Why ASHRAE Guideline 36 is so important.
The lack of commonly accepted standardized control sequences in our industry is a problem.
By recent studies, this issue results in waste that accounts for over 30% of the total building HVAC energy use, or 12% of the total building energy use (Note 1,2,4,5), which could be resolved by following a standardized set of best-in-class sequences of operation for commercial buildings.
The absence of a common understanding of how the basic HVAC sequences should function has resulted in recurring one-off customized specifications and programmed control approaches that cause confusion from design to implementation to operation.
The product of these customized control sequences is often simply wrong, wasting a tremendous amount of energy with a variety of dynamics that can go completely unnoticed throughout the life of the system.
Buildings are unique. Designs for the mechanical systems for those buildings are unavoidably, somewhat, unique. But these sequences that control how those mechanical systems operate don’t have to be unique. There is not such a variety of mechanical types that controls approaches cannot be standardized.
This is where ASHRAE Guideline 36 comes in.
The guideline produced by ASHRAE known as "ASHRAE Guideline 36: High-Performance Sequences of Operation for HVAC Systems" (aka G36) is a cornerstone document, on the level of importance as other documents for the built environment like 90.1 (Energy Standard for Sites and Buildings except Low-Rise Residential Building) and 62.1 (Ventilation and Acceptable Indoor Air Quality). G36 fills an important gap left by 90.1 and 62.1, both of which are required standards for new construction and many renovations in most US jurisdictions. ASHRAE 90.1 and 62.1 explain what is required for a healthy and efficient non-residential building, but not necessarily how the systems are to be operated to get there. This is where G36 fits in. It provides an accessible toolbox of standardized control approaches that have the power to reduce building energy consumption immensely. Initial studies have shown that retrofits for medium-sized commercial buildings’ VAV control sequences provide an average of 31% HVAC energy reduction across various US climate zones (Note 1).
The savings are not minor. The opportunity is pervasive across all climate zones. How our systems function is not meaningless, it is core to our industry.
The opportunity
The authors of G36 identified a major opportunity for improvement in buildings. Control sequences for commercial HVAC equipment do not operate in a standardized approach and often function remarkably poorly, both in terms of efficiency and overall performance for comfort and building health. The root of the issue is a lack of common acceptance of approaches for HVAC sequences of operation. This leads to a process whereby the design engineer specifies a sequence, sometimes from scratch, sometimes copied/pasted from a previous project, sometimes right, sometimes nonsense, that is then given to a controls contractor who takes that specification and programs it, either from scratch or copied from a previous project that also may or may not have worked properly. That product is then handed over to the building operator, sometimes with training, sometimes without training, and the automation is supposed to be well understood, trusted, and work consistently, at that point in time, and for the rest of the life of the system for that operator, and for future building operators.
Wouldn’t it be nicer if everyone in that process had a common understanding of how HVAC systems are supposed to work? Wouldn't it be nicer if design engineers adapted existing standard sequences that have been proven to perform, rather than developing one-off sequences themselves? Wouldn’t it be nicer if the controls programmer could reference a common library of code that has also been proven to work, and all members of the team including commissioning agents, T&B contractors, and owner’s agents had observed work well and reliably at other buildings? Wouldn't it be nicer if when a new building operator was hired, the systems worked like the last building they were in? Wouldn’t it be nicer if the controls programming was de-bugged, not by the technician on your project, but by the large number of technicians and engineers from all previous projects and implementations of the code? Doesn't that sound like it would lead to a better product, happier occupants, and even be easier to implement?
These are fundamental benefits from G36, resulting from a common understanding of the way mechanical systems in the built environment are supposed to operate. The guideline is not perfect. It is the product of a technical committee and reasonable minds can differ on what the "optimal" approach is for any given sequence, but the value of standardization is worth the limitations it places on the designer. In our industry, placing limitations on the designer is a good thing. Our industry has not changed so much since Willis Carrier defined the concepts for modern air conditioning that it is not suitable for a standard approach to HVAC sequences of operations. The guideline is also not exhaustive of all types of HVAC equipment. Far from it, but it covers the basic equipment that makes up the majority of HVAC equipment.
In short, our industry often fails to exceed a basic level of performance with the way the systems are controlled. Poor understanding of the fundamentals, copy/paste design approach leads to systems that fail to perform. This leads to operators not trusting the automation. This leads to operators overriding the automation, which leads to poor performance and energy waste.
A product of collective knowledge.
The guideline was initially released in 2018, focusing on airside sequences of operation for the most common AHU and terminal box configurations. Then, the guideline was updated in 2021, with the addition of chilled water and hot water plant sequences. The guideline was developed through a systematic approach that started with ASHRAE funded Research Promotion (RP) funds: RP-1455, then added content and input from additional funded research. Throughout the development of the standard, the process was transparent, peer-reviewed, open to members of ASHRAE for comment, and then evaluated through both empirical and non-empirical research. The result is a guideline that is not the product of one-off concepts from a single smart engineer or single company, but rather the product of collective wisdom from an open forum of experts, vetted and improved over decades, through a consensus-based approach. Many of the same minds that have been historical thought leaders in ASHRAE, with numerous publications in the ASHRAE Journal and other peer-reviewed periodicals contributed to the guideline. A list of primary contributors to the guideline and referenced research papers includes members from these companies and institutions: Taylor Engineers, ALC, Facility Dynamics, UC Berkley, Drexel, Iowa Energy Center, Price, ALC, U. of Alabama, P2S, Integral Group, U. of Colorado Boulder, TRC and UC Berkley. A useful guideline that describes the controls approaches and background in simpler terms is available online (Note 8).
How much can G36 save?
There have been several studies on the impact of G36 using different approaches, both from energy modeling and in-field measurement and verification of implementations. One study funded by the US DOE and California Energy Commission (Note 1) found an average savings of 31% of HVAC energy for the G36 air-side control sequences compared to a “conventional” control strategies. Another study (Note 4) showed that on average the G36 minimum airflow control saved 16.1%, the supply air temperature reset saved 6.6% and the duct static pressure reset saved 3.6% of the building site energy across different climate zones. Another study (Note 5) found that G35 paired with full retrofits saved 50-60% of the HVAC energy use, and saved 10-25% when implemented as software changes alone. In the larger context, since approximately 13% of all energy produced in the US is used for HVAC (Note 6), the opportunity for impact with this standardized best-practice approach is immense; 4% reduction in all energy produced in the US (Note 7).
For your building, quantification of the energy savings and improved performance from a G36 conversion or a new installation relative to a typical building is a function of how the existing sequences operate. Anyone that has spent time in this industry observing operation of real-world building automation knows just how poor some of the existing sequences in operation can be. For control renovations, calculating the savings can be done with a whole building energy simulation as part of a building energy audit.
Observations on the Performance of G36
This post is not a defense of all aspects of the guideline. I may or may not agree with the "optimal" approach for some of the specific control approaches, but I vehemently agree with the need for this guideline, see the reasonableness of the approaches described, support ASHRAE and the authors for the work done so far, and recommend the guideline for implementation. I've seen sequences in action and seen the positive results. The value of the guideline is as much about the transition to standardization as it is about the immediate savings, but to be clear, the energy savings can be immense.
From experience, one stand-out component of the savings comes from the use of an “Occupied Standby Mode”, and in-particular resetting of the minimum box flow (Vmin) based on space occupancy. Based on this experience, and as predicted by simulation-based research (Note 4), the occupancy-based reset of Vmin is one of the primary opportunities for energy and performance savings that are identified by G36. VAV boxes are very much oversized, as are the initial configurations for minimum flows. This tool eliminates that issue for much of the zone’s operation.
I've also seen the resetting of pressure and supply air temperature perform well but be limited by the mechanical limitations of critical zones, which can only be addressed by correcting downstream mechanical deficiencies. Without training the operators on the use of rogue-zone-elimination, the trim and respond feature can be underutilized, but still no worse off than the status quo, and likely much better for many conditions. With proper training, the identification of trouble zones, in the right operator’s hands, is a win-win for the operator and occupant. The smooth operation of the common control loop for heating valves, cooling valves, and economizer as well as the rational transition into and out of economizer mode is unbeatable.
Acceptance of G36
Common acceptance of G36 will likely be gradual. The issue is somewhat cultural. There is a culture of customized design solutions, particularly for control sequences. Theoretically, the standardized approach should be easier for the design engineer and controls contractor and therefore more cost-effective to install, so that should encourage implementation. Unlike 90.1 and 62.1, G36 is a guideline and not a standard, so not written to be enforceable by a building code. The adoption of energy efficiency standards (which were based on 90.1) as a code-enforceable document in the 2000s was a turning point for building efficiency and was a major contributor to the reduction of commercial building energy use. The gap left by not defining explicitly how to control the systems has been a void and opportunity for improvement for many years. In my opinion, as the benefits from the initial standardized installations are realized by the design, construction, and operations teams, word will spread.
What can you do to benefit from G36?
Use it! Optimization of the existing mechanical assets that you have using G36 is a very accessible way of saving building energy and is demonstrating to be more cost-effective than the industry previously appreciated. The major control vendors have already developed the basic library of code and verified its operation. The upgrade can be for a single mechanical system but is best done as a full building control upgrade. For existing systems, start with an energy audit that includes an 8760-hour energy modeling of your existing operation. The approach must make assumptions about the current operation that are verified through observations of existing performance. The model is of course not perfect but is the best way to estimate savings. The extent of the upgrade and incorporation of G36 is a function of the existing system mechanical layout and controls hardware. Expansion of the existing controls hardware to facilitate the G36 sequences, such as occupancy sensors to enable Occupied Standby mode, as well as other hardware can be evaluated on a case-by-case basis. Then, implement a controls retrofit project, ideally, one which fits the criteria for the “perfect upgrade project”, which is one that:
Improves the performance of an existing system, and ideally one that is nearing its end of useful life and in need of replacement anyway.
Leverages energy rebates to fund the project partially or fully.
Has a lasting reduction in energy costs, that results in a highly attractive rate of return.
In my experience, when coupled with optimization, a controls upgrade project meets this criterion for many sites. I recommend that you consider it for yours.
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References:
7 31% HVAC energy savings on average, with HVAC energy accounting for 13% of US energy consumption.