Renewable heat

The master plan · 07-10-11, 06:07 AM

I have started a large insulated water storage tank in my crawlspace. Why does saving energy always require digging??

In my quest to go total renewable/green heating I am installing stuff in stages and limiting the amount of dollars invested where possible. Most is in the form of sweat, but I have gotten some killer deals on sales, web etc.

The plan calls for a tank that holds 1000 gallons of water. It will be 6ft deep by 5 ft sides. It will be at least 5 ft in the ground and therefore less will be required to reinforce it. Insulation will be at least 2 layers of 2" Foamular 250 for a R20. Black pond liner is used to make it waterproof. Pex coils will be installed and used to both draw heat in/out of the tank.

I currently heat with wood mostly, the back-up is city supplied hot water forced air system. I want off...I have no natural gas line on the property. Anything I use must be reliable, easy to maintain and get parts for should something happen to go wrong.

I was going to use the tank to store heated water via a loop I have in the wood stove. The coil in the stove is currently used to heat a 60 gallon water heater. It heats the water to 140F even 180F...if I don't use enough hot water. I've dumped bath tubs of hot water to get the heat down to normal levels...I run my clothes washer and dish washer on hot water supplied with this system in the winter.

However i am constantly burning wood 24/7 in the coldest parts of the month. I want to use the 1000 gal tank to drag me threw several days. Then I can burn wood for awhile and use the tank to store as much energy as possible and coast for a few days off the stored heat.

Wouldn't a geo heat pump hooked to this large tank be able to draw this heated water and make it more efficient? If I keep the tank temp at around 70F or 80F to a max of 140F. It could draw it to as low as 45F then switch to a ground loop to prevent freezing the tank if I don't use the wood stove.

A water furnace then becomes my back-up when heat isn't supplied by radiant heat off the wood stove. I also save by using a smaller loop field in the ground.

A few solar panels would later be connected to the tank to add hot water also. Basically I'm poring in BTU's from every possible source and taking them out with a water furnace. Only need to supply the electricity to run these and it is completely green heat.

I could gain more space in the basement if I could install the water furnace in the attic. All ducts would then be insulated. I could even insulate the water furnace against the temp swings of the attic.

Any ideas?

randen · 07-12-11, 09:30 PM

Master Plan

I've installed solar hot water panels. I cannot believe how much heat is avalible with the sun. We have heated concrete floors so low temp (hydronic floor) system (100 deg F)with 6 panels and full sun we heat in the depths of winter for 24 hrs. We are adding more for more capacity. If your in an area with ample days with sun, no fires would be required. Soak up the sun. The rule of thumb is 10%-30% flat panel area for floor area. I'm in Canada sometimes we go a week without sun (cloudy) our primary is geo-thermal but when the sun shines geo-thermal is off for 24 hrs about $8.00 dollars worth of electricity.

I would maybe keep the wood burner coupled with the huge water tank and introduce solar hot water. Flat panels you can make DIY. A large wall of panels could be the ticket. No energy involved just a circ. pump.

Randen

AC_Hacker · 07-13-11, 01:33 AM

Quote:

Originally Posted by The master plan

Wouldn't a geo heat pump hooked to this large tank be able to draw this heated water and make it more efficient? If I keep the tank temp at around 70F or 80F to a max of 140F. It could draw it to as low as 45F then switch to a ground loop to prevent freezing the tank if I don't use the wood stove.

Depending on many factors, how well you design and build your radiant surface (floor?), how well insulated house is, etc., your tank of heated water will need to be somewhere in the 115F range or higher for heat to transfer from your floor at a high enough rate to keep you warm.

This is where a heat pump can be useful. A heat pump can pull heat from the water all the way down to freezing. Or in your case, to the point where the water approaches the temp of the earth in your ground loop. At this point you'd want to switch your heat pump water circuit form the storage tank to your ground loop.

Another way to look at this is that if you could insure that your temps from your wood stove Or solar panels didn't exceed the safe limits of your ground loop plastic pipe, you could use the ground as a storage instead of a water tank. You could send excess solar down there, and excess wood stove heat as well.

But you don't want the plastic pipe to see temps over 180F. Some kind of water temperature control valve would be great.

-AC_Hacker

The master plan · 07-13-11, 12:18 PM

Randen, how did you do your pex tubing? I'm thinking along the same lines as you. I am thinking of 1/2 pex and 6"-8" on center. I want to be able to heat with panels also...low temp radiant. People around here aren't that familiar with this type it seems.

Also I have read studies that its better to not staple down the pex to the foam, but rather have it in the top/middle of the slab. (about 2"down)

The effect of tube depth on radiant slab performance | Engineered Systems | Find Articles at BNET

I told my dad of my plans and he talked to a radiant guy and they said it was wrong and should be stapled down to the foam. "Heat travels up" is what I get from all the radiant guys around here. I think why try to heat the foam under the tubing when it could be heating the concrete directly if it was up in the slab...

GaryGary · 07-13-11, 01:51 PM

Quote:

Originally Posted by The master plan

Randen, how did you do your pex tubing? I'm thinking along the same lines as you. I am thinking of 1/2 pex and 6"-8" on center. I want to be able to heat with panels also...low temp radiant. People around here aren't that familiar with this type it seems.

Also I have read studies that its better to not staple down the pex to the foam, but rather have it in the top/middle of the slab. (about 2"down)

The effect of tube depth on radiant slab performance | Engineered Systems | Find Articles at BNET

I told my dad of my plans and he talked to a radiant guy and they said it was wrong and should be stapled down to the foam. "Heat travels up" is what I get from all the radiant guys around here. I think why try to heat the foam under the tubing when it could be heating the concrete directly if it was up in the slab...

Hi,

Heat travels up is wrong. Heat travels to cold. It will happily go downward if its colder in the downward direction.

The thing that confuses people is that warm air is less dense and rises, so hot air ends up transferring heat up, but its not the heat that's traveling up, its the lighter air. When you are talking about transferring heat through solids it will go down just as easily as up -- the colder it is in a given direction, the more heat goes in that direction -- up, down, or sideways.

I guess you are talking about a new slab with insulation under it, and pex embedded in it?
I'd guess that if you put the pex right at the bottom of the slab on top the foam, it will lose a little more heat downward (but probably not a lot), but it seems like it will increase the time lag from when hot water starts flowing through the pex to the time you see heat at the top of the slab. Concrete radiant floor systems are known for being kind of slow to respond to hot water changes, so this lag might be significant.

---
The 1000 gallons of water is about 8300 lbs of water. If you run it between 100F and 140F, then it will store about 332,000 BTU -- quite a bit.
If your wood furnace as a space heater is (say) 50% efficient, then the 332K BTU of stored heat is about equivalent to about 110 lbs of wood (at 6000 BTU/lb) -- or about 5 gallons of propane burned in an 70% efficient furnace.

My radiant floor runs on solar, and I run the storage all the way down to 85F -- but at that temperature I need some supplemental heat plus the solar if its really cold out. Solar collectors don't produce 140F water nearly as efficiently as the do 100F water, so the cooler you can keep the water you can heat the floor with the better for solar.

Gary
Gary

randen · 07-13-11, 04:34 PM

Originally Posted by The master plan
Randen, how did you do your pex tubing? I'm thinking along the same lines as you. I am thinking of 1/2 pex and 6"-8" on center. I want to be able to heat with panels also...low temp radiant. People around here aren't that familiar with this type it seems.

Also I have read studies that its better to not staple down the pex to the foam, but rather have it in the top/middle of the slab. (about 2"down)

If you are installing a radiant floor for heating it is indeed the Cadilac. Yes this is all new technology. Who ever thought you could heat a home with 100 deg water. I may tell you with experience that a concrete slab with 2-3" of ridgid foam underneath and a barrier of say 1" around the outside between the slab and foundation wall is the best. Place you re-bar or steel weld mesh off the foam with bricks to space it , tie your pex to that (6"-8") apart and pour concrete. This will space your re-bar and pex in the middle of the thickness of the slab if its about 5" thick.
We have found that during the coldest days here in Canada that the floor is maintained at a temp of 92 -96 deg F is beyond pleasent. I've mentioned before of enjoying a cup of coffee Sunday morning watching a blizzard out-side -10 deg F with my bare feet on a warm ceramic tile floor. On a sunny day we circulate water at 90-150 deg F from the solar panels though the floor. After 6Hrs of good sun the floor may climb to 98 deg F and carry us though the night to 92 deg in the morn. and the primary heat source has not started.
I believe if your home is also well insulated that a combination of wood stove and solar would be a good option. Gary has demonstrated that as well. I believe he has replaced 1/3 of his heating load with solar. The geo thermal is a great invention as well. If you want geo thermal you could add it later, if your tired of cutting wood.

Randen

gasstingy · 07-20-11, 12:32 PM

My radiant floor isn't completed, but I'd like to pitch in what I was told when I was getting design help from a radiant floor company up north. {Radiant floor system expertise is not easy to find in Alabama.} My project is a 24' x 36' garage / workshop with a 16' x 36' room upstairs. Radiant will be downstairs only, the upstairs is still TBD.

I was told to put the 1/2" pex in the middle of my 4" slab, to insulate under the slab and insulate the perimeter of the slab. I used 2" of insulation around the slab perimeter as a thermal break, but I only put 3/4" under it. I'm certian more insulation would be better even for me, but I'm trying to heat a garage, not a home.

Good luck on your project. BTW, if you haven't been there yet, be sure to check out builditsolar(dot)com. Lots of great stuff over there, too.

The master plan · 07-20-11, 03:50 PM

How much tubing did you use? Mine is going to be 24 X34. But I'm in MN.

gasstingy · 07-20-11, 04:19 PM

I bought three 300 foot rolls of Pex and used one and a half rolls. Again, my requirements are lower than yours. I installed three loops starting about 1' from the outside perimeter of the slab and spaced them at 2' apart. This should be adequate for my needs, I'm betting that the warm water in the tubing will warm the floor 1' in both directions.

And it does feel like a gamble, since if I'm wrong there will be no remedy. One last thing to mention, a little tidbit I found after I finished the slab. You might consider leaving a little extra distance around your toilet(s). I read that too much heat will melt the wax ring that seals your commode. I'm hoping there is an alternative ring available if my floor gets too warm for the ring.

The master plan · 07-20-11, 05:46 PM

I was thinking of using 4 rolls of 300ft 1/2 pex. I built one awhile ago near here that was 22X38 and thought I used 4 rolls then.

I know theres a calculator somewhere to give you a good guess. But why not use all 3 rolls? I would think plumbing the commode on a piece of plywood would eliminate any melting of the wax ring.

07-10-11, 06:07 AM	#1
The master plan Helper EcoRenovator Join Date: Oct 2010 Location: Central MN Posts: 50 Thanks: 0 Thanked 4 Times in 4 Posts	Renewable heat I have started a large insulated water storage tank in my crawlspace. Why does saving energy always require digging?? In my quest to go total renewable/green heating I am installing stuff in stages and limiting the amount of dollars invested where possible. Most is in the form of sweat, but I have gotten some killer deals on sales, web etc. The plan calls for a tank that holds 1000 gallons of water. It will be 6ft deep by 5 ft sides. It will be at least 5 ft in the ground and therefore less will be required to reinforce it. Insulation will be at least 2 layers of 2" Foamular 250 for a R20. Black pond liner is used to make it waterproof. Pex coils will be installed and used to both draw heat in/out of the tank. I currently heat with wood mostly, the back-up is city supplied hot water forced air system. I want off...I have no natural gas line on the property. Anything I use must be reliable, easy to maintain and get parts for should something happen to go wrong. I was going to use the tank to store heated water via a loop I have in the wood stove. The coil in the stove is currently used to heat a 60 gallon water heater. It heats the water to 140F even 180F...if I don't use enough hot water. I've dumped bath tubs of hot water to get the heat down to normal levels...I run my clothes washer and dish washer on hot water supplied with this system in the winter. However i am constantly burning wood 24/7 in the coldest parts of the month. I want to use the 1000 gal tank to drag me threw several days. Then I can burn wood for awhile and use the tank to store as much energy as possible and coast for a few days off the stored heat. Wouldn't a geo heat pump hooked to this large tank be able to draw this heated water and make it more efficient? If I keep the tank temp at around 70F or 80F to a max of 140F. It could draw it to as low as 45F then switch to a ground loop to prevent freezing the tank if I don't use the wood stove. A water furnace then becomes my back-up when heat isn't supplied by radiant heat off the wood stove. I also save by using a smaller loop field in the ground. A few solar panels would later be connected to the tank to add hot water also. Basically I'm poring in BTU's from every possible source and taking them out with a water furnace. Only need to supply the electricity to run these and it is completely green heat. I could gain more space in the basement if I could install the water furnace in the attic. All ducts would then be insulated. I could even insulate the water furnace against the temp swings of the attic. Any ideas?

07-12-11, 09:30 PM	#2
randen Uber EcoRenovator Join Date: Apr 2011 Location: Strathroy Ontario Canada Posts: 657 Thanks: 9 Thanked 191 Times in 129 Posts	Master Plan I've installed solar hot water panels. I cannot believe how much heat is avalible with the sun. We have heated concrete floors so low temp (hydronic floor) system (100 deg F)with 6 panels and full sun we heat in the depths of winter for 24 hrs. We are adding more for more capacity. If your in an area with ample days with sun, no fires would be required. Soak up the sun. The rule of thumb is 10%-30% flat panel area for floor area. I'm in Canada sometimes we go a week without sun (cloudy) our primary is geo-thermal but when the sun shines geo-thermal is off for 24 hrs about $8.00 dollars worth of electricity. I would maybe keep the wood burner coupled with the huge water tank and introduce solar hot water. Flat panels you can make DIY. A large wall of panels could be the ticket. No energy involved just a circ. pump. Randen Last edited by randen; 07-12-11 at 09:37 PM.. Reason: add second paragraph

07-13-11, 12:18 PM	#4
The master plan Helper EcoRenovator Join Date: Oct 2010 Location: Central MN Posts: 50 Thanks: 0 Thanked 4 Times in 4 Posts	Randen, how did you do your pex tubing? I'm thinking along the same lines as you. I am thinking of 1/2 pex and 6"-8" on center. I want to be able to heat with panels also...low temp radiant. People around here aren't that familiar with this type it seems. Also I have read studies that its better to not staple down the pex to the foam, but rather have it in the top/middle of the slab. (about 2"down) The effect of tube depth on radiant slab performance \| Engineered Systems \| Find Articles at BNET I told my dad of my plans and he talked to a radiant guy and they said it was wrong and should be stapled down to the foam. "Heat travels up" is what I get from all the radiant guys around here. I think why try to heat the foam under the tubing when it could be heating the concrete directly if it was up in the slab...

07-13-11, 04:34 PM	#6
randen Uber EcoRenovator Join Date: Apr 2011 Location: Strathroy Ontario Canada Posts: 657 Thanks: 9 Thanked 191 Times in 129 Posts	Originally Posted by The master plan Randen, how did you do your pex tubing? I'm thinking along the same lines as you. I am thinking of 1/2 pex and 6"-8" on center. I want to be able to heat with panels also...low temp radiant. People around here aren't that familiar with this type it seems. Also I have read studies that its better to not staple down the pex to the foam, but rather have it in the top/middle of the slab. (about 2"down) If you are installing a radiant floor for heating it is indeed the Cadilac. Yes this is all new technology. Who ever thought you could heat a home with 100 deg water. I may tell you with experience that a concrete slab with 2-3" of ridgid foam underneath and a barrier of say 1" around the outside between the slab and foundation wall is the best. Place you re-bar or steel weld mesh off the foam with bricks to space it , tie your pex to that (6"-8") apart and pour concrete. This will space your re-bar and pex in the middle of the thickness of the slab if its about 5" thick. We have found that during the coldest days here in Canada that the floor is maintained at a temp of 92 -96 deg F is beyond pleasent. I've mentioned before of enjoying a cup of coffee Sunday morning watching a blizzard out-side -10 deg F with my bare feet on a warm ceramic tile floor. On a sunny day we circulate water at 90-150 deg F from the solar panels though the floor. After 6Hrs of good sun the floor may climb to 98 deg F and carry us though the night to 92 deg in the morn. and the primary heat source has not started. I believe if your home is also well insulated that a combination of wood stove and solar would be a good option. Gary has demonstrated that as well. I believe he has replaced 1/3 of his heating load with solar. The geo thermal is a great invention as well. If you want geo thermal you could add it later, if your tired of cutting wood. Randen

07-20-11, 12:32 PM	#7
gasstingy Journeyman EcoRenovator Join Date: Feb 2010 Location: Arab, AL Posts: 491 Thanks: 109 Thanked 49 Times in 43 Posts	My radiant floor isn't completed, but I'd like to pitch in what I was told when I was getting design help from a radiant floor company up north. {Radiant floor system expertise is not easy to find in Alabama.} My project is a 24' x 36' garage / workshop with a 16' x 36' room upstairs. Radiant will be downstairs only, the upstairs is still TBD. I was told to put the 1/2" pex in the middle of my 4" slab, to insulate under the slab and insulate the perimeter of the slab. I used 2" of insulation around the slab perimeter as a thermal break, but I only put 3/4" under it. I'm certian more insulation would be better even for me, but I'm trying to heat a garage, not a home. Good luck on your project. BTW, if you haven't been there yet, be sure to check out builditsolar(dot)com. Lots of great stuff over there, too.

07-20-11, 03:50 PM	#8
The master plan Helper EcoRenovator Join Date: Oct 2010 Location: Central MN Posts: 50 Thanks: 0 Thanked 4 Times in 4 Posts	How much tubing did you use? Mine is going to be 24 X34. But I'm in MN.

07-20-11, 04:19 PM	#9
gasstingy Journeyman EcoRenovator Join Date: Feb 2010 Location: Arab, AL Posts: 491 Thanks: 109 Thanked 49 Times in 43 Posts	I bought three 300 foot rolls of Pex and used one and a half rolls. Again, my requirements are lower than yours. I installed three loops starting about 1' from the outside perimeter of the slab and spaced them at 2' apart. This should be adequate for my needs, I'm betting that the warm water in the tubing will warm the floor 1' in both directions. And it does feel like a gamble, since if I'm wrong there will be no remedy. One last thing to mention, a little tidbit I found after I finished the slab. You might consider leaving a little extra distance around your toilet(s). I read that too much heat will melt the wax ring that seals your commode. I'm hoping there is an alternative ring available if my floor gets too warm for the ring.

07-20-11, 05:46 PM	#10
The master plan Helper EcoRenovator Join Date: Oct 2010 Location: Central MN Posts: 50 Thanks: 0 Thanked 4 Times in 4 Posts	I was thinking of using 4 rolls of 300ft 1/2 pex. I built one awhile ago near here that was 22X38 and thought I used 4 rolls then. I know theres a calculator somewhere to give you a good guess. But why not use all 3 rolls? I would think plumbing the commode on a piece of plywood would eliminate any melting of the wax ring.