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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 … Continue reading

27. January 2011 by admin
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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 … Continue reading

27. January 2011 by admin
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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 … Continue reading

27. January 2011 by admin
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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 … Continue reading

27. January 2011 by admin
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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 … Continue reading

27. January 2011 by admin
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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 … Continue reading

27. January 2011 by admin
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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 … Continue reading

27. January 2011 by admin
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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 … Continue reading

27. January 2011 by admin
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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 … Continue reading

27. January 2011 by admin
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HVAC Heating and cooling thermostats

Some thermostats can be used for both heating and cooling. The thermostat shown in Fig. 14-15 is such a device. The basic thermostat element has a permanently sealed, magnetic single pole double throw (SPDT) switch. The thermostat element plugs into … Continue reading

27. January 2011 by admin
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