Hot Water Storage

[Eric Johnson]

It's going pretty well. I got the cistern cleaned out and poured a little mortar mix into a form on the top to level everything out, and sunk a few studs to hold the 2x6s down around the permieter of the tank. This weekend I'm going to lay up the block along the one wall to create the 1,000-gallon enclosure and put in the foamboard. Then I have to order the pond liner. Given the price of fuel, probably best to do that before shipping charges go even higher.

I have some concerns about priming the pump and keeping it from cavitating when it's hooked up in a non-pressurized environment. I have a nice Grundfos 20-42 3-speed pump that I was going to use on the tank side of the heat exchanger, but now I think I'll just go with a $50 Taco 007 from Ebay and see how it holds up in a semi-oxygenated, possibly-cavitating application. I thought it would be fun to fool around with the speeds, but I have other places on the system where it will be just as fun if I put the pump somewhere else.

My plan of attack on this project is to peck away at it over the summer, working on different elements of the piping as time and spare change allows. It should be ready to go by late July or early August, and that's when I'll have the boiler delivered.

I'll post pics of my progress on the tank over the weekend.

 

[Reggie Dunlap]

Eric,
Sounds like you are making good progress. When will your new boiler arrive?

I just gave Tarm a deposit on the Solo 40 boiler. I went down to their shop in Lyme NH and looked at how they set up the system that heats their building. It's pretty impressive. I was planning on not having a storage tank, now I'm not sure. I'm tempted to try a 500 gallon pre-cast concrete tank in my basement which I could buy for around $500. Any thoughts on this?

Reggie

 

[Eric Johnson]

I'd wait and see how mine works out, since it's basically the same thing. My pre-cast tank is just built into the foundation, is about the only difference. Actually, you might want to consider building a block enclosure in a corner of your basement. Two walls and you've got your tank, for a lot less than $500 and it's easier to move cinderblocks than a concrete tank. It doesn't even have to hold water, since you have a liner for that. Or instead of concrete, build the two walls out of plywood and studs.

A pressurized tank (like an old lp "submarine" tank) is probably the best way to go. I'm told they go for about $1 a gallon, so for the same price as the concrete tank, you could get a steel tank that doesn't require a heat exchanger. Much better in many ways than a non-pressurized tank.

But if you want to go unpressurized, I should have mine up and running by September, and then you can learn from my experience before making a commitment.

My understanding is that gasifiers will work without hot water storage, just not as efficiently. A tank gives you flexibility to run the thing under optimum conditions. Check out my other thread in this forum for more information about HW storage.

 

[Reggie Dunlap]

I was thinking about lp tanks also. I called my local gas supplier and they claim that a new 500 gallon tank would cost me $2500. I thought that was a little steep. You are right in that a steel tank would be nice-no heat exchanger needed. The precast tank is the lower half of a 1000 gallon septic tank, I was hoping it would be watertight and not need a liner. My plan was to spray expanding foam insulation around the outside of the tank. That way the 5" thick walls of the tank act as a thermal mass along with the 500 gals of water.

Reggie

 

[Eric Johnson]

That might work pretty well. The LP tanks people use for hot water storage are used--they get them right before they go for scrap. What's the difference between a new LP tank and a used one? I have no idea.

 

[Eric Johnson]

I worked on the tank over the weekend and managed to get about half the wall up. It's about as high as I can make it now, and comfortably work inside with the liner and the foam insulation. I guess it's time to bite the bullet and buy that stuff and get this thing done. If it ever warms up, I'll be able to get into the piping end of things. Anyway, here's a few shots of the progress. Obviously, I'm no mason.

 

[Eric Johnson]

Here's a couple of "before" pics.

 

[slowzuki]

That pic reminds me of wifes grandmas house. After she died we were staying there and wh has a cistern. Hadn't thought too much of it and I used the tap to brush my teeth and flush the toilet. After a few days the pump was making noise in the basement and we went down to see. The is was leaking pretty bad and I got to peeking around. Flashed a light across the cistern and just about choked, 4 big bloated rats floating around on top!

 

[Eric Johnson]

Got the 45 mil Firestone pond liner today. It's basically just a rubber sheet, about the thickness and appearance of an inner tube. It's going to be a lot easier to work with than I thought. Think tarp.

 

[wg_bent]

Got the 45 mil Firestone pond liner today. It's basically just a rubber sheet, about the thickness and appearance of an inner tube. It's going to be a lot easier to work with than I thought. Think tarp.

what are you using to seal the seams? What's the top going to be?

 

[Eric Johnson]

Here's the diagram, Warren.

No seams except where the lid meets the walls, as shown. I'm using a 15' x 20' sheet for the tank and a 5 x 10 piece for the lid. I think any roofing cement designed for a EPDM rubber roof will do the trick, but I'm not going to seal it all up until I know it works.

 

[wg_bent]

So just curious... rather than use a heat exchanger, why not use a giant coil of copper? From experience in cooling beer (which includes some knowledge of small commercial installations) copper coils work well. Most large breweries do use heat exchangers but a lot of the reasons for that are ability to sterilize the equipment, but in some smaller installs I've seen, the hot liquid is run through a copper coil immersed in cold liquid. 4 bbls or beer (100 gallons or so) can be cooled from 212 to about 80 in 20 minutes. That's a pretty fast transfer rate and dirt simple.

You'd need a second coil to pick up the domestic hot water and a third for the hydronic heat though.

 

[Eric Johnson]

Copper coil is the way it's traditionally done, but at $2-$3 a foot for 3/4-inch soft copper these days, you're talking real money for any decent heat exchanger. Guys I've talked to who have 60kw Tarms and 800-gallon tanks have about 600 feet of coiled copper. I'm going to try to do it with a $250 flat plate and a $50 pump.

I'm confused about your 3-coil suggestion. Are you saying use one coil to charge up the tank and another one to reclaim the heat? That sounds more efficient, but a lot more complicated on the pumping and piping end of things.

For DHW, I already have a shell and tube heat exchanger hooked up to my electric water heater that works just like another zone on the heating system, and it works great.

 

[wg_bent]

O.k. I missed the point on the DWH and the way you've got it hooked up. so yes, 2 coils. Wow, that would be like 2400 bucks worth of copper tubing. I can see why your going with the heat exchanger. It's been a while since I've bought copper tubing in any form. I wonder if there isn't some sort of radiator system that could work. Like 3 or 4 car radiators hooked together or something like that. I'm just thinking out loud... sounds like the heat exchanger is the way to go. I was wondering about the insulation also though. think 1 layer of the foam is enough? I have no idea, just thinking out loud again. (I tend to over build EVERYTHING I do. My basement has like R26 insulation in it!)

 

[Eric Johnson]

I thought about a couple of cast iron radiators and slowzuki is talking about using a car or truck radiator on his system. I also thought about finned copper baseboard, which I have a supply of. But in the end, I decided to go with something I'm familiar with, which is the flat plate. In fact, I'll be using the same one that's currently getting the heat from my wood boiler (glycol) into the house system (water). It works great hooked up to two pressurized systems. How it will work with an unpressurized tank, remains to be seen. Obviously, there's no optimum way to pipe the inlet and outlets, since the heat exchanger will be delivering heat part of the time and recovering at other times. But tweaking it will be part of the fun.

Every tank design I've seen, including the commercial units, use the 2-inch foam. You need to use the more expensive, foil-wrapped yellow stuff. Conventional blue and pink foam can't take the heat, apparently. So that's $30 for a 4x8 sheet. It makes a really nice surface for the rubber liner to rest against.

 

[slowzuki]

Eric I'm a bit concerned about the idea that it can't take the heat, I've got that stuff under my steel roof.

I've found another milk tank and will be putting in an offer today. It is an 800 gal tank on a skid c/w compressor and condensor and fan. The evaporator coils outside the tank are blown and the compressor seized when it lost the coolant.

I'm thinking 1$ a gallon for my offer.

 

[Eric Johnson]

That's what I've read, but I wouldn't be surprised if it's not true. Anyway, intermittent heat is probably different than more-or-less constant temps between 130 and 190, which is what I hope I can get. Worst case scenario, you might wind up with mildly corrugated foam boards.

That's a big tank. I'd say that $1 per gallon for ss sounds good.

How are you going to get the hx into the tank, slowzuki?

 

[titan]

Copper coil is the way it's traditionally done, but at $2-$3 a foot for 3/4-inch soft copper these days, you're talking real money for any decent heat exchanger. Guys I've talked to who have 60kw Tarms and 800-gallon tanks have about 600 feet of coiled copper. I'm going to try to do it with a $250 flat plate and a $50 pump.
Eric, is the plate exchanger similar to ones found in hot water- to-glycol heating systems?If so,it should be the most efficient, as they offer a lot of exchange-surface area in a reasonably small package.

 

[Eric Johnson]

Yes, the same piece of equipment. The one I have is rated at 150,000 btus per hour. I have no way of verifying that, but it has heated our big old house for the past four winters when mated to a 150 Kbtu wood boiler, so I know it's capable of charging (and discharging) the tank if I can get adequate flow through it. The new boiler is going to be about 200 Kbtu, but not all of its output is going to the heat exchanger and the tank. Some is going directly into the house.

 

[titan]

Eric,200,000 btu's-that's a mother of a boiler!If you were really bored you could run PEX tubing under the driveway and use it as a"dumpzone" from that system.Goodbye shovels-hello snowmelt. :coolhmm:

 

[Eric Johnson]

I've got a 12x24' single-pane greenhouse for a dump zone. I've got a 1" copper line going into the tank and will have a 3/4-inch pex loop into the greenhouse.

 

[wg_bent]

That's what I've read, but I wouldn't be surprised if it's not true. Anyway, intermittent heat is probably different than more-or-less constant temps between 130 and 190, which is what I hope I can get. Worst case scenario, you might wind up with mildly corrugated foam boards.

That's a big tank. I'd say that $1 per gallon for ss sounds good.

How are you going to get the hx into the tank, slowzuki?

The foil lined stuff is more R value/ inch and cheaper anyway. be sort of cool to install one of these things in my crawl space. I have a crawl space that's the size of my dining room and kitchen combined but is only about 3' tall. I'll be watching how this works closely. Keep us posted Eric.

 

[keyman512us]

Yes, the same piece of equipment. The one I have is rated at 150,000 btus per hour. I have no way of verifying that, but it has heated our big old house for the past four winters when mated to a 150 Kbtu wood boiler, so I know it's capable of charging (and discharging) the tank if I can get adequate flow through it. The new boiler is going to be about 200 Kbtu, but not all of its output is going to the heat exchanger and the tank. Some is going directly into the house.

Eric...
I still like your idea of the radiators...I'm no engineer, and I know "everyone has chimed in on the subject" but a cast iron radiator (submerged in water) is going to have a higher heat transfer rate than it would trying to exchange heat to "free/open air"

If you already have the radiators....I would try it out...you "might be pleasantly surprised".

 

[Eric Johnson]

I'm going with the flat plate, keyman, but maybe if I do a second tank I'll give the rad idea a shot. I think you're right that they will transfer more heat in water than in air. That's a lot of surface area on those things.

Anyway, after doing some plumbing re-routing on Saturday, I bit the bullet and bought the insulation on Sunday and since it was raining, decided to put it into the tank. That went pretty well, so I gave the liner a shot. Here's a few pics.

The middle one shows some rough-cut 1x8s that I secured along the top of the tank to have a place to staple the edges of the liner.

The next couple of shots show the insulation, 2-inch poly-whatever, in place.

 

[Eric Johnson]

Here's a couple of shots of the rubber liner being installed. It's not easy to do, in part because the big sheet of rubber (15x20 feet) is rather bulky, and it has to be hung just right to fit. I'm working on it. Patience has been paying off so far. Glad I put in the wood on the top and glad I didn't try to build the whole wall first. I pretty much have to get the liner hung just right before I finish the cinderblock wall, then put the rest of the blocks in, measure the space for the lid, and put that together.