The HVAC Factor: Boiler Maintenance
By Jeff Vallett II
From the April 2013 issue of Today’s Facility Manager
How do you know if your boiler plant is operating as efficiently as possible? In a world where building operating costs significantly affect an organization’s financial bottom line, facility managers (fms) should investigate things such as proper application of boiler technology, maintenance programs, and combustion tuning as avenues to reduce heating bills and maintenance costs. There are a few inexpensive exercises that can be completed to ensure proper and efficient operation.
What water temperature is being delivered? In most instances, hydronic heating systems are designed for a worst case, winter weather scenario, which occurs at very few times during the heating season. Typically, the water temperature needed to heat a facility during these worst case conditions is far hotter than what is required during a mild fall day.
In order to match the heat loss of the building at various outdoor conditions, the water temperature can be varied to match the heating requirements; this is a control philosophy known as outdoor reset. By lowering the temperature of the heating fluid when the outdoor temperature is warmer, heating bills can be reduced. Outdoor reset is standard equipment on many boilers built within the last five to 10 years, but if a boiler plant is not equipped with outdoor reset these capabilities can be added for a relatively low cost.
Boiler construction material is important to consider when deciding whether or not to implement outdoor reset. High efficiency boilers are typically constructed of stainless steel or cast aluminum. These materials allow for low entering water temperature due to their corrosion resistance characteristics. Non-condensing boilers constructed of steel, cast iron, or copper are not designed to withstand corrosive environments; therefore, low entering water temperatures should be avoided with these types of boilers. Non-condensing boilers can still be used in applications with outdoor reset; however, precautions should be taken to protect the boiler from inlet water temperatures below 130°F. Before deciding to implement outdoor reset, an HVAC professional should be contacted to evaluate the boiler plant and heat distribution system to ensure all components will satisfactorily heat the facility using lower water temperatures.
High efficiency condensing boilers operate most efficiently when the entering and leaving water temperature from the boiler is less than 130°F (see chart above). When water temperatures are above this point, the efficiency decreases. If water temperatures less than 130°F can be used in conjunction with condensing boiler technology, this is one way to lower heating bills. Boilers constructed of steel, cast iron, or copper should have entering water temperatures above 130°F to limit the risk of damage from lower entering water temperatures.
Is the boiler in tune? Fuel burning equipment should undergo yearly tune-ups to ensure they are operating as safely and efficiently as possible from a combustion standpoint. A tune-up should include a combustion analysis to analyze the exhaust from the boilers.
During the analysis, oxygen, carbon monoxide (CO), carbon dioxide (CO2), and flue gas temperature should be recorded at a minimum. The levels of oxygen, CO, and CO2 indicate the level of complete combustion or fuel burning efficiency. If any of the elements above are out of spec, this can signal the need for maintenance, including cleaning of the combustion chamber and adjusting the fuel to air ratio of the combustion system. Typically, boiler manufacturers will list the allowable range for each of the elements noted above. For specific operating parameters, facilities staff should contact the manufacturer.
Safety is a factor that should be considered when conducting annual tune-ups. A byproduct of burning fossil fuel, CO is a colorless, odorless gas that can be fatal to humans and animals if exposed in high concentrations. Yearly boiler tune-ups can help ensure that heating equipment is burning safely. Additionally, as part of routine maintenance inspections, the boiler vent system should be inspected for integrity at least on a monthly basis.
Overall maintenance. Buildup of dirt, dust, or deposits on the internal surfaces of a boiler can greatly affect its heat transfer efficiency. These deposits can accumulate on the water side or fire side of the boiler.
Following the manufacturer’s instructions for cleaning and maintenance is paramount for sustained efficiency and long equipment life. Manufacturers’ operation manuals should contain minimum recommended maintenance and inspection schedules for fms to reference. A preventive maintenance plan should then be created and followed for each piece of heating equipment. This will keep equipment properly maintained and allow the boiler plant to serve in the most efficient manner.
These relatively low cost practices enable fms to maximize the efficiency, safety, and service life of their boiler plants. Keeping this equipment in good working order lowers fuel bills and improves the bottom line by increasing efficiency and limiting preventable repair costs.
Vallett is a product manager at Lochinvar, LLC in Lebanon, TN. Lochinvar is a manufacturer of high efficiency water heaters, boilers, and pool heaters.