Đang tải... (xem toàn văn)
HVAC instant answers
[...]... and lighting bills precisely because these add to the ability to get merchandise out the door Introduction and Overview FIGURE 1.1 Typical residential HVAC system components FIGURE 1.2 Typical commercial building HVAC system components 3 4 HVAC Instant Answers A third category of building is the industrial site as illustrated in Figure 1.3 These kinds of buildings come in all shapes and sizes and it... remaining chapters in the book discuss various components of HVAC systems These components are • Pumps and Valves • Water Distribution Systems • Chillers • Condensers and Cooling Towers • Thermal Energy Storage Systems • Boilers • Steam Distribution Systems • Fans and Dampers 5 FIGURE 1.3 Typical industrial building HVAC system components 6 HVAC Instant Answers • Air Handling Units • Air Distribution Systems... troubleshooting HVAC systems that heat, cool, or humidify the air By identifying the starting and ending points of a process on the psychrometric chart, you can determine where problems might be occurring For example, Figure 2.8 shows example psychrometric Air and Ducts 13 FIGURE 2.3 Psychrometric chart for sea level FIGURE 2.4 Psychrometric chart showing lines of constant humidity ratio 14 HVAC Instant Answers. .. at sea level The pressure of the air at these conditions is called 1 atmosphere and is equivalent to the following: 7 Copyright 2002 The McGraw-Hill Companies, Inc Click Here for Terms of Use 8 HVAC Instant Answers • 14.696 psi • 33.899 feet of water • 2116.2 lbs per square foot • 101.325 kilopascals • 29.921 inches of mercury • 10.332 meters of water • 406.782 inches of water • 760 mm of mercury At... pounds Psychrometrics We never experience truly dry air The ambient air around us is a mixture of air and water vapor The standard explanation is that the TABLE 2.1 Air Density Lookup Tables 9 10 HVAC Instant Answers FIGURE 2.1 Velocity pressure of air at low velocities (top) and high velocities (bottom) Air and Ducts 11 air “absorbs” the water vapor, although this is not really true; the air and water... start with saturated air at a high temperature and then lower the temperature, the water condenses out of the air FIGURE 2.2 Amount of water needed to saturate room-temperature air at sea level 12 HVAC Instant Answers The study of moist air is called psychrometrics, and the psychrometric chart (Figure 2.3) is often used to quickly find the various properties of moist air The psychrometric chart has the... have differences in their structure, their use, and the quirks of their behaviors Like people, no two are alike In 1 Copyright 2002 The McGraw-Hill Companies, Inc Click Here for Terms of Use 2 HVAC Instant Answers fact, the idea of a building as a person has some merit: most buildings have a need to take in fresh air and expel contaminated air Many buildings provide a constant circulation of fluids... Psychrometric chart showing lines of constant relative humidity FIGURE 2.6 Psychrometric chart showing lines of constant dry-bulb and wet-bulb temperatures TABLE 2.2 Humidity Ratio Look-up Tables 15 16 HVAC Instant Answers TABLE 2.3 Dew Point Lookup Tables FIGURE 2.7 Psychrometric chart showing lines of constant enthalpy Air and Ducts TABLE 2.4 FIGURE 2.8 processes 17 Wet Bulb Temperature Look-up Tables Example... temperature range is higher than the winter because people are not as heavily dressed FIGURE 2.9 Acceptable ranges of temperature and humidity for buildings in summer (Adapted from ASHRAE, 1981) 20 HVAC Instant Answers FIGURE 2.10 Acceptable ranges of temperature and humidity for buildings in winter (Adapted from ASHRAE, 1981) DUCTS Ducts are aluminum or fiberglass conduits that transport cold and hot... FIGURE 2.11 Die-stamped duct elbow (left), pleated duct elbow (middle), and five-piece gore elbow (right) FIGURE 2.12 Mitered duct elbow (a) simple duct section; (b) elbow with turning vanes 22 HVAC Instant Answers moving or vibrating equipment (such as fan units) should use a flexible duct connector This isolates the ductwork from the vibration source and can help prevent subsequent damage to duct .