Advice needed on DIY chiller

danno14

New member
Greetings- This may be thought of as a continuum of the (many) prior posts asking for advice on a DIY chiller.....with a twist :)

Specifically, I have a lake to use as my heat sink. I have a 300+g system heated by 3 400w MH HQI's, one 250w MH, 12' of VHO, a Sequence 5700, Iwaki 100rlt. At least those are the primary culprits.

Currently I am running a 1/2hp chiller (remote outside) set to keep the system at 76-77 degrees. It does run periodically in the winter due to the 70-72 degree house temp. In the summer it struggles, even with the house AC on. The issue is the eastern sunrise, which beams directly into the three 6'x9' windows. Also the open concept of the house itself.

My intent is to add a primary lake-cooled chiller and keep the 1/2hp as backup, set a few degrees higher, in case the lake doesn't do the trick (too much solar gain, lake too warm, etc.). We have few 100 deg days here but numerous 90 plus in the peak of summer. I have data from fisheries studies that show lake temp. to max in August at 65 degrees and min in January at or close to freezing. These were taken at 10’ depth. Today it was 38 deg.

What I am considering is a closed system with:
• a titanium tube or coil in the sump (don’t yet know which). Cost and efficiency are leading factors.
• a Medusa or Runco controller (I have both) running to a pressure pump (uncertain as to what size pump will be needed). Hoping to make the pump as electrically modest as possible.
• ¾” flex tubing running down to the lake and back (pex?) buried underground.
• either coiled tubing or a titanium tube/coil submerged 10-15’ in the lake. Again cost and efficiency reign.


Better to run a more powerful pump, less frequently? Example would be one of the large Iwakis, pressure rated, at 2.5-3.4 amps.

Efficiency of a coil of PEX or otherwise compared to a ¾” titanium tube 6-8’ long in the lake. I have lots of protected space under the dock for either. 8’ of straight tube would run me about $130, whereas 500’ of ¾” PEX is $200. I could do lots of coils for the money, but acknowledge the increased friction loss due to the longer length. Where is the breakeven? This will help to determine which pump to use as well. I have found a coil type heat exchanger here: Heat exchanger

And a Ti tube here:
Ti tubing

If I do end up using the Ti, the coil reads as 20" long.... arguably more space efficient. Would the 3/4" tube serve as well if at least that long? Is there an advantage to the "coil" versus a straight tube?

Is there a type of tubing which has reasonable cost similar to above and low friction inside, which would be reef appropriate? One of the varieties of PEX or otherwise?

The surface of the lake is roughly 25' lower than the sump room. As it would be a closed loop, with water seeking its own level, I am thinking that all the pump would have to overcome is the internal pipe friction....correct?

I have read a bunch of great input on earlier threads pertaining to Geothermal cooling..... hoping for some sharp folks to weigh in on my idea.
Thanks for your input! D
 

silverwolf72

New member
Copper tubing for the lake side should work good. To the lake maybe use PVC, the larger the less friction . Coiled just uses less room for the same surface area. In a closed loop the only thing the pump fights is friction. The main problem with these is getting enough heat transfered into the heat exchanger.
 

BeanAnimal

Premium Member
For the lake sade you can use aluminum...

http://www.aquaticeco.com/index.cfm/fuseaction/product.detail/iid/9248

They are cheap and you can put as many in series as you need. 1" PEX, polypipe or even hard PVC can be run to the house. It will be a closed loop so the only head pressure will be the result of friction. The larger the pipe diamter, the less friction.

However, consider this. The earth between the house and pond will work against you if the pond water is at a lower temperature than the earth. The faster the flow through the pipe, the less heat the water will absorb on its trip to the heat exchanger in your sump. The larger the pipe diameter, the lower the velocity! So you need to balance pipe diameter and friction with velocity through the pipe.

The larger the heat exchanger in the sump, the better off you will be. This SHOULD be Titanium.... You could likely use SS without problem also.

If freezing of the loop is going to be a problem, then you will need to burry the loop lines below frost depth. This will also have the effect of helping you in the summer by minimiziing heat gain from the earth. The transition area from the ditch to the pind will be critical and hard to keep from freezing. That will take some thought, but should be managable.

You COULD use RV anti-freeze in the system, but a leak into the sump would still be deadly for the livestock.

It should also be noted that Anti-Freeze does NOT carry as much eat as plain old water. It is less efficient!
 

danno14

New member
I concur completely on the earth vs. lake temp, and the potential heat gain as the water is sent uphill. My intent is to sleeve the tubing inside a larger pipe (3-4") in part for this reason.... less direct contact with the earth by the pipe carrying the water.

I was wondering about peoples success with with Stainless as an in sump exchanger.... but Ti would probably be better in the long run. I had seen the Aluminum heat exchanger from AquaticEco and have considered that for the lake side. Detail of how efficient it is so I can compare to the other materials is something I will have to phone them for.

Good feedback on the ground-lake transition (hadn't thought of that). I can insulate it once it comes through the bulkhead. Any more/anyone else with insight, feel free!
Thanks, D
 

AusWog

New member
why not just have it pumped outside and underground into a small pit.the earth is cool and prolly alot closer then remote lake which u would need so many pumps to pump it over atleast 15 meters. which means outside electrical outlets or really long weather proof ext. cables.just dig a couple meters down and the heat it looses from the piping and underground would be better.pretty bad if u have a leak some where tho aswell/some one play with it knowing the idiots we have these days.to bad aswell if anyof it leaks.i see a floor in the design.fixability,by the time u locate the problem,fix it/replace parts.its gonna outweigh the cost of a chiller in the first place,trade in your chiller and put money ontop for a bigger one.not to mention the electricity bill of a 3-4 amp pump!
 

BeanAnimal

Premium Member
The earth is a fairly good insulator. You need a very large surface area to absorb the heat. It would not take long for your "pit" to warm up.

The pump for both systems will be about the same size, as they will both have about the same amount of tubing attached to them.
 

matt_54351

New member
i know it's a crappy drawing, but it gets the job done.

I would just pump the lake water uphill, run it through coils in the sump and have it drain back in the lake. Once you get the water flowing it would only take a small pump to keep the water flowing as you are only overcoming the friction inside the pipe, a siphon that does not go anywhere. you are also ensuring that you always have cool lake water circulating in the coils, plus there is no risk of draining the tank if you have a seal/fitting/etc that leaks or goes bad.

<a href="http://s79.photobucket.com/albums/j141/matt_54351/?action=view&current=lakechiller.jpg" target="_blank"><img src="http://i79.photobucket.com/albums/j141/matt_54351/lakechiller.jpg" border="0" alt="Photobucket"></a>
 

danno14

New member
similar to my sketch...

similar to my sketch...

but different. There are issues with open loop from the lake that I would not have with a closed loop: preventing algae from clogging the inlet, head pressure presented to the pump, and potential contamination from a leak. I am hoping to acheive the same net results (or close) from a closed loop system, with less electrical cost (lower head pressure).

chiller.jpg
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At present, I am looking toward 1" rigid PVC as a first choice, with 3/4" PEX second. Titanium heat exchanger in the sump, with Aluminum in the lake. Propylene Glycol in a 30% mixture with RODI is a possibility, but I want to do an experiment first.

Keep the ideas flowing! Thanks, D
 

Saboral

New member
I don't really know how cost efficent this is going to be for you, I work in construction and have put in several closed loop trenched in geothermal HVAC systems. I don't swear to know the amount of surface area needed etc for appropriate heat transfer, but I do know that to be below the frost line you will need to be somewhere between 2-5 feet depending on your location. Your idea to use a larger PVC to "insulate" the inner cooling loop is flawed as well, because once the PVC becomes the same temperature as the surrounding soil there is no advantage in having it as you will not be pumping heat or cooling into the surrounding pipe.
As for the cost effectiveness the depth you are going to need to dig to install this line will either break your back or your wallet. I don't think you will have much efficency from it either considering the amount of coil you would need in your sump to transfer the heat at nearly the same efficency as a chiller.
So if you are still considering going for this here are my recommendations;
Use the open loop so that the water will drain out of the system when it is not operating, this will allow you to not be concerned about possible freezing in the lines.
Or
Consider digging a "radiator" into your yard about 4 feet underground, this will be nearly as efficent as the lake and will remain the same temperature constantly year round
 

BeanAnimal

Premium Member
The open loop will require a larger pump and much increased maintenance.

The lake is an infiniate heatsink. You will need a large earthed loop to get the same effect.

The loop does not need to be below the frost line if it is filled with the glycol solution.

I agree about the PVC outer pipe not acting as an insulator.

The distance to the lake is fairly short, I don't see the trench being a problem unless you have to dig through pine roots or something.
 

ihavtats29

New member
you dont have to run to your lake if you dont want to, you can use the earth to cool water by burring it in the yard 18 to 24 inchs deep making large s shaped turns spaced about 3 feet apart . this has been used in the hvac industry to cool the condencer water in a water cooled condencer coils.
 

matt_54351

New member
as long as you run the return all the way back to the lake you would have exactly zero head pressure, only loss of friction. Think of siphoning water out of your tank. no matter how high the tubing goes above the tank it will always drain if the bucket is lower than the tank. since the pump and return would be at the exact same water level you would have a neutral system.
 

BeanAnimal

Premium Member
Yes matt, but priming the system is a concern as is keeping it flowing freely. I would opt for the closed system. The lake is pretty much an endless heatsink. As long as the lake side heat exchanger is sized properly, both the closed system and open system will have the about same thermal properties.
 

danno14

New member
An addition to the equation - the trench needs to be dug regardless to run other stuff from the house to the dock. No roots or utilitilies, and an willing sprinkler crew with a ditch witch.
 

BeanAnimal

Premium Member
4" PVC Sewer pipe or even conduit is pretty cheap. I would go ahead and run it along side your loop. It will give you a way to pull anything else you need to the lake. If you are running power down there, then you will want to put it in a decent size conduit as well. You never know what the future will bring.
 
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