Question re: converting 2-pipe steam to hot water

Dan Woolford

I have a commercial project I'm working on where there are presently old cast iron radiators working on a 2-pipe steam system. The client has requested to convert this to a hot water heating system. I feel I have a good grasp on everything involved, except one thing - the compression tank sizing. Is there any rule of thumb to use to estimate the amount of water in the radiators? Any help is appreciated.

Mad Dog

Save your client a ton of money and make the deadmen happy

and restore that steam system. We'll help you do it too. toom many varibles and risks to converting. Mad Dog

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Dan Woolford

Well, that was my original idea...

but was informed until *after* I had made my site visit that the client now wants hot water... blah. I've argued against it, but people who outrank me by a large amount have said "hot water." Sigh...

Jamie Hall

Pity

They'll regret it... and blame all the problems on you. Been there, done that. Don't like the T-shirt one bit.

Steamhead

Dan, have them take a look at this

http://www.heatinghelp.com/newsletter.cfm?Id=22

It describes the pitfalls of this type of conversion.

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Unknown

If they change to hot water

Run far, far away if they intend to use the 90 year old piping for the new hot water system. If they go hot water, strip the old system completely out and start NEW, as they will expect it to perform like a new system.

How can pipe that old be warranteed, when it was never designed to be a water system sized to the job.

I'd keep the steam, for two reasons. It was designed for the building, and it will cost less money to restore the steam than to, A) rip it all out, or B)move in with the customer to handle all of the complaints about the converted steam system.

Of course, there is an outside chance that when you do a heat loss survey, all of the steam radiators are exactly the right size for whatever water temperature you design the "new" water system to run at.

Not likely, though.

Noel

Dan Woolford

This one does worry me...

...but all I can do at this point is all I can do. They are getting all new piping, starting at the boiler all the way around until the pipe works it way back to the boiler (expensive I know). This isn't the worst pipe I ever seen, but it's a close second. Not to mention zero sign of ever having seen anything that remotely resembles water treatment - they are getting that now too.

I have a few of those t-shirts in my closet, each accompanied by a paper trail about 5 miles wide .

Unknown

Well.....

If it gets piped as a two-pipe system, each radiator could be it's own proportional controlled zone, with Thermostatic Radiator Valves.

You would have a very well controlled, reset by load (the TRVs), comfortable system.

Still a winning proposition, keeping the radiators. The maintenance will be much lower than the steam, but it would cost some, up front.

Are the radiators coming out, too? Are the radiators connected across the top and bottom?

Noel

Dan Woolford

They are

connected at the top and bottom. I have to keep the radiators - historical value and all, but I'll have the contractor flush and clean them prior to connecting them to the new heating water piping.

I'm putting air-conditioning into the building as well (split DX), so I was thinking of blowing some air over the radiators during heating to help draw some heat out of them (from a floor register located directly under the radiator), plus that has the benefit of meeting outdoor air ventilation requirements.

Unknown

Sounds like a plan

That set/up is similar to indirect heating, from the beginning of the last century. They brought outdoor air into a box that contained the radiator (usually all located beneath the floor) and let the air rise into the room through a grate.

If you use TRVs, you'll have a really nice system that resets the radiator temperatures to meet the load, without expensive controls.

Noel

Dan Woolford

I think I will

go with TRV's. Seems like the best way to control, especially since the cost will be lower than any other control method. Each space will have it's own control, and capacity will be reset based on each space's current requirements. Works for me.

Thanks to everyone for their input.

Dan