Multi-staging Boilers

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Old 12-23-11, 10:29 PM
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Multi-staging Boilers

saves recently brought up the subject of multi-staging boilers in another thread which got me thinking (again)...

Originally Posted by saves View Post
I have installed seven heating systems using Tekmar controls....

One commercial job with base board and cast iron rads. and two mixing valves with two oil boilers staged.
I'd be interested in hearing more about that installation when you get a chance. What kind of commercial property is it? Do the boilers provide DHW to the building? What kind of piping arrangement did you use? How is the venting of the two boilers handled?

I have limited knowledge of multi-staging boilers, but it sounds intriguing. My main reference point right now on the subject would be THIS article.
 
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Old 12-24-11, 06:04 AM
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This idea has increased in popularity over the last decade. I am seeing it mostly in commercial applications but more and more in residential applications. It saves fuel by not firing one big boiler when you have small demands. Many people have different ideas as to when to start using two boilers instead of just one. My personal opinion is 200k.
One rule when using more than one boiler is to break down the heat loss into the amount of boilers desired to use. There are a few rules I have heard over the years that I have usually followed.
Rule #1
If only using 2 boilers each boiler should be 60% of the load. Almost half of the heating season you will require 60% or less of the heat loss and can be handled by one boiler. If using more than 2 boilers divide the heat loss by the number of boilers desired to use. I believe the number of boilers is determined by the size of the heating zones. I think commercially multi-mod/cons is the best choice due to so many varying loads and usually different zone radiation types.
Rule #2
Always pipe multiple boilers as p/s piping and use one attachment point for the boilers utilizing a common header. This avoids preheating water that would end up going down the return of another boiler.

Multiple_boiler Installation
 
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Old 12-24-11, 06:45 AM
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Good feedback rbeck, thanks. It helps me to better understand the type of piping required when multi-staging.

A quick thought: maybe one reason why you are seeing more staging of boilers these days is because there are more quality controls available that are up to the task.
 
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Old 12-25-11, 08:33 AM
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maybe one reason why you are seeing more staging of boilers these days is because there are more quality controls available that are up to the task.
Maybe so... I believe that the reason those controls has been developed though was probably due more to demand. The cart after the horse so to speak.

Demand would be driven by desire to operate more economically.

It's another way of 'modulating' the heat source.
 
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