Condensing boilers and emissions regulations

For this Shippensburg University boiler replacement project, major consideration was given to local codes, space requirements, boiler control, and emission reductions.

By Andre Pearson, PE, CEM, LEED AP, CBCP, and Jose R. Rodriguez, PEng December 29, 2014

During the replacement of an aging central steam plant at Shippensburg University (S.U.) in Shippensburg, Pa., the operating efficiency and sustainability depended on careful selection and specification of condensing hot water boilers. Fire tubes condensing boilers are used in the new heating plant design.

To select the most appropriate boiler, the engineer must considered the following specifications: local code requirements, cost impact, emission regulations, floor space, boiler control, boiler heat exchanger, flue material and location, drain required, hot water return temperature, minimum flow to the boiler, operating weight of the equipment, heating coil requirements, warranty coverage, and service personnel available in the area. The engineer also must consider high turndown of the boiler, because it might reduce short cycling when demand is low. If the boiler meets the actual system demand, it can reduce fuel cost for the building owner.

For this project, major consideration was given to local codes, space requirements, boiler control, and emission reductions. In 2007, Pennsylvania State Code section IV HG-716 for modular boilers stated that side-by-side installation boilers are acceptable to a maximum of 400 MBh capacity. The only way to install the boilers at the facility was to engage the boiler manufacturer to work together with the Pennsylvania Code Authority, allowing variance approval, before the units could be installed.

The low NOx requirement began with the comprehensive South Coast Air Quality Management District (SCAQMD) program from Southern California, which is used in most of the country.

The boiler industry faces more stringent NOx emission regulations from the EPA. For boilers greater than 2000 MBh, a third-party test is required and NOx should be below 9 ppm. Annual inspections are required as well.

In 2011, the EPA issued a new regulation for boiler maximum achievable control technology, known as MACT. This rule is known as the National Emission Standard for Hazardous Air Pollutants (NESHAP).

To determine the emission limits for NESHAP, EPA and PA DEP use the MACT approach; the regulation was effective in 2012.

The NESHAP regulations define an area source of air emissions as any stationary source or group of stationary sources that annually emit in aggregate less than 10 tons of any single hazardous air pollutant (HAP) or less than 25 tons of multiple HAPs.

Existing coal-fired boilers with a heat input equal or greater than 10 million Btuh are required to adhere to emission limits for mercury and carbon monoxide.

This new regulation determines what a boiler’s emissions are and how often the boiler must be tuned up, based on its size and type. Existing central heating plants do not meet this requirement, and operating an existing central heating plant at the university could be quite costly.

Andre Pearson is lead engineer, infrastructure and optimization at WM Group. Pearson has 11 years of experience in HVAC design, energy audit, and commissioning services for various market sectors. He has completed numerous systems assessments/optimization projects and has identified millions of dollars in savings combined with improved reliability. Jose R. Rodriguez is a technical service engineer at Wallace Eannace Associates Inc. Rodriguez assists engineering consulting firms in New York City on the HVAC product segment of the company.