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Nonresidential High Efficiency Boilers and Service Water Heating

Measure Description 

This proposal is making four recommendations: 

Gas Boiler Systems

The proposed prescriptive requirements for gas boiler systems would raise the minimum thermal efficiency of gas-fired hot water boiler systems for space heating to a weighted-thermal efficiency of 90 percent [Section 140.4(k)]. This change impacts gas hot water boiler systems of capacities between 1 and 10 MMBtu/h installed in any type of newly constructed nonresidential building and high-rise multifamily buildings. Weighted thermal efficiencies are calculated based off the input each boiler provides to the total system capacity. This measure would also add two requirements for the hot water distribution system that aim to optimize condensing operation:

  1. Hot water return entering the boiler(s) must be 120°F or less. 
  2. Flow rates for supply hot water that recirculates directly into the return system must be no greater than 20 percent of the design flow of the operating boiler. 

Gas Service Water Heating Systems

The proposed prescriptive requirements for gas service water heating systems would raise the minimum thermal efficiency of gas-fired hot water boiler systems for space heating to a weighted-thermal efficiency of 90 percent. [Section 140.5(c) –new subsection]. This change impacts gas service water heating systems of capacities between 1 and
2022Title 24, Part 6 Draft CASE Report–2022-NR-HVAC3-D|1210 MMBtu/h installed in any type of newly constructed nonresidential building and high-rise multifamily buildings. Water heating systems that serve individual dwelling units would not need to comply. Individual gas water heaters with input capacity less than 100,000Btu/h are also excepted
.

Oxygen Concentration for Process Boilers

The proposed mandatory changes would adjust the stack-gas oxygen concentration requirements for newly installed process boilers with input capacity between 5 and 10 MMBtu/h from 5 percent to 3 percent. [Section 120.6(d)]. This change would simplify the code by aligning with current requirements for process boilers greater than 10 MMBtu/h. For process boilers, the Statewide CASE Team is also recommending a clarification that the combustion air volume be controlled only by flue gas concentration, eliminating the option to control based on firing rate

Oxygen Concentration for Commercial Boilers

The proposed mandatory changes would require stack-gas oxygen concentrations of no greater than 3percent for boilers installed in new construction with input capacity of 5 MMBtu/h. [Section 120.9(c)]. This change also simplifies the code so all boilers that are subject to oxygen concentration requirements must maintain a concentration of 3 percent or less. Currently, commercial boilers with steady state full-load thermal efficiency of 85 percent or higher are not required to meet oxygen concentration requirements. This exception would be eliminated.As with process boilers, the Statewide CASE Team is also recommending a clarification that the combustion air volume be controlled only by flue gas concentration, eliminating the option to control based on firing rate.

The first two proposals add boiler system efficiency and service hot water heating system efficiency requirements to the prescriptive compliance pathway and apply only to newly constructed nonresidential and high-rise multifamily buildings with large offices, hospitals, hotel/motel, and high-rise multifamily buildings particularly subject to impact.These two changes would align Title 24, Part 6 requirements for the minimal thermal efficiencies of boiler and gas service hot water heating systems with the current requirements in ASHRAE 90.1-2019. The next two requirements are modifications to the mandatory oxygen concentration requirements that apply to newly installed commercial boilers in new construction and newly installed process boilers in new construction and alterations. Applicable commercial and process boilers with an input capacity of 5MMBtu/h or greater would be required to-maintain stack-gas oxygen concentrations at less than or equal to 3 percent by volume; this required level is assessed on a dry basis over firing rates of 20 to 100 percent. The oxygen concentration measure would impact all nonresidential and multifamily high-rise residential buildings that meet the capacity thresholds, as well as process boilers that meet the capacity threshold.

Relevant Documents

Measure proposals, supporting documents, and other outside references will be made public as they become available.

CASE Reports

Round Two Utility-Sponsored Stakeholder Meeting Materials

Round One Utility-Sponsored Stakeholder Meeting Materials

Provide Feedback

Draft CASE Report Now Available (Comments accepted until June 12, 2020)

This measure description will be updated as research is developed to support the 2022 code cycle. For questions or suggestions, email info@title24stakeholders.com. Include the measure name in the subject line.

Give Us Your Feedback

The Statewide CASE Team values input from all stakeholders engaged in the Title 24, Part 6 code change process. We encourage the open exchange of code change comments and concerns.

  • Use the form above to provide feedback on this measure.