Thermal HVAC using a small lake?

[Cadillac Bill]

I am building a display building and a garage near our private lake on our land. It is about 2 acres and to a median depth of about 12-15 feet. A friend was using his lake in the same way as a heat sink for ac.

Instead of an outside condensing unit, he made a heat sink, sunk in his lake. He said it was very efficient. He was using this was for AC only. It would seem to be also efficient for heat along the idea as a heat pump, but underwater.

He passed on and the exact measurements have been lost. Does anybody know how this can be done?

One of my buildings is 100x80 and the other 60x30.

Here is my plat. I am near Atlanta Georgia

 

[bczygan]

Water source heat pump.

http://olympicinternational.com/wp-content/uploads/C_330-1-water-source-heat-pump-design-manual.pdf

Bill

 

[mrpizza]

Basically a pond loop geothermal. I would rather drill vertical wells. If that water ever goes away or gets low you are screwed.

 

[Northislander]

Here is a pic of a lake loop installed in an aluminum cage that can be bolted to the bottom of an existing wharf keeping it out of harms way where there is a lot of wave action etc. A pond loop is usually pretty safe laying on the bottom

 

[OzarkMan]

Learn something new everyday. That is awesome stuff. Whats the water temp at the bottom in the summer months?

 

[yeldogt]

Learn something new everyday. That is awesome stuff. Whats the water temp at the bottom in the summer months?

Water is the coldest at the bottom -- until 4 degrees. H2O is amazing stuff ...

Lakes can work as heats sinks -- especially those fed with cold spring water. The grouped coil bed is what I have seen used as it makes tracing any problem easy.

doing 2T -- is a lot easier vs 10T

 

[finn]

If the body of water has an inlet or outlet, it’s best to check with the DEQ before you begin construction of something that may alter it.

Man made farm pond is likely no problem.

 

[rlitman]

The closed loop idea works with propylene glycol solution, or clean water (which you might have to blow out in the winter to protect from freezing), but has no corrosion issues.
Open loop systems use monel heat exchangers to prevent corrosion, and pump lake water directly through them.

 

[PoorOwner]

It would seem like you need alot of power to pump water through that much distance.

open loop system? if there is a leak, would that mean the whole lake gets pumped into your building.

 

[TangoFoxTrot]

What sort of cost savings are you looking at with a system like this? Have you done any sort of analysis of extra costs vs a more conventional unit?

Just wondering if it may be a lot simpler to just get a higher SEER unit than have to work with a system like this.

I just know I would need to see some major cost savings to justify. But it is a cool way to use your surroundings.

 

[rlitman]

The efficiency of heat exchange on liquid-to-liquid vs liquid-to-air is quite different.
Here at work, we have 20 ton DX cooling systems with glycol recirculating in loops (that is cooled in dry coolers on the roof, so we don't get the benefit of a cool lake), and the 20 ton refrigerant-liquid heat exchanger is about the size of my leg. The equivalent refrigerant-air condenser would be about the size of my car. So there may be a space savings. For cooling a data-center, we also get "free" cooling in the winter by circulating the glycol through a separate coil. But "ice in the wintertime" isn't a selling point for most.

In the past, geo-thermal ground-source heat pumps had significantly better efficiency than air source versions. Especially at the extremes of temperature. Geo-thermal is stupid expensive to install though, and a lake gets you the equivalent to geo-thermal, without the awful installation cost. However, current inverter driven air-source systems are damn near the efficiently of geo-thermal, so I'm not sure if there is much benefit for home heating/cooling, as the ROI on the installation cost is going to be very long.

 

[TangoFoxTrot]

However, current inverter driven air-source systems are damn near the efficiently of geo-thermal, so I'm not sure if there is much benefit for home heating/cooling, as the ROI on the installation cost is going to be very long.

Not an engineer on this, but at least some of the real world examples I've seen, geothermal seemed to make a lot more sense in like the 1970s when heat pumps were 6 SEER.

Today, geothermal seem crazy expensive and elaborate, even if I do think it's a really interesting technology.

I would think something like a 20+ Seer heat pump or mini splits, modern insulation and solar panels would be a much easier way to go extreme green. Easier to service and easier installation.

 

[Radix2]

Looking at that lake loop system above, I'd be skeptical of high efficiency considering that the loops are tightly packed which will greatly lower the transfer efficiency. Sitting in a pond you only have the water convection to circulate the water past the coils, so I'd agree that the pumping cost might get high compared to something with a better design.

OP - it can certainly be done, the problem is that it is hard to compete with a engineered turn key solution with a home brew. All things considered , there is no real magic to dumping the heat to water vs. to air.

 

[theoldwizard1]

I am building a display building and a garage near our private lake on our land. It is about 2 acres and to a median depth of about 12-15 feet. A friend was using his lake in the same way as a heat sink for ac.

Instead of an outside condensing unit, he made a heat (s̵i̵n̵k̵ ) exchanger, sunk in his lake. He said it was very efficient. He was using this was for AC only. It would seem to be also efficient for heat along the idea as a heat pump, but underwater.

This works very well IF THE HEAT EXCHANGER CAN TRANSFER SUFFICIENT HEAT to the water ! It might be easier to have the heat exchanger near/in the home and pump the water back and forth.

 

[Northislander]

Looking at that lake loop system above, I'd be skeptical of high efficiency considering that the loops are tightly packed which will greatly lower the transfer efficiency. Sitting in a pond you only have the water convection to circulate the water past the coils, so I'd agree that the pumping cost might get high compared to something with a better design.

OP - it can certainly be done, the problem is that it is hard to compete with a engineered turn key solution with a home brew. All things considered , there is no real magic to dumping the heat to water vs. to air.

Radix
Hard to see in the pic but those coils have pieces of 1" pvc horizontal and vertical in the coils separating the individual pieces so the water can flow around each individual piece.

 

[ripperd]

This works very well IF THE HEAT EXCHANGER CAN TRANSFER SUFFICIENT HEAT to the water ! It might be easier to have the heat exchanger near/in the home and pump the water back and forth.

Only problem with that is you would have to keep the fresh water lines below the frost line. If you don't, and your power goes out for too long, busted pipes!

 

[arrowhead]

Cornell uses lake water for cooling, the water is so cold down deep they don't need chillers or heat pumps.

https://medium.com/cornell-university/lake-source-cooling-d307913dfc47

 

[Jackfre]

I did a lot of this back in the late 70's, using ponds or swimming pools to run a geo heat pump. You can end up with issues running the open loop water to equipment. It can become a service nightmare. The "lake loop" in the bottom of the pond works, but someone, somehow will find a way to put a fish hook or anchor through it. Swimming pools worked well. We put a glazed solar system heating the pool to maintain the winter water temp at 55+, which is all we needed for the HP. We rejected heat to the pool in the summer and didn't cover the pool so it would give up the heat at night. Possible to need a small cooling tower if the numbers don't work. Geo can be great but it is generally big dough for the install and you have to have an "A" guy not only for the design & install, but also for the service. I, too, would suggest that you look at some of the new inverter HP's out there before going geo.