ET25SWE0013 - Simplified HVAC Control Retrofits

More than 80% of the buildings that will exist in 2050 are already built and are existing buildings. Created for new construction projects, American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE) Guideline 36 (G36), “High-Performance Sequences of Operation for HVAC Systems”, provides detailed instructions for how to control heating, ventilation, air conditioning (HVAC) systems efficiently. Applying these strategies to existing buildings offers the potential for cost effective energy savings and significant decarbonization. This project will create a guide for identifying low cost, high impact control retrofit measures and a package of recommended control sequences that are adapted from G36 to address typical conditions in existing buildings.

For full control system replacements, previous demonstration projects (see reference list) have cost-effectively achieved up to 50 to 60% HVAC energy savings where all of G36 is implemented, but these efforts involve costs and complexities that are barriers for scaling. For retrofits, the existing control infrastructure is often incompatible with G36 and so either the hardware must be revised to match G36, or the sequences of operations must be adapted to match the hardware. Most practitioners do not have experience with G36, do not know which sequences are most effective for energy savings, and do not know how best to adapt the sequences to match typical existing HVAC control conditions.

A simplified version of G36, “Guideline 36 Lite” (G36 Lite), targeted to retrofit projects in existing buildings, will focus on measures that can be implemented easily and economically, including ones that have often been overlooked by retro-commissioning providers. This G36 Lite approach will promote application and adaptation of key portions of G36 to the existing building stock to help achieve rapid and cost-effective energy savings. Similar past projects (see reference list) have achieved over 20% HVAC energy savings from simple programming and setpoint changes with short simple paybacks. Through this project, the final outcome of a new guide will help practitioners apply high impact measures to retrofits and support scaling these concepts from G36 to reduce energy use and emissions in the existing building stock.

For utility programs supporting existing commercial buildings in California, G36 Lite strategies will help set the bar for implementers, utilities, and regulators regarding what is achievable in existing buildings and how such improvements can be estimated and verified. The results of this work will support program design.

Existing commercial buildings represent a significant opportunity for energy savings and emissions reductions, yet many continue to operate with outdated or inefficient heating, ventilation, and air conditioning (HVAC) control strategies. Although American Society of Heating, Refrigeration, and Air-Conditioning Engineers Guideline 36 (G36) provides a proven framework for high-performance HVAC controls, its complexity, implementation requirements, and compatibility challenges with existing building systems have limited its adoption in retrofit projects. Building owners, engineers, controls contractors, and utility program administrators need practical guidance that translates advanced control concepts into solutions that can be applied cost effectively in existing buildings.

To address this need, this project developed the Simplified HVAC Control Retrofits Design Guide, a practical tool intended to help practitioners identify, evaluate, and implement high-impact HVAC control improvements in existing commercial buildings. The guide focuses on retrofit applications where full G36 implementation may not be feasible, providing a structured approach for selecting control strategies that deliver meaningful energy savings while accommodating the operational and technical constraints commonly found in existing facilities.

The project pursued four primary objectives:

• -Identify HVAC control measures with the highest energy-saving potential for existing commercial buildings.
• -Evaluate how key G36 sequences can be adapted for retrofit applications.
• -Develop a user-friendly design guide that supports the planning, design, and implementation of HVAC control retrofits.
• -Assess opportunities to integrate these measures into utility energy efficiency programs and broader market transformation efforts.
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The project combined literature review, technical analysis, industry engagement, and market assessment. The team reviewed published research, evaluated documented retrofit case studies, examined common HVAC system configurations and control deficiencies, and assessed the applicability of G36 strategies across a variety of existing-building conditions. Stakeholder engagement activities included discussions with design engineers, controls contractors, commissioning professionals, researchers, utility representatives, and other industry experts. This feedback helped ensure that the guide reflects real-world implementation challenges and industry needs.

A key finding of the project is that many of the benefits associated with advanced HVAC controls can be achieved through a focused set of retrofit measures that are both practical and cost effective. The resulting design guide emphasizes strategies such as dual-maximum variable air volume control, duct static pressure reset, supply air temperature reset, optimal start and stop sequences, demand-controlled ventilation, occupied standby operation, dynamic outdoor air control, and chilled- and hot-water temperature reset. The team selected these measures because they offer a strong combination of energy-saving potential, operational benefits, and feasibility for implementation in existing facilities.

Stakeholder feedback reinforced both the importance of the opportunity and the challenges facing the market. Participants consistently identified HVAC controls as a major source of untapped energy savings but noted several barriers to broader adoption, including limited familiarity with G36, perceived implementation complexity, lack of standardized guidance, control-system constraints, missing field instrumentation, and workforce training needs. Stakeholders responded positively to the concept of a simplified retrofit-focused resource and emphasized the value of practical implementation guidance, decision-support tools, and educational materials that can be applied across a wide range of building types and system configurations.

Based on the findings, the team recommends expanding the use of simplified advanced control strategies in existing building retrofit programs, increasing workforce training and technical assistance related to HVAC controls, and developing standardized approaches for evaluating and verifying control-based energy savings. Utility programs should consider incorporating these measures into commercial energy efficiency offerings, particularly through Strategic Energy Management and other programs focused on operational improvements. Continued promotion of commissioning and retro-commissioning practices is also recommended to ensure that control improvements achieve and maintain their intended performance.

The significance of this project lies in its ability to bridge the gap between advanced HVAC control theory and real-world retrofit implementation. By translating complex control sequences into practical guidance that can be applied in existing buildings, the Simplified HVAC Control Retrofits Design Guide reduces barriers to adoption and supports broader deployment of high-performance control strategies. The design guide provides a valuable resource for engineers, controls contractors, commissioning providers, building owners, and utility program implementers seeking to improve building performance without requiring extensive equipment replacement.

Ultimately, the project demonstrates that significant energy savings, operational improvements, and occupant comfort benefits can be achieved through thoughtful HVAC control retrofits. By enabling wider adoption of proven control strategies across the existing building stock, the guide has the potential to reduce operating costs, improve building performance, advance utility energy-efficiency objectives, and support long-term decarbonization goals.