HVAC – What does it mean to indoor air quality?
Copyright (c) 2009,
Robert Bean, All rights reserved, originally published in
Mention “radiant based HVAC” to
anyone raised on “air only systems” and you get the
same look one gets from a puppy cocking his head as he tries
to understand why all the fuss for peeing all over the
Those who have remained loyal to the air
only system but understand the benefits of a direct ducted
ventilation system may be missing a significant opportunity
to learn a few new skills using radiant for comfort
conditioning of occupants whilst continuing to apply your
air based skills to smaller, more compact and simpler
ventilation and air conditioning systems.
The eureka moment that often causes the
HVAC service provider to leap into the latter arena is the
the acronym HVAC has a much broader meaning than its
traditional use. Let me explain; heating (H) influences the
relative humidity, surface and interstitial vapor pressures,
drafts, material durability, and material VOC emission
rates; ventilation (V) in and by itself does not guarantee
air quality as its function is to exhaust indoor air and
replace it with outdoor air, this provides the opportunity
to condition the air (AC) through dilution, filtration,
deodorization, temperature regulation, dehumidification,
humidification, and air velocity control.
Thus, the H in HVAC is not exclusively
heating comfort, the V is not exclusively
air quality and the AC is not exclusively cooling
Once you can get beyond HVAC as being an
air based system for thermal comfort and air quality you can
begin to understand the value of incorporating the building
itself into the definition of HVAC and by doing so can
assign the thermal comfort component to a radiant surface
and assign the ventilation and conditioning of incoming air
to a direct ducted or as many in ASHRAE have adopted, a
“dedicated outdoor air system” or DOAS.
The dedicated outdoor air system can be as
basic as an ERV or HRV and it could include the use of stand
alone or integrated high performance humidification and
filtration equipment. It could be defined by separate
exhaust fans with a makeup air unit which could offer many
options for conditioning incoming air such or the DOAS might
be defined as an integrated system using desiccants and
renewable resources for regeneration.
Regardless of the DOAS, the removal of the
sensible cooling and heating for comfort results in a
significantly smaller ducted system of various capabilities.
How the 10/20/30 Challenge Might Influence
the World of HVAC?
The 10/20/30 challenge adopted by hundreds
of thousands in a worldwide coalition representing the built
environment are challenging the global construction industry
to achieve net zero or what is known as carbon neutral
buildings by 2030.
What does this mean in practical terms to
the HVAC industry?
It means that as building performances
increase, there will be a corresponding decrease in the need
for thermal comfort systems. More specifically the interior
surfaces will be warmer in winter and cooler in summer, both
cases resulting in a reduction in the comfort
responsibilities from the HVAC system. This is interesting
stuff because if today’s designer can get their heads around
the likelihood of thermal comfort as being something that
will evolve from today’s typical mechanical solution -
gradually becoming smaller in scope and purpose - then they
should be able to get the heads around the fact that the
same increase in building performance also means the
potential for significantly increasing the combustion and
compression efficiency in boilers and heat pumps
respectively, provided that radiant based systems are used
to compensate for building short comings.
In fact, over time if the coalition is
successful, there will be little need for combustion or
compression as a simple ground loop to radiant based system
might be sufficient to prevent over and under heating by
controlling the sensible exchanges occurring within the
Aside from the thermal comfort discussion,
it also means during the next 20 years we will likely bear
witness to the conditioning of indoor air and
domestic water heating as becoming the predominant
loads…something the folks at NRC-IRC have been talking about
What do you know and what can you do with
Constructing or restoring buildings to a
net zero or carbon neutral format over the next several
decades is going take an integration of building science,
architecture, interior design and electromechanical know
how. This undoubtedly will create new and as yet
undetermined challenges of various magnitudes for which the
HVAC service provider is well suited especially if they have
a good understanding of building science.
If today’s designers started to
incorporate radiant based HVAC systems, buildings would be
far better prepared for the upcoming journey into dedicated
outdoor air systems.