Cut-in/cut-out on Vaporstat

chuckNJ

Hi Mel, I'm a HO also, happily learning about steam heating since my wife and I aquired our one pipe system and accessory 80 year old house about 9 months ago. Constant learning via TLAOSH, constant lurking on the (great) Wall with a few postings along the way and the knowledge of the pro I used to install my new boiler. I do admit to a certain (genetic?) knack for technical systems of all types, and quite a bit of experience with electronic and electromechanical control systems in non-heating related realms.

To answer your question, let me first restate and perhaps clarify a key point: when I say "system full of steam" I mean not just the mains, but every radiator hot end to end - ie both mains and radiators fully vented. To me this represents the load of the system "fully picked up" (all the iron hot). My calcualtion of an implied real pickup factor is intended for this condition ONLY - I doubt it is meaningful if the system is building preassure during the pickup phase because other factors, such as mismatch between the distribution piping network and boiler's steam generating capacity may be in play.

So my calculation of a real, or observed, pickup factor is based on the idea that for the "fully picked up" system as described above, a 99.99% (ie just 100%) "on" time, when being controlled for preassure, would represent an exact match of boiler capacity to the load. If the boiler has just this capacity, it would have a pickup factor of 1.0. Therefore I figure the "off" time represents the "excess" (pickup) capacity of the boiler and so I calculate the capaity above 1.0 by dividing your total cycle length (62 sec) by the on time (40 sec) to get a factor of 1.55. (the above also assumes well insulated mains and risers which, when hot, should add very little to the load, since the pickup factor is intended for use against the connected EDR of the radiation).

I could well be missing something, or making a bad assumption somewhere in proposing this caculation, in which case I certainly hope and expect someone here will point out the error(s) of my thinking!

Dave_4

When my old Pressuretrol started dying, I got help from Wallies to find out which Vaporstat I should use for a direct replacement. From some tech literature someone provided a link for, I thought the L4081009 or 1025 were the correct ones. After much difficulty I confirmed through Honeywell and distributors, this Series Vaporstat is only available to OEM's at this time. So I found a source for the older, mercury switch type, the L408A series. I installed it in place of the Pressuretrol, wiring and all, and it is working fine. I currently have the cut-out set at 10 oz. and the cut-in at 5 oz.. After the pressure hits the cut-out for the first time, I get lots of cycling, until the stat kicks the boiler off. The cycle is about 40 sec. on and 22 sec. off. Does this sound like the best way to set up the Vaporstat and run the boiler efficiently?

Unknown

> When my old Pressuretrol started dying, I got

> help from Wallies to find out which Vaporstat I

> should use for a direct replacement. From some

> tech literature someone provided a link for, I

> thought the L4081009 or 1025 were the correct

> ones. After much difficulty I confirmed through

> Honeywell and distributors, this Series Vaporstat

> is only available to OEM's at this time. So I

> found a source for the older, mercury switch

> type, the L408A series. I installed it in place

> of the Pressuretrol, wiring and all, and it is

> working fine. I currently have the cut-out set

> at 10 oz. and the cut-in at 5 oz.. After the

> pressure hits the cut-out for the first time, I

> get lots of cycling, until the stat kicks the

> boiler off. The cycle is about 40 sec. on and 22

> sec. off. Does this sound like the best way to

> set up the Vaporstat and run the boiler

> efficiently?



How about trying this?

Dave

Unknown

How about trying this?

Dave

Steamhead (in transit)

You might be slightly overfired for that system

have a pro downfire the burner a bit.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

JB_8

vaporstat

chuckNJ posted a great idea on 12/27/06. He would leave the preasuretrol in circuit where it is as a high limit safety. He didn't see any reason to keep cycling the vent damper while the vaporstat is modulating the burner. I used it on my vent damper and it works great. If you pop off the plastic cover on the vent damper there is a wire diagram inside. My vent damper has one yellow wire to the gas valve. I cut the yellow wire and wired the vaporstat between the vent damper and gas valve. Now the vent damper stays open and the vapor stat goes on & off.

Dave_4

Thanks for the good ideas. Happy New Year to you!

chuckNJ

firing and real pickup

Wouldn't the key question about fine tuning the firing be: When does the system first build preasure to cutout? If a particular system (with no other issues) is building preasure to cutout before the system is full of steam (and no air) then I would think that would be a key sign of being overfired, or worse, oversized. If the system is only building preasure after being fully "picked up" then a down firing would only reduce energy available for cold start pick up. In Mel's case, if I'm figuring correctly, his 65% on time when the vaporstat is controlling implies he has a real pickup factor of of about 1.55 on his system (assuming this is occuring when the system is full of steam).

In my own case, my system fully fills with steam in about 50 min, running continuously at a "natural" preasure of 5-6 oz. It only builds to cutout after that point, and with my new vaporstat installed (wired as I previously proposed) I'm seeing an 80% on time duty cycle running between 5 and 9 oz. (readings per my low preasure gauge). By the same calculation, this gives an implied real pickup of 1.25, significantly less than the 1.5 that observed EDR and boiler rating suggest for my system so I would say, if anything, my system might be a little underfired...

Another interesting observation: under the factory new preassuretrol, the lowest range I could get was a 2 lb cut out and 1 lb cut in, and this ran at a 93% on duty cycle. So in my case there is a noticable efficiency gain (13%) with the vaporstat maintaining a tight, low range during those times that the system is being controlled for preasure. Of course wrt all the above, every system is different.

Happy New Year to all!

mel rowe

What I know about one pipe steam systems comes from reading TLASH numerous times, working on my system and reading a lot of posts on the Wall. I feel I have learned a lot, but only scratched the surface. At any rate it has all been very helpful and much appreciated. I have mentioned here before that I have a Utica boiler of 300KBTUH capacity. When I calculate the EDR of my rads,I get 612 sq. ft., so my sysstem is over capacitized. When running at design capacity, it uses 4.8 cu. ft. of gas/ min., takes about 10 min. to fill the system and shut off the 3 main vents. I've changed most all of my wet returns,which were 77 years old, so I've used a factor of 1.3. When running in this mode, the boiler ran for approx. 30 minutes and then was off for 60 min. As I've learned more and tried to get the sysstem to be more efficient, I've gradually reduced the gas flow to a current level of 3.7 cu. ft./min., which theoretically should be to the attached load. This has slightly lengthened my cycle on time but overall has reduced the gas usage. From the results since installing the Vaporstat, it seems I may be able to reduce gas flow a slight bit more and not have the Vaporstat cutting in and out as much. I was curious as to how you came up with a pickup factor from the info I gave. Thanks.