ASHRAE 90.1 comes up in almost every conversation we have with engineers and building owners about new construction and major renovations, but the controls-specific requirements within the standard are frequently misunderstood or overlooked. The standard is published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, and it establishes minimum energy efficiency requirements for commercial buildings. More importantly for this conversation, almost every state building code in the country adopts some version of ASHRAE 90.1 by reference. In Louisiana, the state energy code is based on ASHRAE 90.1 as well. Compliance is not optional for new construction, and major renovations can trigger compliance requirements for existing systems.
What ASHRAE 90.1 Actually Requires from Controls
The standard has an entire section (Section 6 for HVAC, Section 9 for lighting controls) dedicated to controls requirements. The controls provisions are more prescriptive than most people expect.
Automatic setback and setup. The standard requires that thermostats and control systems automatically reduce heating setpoints and increase cooling setpoints during unoccupied periods. Specifically, during unoccupied times, heating setpoints may not exceed 60 degrees Fahrenheit and cooling setpoints may not be lower than 85 degrees Fahrenheit unless the zone has occupancy sensor control. This is a basic requirement that a properly programmed BAS handles automatically, but we routinely find buildings where the occupied setpoints run 24 hours a day, seven days a week because nobody set up the schedules.
Economizer controls. In most climate zones, ASHRAE 90.1 requires that cooling systems above certain capacity thresholds include economizer capability. The standard specifies both temperature-based and enthalpy-based economizer control, with specific requirements for high-limit shutoff setpoints. Louisiana falls into a humid climate zone where the standard's economizer requirements include provisions for humidity-based lockout, which is appropriate given our outdoor air conditions.
Demand-controlled ventilation. For spaces designed for high-density occupancy (assembly rooms, conference rooms, classrooms) above 500 square feet, the standard requires demand-controlled ventilation using CO2 sensors to modulate outside air based on actual occupancy rather than design maximum. This is both an energy savings measure and a code requirement.
Simultaneous heating and cooling limitations. ASHRAE 90.1 prohibits, or severely restricts, control sequences that heat and cool the same air simultaneously. A PNNL study (PNNL-26348) found that compliance with this requirement was the lowest of all controls measures tested, at just 10 percent during first-pass functional testing. The standard allows some reheat for humidity control, but within strict limits, including a requirement that VAV boxes limit airflow to no more than 30 percent of design during reheat.
What Happens When Your Controls Do Not Meet Code
Failed compliance inspections are the most direct consequence, and they happen more often than people expect on renovation projects. When a building permit includes mechanical systems and the inspector reviews the control sequences, non-compliant programming can result in a failed inspection and required corrections before a certificate of occupancy is issued.
The less obvious consequence involves utility incentive programs. Both Entergy and CLECO run energy efficiency incentive programs that provide rebates for qualifying HVAC upgrades. Almost all of these programs require that the completed system meets or exceeds applicable energy codes. If your controls do not meet ASHRAE 90.1, you may be disqualified from rebates that could have offset a significant portion of your project cost. We have helped building owners recover tens of thousands of dollars in utility incentives by ensuring their controls sequences met the standard's requirements and documenting that compliance for the utility's application process.
The Standard Applies to Renovations Too
This is the point that surprises people most often. ASHRAE 90.1 is not just for new construction. Section 11 of the standard addresses existing buildings and alterations. When you make a "major renovation," defined as a change in the building envelope or HVAC system that requires a permit, the altered portion of the building is typically required to comply with current code.
In practice, this means that if you are replacing an air handling unit or adding a new zone to an existing system, the controls for that work need to meet current ASHRAE 90.1 requirements. If you are already going through the permitting and construction process, it makes sense to understand what the controls compliance requirements are before the installation is complete rather than after.
How a Properly Programmed BAS Makes Compliance Straightforward
A BAS that is correctly programmed for an occupied/unoccupied schedule, with appropriate setback setpoints, economizer logic with proper high-limit controls, demand-controlled ventilation in applicable spaces, and sequences that prohibit simultaneous heating and cooling, satisfies the core controls provisions of ASHRAE 90.1 as a natural consequence of doing the job right.
The documentation piece matters as well. Part of demonstrating compliance is being able to show an inspector or a utility program reviewer what the system does and how it is configured. A BAS with well-organized graphics, clearly labeled sequence logic, and trend data showing the system operating as intended is much easier to verify than a system where the only documentation is a wiring diagram from the installation contractor.
Optimal start is one of the ASHRAE 90.1 requirements that often gets overlooked. The standard requires that systems above certain thresholds use optimal start logic that calculates the latest possible start time to achieve setpoint at the beginning of the occupied period, rather than starting at a fixed time that is arbitrarily early. A BAS handles optimal start through programming that accounts for outdoor temperature, space temperature, and historical warm-up or cool-down rates. It is a feature that most platforms support out of the box but that requires intentional configuration to activate.
Fan Power Limitations
ASHRAE 90.1 also establishes maximum allowable fan power for air handling systems, measured in brake horsepower per cfm. This is primarily a mechanical design issue, but the controls side touches it in a specific way: variable speed drives on supply and return fans are generally required above certain system sizes because they allow fan power to vary with actual load rather than running at full speed continuously. A BAS that controls VFDs, trims fan speed based on duct static pressure, and resets static pressure setpoints based on zone demand is doing exactly what the standard intends.
The standard is updated on a periodic cycle, and the version adopted into your local code may not be the most recent edition. Louisiana's current code references a specific edition, and it is worth knowing which version applies to your project. We stay current on this because the compliance requirements we are programming to need to match the version that governs your permit.