For most of the history of commercial building controls, the quality of a building's control sequences depended almost entirely on the experience and diligence of whoever programmed them. One controls contractor might write a technically sound supply air temperature reset sequence with well-tuned PID parameters. Another might hard-code the supply air temperature at 55 degrees Fahrenheit and call it done. Both buildings would have "controls," but their energy performance and occupant comfort would be very different.
ASHRAE Guideline 36, formally titled "High-Performance Sequences of Operation for HVAC Systems," is a serious attempt to address this problem by defining what good control sequences look like for common HVAC equipment types.
What Guideline 36 Is
Guideline 36 is an ASHRAE publication, not a standard or a code. At present, it is not legally binding unless a project specification or local energy code references it explicitly. What it is, however, is a carefully engineered set of control sequences developed by a committee of experienced mechanical engineers and controls specialists, validated against real building performance data, and written with enough specificity to actually be programmed.
The current version covers: - Variable-air-volume (VAV) air handling units - VAV terminal boxes with and without reheat - Dual-duct VAV systems - Fan coil units - Chilled water plant control (chillers, cooling towers, primary and secondary pumps) - Boiler plant control
For each equipment type, Guideline 36 specifies the complete sequence of operations: startup and shutdown procedures, operating modes, setpoint reset strategies, economizer control, demand-controlled ventilation, minimum ventilation rate calculations, alarm conditions, and the specific control logic for each operating mode.
The sequences are not minimal-compliance sequences. They are designed to produce high energy efficiency while maintaining occupant comfort. The supply air temperature reset strategy in Guideline 36, for example, is based on actual zone demand feedback rather than a simple outdoor air reset, which consistently produces better energy results.
Key Sequences Worth Understanding
Several of the Guideline 36 sequences have a meaningful impact on energy performance that is worth understanding even if you are not a controls programmer.
Supply air temperature reset based on zone demand. Instead of resetting supply air temperature based solely on outdoor air temperature (a simple but imprecise approach), Guideline 36 uses feedback from VAV terminal boxes to determine the actual cooling demand across all zones. The supply temperature is reset as high as possible while still satisfying the zone with the highest cooling requirement. This reduces reheat energy significantly in buildings where many zones are in partial-load conditions.
Static pressure reset. The duct static pressure setpoint resets down as VAV box damper positions decrease. This reduces fan energy when load is low, which in a typical VAV system is the majority of operating hours. Guideline 36 specifies the reset logic in detail, including the damper position thresholds that trigger the reset.
Demand-controlled ventilation integrated with the AHU sequence. Rather than treating DCV as a separate add-on, Guideline 36 integrates CO2-based ventilation control directly into the AHU operating sequence, with defined interactions between zone-level CO2 control and AHU minimum outside air damper position.
Chiller plant staging. The chiller plant sequences define how multiple chillers should be staged based on load, how cooling tower fans should be controlled to optimize approach temperature, and how the differential pressure setpoint for the chilled water loop should reset based on valve positions. Properly implemented, these sequences can reduce chiller plant energy consumption by 15-25% compared to fixed-setpoint operation.
Why Guideline 36 Matters for Building Owners
Building owners typically do not read control sequences, and they should not have to. But understanding why Guideline 36 matters helps you ask better questions of your controls contractor.
Predictable performance. When your controls contractor specifies Guideline 36 sequences, you know what you are getting. The sequences have been validated. Their energy performance characteristics are documented. You do not have to trust that the programmer made good decisions based on their individual experience.
Competitive bidding on equal terms. When a project specification requires Guideline 36 sequences, every bidding contractor is pricing the same scope. You can compare bids based on installation quality, licensing costs, and service approach rather than trying to evaluate the quality of each contractor's proprietary sequences. This often results in better bids and clearer scope.
Easier commissioning. Commissioning agents who work on Guideline 36 projects have a defined reference document. The functional performance test procedures can be developed against the specific sequence requirements rather than against a general description of intent. This makes commissioning more thorough and faster.
Documentation that follows the building. Ten years from now, when a new facility manager or a new controls contractor is working on your building, the Guideline 36 documentation tells them exactly what the sequences are supposed to do. Buildings with well-documented Guideline 36 sequences are easier to maintain and troubleshoot than buildings with proprietary sequences that lived in one programmer's head.
Where Guideline 36 Falls Short
Guideline 36 does not cover every equipment type, and some buildings have requirements that do not fit neatly into the standardized sequences.
Dedicated outdoor air systems (DOAS), which are increasingly common in Gulf South applications because of humidity control requirements, are not comprehensively addressed in the current version of Guideline 36. Custom sequences are still required for many DOAS configurations.
High-humidity climates like ours sometimes require modifications to the economizer sequences specified in Guideline 36. The standard differential enthalpy economizer control is generally appropriate, but the specific enthalpy lockout thresholds may need adjustment for coastal Louisiana conditions where outdoor humidity can exceed what the standard thresholds expect.
Process cooling applications, data center cooling, and specialized laboratory HVAC also fall outside the Guideline 36 scope.
How We Use Guideline 36
We use Guideline 36 as our starting point and customize from there. For standard VAV AHU and terminal box applications, the Guideline 36 sequences are the right answer, and we program to them with minimal modification. This gives our clients all the benefits of standardization while keeping programming effort reasonable.
For equipment or applications that Guideline 36 does not address, we use the same engineering rigor to develop custom sequences: defined setpoints, defined control logic, defined safeties and alarms, and a written sequence document that gets reviewed and approved before programming begins.
The Future: Guideline 36 in Energy Codes
There is a reasonable expectation within the industry that Guideline 36 sequences, or sequences of equivalent performance, will eventually appear in energy codes. California's Title 24 energy code already references Guideline 36 sequences for VAV systems in some applications. ASHRAE 90.1, which is the national commercial energy standard, has been moving in this direction as well.
For building owners who adopt Guideline 36 now, this is an investment that positions you well for future code compliance regardless of which direction the regulatory environment moves. For building owners who have proprietary, undocumented sequences in their existing systems, it is worth understanding what migration to documented, high-performance sequences would require.
If you want to understand how Guideline 36 sequences would apply to your specific HVAC systems, we are glad to review your mechanical design and walk through what implementation would look like.