Vacuumized Steam

Christian Egli

Hello everyone. We are working on the replacement of a vacuum condensate return system. The unit is big and beautiful and has got me dreaming about pipes, I must be walking around with a big grin on my face.

The system was installed in the 50s. Two pipe system, no air vents, thermostatic traps on the heating units, F&T traps at the end of the mains. All air gets sucked out through the dry returns and condensate gets pumped back into the boiler.

In this set up the vacuum pump only serves to remove the contents of the return lines because once all the traps close it does not affect the steam side. It only saves fuel by quickening the heat up stage. Claims are made that this will save 35% on fuel because the boiler is on for less time. But can this be improved?

Remembering the coal operated vacuum systems that would boil water well below the standard 212F, I would like to have my vacuumizer affect the steam side of my two pipe system. To do that, I am thinking that I could open the condensate returns to the steam main by replacing some or all of the thermostatic traps by orifice traps that would be meant to leak only very little steam into the returns.

This is an idea inspired by Dan Holohan's Lost Art, page 251, where he mentions reviving Paul systems.

Has anyone seen or done something like that? Any idea on the fuel savings? Would I get very even heat? Would I really have an orifice trap system without the slow venting because of my vacuum? It won't work with an undersized vacuum pump, but will 1 CFM for every 1000 EDR be enough for this scheme since I am aiming for more than just a glorified condensate return pump?

The system I mentioned is not my own, so I won't implement any of these ideas yet, but if it is possible to save fuel and trap repair this way, it would be a big argument in favor of the value of vacuum pumps.

By the way, I have already asked the TLV trap and vacuum pump manufacturer about this - they do precisely what I talked about for process steam applications - but to my surprise they did not think steam was much good at heating buildings. At any rate, their very accurate temperature controlling equipment is neither meant nor priced for space heating. But I could make my own orifice trap conversions. Am I a sucker?

Is there anyone interested in small sized and reasonably priced vacuum pumps to be installed in homes? Does anybody have one? 35% fuel savings, is that too good to be true?

Oh, don't tell me my ideas suck... but I'll love your comments anyway.

Christian Egli

Mark Eatherton1

Steam sucks...

rail road cars flat as a penny if you'll let it:-)

Why not generate your vacuum using the boilers stack? .02 to .05 negative pressure out the wazoo. Stainless steel lined flue pipe and you're rocking with vacuum!

Doesn't sound too crazy to me, but then again, I've been called a Mad Man by some people too:-)

ME

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DaveGateway

Vacuum Steam

> Hello everyone. We are working on the

> replacement of a vacuum condensate return

> system. The unit is big and beautiful and has got

> me dreaming about pipes, I must be walking around

> with a big grin on my face.

>

> The system was

> installed in the 50s. Two pipe system, no air

> vents, thermostatic traps on the heating units,

> F&T traps at the end of the mains. All air gets

> sucked out through the dry returns and condensate

> gets pumped back into the boiler.

>

> In this set

> up the vacuum pump only serves to remove the

> contents of the return lines because once all the

> traps close it does not affect the steam side. It

> only saves fuel by quickening the heat up stage.

> Claims are made that this will save 35% on fuel

> because the boiler is on for less time. But can

> this be improved?

>

> Remembering the coal

> operated vacuum systems that would boil water

> well below the standard 212F, I would like to

> have my vacuumizer affect the steam side of my

> two pipe system. To do that, I am thinking that I

> could open the condensate returns to the steam

> main by replacing some or all of the thermostatic

> traps by orifice traps that would be meant to

> leak only very little steam into the

> returns.

>

> This is an idea inspired by Dan

> Holohan's Lost Art, page 251, where he mentions

> reviving Paul systems.

>

> Has anyone seen or done

> something like that? Any idea on the fuel

> savings? Would I get very even heat? Would I

> really have an orifice trap system without the

> slow venting because of my vacuum? It won't work

> with an undersized vacuum pump, but will 1 CFM

> for every 1000 EDR be enough for this scheme

> since I am aiming for more than just a glorified

> condensate return pump?

>

> The system I mentioned

> is not my own, so I won't implement any of these

> ideas yet, but if it is possible to save fuel and

> trap repair this way, it would be a big argument

> in favor of the value of vacuum pumps.

>

> By the

> way, I have already asked the TLV trap and vacuum

> pump manufacturer about this - they do precisely

> what I talked about for process steam

> applications - but to my surprise they did not

> think steam was much good at heating buildings.

> At any rate, their very accurate temperature

> controlling equipment is neither meant nor

> priced for space heating. But I could make my own

> orifice trap conversions. Am I a sucker?

>

> Is

> there anyone interested in small sized and

> reasonably priced vacuum pumps to be installed in

> homes? Does anybody have one? 35% fuel savings,

> is that too good to be true?

>

> Oh, don't tell me

> my ideas suck... but I'll love your comments

> anyway.

>

> Christian Egli

DaveGateway

Vacuum Steam

Christian,
I worked on a Dunham-Bush Vari Vac when I was a pup. Jack was a steam guru. He was a dead man in living color. Vary the vacuum and vary the steam temp. It was the early eighties and he was outdoor resetting a vacuum system with Penn-Johnson electronics. This was in a school.

As far as I remember the rads had thermostatic traps. Can't say about the F&T's. A thermostatic rad trap won't close till 212* so you'll pull vacuum through all rad traps and F&T's. You can control delivery temps based on OD temps. You may have to engineer some orifices for balancing but it is kinda cool to be able to vary steam temp with vacuum.

Your mechanical vacuum system is NOT just for condensate removal. If the traps don't see temps they WON'T close. Vacuum can be pulled through the WHOLE system. Dan or somebody has a steam temp vs. inches vac. chart out there. Vacuum pumps can be rebuilt. Modern controls can be installed. I did it 23yrs. ago with a guru's guidance. To install a system like that now would be ludicrous and extremely cost ineffective. To restore a system like that to it's original glory is a unique opportunity.

Keep us posted.

Mad Dog

I admire your goal

You've got your work cut out for you, though. I would wait for Noel and Steamhead to weigh in - they done things just like that. I'm sure they've got those charts. Keep us posted. Mad Dog

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Unknown

You can still build a Vari-Vac system

At least I think you can....

http://www.mepcollc.com/VV.htm#mepco2

The way that the steam was delivered in a vacuum, was with the use of a modulating steam valve (on each zone). The vacuum would be applied all the way through the traps to the boiler water line before start-up. As steam is made, and the vacuum falls off to the point that the controller is hunting for, the steam valve modulates to maintain this level of vacuum in the supply mains. In effect, it is matching the steam delivered to the steam condensed. The extra energy stays in the boiler, as pressure, and satisfies a pressure controller, eventually, at 2 PSIG.

By having more than one king valve, different zones can be fed at different pressures from the same boiler(s) and be better able to control temperatures in the building.

Traps are a unique thing. The thermostatic elements in traps, because of the bellows construction, have the same pressure within them as outside of them, acting on the mixture. What this means is that if there is air pressure, or steam pressure on them, the boiling point of the steam in the system will be higher, as will the boiling point of the liquid in the trap. Net effect, the hotter condensate still gets out because the trap opens at a higher temperature.

In a vacuum, the temperature that the trap flexes at is below the normal operating pressure, which means that the vacuum IS felt through the traps and into the radiators, lowering the temperature of the steam in the radiator until the trap actually needs to shut on steam temperature (albeit a lower temp than normal). Once it shuts, the pressure in the radiator will climb to whatever is in the mains.

I kind of prefer thermostatic radiator valves on the radiators, and a very low delivery pressure in the supply mains, and modular boilers to shed the load as the building load decreases in the afternoons. I've done this and like it very much.

The vacuum pump would work on the condensate system with or without the TRVs. I prefer the lowered maintenance of using gravity, rather than vacuum, if the pipes are big enough to return the condensate properly.

Noel

Mike T., Swampeast MO

This Chart Might Help

"The chart shown in Fig. 40 has been developed by the Dunham Company, this chart having two curves, one based on a minimum temperature of zero and one based on a minimum temperature of 10° F. below zero. Assuming a maximum operating pressure of 2 lb. in extreme weather (either zero or 10° below, as desired) and locating the outside temperature on the left-hand side of the chart, a horizontal line can be run to the right until it intersects with the curves desired. Then directly under this intersection, at the bottom of the chart will be found the pressure in pounds or the vacuum in inches which should be carried to compansate for this particular outside temperature. This chart is based on the assumption that a constant inside temperature is to be maintained and that the heat loss of the building is directly proportional to the difference in temperature between the outside and inside of the building, also that the heat emission of the direct radiator is directly proportional to the difference in temperature between the steam in the radiator and the constant room temperature. The above assumptions are not strictly accurate but are ordinarily sufficiently close for practical application."

Source: Mechanical Equipment of Buildings, Harding and Willard, 1929

Mike T., Swampeast MO

Here's a Table for at Sub-Atmospheric pressure

http://www.steamonline.com/sat_steam.html

Note that latent heat increases as you get closer to vacuum.

Constantin

Yikes!

Am I correct in assuming that what happened here is steam cooling down and condensing sufficiently to create a vacuum, hence causing the walls of the car to implode?

Mike T., Swampeast MO

If I recall properly, the tanker car was being cleaned with steam. The worker left and closed the lid...

Steamhead

Noel nailed it, as usual

and yes, as far as I know you can still retrofit Vari-Vac to an existing system. In the old dsys this retrofit saved lots of fuel, so I can't see why it wouldn't work now.

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Christian Egli

Neat, thanks for the love

Thanks for all the contributions.

I had not thought at all about the Vari-Vac (I didn't know about it) and about resetting the steam pressure to follow the weather.

In fact, I am not sure I see the value of outdoor reset for steam heat since steam heat is so quick to adapt even when the weather is moody. But I see the necessity of outdoor reset with, for instance, floor heat, where the reaction time is slow and anticipating the heat loss according to the weather is a good way to go.

Thanks Noel, for pointing out that the thermostatic traps are just as affected by the vacuum as the boiling water. Vari-Vac has a control that seems to ensure that the pressure difference between boiler and return lines stays at around 2 PSI. I am guessing that if you let the difference go to 10 PSI or more, the thermostatic valves will either not be able to reopen, or will cycle very quickly.

Actually, with the traps working according to general pressure, this would mean that in a standard vacuum hook-up the vacuum should already go back to the boiler, but I have not seen that. I do think that the vacuum pump, even at 1CFM per 1000 EDR are undersized to keep up. Has anybody supersized a vacuum pump on a standard vacuumized job?

My idea of boiler control in this case has revolved around under-sizing the fire, that way no head is generated through steam pressure but only by the vacuum pump. I would not worry about steam not reaching all the radiators because the way for it to flow is cleared by the vacuum pump, there is no air to push out. I do think I would not fully fill the radiators with steam, but so what? The idea was to save fuel, and a half hot radiator here means a half bill, it is not the ordinary air bound radiator case which is wasteful.

Does the Vari-Vac work this way:

1) measure outdoor temperature

2) according to outdoor temperature set value for vacuum and control vacuum pump with vacuum gauge

3) measure pressure difference between vacuum line and boiler

4) control fire to maintain pressure difference at say 1/2, 1, or 2 PSI

or

3) set boiler pressure at say 2 PSI

4) control fire like any boiler, with a pressure control

5) use special reducing valve to bring steam pressure down to the desired radiator pressure

I am anxiously waiting for the technical info which I just ordered from MEPCO.

I don't like the idea of using either throttling valve or pressure reducer, their operation is totally wasteful of developed pressure head, plus its another gadget that breaks.

Lastly, I fully agree with you about gravity. It works and it is free. But if I have 10 PSI difference from the vacuum to the boiler I'll either need a tall A dimension or a Differential loop or an alternating receiver. As far as pipe size, I am sure it is cheaper in the long run to buy big pipes than it is to pay for the pumping (without even considering pump cost).

Outdoor reset, Vari-Vac, pressure reducing vavles, differential loop, I hear the Dead Men laughing and banging away at my pipes. What a party to have, they knew how to have fun.

Best regards to all

Christian Egli