Humidification from steam heating system

Brad White_191

Hi Carl,

Firstly, congratulations on getting your steam system to the point that you did.

On the off-chance that someone might think to use direct-injection of boiler steam, let's stop that idea in it's tracks. I know you said re: radiator pans and that is fine, but I just want to cover the "what about boiler steam" issue as it comes up in my work often enough.


Every pound of steam you emit into your space to be humidified is a pound of water to be made up into your boiler if that is the source. It is lost forever as far as the boiler is concerned. Cast iron steam boilers are not made for this and it will shorten the life of the boiler.

One way that I have done uses higher pressure steam to make lower pressure steam in a stainless steel vessel made for the purpose. This too is perhaps above what you need.

I would suggest ultrasonic humidifiers for you or these "slipper pans" which were made and are again made for the large-tube radiators. I have seen these in some large houses with a small bleeder valve of cold water, copper-plumbed to the pan for convenience. Not saying you should, just that it was done.

But there is something else I would consider: Your 1920's structure. Can it and the materials which comprise it, withstand artificially generated humidity? If the envelope is tight, you may force enough vapor into the wall to damage masonry (this if not controlled) and if the building is not tight, your humidity quantity will be large to meet setpoint.

Back to the quantity of steam you need, just a ballpark. I have no idea how many SF your building is, but let's say that each floor is 2,500 SF and 16 floors brings that to 40,000 SF, just a guess. If you have 9 foot ceilings, that would be about 360,000 cubic feet.

If the entire building loses 0.5 air changes per hour to infiltration (forgetting diffusion through the building walls for now), you would have an hourly loss of 3,000 Cubic feet per minute (CFM). This at winter outdoor temperatures (10 degrees F. and even if saturated) is 15,165 pounds of air per hour leaking in and out....from 10 degrees to 70 degrees and say 30% RH.

(OK, Brad, get to the point now...)

You need over 424,000 grains of moisture per hour or 60.6 pounds of moisture per hour (over seven gallons per hour) of make-up water if you used your boiler.

If you had a leak like that in your steam boiler or system, you would do something about it.

Think about not humidifying at all or just let folks use their own ultrasonic humidifiers if not pans on or in their radiators.

That would be my $0.02 anyway!

Brad

Carl_21

Humidification from steam heating system

I am on the building committee of a 1920's era, 16 story coop apartment building in Chicago. My building is heated by a true 2 pipe steam heating system that has been well maintained and upgraded as new fuel and control technology has become available. In fact we have increased efficiency so much over the years that we have removed one of the original 3 boilers and now run only one of the remaining two, using the other as a backup (which we test annually). As a result, our ability to generate steam is far greater than what we need to heat the building. My question is whether we might use this capacity to increase relative humidity during the heating season through some kind of device mounted on selected radiators in our apartments.

Big Ed_4

What a Nice Idea Carl

A simple humidistat and valve to release a little steam into the room would do the trick .We have to be careful as the out door temperature drops so must the percentage of humidity or condensing will form on and in the outside walls . Adding an outdoor sensor would make it fool proof . A self contained screw in type would be nice for residential like a HRV .


Better then putting pots of water on the radiators..........

nicholas bonham-carter

humidity

my hygrometer tells me my indoor humidity is 2% in spite of having nice copper pots on the rads. a fish-cooker [long and thin] is very atractive, but not so effective.
i would be worried about adding all that fresh water into the system with its oxygen. in addition there could be some sort of problem if at the start of the steam cycle all the humidistats were calling for steam release.
the simplest method would be to buy some very cheap air vents, and modify them to close on a higher temperature, so they leak some steam at the start of each cycle.
perhaps someone here has a bucket of vents with just those qualities!--nbc

David Nadle

Time for a new hygrometer!

nbc, 2%? That's really dry. I would check that hygrometer against a known good. Or leave your hygrometer overnight inside a ziploc back with a cup containing salt and just a little water to make it moist. In the morning the hygrometer should read 75%.

Big Ed_4

Ok I hear you Brad , but I like the idea too much

How about installing a hot water heater to preheat the make up water. Would that take the sting out of the water ?

Frenchie

Big Ed, I like your idea. If the incoming makeup water was good and hot from a WH, that should strip a lot of the oxygen out, no? Am I missing something? Maybe an air vent on top of the WH?

Carl_21

Thanks for all of the input!

My building is largely self-managed and luckily we have always had somebody in residence that knew boiler technology. I am the "new generation" of resident taking over this responsibility but even though I am an engineer, I am new to boiler tech. I just ordered "The Lost Art..."

Increased Oxygen and therefore accelerated corrosion due to the increased demand for makeup water -- I hadn't thought of that. Impact on our masonry is another good point and a topic I know very little about.

Brad, I realize this may be economically impractical but assuming we could make the economics work (and we could address the masonry / condensation issues), would a deaerator rebalance the scales for boiler lifetime?

Ours is a pretty big building as vintage buildings go: 66 units total averaging 3,000 sq ft each (4 per floor plus a couple of penthouses). As a result, we tend to be able to justify add-ons like this that smaller buildings could not. For instance, we already have an automatic flue damper, a parallel positioning air-fuel mixer, multiple temperature and wind sensors, and 4 independently controlled steam circuits all managed by a modern control computer -- and all of this attached to our 1926 boilers and economically justified by input-output analysis of the system and, I was happy to learn, confirmed by follow-on analysis.

Adding humidification would obviously cost us net -- both the equipment and increased fuel and water consumption. So I realize that it wouldn't really "pay for itself" like the efficiency add-ons. But with this our objective is obviously to improve comfort and health, not fuel efficiency. I love the fact that steam is fundamentally safe biologically, especially when compared to typical humidifiers attached to forced air systems.

So assuming the cost didn't scare the residents and we could control RH so as not to damage the structure, would a deareator allow our boiler to generate humidity by direct injection without sacrificing lifespan? Or are there other issues at play, such as, as Nicholas fears, messing up the cycling and thereby stressing the boiler in other ways?

(Big Ed -- we are on the same frequency.)

Brad White_191

Big Ed

Hi Ed!

Well, if you pre-heat the water on the way to the vapor state, you only get, at most, 162 BTU's per pound, assuming you can pre-heat the water from 50 to 212.

The next 960 BTU's per pound will bring that into vapor state. In other words, you don't get a huge "baseline" boost, but it cannot hurt either.

A water heater might get you to 140-150 depending on through-put, so your net baseline would be lower of course.

Point of fact, we used to design all of our "electric to steam" humidifiers that way, using domestic HW for make-up. Of course, with cycles, the water that was to be "hot" was often room temperature and only got hot by the end of the fill cycle, so now we use whichever is the nearest quality source.

Cannot fault your logic, but it is less of a benefit than one would hope, in my opinion.

Brad White_191

Carl

OK, so my hypothetical example was off by a factor of almost five. Your humidification "Q" would be that much higher of course.

Deaerator- Sure, that is often done, but with steel tube steam boilers using higher pressure. To really deaerate the feedwater, it is brought to very near boiling and often has steam injected right into it via a "sparger tube". I have never done this with low pressure, but it is interesting to explore.

The masonry- not sure how one would address that. Sealing is out (it will trap moisture unpredictably for one thing and may begin a spalling issue. Insulating some older brick buildings does this too. That is a whole different topic!

Air sealing is probably your best friend here. Years of wall paint also help slow down the humidity moved by vapor-pressure. Lessening gross air leakage and the moisture associated with that, is thus more beneficial for the effort.

Regardless, a light hand is required. I use glass surfaces as my sentinel indicator of "too much humidity". If water begins to condense, you have hit your personal saturation point.

Here is the larger questions I would ask: Why do you want to humidify? Just because...? Or are there respiratory issues? Pianos and other musical instruments? What is your target RH at what temperature?

If you want comfort, maybe 25-30 is about as high as I would go. For instruments, that is probably just below where piano guilds recommend, but acknowledge that it is the rate of change, not the RH itself, that is to be controlled. If it were the RH itself, there would not be any pianos in Arizona, right?

The other question is, "how will the humidity finally be delivered?". "How injected into the space and how controlled?".

Getting a knowledgeable architect and engineer in there, both of whom are well-versed in building sciences and psychrometrics, would be money well-spent in my opinion.

Hope that is not TMI... just some ideas.

nicholas bonham-carter

more humid thoughts

one thing to note-the radiators are usually next to outside walls and windows, so there could really be a codensation problem.

i don't know whether you have any sort of boiler chemical injection system in the 1926 boiler; but if so, then your steam might not be as "pure" as you would like wafting around your apt!

no doubt you have a backflow preventer to prevent accidental cross-contamination between the boiler water and the potable water piping.exposing the occupants to that water [even in vapor form ] might expose you to liablity.

as you know, there are bacteria living in the high temperatures of undersea volcanoes-others might live in the steam piping.

chicago's millenium park is a true masterpiece-especially anish kapoor's bean!lucky you!--nbc

Carl_21

More good points

Yes, we do have chemical treatment for the steam boiler and venting these chemicals into the apartments is the strongest argument yet for not doing what I had in mind.

Sigh.

Thanks for exploring this with me everybody.

--Carl

Big Ed_4

It Gives Reason .....

.... why a open mind is needed for growth .

nicholas bonham-carter

some other problem?

surely there must be some other steam problem in the building, we can help you with...nbc

mark ransley

It also a bad idea from the minerals you will be depositing in the boiler from excessive makup water, it will sludge up the bottom of the boiler increasing maintenance, cleaning costs. It is an expensive way to humidify, just look at the efficency of steam boilers. The objective is to not need to add water makup. figure also Chicago water at 55f or much less in winter and you are bringing it to steam temp, the differential is greater than evaporating water from 70f room temp. Its a bad idea.

Tony Conner_2

Unless...

... you've got carry-over of the boiler water leaving with the steam, the chemicals will remain in the boiler. The exception is something volatile like amines - which are typically used for dealing with condensate system corrosion. Unless you've got a lot of make-up water entering the system - which is very unlikely in a straight heating system like this, where all the condensate is returned - there's no need for amines. If there's minimal make-up (and that should be the case here), there's very little need for chemicals at all in a system like this. If there's any concern, food-grade water treatment chemical programs are available.

Carl_21

Of course

...but I'll start other threads on those. Cheers.