Steam to Hot Water Retrofit / Conversion

[CDFO3]

I'm investigating the feasibility of converting an old steam system (circa 1980) to hot water. This is part of a major HVAC retrofit, and the goal is to do this as cheaply as possible. I've heard rumors that it's possible to retrofit steam coils and piping networks for hot water, at some reduced capacity, but I haven't been able to find any information on this.

Has anyone been involved with a project where this was done? Do you know of any articles / case studies about this? Please advise.

A little detail on the system:
Large air handling units (AHUs) have low pressure steam heating coils. Replacing the coils and piping may be cost prohibitive. Total heating capacity is about 2500 MBH. Most existing steam coils are over-sized by 100-800% based on recent peak load analysis.

 

[MechEngNCPE]

Never heard of this therefore I do not recommend. You would need to demo quite a bit if not all of your condensate piping due to pipe size, and all the prv's, traps,control valves, etc. along the way, install circuit setters, new control valves, pumps, etc... The rumors you have heard are just that... rumors.

 

[chicopee]

If you check the nameplate on the boiler, it should have an indication about its heat output either for steam service or hot water service. If the nampeplate does not bear that info, get a catalog about this boiler either on line or from its manufacturer for that info. With the appropriate control changes and the installation of a circulating pump your boiler should be able to be converted to hot water service. Steam lines may have to be downsized and heat exchangers may have to be replaced, check with the HX manufacturer.

 

[ChasBean1]

Agree with above - cheap here means keep everything. Also 100-800% oversize means have some good air blending because you'll be constantly tripping on freeze.

 

[willard3]

It's a bad idea to set the budget before you do the Engineering scope, only bean counters do that.

Most steam boilers can be converted to hot water, but many, many, many things other than the boiler must be changed/replaced top convert to hot water, ie, piping, valves, controls, terminal units and etc.

 

[Waramanga]

ha ha willard! budget before engineering! I have never seen that before!

seriously though, I would not utter one word on possible solutions (retrofit) etc until all the homework is done. I learnt that the hard way, opening my mouth and not putting the appropriate caveats out at the same time ie spatials, budget, service access.

 

[TBP]

The statement "the goal is to do this as cheaply as possible" should be a HUGE red flag. I know a mechanical contracting outfit that flat-out will not touch jobs like this, due to several disasters they've been involved in. Not only will they not perform such a conversion, they won't even work on a system that has been converted by somebody else.

I'd be willing to bet that for a fraction of the conversion cost, you can make your existing steam system almost as efficient as the proposed hot water conversion.

Good luck.

 

[Ziggypump]

Do you even know how a heating coil works, or how heat is transferred by hot water and steam? Steam has a few more BTUH capacity than 180 hot water. A hot water heating coil will be larger than a steam coil. Plain and simple. If you could retrofit the steam system, the heating coil will not heat the air properly.

How a bout the coil connections? None of the existing steam valves can be reused. All of that will have to be replaced for proper hot water usage.

What about the piping? If it is even possible to reuse the steam and condensate piping (very hard to believe you could), the size of pump for connecting would be outrageous. The artificial head from the triple-duty valve would be so bad you might not even be able to balance the system.

As an engineer, I wouldn't touch this without replacing the whole system. Keeping the boiler may be the only cost savings available. But now you have control changes and a new relief valve to install.

 

[seasicksteve]

Have you ever seen the inside of a steam boiler and piping?

very nasty black sludge that will be coming loose and circulating in the system,clogging valves,air seperators etc...
solution? water treatment to clean out the sludge.
however, the sludge is most likely sealing leaks in the system.
add this to the increased pressures you will encounter with hot water, and there will be leaks everywhere.

I have been involved in these types of projects before and they never turn out good.

Can you say change order?