Issue link: https://hi.iaq.net/i/630729
Common IAQ Measurements — A General Guide 111 ments. For each measurement, time should be allowed for the reading to stabilize to room conditions. Refer to the specifica- tions for the measuring device; some take several minutes to stabilize. Electronic relative humidity (RH) meters must be calibrated frequently. Indoor relative humidity is influenced by outdoor conditions. A single indoor measurement may not be a good indication of long-term relative humidity in the build- ing. Programmable recording sensors can be used to gain an understanding of tem- perature or humidity conditions as they change over time. Using the Results Temperature and humidity directly affect thermal comfort. They may also provide indirect indications of HVAC condition and the potential for airborne contamina- tion from biological or organic com- pounds. There is considerable debate among researchers, IAQ professionals, and health professionals concerning recom- mended levels of relative humidity; how- ever, the humidity levels recommended by different organizations generally range between 30% and 60% RH. Comparison of indoor and outdoor temperature and humidity readings taken during complaint periods can indicate whether thermal discomfort might be due to extreme conditions beyond the design capacity of HVAC equipment or the build- ing envelope. Measure next to thermostats to confirm calibration. Measure at the location of complaints to evaluate whether or not temperature and humidity at that location are within the comfort zone (see Figure 6-2 on page 57). Readings that show large variations within the space may indicate a room air distribution or mixing problem. Readings that are highly variable over time may indicate control or balance problems with the HVAC systems. Tracking Air Movement with Chemical Smoke Chemical smoke can be helpful in evaluat- ing HVAC systems, tracking potential contaminant movement, and identifying pressure differentials. Chemical smoke moves from areas of higher pressure to areas of lower pressure if there is an opening between them (e.g., door, utility penetration). Because it is heatless, chemical smoke is extremely sensitive to air currents. Investigators can learn about airflow patterns by observing the direction and speed of smoke movement. Puffs of smoke released at the shell of the building (by doors, windows, or gaps) will indicate whether the HVAC systems are maintain- ing interior spaces under positive pressure relative to the outdoors. Methodology Chemical smoke is available with various dispensing mechanisms, including smoke "bottles," "guns," "pencils," or "tubes." The dispensers allow smoke to be released in controlled quantities and directed at specific locations. It is often more informative to use a number of small puffs of smoke as you move along an air pathway rather than releasing a large A psychrometer. Used to measure dry bulb and wet bulb temperatures and to determine relative humidity based upon a psychometric chart. The NIOSH protocol for indoor air investigations always includes measurement of indoor and outdoor relative humidity. There are two types of psychrometers: aspi- rated (with a fan) or sling (without a fan).