indoor environmental quality
Not for profit educational resource on indoor environmental quality.
education on radiant based HVAC


Radiant Based HVAC – What does it mean to indoor air quality?
Copyright (c) 2009, Robert Bean, All rights reserved, originally published in HPAC Canada

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 floor.

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 understanding that 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 comfort.

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 built environment.

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 for decades.

What do you know and what can you do with it?

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.


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