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Chapter 11

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Chapter 11

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  1. 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

  2. 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. Most air distribution systems of commercial buildings operate for occupant needs 24 hr a day, 7 days a week.

  4. Recommended temperature ranges differ between the summer and winter seasons.

  5. 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.

  6. HVAC systems that use 100% outside air do not use any return air because the return air may contain contaminants.

  7. Mixed-air systems allow a percentage of outside air to combine with return air for space use.

  8. 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.

  9. Enthalpy economizers use temperature and humidity levels of the outside air to control the operation of the HVAC system.

  10. 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.

  11. Fans provide the mechanical energy to move air through an HVAC system and to building spaces.

  12. 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.

  13. Proper operation of all HVAC system dampers must be periodically checked to ensure proper indoor air quality and energy efficiency.

  14. The formula used to determine the percentage of outside air being used by air temperature varies between summer and winter.

  15. When the temperature of the outdoor air and indoor air are too close to truly determine, measuring CO2 becomes the pre-ferred method for determining the percentage of outdoor air being introduced into a system.

  16. 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.

  17. Ultraviolet (UV) air-cleaner systems kill biological contaminants using a specific light wavelength (approximately 450 nanometers) not visible to the human eye.

  18. 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.

  19. 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.

  20. Filters are rated for efficiency (MERV rating), airflow resistance, and dust-holding capacity.

  21. 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.

  22. The proper sizing of ducts and the location and design of diffusers, registers, and grills affect the amount of air movement in building spaces.

  23. Cooling coils usually consist of a finned coil, copper tubes, and aluminum fins that allow chilled water to be used for cooling air.

  24. Drain pans must be pitched to allow drainage and must be periodically checked for blockages in the pan and/or drain pipes.

  25. Humidifiers use various design methods to introduce water vapor into the duct airstream for occupant comfort.

  26. Single-zone air-handling units provide primary HVAC capability to one zone or area.

  27. Multizone air-handling units use mixing dampers in the air handler to provide HVAC to a small number of zones.

  28. 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.

  29. Reheat systems utilize independent heating coils in the duct of each zone controlled by a thermostat in the zone.

  30. 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.

  31. 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.

  32. 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.

  33. All pan and floor drain traps must be filled with water to prevent sewer gases from entering a building or HVAC system.

  34. 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.

  35. Two-pipe hydronic systems have a separate supply pipe and return pipe at each terminal unit.

  36. 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.

  37. A four-pipe hydronic system uses supply and return heating piping and supply and return cooling piping.

  38. Steam heating systems consist of a high-pressure boiler, fittings, accessories, steam supply piping, ter-minal units, a condensate return system, and controls.

  39. In direct-return systems, the shortest supply line has the shortest return. In reverse-return systems, the shortest supply line has the longest return.

  40. Large complexes such as hospitals and university campuses use primary/secondary systems to distribute water to buildings.

  41. Radiant heat panels have resistance heating elements and radiate heat directly to the area below.

  42. Electric baseboard heaters are smaller than electric space heaters, and are less expensive to install but more costly to operate than other heating systems.