The diffuser or grille minimum pressure for a given air volume reflects itself in ultimate system fan horsepower requirements. A diffuser or grille with a lower pressure rating requires less total energy than a unit with a higher pressure rating for a given air volume and effective area. Diffusers and grilles of a given size […]
Read More…Archive for January, 2011
HVAC Throw Requirement
Throw and occupied area air location are closely related. Both could be considered in the analysis of specific area requirements. The minimum maximum throw for a given condition of aeration is based upon a terminal velocity at that distance from the diffuser. The residual room velocity is a function of throw to terminal velocity. Throw […]
Read More…HVAC Air volume requirement
The air volume per diffuser or grille is that which is necessary for the cooling, heating, or ventilation requirements of the area served by the unit. The air volume required, when related to throw, sound, or pressuredesign limitations, determines the proper diffuser or grille size. Generally, air volumes for internal zones of building spaces vary […]
Read More…HVAC Air-flow distribution
Bottom or side outlet openings in horizontal or vertical supply ducts should be equipped with adjustable flow-equalizing devices. Figure 17-6 indicates the pronounced one-sided flow effect from an outlet opening. This is before the corrective effect of air-turning devices. A control grid is added in Fig. 17-7 to equalize flow in the takeoff collar. A […]
Read More…HVAC Designing a Perimeter System
After the heat loss or heat gain has been calculated, the sum of these losses or gains will determine the size of the duct systems and the heating and cooling unit. The three factors that ensure proper delivery and distribution of air within a room are location of outlet, type of outlet, and size of […]
Read More…HVAC Water Tower Controls
Temperature controls for refrigerating service are designed to maintain adequate head pressure with evaporative condensers and cooling towers. Low refrigerant head pressure, caused by abnormally low cooling water temperature, reduces the capacity of the refrigeration system. Two systems of control for mechanical and atmospheric draft towers and evaporative condensers are shown in Figs. 14-23 and […]
Read More…HVAC Pressure Control Switches
One safety feature for air-conditioning units with a compressor and condenser is a pressure-controlled switch. This switch is wired into the circuit to protect the system in case the system develops a leak. If a leak develops, it is possible to draw in moisture and air and damage the whole system. If the pressure builds […]
Read More…HVAC Cold Anticipator
The cold anticipator is a fixed resistor and is not adjustable. It heats the bimetallic coil that operates the points whenever the air-conditioner compressor is not on. When the compressor is on, the resistor is shorted out by the thermostat points being closed. The heating of the coil while the points are open causes it […]
Read More…HVAC Heat Anticipator
The reason for the heat anticipator is to limit the degree of swing between turning on the furnace and the temperature of the room. It is a resistance heater element that is inserted in series with the thermostat line that runs to the heat-contactor coil. Once the thermostat contacts are closed current flows through the […]
Read More…Mercury Contacts
Some thermostats use the expanding bimetal arrangement to cause a tube of mercury to move. As the mercury moves in the tube, it comes in contact with two wires inserted into the glass tube. When the mercury comes in contact with the two wires, it completes the electrical circuit. This type of thermostat needs to […]
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