any heating/cooling engineers here?

[echo4747]

At my residence I have(what I think is)an unlimited amount of year round 52-55deg f supply of water. I am currently in need of a new driveway and was thinking of using this water supply to devise some sort of snow melting system. My plan is to run some sort serpentine coil embedded or under the new concrete slab and run this water thru it. For cost reasons, I do not want to add any aux heat if possible. I plan on dischargarging the water into the storm sewer near the base of my driveway. The driveway has a fairly steep slope so the melted snow will run down it rather easily. The driveway is 18.5 ft wide x 58ft long. The driveway is located in suburb south of Buffalo NY.Some of my questions are:
-What mat'l should be used for the pipe /tubing that makes up this coil?
- What size/diameter pipe tubing should be used?
- Should the coil in the slab or under the slab?
Anyone care to comment/advise or point me in the right direction?

 

[iwantanewcomputer]

why bother installing a coil in/under the concrete? if it is >50 just pour the water on the top of the driveway and let it run down, the driveway will be wet anyway from melting snow

 

[Analog]

Originally posted by: echo4747
At my residence I have(what I think is)an unlimited amount of year round 52-55deg f supply of water. I am currently in need of a new driveway and was thinking of using this water supply to devise some sort of snow melting system. My plan is to run some sort serpentine coil embedded or under the new concrete slab and run this water thru it. For cost reasons, I do not want to add any aux heat if possible. I plan on dischargarging the water into the storm sewer near the base of my driveway. The driveway has a fairly steep slope so the melted snow will run down it rather easily. The driveway is 18.5 ft wide x 58ft long. The driveway is located in suburb south of Buffalo NY.Some of my questions are:
-What mat'l should be used for the pipe /tubing that makes up this coil?
- What size/diameter pipe tubing should be used?
- Should the coil in the slab or under the slab?
Anyone care to comment/advise or point me in the right direction?

If there's a chance of freeze-up, I would recommend a glycol system. These are fairly common, and are embedded in the concrete. Using water by itself may cause problems if you get plugged etc.

Look up glycol concrete slab heating, I'm sure you'll see complete kits out there.

 

[woowoo]

The "Tubing" is called Plex.
You would want to have a closed loop Glycol system and a liquid to liquid heat exchanger.

I don't think the city would like an "Endless" supply of water in the storm sewer

 

[echo4747]

I would like to like have an open loop system because my water source is 52-55 deg . If i go with a closed loop system with glycol I will need to add aux heat ( boiler or electric) I an not too worried about the pipe/tubing clogging up.

 

[iwantanewcomputer]

yellowfiero, what is a liquid liquid heat exchanger? are you talking about mixing the liquids? or just flowing one in a pipe/coil through the other

 

[echo4747]

the liquid to liquid heat exchanger is an idea but would require an additional pump. As far as the town storm sewer goes .. there is already a constant heavy flow of water due to the many springs around the neighborhood.
Can you tell me more about this "plex". Is it embedded in the slab or under the slab?
-How far apart should the tubing be laid out?

 

[EagleKeeper]

The city will not tolerate you putting chemicals into the water and then dumping it into the storm sweres. Hazard waste rules.

Also, the temp of the water will cool down as it releases heat to warm the driveway. The final output temp may be cool enough to create some ice-rink near the dischard point.

Also, you may only warm the initial suface, the outside air could cause icing above the surface and set up you with a glacier type effect.

You would be best to actualy have some engineer/inspectors look at the actual situation and also create a test area for 1-2 winters before installing something that may not work.

You will need the ability to shut off the water source and drain/blow out what-ever liquid exists in it, if you change your mind later on.

 

[dullard]

I don't see this as a good project, due to many issues that will arise. But I guess we can still think about it for fun.

We need some data to begin a heat transfer calculation.
[*]Water temperature. Lets assume the water inlet is 50°F (it will cool on the way to the driveway, and we always have to take the worst case senerio as an engineer not the best case senerio).
[*]Slab temperature. This one is of course variable. It may snow when it is very cold (contrary to popular belief there isn't a temperature too cold for snow). Or it may snow when it is a bit above 32°F. As an engineer, you need to consider the cold end as that is the worst case senerio. Buffallo, NY gets as cold as -20°F. So there are two extremes to think about: -20°F and 32°F. If we look right in the middle, we get 12°F. Decent estimate, but for safety margin lets bump that down a bit to 5°F.
[*]Check on estimate. Does Buffalo actually get much snow at 5°F? Tough question. Most of Buffalo's heavy snow is lake effect snow. Lets focus on that. The lake cannot be frozen for lake effect snow to take place. Thus the lake must be at least 32°F. Lake effect snow cannot take place unless the air is 23°F less than the water temperature. Thus, if the lake is near freezing, the air must be no warmer than 9°F. That isn't a really scientific number (since the lake could be warmer than 32°F or the air could be more than 23°F below the lake temperature). But it is one more good reason that our 5°F number is acceptable. If the slab is <5°F, just don't use the water and you should be fine.
[*]How much water is actually available. I'll just use numbers for a large diameter garden hose. That is roughly 0.5 gallons per second if you have good water pressure. Or are you going to be building in a larger diameter pipe to your water supply?

Do those numbers seem accurate?

 

[dullard]

Continued.

We have a constraint. Pure water cannot drop below 32°F. Due to complexity issues, cost issues, and disposal issues, you have already ruled out additives in this thread. Anything you add to water would drop this temperature at the same amount per mass added. It is an interesting propertly that it doesn't matter what material you add to the water (up to a reasonable point), the temperature will drop the same if you add the same amount of mass. But we will just take 32°F as our number.

So the water can drop 50°F-32°F = 18°F maximum. If it drops more than that, it will freeze up and your project is useless.

How much heat is that?
[*]~0.5 gal/s.
[*]Water heat capacity: ~4.184 J/g°C.
[*]Water density: ~1 g/ml.
[*]Water temperature drop: ~18°F.
Multiply all those numbers together and you get 79 kJ/s.

Can you calculate the amount of snow that will melt? Or do you need us to do more?

 

[echo4747]

Originally posted by: dullard
I don't see this as a good project, due to many issues that will arise. But I guess we can still think about it for fun.

We need some data to begin a heat transfer calculation.
[*]Water temperature. Lets assume the water inlet is 50°F (it will cool on the way to the driveway, and we always have to take the worst case senerio as an engineer not the best case senerio).
[*]Slab temperature. This one is of course variable. It may snow when it is very cold (contrary to popular belief there isn't a temperature too cold for snow). Or it may snow when it is a bit above 32°F. As an engineer, you need to consider the cold end as that is the worst case senerio. Buffallo, NY gets as cold as -20°F. So there are two extremes to think about: -20°F and 32°F. If we look right in the middle, we get 12°F. Decent estimate, but for safety margin lets bump that down a bit to 5°F.
[*]Check on estimate. Does Buffalo actually get much snow at 5°F? Tough question. Most of Buffalo's heavy snow is lake effect snow. Lets focus on that. The lake cannot be frozen for lake effect snow to take place. Thus the lake must be at least 32°F. Lake effect snow cannot take place unless the air is 23°F less than the water temperature. Thus, if the lake is near freezing, the air must be no warmer than 9°F. That isn't a really scientific number (since the lake could be warmer than 32°F or the air could be more than 23°F below the lake temperature). But it is one more good reason that our 5°F number is acceptable. If the slab is <5°F, just don't use the water and you should be fine.
[*]How much water is actually available. I'll just use numbers for a large diameter garden hose. That is roughly 0.5 gallons per second if you have good water pressure.

Do those numbers seem accurate?

Dullard here is some info: This water source is from a well (which I'm told is an artesian well) I don't need to use any of this water for household use as I'm also on a public water system. I currently use this well water to cool my house in the summer. I bought a liquid to air heat pump that does a wonderful job cooling the house. If I remember correctly my current well pump(1/2 hp) gives me ~7.5 gal/min. As far as your other numbers (they are resonably accurate although temps near or below zero are rare and when they are that low it rarely snows. Most snow occurs when the temps are between 15-30 deg) If you need me to provide more info let me know. I think I could go with a bigger (3/4-1 hp) well pump if needed

 

[echo4747]

Originally posted by: dullard
Continued.

We have a constraint. Pure water cannot drop below 32°F. Due to complexity issues, cost issues, and disposal issues, you have already ruled out additives in this thread. Anything you add to water would drop this temperature at the same amount per mass added. It is an interesting propertly that it doesn't matter what material you add to the water (up to a reasonable point), the temperature will drop the same if you add the same amount of mass. But we will just take 32°F as our number.

So the water can drop 50°F-32°F = 18°F maximum. If it drops more than that, it will freeze up and your project is useless.

How much heat is that?
[*]~0.5 gal/s.




[*]Water heat capacity: ~4.184 J/g°C.
[*]Water density: ~1 g/ml.
[*]Water temperature drop: ~18°F.
Multiply all those numbers together and you get 79 kJ/s.

Can you calculate the amount of snow that will melt? Or do you need us to do more?

What about the fact that water is moving? That should keep from freezing provided the flow is adequate. If it flows too fast It may not stay in the tubing long enough to transfer heat

 

[dullard]

Originally posted by: echo4747
Dullard here is some info: This water source is from a well (which I'm told is an artesian well) I don't need to use any of this water for household use as I'm also on a public water system. I currently use this well water to cool my house in the summer. I bought a liquid to air heat pump that does a wonderful job cooling the house. If I remember correctly my current well pump(1/2 hp) gives me ~7.5 gal/min. As far as your other numbers (they are resonably accurate although temps near or below zero are rare and when they are that low it rarely snows. Most snow occurs when the temps are between 15-30 deg) If you need me to provide more info let me know. I think I could go with a bigger (3/4-1 hp) well pump if needed

Thanks for the data. We can go with that. Lets use 15°F then instead of my 5°F. 7.5 gal/min is 0.125 gal/sec. If you double the horse power would that just double the flow rate? I don't know what the larger pump will pump, but lets pretend you can get one that is really, really large up to 0.5 gal/sec that I used above.

How much snow to melt?
[*]Lets assume you want to melt the snow as it falls (so the device has to be good enough to keep up).
[*]Lets for not assume no heat is lost to the air or to the ground below (not accurate, but it will give us a rough number to decide if we should continue the math).
[*]Lets assume you have wet snow (worst case senerio).
[*]Wet snow is about 1/7th the density of water.
[*]Lets assume the wet snow has to be heated from 15°F to 32°F and then your water heater needs to give enough energy to melt it at 32°F.
[*]Lets assume 1"/hr of snow falls as a fairly heavy snow.
[*]Thus you have 1"/hr * 18.5 ft * 58 ft = 86 in^3/s of snow to melt.
[*](1g/ml) / (7) * 86 in^3/s = 0.201 kg/s of snow to heat up and melt.

More math.
[*]The snow needs to be heated by 17°F.
[*]The heat of melting is 334 J/g.
[*]Thus you need 405 kJ/kg of snow.
[*]Multiply by amount of snow: and you need 81 kJ/s of heat.
[*]If we include heat loss to the atmosphere or the ground, you'll need significantly more than that.

Compare that number to the 79 kJ/s that you have available. You just barely won't be able to keep up.

 

[dullard]

Originally posted by: echo4747
What about the fact that water is moving? That should keep from freezing provided the flow is adequate. If it flows too fast It may not stay in the tubing long enough to transfer heat

Doesn't matter. If the snow is actually melting, then the slab must be at 32°F (no higher and no lower). So the water cannot get colder than 32°F if the device is functioning. If it isn't functioning, then yes the water could get colder. But lets not go down that road (why do the science if we know it isn't functioning?)

Or do you want to assist your machine by puting something on the snow (salt is common, but anything would work)? In that case, the snow would melt at a lower temperature. Thus the slab could get colder than 32°F, and we'd have to see if the water could cool below 32°F.

 

[echo4747]

Originally posted by: dullard

Originally posted by: echo4747
Dullard here is some info: This water source is from a well (which I'm told is an artesian well) I don't need to use any of this water for household use as I'm also on a public water system. I currently use this well water to cool my house in the summer. I bought a liquid to air heat pump that does a wonderful job cooling the house. If I remember correctly my current well pump(1/2 hp) gives me ~7.5 gal/min. As far as your other numbers (they are resonably accurate although temps near or below zero are rare and when they are that low it rarely snows. Most snow occurs when the temps are between 15-30 deg) If you need me to provide more info let me know. I think I could go with a bigger (3/4-1 hp) well pump if needed

Thanks for the data. We can go with that. Lets use 15°F then instead of my 5°F. 7.5 gal/min is 0.125 gal/sec. If you double the horse power would that just double the flow rate? I don't know what the larger pump will pump, but lets pretend you can get one that is really, really large up to 0.5 gal/sec that I used above.

How much snow to melt?
[*]Lets assume you want to melt the snow as it falls (so the device has to be good enough to keep up).
[*]Lets for not assume no heat is lost to the air or to the ground below (not accurate, but it will give us a rough number to decide if we should continue the math).
[*]Lets assume you have wet snow (worst case senerio).
[*]Wet snow is about 1/7th the density of water.
[*]Lets assume the wet snow has to be heated from 15°F to 32°F and then your water heater needs to give enough energy to melt it at 32°F.
[*]Lets assume 1"/hr of snow falls as a fairly heavy snow.
[*]Thus you have 1"/hr * 18.5 ft * 58 ft = 86 in^3/s of snow to melt.
[*](1g/ml) / (7) * 86 in^3/s = 0.201 kg/s of snow to heat up and melt.

More math.
[*]The snow needs to be heated by 17°F.
[*]The heat of melting is 334 J/g.
[*]Thus you need 405 kJ/kg of snow.
[*]Multiply by amount of snow: and you need 81 kJ/s of heat.
[*]If we include heat loss to the atmosphere or the ground, you'll need significantly more than that.

Compare that number to the 79 kJ/s that you have available. You just barely won't be able to keep up.

The largest pump (using data from W.W. Graingers) 1.5hp model will flow 35.2 gal/min or .586gal/sec @20psi. Will this get me over the hump? There is a 5hp pump that will do 114gal/min which I'm sure can do the job but will have to measure to see if it can fit in my existing well casing. I suppose I could plumb a natural gas tankless water heater to assist the system during periods of heavy snow/extreme cold

 

[dullard]

Originally posted by: echo4747
The largest pump (using data from W.W. Graingers) 1.5hp model will flow 35.2 gal/min or .586gal/sec @20psi. Will this get me over the hump? There is a 5hp pump that will do 114gal/min which I'm sure can do the job but will have to measure to see if it can fit in my existing well casing. I suppose I could plumb a natural gas tankless water heater to assist the system during periods of heavy snow/extreme cold

I think that is as far as I'm going to go. I showed that under extreme conditions, you'd be almost able to do it. Under mild conditions, you should have the available water. Under the really, really bad cases you can simply turn it off.

But you have to think about problems: expense to build it, expense to run it, angering the city with the additional sewer load, potential for leaks, potential for freezing in the lines (or will you be running this 24/7 the whole winter?), etc.

I really think the problems may outweigh the benefits. I'd consider prebuild solutions instead of doing it yourself.

 

[Scarpozzi]

If it's a small area, I recommend looking into a radiant heating solution. They make electric systems that run on 24 volts... They're low power consumption and can be set just high enough to melt the snow. They're expensive to install, cheap to maintain.

 

[Dubb]

I'd actually say that dullard's calculations are being a bit too forgiving. ground and air heat loss will dwarf the snow issue (the ground is one hell of a thermal mass problem). To me this has "bad idea" written all over it.

In addition to the problems he mentioned, that is one massive waste of water, and you should be ashamed for even considering it. look into a closed system with additives or other solutions + evacuated tubes if you really want to do something like this.

 

[skimple]

Yes - you will lose heat to the ground rapidly. I don't know the exact numbers, but in the Northeast the frost line will extend several feet below the surface - certainly well below the depth of your tubing. Being in Buffalo, you should know that the temperature of the ground can get well below 32. In most cases, it is likely that the ground will be colder than the ambient air. So now you have to factor in an estimate of the worst case surrounding ground temperature, and combine it with the transfer coeffiecient for the earth.

Running water will have negligible impact. Consider Niagara Falls, which you should be intimately familiar with. That freezes up every year, with the amount of water running through it dropping drastically.


I think you can't get away without a heating device.

 

[echo4747]

Originally posted by: Dubb
I'd actually say that dullard's calculations are being a bit too forgiving. ground and air heat loss will dwarf the snow issue (the ground is one hell of a thermal mass problem). To me this has "bad idea" written all over it.

In addition to the problems he mentioned, that is one massive waste of water, and you should be ashamed for even considering it. look into a closed system with additives or other solutions + evacuated tubes if you really want to do something like this.

Aside from the fact that I may not have adequate(water pumping) capacity at this point; I agree with dullard that there are many other problems to consider. However this water is currently flowing into a sewer without being put to any use. Since my original idea was just to extract the geothermal heat from this water and let the water go back into the sewer it is going into presently. I have to disagree with dubb that this is wasting water. If the system springs a leak -I just shut it down no harm done to the environment- Should a closed loop system spring a leak, a water /glycol mix would seep into the ground (not good) If I could get away with not having to add any extra heat energy(oil or electricity derived from fossil fuel) the system is even more earth friendly.

 

[Dubb]

Originally posted by: echo4747

Originally posted by: Dubb
I'd actually say that dullard's calculations are being a bit too forgiving. ground and air heat loss will dwarf the snow issue (the ground is one hell of a thermal mass problem). To me this has "bad idea" written all over it.

In addition to the problems he mentioned, that is one massive waste of water, and you should be ashamed for even considering it. look into a closed system with additives or other solutions + evacuated tubes if you really want to do something like this.

Aside from the fact that I may not have adequate(water pumping) capacity at this point; I agree with dullard that there are many other problems to consider. However this water is currently flowing into a sewer without being put to any use. Since my original idea was just to extract the geothermal heat from this water and let the water go back into the sewer it is going into presently. I have to disagree with dubb that this is wasting water. If the system springs a leak -I just shut it down no harm done to the environment- Should a closed loop system spring a leak, a water /glycol mix would seep into the ground (not good) If I could get away with not having to add any extra heat energy(oil or electricity derived from fossil fuel) the system is even more earth friendly.

I guess I don't understand...if all that water is currently going into the sewer, why do you need a bigger pump? how is it getting from the well to the sewer at the moment?

also: I'm saying that for this to be feasible, it seems like you'd need a pump that would probably cost more to run than simply doing evacuated tubes + auxillary heating unit on a closed loop system. and with the closed loop you don't have the potential hassle of a frozen line (which WILL happen, either pump fails, elecctricity goes out...it's asking for disaster)

yes, if the closed loop system leaks, it's a bigger environmental problem. however I think it's a virtual certainty that the open water system you're considering will catastrophically fail in 5 years or less. if it ever shuts down for more than a brief period while the ground is frozen, your whole system is fsked. new driveway. new system. then the same thing happens again. A well done closed loop system will tolerate pump + other mechanical failures and should last 15-20 years with only the occasional replacemnet of an evacuated tube or other misc. easily replaceable part.

I think you'd be absolutely daft to attempt this.

 

[echo4747]

Originally posted by: Dubb

Originally posted by: echo4747

Originally posted by: Dubb
I'd actually say that dullard's calculations are being a bit too forgiving. ground and air heat loss will dwarf the snow issue (the ground is one hell of a thermal mass problem). To me this has "bad idea" written all over it.

In addition to the problems he mentioned, that is one massive waste of water, and you should be ashamed for even considering it. look into a closed system with additives or other solutions + evacuated tubes if you really want to do something like this.

Aside from the fact that I may not have adequate(water pumping) capacity at this point; I agree with dullard that there are many other problems to consider. However this water is currently flowing into a sewer without being put to any use. Since my original idea was just to extract the geothermal heat from this water and let the water go back into the sewer it is going into presently. I have to disagree with dubb that this is wasting water. If the system springs a leak -I just shut it down no harm done to the environment- Should a closed loop system spring a leak, a water /glycol mix would seep into the ground (not good) If I could get away with not having to add any extra heat energy(oil or electricity derived from fossil fuel) the system is even more earth friendly.

I guess I don't understand...if all that water is currently going into the sewer, why do you need a bigger pump? how is it getting from the well to the sewer at the moment?

also: I'm saying that for this to be feasible, it seems like you'd need a pump that would probably cost more to run than simply doing evacuated tubes + auxillary heating unit on a closed loop system. and with the closed loop you don't have the potential hassle of a frozen line (which WILL happen, either pump fails, elecctricity goes out...it's asking for disaster)

yes, if the closed loop system leaks, it's a bigger environmental problem. however I think it's a virtual certainty that the open water system you're considering will catastrophically fail in 5 years or less. if it ever shuts down for more than a brief period while the ground is frozen, your whole system is fsked. new driveway. new system. then the same thing happens again. A well done closed loop system will tolerate pump + other mechanical failures and should last 15-20 years with only the occasional replacemnet of an evacuated tube or other misc. easily replaceable part.

I think you'd be absolutely daft to attempt this.

Dubb.. From what I've been told this ground water that my well taps into must be from some sort of underground river. My house is located near the top of a hill .. when I go down the street about 1/4mile at the base of this hill where the next street intersects, there is a grate with about a 12-14 inch dia pipe with water constantly rushing out of it. A friend and i dropped a few tablets of a red plumbers tracing dye into my well casing .. went down to the end of the street and saw the presence of the dye in the aforementioned grate/storm sewer. There have been times that it hasn't rained for 10-14 days and water still rushes out. Funny thing is several of my surrounding neighbors wells run dry after pumping for 5 min. My well never goes dry as well the neighbor directly across from me. My well is only 21ft deep his is 40ft deep.
Dubb .. what is exactly the purpose/use of the evacuated tube?

 

[dullard]

Originally posted by: Dubb
I'd actually say that dullard's calculations are being a bit too forgiving. ground and air heat loss will dwarf the snow issue (the ground is one hell of a thermal mass problem). To me this has "bad idea" written all over it.

In addition to the problems he mentioned, that is one massive waste of water, and you should be ashamed for even considering it. look into a closed system with additives or other solutions + evacuated tubes if you really want to do something like this.

Like I said above, the heat loss to the ground will be significant. Lets just do really rough numbers.
[*]Assume the frost line is 1 m below (about right for NY). Thus 1 m below it is 32°F.
[*]Assume that it is 15°F outside, so the top of the ground is 15°F.
[*]The ground should linearly vary from 15°F to 32°F. The mass averages 23.5°F. Or on average it needs to be 8.5°F hotter.
[*]Density of ground is about 2500 kg/m^3. Multiply by 1 m thick and the area of the driveway and you get 250,000 kg of dirt.
[*]Heat capacity of dirt is about 0.837 J/gm*K.
[*]Multiply it all together and you need 1 trillion joules of heat to warm it up.
[*]If we could get all 81 kJ/s of heat to the ground (ignoring loss to the air), it'll take 3.5 hours to warm up. Including loss to the air, will roughly offset the heat flowing from the center of the earth to the surface (I'm not going to bother doing that calculation). Turning it on 3.5 hours before snow falls is doable I guess.

Once the ground is warm, it really isn't an issue.

 

[91TTZ]

Just buy a shovel.

 

[Dubb]

Originally posted by: echo4747

Dubb.. From what I've been told this ground water that my well taps into must be from some sort of underground river. My house is located near the top of a hill .. when I go down the street about 1/4mile at the base of this hill where the next street intersects, there is a grate with about a 12-14 inch dia pipe with water constantly rushing out of it. A friend and i dropped a few tablets of a red plumbers tracing dye into my well casing .. went down to the end of the street and saw the presence of the dye in the aforementioned grate/storm sewer. There have been times that it hasn't rained for 10-14 days and water still rushes out. Funny thing is several of my surrounding neighbors wells run dry after pumping for 5 min. My well never goes dry as well the neighbor directly across from me. My well is only 21ft deep his is 40ft deep.
Dubb .. what is exactly the purpose/use of the evacuated tube?

so the city connected the underground river to the storm sewer? Interesting to say the least, have you checked with the city to see what info they have on it? as you know that's one hell of a resource for summer cooling.

evacuated tubes are used for solar water/fluid heating. basically it's a clear plastic (or glass) tube set inside a much larger clear tube. fluid is pumped through the small diameter tube, and there's essentially zero heat loss because the larger tube contains a vaccum. So the fluid picks up heat from any solar radiation that strikes the tube. combined with solar reflectors, it can be a nice boost of free energy, even in winter. They're often used to pre-heat water for radiant floor systems or even for potable water (but in that case you need to install a device to mix in cold water with the output if it gets above a certain temp - evacuated tubes easily produce near-boiling water, or much higher temp glycol under direct sunlight.)

here's one guy's setup:

http://www.radiantcompany.com/system/evacuated.shtml