short cycling

Paul S_3

i just installed a 103,000 btu steam boiler this morning in brooklyn, everything went fine. radiators heated.....until the boiler started short cycling it will run for 2 minutes to 1 1/2 psi and go off on pressure...then 2 mins later come on again at .5 psi.....this system has no main venting at the end of mains....only radiator vents....i am going ahead with the main venting would this solve this short cycling???...(. i know its normal for pressure trol to shut burner down and turned it on again dep on pressure in system....but its too frequent every minute or so it will go off)

Hap_Hazzard

It should.

But bear in mind that those vents will shut when the mains fill up. At that point the pressure depends on the balance between the steam output of the boiler and the connected load. If the boiler is sized correctly it should stay a little ahead of the radiators without building more than 1 psi. If it's a little oversize it will cycle on pressure. If it's way oversize it will short cycle. You are definitely on the right track. There shouldn't be more than a couple of ounces before the mains fill.

Rod

Main Vents

Hi -  It sounds like this is a fairly small system, Probably a Gorton #1 main vent located at  the end of each steam main or on the dry return before it drops down to the wet return, should do the job, If cycling still continues to be a problem after you have the new main vents installed,  you could up the cut off pressure to 2 PSI as it would give you a little more leeway .

    There is a really good book on venting in the Shop section of this website. It gives you the venting capacity of the different make/models of vents, both Main and Radiator and also traps.  It has the figures so that you can calculate the size of main venting needed. It’s a downloadable booklet.   I’ve found it very useful an refer to it regularly. Here is a link to it:

http://www.heatinghelp.com/products/Steam-Heating-Books/25/146/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-by-Gerry-Gill-and-Steve-Pajek

- Rod

Paul S_3

btu

sized new boiler to connected load....went from 118,000 btu to 103,000 no big difference...im going to give more main venting, clock gas meter , check gas press to see if its over fired .....thank you for all the info....Paul S

Paul S_3

thanks

yes very small system , bungalow in manhattan beach in brooklyn, thank you for the info on the book, will buy it now ......one of my workers just raised it to 2 psi and its still the same ....i know i shouldnt go any higher....guess i will go tomorrow and do further testing....thank u guys.... Paul S

Paul48

EDR

What's the total EDR and what boiler do you have?

Paul S_3

edr

270 sq ft..... i use a crown aruba bsi103.....i am sorry i posted higher btu's before....its a 103,000 btu steam boiler......

Paul48

gauge

Do you have a 0-3lb gauge on it?

Paul S_3

yes

yes i do...and the p-trol shuts off at 1.5 psi with a subtractive diff of 1 psi....comes on again at .5 psi

Paul48

Better Question

Are all the radiators fully hot, in a single cycle? Or does it take many short cycles?

Paul S_3

radiators

all radiators get hot on first cycle....

Steve Nichols

programmable thermostat?

Paul,

Do you have a programmable Tstat?  If so, do you have the nighttime/overnight temp. different from daytime?  I know that you stated that the boiler is sized to the EDR, but I have having the exact same situation due to an oversized boiler.  I have managed to tame it with really good main venting, but once those mains close, after all convectors are hot, boiler runs up to 1.5psi and shuts off...takes about 1 minute to hit 0.5, then refire.  If still calling for heat, it will then take about 2mins to cut out on pressure.

Here's the kicker.  This cycling happend routinely when boiler needed to recover from a multi-degree setback.  There is a lot of discussion on the board about whether or not using a setback with steam systems is economical for short "day long" reductions in temp.  If you're gone for a week, then that's another story.

I keep my tstat at the same temp all the time and right now the boiler can satisfy Tstat at about the same time it hits 1.5psi.

If system is matched to EDR, it should never hit high pressure if venting is proper, or so that has been the information I have gleaned off of the board.  So, there must be another issue lurking here. 

Paul S_3

main venting

steve,

     that is why i asked on my earlier post about the main venting....for some reason this system does not have one main vent at the end of mains......i am going to go ahead and install multiple main vents.....( no i do not have a programmable tstat ....i have a digital t87 which is set up for steam...).....

Paul48

Issues

As you said......Clock the firing rate, then double-check the total EDR. Did you add or multiply the total EDR by something?

Paul S_3

no pick up factor??(1.33)

i did not multiply pick up factor....i insulated every bit of steam lines....should i always use the pick up factor?....whenever i do steam install i always figure in new insulation for mains and risers....basically i just size it by net not gross(residentialy)never had a problem....let me know if im wrong please....

Paul48

You're Right

Just making sure you hadn't used it.

Paul S_3

thank u

thank u guys for all the help

Steve Nichols

main vents!

Sorry I missed that Paul,

You are going to notice a pretty nice difference once you get those main vents in there.  I am assuming you know how to calc the amount of venting needed, so I won't rehash.  In my case, I have two mains, one 30' @2" and one at 40' @ 2" and I have antler arrangements on both with multiple Gorton 1's.  When steaming the 3psi gauge barely gets off the pin.  Once the mains shut and all convector vents close, then the oversized nature of the boiler shows up,

I think with increases main venting,you're going to notice a big difference; I certainly did!  I'm sure the homeowners will appreciate the fuel savings.

Good luck and happy holiday!