Category Archives for Control Devices

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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HVAC Bimetallic-type thermostat

Temperature changes can cause a bimetallic strip to expand or contract in step with changes in temperature. These thermostats are designed for the control of heating and cooling in air-conditioning units, refrigeration storage rooms, greenhouses, fan coils, blast coils, and … Continue reading

27. January 2011 by admin
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HVAC Bellows-type thermostat

On modern condensing units, low-pressure control switches are largely superseded by thermostatic-control switches. A thermostatic control consists of three main parts: a bulb, a capillary tube, and a power element or switch. The bulb is attached to the evaporator in … Continue reading

27. January 2011 by admin
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HVAC Solenoids

Solenoid valves are used in many heating and cooling applications. They are electrically operated. A solenoid valve, when connected as in Fig 14-10, remains open when current is supplied to it. It closes when the current is turned off. In … Continue reading

27. January 2011 by admin
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