Comfort Zone for Conditioned Space

Air conditioning unit is never useful, until it can condition air, into the comfort zone.

Sizing of air conditioners has to be based on general guidelines for comfort air.

What is comfort zone for air?

It is the region of temperature and humidity, of air, where most people feel comfortable.

How was it initiated?

ASHRAE (American Society of Heating Refrigeration and Air Conditioning), stated that the problem of air comfort was recorded as early as Ancient Egypt times.

Workers in confined space felt more uncomfortable than those with better air circulation outdoor.

A separate set of occurrences in smoke “congestion” from fireplaces around residences within England, has triggered the rule to make high ceiling and high windows. All for the reason of comfort air.

Fast forward to 20th century:

ASHVE (American Society of Heating & Ventilating Engineers) has created a chart, stating the comfort zone felt for most people around The US.

The study was carried out within The US, but the results are reasonably applicable worldwide.

The study has to be carried out by getting feedback for comfort, from a very large sample of people.

Feedback of whether the air was comfortable or not, was provided based on various air temperature and humidity.

Study has to be carried out as comfort is a subjective matter, and varies from people to people. It can never be, or impossible to derive from calculations.

Feedback was used and plotted against psychrometic chart, as well as air comfort chart.

Comfort zone for air:

Results from the feedback revealed that the range of comfort zone is within the boundary of;

  • 30% to 70% of relative humidity. Condition is not too dry to dehydrate our body, and not too humid, to “suffocate” us with sticky sensation.

  • 29 oC (85 oF) and 18 oC (65 oF) of dry bulb temperature

Comfort zone for air, as per <I>ASHVE</I>

A tighter range for comfort, where almost 100% of people feel comfortable, is within;

Summer condition

  • 30% to 70% of relative humidity

  • 23 oC (73 oF) and 25 oC (77 oF) of dry bulb temperature


Winter condition

  • 30% to 70% of relative humidity

  • 19 oC (67 oF) and 22 oC (72 oF) of dry bulb temperature

Tight ranges are quite strict for air conditioning design and sizing. Therefore, more lenient and acceptable range provided earlier, is used.

Other factors of comfort include:

  • fresh air supply of 5 litres/s per person, per compartment of air, for an average person’s respiratory requirement, and

  • maximum air velocity from duct of less than 1 m/s (3 ft/s), to avoid direct draft

Design and air conditioner and duct sizing has to be carried out based on these guidelines so that you can be in comfort zone.

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