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I have lost count of how
many years I have been harassing industry and its
various constituents to adopt radiant cooling for
conditioning occupants and spaces. Even to this day
naysayers argue against it spouting over condensation
potentials. Few of these reluctant cynics ever consider
that 100 per cent of all condensation problems in
buildings conditioned exclusively with air did not have
radiant cooling to blame so let’s stop blaming radiant
panels for condensation problems.
This in fact was the message in my 2012 ASHRAE San
Antonio and ACCA Rhode Island presentations where I and
my learned colleagues demonstrated that humidity
management is necessarily required by the HVAC system
for microbial control over pathogens (bacteria, viruses)
and allergens (molds and dust mites; and to promote
respiratory and thermal comfort for occupants; and for
the dimensional stability in hygroscopic materials like
wood. When managed for these priorities, condensation on
radiant cooling panels becomes a moot point. Do not get
me wrong, I am not saying you do not need to monitor
surface dew point temperatures and space humidity with
radiant cooling systems. I am saying: get your design
priorities in order and follow up with systems and
controls that enhance the indoor climate for health of
the environment and by association health of the
occupants and for the dimensional stability of
architectural materials. Do this and the condensation
issue disappears.
To illustrate examples of what I am talking about, I
have selected three large commercial projects, which
represent a plethora of other buildings around the
world. All of these follow a common HVAC recipe for
success; that being a hybrid radiant-based comfort
system using dedicated outdoor air for deodorization,
decontamination and dehumidification of ventilation air.
These buildings represent seasonal climates ranging from
cold/dry to hot/humid; cold/dry to hot/dry and warm/hot
and humid; and serve as examples of radiant cooling in
high rise office towers, low rise office buildings and
large scale transportation centres. In this they also
demonstrate the ability to handle the variable flow of
human traffic typical of the proverbial 9:00 a.m. to
5:00 p.m. employee or the seasoned air traveler.
What these diverse buildings in diverse climates
initially have in common is an integrated design process
with exhaustive planning around Indoor environmental
quality and energy. No building discipline was excluded
and energy models and simulations were done early in the
concept phases to develop best practices and strategies.
Since energy conservation was of upmost importance in
these examples, comfort systems were based upon high
temperatures for cooling and low temperatures for
heating, both of which enable maximum efficiency from
cooling and heating plants. By low temp/high temp we
mean “tepid”...learn to forget the phrase, “hot water
heating” or “chilled water cooling.” In the former we
are talking radiating heating surfaces cooler than skin
temperatures with fluids often cooler than blood
temperature; and in the latter, cooling surface
temperatures within 10°F
(6°C) of space temperatures using
fluid temperatures similar to tap water.
As discussed in previous articles, the beauty of these
buildings and their indoor climate systems is the
separation between thermal comfort and indoor air
quality, which models human physiology and reflects the
individual ASHRAE standards addressing indoor
environments (ASHRAE Standards 55, 62.1, 62.2). By removing the inherent conflicts with
all air systems, each individual system of the hybrid
actually enables the other to do its job without
sacrificing performance for the other.
So let me now briefly introduce the three buildings and
encourage you to do your own detailed discovery of these
amazing buildings and their HVAC systems.
Suvarnabhumi International Airport (Bangkok, Thailand),
Manitoba Hydro Place (Winnipeg, MB, Canada), and
National Renewable Energy Laboratory (NREL) Research
Support Facility (Denver, CO, USA) are three large
projects (see Table 1), which successfully handle
variable loads in diverse climates using the systems
above. Each in its own way handles the external
environmental conditions and variable occupant’s loads
with a combination of architecture, interior design,
lighting and radiant based HVAC systems. In the case of
the Bangkok project we find a hot humid climate at
summer design conditions of approximately 36°C dry
bulb/26°C wet bulb with an internal occupant load
estimated at 12,025 people per hour. Next in line is
Manitoba Hydro Place with an approximate summer
condition of 35°C dry bulb/20°C wet bulb and an internal
daily occupant load estimated at 1650 people, followed
by the NREL Research facility with a summer climate
condition of approximately 33°C dry bulb/15°C wet bulb and
an internal daily occupant load estimated at 850 people.
Notice the similar summer dry bulb temperatures but
vastly different web- bulb temperatures.
Let me put the occupant effect into perspective. The
metabolic rate of a seated airport traveler or office
worker might be 350 Btuh spiking to 1000 Btuh for
someone walking briskly to catch a plane. Of this
combined load, one third to two thirds can be a latent
load of about 105 Btuh (seated) or 625 Btuh (walking) or
two thirds to one third being a sensible load of which
the radiant cooling is very effective at absorbing. The
latent load due to ventilation, infiltration and
occupant load is effectively managed by delivering 100
per cent outdoor air, cool and lean enough to absorb the
anticipated space moisture to a minimum 1°C to 2°C (2°F to
3°F) wet bulb differential below the dew point of the
cooling surface.
There you have it. It is thumbs up for large scale
radiant cooling and you now have projects to explore at
your own pace. This hybrid design process is the subject
of upcoming courses (see www.healthyheating.com) in
Vancouver, Toronto and Montreal so that you too can
practice what skilled indoor climate engineers are doing
here and abroad.
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