The central inefficiency of conventional
HVAC is volumetric: it conditions an
entire room to serve the people in it. A
typical office has 200 cubic metres of air
volume for 20 occupants. Each person
occupies roughly 2 cubic metres of that
space at desk height. The system chills
200 cubic metres to cool 40 cubic metres
of occupied zone. The other 160 cubic
metres, above head height and in
unoccupied corners, receive the same
conditioning and waste the same energy.
Personal comfort systems (PCS) address
this by targeting the individual. Kim,
Bauman, Raftery, Arens, Zhang, Fierro,
Andersen, and Culler (2019) published a
6-month field study in Building and
Environment with 37 real office workers
using internet-connected PCS chairs with
embedded sensors. The chairs generated
continuous streams of heating and cooling
usage data at high temporal resolution.
Key finding: personal comfort systems
extended the acceptable temperature range
by 4 to 5 degrees Kelvin. A cooling
cushion combined with a desktop fan raised
the upper comfort limit to 29.5 degrees
Celsius, while a heated cushion extended
the lower limit to 15 degrees Celsius.
[8]A 2025 meta-analysis published in Applied
Energy evaluated 64 peer-reviewed studies
on personal comfort systems across
multiple climate zones and device types.
PCS improved thermal sensation and overall
comfort by an average of one scale unit on
standard comfort scales. Comfort
temperature thresholds shifted by 2.2
degrees Celsius lower in heating and
higher in cooling modes. The developed
Coefficient of Comfort Temperature Shift
(CCTS) metric quantified this: an average
corrective energy power of 42.6 watts per
degree Celsius. Among heat transfer
methods, conduction and hybrid approaches
outperformed others in both heating and
cooling.
[20]ASHRAE Standard 55 (2023) defines thermal
comfort as the condition of mind
expressing satisfaction with the thermal
environment, assessed by subjective
evaluation. Six factors determine this:
metabolic rate, clothing insulation, air
temperature, radiant temperature, air
speed, and humidity.
[7] The adaptive
model, based on worldwide field data and
incorporated since the 2004 standard
revision, recognises that occupants
actively interact with their environment.
Behavioural, physiological, and
psychological adaptation means that
comfort preferences vary with contextual
factors and available adaptation
opportunities.
[21]Biothermal Microconditioning applies the
personal comfort principle using living
systems rather than mechanical devices. A
managed plant cluster creates a
microclimate at the occupied breathing
zone, 0.5 to 2 metres above floor level.
The canopy shades the person from radiant
heat. Evapotranspiration cools the air
within the cluster radius. Transpiration
adds moisture to counteract the dry air
that mechanical cooling creates. The
building HVAC handles the bulk room
volume. The plant cluster handles the 2
cubic metres around the person.
The energy implication: when personal
comfort is handled at the zone level, the
central HVAC setpoint can relax. Research
shows setpoint increases of 2 to 5 degrees
save 10 to 60 percent on cooling energy.
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