new vaporstat old 4 story building --- burner cycles too often

100yrOldBuilding

I am a trustee in a 9 unit apartment building also I am a retired engineer electrical.
Sadly we have just one zone for the 4 story building so not all units are happy with the heat.
We have Steam Heat by oil and have recently installed a Honeywell vaporstat and have a Honeywell pressure control for series backup. Some radiators have adjustable steam release valves but others do not have the adjustment. With the thermostat calling for 73deg. and the sensor on the 3rd floor --- most units have enough heat(some windows are opened).
The vaporstat is set to 1.0psi and the pressuretrol is much higher 6 or 8psi.
My apartment is next to the boiler room so I readily hear the Carlin burner cycle on and off.
The burner cycles on and off too frequently, sometimes with only a 30 sec. off time. Of course this varies with outside temperature.
Do I need to calculate the Duty Cycle ? Or raise the vaporstat to 1.5psi ?

nicholas bonham-carter

Hopefully, the air vents on the radiators, are not releasing steam!
What sort of main venting is on the system, and, if the boiler is oversized, can the burner be down fired to more closely match the EDR?—NBC

Jamie Hall

The off time is interesting, but what is the on time? That vapourstat setting probably is too low (don't get to say that very often!) but the only reliable way to be sure is to look at how the pressure varies while the boiler is firing up from a cold start.

Do you have any idea as to what the boiler capacity is and what the installed EDR is? O course, if there is a significant fraction of the units with individual control, that is almost irrelevant, as if they have their radiators off the boiler will be oversized when they are off anyway.

There may be better ways to control a system of this type, such as a heat timer

EBEBRATT-Ed

I agree with @Jamie Hall

Look into a "Heat Timer" type control. Actually Tekmar makes one that is cheaper than heat timer easier to set up and works well. Not sure of the model # may be a #265?

But first you need to get the system working as best you can. A new control system wont fix a bad system.

Make sure the boiler is cycling on pressure and make sure it is not cuclng on low water cutoff.

A good burner technician could downfire the burner and do a combustion test.

And fix any venting issues, main vents and radiator vents

With the tekmar you put a sensor on the pipe on the last radiator on the system maybe on the top floor or in the basement depends on how the system is piped

nicholas bonham-carter

I would rectify any lack of main, (not rad) venting first, before changing the thermostat/control system. A low pressure gauge, (0-3 psi) will show you when the 2 ounce back-pressure value has been obtained, indicating the air is escaping with absolute minimal resistance.
Is the water level in the glass steady with minimal movement, as the boiler is firing?--NBC

100yrOldBuilding

Thanks for GREAT mutual insights!
Heat timer is a good idea.
Today I spent 15 min. in front of the boiler and did ON/OFF interval timing of the Carlin burner.
Also watching water level in glass tube. ON = 427.5sec/ON + OFF= 644.5, ON time was 4 time segments
and OFF time was 4 time segments as well.
Gives a Duty Cycle of 66% for the Carlin burner, higher than I expected and maybe will shorten burner lifespan ?? Max water level bounce was about 1/4" during OFF time and 1/2" for ON time.
How do I measure 2 ounce back-pressure ?? What gauge do I use ?
Thank You All.

Jamie Hall

Well, that gives you a pretty good idea as to how much too big your burner/boiler is, anyway... roughly 7 minutes on over a total 17 minute cycle time, if I read your numbers correctly. You could really benefit from a downfire if it can be done.

However, a timer might help -- and might not, but a Heat timer or some such most likely would.

On the gauge -- a 0 to 3 psi gauge will work nicely. I'd put it on any handy pigtail (remember you need to keep the 30 psi gauge for your insurance and building inspector friends!) -- and in an application like that I'd put a ball valve below it, to turn it off when you weren't using it.

100yrOldBuilding

Jamie --- can U give me a link to the 0 to 3 psi gauge with ounces as well ??
Thanks,
Bill

nicholas bonham-carter

I think I ordered this one 10 years ago, but double check the specs.

https://www.pressureworx.com/product/low-pressure-gauge-25-0-3-psi

The pigtail will keep steam out of the gauge, so you are only measuring the air pressure.
Post a picture of your main vents, and the rating plate on the boiler, and burner, for more advice on downfiring.
Remember that the aim is to have steam arrive at all radiators on each floor simultaneously. Low resistance main venting will fill the supply pipes first, then all the individual radiator run outs together.
On my 55 radiator, 1 million btu system, I have 6 dry returns, with 3-4 Gorton #2 main vents each. Since then, the Big Mouth main vent has become available, with even greater capacity, but some people here have had some problems with them, especially if you have wet steam.
This may enable you to cut back the target temperature on the thermostat to a constant 68 degrees, with no setback, and no open windows!
Thermostats are better, in my opinion, as everyone knows how to adjust them, and with remote sensors, the control can be in a secure area, with the sensor in a more exposed room on the north side of a large building, which of course must have a no TRV vent on the radiator in it. I like the Honeywell VisionPro, set for 1 cycle per hour, (or steam).
Digital indoor/outdoor thermometers will generally show the maximum, and minimum temperatures in various locations, which is useful for balancing the system.—NBC

MilanD

https://www.amazon.com/dp/B00H9ZWLZG/ref=cm_sw_r_cp_apa_fabc_.TVdGb1GSAZQ1

Good gauge, too. 

EBEBRATT-Ed

@100yrOldBuilding

Check out the Tekmar #279. That and down firing the burner is about all you can do. What model Carlin burner do you have? Is it lo-hi fire?

SteamCoffee

The vaporstat is a thing of wonder.....if it’s reading right! Out of the box, Honeywell’s pressures can be off.....by quite a bit. Sounds silly, but it’s been documented numerous times. Some competition in this area from other manufacturers would be nice. Double check the pressures...it’s critical to your success!

100yrOldBuilding

So DUTY CYCLE =ON time divided by ON + OFF time. Say for example if ran all the time: get 1 x 100 = 100%.
In my case got: ON = 427.5sec / ON + OFF= 644.5, ON time was 4 time segments
and OFF time was 4 time segments as well.
Thus 427.5sec / 644.5sec yields 66% DUTY CYCLE. Means that burner runs more than it's off but outside temp. was ab. 20degF.
Today much warmer (38degF) DUTY CYCLE much less(boiler not running much).
Wonder if a data logger can record DUTY CYCLE since it varies with outside temp. and would be a handy
bit of info to help tune system?

-----------------------------------------------------------------------------------

Bill nr. Boston Trustee(1 of 3), In snowy New England. Steam Heat for 9 apartments
Smith Cast Iron Boiler: Series 19A S/W 6, oil 6.5 GPH Steam 2308 Sq. Ft., 554,000 BTU/HR
Burner: 6 to 13 GPH Carlin #702CRD
Primary Control: Honeywell #R7284
Pressuretrol: Honeywell @ 10 psi, Vaporstat @ 1.0 psi

nicholas bonham-carter

Let's see what your main vents, and boiler piping look like.
You want your boiler to produce just enough dry steam, without too much water being thrown up into the mains, to satisfy the radiation EDR, and also you want the air to be able to escape with no resistance. A low pressure gauge will show you more at the moment than any data loggers.
Don't forget to add up all the radiators EDR for the rest of the equation.
Later on, when you know if the boiler is oversized, the data loggers will enable some fine tuning.--NBC