Every cooling system operates on one
principle: move heat from where it bothers
people to where it does not matter.
Mechanical air conditioning uses
refrigerant compression, consuming
electricity at every step. Plants use
water and sunlight, consuming nothing from
the grid.
The mechanism is evapotranspiration. Water
enters through roots, travels up the
xylem, and exits through stomatal pores on
leaf undersides. As liquid water becomes
vapour, it absorbs latent heat: 2,260
kilojoules per kilogram. This energy is
drawn from air immediately surrounding the
leaf, producing a localised temperature
drop that is measurable with standard
instruments at close range.
[1]Bakhshoodeh, Ocampo, and Oldham (2022)
studied evapotranspirative cooling of a
green facade in controlled conditions.
Their findings, published in Sustainable
Cities and Society, showed wall
temperatures behind the green facade were
up to 7 degrees Celsius cooler than those
behind shade sails. Evapotranspiration
contributed 25 to 35 percent of the total
cooling gap induced by the green facades.
The remaining cooling came from shading,
with the combination producing temperature
reductions up to 11 degrees below ambient.
[1]Convertino, Vox, and Schettini (2022)
published parallel findings in MDPI
Sustainability. Green facades reduced
indoor air temperature by 4.57 to 5.64
degrees Celsius and decreased heat flux by
7.84 to 16.79 watts per square metre. Leaf
area index and plant coverage positively
correlate with cooling magnitude. A soil
substrate without plants could not produce
the same temperature reduction: canopy
transpiration and shading, not soil
moisture alone, drove the cooling effect.
The living canopy was the active agent.
[3]Bucher et al. (2025) examined vertical
indoor greening with tropical ornamental
plants in Indoor Air. They characterised
transpiration rates and stomatal
conductance under different indoor climate
parameters. Light intensity
(photosynthetically active radiation)
showed a positive correlation with
transpiration rate and stomatal
conductance, while ambient air temperature
showed a negative correlation. Indoor
greening contributed to keeping both
relative humidity and temperature at
levels suitable for building occupancy.
[6]A 2024 study in MDPI Buildings found that
integrating potted plants in tropical
urban buildings significantly enhanced
thermal comfort and reduced cooling energy
consumption. The evapotranspiration
mechanism, followed by shading throughout
the day, played the major role in the
measured temperature drop at the occupied
zone where people sit and work.
[17]The latent heat equation has been
understood since the 18th century.
Transpiration measurement dates to the
1890s. What no building system had done,
until Biothermal Microconditioning, was
engineer managed indoor plant clusters
that harness evapotranspiration as a
primary occupant cooling mechanism at the
breathing zone. Easy Retrofit. 1 day to
deploy.
