Green: Personal Comfort Systems

Judhajit Chakraborty By Judhajit Chakraborty, Assoc. AIA, LEED AP WSP Built Ecology

The Center for the Built Environment’s (CBE) semi-annual symposium on Human Thermal Comfort and Energy was held at the UC Berkeley Campus and the Pacific Energy Center from April 22-24, 2015. The next symposium for this year is scheduled from October 7-9, 2015. For those who are not aware of this, this is one of the best symposiums related to building design and sciences where practice meets research. The Center for the Built Environment in UC Berkeley, as many of you might know, is a one of a kind institution where high level research and experimentation of building and human comfort is undertaken and is purely driven by the needs of the industry. There are partner organizations who direct the research topics and advises what the industry wants to see more of from CBE.

ASHRAE 55 standard for thermal comfort was primarily developed by CBE and it has an amazing thermal comfort tool which we regularly use for thermal comfort design and verification. There were two hot topics in this symposium – Building Metrics (LEEDv4, Living Building Challenge and Well Building Standard which I will write about in my next article) and Personal Comfort Systems (PCS). This article is about the PCS systems and how they help in more personalized thermal comfort and energy savings. ASHRAE 55 standard defines thermal comfort as the “condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation”. Maintaining this standard is one of the major goals of the building HVAC and envelope systems. Workplace design has improved by leaps and bounds. However, much less attention has been directed towards the thermal comfort of the workspace and individuals.

Sitting in Chair

There are surveys which show the majority of occupants in an office environment find their thermal environment uncomfortable, even though commercial buildings spend huge amounts of energy on HVAC systems to provide adequate thermal comfort. Upon the requests from partner companies to pursue research in providing a solution to this, CBE faculty and graduate students started looking into providing occupants with low-power devices to control their local thermal environment, and could allow them to remain comfortable over a wider range of ambient temperatures or set point temperatures (thermostat settings) for heating and cooling. Normally the range is 70°F – 75°F (heating and cooling).

Building simulations show that varying these set points by even a few degrees can result in large energy savings because the building is conditioned less intensely and less often, and can more often use outside air for conditioning (economizer mode). The savings vary by climate, but generally, widening the thermostat setback by one degree Celsius can reduce building-energy consumption by 5-15%.

CBE researchers have thus developed and designed a user-controlled chair which allows occupants to control heating and cooling directly through the surfaces of an office chair. This provides comfort under a wide range of room setback temperatures (previous tests that CBE conducted with another “active” chair kept people comfortable from 61°F to 84°F). CBE’s chair uses low-energy fans, reflective exterior, small heating elements, and an occupancy sensor to save energy when not in use. The chair is battery powered, and can last for several days between charges. The chair has a simple control in the armrest which sets the heating and cooling intensity.

These PCS chairs have been laboratory tested by use of thermal manikins for calibrated measurements of cooling fan efficiency. The field-study portion of the project included user surveys with measurements for occupancy, energy consumption and ambient conditions collected by the PCS units. This research, design, development and testing of PCS units or chairs is based on previous findings that show that cooling of the head and “breathing zone,” and providing warmth to the occupant’s feet are two of the most effective ways to provide individualized thermal comfort.


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