A property of refrigerant that makes it useful to air condition a house or building is the ability to read the pressure of the refrigerant and know it's temperature. Refrigerants will change from a liquid state to a vapor state at a very low temperature. If you control the pressure of the refrigerant you can control the temperature it changes state at.
For example, a drum of liquid R-22 at 80 degrees will change from a liquid to a gas and the pressure will increase as the gas expands. When the pressure reaches around 143 lbs, the boiling will stabilize and as long as the temperature remains constant the pressure will remain constant.
If the drum is moved to a cooler area the pressure will be affected. If the new area is 60 degrees the refrigerant gas will condense back to a liquid and the pressure will drop. When the pressure reaches around 102 lbs the condensing of the gas will stabilize.
If you connected a regulator to the R-22 refrigerant drum and allowed liquid refrigerant to pass through it into a coil and set the regulator at 58 lbs the coil temperature would be controlled to 32 degrees until you ran out of refrigerant. If you blew 75 degree air across the coil some heat in the air would be absorbed by the refrigerant and the air temperature would drop.
More later.
Thursday, May 10, 2007
Friday, May 4, 2007
Understanding Simple Thermostats
The basic terminals on a thermostat are R G Y and W. The wiring should be color coded R for red, G for green Y for yellow and W for white.
R is the terminal coming from the transformer that is powered all the time. The thermostat is actually a group of switches designed to energize different circuits. R is the main power source. The G terminal receives power from R and energizes the fan circuit when the fan switch is turned on. When the fan switch is in the automatic position G is connected to the Y terminal. Y is the terminal that is used to turn on the cooling circuit. The Y terminal is connected to the R terminal when the Heat/ Off / Cool switch is in the cool position and the temperature has risen above set point. This energizes the cooling circuit and the fan circuit.
The W terminal is used to energize the heating circuit. When the Heat/ Off/ Cool switch is in the heat position and the temperature has dropped below setpoint R terminal is connected to the W terminal and the heating circuit is energized. On a typical gas furnace the fan is energized from a temperature switch that senses the temperature of the heat exchanger or a timing mechanism in a circuit board that senses power on the W terminal.
Some thermostats have other terminals. The most common are RC and RH which are used if you have a system with seperate 24 volt power supplies for heating and cooling. If you have 1 power supply the RC and RH must be jumpered together. Another teminal is C. It is used to connect the other terminal on the transformer if this particular thermostat requires a common wire for operation. One other common terminal is O or B and is used to power the reversing valve for a heat pump.
R is the terminal coming from the transformer that is powered all the time. The thermostat is actually a group of switches designed to energize different circuits. R is the main power source. The G terminal receives power from R and energizes the fan circuit when the fan switch is turned on. When the fan switch is in the automatic position G is connected to the Y terminal. Y is the terminal that is used to turn on the cooling circuit. The Y terminal is connected to the R terminal when the Heat/ Off / Cool switch is in the cool position and the temperature has risen above set point. This energizes the cooling circuit and the fan circuit.
The W terminal is used to energize the heating circuit. When the Heat/ Off/ Cool switch is in the heat position and the temperature has dropped below setpoint R terminal is connected to the W terminal and the heating circuit is energized. On a typical gas furnace the fan is energized from a temperature switch that senses the temperature of the heat exchanger or a timing mechanism in a circuit board that senses power on the W terminal.
Some thermostats have other terminals. The most common are RC and RH which are used if you have a system with seperate 24 volt power supplies for heating and cooling. If you have 1 power supply the RC and RH must be jumpered together. Another teminal is C. It is used to connect the other terminal on the transformer if this particular thermostat requires a common wire for operation. One other common terminal is O or B and is used to power the reversing valve for a heat pump.
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