This CASE Report presents code change proposals and associated justifications for laboratory HVAC requirements. These proposed code changes address the challenges commercial buildings face in electrifying and will continue to drive increases in efficiency in the following areas:
- Reducing air changes per hour during unoccupied times.
- Providing a new compliance option by way of a simplified fan control.
- Making heat recovery mandatory.
- Limiting reheats for large systems with multiple zones.
Each proposal is described in more detail below.
The proposed code change would extend the existing laboratory variable air volume (VAV) requirement in Section 140.9(c)1 to clarify that labs must have the ability to reduce airflows when occupied, and that they would need to further reduce airflows when unoccupied. With this change, variable airflow systems will save energy at all required occupied. It would also modify existing requirements so they would apply to all laboratory spaces instead of just applying to spaces with minimum circulation air changes per hour (ACH) and spaces with 10 ACH rates or less.
The proposed code change would add a requirement for heat recovery for laboratory exhaust systems. Specifically, it would add a new requirement in Section 140.9(c)6 (Prescriptive Requirements for Laboratories and Factories) requiring exhaust air heat recovery for some labs.
Exhaust Fan Control
Currently the energy code allows a relatively low design fan power of 0.65 W/cfm unfiltered exhaust or 0.85 W/cfm for filtered exhaust or there is no limitation on fan power if the fans are controlled in response to wind speed or contaminant concentration in the exhaust system plenum. This proposal increases the flexibility of the fan control options by allowing all three of the exhaust fan controls specified by ANSI Z9.5-2022. Thus, the simplified turn-down fan control, based on lab exhaust airflow is allowed, in addition to the wind-responsive and contaminant-monitored control. This proposal would limit the allowed design exhaust fan power to 1.3 W/cfm controlled by these three control systems. These controlled systems would be designed with variable speed control and with the capability of safely decreasing exhaust stack flow by at least 40 percent (reduce to 60 percent of design flow) in response to one of the three control inputs (zone flow, wind speed and direction or contaminant concentration). At the minimum flow rate for the system, the fan shall reduce fan power to 40 percent of its design power.
The simplified turndown control does not rely on the maintained accuracy of windspeed or contaminant sensors but rather the inherent modelled design of stack height, minimum velocity of exhaust flow and the dispersion characteristics of the site.
This proposed change would add an additional design fan power and control combination to the prescriptive requirements in Section 140.9(c)3 for laboratory exhaust fan system power consumption. These requirements would apply to all laboratory fan exhaust systems with a design flow rate greater than 10,000 cubic feet per minute (cfm). The laboratory occupancies covered are occupancy classes B (business), L (laboratory) and H (hazardous). This requirement would also apply to replaced laboratory ventilation systems.
Reheat Limitation (4-Pipe VAV)
The proposed code change would add a new requirement in section 140.9 (prescriptive requirements for laboratories) that would eliminate reheat in most labs. The proposed change will not prevent any labs from meeting any special pressurization or cross contamination or humidity control or high exhaust requirements.
Code Clean-Up Including Scope of Laboratory Requirements
This proposal specifically includes L occupancies in the scope of Title 24, Part 6. In section 100(a)1, the current scope includes “all buildings that are Occupancy Group A, B, E, F, H, I, M, R, S, or U…” These are all the Occupancy Group types in the International Building Code (IBC). The scope does not include Group L (laboratory) occupancy classification special occupancy classification developed for the California Building Code (CBC). The CBC is the IBC with the California amendments such as the definition of the Group L classification. Title 24, Part 6 regulates the mechanical and lighting systems of labs, and it currently regulates buildings with lower quantities of hazardous materials Occupancy Group B (business) as well as those with higher amounts of hazardous materials Occupancy Group H (high hazard). Occupancy Group L is an evolution of Occupancy Group H8, and should have been added under the list of covered buildings when Group L became a part of the Occupancy types.
This proposal adds to the definitions section a definition of laboratory as “A room, building or area where the use and storage of hazardous materials are utilized for testing, analysis, instruction, research or developmental activities.” This definition is a direct quote of the definition of laboratory in the California Building Code. For completeness, this proposal updated the definition of nonresidential buildings to include Occupancy Group L so there is no ambiguity whether a laboratory building or laboratory space is considered a nonresidential building.
In the current code, the exhaust fan power requirements are based on units of watts per cfm. However, it was not fully clear what the cfm refers to. As shown in Figure 5 laboratory exhaust systems there are three different airflow rates associated with the same fan system:
- The exhaust flow from all spaces served by the exhaust system.
- The flowrate of air entering the exhaust fans including the exhaust air from the lab spaces served by the exhaust system and the bypass air entering the fans.
- The flowrate leaving the exhaust stack. This includes the flowrate of the air entering the exhaust fans plus any entrained air by an induction fan system.
It was clear that the cfm did not include entrained air such as one might have in an induction fan, but it was not clear if the airflow rate included bypass air or not. Strictly speaking the bypass air is not exhaust air but rather outside air that is mixed with exhaust air to increase the velocity of stack velocity without increasing the use of conditioned indoor air. The new update clarifies in Section 140.9(c)3 that “exhaust fan system airflow rate is the total of the airflow rates entering the exhaust fans which includes exhaust air and bypass air but does not include entrained or induced airflow downstream of the exhaust fans.”
Round Two Utility-Sponsored Stakeholder Meeting Materials
- Stakeholder Meetings, Round 2 Introduction
- Laboratory Airflow – Proposal Summary
- Laboratory Airflow – Presentation (May 10, 2023)
- May 10, 2023 Meeting Notes
Round One Utility-Sponsored Stakeholder Meeting Materials
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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.
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