ASHRAE Journal - November 2021 - 57

COLUMN SOLVING PROBLEMS
panel can effi ciently be maintained
at a temperature lower than the
dew-point temperature, allowing for
radiant-only cooling without condensation.
Condensation risk is what
makes reliance on radiant cooling a
relatively untapped potential.
Testing the Technology
The researchers tested the technology
in 2020 in one of the world's most
hot and humid climates: Singapore.
They constructed a demonstrative outdoor radiantcooling
pavilion (Photos 1 and 2) that used an infraredtransparent
membrane that provided radiant cooling at
temperatures below the dew point without condensation.1
Thirty-seven people experienced the pavilion and
reported a " satisfactory " thermal sensation 79% of the
time-despite the hot and humid climate and low air
movement, according to the research.
" Our membrane-assisted radiant cooling demonstration
in Singapore was a good example for how to keep
people comfortable using only thermal radiation in
warm, humid environments, " said Teitelbaum.
The Cold Tube yielded no condensation, meaning the
membrane successfully protected the cold surface from
the hot humid air, minimizing heat loss to the air and
preventing condensation that would otherwise prevent
cooling panels from being used in outside air in
Singapore, said Meggers, who is an associate professor at
Princeton University's Andlinger Center for Energy and
the Environment and School of Architecture.
" It's really easy to get people excited because so many
industry people are aware of the challenge of condensation
on anything radiantly cold, and condensation
and moisture is just a really big deal in buildings and
construction in general at the moment, " said Meggers.
" But at the same time, condensation mitigation is just
one aspect of the technology to change mindsets more
broadly about how we heat and cool buildings. "
Radiant Cooling and Thermal Comfort
The Cold Tube's radiant cooling technology is simple,
Teitelbaum said.
" A lot of popularized, high-tech comfort systems are
moonshot ideas that are very complicated, very expensive
and proven at very small scales, " he said. " [The Cold
Tube is] nothing too expensive, nothing too crazy in
terms of the technology itself. "
Air temperature, air speed and humidity affect
thermal comfort signifi cantly and intuitively, said
Teitelbaum, adding that thermal radiation is also an
equally important input.
" Thermal radiation is emitted from all surfaces proportional
to their temperature and emissivity, and
humans interact with this thermal heat. Air temperature
and surface temperature are often linked since all
surfaces are in contact with the air. However, comfort
can still be manipulated with thermal radiation independent
of the air temperature, " he said.
Their research focuses on how to effectively and effi -
ciently do this, allowing more fresh air to be brought
into spaces without huge increases in energy bills.
" Air is no longer a required comfort medium for purely
radiant heating or cooling, as air does not need to be a
heat transfer fl uid if all comfort is managed with radiant
systems, " Teitelbaum said. " This has huge implications
when ventilation air is required to be increased,
as shifting away from conditioning incoming air means
that more fresh air can now be brought inside without
conditioning it, improving occupant health, the tenant's
electricity bill and not sacrifi cing thermal comfort. "
With traditional radiant cooling, there is some associated
air cooling, which is usually thought of as a benefi t.
When a ceiling panel is chilled, the panel's thermal radiation
and some air conditioning will directly enhance
thermal comfort, he said. But, with conventional radiant
cooling, the air must be precooled and dehumidifi ed, so
the chilled panels do not create condensation, which can
cause mold and reduce performance.
" By far, the most common commercially available
way at the moment to produce dehumidifi ed air is to
N O V E M B E R 2 0 2 1 ashrae.o rg ASHRAE JOURNAL
57
PHOTO 1 The Cold Tube circulates chilled water
through a radiant cooling panel. With this technology,
air in the conditioned space does not come in
contact with the chilled surface.
PHOTO 2 The Cold Tube's chilled panel surface is
separated from the ambient air. This means the air
cannot heat the panel, so the panel can efficiently
be maintained at a temperature lower than the air,
allowing for radiant-only cooling.
PHOTO LEA RUEFENACHT
PHOTO LEA RUEFENACHT
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ASHRAE Journal - November 2021

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