Methodology for the Evaluation of Natural Ventilation in ... - Cham

airflow characteristics also play an important role in how effectively the fresh air is introduced tothe occupied area. Some important ventilation characteristics for all buildings include airvelocity, airflow patterns, and carbon dioxide levels.The speed at which air enters into a space is part of what determines its impact on the conditionswithin the space. Air velocity can be measured in various ways, but one of the most common andaccurate methods is using a hot-wire anemometer. This device measures the speed at which air ismoving at a particular location. The hot-wire anemometer is useful for point measurements atspecific locations, rather than for overall air velocity within a building. If the conditions are notsteady state but change with time, then the point by point method of measuring air velocity canprovide questionable results. Air velocity must be controlled within a space to avoid draftconditions, which can cause not only occupant discomfort due to increased evaporative cooling ifthe skin is exposed, but also disruption of papers and objects in the occupied space. Allowablelevels of air velocity within an occupied space are normally below 2 meters per second. On theother end of the spectrum, stagnant air is also undesirable, as fresh air is important to theoccupants‘ health and productivity.Proper air movement in an occupied space as well as within the building as a whole can impactenergy usage, indoor air quality, and thermal comfort. Airflow patterns include direction andmovement through a space and throughout a building. Understanding how air flows within aspace can be indicative of the effectiveness with which fresh air is reaching occupants and staleexhaust air is leaving the building. Smoke pencils are often used for local visualization of airflowpatterns within occupied spaces. These devices provide a visible, neutrally buoyant stream ofsmoke that dissipates after several minutes and is harmless to occupants or furnishings.Measurement and monitoring of carbon dioxide levels is another method of evaluatingventilation effectiveness. Through a series of measurements and calculations, the air exchangerate of a building can be determined. People exhale a certain amount of carbon dioxide, basedprimarily on their activity level, but also on their age and fitness. The determination of airexchange rate is based on the number of people within a building, along with the indoor andoutdoor carbon dioxide level. The indoor carbon dioxide levels can also be compared to levelsconsidered acceptable for indoor air quality and health, safety and environment standards.2.4.3 Energy PerformanceA key parameter contributing to a building‘s performance is energy consumption. Energyconsumption analysis can be completed in different ways; using either a simple method or amore detailed means. The energy use of a building can be easily compared to other similar-typebuildings. The more detailed the analysis of energy usage, the easier the ability to target areas forimproving performance.A very simple method, which looks at monthly energy, electric and natural gas, usage and costbills provided by the respective utilities can provide some information on and trends in abuilding‘s energy usage. Although obtained only on a monthly basis, seasonal data can beextrapolated based on some known characteristics of the building. These characteristics includeplug loads, such as number of computers, printers, and ancillary equipment, and lighting loads,such as number and type of lighting installed. Once the baseline consumption that remainsconstant over the course of the year is known, energy usage that is weather dependent can bedetermined. If the heating and cooling degree-day data or other measures of external37