Gravity Conversion-PGP

Steamhead (in transit)

that old all-fuel boiler was probably lucky to hit a 65% AFUE. And I've never seen a burner like that old one- what was it?

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Paul Pollets

Conversion with 4 Way

We just commisioned this sytem last week. The 1911 home uses 18 cast iron radiators. The Viessmann Vitogas 100 boiler, Vitotronic 200 control, V300-53g Indirect DHWT were installed using a 1" 4way mixing valve with a System Bypass and Pressure Bypass Differential. We are very careful to make sure system design avoids the dreaded
"thermal shock". The existing mains were 31/2" but conversion bushings were still available at the local marine hardware store.

All the radiators were revalved with Danfoss TRV's and Oventrop heads. The boiler was revented using a 6" SS insulated chimney liner. This home should see a significant energy savings.

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Paul Pollets

Economite

or a close relative. Like most gravity boilers in Seattle, they started with coal, then oil, then nat gas.

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Steamhead (in transit)

And I'll bet

there wasn't one brick or baffle in the flueways. What a waste of gas. They'll be sitting pretty with that new setup.

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Paul Pollets

Original flue

was unlined 16 x 16", 3 sides exposed...Good thing we have a temperate climate in Seattle. The new owner of the home was greatly concerned with maximizing energy savings. He spent the additional dollars for the insulated SS liner when presented with the options. He saw the advantages of increasing combustion efficiency. It's not a coincidence that the most pro-active owners are the best customers.


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Steamhead (in transit)

That customer

will no doubt give you many referrals.

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bob_50

Paul

great work. I am curious as to the dicision process. What made you choose a non-condensing boiler? How do you set the pressure differential by-pass? Do you use it just to prevent dead-heading or do you also use it to regulate the total flow to the system? I thought Wiessmann boilers were immune to low temp return? I'll bet setting it all up was fun. I think Econ-o-mite buners were made here in Chi. by Mid-Continent burner. bob

Paul Pollets

Design

I base the system design on several factors when converting Gravity systems...I like to take advantage of the casting lag of a cast iron boiler when coupled to the mass of the cast iron radiators. I chose a non-condensing boiler because the radiator sizing was not in the condensing range 80% of the heating season, and the additional costs were negligible. Also the venting would have been a problem. The Oventrop PBD sets at "16" bars for a 26-64 Grundfos pump...the instructions give all pump ratings and settings. The PBD only prevents the pump from dead-heading and does not affect boiler flow rates. The Vitogas GS1 boiler is not designed for LW temps like the Vitola or Vitodens. It must have either a system bypass or boiler bypass installed on large water content systems.

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bob_50

Thanks

Paul, I was thinking that maybe on a gravity conversion you would want a real low flow rate and use the PDB to limit pump output to the system. bob

Constantin

Wow...

... what a difference having the likes of Paul in the basement makes. The piping is well-insulated, well-mounted, plumb, and easy to follow. The boiler looks happy, the TRVs are going to allow the occupants to micro-zone their environments, and the honking tank ought to allow some very luxurious showers. The electrical work and the documentation at the boiler are the finishing touches... voil

Paul Pollets

B-Vent

Viessmann requests insulated B-vent from the vent damper to the liner. Inner wall is SS only ext wall is alum. Metalbestos.

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Paul Pollets

Flow rate

the system circuit needed 8gpm at 18ft head. I may have gotten away with a 15-58 pump, but used the 26-64. The PBD will shed excess pump energy to the return, when the TRV's are closed or turned down.

The boiler has virtually no pressure drop and a "P1" pump is not required. The control will keep the boiler firing above the condensing mode and then open the mixing valve circuit accordingly. Ideally, a condensing boiler is ideal for gravity conversions as long as the design works, and the DHW tank can be recovered in a reasonable period of time. Modulating all circuits are the cat's meow.

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