Comfort: The Undervalued Feature
By: Michael Scharing

Home and building owners may not be giving enough importance to comfort when purchasing heating and air
conditioning equipment. This may be due to the subjective nature of comfort and the difficulty in quantifying the value
of comfort in cost analysis. Consider the following when valuing comfort.

Comfort is defined by the American Society of Heating and Refrigeration Engineers (ASHRAE) by both temperature and
relative humidity. For a resting person in trousers and a long-sleeve shirt, optimum temperature is 75°F with a zone of
comfort about 3°F above and below this optimal level.1 Relative humidity in the range of 30% to 60% is optimal for
human comfort. 2 It has been reported that females are more sensitive to temperature while males are more sensitive
to relative humidity.3

Comfort is closely linked to health. While almost any functioning heating and air conditioning (HVAC) system will
prevent the extremes of temperature that cause physical injury, the same cannot be said of relative humidity. Relative
humidity below 30% and above 60% causes growth of pathogens including bacteria, influenza, and mites. Low humidity
is associated with an increase in allergic rhinitis, asthma and respiratory infections. 4

Most homes are heated by a gas furnace using “forced-air” heat. These systems tend to create low humidity indoor
environments that dry the skin and lungs and expose occupants to health risks as noted above. Homes with these
systems should monitor humidity and consider the addition of a humidifier should it be required. Hydronic boiler
heating systems operate at higher ranges of relative humidity reducing the need for humidification.

Comfort is linked to efficiency. Systems that have broad temperature swings create discomfort and may waste energy
when they are too warm for normal occupant comfort. Homes that have drafts reduce occupant comfort and lower
perceived temperatures, and increased energy use. Drafts may be caused by leaks or by air movement induced by
whole-house ducting systems. One alternative is the use of multiple zones; where individual rooms operate at different
temperatures and reduce energy demand and drafts.

So what? Comfort is not something designers and installers should turn a blind eye to because it is hard to describe and
value. A comfortable space is healthier and more efficient… and more comfortable. Building owners and occupants
need to demand their comfort, health and energy use be maximized.

How? Investigate the role of hydronic chiller/boiler systems and consider this viable option in the design of HVAC
systems for residential and commercial systems. Don’t compromise and don’t settle.

1 2004 Ashrae Handbook. HVAC Systems and Equipment – Chapter 20
2 2005 Ashrae Handbook. Fundamentals – Chapter 9.11

3 Lan, L., Lian, Z., Liu, W., & Liu, Y. (2008). European Journal of Applied Physiology, 102(4), 471
4 2005 Ashrae Handbook. Fundamentals – Chapter 9.1