Boiler Oversizing %

[Intern2009]

The question is about a steam boiler replacement happening in Massachusetts. A limitation stating, the replacement boiler capacity must not exceed 125% of the total building load, was brought up by the inspector. To the best of our ability we were unable to locate this limitation in any code. Does anyone know about this limitation or where it can be found?

 

[mauricestoker]

One place this would be is ASHRAE 90.1. Design shall not exceed 25% on heating load, as per Appendix G.

 

[Intern2009]

The AHJ inspector in Massachusetts wanted documentation showing that the replacement boiler is no larger than 125% of the load. We have very little information about the building making it difficult to accurately model the building. In addition, we cannot find where the 125% is coming from. We did see the 25% in 90.1 but this value is more useful for modeling and does not relate to what the inspector is asking. Thank you for the help.

 

[DRWeig]

You should re-read mauricestoker's post. ASHRAE 90.1 limits heating plant size to 125% of load.

If you need to satisfy the inspector, you'll have to calculate the building's heating load. If there's not enough info available (such as as-built drawings), get your field clothes on and get to measuring and interviewing.

Good on ya,

Goober Dave

 

[cdxx139]

Doc, that 125% is in appendix G of 90.1 which is for modelling a base building, it is not officially part of 90.1 per se and not enforceable.

Intern, why not provide a block load of the building? Shouldnt be too time consuming. You dont need a space by space analysis.



knowledge is power

 

[mauricestoker]

I won't speak for State enforcement, but this is a mandatory requirement for federal projects. I believe that this is also mandatory for ARRA/energy funded projects provided from Federal to State level. I am certain of that, as it was also a requirement for the chiller plant I just finished, and for the boiler plant just beginning design.

 

[Intern2009]

So is there a specific document in which the 125% requirement is written other than 90.1?

 

[Intern2009]

The building inspector got back to us and described the 125% more clearly. The number is just a reasonable goal and he referenced IECC 503.2.1

503.2.1 Calculation of heating and cooling loads. Design loads shall be determined in accordance with the procedures described in the ASHRAE/ACCA Standard 183. Heating and cooling loads shall be adjusted to account for load reductions that are achieved when energy recovery systems are utilized in the HVAC system in accordance with the ASHRAE HVAC Systems and Equipment Handbook. Alternatively, design loads shall be determined by an approved equivalent computation procedure, using the design parameters specified in Chapter 3.

From the inspector,"he wouldn’t have a problem with redundant systems if the control strategy takes care of preventing over firing."

Thanks for the help

 

[DRWeig]

Thanks for the correction, Intern --

I was actually sitting within arm's reach of 90.1 and didn't bother to open it up...

A mea culpa,

Goober Dave

 

[cry22]

I think you need to check the published county design weather data.
They should have published outdoor design temperature for your local climate for equipment sizing. This will establish the maximum heating load.
A boiler is ALWAYS way oversized, we size for say 0 degrees outside (99.6% for our area), but the boiler is well oversized when OA is around 40 for example.

90% of the time, boilers operate at no more than 60% of building heating load.
I think his comment should've been specific about sizing the boiler for the published design OA temp. say if it is 10F, then you should not design for 0 degrees OA, typical of designers built-in safety factors.

ASHRAE is not a code. Cannot quote ASHRAE as a reference with code offcials.

 

[willard3]

If you check the code, at least in NY, the code includes all ASHRAE standards as the code by reference.

 

[Waramanga]

Errr, maybe I am missing something but the boiler isnt the system in my opinion. The heat rejection devices (AHUs etc) are the bits I would imagine cant be oversized by your codes. Who would care if a boiler was %1000 oversized if you couldnt reject the heat it would have no impact (well you know what I am getting at) on the buildings energy consumption. I assume you are just matching the existing production capability right?