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Generating hot water from one-pipe steam?

ColdPump Member Posts: 3
New Wallie here, posting for the first time, from the Great Wasteland o' Scorched Air no less (hydronics exist, but are not common in residential work, and steam? unless you're on district/campus heat, what's that?), with a bit of a steamy theorycrafting question as I've been mulling over loads of alternative ways to get heat around a building, if nobody minds.

One of the goals that I have for any non-scorched-air heating system (hydronic, steam, or the likes) is that it be able to service all types of heating demand in the building or space from a single plant, as there's no sense in having two appliances that take fuel and cold water in and spit heated water and flue gases out. It's more fuel piping, more combustion air intake work, more venting, more places for gas to leak, more potential for venting problems, and generally just not as good as having one combustion plant that does all the work. (If you need redundancy, it's better to have multiple boilers in one plant instead of multiple plants serving individual loads; that way, no single load can be rendered unserviced by a single failure.)

For hydronics, this is relatively easy using (regular or reverse) indirect tanks to feed DHW loads, or brazed-plate exchangers if you want a fully tankless approach for that matter. On first blush, the steam folks have taken that gambit and matched it, with a variety of heat exchanger setups (steam in shell, steam in tube, and even brazed plate) available for generating hot water from steam, in both instantaneous and storage setups. However, while I was reading the IOMs for several different makes and types of steam-fired hot water generators, I noticed something odd: every single unit I can find provides installation instructions that are exclusive to two-pipe steam systems, even for your most basic steam-in-tube storage configurations.

This, to me, makes not a whit of sense. How is a heat exchanger coil in a tank of water any different from a radiator in a room in terms of thermal massing and ability to condense steam? What stops you from connecting the branch line to the lower port on the steam side of the exchanger and a one-pipe TRV with an air vent and a suitable actuator/remote sensor (Danfoss makes a version of the RAVK that's set up for hot water cylinder service, with a maximum setpoint of 65degC) to the upper port on the steam side? Would this not work, for some reason or another? What am I missing here? Surely, I'm not the first bloke on the planet to think of this idea!


  • Jamie Hall
    Jamie Hall Member Posts: 23,272
    You're not the first bloke. It's done all the time -- well, not all the time, but it's common enough. You can take hot water direct from the boiler or through a heat exchanger arrangement, and it doesn't matter one bit whether it's one pipe steam or two pipe steam...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ColdPump
    ColdPump Member Posts: 3
    edited March 2020
    I am aware of setups that derive a hot water zone from the condensate in the boiler and use that to fire a hydronic-type indirect tank or water to water heat exchanger, yes. However, that's not what I'm wondering about here -- I'm thinking of water heaters that accept live steam as their heat input. (Why? Because it means you don't need two separate sets of heating piping if you have more than one hot water generator in the building. Think of a multi-tenant application with individually metered water, for instance.)
  • JohnNY
    JohnNY Member Posts: 3,229
    So you want to use a steam-to-water heat exchanger and make steam every time you need hot water? Sure. It's done in high volume restaurants and in industrial applications. Look at Aerco for your heat exchanger. It'll cost you a fortune in equipment.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
  • pecmsg
    pecmsg Member Posts: 4,837
    Plate frame or Shell & tube heat exchangers will work but a indirect water heater using the boilers water is easier.
  • ColdPump
    ColdPump Member Posts: 3
    The Aercos were among the hot water generators I looked at, yes, although I am more interested in simpler designs (such as the Hubbell PS series) for the purposes of this question.
    JUGHNE Member Posts: 11,058
    Redid a hospital job that fired a good sized steam boiler all summer long to produce hot water, via insert heat exchanger. The boiler room would approach 120.....the temp of the water delivered to DHW system.

    We added HTP condensing water heaters. Simpler system....less hours on 40 year old steamers.....cooler room. Could shut down both steamers for summer maintenance.

    EBEBRATT-Ed Member Posts: 15,512

    It's not so cut and dried as to have a heating boiler and a water heater or one combined appliance.

    Like @JohnNY pointed out a commercial or industrial job that require a lot of DHW may be better serves by on appliance

    Other jobs such as residential maybe not somuch. Depends on the heating and hot water loads, available fuel etc
  • dopey27177
    dopey27177 Member Posts: 887
    looking at the topic name. generating hot water from one pipe steam the solution is to lock out the the heating system in the summer by installing a zone valve. The installation of the zone valve will require a master steam trap and a condensate feed pump and tank set.

    This method to use a boiler that supplies steam to a one pipe steam system is quite expensive plus the cost of of a unit that will use steam to heat the water,

    Basically the most economical way to use the boiler for producing dhw is installing a submersed coil. Or a separate dhw generator using gas or oil as the fuel to produce dhw.

    Been around for many years and seen hundreds of installations.
    We need to separate commercial and industrial use from residential use.

    In residential use the amount of dhw needs is paramount. Some times running a large boiler to produce steam is not cost effective. In situations such as this there better options on being a Laars unit gas or oi fired not part of the heating system.