modulating burner control

[jeffk91467]

Lately I have been seeing the majority of jobs with boiler plants using modulating burners. I was looking for some guidance on burner control.
For a sequence I have been starting the burner (digital out). The analog is at 0 (%). Then after the burner has been running at minimum for 60 sec (adj), starting to modulate the burner up.
I know it probably varies by burner mfg, but does anyone see any problems with this.

[core]

Sounds like your clue-less on boiler operation. Before you start tinkering with boilers you may want to understand there operation first. Boilers as you may know are bombs just waiting to explode.

The modulating operation of a burner is done by temp. and setpoint. So a burner will modulate its dampers based on how far it is from setpoint.

Most people allow local controls to operate the burner.

Core

[Noel Murdough]

You sound like you want to get it right the first time. I'm with you on that.

Call tech service at the boiler company and have them fax you the instructions or guidelines for the adjustments. You'll need to give them the boiler model number, serial number, and the part numbers for any controllers that are linked to the boiler. You'll have to give them your company name and phone number, too.

Having what you work on documented in writing, along with the faxed factory specs, and documenting anything else that they require, is a good thing.

This also is a good way to learn when you can do something alone, or when you need outside help, from the factory or from another contractor.

I do the tech service end of the phone. These things help us work together.

Noel

[dapper]

I wouldn't even go there. I agree with core on this one. Pre-purge and post-purge times on the boilers are engineered by the factory based on chamber capacity, blower capacity, flue size, static pressure and probably other factors. If you by-pass or over-ride these flame safeguard functions I believe you are opening yourself up to some serious legal action if anything goes wrong. Check with your insurance agent or boiler inspector. I think they will agree with me.

Burner modulation in my opinion should also be controlled by the factory controls. I cant see any purpose to do otherwise unless you are doing the job based on point count and want to add points where ever possible. Enable, alarm, status, and temps or pressures is probably all that you should need on a boiler. Just my 2cents.

[amigo]

Originally posted by core
Sounds like your clue-less on boiler operation.
Core

Ouch..., Core you may be a little harsh. Remember Jeff is new member.

Jeff, I hope when you are talking about modulating signal, you are talking about demand signal from DDC into the boiler's factory installed controls. Then your startegy may be okay.

As Core, Noel, and Dapper have mentioned you do not want to directly control the boiler's flames.

[core]

[i]Quote{/i]

"Ouch..., Core you may be a little harsh. Remember Jeff is new member."

Sometimes you have to be direct.

When was the last time anyone saw a chiller blow through a wall, and take down a building???

I have seen and met in my career many so called "hot shot" control guys who think they can control anything with NO respect to proper operation or occupant safety.

Anyone who attemps to control from an outside source burner modulation and bypass local control is clueless and is going to get someone or themselves hurt.

Also you and your company become personally liable for damage.

Core

[jeffk91467]

I guess I should have been a little more specific with my question. My fault, sorta new here.
I was looking for some info on setpoint control for a boiler with modulating control, not replacing the boilers burner controls.
Normally we replace the slide wire potentiometer (Honeywell T991 proportinal controller) and tie our controls signal in with a 0-10vdc to 0-135 ohm converter for the modulating control. So for a boiler plant with three boilers we would start boiler-1, wait for a delay period while burner controller goes through its pre-purge and safety check, then start to modulate burner up. If more heat was required and first boiler at 100 %, then start second boiler at low, delay, then modulate #2 boiler. Same thing for third.
My question was more in the line of has anyone seen any different ways you had to interface with boiler/burner controls out in the field. I am seeing the majority of jobs being spec'd with modulating boilers and just was curious if the newer heating equipment was different.
I'll make sure I write question a little better next time I post.

[hvac_czar]

Originally posted by core



Sometimes you have to be direct.

When was the last time anyone saw a chiller blow through a wall, and take down a building???

I have seen and met in my career many so called "hot shot" control guys who think they can control anything with NO respect to proper operation or occupant safety.

Anyone who attemps to control from an outside source burner modulation and bypass local control is clueless and is going to get someone or themselves hurt.

Also you and your company become personally liable for damage.

Core

Drama Queen... calm down, if you treated someone with a question like that and you were face to face I'd bet that would be the last question they ever asked you. And it would be a shame if they never asked the question that would've kept someone from getting hurt or equipment from damage... Funny how it turns out you assumed the worse too.

[Edited by hvac_czar on 09-02-2005 at 05:03 PM]

[Control Man]

Just did the final work on a 5 boiler installation this afternoon. I enable the boilers ( DO ) based on indoor / outdoor reset schedule , monitor the boiler header supply and return water temperature as part of the RESET program and let the boilers OPERATE on their own INTERNAL CONTROLS.

[sonc]

"Drama Queen"...hehehehe

[core]

Hello Jeff

I like what "ControlMan" did that is a very common set-up.

But in your case your are looking to control the fireing output of the boiler (thats what I get from your post)

Check out this article:
http://www.esmagazine.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2503,125711,00.html

Check out the "Modulating Logic" section you may find this control strategy interesting.

Depending on the process your Control Strategy may vary. The strategy that "ControlMan" posted is one I myself have used for Comfort Heat.

This strategy may not work in a situation where combustion products may be limited by State guidelines an example would be "Acceptable CO output for boilers" an acceptable output will vary on application "Nursing homes" to "Open Industrial areas"

Some control strategy monitor Flue gas products and will modulate the burner or stage burners to maintain exceptable levels. It is always recommended to review engineering design parameters and then design software control based on job spec's.


Hope this helps

Core

P.S.
Hey "hvac_czar" it would of been nice to hear from a pro like you. It's very sad to see you decided to resort to name calling in your Post as oppose to providing usefull information. I don't know you or if you work for a proffesional outfit or not. I do believe my warning was warrented there isn't a pro. here that would disagree that before you can "CONTROL" a machine you must know its "SAFE" operation. As you can read the "original" post was very vague and before one starts trying ideas he should learn the basic operating principles first, i'm shure you agree with this friend. On his second post he was able to clarify his original post and that is why I posted the LINK above. We would like to hear from a seasoned pro like you on this topic.


Core

[rich pickering]

Bunch of info on modulating control.
http://tekmarcontrols.com/acrobat/d265.pdf

[tb7025]

If a boiler's IBR rating is 183,000 btu/hr and can modulate the burner from 20%-100% does that mean it can lower its IBR rating to 36,600 btu/hr?

[sonc]

yes