Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
Not for profit educational resource on indoor environmental quality.
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The Natural Choice

What is indoor environmental ergonomics?

What is radiant based HVAC?

 

The Complete Definition of HVAC

HVAC is the acronym for Heating, Ventilation and Air Conditioning.

Most people including many industry professionals wrongly assume that HVAC exclusively means thermal comfort and air quality, but this limited interpretation prevents many to appreciate the more accurate meaning, let us explain;

  • Heating (H) influences the relative humidity, surface and interstitial vapour pressures, surface temperatures, drafts, material durability, and material VOC emission rates ergo its more than thermal comfort.

  • 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. One would think that a higher ventilation rate and dilution would be better than a lower ventilation rate but if the outdoor air is moisture laden and contaminated with toxic gases, particulate matter and odours bringing more air in from outside actually makes the inside worse, ergo ventilation does not equal indoor air quality.

  • Air Conditioning (AC) or conditioning the air is about decontamination, deodorization and de(humidification) as well as temperature regulation and air velocity control ergo it is not just thermal comfort cooling.

You can see now that 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 and materials of construction 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 significantly smaller ducted system.

Conclusion

One can be riding up a ski lift freezing your buns off but inhaling great air quality or one could be totally comfortable laying back on the sofa but inhaling radon gases - so never confuse air quality with thermal comfort and vice versa.

  • Heating the air in a space by itself does not make you comfortable. See radiant based HVAC.

  • Heating a space does not control the quantity of moisture in the air. See Myth #9 in Radiant Mythology.

  • You can be thermally comfortable in an environment with poor air quality.

  • Conditioned air can be cool-dry and dirty or hot-moist and clean...ideally it should be clean and between 35% to 55% rh and 65 deg F to 80 deg F. See indoor air quality.

  • When discussing HVAC with your builder or mechanical contractor please understand the folks designing your interior environment very rarely study the relationship between architecture, mechanical systems and human physiology. Unfortunately that's our North American system.

Fortunately good information on indoor environmental quality is readily available, is based on science, is desirable, specifiable and obtainable in your new or refurbished building.

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