Purchase a 30% larger than spec N/G boiler, what effect will it have?
Purchase a 30% larger than spec N/G boiler, what effect will it have?
(OP)
I am going to purchase an AJAX boiler which is 30% more capacity than then RITE boiler because the AJAX salesman told me they do not have the 1,050,000 btuh so we have to purchase the 1,500,000 btuh. What effect will we have to use an oversize Natural Gas boiler. Please help ASAP!!!





RE: Purchase a 30% larger than spec N/G boiler, what effect will it have?
RE: Purchase a 30% larger than spec N/G boiler, what effect will it have?
RE: Purchase a 30% larger than spec N/G boiler, what effect will it have?
RE: Purchase a 30% larger than spec N/G boiler, what effect will it have?
1) Less efficiency. It is better to use a boiler running near 100% rather than one that cycles off and on. This is partly because there is a purge air cycle (required by law) at the start and end of every combustion cycle. I.e., the blower purges ambient air through the system and out the stack, wasting heat. I think about a 30 second purge at the start and end is required for a 1.5 Million BTU/hr boiler.
Boilers that operate at various turndown ratios (25, 50 & 75% for a small boiler) are better than cycling on and off, but you still have greater thermal mass and surface area to lose heat from, plus your boiler must be certified to meet the emissions limit at each firing ratio.
2) Air pollution regulations are more stringent for larger boilers, both the NOx and CO limits and the frequency of testing. I have dealt with both Ajax and Rite, and both can supply boilers rated at say 990,000 BTU/hr to avoid the step up in regs at 1 Million BTU/hr. You need to talk to the right people, or maybe a vendor of multiple brands, e.g., R.F. MacDonald Co.: http://www.rfmacdonald.com/
The South Coast AQMD regulations are on-line at http://www.aqmd.gov/
Even if you are outside the SCAQMD, the other California APCD’s typically adopt the SCAQMD rules after a year or so (at least, Ventura & Santa Barbara do). Make sure to buy a boiler/burner combination factory pre-certified to meet the SCAQMD regulations (other districts will accept SCAQMD certs).
Our company recently had a Rite boiler overhauled, and we had it derated to < 1 Million BTU/hr. Estimated savings in fuel and testing > $2500/year.
Hope this helps,
Ken
RE: Purchase a 30% larger than spec N/G boiler, what effect will it have?
You don't say how if the new boiler is a replacement, or additional capacity, or what type of cycling it will be under, so its difficult to guess at what effects the larger size may cause.
In general if it is oversized you will lose some eff. It is probably a negligible amount. If it is a concern, you may be able to tune the boiler controls so it is at peak eff at 70%.
RE: Purchase a 30% larger than spec N/G boiler, what effect will it have?
RE: Purchase a 30% larger than spec N/G boiler, what effect will it have?
If the sulphur content is appreciable, then reducing the gas path area to bypass some heat transfer surface will keep your back end / stack temperatures up.
The burner should be easily trimmed to reduce the output to your requirements. Modulating burners pay themselves off fairly quickly in variable load situations, and are fairly cheap anyway.
The larger thermal mass of the larger boiler may actually help you meet peaks.
Personally, I wouldnt be especially worried, assuming low sulphur. But make sure the supplier knows what maximum and minimum loads to set the burner up for.
Cheers
Steve