Commercial boilers are used to heat commercial and multifamily residential buildings. Boilers heat water using fuel inputs (principally natural gas or oil) and generate either hot water or steam. The heated water or steam is circulated through radiators, baseboard units, or fan coils. Commercial boilers are also used in some industrial process applications. Boilers used in commercial or multifamily applications have an input of 300,000 Btu/h (British thermal units per hour) or more.
In 2005, efficiency advocacy organizations (including ASAP, ACEEE, NRDC, and the Alliance to Save Energy) negotiated an agreement with the commercial boiler manufacturers calling for new ASHRAE (American Society of Heating, Refrigerating, and Air Conditioner Engineers) boiler standards. ASHRAE finalized adoption of those recommended new levels in 2007, triggering a DOE rulemaking. (Whenever ASHRAE Standard 90.1 is amended, DOE must either establish amended national standards for the products at the levels specified in ASHRAE 90.1 or establish more stringent standards if they would result in significant additional energy savings and are technologically feasible and economically justified.) In July 2009, DOE published a final rule for commercial boilers, effective March 2012. These national standards are equivalent to the standards in the 2007 version of ASHRAE 90.1.
The earlier standards, effective in 1994, called for a combustion efficiency of 80% for gas-fired boilers and 83% for oil-fired boilers. However, combustion efficiency is not a good efficiency descriptor as it only accounts for combustion inefficiencies and does not account for thermal inefficiencies such as heat radiated from the warm boiler. A better efficiency metric is thermal efficiency, which measures the heat contained in the water or steam as it leaves the boiler relative to the heat content of the fuel that is burned. Typically, the thermal efficiency of a boiler will be 2-3% less than its combustion efficiency.
The new federal standards change the efficiency metric from combustion efficiency to thermal efficiency, requiring 80% thermal efficiency for gas-fired boilers and 82% thermal efficiency for oil-fired boilers. DOE estimates that these standards will save 0.11 quads of energy over 30 years. Greater savings could be realized by using gas-fired condensing boiler(s) with low-temperature distribution and optimizing controls. This technological advance saves 40% (hot water) – 70% (steam) relative to non-condensing systems with minimum 140°F return water temperature.
DOE is conducting a rulemaking to update the standards and issued a proposed rule in March 2016.
Almost 38% of commercial end-use energy consumption is dedicated to space heating, while about 60% of all commercial space heating uses natural gas as the primary fuel source. Fuel oil, on the other hand, is consumed for only 9% of space heating in commercial buildings, though this figure is much higher in certain sections of the country where the building stock is older, such as the Northeast. And because oil is an unregulated fuel in these areas and not addressed through ratepayer-funded energy efficiency programs, the importance of standards is even greater.