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.
Most of the commercial buildings that will exist in 2050 have already been built, and many still run their heating and cooling systems on outdated or poorly tuned controls. ASHRAE Guideline 36 (G36) offers modern control strategies proven to cut HVAC energy use dramatically — control retrofits following G36 have achieved 50 to 60 percent reductions in past demonstrations — but applying it to existing buildings is challenging given older systems, tighter budgets, and limits on what can change without disrupting occupants.
This project developed design guidance that aims to simplify HVAC control retrofits, distilling G36 into a smaller set of high-value upgrades suited to real-world retrofits. The team reviewed past projects and published research, analyzed common existing HVAC configurations, and interviewed engineers, controls contractors, and utility program staff to identify the most cost-effective measures and the barriers holding back wider adoption.
The result is a short list of proven, retrofit-friendly measures — smarter room-by-room airflow control, automatic temperature resets based on real-time demand, and more aggressive shutdown when spaces are empty — often achievable through software changes alone. Software-only projects in the field have delivered 10 to 25 percent HVAC energy savings with paybacks of eight years or less. Stakeholders agreed that HVAC controls remain one of the largest untapped savings opportunities, but cited unfamiliarity with G36 and a lack of standardized guidance as key barriers.
This guide gives utility programs a practical tool for capturing that opportunity, particularly through Strategic Energy Management (SEM). The guide's simplified approach aligns with SEM's emphasis on ongoing operational improvement and is well suited to driving the outreach and training programs needed to build contractor and customer awareness of G36. Wider adoption could meaningfully lower operating costs while supporting long-term energy efficiency goals.
