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PowerPoint ® Presentation Chapter 11 HVAC Air Systems HVAC Systems Common HVAC System Designs Air-Handling Unit Components Air-Cleaning Methods Ventilation.

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Presentation on theme: "PowerPoint ® Presentation Chapter 11 HVAC Air Systems HVAC Systems Common HVAC System Designs Air-Handling Unit Components Air-Cleaning Methods Ventilation."— Presentation transcript:

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2 PowerPoint ® Presentation Chapter 11 HVAC Air Systems HVAC Systems Common HVAC System Designs Air-Handling Unit Components Air-Cleaning Methods Ventilation Air Common Air-Handling Systems Facility Pressures

3 PowerPoint ® Presentation Chapter 11 HVAC Air Systems HVAC Systems Common HVAC System Designs Air-Handling Unit Components Air-Cleaning Methods Ventilation Air Common Air-Handling Systems Facility Pressures

4 Chapter 11–HVAC Air Systems Most air distribution systems of commercial buildings operate for occupant needs 24 hr a day, 7 days a week.

5 Chapter 11–HVAC Air Systems Recommended temperature ranges differ between the summer and winter seasons.

6 Chapter 11–HVAC Air Systems When water is present, even a small collection of dirt and dust provides a breeding ground for microbial contaminants in HVAC equipment such as drip pans, humidifiers, ducts, and coils.

7 Chapter 11–HVAC Air Systems HVAC systems that use 100% outside air do not use any return air because the return air may contain contaminants.

8 Chapter 11–HVAC Air Systems Mixed-air systems allow a percentage of outside air to combine with return air for space use.

9 Chapter 11–HVAC Air Systems A dry bulb economizer is an economizer that operates in proportion to the outside-air temperature, with no reference to the humidity values of the air.

10 Chapter 11–HVAC Air Systems Enthalpy economizers use temperature and humidity levels of the outside air to control the operation of the HVAC system.

11 Chapter 11–HVAC Air Systems Air-handling units are found in many designs, but small units are usually known as terminal units, and large units are usually known as makeup air units.

12 Chapter 11–HVAC Air Systems Fans provide the mechanical energy to move air through an HVAC system and to building spaces.

13 Chapter 11–HVAC Air Systems Due to the amount of contaminants that can be present in inside air, the American National Standards Institute (ANSI) and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) have set ventilation standards as a guide for maintaining proper indoor air quality.

14 Chapter 11–HVAC Air Systems Proper operation of all HVAC system dampers must be periodically checked to ensure proper indoor air quality and energy efficiency.

15 Chapter 11–HVAC Air Systems The formula used to determine the percentage of outside air being used by air temperature varies between summer and winter.

16 Chapter 11–HVAC Air Systems When the temperature of the outdoor air and indoor air are too close to truly determine, measuring CO 2 becomes the pre- ferred method for determining the percentage of outdoor air being introduced into a system.

17 Chapter 11–HVAC Air Systems Electronic air cleaners effectively separate out dirt from the air for small air volumes, but large air volumes require that multiple units be used, which consumes large amounts of energy.

18 Chapter 11–HVAC Air Systems Ultraviolet (UV) air-cleaner systems kill biological contaminants using a specific light wavelength (approximately 450 nanometers) not visible to the human eye.

19 Chapter 11–HVAC Air Systems A carbon filter uses an activated carbon-filtering medium to remove most odors, gases, smoke, and smog from the air by means of an adsorption process.

20 Chapter 11–HVAC Air Systems In order to not contaminate building spaces, filters must be inspected periodically, of the proper thickness, stored and used properly, correctly installed, and handled correctly when replacing.

21 Chapter 11–HVAC Air Systems Filters are rated for efficiency (MERV rating), airflow resistance, and dust-holding capacity.

22 Chapter 11–HVAC Air Systems The pressure drop across a filter is checked by an electronic manometer to determine if a filter is clogged, which would result in filter replacement.

23 Chapter 11–HVAC Air Systems The proper sizing of ducts and the location and design of diffusers, registers, and grills affect the amount of air movement in building spaces.

24 Chapter 11–HVAC Air Systems Cooling coils usually consist of a finned coil, copper tubes, and aluminum fins that allow chilled water to be used for cooling air.

25 Chapter 11–HVAC Air Systems Drain pans must be pitched to allow drainage and must be periodically checked for blockages in the pan and/or drain pipes.

26 Chapter 11–HVAC Air Systems Humidifiers use various design methods to introduce water vapor into the duct airstream for occupant comfort.

27 Chapter 11–HVAC Air Systems Single-zone air-handling units provide primary HVAC capability to one zone or area.

28 Chapter 11–HVAC Air Systems Multizone air-handling units use mixing dampers in the air handler to provide HVAC to a small number of zones.

29 Chapter 11–HVAC Air Systems Dual-duct systems use hot ducts and cold ducts to carry conditioned air to mixing boxes in several zones to provide whatever comfort is required in a specific zone.

30 Chapter 11–HVAC Air Systems Reheat systems utilize independent heating coils in the duct of each zone controlled by a thermostat in the zone.

31 Chapter 11–HVAC Air Systems VAV air-handling units usually use a variable- frequency drive-controlled fan to vary air volumes in a duct in order to maintain the desired static pressure.

32 Chapter 11–HVAC Air Systems Even though variable-air-volume terminal boxes can throttle airflow from 100% to 0% of design flow, all VAV terminal boxes have a minimum flow setting to maintain ventilation standards.

33 Chapter 11–HVAC Air Systems The stack effect in a building occurs when hot air rises up through the building elevator shafts, stairwells, and service columns, similar to the operation of a boiler chimney.

34 Chapter 11–HVAC Air Systems All pan and floor drain traps must be filled with water to prevent sewer gases from entering a building or HVAC system.

35 Chapter 11–HVAC Air Systems One-pipe hydronic systems have a single pipe that acts as the supply pipe and return pipe for the flow loop, connecting one terminal unit to the next terminal unit.

36 Chapter 11–HVAC Air Systems Two-pipe hydronic systems have a separate supply pipe and return pipe at each terminal unit.

37 Chapter 11–HVAC Air Systems Three-pipe hydronic systems have a hot-water loop and a cold-water loop so that hot or cold water can be introduced to any terminal unit at any time.

38 Chapter 11–HVAC Air Systems A four-pipe hydronic system uses supply and return heating piping and supply and return cooling piping.

39 Chapter 11–HVAC Air Systems Steam heating systems consist of a high-pressure boiler, fittings, accessories, steam supply piping, ter- minal units, a condensate return system, and controls.

40 Chapter 11–HVAC Air Systems In direct-return systems, the shortest supply line has the shortest return. In reverse-return systems, the shortest supply line has the longest return.

41 Chapter 11–HVAC Air Systems Large complexes such as hospitals and university campuses use primary/secondary systems to distribute water to buildings.

42 Chapter 11–HVAC Air Systems Radiant heat panels have resistance heating elements and radiate heat directly to the area below.

43 Chapter 11–HVAC Air Systems Electric baseboard heaters are smaller than electric space heaters, and are less expensive to install but more costly to operate than other heating systems.


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