ultra low pressure ARCO system maintained at higher pressure

elfie

have an old arco system (ie. ultra low pressure) where rads are design without vents and traps (ie. have orafices to regulate steam flow to rad).  there are about 35 rad in the system



the system is currently running at 5 psi. and has worked just fine with lower pressures 1-2 psi



there is reluctance to reduce pressure and install a vaporstat to better manage a lower pressure level (vaporstat range is 0-3 psi) vs the basic and more common pressuretrol device



will higher pressures be less efficient and will the higher pressure impact wear on rads? and will the welded main connections to boiler, which is not ideal, also be stressed moreso at higher pressures. .



unfortunately, current day commercial boiler systems (a weil mclane 6 section cast iron boiler is in use) are not designed for low pressure systems

mcsteamy

Where are you coming up with...

Where are you coming up with the idea that modern boilers are not designed for use with low pressure?  Lots of people are using them at very low pressure without problem.  There is certainly no reason to run it at 5 pounds.  If you know it is designed for less, and has run successfully at a lower pressure, CRANK IT DOWN. 



Are you wasting fuel?  Of course.  But it sounds like you already knew that.

elfie

modern boiler

hi,

when boiler was operating at a lower pressure setting, it tends to cycle on and off more frequently (maybe not so bad)



the boiler is abit oversized but still, maintaining lower pressures results in increased cycling of burner (burner size can not be really be reduced for purposes of lengthening cycle, which would be great if possible)



thanks

mcsteamy

That is how it is supposed to work!

All of that cycling is the boiler working how it is supposed to work.  The lack of cycling is the sound of money burning up.  Cycling is the sound of money being saved.



Crank it down as low as it will possibly go.  This system ought to be running at a pound and a half, tops.  It was designed to run on OUNCES of pressure.  Running it at FIVE POUNDS is a very bad idea.

JStar

ARCO

How are the main vents? Probably not venting enough, causing rapid cycles. A system like this will probably work at 3 ounces of pressure.

elfie

vents

thanks



how would adding vents to the two mains decrease cycling at lower pressures?



there are ancient traps at the end of two mains that no longer work (steam blows thru) and it may be thru use of lower pressures that these end of main traps may not need to be repaired (A or B dimension rationale).  no vents are installed on the mains (used to use coal and was a vacuum system awhile back, does have a deaireator device connected to condensate return near boiler, which is no longer needed/functional).



there is a vent pipe from the condensate pump alongside boiler and is only system vent.



the system tends to lose pressure very quickly (no known leaks), and maybe the dysfunctional end of main traps might be the reason.

JStar

ARCO

Having proper venting will prevent excess back-pressure on the system, keeping the overall pressure lower, and allowing the boiler to make a full head of steam, slowly dying down as the steam is used up. If the pressure goes back to 0 almost immediately after the boiler shuts down, I would suspect bad piping, causing wet steam. Maybe something with the traps.

Jamie Hall

First thing to do

is to add a vapourstat, set to cut out at about 12 ounces and cut back in at about 6 ounces.  Probably not a bad idea to put a low pressure gauge on, too, to make sure that the vapourstat is properly calibrated.  I can't tell you how much money that will save, but it will most assuredly save you money.



I can't imagine where the reluctance to run low pressures is coming from.  Nor can I understand the comment that modern boilers are not able to run at lower pressures.  Phooey.  They do it just fine, all the time.



Yes, it will cycle off on pressure on longer runs.  This doesn't hurt anything.  It's how they work.  It will save you money -- while the boiler isn't running, it isn't burning money.



It sounds as though the maintenance on the system has been let slide enough that fully restoring it is probably not worth the effort.  That being so, first repair those traps that the steam blows through.  That isn't helping your efficiency a bit, and it shouldn't be that hard to do.  At the same time, you will need to add vents at the end of each of the steam mains -- good big ones (there are references on this site to help you size them) and also on any dry returns -- again, good big ones.  That will let steam get to all of the system quickly and efficiently at low pressure (it's quicker at low pressure!) which will, again, save you money.

elfie

electric pressure control

has anyone used the honey well electric pressure control device vs their vaporstat?



is this a better device (seems more expensive)

Dave in QCA

System Question

Is the ARCO system with 35 cast iron radiator all that is connected to this boiler, or are there other parts to the overall system?

vaporvac

Pressure transmitter

MarkS uses something he calls a "pressure transmitter" with his Midco radial modulating burner and loves it. In fact, he ditched the Vstats. Not sure if this is the same thing or would work as well without the modulating burner, but maybe someone who knows will pipe in.

elfie

boiler supports only rad

only about 400 thousand btus of rad capacity are supported by this 6 section weil mclane boiler boiler (boiler capacity is about 600 btu)



thx

Dave in QCA

condensate lift?

is there any modifications to the original piping, such as places where the condensate has to be pushed up to a higher elevation?

elfie

orginal piping is the same

piping of mains and returns is unchanged.

MDNLansing

Homemade

I think MarkS uses a pressure sensor connected to his home made controller. I don't believe it's an off the shelf device that connects to a boiler.

MDNLansing

Try It Out

Put an engine meter on it and start recording daily run times. Then, lower the pressure and do the same thing. You'll find out that long high pressure runs will fire the burner more in a day, than short low pressure runs. MarkS and I have both done extensive testing with this short cycle concept and it really does save a lot of fuel. In fact, the controller I am building is based on heating the house by calculating run time length and frequency and not using a thermostat to call for heat at all. MarkS is already doing this with the controller he built and has seen reduced fuel consumption and better overall comfort. The building temp is much more even and consistent. There is no doubt that running the boiler for short and frequent cycles is far more efficient than running your system up to 5 psi. In fact, at 5 psi your water doesn't boil until 225 degrees. You need a 5% temperature increase just to make the steam so it can be delivered.

elfie

short cycles

MDN

thanks so much the comments, i am very hopeful increased shorter cycles at the lower pressure will be better



can you provide info on an engine meter



there are two large boilers (steam and hot water) that share the same NG line and it would be interesting to measure NG use stats for each boiler

MDNLansing

Meters

http://www.northerntool.com/shop/tools/product_200246424_200246424



This is the one I used. No reason for this model except I use these on my snowmobiles and had several already laying around. There are many different kinds. Some are analog like this one, some are digital. Just Google Engine Hour Meter. Make sure it runs on whatever voltage you have available. They will all be DC, some come in multiple voltages, others are a single voltage like 12vdc or 24vdc only. Jut find a circuit on your boiler that is closed and energized only when firing and check the voltage. Then buy a meter that runs on that voltage. Most boilers are 12vdc or 24vdc I think. For example, my boiler has a 12vdc gas valve, so I tapped into the gas valve terminal on the terminal block. The meter I linked to runs on multiple voltages so if you get that one it would most certainly work for you. Just make sure you are tapping into a DC circuit and not a 110v AC circuit. If you want a different kind and have questions about it, post a link here and I can look at it for you.