Hey I love this thread, fun stuff. There are many great thoughts and some not so but it is a cool forum.
falconut made a great point about the growth, something that I hadn't considered. AND running the water through an exchanger will reduce efficiency - some.
As far as the black poly pipe lasting, I am not sure. I believe it is NOT code approved for use inside of the house because of some major catastrophes and huge lawsuits a few years back.
Now PEX the radiant heating tubing is much better, stronger, has an oxygen barrier, and can withstand a broad range of pressure. But, it is costly compared (I think) to the black poly stuff. Runs around $0.45 to $0.60/LF. The most typical size used for radiant heating systems is 1/2" and the pipe is not really well known for it's thermal transfer properties, which are poor. But it does the job with enough pipe out there and a big enough temp diff.
So just crunching a few numbers . . .at a velocity of 6 FPS in a 1/2" line you can expect a pressure drop of around 20 PSI/100 feet of pipe. Say you put out 200 feet, that translates to 92 feet of head! Most aquarium pumps are rated for high flow and low head. Your GPH at 6 FPS is 210 or 3.5 GPM. This doesn't look good.
So what if we lowered the flow to say 1.5 GPM (90 GPH) which translates to 4 PSI/100 feet of pipe. That would drop the total head to around 20 feet which is manageable.
Now at 1.5 GPM and an entering water temp (via the exchanger) of around 75 deg F you could expect a temp drop of maybe 10 degrees through the loop then you will lose a couple of those degrees again at the exchanger. So if you were able to get 1.5 GPM at a 6 deg F drop you will be dumping 4500 BTUH to the Earth. (Provided you were deep enough to get constant temp which would have to be from 2' to 6' and it's better if the ground is WET). One watt of electricity equals 3.4 BTUH so you are getting rid of about 1323 watts.
I think this is starting to look attractive but cost is going to be a factor. 200 feet of 1/2" PEX = $100. A heat exchanger of titanium will run around $100 (I am now officially WAGGING) and a decent pressure circulator will run $225 and you had better add another $100 for what if's. Still $600 for essentially FREE cooling isn't bad. You still have to provide the labor and misc stuff but I am liking it.
Unless of course you have a day job and kids and a bad back . . . well maybe working a few hours overtime to pay for that $600 chiller doesn't look so bad either.
Sorry for the run of the fingers here, I kind of dig this stuff.
UPDATE INFO. I just noticed on Ebay, 500 LF of 3/4" PEX for $150 which includes shipping. 3/4" could handle a higher flow rate and maybe it would end up at a lower PD. Velocity at around 1.5 FPS is enough to elimate laminarity as I recall.
falconut made a great point about the growth, something that I hadn't considered. AND running the water through an exchanger will reduce efficiency - some.
As far as the black poly pipe lasting, I am not sure. I believe it is NOT code approved for use inside of the house because of some major catastrophes and huge lawsuits a few years back.
Now PEX the radiant heating tubing is much better, stronger, has an oxygen barrier, and can withstand a broad range of pressure. But, it is costly compared (I think) to the black poly stuff. Runs around $0.45 to $0.60/LF. The most typical size used for radiant heating systems is 1/2" and the pipe is not really well known for it's thermal transfer properties, which are poor. But it does the job with enough pipe out there and a big enough temp diff.
So just crunching a few numbers . . .at a velocity of 6 FPS in a 1/2" line you can expect a pressure drop of around 20 PSI/100 feet of pipe. Say you put out 200 feet, that translates to 92 feet of head! Most aquarium pumps are rated for high flow and low head. Your GPH at 6 FPS is 210 or 3.5 GPM. This doesn't look good.
So what if we lowered the flow to say 1.5 GPM (90 GPH) which translates to 4 PSI/100 feet of pipe. That would drop the total head to around 20 feet which is manageable.
Now at 1.5 GPM and an entering water temp (via the exchanger) of around 75 deg F you could expect a temp drop of maybe 10 degrees through the loop then you will lose a couple of those degrees again at the exchanger. So if you were able to get 1.5 GPM at a 6 deg F drop you will be dumping 4500 BTUH to the Earth. (Provided you were deep enough to get constant temp which would have to be from 2' to 6' and it's better if the ground is WET). One watt of electricity equals 3.4 BTUH so you are getting rid of about 1323 watts.
I think this is starting to look attractive but cost is going to be a factor. 200 feet of 1/2" PEX = $100. A heat exchanger of titanium will run around $100 (I am now officially WAGGING) and a decent pressure circulator will run $225 and you had better add another $100 for what if's. Still $600 for essentially FREE cooling isn't bad. You still have to provide the labor and misc stuff but I am liking it.
Unless of course you have a day job and kids and a bad back . . . well maybe working a few hours overtime to pay for that $600 chiller doesn't look so bad either.
Sorry for the run of the fingers here, I kind of dig this stuff.
UPDATE INFO. I just noticed on Ebay, 500 LF of 3/4" PEX for $150 which includes shipping. 3/4" could handle a higher flow rate and maybe it would end up at a lower PD. Velocity at around 1.5 FPS is enough to elimate laminarity as I recall.
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