Water storage; too hot in summer?

[jklingel]

The idea of running a boiler hot and heating a million gallons of water sounds great. I wonder, though, does that not make your house pretty warm in the summer, or are these tubs insulated well enough to avoid that? It seems that 1500 gallons of hot water has got to lose some of its heat. Curious. john

 

[Eric Johnson]

I'll let you know next summer, because that's what I'm planning to do.

I think the tank insulation will keep things under control. I think with 1,000 gallons of hot water in the tank, we should have enough domestic hot water for a week.

 

[Nofossil]

Mine's outside - no problem here. My solar panels did heat it to over 150F, though.

I really insulated the snot out of it - it only loses a degree or two per day through the insulation, even when there's a 150 degree difference.

 

[jklingel]

Nofossil: Thanks for the data. I wonder what an outside one would do when there is a 210 degree differential. It sounds like one inside would do very little heating, though I need to look at how many btu's a one degree change in X gallons of water equates to. What is it, again? One btu = 1 quart, 1 degree at STP? Or is that a calorie? Too many equations in the world.

 

[Eric Johnson]

I think a Btu it's the energy required to raise a gallon of water one degree, F. Or is it C?

 

[Nofossil]

1 pound of water 1 degree F.

Note that you will run into the problem of the difference between heat and usable heat. As I mentioned in another thread, thermal stratification is your friend. Think about it this way: Start out with a tank of 55 degree well water. In the stratified case, you manage to get the top of the tank to 155, with a uniform gradient to 55 at the bottom. With a decent heat exchanger, you could get very usable hot water out of it at 145 or so.

In the second case, with no stratification, you heat the whole tank to 105. With the same heat exchanger, you're not going to get hot water at more than about 100 - not very useful, even though the heat energy and average temperature is the same in both cases.

If I had it to do over, I'd have two tanks, with the smaller one for storing high temperature water.

 

[leaddog]

[
If I had it to do over, I'd have two tanks, with the smaller one for storing high temperature water.[/quote]

How would you pipe that. I have two stainless tanks that my son wants to use. One is 500gal and the other is 300
leaddog

 

[Nofossil]

[
If I had it to do over, I'd have two tanks, with the smaller one for storing high temperature water.

How would you pipe that. I have two stainless tanks that my son wants to use. One is 500gal and the other is 300
leaddog[/quote]

In my fantasy setup, I'd mount the small one above the big one, and plumb the HX coils in series. During heating, I'd introduce hot water into the top of the upper tank hx, where it would flow downward through that tank and then downward through the lower tank.

When withdrawing heat, I'd flow in the opposite direction, but I'd choose the lower, upper, or both depending on where the water was going. For radiant heat, I'd use only the lower tank. For domestic hot water, I'd use both in series. For heating baseboards, I'd use only the top tank.

If I couldn't place them one above the other, I'd place them side-by-side, but plumb them the same way.

I heat my storage tank with solar in the spring, summer, and fall. It ticks me off that I have 170 degree water coming off the solar panel but in some cases I can't get warm enough water out of the big tank to take a shower. The solar panel can only raise the tank temperature 6 to 8 degrees per day, so that 170 degrees going in may translate to a tank temperature of 110 - not nice. If the panels were heating a smaller tank first, it would get to usable temperature much more quickly.

If I didn't post a link to my system block diagram already, here it is. There's actually a lot of other info on the site - hope it helps.

 

[leaddog]

In your situation couldn't you take a 80 gal hotwater tank and use it for your top tank and your solar? Its not too hard to find a good 50-100 gal tank that is slighty used and that way your solar would give you hotter water and still heat your other tank.

also. what did you insulate your tank with. I looked on your site but you didn;t say what you used and why
leaddog

 

[Nofossil]

In your situation couldn't you take a 80 gal hotwater tank and use it for your top tank and your solar? Its not too hard to find a good 50-100 gal tank that is slighty used and that way your solar would give you hotter water and still heat your other tank.

also. what did you insulate your tank with. I looked on your site but you didn;t say what you used and why
leaddog

I have no good spot for an 80 gallon tank :-(

I haven't written up the insulation saga yet. Short version:

Sides:
1" EPDM foam
Aluminum foil (radiant heat loss preventions)
3/4" bubble wrap
1/4" aluminized double layer bubble wrap
1" foil-faced foam board
1/4" bubble wrap
fiberglass as needed to make it trectangular
1.5" foil-faced foam board
3/4 air space
1" foil faced foam board
1/2" plywood

Top:
parrafin evaporation reduction film
vapor barrier
EPDM sheet
16" layers of foil-faced foam board with air gaps

Bottom:
6" - 12" styrofoam peanuts
2" polystyrene foam
slab

 

[jklingel]

Nofossil: Interesting insulation layering. Why this over, say, 12" of some kind of foam board? What is EPDM, anyway? thnx. j

 

[Nofossil]

Nofossil: Interesting insulation layering. Why this over, say, 12" of some kind of foam board? What is EPDM, anyway? thnx. j

Heat is transferred three different ways: Conduction, Convection, and Radiation. In most cases, R-value is a conduction-only measurement. Materials with low emissivity such as foil radiate almost no heat at all. A 3/4" gap of still air with aluminum foil on both sides is a remarkable insulator, especially dealing with high temperatures.

Part of the reason for the materials is an attempt to minimize heat loss through radiation, part of it is driven by what I had lying around. The bubble wrap provides still air to help the foil do its thing, and I had a ton of it. Foil faced foam board is expensive. I'm cheap.

EPDM is rubber roofing membrane - also sold as 'pond liner'. It normally comes as a rubber-like sheet. It can handle high temperatures very well compared to most plastics. Roofing companies will sell used or leftover scraps cheap sometimes. I use it to cover my woodpiles as well.

 

[ozarkjeep]

the definition for calorie that I have always seen is the energy required to raise 1 gram of water 1 degree Celsius or (1.8 degrees Fahrenheit)

BUt Wikipedia breaks it down evven further.

* The small calorie or gram calorie approximates the energy needed to increase the temperature of 1 gram of water by 1 °C. This is about 4.184 joules.
* The large calorie or kilogram calorie approximates the energy needed to increase the temperature of 1 kg of water by 1 °C. This is about 4.184 kJ, and exactly 1000 small calories.
* The megacalorie or ton calorie[citation needed] approximates the energy needed to increase the temperature of 1 tonne of water by 1 °C. This is about 4.184 MJ, and exactly 1000 large calories.

 

[jklingel]

Nofossil: gotcha. good to know. man, by the time i get to installation, i may just know something....

 

[jklingel]

ozarkjeep: thanks. that explains the flush i get when i eat a few MJ's worth of peanut m&m;'s....

 

[alternative energy addict]

The idea of running a boiler hot and heating a million gallons of water sounds great. I wonder, though, does that not make your house pretty warm in the summer, or are these tubs insulated well enough to avoid that? It seems that 1500 gallons of hot water has got to lose some of its heat. Curious. john

I have installed many storage tanks, factory built and custom, the secret in my book is insulation, If you have about 6 inches of good rigid foam insulation , that seems to keep most the heat where you want it. 2 inches is barely enough , 4 is better , and I have found 6 to be enough to not know you have a tank of hot water in the basement in the middle of the summer.

 

[jklingel]

Wow. Has it been 4 yrs since I posted? Seems like last year. Agreed on the heavy insulation. I have been studying a lot over the years. My "problem" now is I will have very little heat loss (less than 2 btu/sf/hr, ignoring what we may be able to tweak out with passive solar) and it will be harder to justify the expense of a gasser, vs a couple of solar panels. I'll have to read up on solar. According to the procedure in Siegenthaler's "Modern Hydronic Heating", I will only need 83 degree water, and solar panels just may be able to heat 150-200 gallons that hot. A Garn is out of the question now, but a small gasser w/ 500 gallons of storage may do the trick. I have learned about masonry heaters now, and would love to have one of those in the center of the house, but my wife does not want the new place to "look like a hunting camp". And what is the problem w/ that, woman? Thanks for the info. With 8" to 10" of foam under the slab, 4" to 6" under the footer, and 12" outside the foundation wall, I can certainly justify 10" around a little water tank.

 

[alternative energy addict]

If you can make sure the tanks stratify, then the tank/s you have will be 100-200 or 1500 as long and the heat is put IN at the top, and taken OUT at the top, you don't have to worry about the size of the tank, and of course you have a nice BIG space to put, lots of solar or fire the boiler hard when you have time and "coast" on the tank.... EVERYONE that I know of that has 500-800 gallons , a year later wish they had at LEAST twice the storage
NO ONE has ever said they wish they had a smaller tank

 

[jklingel]

EVERYONE that I know of that has 500-800 gallons , a year later wish they had at LEAST twice the storage
NO ONE has ever said they wish they had a smaller tank

It's all a matter of how many btu's you need, how you'll heat the water, and how frequently you can regenerate what you use, as far as I can see. If you efficiently heat 200 gallons every day, and that satisfies your btu needs, then why have a larger tank? For my needs, I will have to first find out how much solar I have available (3 months will be kind of tough), and then calc how much storage water I need to provide the btu's I'll use. Then I can determine if a wood boiler is better than solar. A builder here, some of whose ideas I have shamelessly copied, heats primarily with passive solar. In the dead of winter, he burns a double armful of wood every day in his masonry heater. On approx Feb 15, when it was still dipping to nearly 30 below at night, he shut down his masonry heater. He has some features that I won't have, too. It is an impressive house. You can read about it here, if interested, and there is a blog about it on that site, too. http://www.greenbuildingadvisor.com/community/forum/general-questions/19942/sunrise-home I've got some data to collect and some numbers to run.

 

[ewdudley]

EVERYONE that I know of that has 500-800 gallons , a year later wish they had at LEAST twice the storage

NO ONE has ever said they wish they had a smaller tank

Well it's a year later for me and for as often as I ever heated enough water for all three 250 gallon tanks there would definitely be a case to be made for relying on just 500 gallons and freeing up the extra real estate for the third tank. I could sure use the space in the boiler room.

In our case there are a couple factors that would be significant.

First we delayed the boiler project for a year and in the meantime took to heart the hearth.com mantra that recommends eliminating infiltration, adding insulation, and eliminating infiltration.

Second it's a very old house with doors, and thus can be operated in the traditional warm living room / cold bedroom mode during the winter, with the option of heating up other spaces for guests and entertaining.

Third, I've set up the boiler to run flat-out at about 60k btu per hour, so there's more btus being stored in unburnt fuel in the firebox. I've throttled back the nozzle of a 150k btu per hour unit to do this and it works quite well, but if I had it to do again I think I'd get a nominally 25 kW / 85k btu per hour unit with a shorter and taller firebox that is more of a silo, like a Vedolux or a Froling.

--ewd

 

[jklingel]

There is no doubt about "build tight, ventilate right", and insulate more than you think you need. All the btu's in the world won't help much if the shell is open air.