbers", LoL.

I'm sorry, I didn't mean to whack you upside the head with a 2x4, I just wanted to let you know that BTU ratings are not all the same, and comparing apples with oranges doesn't work. Swamp cooler BTU ratings are air temp ratings, that's why they don't apply. If you want to figure BTU's you need to calculate heat exchange for water volume. It takes a lot more BTU's to cool water than it does for air. Also you can increase the BTU's of the reverse swamp cooler without using any more electricity, simply by increasing the water volume. If you want to calculate BTU's for the reverse swamp cooler, try this.

Using the last swamp cooler I built as the test subject.
First, calculate how many BTU's it takes to cool down 40 gallons of water from 110 degrees Fahrenheit to 64 degrees Fahrenheit. That's a good starting point, and how many BTU's I got for my 200 watts. Now double the water volume to 80 gallons. Now you have just doubled the BTU's using the same 200 watts.

Now take it another step. The pump I used is capable of 500 gallons per hour. To be safe because you'll most likely want to turn over the complete water volume about every 30 min, and taking into account for head height, say your turning over 200 gallons every 30 min. Using a 200 gallon reservoir, you have now increased the BTU's to five times more, using the same 200 watts. You can also easily change the amount of cooling pad surface area without using any electricity (watts), and you can also easily increase water flow with very little wattage. This is why I say don't get stuck on BTU's.

[MontyJ]

I am probably have to build me a test swamp cooler to see how it really works...being from Missouri and all, LoL.

I am not hung up on BTU's, watts, or tons. But heat exchange rates can be defined by those numbers, and bottom line this is a heat exchange issue. If you start with 100F air and 100F water and simply blow the air across the water at some rate, you claim both the air and the water get cooled down.

Where does the heat exchange come from? Just the evaporation process itself? In simplest terms, heat is being withdrawn out of the water if the water gets colder. Where is that heat going? It ain't going into the air, as the air is colder as well, right? If it is evaporation, then the nutes will be evaporating if that is the media I am trying to cool.

I've already admitted I don't know much about how swamp coolers, reverse swamp coolers, etc work, no need to swing the 2x4 in that direction again.

My plan is to insulate the buckets and reservoir as well as I can. I may move the reservoir closer to the buckets to eliminate as much connecting hose as possible and wrap them as well right up to the bucket itself.

At that point I need to calculate cooling needs. Using ice bottles, I will see what kind of heat transfers happen with the system running normally with the insulation in place. This is not an ideal way to do it, but I need to have a better handle on the insulation effects on the system, then I can start looking what it will take to keep the reservoir at some ideal temp.

One thing I noticed is that most online calculations deal only with a given volume of liquid to be cooled, and that is simply recirculated until the desired temp is reached. There is seldom any thought about every cycle, in my case one cycle per hour, injecting NEW heat into the reservoir for. That new heat load has to be handled before the next cycle starts, which is only 30 minutes. That is why I went with the worst case of asking the 'experts' how to cool the water 'real time' and that is how they (two separate resources) came up with pretty much the same ton-btu-watt requirements to do it.

With some very thick insulation on my system, hopefully the energy to keep it at 65F-70F or so will not be too overwhelming.

Again, thanks for your ideas. I learn a little more with every read!

Monty

[GpsFrontier]

Hello MontyJ,

If you start with 100F air and 100F water and simply blow the air across the water at some rate, you claim both the air and the water get cooled down.

Yes.. Heat is a form of energy, and you cant eliminate energy, it can only change form. So it stands to reason that the heat energy needs to go somewhere. But were does it go? I can't explain that at this point, and I don't claim to be a scientist. I also have a good friend that has been working in the heating and air conditioning field for over 20 years, and he services swamp coolers on a weekly basis. I have asked him where that heat energy goes, and he can't explain it either. I have thought about e-mailing that question to some university professors, but haven't done that yet. You asked me if I think it would work, and yes I do. Otherwise I never would have mentioned it, or planed to build it. I have been planing to build a working model for a couple of years. But when I had the money it was winter, and I couldn't test it. Now that it's summer again I need to make it a priority or it will be winter again soon.

If it is evaporation, then the nutes will be evaporating if that is the media I am trying to cool.

I think I have confused you. There are two separate reservoirs in the reverse swamp cooler design. One is the nutrient reservoir, the other is the reverse swamp cooler reservoir. You don't run the nutrient water through the reverse swamp cooler. That would cause problems. You can use the reverse swamp cooler water to cool the nutrient solution two ways. Either by pumping it through coils that are submerged in the nutrient solution (or vice versa) to act like a radiator. Or by placing the nutrient reservoir directly in the reverse swamp cooler water. Something like placing a smaller trash can (used as the nutrient reservoir) inside a larger trash can (used as the reverse swamp cooler reservoir). Thus cooling the nutrient solution by direct contact with the surface area of the nutrient solution container. The same way geothermal energy works by placing the reservoir in the ground (surrounding it with a cool surface that wicks away heat).

Yes, your right, the water in a swamp cooler does evaporate. That's why another term for swamp cooler is called evaporative cooler. I forget exactly, but I think it evaporated at a rate of something around one gallon of water per hour in the swamp cooler I built that I used as an example earlier. A simple float valve connected to a water line can be used to maintain a specific water level. That way you don't need to keep an eye on the water level. That's what they use in commercially built swamp coolers to make sure it never runs dry. You can get a float valve here for about $4 to $8. You also want to use a inline calcium filter (here that's about $10-$15), otherwise you will get a lot of lime scale buildup.

in my case one cycle per hour, injecting NEW heat into the reservoir for. That new heat load has to be handled before the next cycle starts, which is only 30 minutes.

That's exactly why I said that you'll need to dump ice in it multiple times daily. And that will take a lot of time, space in the freezer, as well as energy, and everything in the freezer starts to thaw. I've done it myself so I know exactly how much of a pain it is. In fact I'm doing it right now for my pepper plant. It takes about 1/2 gallon of ice twice a day for a 7 gallon reservoir.