Water (nutrient-) cooling with Peltier elements (fail)


#1

Hi,

I would like to share my experience that I had with a Peltier element to cool down the water in the basin.
During our hot ‘indian-summer’ the water temperature raised to 30° C. That was when I started thinking of a way to cool down the water temperature.
I ordered a Peltier DIY kit from china and connected the cooling elements to the circulation pump int he water (this one)
Here you see some images of how this looks like:



As you can see, it comes with 2 heatsinks and small fans.
The total power consumption of this device is around 70 Watts ( 6A @ 12VDC)
I started to measure the water temperature just to find out that the water temperature actually increased (!) after a couple of hours…That made me thinking and exploring.
I found out that the Peltier elements are actually very inefficient: around 10% effective. That means that 70Watt of energy consumption leads to 7 Watts of effective cooling.
The pump in that basin needs to run during the cooling in order to avoid overheating of the element. But this pump is submerged so it actually heats up the water, either by heat exchange or by icreased entropy. This is a 7 Watt pump !
So my conclusion: Using Peltier elements to cool down the water temperature is highly inefficient.


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#2

Meanwhile the outside temperature has come down here in NL, so no direct need for cooling anymore.
However, when next summer season comes I might have to fugure out an alternative solution and what I am thinking of right now is to use adiabatic cooling:
I would use a radiator with fan (120 mm) which are available for around25-30 euro. If this would not be enough to cool down the water I think that adding a similar mist generator as is used to increase the internal air humidity in front of the radiator. This will cool down the air temperature and therefor the water temperature as well.
Is there anyone out there who has already tried it ?


#3

@Peperoni, interesting experience. Thanks for sharing!

And what do you think about pump-less design? I.e. using stainless steel container to hold the water and attach peltier directly to container with one side and radiator and fan on the other.

UPDATE: It may still be possible to stay with plastic container I guess with some elastic sealant to keep up with thermal material expanse/shrink fluctuations


#4

OK, good idea, but what about the heat that comes from the heatsinks ? The whole concept is already high on energy consumption. I think it is important that we try to keep it as low as possible. However, if you find a good way to re-use the heat from the heat sink, it might be worthwhile to investigate.
In the BOM an air-heater is included, but until now it has not been activated as the temperature inside is high enough. The led lights (90 watts or more) and the plant activity are heating up the air to such a level (29-30°C in my case) that the heater has no real function. (this might change during the winter…)
I think you need to have a pump anyway in order to make sure that the water is regularly mixed. But in my current design it is only activated a couple of minutes per hour. Also to make sure that the water temperature is within limits.


#5

Well, following the lean principles, I guess, I need to make working V2 design first and then experiment with issues as they appear :slight_smile:

Just that those specs are not published yet. Hopefully OpenAg guys will do the demo for White House event and will share more info so I can start building.


#6

Here we go with some preview for V2 https://twitter.com/calebgrowsfood/status/782686227996618752
Seems that on 2nd picture in the bottom left there is some kind of cooling solution visible…


#7

@Peperoni thank you for sharing this experience, I was just going to ask you how much your solution can cool the water but you already asked.

I’ve been looking for water coolers and I found this one, the issue is that it costs US$140, aprox 10% of the whole BOM.

I am also waiting to see whether the V2 includes some mechanism to keep the water under 25 C.


#8

To me it looks like pump-less design with Peltier element. The only know-how is the “durable aluminum probe is coated with an FDA-approved finish”. And I guess ‘FDA-approved finish’ bears most of the cost :slight_smile:

I will try to make a DIY version with just aluminium probe and insulated tank (will start with plastic one first).


#10

This was already mentioned above regarding the V2 cooling device.


#11

Here is an update on my progress so far.

Here is the chart of water temperature when this DIY version of ice probe like design was put directly on top of 1L thermos.

As you can see it was possible to cool down water from ~22° C to ~7° C in 5 hours with just one Peltier element (TEC1-12706 to be specific)

However once I tried to do the same for much bigger (about 20L) uninsulated plastic container I was only able to drop down water temperature by 1° C withing 24 hours, which is not impressive.

So will continue my experiments with a) insulated tank and, maybe, b) two TEC1-12706 Peltier elements.


#12

I once tried using liquid nitrogen to cool my nutrient reservoir, but with no success. Even after pouring a whole gallon of liquid nitrogen into a 30 gal reservoir, you would think there would be some change in temperature. But I got 0 temp change, it was exactly the same temperature after as before. I was told it might all evaporate before doing much good, and they were right. However I haven’t completely given up the idea.

If you could pump liquid nitrogen through stainless steel coils submerged in the nutrient reservoir, or pump the nutrient solution through coils submerged in the liquid nitrogen, that should work. Doing it that way should allow good heat transfer without evaporation as long as the liquid nitrogen is completely sealed so it doesn’t evaporate.

The biggest problems in doing so is either finding a small pump that can pump liquid nitrogen and wont freeze. Or if pumping the nutrient solution through coils, then the problem would be keeping the nutrient solution from freezing in the coils when the pump isn’t on. Either way it’s very important that the sealed container holding the liquid nitrogen have a pressure gauge, as well as a pressure relief valve or the slightest change in temperature can cause too much pressure and an explosion.

.


#13

I’ve actually used something quite like this in industrial applications. We call this evaporative cooling, or swamp cooling, that’s the way cooling towers work in large industrial power plants.
Try putting a damp media in front of your fan. A small percentage (3-4%) of your liquid water (dampness) will evaporate and pull energy from the environment to do so. With outside temperatures of 30°C or approx, we reach 14-15°C of cooling, (from 45C to 30C).

The only down side is that you actually increase the RH% in the air, but that’s not necessarily an issue here…

I’m currently trying to build one for my project, I’ll let you know when its working. Its a bit on the hard side to control tough.


#14

A swamp cooler works fine to cool air assuming the incoming air has low humidity. But if your trying to cool the nutrient solution, you can’t just pump nutrient solution through a swamp cooler without big problems. The problems being drastically changing the balance of the nutrient solution as some of the mineral salts deposit on the cooling pad. As well as the constant concentrating of nutrients/mineral salts as the water evaporates, both from the nutrients themselves as well as from the minerals in the water source. You can design it to cool the nutrient solution, but you have to keep the nutrient solution and swamp cooler water separate. I have a design to do it I call a reverse swamp cooler.

A typical swamp cooler is designed to cool air, but if you have ever built one or ran one you know the water gets cold, and you can use that cold water to cool the nutrient solution. The emphasis of the reverse swamp cooler design is on the cool water rather than maximizing air flow. That’s why I call it a reverse swamp cooler. The revers swamp cooler is designed to maximize cooling pad space and surface area, while minimizing fan size (electricity use). You still want a good amount of cooling pad surface area to cool the water, but you don’t need a lot of air flow like typical swamp coolers since the point is to cool the water, not getting a lot of cubic feet of cool air.

You need to keep the swamp cooler water and nutrient solution separate, but that’s easy to do by running one through coils submerged in the other to get the heat transfer. The more cool water, the more heat (Btu’s) it can absorb without changing temperature quickly. The air flow and cooling pad of the swamp cooler keeps circulating cold water to the coils. Cold moves towards heat, so the cold water pulls heat out of the coils, thus heat from the nutrient solution.


#15

Actually, in industrial power plants, we use the cooling towers to cool
down water from steam turbine condensors. My numbers (45 to 30) are water
temperatures.


#16

If you take a close look at the images of the v2 model, you can clearly see that there is some kind of chiller in place. I wonder how that would make the price lower than model 1 :flushed::flushed:


#17

Patate
You said you used “evaporative cooling, or swamp cooling” and that’s what I was referring to. I understand swamp coolers well. I’ve worked on industrial swamp coolers my company had to cool the shop, and I have built many swamp coolers for my own use. If your referring to something else, do you have a diagram so I can see what what you mean and how it works?

Water temps of 45 to 30 C (113 to 86 F) is very high to me and will kill plants. With my swamp cooler and it’s water reservoir sitting in direct sunlight most of the day, and outside temperatures above 110 F (44 C), my swamp cooler water temps were between 60 and 65 F (15 and 18 C), using nothing but a fan and water pump. Both the swamp cooler and it’s water reservoir had no insulation either.


#18

Yes, the new FC includes a cooler system - I’ve seen it - it’s really cool but very sophisticated. I understood that it is an adaptation of an expensive cooler system, and I am not sure whether this element is going to be something that we can build easily. Let’s see the details when the OpenAG team releases the 2.0