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One of the greatest opportunities for energy savings in buildings through retrofits and retro-commissioning is optimized HVAC control sequences. ASHRAE Guideline 36: High-Performance Sequences of Operation for HVAC Systems (G36) provides standardized and optimized control sequences for HVAC systems. With demonstrated 50 to 60 percent HVAC energy savings with six to eight-year simple paybacks (where the control systems were fully replaced), G36 has the potential for deep, cost-effective energy savings in addition to further benefits across the industry. Multiple research and field demonstration projects have demonstrated the application of G36 in buildings and provided supporting data for efforts to drive the adoption of G36 by HVAC designers, contractors, and building owners.
In an earlier article, we discussed training developed for Department of Defense facility managers, including ASHRAE Guideline 36. In this article, we dive deeper into G36, including an explanation of the Guideline and benefits provided. Data from real-world G36 applications shows how you can apply the Guideline in your buildings.
What is ASHRAE Guideline 36?
G36 is a library of standardized sequence logic for the control of HVAC systems and equipment. The latest version (released in August 2021) contains sequences for single- and multi-zone variable air volume (VAV) reheat air handler units (AHUs), terminal units, and hot water and chilled water plants, and applies to both new construction and retrofits. The guideline continues to evolve and will ultimately cover other equipment and system types such as dedicated outdoor air systems, and more.
Energy-savings features of G36 include “trim and respond” demand-based temperature and pressure resets, VAV terminal dual-maximum logic, demand response, demand-controlled and occupied-standby ventilation, and economizer sequencing. In addition to energy savings, G36 helps improve building operation through real-time fault detection and diagnostics and hierarchical alarm suppression.
G36 has been gaining market momentum. In a recent survey that we conducted of 488 individuals at controls contractors across the US, 68 percent of respondents had heard of G36, with 43 percent of those having implemented it on at least one project. With growing market penetration, implementation costs will decrease, improving the cost-effectiveness of retrofits.
Benefits of G36
Modern direct digital control (DDC) systems are generally operated with custom programming logic created by the installing contractor. Though most building HVAC systems are generally similar, the current standard industry practice is to develop custom sequences and control programming for each application, or to adapt sequences from a similar recent project. In addition to the process inefficiency of reinventing the wheel for each project, this practice also introduces the risk of problems and operational inefficiencies, such as poorly written sequences or incorrectly implemented programs. G36 helps address this industry issue by providing a collection of high-performance sequences of operation for HVAC systems. Beyond simply establishing a set of best practice sequences, industry standardization around G36 offers the potential for market transformation by streamlining the Building Automation Systems (BAS) implementation process through design, installation, and operation. With standardization, BAS manufacturers can centrally pre-program, pre-debug, and pre-validate the logic in their software libraries, which improves quality and greatly reduces the effort required on each project for programming and commissioning.
G36 provides value to wide a range of industry stakeholders throughout the design and construction process. With G36, facilities management, building owners, design engineers, controls contractors, controls manufacturers, and commissioning providers will see cost savings, increased revenue, and improved occupant comfort. The building owner will see lower design and construction costs and improved thermal comfort, leading to fewer occupant complaints. Overall, design engineers, controls contractors, and commissioning providers will put in less effort to design, implement, and test systems, and they will see an increase in customer satisfaction. As a result, controls contractors and commissioning providers can expect an increase in market demand, which can have significant economic benefits such as new jobs.
With further market penetration, G36 will bring market efficiencies. The controls industry will benefit from pre-programmed and vetted G36 logic that can be used over and over. Centralized pre-programmed and pre-tested application libraries ensure quality and reduce project field implementation time. Eight large BAS manufacturers have already released at least partial libraries.
Demonstrated Results of G36
Early implementations of airside sequences of operation in G36 showed savings of 50 to 60 percent HVAC energy were achieved with six- to eight-year simple paybacks where the control systems were fully replaced. These are for buildings with complete hardware retrofits to replace older DDC systems with zone-level DDC or pneumatic controllers. Most of the savings came from:
In buildings with existing modern control systems, there is an opportunity to do a retrofit with just re-programming the control sequences to Guideline 36. Implementations of G36 where only software updates were performed showed HVAC savings of 10 to 25 percent with two- to seven-year simple payback.
The retrofit has the most potential for energy savings if the existing system has older DDC or pneumatic zone-level controllers, fixed or limited reset ranges for duct static pressure and supply air temperature, and the VAV terminal units have single-maximum sequences with high minimums.
How you can take advantage of G36
With proven energy savings, additional benefits of standardization, and market momentum, anyone involved in the ownership, design, construction, and building commissioning process should take advantage of Guideline 36. As an owner, you can require G36 in your RFPs. We recommend contract requirements for standard libraries as they become available.
ASHRAE G36 is a proven, cost-effective opportunity to achieve large reductions in energy consumption through standardized high-performance sequence logic for control of HVAC systems and equipment. Early implementations of G36 showed up to 60% HVAC energy savings. G36 works great in new construction, as well as in retrofits where older control hardware is being replaced or a modern DDC system already exists. The building controls industry is rapidly adopting G36, with 68% of controls contractors indicating they have heard of it and 43% having implemented it on at least one project. All major BAS manufacturers have committed to pre-programming G36 into their factory application libraries. As a contractor, designer, owner, or any other industry stakeholder, there are resources to support you in applying G36, including trainings and a best practices guide.
Rupam Singla is Technical Project Manager, TRC. Gwelen Paliaga is Technical Director, TRC. TRC is a national leader in advanced energy services with direct experience in energy advisory services, distributed energy resources, research and technology commercialization, technical and engineering services, and energy program delivery.