What Happened to Dunham DH Home System?

Christian Egli_2

Vacuum starts at the vacuum pump and works its way back up to the boiler. Depending on which of the pump or the boiler has the biggest volumetric output you can determine where that balance pressure is. You can also determine which of the two (not both) devices is worth controlling beyond a simple on/off on a call for heat.

To have true subatmospheric boiling you need an oversized pump that will dominate the game. You can then control the amount of vacuum you want with a pressure switch. The boiler will follow the lead since it should not be able to overwhelm the pump.

But, I believe in most cases a boiler will overpower the pump, particularly if the pump is getting old. The opposite of what we want.

You have a Paul system, how does the pressure in the radiator move once the Paul shuts? Since these vents work on temperature only, how does the vacuum pump have any more effect on the system, once shut? I have those same ambiguities towards thermostatic traps.

I have two pipe vacuum, and I find the vacuum effect hard to track back up to the boiler under full fire, no vari-vac pressure reducing valve. I never fiddled with limiting the fire to guarantee subatmospheric boiling. Everything goes deep vacuum on total shut off until small system leaks refill the system.

The big success is really in the start up / air purge period where vacuum really gets things going quick before traps close, and, in the end cycle with the fire off to finish the last bit of heat in the boiler when steam output drops and traps reopen. In between, I am not sure how effective the pumping is.

So, I control the pump most simply with a timered delay, on for a while at fire on, on again for a while at fire off. Doing nothing in the middle of the cycle also protects the condensate pumps by not actively pulling in steam into the returns.

An overpowering pump running continuously sucking on a smallish boiler or heat source would make for guaranteed subatmopsheric boiling. This is what freeze dry instant coffee, sugar, salt, etc... producers use.

I believe the Paul systems had the vacuum pump running continuously since in the beginning they would have been steam powered themselves. I doubt some on/off on pressure scheme would have been sought, to save on what? a coal fire you can't modulate as fast as the switch anyways?

Historically, vacuum systems where often an add on to make an already existing steam engine more powerful without the complication of enlarging it, like adding a supercharger to your automobile. Sucking on the radiators was the next logical thing to do.

So,

Think steam cycles are so antique no one in his right mind would use them, particularly this vacuumized scheme? Old, Ohhhh,

Can you tell me exactly what a heat pump does? hmmm? Everyone wants to have that! Funny! Think how these are controlled.

I had written one of those analogies of mine to noodle out this problem but it took a bad turn and became disturbingly kinky. I am omitting it and proposing instead a sobering mathematical analysis.

Here goes

Pump side

Vacuum pumps suck electric power on one side while they suck air on the other. From measuring a 2hp pump I have, I get to suck a volume of about 100 ft3/min under a vacuum of -5 lb/in2; and about 250 CFM under -1 PSI. That's with a jet pump. With another 2 hp pump I have, an impulse pump, I get 150 CFM under -3 PSI.

250 CFM at -1 PSI

150 CFM at -3 PSI

100 CFM at -5 PSI

Seems good.

So, for this pump (2 hp * 736 W/hp) about 1.5 kW, eats an amount of energy equal to about (1.5 kW * 3414 BTU/kWh) 5000 BTU/h.

Boiler side

What sized fire should we expect to snuff out for those sucking rates?

That's easy, about 1000 BTU boils away 1 lb of water, and at atmospheric pressure, 1 lb of boiled water occupies a volume 1700 times bigger, or from a steam table: 27 ft3/lb at 0 PSI, 29 ft3/lb at -1 PSI, 33 ft3/lb at -3 PSI, and 40 ft3/lb at -5 PSI. For our case, we work from 250 CFM at -1 PSI to get: (250 ft3/min * 1 lb/29ft3 * 1000 BTU/lb * 60 min/h = 517,241 BTU/h) I also include the ratio between CFM and BTU/h as: (520,000BTU/h / 250 CFM = 2080 (BTU/h)/CFM)

520 000 BTU/h at -1 PSI; ratio 2080 (BTU/h)/CFM

270 000 BTU/h at -3 PSI; ratio 1800 (BTU/h)/CFM

150 000 BTU/h at -5 PSI; ratio 1500 (BTU/h)/CFM

The smallest vapor generator I have married to my 2hp pump puts out about 730,000 BTU/h. See how under full power I can't ever hope of going below even -1 PSI. My boiler is overpowering.

In my case, the economics considering electric cost and fuel cost make it worthwhile. I suspect a bigger pump would still make sense, up to the point where efficiency increases are lost to the electricity burned.

I could also install a 150,000 BTU/h boiler with my pump and go deep atmospheric, at -5 PSI, we're at 190 F, but (150000 + 5000) 155,000 BTU/h is not enough to heat this building, however, this is what I do on cycle end.

There may be something more (or less) to this calculation. Page 190 of The Lost Art gives a ratio of 480,000 to 240,000 (BTU/h)/CFM, this is the 1/2 to 1 CFM per 1000 EDR, the trouble is, I find no mention of what pressured CFM we're looking at.

What measurements do you get with the Dunham at the Fisher home? Does your literature give you numbers?

Hope to hear from all of you.

Long Beach Ed

Why did they stop making them?

In 1929, Dunham introduced the DH home heating vacuum system. They said the system would save 30% - 50% on heating bills. It was designed for gas or oil burning.

By 1935, they no longer made the small pump and removed the system from their catalogue.

A photo of the pump is shown below. Links to high-resolution images of catalogue pages are attached that show the pump insides. It was an exhauster that stored a few gallons of water in its tank and circulated the water through a venturi to create suction, similar to the way big commercial vacuum pumps for heating work.

By 1937 only a larger vacuum pump was available, and Dunham seemed to abandon vacuum heat for the small home market.

Was pump maintience too troublesome, or was the payback not what was expected?

We've operated a Paul type air line system with great success, and will probably be building a pump similar to this Dunham to try out the principles...

Any ideas?

Long Beach Ed

Steamhead (in transit)

Probably

because it didn't sell too well. Remember, 1929 was the start of the Great Depression, and most home owners couldn't afford this kind of equipment. Owners of bigger buildings probably still could, so Dunham focused on that market.

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Christian Egli_2

It broke your heart, sucked a void in it, didn't it? This vaccum

Maybe it was the language style then, but from reading the Dunham literature, you really have to grab on to your seat to not get sucked up into a whirlwind of confusion.

Now, you and I like things that suck, we'll gladly scratch our head for as long as it takes, but the homeowners who's only interest in heating stops at the thermostat?

Add the fact that their biggest promised subatmoshperic output was achieved not automatically but by having the homeowner fiddle with the burner output... you can guess that as soon as the novelty of all this wore off, the vacuum system would be idled.

Frankly, I think the differential pressure control scheme they came up with was totally counterproductive to what a vacuum pump does. I don't know that this scheme is ever used today in subatmospheric vaccum kettle applications.

Dunham should have stuck to the simple message that vacuum pumps accelerate uniform steam delivery time on cycle start up and they suck out the last bit of boiler heat on cycle shut off - thus saving on fuel cost. Automatic electronic control would have been helpful too.

There, I give it a kick.

Long Beach Ed

What do you think...

What would be a better way to control this thing using a gas or oil boiler?

How about control of an air-line "Paul" system?

Ed

Steamhead (in transit)

This is where stage-firing

or modulation would have been real nice.

In the larger installations the modulation is done with a motorized valve since the boiler also provides steam for process applications.

I like the idea of using vacuum on the steam side as well as the return side since you can vary the steam temperature this way.

Ed, Dunham also had a way of applying their vac pumps to one-pipe systems. The piping was similar to the Paul system.

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Long Beach Ed

Paul System

Yea, I see they promoted their wares as a system to retrofeit one pipe systems using the Paul Vents.

None of their books seem to go into detail except by describing the Paul vents, whcih are similar to the ones that Hoffman still makes.

Do you have any idea how they controlled the pum on these? I suppose they just ran it all the time with the burner, but I'm not sure. They may have let a thermostatic contol in the main turn off the pump after they had steam distribution?

Ed

Steamhead (in transit)

I think

the pump came on with the burner, and a vacuum-operated switch stopped it when there was enough vacuum.

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Long Beach Ed

Ahh ... now...

Would that vacuum point be controlled by the weather?

I don't see any pressure switches in Dunham's books other than those differential things. Unless they used that between the main and the suction manifold? This way the vacuum would be relative to the pressure.

Or did they just use the Paul vents for distribution, without actually truing to draw much vacuum?

Ed

Steamhead (in transit)

Indirectly

by varying the boiler's run-time. The later Differential and Vari-Vac systems included outdoor-reset to do this. On a mild day, the vacuum got deeper. On a 2-pipe system, the pump would then maintain more vacuum in the returns than in the supplies, and the steam would flow.

If the boiler ran long enough, the vacuum got shallower and the steam temp went up. This took care of cold days.

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Steamhead (in transit)

Indirectly

by varying the boiler's run-time. The later Differential and Vari-Vac systems included outdoor-reset to do this. On a mild day, the vacuum got deeper. On a 2-pipe system, the pump would then maintain more vacuum in the returns than in the supplies, and the steam would flow.

If the boiler ran long enough, the vacuum got shallower and the steam temp went up. This took care of cold days.

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