Reducing energy use in buildings, while improving occupant comfort.

Status: Completed

Funding Sources: California Energy Commission PIER Program CBE Industry Consortium

Project Objective

This project developed, integrated, and demonstrated heating, ventilation, and air-conditioning (HVAC) control and Personal Comfort Systems (PCS) technologies. This work was accompanied by steps potentially leading to adoption, including development of proposed changes to standards, guidelines and codes. The project synthesized three innovative components that provide an integrated, comprehensive approach to correcting frequently occurring control problems in buildings that improve both occupant comfort or energy efficiency. The technologies included: (1) low-energy PCS that provide decentralized local heating and cooling to building occupants and methods of test for assessing efficiency of PCS; (2) innovative control improvements to VAV systems, including lower minimum zone airflow rates and cost-responsive supply air temperature reset; and (3) information technology in the form of open-source software for implementing control logic across a full range of existing direct digital control (DDC) systems. The project also explored commercially available occupant voting-based controls along-side these innovations.

Project Results

This project resulted in numerous insights and new practical strategies for the control of commercial buildings. The most successful energy-saving and immediately applicable innovative technology demonstrated in the project was time-averaged ventilation (TAV) for VAV reheat air distribution systems. As a result, TAV has been incorporated in ASHRAE Guideline 36, which when published later in 2017, will reach a wide audience and encourage widespread adoption.

The project also demonstrated how innovative open-source software can enable the development and integration of the occupant-based HVAC technologies explored. The software platform used was sMAP (simple Measurement and Actuation profile), developed by the UCB Electrical Engineering and Computer Science Department. Applications included the connectivity of PCS chairs, underlying technology for commercially available occupant voting-based temperature control, and deployment of advanced VAV control algorithms. Peffer et al. (2016) present a few examples of how sMAP can be used to write advanced control sequences in real buildings and test innovative energy efficiency algorithms and components. Andersen et al. (2016) show that by using sMAP to develop well-connected microzone devices that report real-time telemetry and respond to programmatic actuation requests, thermal microzones, such as those created by PCS chairs, can be synergistically combined with occupant-aware building applications to enable new methods of comfort and energy efficiency maximization.

The research team evaluated and identified code change potential for Personal Comfort Systems and VAV controls at both the state energy code level (Title 24 Building Energy Efficiency Standards, Title 20 Appliance Efficiency Standards), as well as national energy and comfort standards (ASHRAE Standards 90.1, 189.1 and 55).

Draft Final Report has been written and is available.

Of the 40 field study subjects with heated/cooled 'personal comfort chairs, 97% reported thermal satisfaction. Data from the field study has also been used to create a new personal comfort model paradigm that improved prediction accuracy 40% compared to conventional models such as the PMV.

Significance to Industry

By building on recent research and technological innovations in several fields, the project will create and demonstrate new products and operational practices, and perform the tasks leading to adoption of these products and operational practices in standards, codes, and common practice. The new technologies employ the improved sensing and information feedback that is now possible among the building, its operators, and its occupants. The combination of these techniques has the potential to eliminate 39% of natural gas use and 30% of electricity use for HVAC in typical California commercial office space. The new control paradigm applies equally to existing buildings as well as new designs, and will be a cost-effective way to achieve substantial reduction in HVAC energy use.

Research Approach

This project consisted of a broad set of research activities and findings:

Fifty low-energy heated and cooled chairs (PCS) with wireless internet connectivity were designed and fabricated for use in the demonstration field studies. A method of test using a thermal manikin was developed to determine personal heater efficiency (PHE). Experiments on 12 personal heaters found that conductive heaters (heated chairs or foot-warmers) are far more efficient than radiant or convective heaters. A report summarizing the method of test and the test results was written by Cohn (2017).

Three demonstration field studies were conducted to study the project innovations. Two were in office buildings with conventional VAV reheat with overhead air distribution: (1) San Mateo County (SMC) office building in Redwood City, and (2) Sutardja Dai Hall (SDH) on the UC Berkeley campus. A third was in an office building with advanced low-energy space conditioning: (3) Integral Group office building in San Jose, which uses radiant slab heating and cooling.

The SMC field study involved PCS chairs alongside occupant vote-based HVAC control (Comfytm). Key results showed that the PCS chair users have high thermal satisfaction across the investigated setpoint range of 20.5-24.5°C (69-76°F) and continuous PCS data provide insights into occupant comfort and behavior.

Occupant and management response to voting-based temperature control (Comfytm) was positive, although we were unable to directly confirm energy use reduction resulting from expanded temperature deadbands. Technical papers are nearing completion for the SMC field study and thermal comfort analysis. Hoyt et al. (2015) performed a large parametric simulation study of seven climates and six model types to examine the benefit of widening thermostat heating and cooling setpoints, as enabled by the presence of PCS chairs to maintain local comfort, to save centralized HVAC energy in a typical medium office building.

The SDH field study focused on implementation and testing of advanced VAV control strategies in combination with occupant vote-based HVAC control. Detailed field trials were completed for two promising advanced VAV control strategies: (1) time-averaged ventilation (TAV) and (2) cost-based supply air temperature (SAT) reset. TAV testing showed a reduction in fan (15%), reheat (41%), and chilled water (23%) energy (Kaam et al. 2017). Cost-responsive SAT reset testing showed an additional reduction in total HVAC energy costs of 29% (Raftery et al. 2017).

Publications and Reports

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