Steam to snowmelt ...HELP!

kevin_5

Here's the deal. 2,100 square foot of snowmelt on a rural 1959 highschool. (315,000 btu load)A Huge Fitzgibbons Boiler Co. New York NY
steam boiler. (only I didn't realize it was STEAM) Something like 4500 MBH input. Shut down for the summer months. They have it opened up for cleaning and inspection. I thought to myself that it's big enough for Dan to have been birthed in the thing.

I foolishly thought I could tap into a 6 inch line, add a simple brazed plate heat exchanger a couple circulators, and the rest of the usual stuff.

After hanging out in the tunnel O' Pipes for a while, a dim light started to glow in the back of my mind, I recalled a few things I'd recently the read in, "The lost art of steam heating", and I recognized two things.
#1 This was two pipe steam. and
#2 I suddenly didn't have a clue.
I should have recognized it immediately, but I didn't. Looking around a bit more, I found a vacuum pump the size of a small dishwasher. That should have been a good clue.

It all seems so obvious now, but when I first saw the place, I hadn't yet bought "The Lost Art" and I was even more ignorant than I am now.

My supplier is very on the ball hydronically, but admits to being a little short on steam knowledge. I told him I'd swallow my last bit of pride and tell the wallies what I did. (or wanted to do)
He's looking into either:
#1, a B&G SU shell and tube heat exchanger to utilize the steam line,
or #2,tapping into the boiler for some hot water like we read about in "How Come?"
The worst part of #2 would be that it's roughly 150 feet of 44" X 44" tunnelfrom the boiler room to where my manifold leaders enter the footing/tunnel and my heat exchanger wants to be. Also, 10 foot lengths of pipe is the longest you can get in there. I don't even know what the worst part of #1 is. Is it even possible? How big of tappings would you need. There is a local portable welding service that is very good. The boiler inspector tells me that down in the tunnel and away from the boiler room there is no need of an "R" stamp, so this welder is qualified. 6 inch steam line and 2 inch condensate returns.(The condensate lines had all been insulated and then had all the insulation removed and laying in the tunnel, how's that for another clue?)

So what would be the best option guys? Pros and Cons? Is there even an option at all.

Also in the boiler room is a recently added Raypak 500,000 BTU output water boiler. It appears to supply all the domestic hot water though a 1 1/4 supply and 3/4 return. It and the monster boiler both are connected to a big tank about 16 foot by 4 foot that is way up in the air over the boiler.
Please educate me a bit on the function of the tank. I'm guessing it is some sort of heat exchanging steam/water tank to couple the two boilers together and share the load.

As humbling as it is to get in over your head, it sure feels great to have access to a place like this. Thanks in advance for the help! Kevin PS sorry I can't post photos yet, we are still trying to make that work. Ill be gone till Tues, but will check back then.

Mark Eatherton1

Weighing the costs...

You must first look at feasability and future service. If you go with the remote HX idea, can it be worked on in the tunnel? It occasionally becomes necessary to yank the tube bundle. If yes, then begin weighing the costs. The HX needed to use the condensate will be slightly more than the remote HX, but then again, you won't need the accouterment of steam traps and modulating steam valves etc.

My gut hit says set a HX next to the boiler and use the hot condensate for the heat source. But then again, theres a little bell going off in the back of my head that says "Hey, just use the hot condensate return line in the tunnel as your heat source!!" Have you thought of that avenue? Only negative I can think of there is that the returns are usually loaded with a lot of gunk. You'd definately want to use a low fouling factor heat exchanger...

The tank over the Raypak is probably just storage, and used to be hooked to the steam boilers, and may still be for winter use or summer back up in case the Raypak goes down.

Let's see what the others have to say.

ME

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Tony Conner

Usually, The Tricky Bit...

... with steam to "whatever" HXs is condensate removal. The vacuum pump should help take care of that, but I'd think about locating the HX right in the boiler room. The condensate could just drain by gravity (assuming you've installed a vacuum breaker), right into the receiver. Put the pump/expansion tank, etc for the snow melt in the boiler room, and run the supply & return glycol lines in the tunnel.

My experiences with running steam at any pressure in plate HXs (brazed or gasketed) are not great. The brazed ones tend to crack, and on the other style, the gaskets are prone to failure.

One nice thing about steam HXs in applications like this, is that there's no worry about condensing flue gases in a boiler because of low return temps from the loop.

Canuck

I can't concur

about the plate exchanger not being a good idea (non-brazed). Alpha-Laval offers great technical help into applications much like the situation you're in. We've done a fair bit of work up here with steam to domestic hot water on plate HX's. A Honeywell or equivalent modulating valve on the steam side to regulate your glycol temp. and piping with trap as per usual for the condensate return after the HX.

http://www.hvac.alfalaval.com/