storage tanks

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
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.

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

From what I think I understand from several engineering sites online, nitrogen is quite a bit less soluble in water than oxygen, especially at higher temps. I'm going to have 1000 gallons of propane storage,too. I'm really inclined toward using nitrogen. Here in Maine a 60 cu.ft. bottle of nitrogen and regulator are about $200. A big water heater or even another propane tank (100 gal.?) and some small fittings and valves could be a lot cheaper than a $500+ bladder tank of sufficient size. So it would take less nitrogen to keep the system topped up and it's less corrosive.
A question I have about non-bladder expansion tanks in systems is whether the gas in the expansion tank dissolves into the water and then effervesces off at a circulator and gets vented and then needs to be replaced by more gas,etc. or does the system water become saturated with the gas at some point and just go along after that in some blissful little equilibrium? This is a question for you pro boiler system guys out there.

The question isn't strictly nitrogen versus oxygen, but rather nitrogen versus air (which is already mostly nitrogen, anyway).

The air separator should feed back into the expansion tank, instead of venting to the atmosphere.

Joe

Yeah, I know. 70% N2. I was just trying to keep my pitch simplistic enough for my level of enthusiasm. I'm just trying to eliminate the corrosive component of the air. I just can't yet swallow the idea of paying as much for the expansion tank as the entire storage tank.

This is a revelation to me. Just can't exagerate how much I've learned on this forum from people who actuallly know something about these systems.
Is it as simple as just a tubing run from the top of the air seperator to the top of the expansion tank. Is this line left open between them all the time or valved off most of the time?
Sounds to me that the waterlogging of the expansion tank WILL eventually reach an equilibrium and need less gas added as the system 'matures'.

Just saying that the benefit will only be removing the 21% of the air that is oxygen, so whether that justifies $200 for a nitrogen tank, is up to you.

An example of the fitting used (a variety of manufacturers make them - this is just the first one that came up with a good picture):
http://www.bellgossett.com/productPages/Parts-Airtrol-Tank-Fittings.asp

Joe