Written By: Robert E. Sheriff, MS, CIH, CSP, President
June 5, 2019
Providing indoor air quality to meet the comfort requirements of the occupants is a daunting task—at best.
Ventilation –that is—supplying both outside air and re-circulated are at a rate that the majority of occupants of an office, meeting room, restaurant, sports arena or any other occupied space, would find comfortable has been undertaken by such professional groups as ASHRAE (American Society of Heating, Refrigeration and Air Conditioning Engineers) and regularly they publish updated standards on the subject.
Air change rates for various types of buildings and occupancy can be found in the 2015 ASHRAE Handbook, “HVAC Applications.” This document provides guidance on the amount of air movement—both outside air and re-circulated air—that is intended to achieve good—and comfortable—air quality to the occupants.
Another ASHRAE publication that addresses the need for the amount of outside air for achieving reasonable air quality is: ASHRAE Standard 62.1-2016 titled, “Ventilation for Acceptable Indoor Air Quality.” This document provides information on the amount of recommended outside air per person and air volume rates per unit area of floor space.
Although it may be obvious, it is also important to heat or cool the incoming air.
The recommended comfort range according to ASHRAE is 67°F to 82°F but a more specific range depends upon relative humidity and other factors. It is our recommendation that the temperature range be kept between 68°F and 74°F.
The relative humidity is also a very important factor in maintaining acceptable air quality. The recommended range is 30% relative humidity to 60% relative humidity. Below 30% may cause dry skin, dry burning eyes, static electricity, and upper respiratory irritation. Above 60% may encourage mold growth.
ASHRAE lists about 80 different occupancy categories where a minimum ventilation rate has been established. The following are some examples from the ASHRAE Standard 62.1:
|Occupancy||Outdoor Air Rate CFM/Person||Occupancy Density (per 1000 ft²)|
|Restaurant Dining Room||7.5||70|
|Hotel Bedroom/Living Room||5||10|
|Pharmacy (Prep Area)||5||10|
|Beauty and Nail Salons||20||25|
|Gymnasiums (Play Area)||20||7|
If a measurement is necessary, the first approach is to identify the main supply duct, usually located on the roof, and measure the incoming air using a velometer, thermo anemometer or other air flow measuring device. Drawings should identify the area that the system services.
Formulas for calculating air exchange rates can be found in Appendix (Appendix E) of the ASHRAE 62.1-2016 document.
The most direct method of measuring the CFM per person in a particular occupied space is to use a Balometer—which is a hood-type instrument placed over a ceiling, wall or floor diffuser and measures the CFM of air for each diffuser. Measure the total supply air volume for each diffuser in an area and divide by the number of occupants in the occupied space.
Number of occupants
Our primary service areas for Ventilation Testing are: NJ, NY, NYC, PA, CT, DE, MA, RI, Wash DC, WI, MD, MI, IL, VA, IN, GA, AL, NC, SC, TN, TX, OK, DC, AR, we can service most other areas of the U.S. but with some added travel charges.