Question on cycling of a mod/con boiler

Coffem

Hello,



Just recently installed natural gas in our home in Boston, MA.  We are half way done with a 50 year old oil+tankless+steam system converted into a gas multi-zoned radiator-free hydro air system with a superstor indirect 45.



(apologies in advance to all the steam folks who want to chase after me, needless to say we had our reasons... )



As mentioned, we're going hydro air and with a Burnham Alpine 150 boiler.  The first phase of the project was to setup the Superstor and boiler and leave the heating zones for the hydro air capped off until the air handlers and ductwork is done, at which point those will get setup as well.



So what I have is basically a very expensive hot water heater for the next few weeks!  Alpine 119BTU output, TACO 14 boiler loop circulator, TACO 007 superstor circulator, an expansion tank, a few valves, the proper boiler loop and stubs for the zones and returns as Burnham specified, and basically that's it.



MY QUESTION: Given this is how the bolier is going to run during the summer months (no calls for heat), it sure seems like it does a lot of cycling on/off for just the hot water needs, after we take a couple long showers (with cold input water here in New England).  The boiler fires up, and since it's only circulating the boiler loop and the superstor, there really isn't much water to heat.  Within 45-60 seconds it's up to 180 degrees supply and maybe 170 return.  It then goes into its shut-down sequence, which takes about 45 seconds.  By the time the shutdown sequence is done the boiler is back down to 140 degrees supply side and it begins its startup sequence again which takes another 45 seconds or so.  At this time the supply temp is down to 130 or so, and the process repeats.



As it repeats the lowest point it gets to creeps higher and higher as the superstor heats up -- creeping to about 155 where finally the boiler is returning 155 and the superstor is set at 130.  It can take 5 or 6 cycles like this to heat up the superstor after it's been "emptied" -- emptied meaning filling a tub for example.



Does this cycling seem normal and will it result in abnormal wear and tear?  As a non-boiler guy but an engineer by trade I don't get why the boiler wouldn't just fire at a low-enough rate t keep a constant 180 and heat up the superstor quickly and then be done.  Why cycle on/off/on/off/on/off/on/off again?  Guess that's just how they are?

meplumber

I would have to see your piping diagram.

I would need to see a piping diagram to know for sure, but some of these smaller Mod/Con boilers have a problem with the indirect not exchanging the heat fast enough to keep the boiler from bouncing off high limit.  Did they pipe it thru a hydronic separator/ low loss header or maybe closely spaced tees?  Or is it piped like a traditional boiler (which presents problems with smaller Mod/Cons)?

Ironman

Agreed

Need to see your piping diagram. I would also suspect that the 007 pump is not sufficient to maintain the proper flow rate.

Mark Eatherton

Multiple reasons...

The storage tank is a typical North American storage tank with a relatively small surface area on its coil. It requires 180 degree F water supply temperatures in order to overcome the small heat exchangers surface area. In days of old, when energy was cheap, this system worked OK. In todays era, these manufacturers need to substantially increase their coil sizes to allow for better heat transfer. I prefer the use of a reverse indirect, like Turbomax www.thermo2000.com



It is more expensive, but it keeps the condensing appliance in the condensing mode, even when it is doing DHW.



The other issue, is the way the boiler controller is programmed, which is not field adjustable.



I have a Munchkin MC50 that does the same thing, and it has to do with the timing of the program. It pre purges at a high RPM, then light off occurs, then flame confirmation occurs, and it takes about 30 seconds for the fan speed to idle back, and by that time, just due to the heat being generated by the high fan speed on start up, the boiler is at its dictated operating limit (outdoor reset) and it shuts down, cools off and recycles. It does this during a marginal call for heat. Yours probably will too once you get your heating system hooked up.



Due to my reverse indirect for DHW, it never short cycles on a call for DHW.



The Lochinvar Knight boilers don't have this long flame confirmation/stabilization time frame. It purges at high speed, then lights off, and as soon as flame is confirmed, it idles back, avoiding temperature overshoot.



Not sure who's controller your boiler uses, but it is a moot point anyway, because this part of the logic can not be field adjusted. It is programmed into the controller at the factory.



You would need to either significantly increase the surface area of your heat exchanger, or re-program your boilers master controller to avoid the issue at hand.



And yes, the worst thing you can do to ANY device, is start it up. That is hardest on components.



ME

Tim McElwain

The Alpine boiler

probably has the SAGE 2 system which allows adjustment to overcome most cycling issues. Talk to your installer or get in touch with Glenn Stanton at Burnham he is the rep here in New England he will be able to tell you what to do.

BoilerLady

Boiler Lady

I'm trying to locate Glenn Harrison (formerly with Althoff in Crystal Lake).  Any leads would be appreciated.

Tim McElwain

I sent you an

e-mail with his e-mail address.