lead dog, that’s exactly what the propane guy told me. He said the leak is so small it probably would fill with rust and be no problem. they test tanks over 200lbs. Zenon emailed me and said the same thing about expansion.the only problem Ive had is the propane guy sells heatmore , so access to hunt my property is payoff. thanks for all the help everyone. Im going to need alot more as I move along. Time to price the barn .Storage room getting bigger to hold a 16’ long tank. I’m a carpenter so at least I have a clue with pole-barns.

verne - 30 November 2007 09:00 AM

lead dog, that’s exactly what the propane guy told me. He said the leak is so small it probably would fill with rust and be no problem. they test tanks over 200lbs. Zenon emailed me and said the same thing about expansion.the only problem Ive had is the propane guy sells heatmore , so access to hunt my property is payoff. thanks for all the help everyone. Im going to need alot more as I move along. Time to price the barn .Storage room getting bigger to hold a 16’ long tank. I’m a carpenter so at least I have a clue with pole-barns.

Sounds like a go - excellent! Don’t scrimp on the insulation. A house has maybe a 70 degree difference between inside and outside. With the tank, you’re looking at more like a 170 degree difference. I missed a couple of posts - did anyone talk about sizing the expansion tank based on the extra volume of water in the system?

I was told I needed larger expansion but not how large.also would you use laddomatt 21. If so how do you wire it to go on off auto?

verne - 30 November 2007 10:06 AM

I was told I needed larger expansion but not how large

Okay, it’s been a while since I’ve done this (I typically deal with non-pressurized storage tanks, so my expansion tank sizing is usually for the heating loop itself)…

If I’m using the chart correctly, you have an expansion factor of 0.0351 (assumed for a worst-case 40-200 degree reheat).

So, if you have 1000 gallons, that means you need a tank that can accept 35.1 gallons.  Of course, you want to size this for the whole system, not just the tank, so add the fluid volume of each boiler, and a few percent more for piping.  It never huts to over-size an expansion tank, except when you have to write a check for it… (let’s call it 40 gallons, for the sake of discussion)

I’m assuming that you’ll go with a non-bladder tank, due to the cost involved with a bladder tank of the size you’d need…

You typically want to size your expansion tank to never fill more than 2/3 with water.  And you’re going to have some water in the bottom under “cold” conditions, to make sure that the air doesn’t leak down into the main tank.  So I’d suggest at least doubling the acceptance volume when sizing the tank.  Find an 80-gallon or larger tank, and use that.  I think a used water heater would likely be a good choice.  You can mount it above your propane tank, connecting to the “drain” tapping at the bottom.  Do yourself a favor, and have a valve immediately after the connection to the propane tank, so you can isolate the expansion tank if needed for service.

You’ll want to use a tee fitting there, add a valve and then a barb adapter facing up, and the same at the top, but with the barb facing down.  Connect a high quality (don’t skimp on this) nylon-reinforced clear hose between these two barbs, and double-hose-clamp each connection.  This is your “sight glass” which will let you monitor the tank.  The valves let you isolate it, for periodic replacement, if it hazes or leaks.

You’ll have to pre-charge it with compressed air, so that’s what the extra tapping on the top tee is for - add a valve, then a tee with a pressure gauge, then another valve and an air adapter of some sort (that’s up to you).  When you are filling, wait until you see water entering the bottom of the sight glass, then start adding pressure.  You want to keep at least 10 gallons of water in there, so make a mark roughly 1/8 of the way up.  Add pressure as you fill, making sure not to add enough pressure to push the water below that line.  Make another mark 1/4 of the way up, and make sure the water ends up below that (this is the cold fill - it’s going to go up as it heats).  Record the final air pressure (do it on scrap paper, then when you’ve run the systen a while and are confident that things are set right, mark it right on the tank with a Sharpie).

Since it is a non-bladder tank, the air will slowly dissolve into the water, so keep an eye on that sight glass.  Get used to how the water level raises as the system heats, and mark the initial “high” water line, the first time you fully heat the system from cold.  As the air is absorbed, that’s going to creep up.  Keep a decent safety margin, and periodically drain some water and add some more air.  This is what that valve on top of the propane tank was for - close it, then you can drain the expansion tank and re-adjust it without fighting the pressure in the main system.  Drain it to that 1/4 mark, and re-pressurize the air to the previous pressure.  Then re-open the valve on the propane tank and you’re good to go.

Joe Brown
Brownian Heating Technology
http://www.brownianheating.com

I was wondering about oxygen being absorbed from a non-bladder tank and is it a problem in a closed system. Would it be better to charge the tank with nitrogen. If you used nitrogen would it desolve in the water like air does .
leaddog

leaddog - 30 November 2007 11:29 AM

I was wondering about oxygen being absorbed from a non-bladder tank and is it a problem in a closed system. Would it be better to charge the tank with nitrogen. If you used nitrogen would it desolve in the water like air does .

Nitrogen will dissolve, as well.  It won’t cause corrosion when it does, so it is beneficial in that way.  I’m not certain, but it might dissolve quicker than air.

And yes, having dissolved air in the system can cause issues, aside from the corrosion.  It can bubble out and air-lock components, so having a microbubble resorber (eg, Spirovent) is very important.  Actually, it might be beneficial to actually use multiple resorbers, in critical locations, depending upon the design of the system.

Joe

I will be building my tank in the next few days, I have decided to use the wood approach with an EPDM liner, this will fit my location well. The tank size will be 6’ wide 6’ long 4’ high I will be using a flat plate heat exchanger to charge the tank. I will not have any heat exchanges in the tank, I am basically going to pull out of the bottom of the tank and then dump back into the top.
I will be using a completely separate loop to take the heat back out of the tank, I will pull out of the top of the tank to water to air floor or kick heater and then back to the tank. My thoughts are I will be able to pull more useable heat out of the tank with the forced air through the heater.

Any thoughts or ideas

Steve

Storage with water looks complex and expensive, expansion, corrosion, etc. Has anyone tried an insulated box full of pea gravel with a pex loop inside? Seems like it would eliminate expansion problems and pex seems pretty darn cheap to me. A crude estimate tells me a 4’ or 5’ square cube could replace 1000 gal water. I’ve got less than $3000 in my entire system (no storage). Bought junk Global hydronics OWB $300 wrapped firebox in copper tube replaced water jacket and filled with pea gravel for thermal mass. All this runs through a side arm heat exchanger for domestic hot water then to a pex floor radiant system with a small water to air exchanger for really cold days. Oh and I don’t use the blower on the OWB the aquastat set at 130 F only opens the air supply. That blower on the OWB looks like a HUGE WASTE of heat out the chimney. I,m only heating a modest home so this system isn’t for everybody. I’ve had a fire going every day for about 2.5 years now winter and summer. The boiler is off more than it is on. Pex in floor radiant is great I highly recommend especially for new construction.

atlarge54 - 03 December 2007 10:18 AM

Storage with water looks complex and expensive, expansion, corrosion, etc. Has anyone tried an insulated box full of pea gravel with a pex loop inside? Seems like it would eliminate expansion problems and pex seems pretty darn cheap to me. A crude estimate tells me a 4’ or 5’ square cube could replace 1000 gal water. I’ve got less than $3000 in my entire system (no storage). Bought junk Global hydronics OWB $300 wrapped firebox in copper tube replaced water jacket and filled with pea gravel for thermal mass. All this runs through a side arm heat exchanger for domestic hot water then to a pex floor radiant system with a small water to air exchanger for really cold days. Oh and I don’t use the blower on the OWB the aquastat set at 130 F only opens the air supply. That blower on the OWB looks like a HUGE WASTE of heat out the chimney. I,m only heating a modest home so this system isn’t for everybody. I’ve had a fire going every day for about 2.5 years now winter and summer. The boiler is off more than it is on. Pex in floor radiant is great I highly recommend especially for new construction.

Been a while since I’ve done the math, but water has at least five advantages:

1) More BTU storage per cubic foot, despite being lighter than rock.
2) Convection means that HX coils can easily access heat from water that’s not near the pipes.
3) You can pump the heat storage medium itself if desired.
4) Thermal stratification happens much more readily - gives a higher outlet temperature for the same average temperature.
5) Easier to service if there’s a problem.

You’re right that these advantages come at a price, and rock piles are a reasonable piece of the puzzle when designing heating systems. However, water was a clear winner in my situation at least.

I’m completely with you on radiant heat, by the way.

Rock works fine… if you have a lot of piping to get at all the heat.  As nofossil mentions, heat won’t flow around in a block of rock the way it will in water.

And, of course, all that air space in the pea gravel acts as an insulator (okay, that’s an over-simplification, but it detracts from heat flow).  Filling it in with sand can help.  Casting pipes into a big block of high-density concrete would be better.

Intentionally pouring an overly-heavy radiant slab (and adding baseboard or fan convectors to give you recovery - a heavy slab won’t respond quickly) can have some of the same benefits, in adding thermal mass to the system.

Joe Brown
Brownian Heating Technology
http://www.brownianheating.com

I’m thinking about putting a tile floor in my greenhouse, which is currently made up of bricks and pea gravel. One thing I’d like to put in is a floor drain. The other thing that occurred to me over the weekend is infloor radiant. I think that would be a more efficient way to heat a very inefficient space. Should help the plants on the floor, too.

Eric Johnson - 03 December 2007 10:57 AM

I’m thinking about putting a tile floor in my greenhouse, which is currently made up of bricks and pea gravel. One thing I’d like to put in is a floor drain. The other thing that occurred to me over the weekend is infloor radiant. I think that would be a more efficient way to heat a very inefficient space. Should help the plants on the floor, too.

Not only can you put radiant in the floor, but you can cast concrete planting beds/tables, with radiant in them.

If you keep the roots of the plants warm, they will do fine with lower air temperatures.  Less air temperature difference across the glass (indoor air temp - outdoor air temp) means less heat loss, and correspondingly less fuel usage.

Joe