HVAC

• Definition of Air-Conditioning the simultaneous control of the temperature, humidity, motion and purity of the air in a confined space
• Cooling and De-humidifying or summer cooling, temperatures of 68deg to 74 deg F and 50% relative humidity are a frequent design average
• Heating and Humidifying for winter cooling, temperatures of 70 deg to 75 deg F and relative humidity of 30%to 35% are found most satisfactory
• Air Motion air velocity should average 4.57 to 7.6meters per min measured 36” above the floor.
• Air Supply 5 cuft to 7-1/2 cuft of air per minute per person (5-71/2 cuft/min/pers). In rooms where smoking is not allowed. 25 cuft to 40 cuft of air per minute per person allowed in rooms where smoking is permitted.
• DIRECT EXPANSION COILS - Passing the air through coils containing the refrigerant itself.
• Freon is a gas at normal temperature and pressure. It is first subjected to high pressure in a compressor which raises its boiling point and temperature.
• Piston Type or Reciprocating Compressors for tonnages up to 100 tons
• Centrifugal Compressors these are quieter, have fewer vibration problems, require less maintenance and with better operating control
• Air-cooled Condensers used in unit and packaged-type air-conditioners up to 3 tons refrigeration
• WATER-COOLED CONDENSERS is a heat exchanger that removes heat from refrigerant vapor and transfers it to the water running through it.
• Shell and Tube Heat Exchanger similar in operation to the shell andtube condenser. The refrigerant is expanded into a shell enclosing the tube through which the water flows
• Direct Expansion Coils (coils containing the refrigerant itself) This may either be installed in the spray chamber so that the waters prayed into the air comes into contact with the cooling coils or the air itself comes into direct contact with the cooling coils, as in the window type unit.
• Tempering Coils contains steam and are used to heating the air ie.,preheaters and reheaters
• Water Heaters used for heating the water which will be used in the spray chamber to add heat and humidity to the air.
• Dry Filters consist of wire frames enclosing felt, cotton or sponge through which the air is screened.
• Viscous Filters consist of metal deflecting plates or screens coated with viscous oil.
• Eliminator Plates consist of corrugated galvanized iron sheets placed 1-1/8” apart which deflect the air flow about 30 deg catching the wet dust on the surfaces.
• DUCTS are usually of galvanized sheet metal, or aluminum sheets, usually rectangular in section, depending on the aspect ratio*, although circular ducts are also used for high velocity systems.
• Centrifugal fans (radial fans) these are intended for moving air at comparatively high pressures and are commonly used in duct systems.
• Propeller or axial fans commonly used for wall exhausts
• Air Outlets these are made for two locations: wall and ceiling.
• Wall outlets include the following: Vaned outlets and Perforated grills
• Ceiling outlets include the following types: Plaques, Perforated panels, and Perforated ceilings
• Humidistat or Hygrostat is a controller, sensitive to the amount of humidity in the air.
• Thermostat a controller which responds to changes in temperature.
• Pressure Regulators are instruments sensitive to changes in pressure. They may control a single pressure or a differential between two pressures.
• Dampers these control the flow of air and are in the form of louvers.
• Control Valves these are valves with variable orifices which are moved by motors to present smaller or larger openings as directed by a thermostat.
• Relays these are devices that use electrical energy to amplify or convert the power of a thermostat or other controllers so that the resultant force will be sufficient and adaptable to operate a valve or damper.
• Accidental Contact Any in advertent physical contact with power transmission equipment, prime movers, machines or machine parts which could result from slipping, falling, sliding, tripping or any other unplanned action or movement.
• Air Conditioning the process of treating air so as to control simultaneously its temperature, humidity, cleanliness and distribution to meet the requirements of the conditioned space
• Boiler A closed vessel for heating water or for application of heat to generate steam or other vapor to be used externally or to itself
• Capacity of Works, Project or Plant The total horsepower of all engines, motors, turbines or other prime movers installed, whether in operation or not.
• Compressor A mechanical device for the purpose of increasing the pressure upon the refrigerant
• Condenser a vessel or arrangement of pipes or tubing in which vaporized refrigerant is liquefied by the removal of heat
• Condemned Boiler or Unfired Pressure Vessel a boiler or unfired pressure vessel that has been inspected by the Building Official and declared unsafe or disqualified and power stamped or marked designating its rejection.
• Crane Means a machine for lifting or lowering a load and moving it horizontally, the hoisting mechanism being an integral part of the machine
• Duct A passageway made of sheet metal or other suitable material not necessarily leak tight, for conveying air or other gases at low pressure
• Enclosed means that the moving parts of a machine are so guarded that physical contact by any part of the human body is precluded or prevented. This does not however prohibit the use of hinged, sliding or otherwise removable doors or sections to permit inspection, lubrication or proper maintenance.