dual boilers- VS- Single

The Kid

I have a customer in need of a new boiler and he would like to benefit from todays technology and after some research I have suggested a Buderus g215/5 oil fired w/ the R2107 logomatic control.So I started to do more research and this has lead me to the thought of dual boilers, would that be worth the extra money....How much in fuel savings are we looking at?

chuck shaw

Buderus has an

add in card, that will stage two boiers. I belive it is the FM-242. It will allow one Logomatic 2107 to control two boilers. I do not know how it is wired, you would have to check with Buderus.

Chuck Shaw

The Kid

fm242

thanks chuck, i do see that in the info, but how much will the customer benefit from the dual application?

doug_16

Now this is a good question.

I opted for two little boilers instead of one bigger one. I calculated that something about half the size of the original steamer would be just fine and then divided that in half. The theory being that for the shoulder seasons which can be long enough here in ME, one boiler would do and when needed the other one would fire.

It mostly works. But the version of the tekmar dual boiler control was not quite ready for prime time P/S. It has only one P1 output but there are two boilers with 2 007's. The delay between firing the second boiler is not adjustable enough so the second boiler may short cycle. With a real dual boiler control this should have more adjustable inputs to the decision to fire the second boiler. And no P2 output requires more stuff. So I sometimes just shut the second one down till it gets cold enough. It is interesting to note that if we don't fill the tub, start the dishwasher, turn on the upstairs heat, and shower all at the same time that one of the boilers is sufficient and has long run times.
Extra cost: more 007's, more valves, more pipe, more wiring blah blah. I had to change the Field Controls vents, they rusted out so the cost of insulated Z-Flex and custom vents was double. We are definitely using less oil though. And the redundancy is cool and we used that when we had problems with the original beckett burners. We now have Reillo's and appear to be in smooth operation.

If I had known working out the bugs in the lack of direct vent design expertise on the part of the installer was going to be so long and costly, I would have put in a hunkin mass of cast iron, cut thru the roof for a chinmey and messed up the space in the building. Or I would have put the boilers outside in an attached dog house.

Oddly enough, in the refit of one of our school buildings, we are going to dual Smith 7 sections with Carlin dual fire burners and tekmar control. On that scale, duals have to be a winner. For homes, ask me in a couple of years.

kevin coppinger_4

Doug....

I just did the same thing with an AF2 also...dumped it for a Riello BF5...after 2 years I could not deal w/ the problems any longer...so far so good.kpc

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hydronicsmike

Doug, You musy have missed...

...the release of the 264 just by months or even weeks. It can stage and rotate two boilers and has individual Boiler Pump Control for Pre and Post Purging. It also has an adjustable interstage delay that can be set up to almost 20 minutes to force the second boiler off longer, before letting PID decide whether or not to bring on the next stage.

The 262 has a fixed interstage delay. You may try to set your BOIL MASS from MED to HEVY. On this control, the interstage delay is based on the MASS setting.

LITE = 2 minutes, MED = 4 minutes, HEVY = 6 minutes.

Maybe try that. The Controls are designed to achieve and maintain a target within a short period of time, but without creating short cycling issues.

Now staging multiple boilers vs one, I always like to recommend it. Short cycling is a problem and we want to eliminate is as much as we can. The more boilers, the more individual control to match the load of the building.

I hope this helps.

Mike

\"Maine\" doug

Thanks Mike but

I set that option long ago. Since I use an Ergomax 44 for DHW and to add boiler mass, I found that all options had to be set to prolong the delay for the second stage. I also played with the setting of the emitters. When there is a large demand, the 262 correctly senses that there is no way one boiler will do. When just the VSI for the floor is running, there is no need for both to fire just because PID says it is a bit slow in recovering. I played with the DeltaT setting and when set small enough, the second boiler does not come on because the first boiler now has a smaller increase in temp required. But this causes the lead boiler to short cycle. Basically I need just a bit more delay so that the second boiler does not come on till my wife starts filling the large clawfoot tub. There is sufficient reserve for showers.

What really annoys me was that I missed the chance to wait a bit for the 264 which would also directly control independant boiler circs. I think the Mass. Tekmar outlet was getting rid of the 262's. So for now I manually turn off the second boiler. Perhaps I can add two delay relays but of course I only want the delay on the second boiler firing, not the first and this complicates the wiring. Sigh!

If you have a refurbished 264 someday and I can trade in my 262, I'd be interested. The two boiler concept I like, I was just a bit early.

Thaks

Doug

hydronicsmike

Doug

Call me in the morning at 250-545-7749, Ext. 214 and we'll see what I can do for you....Will try my best.

Best Regards,

Mike