Radiant cooling using deep lake for summer

[AngelLestat]

TL;DR Summary

Radiant cooling loop between 15 c water lake and radiant floor installation.
Estimative calculation of the Copper or plastic heat exchange loop in length and flow speed.

This is a project that I wanted to do in the past 3 years, but I never was sure enough because I don't know how to calculate thermal transfer in a submerged coil to at least have an approximation of what to expect.
I want a cheap solution to pass the summer days without cook myself or wasting a lot of energy in the process.

I have the fortune to have a lake at the end of my yard, I measure the water temperature at its deepest point, which was 15 c at 10 meters deep, but a place of 8 meters deep is much closer and according to my measures is also between 15 c and 16 c (these measures were taken passing mid summer last year).
Is not a surprise, because cold temperatures of the winter reach the bottom of the lake, which by stratification stay there until the next winter because sunlight does not reach that depth.
I want to exploit those cold temperatures to cool my house in summer, my house already has a radiant floor in all the rooms which is used with a boiler to heat the house in winter.
I want to add the cool loop to the collector with an extra pump, I will hire a professional for the connection, but I want to make and install the Polypropylene pipe and a cooper loop myself (or PVC if there is no other choice).
Some diagrams:

I want to use 1´ 1/4 of polypropylene black hose (the one that it is used for automated irrigation) to connect the collector to the loop in the lake (to avoid energy lost by friction), it would be thermal insulated with an extra layer and 20 cm buried until it reach the lake.

I have doubts about the material of choice for the loop, I know cooper is the best thermal conductor, but not sure about its corrosion, because water samples that I took from the lake bottom has a bit of rotten egg smell, which could mean hydrogen sulfide which in fact can corrode cooper (I guess). Another issue with cooper is that (if corrodes), high levels of copper sulfate could be bad for aquatic life, but some levels of copper sulfate are used for algae control, I made some math, and even if all my loop stays trap down there and dissolves (not my intention), it would be still 2 order of magnitude lower than the recommended level (I can add those calculations if you want).

The problem with polypropylene loop, is that it looks ugly due how massive it is, which can be seen in this picture https://plasticpipe.org/building-construction/12-geo_files/csss_images12/12geo.jpg
Then we have the fact that plastic is also polluting.
But those polypropylene loops are used to extract heat from ponds that are not deep with the help of a heat pump, so I am not sure how long they would need to be for my special case.

I can't do the math, but my common sense tells me that 2 copper loops in parallel of 3/4 by 10 meters each, could be enough for what I want, of course that is a total blind guest, because I am not sure how fast would be the cold water natural convection from the lake touching the copper pipes in order to cool them.
I will enclose the cooper loop in a cylinder tank with holes to avoid any fishing line stuck, but nobody fish there anyways.

So.. the question is.. Somebody knows how to approximate the length needed to accomplish at least 29 c inside the house on days of 40 c?
I was searching for some tables on heat transmission for submerged cooper or plastic loops, but I did not find nothing.
I understand that if I achieve 29 c inside my house, I will still have all the latent heat from moisture, and I also know that if the moisture is high the dew point could be reached which the floor would start to condense water.
But those problem seem easier to manage, because I can control the pump speed and I also have a medium AC unit for the living room of my house to help to reduce air moisture. I also have ceiling fans in many parts of my house which can help to vent hot air over the floor to maximize efficiency.

Something that I know for sure, that all that thermal mass at such cold temperatures just outside my house, looks like a waste opportunity when I am being cooked by floors, furnitures and walls at 40c, with no object to absorb that heat.

 

[berkeman]

Fun project.

Others will be able to help you more with your questions, but one thought comes to my mind initially. The reason that a "radiant" floor heating system works is that heated air rises and warms the rooms by convection. If you cool the floor in the summer, I'm guessing it will keep your bare feet comfortable, but do little to cool the air in the rooms.

Instead, it seems like distributing cool air to the rooms via ceiling ducts would work better. Do you have a central air conditioning system installed already? Or any kind of central air distribution system?

 

[AngelLestat]

Fun project.

Others will be able to help you more with your questions, but one thought comes to my mind initially. The reason that a "radiant" floor heating system works is that heated air rises and warms the rooms by convection. If you cool the floor in the summer, I'm guessing it will keep your bare feet comfortable, but do little to cool the air in the rooms.

Instead, it seems like distributing cool air to the rooms via ceiling ducts would work better. Do you have a central air conditioning system installed already? Or any kind of central air distribution system?

Hi, thanks for answer.
I was researching this method over long time now, I can't do the math because is quite complicated, it deals with conduction and convection at the same time, then you also need to add the flow speed and thermal mass, but I know the overall mechanic well enough to be sure that this could work.

This method works by using a large surface to absorb the heat radiated by other objects (in this case the floor), you also have some heat conduction by convection between the air and the floor which reduce the efficiency vs "roof radiative cooling", but not by so much, in fact floor + ceiling fan would improve the efficiency vs roof alone.
This method of radioactive floor cooling is even used in some public infrastructure.

The average temperature of a room depends on the thermal mass of all objects in the room + the air temperature with its latent heat.
The thermal mass in furnitude, walls, roof and floor is much higher than the thermal mass in the air.
All objects had similar temperature because all objects radiate and absorb heat from other objects.
If one is at lower temperature, it would absorb more than the heat it would radiate, reducing the temperature of all other objects.
The air can also radiate and absorb heat, but mostly interact by convection.
Even if the air would stratify in a room reducing the interaction between the floor and the air.
You would still feel a cool sensation even if the air stays hot, because your body is radiating more heat than the one it absorb.

The advantage of radiating heating or cooling, is that you need lower temperature difference because your radiator/absorber area is larger, this also improves your efficiency. If I use splits to distributing cool air cooled by cool water, first I need lower temperatures than 16 degree to make those work and they are more expensive than normal AC units working by compressor.
In my case, I already have the radiating floor for heating, I also have the lake, so I want to merge those two, I am not expecting huge results either, just keeping the temperature below 30 c is way better than dealing with 40 c.
For example today in buenos aires we have 37c, tomorrow would be 39 c.
The AC split that I have is not enough to cool my house, and the amount of energy required to keep it cool all day would be huge.
Moving thermal mass (water in this case) requires way less energy (1/5 maybe) than reducing the temperature in a conventional way.

 

[berkeman]

Thanks for the reply. It does sound like you've done your homework.

And I like your ceiling fan idea to help circulate the cooler air from the floor area up and around the room. It would be interesting to experiment to see which direction of ceiling fan rotation works best for that. Also, you can add small portable fans at floor level to help get the cooler air to mix more in the room.

That's awesome that you have the resource of that lake right there.

Paging @russ_watters @Chestermiller @OmCheeto

 

[OmCheeto]

...
That's awesome that you have the resource of that lake right there.
...

A lake like that in everyone's back yard would solve a lot of the world's problems, IMHO.

The first thing I would do to solve this, would be to figure out what the aggregate effective insulation value is.
No sense in spending a week solving a bunch of calculations, only to find out that the kids leave the doors open all day.

 

[AngelLestat]

And I like your ceiling fan idea to help circulate the cooler air from the floor area up and around the room. It would be interesting to experiment to see which direction of ceiling fan rotation works best for that. Also, you can add small portable fans at floor level to help get the cooler air to mix more in the room.

Thanks for invite your friends to take a look to my question Berkemann! That was really kind.
Yes, a portable fan can work very well, I have 2 of those, about ceiling fans, I guess just moving a bit the air could be enough, air is quite chaotic, it mix easily and fans produce a lot of turbulence.

I am not sure how much efficiency in heat transmission could be lost if I don't use the fans.
It would depend on the lake loop, because if that loop can not transfer enough heat, then I will have a bottleneck and it would not matter if the fans are activate or not.
In case I don't have a bottleneck, we have to compare between radiation roof vs floor, for both the radiation heat transfer is almost the same (the floor case could gain a bit of efficiency depending if there is a part of the house which receive direct sunlight radiation over the floor).
Now adding the convection factor, in the case of the roof it would have natural convection, when the air touch the roof it would go down cooling other objects.
But in the reverse case, we have that radiating floor heats a 75% by radiation and a 25% by convection.
https://www.sciencedirect.com/science/article/pii/S0196890411001014

In this example 7 degrees of difference are calculated by the heating case and 5 degree of difference for the cooling case: (it is in spanish, sorry, I could not find an english version).

Source: http://vgatec.blogspot.com/2011/11/

Heating case: deltaT= 7 degree = 75W/m2
Cooling case: deltaT= 5 degree = 35W/m2
So if we count those 2 degree of difference, it looks like it would reach 55W/m2 which it would match with the 25% of natural convection which is lost in the cooling floor case.

I think that using fans those 55W/m2 could be double, which can help to accelerate the cooling until the house reach comfort temperatures.
Here it said that decreasing the temperature under the dew point for short periods of time does not produce condensation.
https://en.wikipedia.org/wiki/Radiant_heating_and_cooling#Advantages

A lake like that in everyone's back yard would solve a lot of the world's problems, IMHO.
The first thing I would do to solve this, would be to figure out what the aggregate effective insulation value is.
No sense in spending a week solving a bunch of calculations, only to find out that the kids leave the doors open all day.

Yeah, there are many houses around these artificial lakes and I quite sure nobody tried something like this, so I hope to be the first one that would not waste this resource.
(These lakes are created because these original terrain were low and flooded, they bought them cheap and then they dig the center creating a lake and raising the perimeters with that digged soil, which can be sell for residential)

About the house insulation, it has a cover area of are 170m2, all windows are double glass with 35m2 of total area, the roof has 1 layer of 50mm of glass wool followed of 15 mm polyethylene foam with reflecting face.
The bricks are Retak, which had 15 cm of thickness with tons of tiny air pockets.
No air currents worth to mention based on sealing failures.
So the house has an average good insulation, although it could have been better with less windows.

I know that these type of calculation are hard to do, even as a rough approximation.
I just need to have an idea base on some numbers or experience in order to not fail big.
What should be the deltaT between the wished temperature (around 28 c) and the floor water temperature?
20c could be fine? The return then could be 24 c? to exchange heat with 16 c from the lake?

Of course, I am not helping because I don't know :)
Thanks for your interest.

 

[256bits]

Summary:: Radiant cooling loop between 15 c water lake and radiant floor installation.
Estimative calculation of the Copper or plastic heat exchange loop in length and flow speed.

I have doubts about the material of choice for the loop, I know cooper is the best thermal conductor, but not sure about its corrosion, because water samples that I took from the lake bottom has a bit of rotten egg smell, which could mean hydrogen sulfide which in fact can corrode cooper (I guess). Another issue with cooper is that (if corrodes), high levels of copper sulfate could be bad for aquatic life, but some levels of copper sulfate are used for algae control, I made some math, and even if all my loop stays trap down there and dissolves (not my intention), it would be still 2 order of magnitude lower than the recommended level (I can add those calculations if you want).

The problem with polypropylene loop, is that it looks ugly due how massive it is, which can be seen in this picture https://plasticpipe.org/building-construction/12-geo_files/csss_images12/12geo.jpg
Then we have the fact that plastic is also polluting.
But those polypropylene loops are used to extract heat from ponds that are not deep with the help of a heat pump, so I am not sure how long they would need to be for my special case.

If the amount of pipe submerged in the water is adequate enough, then you don't have to worry about its type. The amount of surface area exposed to the temperature can compensate for difference in thermal conductivity.
Copper would be more expensive, and as you say, possibility problematic with corrosion - do you want to bring the thing up every so many years to replace if it does corrode - and if it does your system under the floor will become contaminated with lake water, further complicating your problems. Ugliness is hidden under the water.

Would the possibility of a leak in the river water system necessitate a heat exchanger as a barrier between floor system and river water system - so that you then have two loops -river water system and floor system. There might be something in the code for housing to follow. See geothermal.

What is your cooling load for the residence - you will have to know that figure to size your river system.
At least we know what you have already is inadequate as you say, but it is dealing with sensible and latent heat.
The river system deals only with sensible, and you will have to make up for latent, or as you have mentioned condensation on the cooler surfaces can occur.

So while the 1/5 the energy use for liquid pumping vs air pumping is general in scope, the latent heat extraction will up the energy use, and that could be substantial, depending upon whether you are in a dry area or humid.

 

[256bits]

About the house insulation, it has a cover area of are 170m2, all windows are double glass with 35m2 of total area

The large window area might be a plus for radiant cooling - the cooler floor will directly remove the solar irradiation falling upon it.

 

[Rive]

Cooling case: deltaT= 5 degree = 35W/m2

I think this part will be the key. It goes a bit sideways, but you should be able to find some details about ground heat exchanger size requirements for heat pump systems: in your case it's water instead, but still, it should work as a guide anyway.
WIth some digging you should be able to find the calculating method too.

I want to use 1´ 1/4 of polypropylene black hose (the one that it is used for automated irrigation) to connect the collector to the loop in the lake (to avoid energy lost by friction), it would be thermal insulated with an extra layer and 20 cm buried until it reach the lake.

Such pipes should go below the local frost line. Are you sure 20cm will be adequate?

The problem with polypropylene loop, is that it looks ugly due how massive it is, which can be seen in this picture https://plasticpipe.org/building-construction/12-geo_files/csss_images12/12geo.jpg
Then we have the fact that plastic is also polluting.

Not really: less polluting than copper. And you actually not expected to see it since it will be submerged, no?
Also, that system on the picture is not for a small household sized one, I guess?

One more thing to consider: in heating mode the floor heating system temp. valves keeps the water in the pipes below a given temperature: in cooling mode it should be above instead - unless you takes the risk going below the dew point.

A carefully planned, steadily advancing project, BTW

 

[OmCheeto]

I understand that if I achieve 29 c inside my house, I will still have all the latent heat from moisture, and I also know that if the moisture is high the dew point could be reached which the floor would start to condense water.
But those problem seem easier to manage, because I can control the pump speed and I also have a medium AC unit for the living room of my house to help to reduce air moisture

Good! You've noted the problem with condensation.
I nabbed todays forecast temps and humidities from weather.com and discovered that without a fancy controller, you're going to have an indoor swimming pool!

 

[anorlunda]

In my case, I already have the radiating floor for heating,

You are well positioned, with the lake and the sub-floor pipes already in place. I think I would proceed by experiment rather than calculation. There are so many unknown parameters in the calculation that confidence in any answer would be low.

You mention existing AC. If you have a heat pump, then lake water could be used to pre-cool external air coming into the heat pump. It could also pre-heat incoming air to the heat pump in winter when you are using heat. In both cases, it would improve efficiency (COP) of the heat pump. That is not exclusive of the sub-floor idea. The water could be circulated to both the heat pump and under the floor. Those two uses could be connected in serial or in parallel. I'm not sure which would be best, but it would be easy to include some valves to choose serial or parallel pipe connections.

I would worry about condensation on the floors if they are cooler than the room. The dew point of the air in your house is an important parameter. Also beware the risk of freezing pipes in winter.

By the way, your proposal is a form of geothermal heating/cooling. As you do research, use geothermal as a search keyword.

Geothermal home heating/cooling is not widespread, but there are precedents. Sometimes, they put the pipes deep underground to tap the heat capacity of below ground soil/rock/aquifers. A lake is easier. I read about one man who did cooling by burying pipes less than 2 meters underground. You may be able to find other homeowners who have done it who are willing to share their experiences and calculations.

 

[DEvens]

Before you start this project, it would be a good idea to do a little discreet investigation of the relevant laws and regulations, particularly the environmental regulations. In many places, warming the bottom of a lake may have very strict limits. Possibly your application is small enough that you won't get noticed, and may not come close to violating the limits.

But it's probably a bad thing to get noticed doing something you should have gotten permission for. The Powers That Be are usually not prone to forgiving such things. They are quite capable of ordering you to return things to the condition you had before you started, and refusing to even look at your plans until that is done. And maybe making you pay a big fine as well.

Maybe I'm worried about nothing. But I know that thermal power plants (nukes, gas fired, and coal fired, probably wood-burning as well) have to meet very strict limits on how much they can warm up the lake.

Maybe in your neighborhood it is not so crucial. Maybe this lake is not particularly sensitive. Or maybe the heat from your building's cooling won't make any significant difference to the lake. Or maybe, once you look at the relevant regulations, you will just go ahead anyway.

But better not to blindly walk into the government regulatory process.

 

[AngelLestat]

If the amount of pipe submerged in the water is adequate enough, then you don't have to worry about its type. The amount of surface area exposed to the temperature can compensate for difference in thermal conductivity.

The difference in thermal conductivity may help to the flow convection from the lake water over the loop, plus the length and proximity between the hoses (if I want to keep the heat exchanger small enough) would block part of that natural flow.
I don't think my neighbors see me with good eyes if I want to put so many rolls down there.
I would like to have a better idea of how many meters of polypropylene are required over each meter of copper.

Copper would be more expensive, and possibility problematic with corrosion - do you want to bring the thing up every so many years to replace if it does corrode - and if it does your system under the floor will become contaminated with lake water

It depends how long would need to be each one, if I need just 20 meters of 3/4 copper, then we are talking about 120 usd, if that last 6 or 7 years, I guess I could live with that in base that I can also do inspections once a while.
If it corrodes enough to make a hole, yeah it could allow some dirt or particles to enter in the loop, if that happen it may also lost pressure in the system which it would help me to advert the issue, but still, even in that case it does not mean I will lose the radiant floor, but yeah, if I can avoid that with a normal plastic loop who does not take 4 times the length, I would use it.

Would the possibility of a leak in the river water system necessitate a heat exchanger as a barrier between floor system and river water system - so that you then have two loops -river water system and floor system. There might be something in the code for housing to follow. See geothermal.

Those code are used by companies to avoid any weird case in order to provide a guarantee, but an extra heat exchanger would increase the cost and reduce the efficiency (which is what I most hate).
I can place two valves to completely close that loop in case something happen.

What is your cooling load for the residence - you will have to know that figure to size your river system. At least we know what you have already is inadequate as you say, but it is dealing with sensible and latent heat. The river system deals only with sensible, and you will have to make up for latent, or as you have mentioned condensation on the cooler surfaces can occur.

I have a chinese AC unit which not sure if I can trust in the values: But it said:
AC for Cold: Capacity: 5100W / Nominal power: 1680W / Nominal current: 7.6A / Air flow: 750 m3/h / I think it is equivalent to 18000 BTU (we use different units).
It is located in the biggest volume of the house (60% of the house volume), in days of 38 degree, it just help to reduce the temperature to 29 c with some luck.

So while the 1/5 the energy use for liquid pumping vs air pumping is general in scope, the latent heat extraction will up the energy use, and that could be substantial, depending upon whether you are in a dry area or humid.

Yes, but what happen if I don't really care about the latent heat? I guess I would still have some cool feeling if my body radiates more heat than the one it receives, I am not expecting a climate system that force 24 c and dry air when outside you have 40 c, that is what all Hvac companies sell, which is ok, but I just want to have something that helps me to do my stuff of the day without dying on, without being scared of the future electricity bill or with guilt of my carbon footprint.

The large window area might be a plus for radiant cooling - the cooler floor will directly remove the solar irradiation falling upon it.

Yeah, but in summer, only few hours by day on few windows the sun enters directly, but in those places I don't have ceiling fan so is a good news.

I think this part will be the key. It goes a bit sideways, but you should be able to find some details about ground heat exchanger size requirements for heat pump systems: in your case it's water instead, but still, it should work as a guide anyway.
WIth some digging you should be able to find the calculating method too.

I try that before, but those systems are very different from what I am looking for, they work with different delta T, with very different expectations, they used that mostly for heating, the ponds are low and they have a heat pump, I would not be sure from where to start in order to have some values that can work for my case.

Such pipes should go below the local frost line. Are you sure 20cm will be adequate?

I am not 100% sure, but with insulation for the hose and then 20 cm of ground above, I think it is enough.
In the graphic that was posted here about buenos aires climate, it said that you can find some days with -5c, but in my experience are very rare the days with less than 0c, and if that happen (-5c) it would be over few hours on the night.
Still it is a concern as you said, not sure what would be cheaper, to add more insulation, to pay for a deeper ditch, or to circulate just that loop if the temperature goes very low.

Not really: less polluting than copper. And you actually not expected to see it since it will be submerged, no?
Also, that system on the picture is not for a small household sized one, I guess?

It's not because of me, it's because of how my neighbors may see it when I'm installing it, and the extra work that might take me if the loop is really big.

One more thing to consider: in heating mode the floor heating system temp. valves keeps the water in the pipes below a given temperature: in cooling mode it should be above instead - unless you takes the risk going below the dew point.

Yeah, I would see if I can figure out myself buying sensors and commanding the pump, or if I would ask to the professional that I will hire for the cool loop connection and pressure tied test to do it for me.
Thanks for the insights.

Good! You've noted the problem with condensation.
I nabbed todays forecast temps and humidities from weather.com and discovered that without a fancy controller, you're going to have an indoor swimming pool!

View attachment 253963

What site is that? I like the dew point data.
It is a special software?
Even in this case, the dew point would be 17c, why the floor is at 16c if the lake is at 15c-16c, that would not require a huge large loop for such small detalT?
Now the temperature in (Buenos Aires, Benavides) is 37c :(
But yeah, I will see what controller I can buy, I defend myself with electrical commands and installations.

You are well positioned, with the lake and the sub-floor pipes already in place. I think I would proceed by experiment rather than calculation. There are so many unknown parameters in the calculation that confidence in any answer would be low.

This is true, but not sure if I want to be extracting and adding loops at the sight of others.
I can ask permission to the neighborhood administration, but this is something that is not regulated, there are not norms about this type of installations here in Argentina.
So I am not sure if someone could complaint or not if he/she see me experimenting much on the lake.

You mention existing AC. If you have a heat pump, then lake water could be used to pre-cool external air coming into the heat pump. It could also pre-heat incoming air to the heat pump in winter when you are using heat. In both cases, it would improve efficiency (COP) of the heat pump. That is not exclusive of the sub-floor idea. The water could be circulated to both the heat pump and under the floor. Those two uses could be connected in serial or in parallel. I'm not sure which would be best, but it would be easy to include some valves to choose serial or parallel pipe connections.

I have an AC air unit that works with a compressor, but is not the type of heat pumps that are being used for geothermal climate systems that are being sold in europe or USA.
In fact, those are incredible expensive here because nobody used them, they are also reversible.
But even if I would have one, I guess it would not help me much. Because for cooling I don't need lower temperature than 20c, so the lake temperature is enough for that, and for heating I have a boiler that heats the radiating floor water that may be at 20c when it starts.

By the way, your proposal is a form of geothermal heating/cooling. As you do research, use geothermal as a search keyword.
A lake is easier. I read about one man who did cooling by burying pipes less than 2 meters underground. You may be able to find other homeowners who have done it who are willing to share their experiences and calculations.

Yeah I know, in fact the first time I thought about this was when we were building the house, I wanted to make a hole and install a vertical loop, but no perforations were allowed in that time because they could pollute lower aquifers. Lucky that I did not try that, because at that time I could not imagine that the lake had those temperatures all year in the depth.
But the problem to get information from those systems remains.
That is why after 3 years of personal research, I give up and here I am asking if someone can give me a bit more of clue of what to expect.

I will see if I found extra data to share, but something that I want to know, is the difference in performance between a submerged copper loop vs polypropylene, copper is not used in geothermal on lakes, so there is no way on how to ask.

 

[AngelLestat]

Before you start this project, it would be a good idea to do a little discreet investigation of the relevant laws and regulations, particularly the environmental regulations. In many places, warming the bottom of a lake may have very strict limits. Possibly your application is small enough that you won't get noticed, and may not come close to violating the limits.

But it's probably a bad thing to get noticed doing something you should have gotten permission for. The Powers That Be are usually not prone to forgiving such things. They are quite capable of ordering you to return things to the condition you had before you started, and refusing to even look at your plans until that is done. And maybe making you pay a big fine as well.

Maybe I'm worried about nothing. But I know that thermal power plants (nukes, gas fired, and coal fired, probably wood-burning as well) have to meet very strict limits on how much they can warm up the lake.

Maybe in your neighborhood it is not so crucial. Maybe this lake is not particularly sensitive. Or maybe the heat from your building's cooling won't make any significant difference to the lake. Or maybe, once you look at the relevant regulations, you will just go ahead anyway.

But better not to blindly walk into the government regulatory process.

Yeah, I explain I bit of this in my previous answer
That is why I want to just ask permission to the administration, and then make the installation without call too much attention.
In Argentina if you want to go by the Legal path, you would not do nothing in your life, it is a bureaucratic nightmare. The laws only bother to the "good guys".
About the heat it would be something good for the lake, because that cold water with low oxygen that stays down there for most of the year, it makes an inversion when the first cold days of the year arrive, and the low oxygen water goes up, sometimes this generate a bloom in algaes that kills many fishes. In fact, we (the neighborhood) are planning to place PV solar pumps to reduce that problem.

 

[berkeman]

That is why I want to just ask permission to the administration, and then make the installation without call too much attention.

Sorry, I missed if you mentioned that before. Who is the administration?

About the heat it would be something good for the lake, because that cold water with low oxygen that stays down there for most of the year, it makes an inversion when the first cold days of the year arrive, and the low oxygen water goes up, sometimes this generate a bloom in algaes that kills many fishes. In fact, we (the neighborhood) are planning to place PV solar pumps to reduce that problem.

That's encouraging. Here in the US, that takes an Environmental Impact Report. Is there a similar procedure that your neighborhood will pursue to get this approved?

 

[AngelLestat]

I found out some numbers and equations for submerged copper coils, it seem that the heat transfer lost by conductivity is so negligible that it is possible to reach an approximation just focusing in the water convection outside the pipe.
But even that step is not easier.
Here is the paper:
https://www.mdpi.com/2227-9717/7/9/553/htm

Then we have this small experiment, which lack of any type of number or evidence, but it could give us a bit of idea on how good could be copper


Then we have this professional geothermal loop lake installer, that talks a lot about different ways to set polypropylene loops, with some values that sadly lack of context in order to be useful.

All loops looks really large. The application and environment for those loops is really different from mines, so is hard to pick useful data from all that.

Sorry, I missed if you mentioned that before. Who is the administration?
That's encouraging. Here in the US, that takes an Environmental Impact Report. Is there a similar procedure that your neighborhood will pursue to get this approved?

The administration It is made by 5 people who also lives in the neighborhood plus 1 employee.
Then you have commissions which also are integrated by neighbors who manage different aspects of the neighborhood, one of those aspects is the lagoon care which I am part of that.
In my case, I would go to the administration to tell them that I want to install a small heat exchanger in the lagoon, I don't think they would made many objections as long as I keep a low profile, because if I do not do that, then others can call the administration and pressure them to see if they really can allow me or not.
Even proving that my installation does not do any harm, someone could said that he does not want that in the lagoon and I would not be able to said much, because the lagoon is not just mine.

About an environmental impact report, there is a said here in Argentina, that if you ask permission to plant a tree, you would have to visit office after office, signing papers over years until you die of old and you still did not plant the tree. Meanwhile you can find factories verting poison to rivers in ways that are not hard to proof and those people continue doing that over decades without any justice being applied.

 

[gmax137]

As to the difference between the performance of the submerged copper tube and the poly pipe, can you identify the pipe outer diameter and wall thickness for each option? We can use those to estimate the difference in heat transfer. If you also have an idea of the cooling loop flow rate, that would also help.

A quick search shows that the thermal conductivity of the polypropylene is roughly 2300 times lower than for copper. This doesn't mean you need 2000 times more poly pipe; because the natural convection coefficient at the outer surface of the pipe is low, it is kind of a bottleneck to the heat transfer. As you mentioned above for the copper option the thermal resistance of the pipe wall is entirely negligible. For the poly option this is not true, the wall resistance is the same order of magnitude as the convection resistance (depending on the wall thickness). So you might need two or three or four times as much poly pipe as copper. If you can find the wall thickness dimension a better estimate can be made. If you know the flow rate through the cooling coil we can also confirm that the inside convection is not limiting.

 

[AngelLestat]

As to the difference between the performance of the submerged copper tube and the poly pipe, can you identify the pipe outer diameter and wall thickness for each option? We can use those to estimate the difference in heat transfer. If you also have an idea of the cooling loop flow rate, that would also help.

A quick search shows that the thermal conductivity of the polypropylene is roughly 2300 times lower than for copper. This doesn't mean you need 2000 times more poly pipe; because the natural convection coefficient at the outer surface of the pipe is low, it is kind of a bottleneck to the heat transfer. As you mentioned above for the copper option the thermal resistance of the pipe wall is entirely negligible. For the poly option this is not true, the wall resistance is the same order of magnitude as the convection resistance (depending on the wall thickness). So you might need two or three or four times as much poly pipe as copper. If you can find the wall thickness dimension a better estimate can be made. If you know the flow rate through the cooling coil we can also confirm that the inside convection is not limiting.

Hi, thanks for the reply.
I tried following the math from the last paper I quote, but there are some parameters which are hard to get, and the ones I get I am not sure if they can be used for my case either.
The flow rate would be determined by the circulating pumps that I can get in my local market, usually they are around 30 or 50 liter/ min. I guess to that I need to subtract the pressure drop by friction for the whole system.
For radiant floor some sources said that 1 meter by second is fine, not sure if that is for the main pipe or for each loop.

How I fail in calculation, I did a deeper research trying to find differences between copper and polypropylene loops, which I found this:

https://books.google.com.ar/books?id=351iDwAAQBAJ&pg=SA34-PA40&lpg=SA34-PA40&dq=thermal+conductivity+copper+loop+vs+hdpe+submerged&source=bl&ots=nyMsjs9WiU&sig=ACfU3U1ACUAz6Ed7FssLSPjw3G_eYUhGEQ&hl=es-419&sa=X&ved=2ahUKEwigiqSQzbDmAhUwIbkGHTM9CeEQ6AEwAHoECA4QAQ#v=onepage&q=thermal%20conductivity%20copper%20loop%20vs%20hdpe%20submerged&f=false
For submerge in lake environment it said: "Copper coils have also been used successfully. Copper tubes have a very high thermal conductivity, so coils only one-fourth to one-third the length of plastic coils are required. However, copper pipe does not have the durability of HDPE and if fouling is possible, coils must be significantly longer."

This is another source that can give us a difference between metal and plastic:
https://www.awebgeo.com/coiled-hdpe-piping-loop-systems/

So it was exactly as I imagine. I need around 4 times the length with HDPE.
This give me more confidence in my intuition, because in my early comments I imagine that 20 mts of 3/4 copper coil might be more than fine for my case , which seem to correlate with the 120 mts long loops we see in similar pond examples, taking into account they usually have less thermal difference to work.

I did not discard HDPE yet but I am trying to see the pros and cons for each one before I make my choice.
I am also trying to improve my heat exchanger design:

The benefit of this approach is that I enclose all copper (or hdpe loop) inside an open PVC tube to exploit a kind of chimney effect which I guess it can improve the heat transfer.
This also reduce the dirt that can accumulate over the copper, because the cooper coil horizontal section is almost non existent. It seem also easy to deploy in case the lake floor is not flat.
It is also easier to raise lifting from another rope attached to the buoy vs my previous version, this could be also used to shake the whole exchanger to remove any dust sticked.
The PVC tube also provides structure and protection vs fishing lines.
Joints or "U" turns were not drawn to simplify the sketch.
The U turns could be in the outside of the tube in order to not block the natural convection.
It does not matter how long is the PVC tube because it extract always cold water from the bottom.

In case I use HDPE, I would have to make 4 of those or increase the diameter.

About pros and cons about HDPE vs Copper:

1-Copper cost around 10 times more than HDPE by meter, but you require 4 times less, this also reduce the cost of the external structure needed, it may also require less work, so copper cost around double or less.
We have to take into account that the copper loop cost would represent less than 1/5 of the whole system cost, I have to buy a pump, sensors, a controller, connection and pressure test to a company, extra pipe and insulation, etc.
I don't have the tools for HDPE fuse either.

2-HDPE would last way more, not sure how much copper could last, but if we are talking about more than 7 years, It would be fine for me.

3- I think the less volume of copper would be easier to sell to the to neighborhood administration and attracts less attention, but I didn't talk to them yet, so I don't know.

4- copper require less length so it may help a bit with the flow rate at equal pump power.

Well, I guess it was right the one who told me that calculation would be very hard with so many variables and experimentation might be the best strategy, at least those calculations are way beyond knowledge.
I also don't think it's likely to miss my estimate so much to end with almost null benefits.

 

[AngelLestat]

One quick edit (sorry for double post)

Something I did not take into account in my new heat exchanger design, is that the lake water temperature at the top of the PVC tube would be higher temperature than in the bottom, this in part interrupt the natural convection that I wanted to achieve.
I still love many of the benefits of the vertical approach with the counterweight and the buoy. But I would need to make it shorter I guess, maybe 2 meter with higher diameter.

 

[gmax137]

I still think condensation (= wet floors) is going to be a problem. Traditional A/C units discharge a lot of condensate as the air is cooled in the evaporator section. I flooded my basement once when the condensate line plugged, I had probably 40 liters of water to mop up after a day's operation with the condensate spilling to the floor. I don't think ceiling fans will solve this, and if they do it means you air will be cooler but damper. I don't think that will be more comfortable.

Once again calling @russ_watters to chime in

 

[bigyabbie]

Surely the trick to overcome the dewpoint issue is simply to use a thermostat to control the system and ensure the floor never drops below say 18 or 19 degrees. ..

 

[gmax137]

The OP said average summer temp is 29C. At that temperature, the RH has to be below ~50% for the dewpoint to be above 19C. So depending on where the OP lives (hot & dry - or - hot & humid) a 19C floor could be OK, or not.

 

[anorlunda]

The temperature right now in Buenos Aires is 26C the dew point is 18C.

The average relative humidity for January is 66%, so on a hot day when the temperature is 35C, the dew point would be about 28C.

 

[Tom.G]

Sounds like the control solution is use a thermostat for temperature control, and add either a humidistat to override the temperature control, or add a dehumidifier.

(Or move to a different climate! )

Cheers,
Tom