Chilled-Water VAV Systems - HVAC.Amickracing

Primary System ComponentsThe modulation range of the supply fan is limited by how far the variablespeeddrive can be turned down (typically 30 to 40 percent of design airflow).Air cleaningAnother requirement of the HVAC system is to ensure that the air delivered tothe conditioned space is relatively clean. This improves system performance(by keeping the coils cleaner, for example) and keeps the air distributionsystem relatively clean. Some of the contaminants that affect indoor airquality can be classified as particulates, gases, or biologicals. The methodsand technologies for effectively controlling these contaminants differ, so it isimportant to define the contaminants of concern for a given facility.Particulate filtersFor more information on the varioustypes of particulate filters, refer toChapter 28, “Air Cleaners for ParticulateContaminants,” in the 2008 ASHRAEHandbook—HVAC Systems andEquipment (www.ashrae.org) or theNAFA Guide to Air Filtration(www.nafahq.org).Particulate matter (“particulates”) describes a broad class of airbornechemical and physical contaminants that exist as discrete grains or particles.Common particulates include pollen, tobacco smoke, skin flakes, and finedust.Airborne particulates vary in size, ranging from submicron to 100 microns(µm) and larger (Figure 34). Many types of particle filters are available(Figure 35). Some are designed to remove only large particles, while others—high-efficiency particulate air (HEPA) filters, for example—also removeparticles with diameters less than one micron.Figure 34. Typical particle sizesUltrafine (PM 0.1) Fine (PM 2.5) Coarse (PM 10 ).001 .005 .01 .05 .1 .5 1 510 50 100 1000Atmospheric Dust Atmospheric Dust HumanHairparticulatecontaminantsVirusesCarbon BlackTobacco SmokeOil SmokeMold SporesBacterial SporesPaint PigmentsPollenInsecticide DustfiltertypesHigh Efficiency - (Pleated) Air FiltersElectrostatic PrecipitatorsPanel Filters.001 .005 .01 .05 .1 .5 1 5 10 50 100 1000particle diameter, μm40 Chilled-Water VAV Systems SYS-APM008-EN