Replace church 60's steam system with hot water?

Chuck_17

I don't know why the engineer in 1964 selected steam for a church system that has fintube and reheat coils - but they did. (vacuum system)
The question is - Is it worth it to replace with hot water at this point.
There are 7 reheat coils all in the boiler room.
The piping is all steel but is easily accessed in a tunnel around the perimeter of the church.
I think they had water treatment at one time but there is none now. They do have a make-up water meter (so perhaps we can determine how much they are makeing up if they kept decent record).


My feeling is - if it ain't broke, don't fix it.
Any ideas? Things to look for?

The air handling units will likely have new cooling coils installed. So perhaps replace the re-heat coils with hot water but leave the fintube steam. (thinking out loud)

Jamie Hall

If it were mine to do, I'd definitely keep the steam -- both for the fintube and the reheat coils.

Makeup water should be minimal; if it isn't there is a leak -- or leaks -- somewhere and you'd need to fix those whatever you do.

The main two reasons I'd keep the steam for both are first, simplicity - not only, as you say, if it ain't broke, don't fix it, but also few moving parts. The second is the drastic loss in heat output when you go to hot water -- at best two thirds of the heat that you get from steam. This will affect the fintube more than the reheats -- you could probably go with much bigger reheat coils without that much fussing with the ducting, but why?

An argument is sometimes made that the older systems are oversized for modern conditions, what with improved insulation and better windows and yada yada. I doubt very much that this argument would hold water in a church, unless there has been major refurbishment (unlikely). Besides, one of the things usually wanted in a church occupancy is the ability to recover from a setback in a short period of time -- and that takes heating capacity.

Dave0176

The one question is “Why”? What’s wrong with the steam system, usually when this idea comes up the steam system doesn’t operate properly and most plumbers don’t know what their looking at or how to fix it?

JUGHNE

I work on steam systems in churches and schools that are anywhere from 102 years to 55 years old.
Even the youngest one from 1953 has fin tube convectors.
There are at least 4 minor leaks in that one and 2 of them would be a major PITA if not nearly impossible to repair. And this system never gets over 1 PSI operating......imagine 12-15 PSI of water.....the worst leaks would be in the piping tunnel. Never a fun place to try to use a 4' wrench.

One 100 year old school had a flange leaking, just dropping the pressure from 5 down to 2 stopped the drip. There is at least 300' of pipe tunnel for this one. Again try water at the 12-15PSI.
There are leaks that wait to be created there.

And then there of course will be the advantage of 95+% efficiency of a modern water system......which you will never get with fin tube that needs perhaps at least 180 temp.

A hospital I work on occasionally has steam heated heat exchangers for reheat on the rooftop units. That steam pressure cannot be dropped because of temp drop that may not operate the reheat correctly. So this implies high temp hot water needed for this purpose.

And as Jamie stated, when we want heat we want it now.
I was impressed how quick steam would bring a building out of setback, a fraction of HWH time and FAF would be forever.
IMO, FWIW

Chuck_17

Thanks for the replies.
Keep them coming.
I'll check what operating pressure they are using.

Chuck_17

I think to convert to hot water:
Assuming the fintube capacity is OK,
The fintube would stay, but all piping would be replaced.
Maybe some of the steam piping can remain?
The fintube has main (heat timer type) control valves on the steam mains. The traps are mostly below the floor (in the piping tunnel).

BTW I am leaning to recommending to retain steam but want to look at the options.
One option is to keep the steam for the fintube but put in a new hot water system for just the reheat coils.

Jamie Hall

Before you start tearing out pipe and otherwise costing the congregation a bundle of cash which they don't have, do them -- if not yourself -- a favour and leak test all the steam piping and intubes. All of it. If it passes, there is no need to replace any of the pipe. And do the leak test at an acceptable pressure for steam: no more than 5 psi, which is where the manual reset safety backup pressuretrol should be set.

This will most likely result in the discovery that you don't have to replace any of the steam feed lines, but it is possible that you will find a leak in the wet returns -- which are the only pipes in a steam system which are likely to corrode.

Then when you get steam back on the system, you can test the traps and the vents and repair the traps and replace (or add to) the vents as needed.

Now as to the reheat coils. What is the matter with them as they are? If there is some overwhelming reason why they can't be used as is, on steam, then either figure replacing them and keep them on the steam, or replace them and hook them up to hot water. Keep in mind, in the latter case, that, as I said above, they will have to be half again as large (that is 1.5 times as big) to put out the same amount of heat on hot water as they do on steam.

Chuck_17

Thanks again.
The reheat coils may need replacing or the entire air handling system (less the duct) may need replacing.
At the very least the controls (including valves)will be replaced.

Henry

We have done a number of steam to hot water conversions including Notre Dame Cathedral. During the winter we can have 30 straight days of -20F. Is there a problem to heat, nope. We did a large temple 6 years ago. The rooftop steam coil was converted to a glycol system. The rest was hot water. We took out two Cleaver Brooks 3 million BTU steam boilers (redundancy). We installed 3 HTP ModCon 500. We pulled the guts out of the steam traps and reused the return pipes. We had two leaks in the return piping over the years. Here is the new install.

Steamhead

Oh, yeah- this was the job you mentioned in this thread:

https://forum.heatinghelp.com/discussion/145002/actual-savings-over-steam-heating

where you tried to justify the horribly expensive conversion by claiming you reduced their fuel consumption by a third. Well, we've done the same thing for a lot less cost by fixing the steam. See our Find a Contractor ad for pics of one such job.

Canucker

Notre Dame cathedral in Montreal? @Henry

Jamie Hall

Canucker said:

Notre Dame cathedral in Montreal? @Henry

I do believe so, @Canucker -- if so, keep in mind that very strange things indeed happen in Montreal...

And if it was, I dare say that the Archdiocese had the money to pay for it. Not all churches do... I will say he did a beautiful job, and I'm sure the result is wonderful. Whether it was necessary to spend that much money to get a nice efficient heating system... well, that's another question, isn't it?

Ken D.

My experience has been that most leaks on a steam system have been on the return side, because that is where most of the water is, especially where the piping goes underground. With poor water treatment, it could be a good place to start.

Chuck_17

Any thoughts on controllability of steam air reheat coils vs. hot water air reheat coils? (assume reset on the hot water system)

Jamie Hall

Both are perfectly controllable. It's just the strategies that change. With steam, the simplest solution is to install a shutoff valve on the supply (full port, unless it's right at the coil) and turn it on or off based on the desired temperature of the airflow. There is, inherently, a dead band of anywhere from a degree to two or three degrees, depending on the thermostat used to control the valve. You can also use a throttling valve, if and only if you are right at the coil inlet. That will require a thermostat with a variable output and probably a driver. With hot water the principles are exactly the same -- turn a zone valve or pump on or off, or throttle the input.

Depending on your control system, you can use a reset or relative humidity control or whatever. That's a control problem, and has nothing to do with the heat source.

Chuck_17

The question is - is the dead band (if I have the term right) for steam coils inherently higher than a hot water coil with the hot water temperature reset based on outside air?

Jamie Hall

Chuck said:

The question is - is the dead band (if I have the term right) for steam coils inherently higher than a hot water coil with the hot water temperature reset based on outside air?

No -- the dead band will be a function of the sensor, the control logic -- and the desired outcome. Generally speaking one sets the dead band as a compromise between how often wants to start and stop the heat source (in this case, since we are talking heating here) and how much variation in the output one wants. More frequent starts, smaller variation.

There is a theoretical difference between hot water coils and steam coils; the latter do cool off more rapidly since there is no hot water left in them. They also heat up faster. This is not a factor if the air flow also stops, but needs to be considered if it is continuous. The practical difference is, in my opinion, not really significant.