Richard – What are refrigeration pressure switches used for in refrigeration circuits and how do refrigeration pressure switches protect the system from further damage?
Thanks for the question and for being a reader of High Performance HVAC! First there two types of basic refrigeration switches in the typical high grade residential system. I say high grade because not every refrigeration system in air conditioners and heat pumps have refrigeration switches to protect the refrigeration system.
High Pressure Refrigeration Switch – The high pressure switch will kill the compressor circuit if the pressure exceeds the rating on the pressure switch. These pressures will vary depending on the type of refrigerant the air conditioner or heat pump uses in the system. On some air conditioners or heat pumps this switch is manually reset only simply because if it trips there is definitely a problem that needs to be resolved before the system should run again. On Rheem and Ruud heat pumps and air conditioners the reset button is usually red on located near the control panel. A simple push of the switch will reset the switch and the operation of the air conditioner should return to normal until the pressure exceeds the rating of the switch. Things that can cause the pressure switch to trip include:
These issues, if they exist, should be taken care of before before the switch is reset. The high pressure switch prevents the system from operating at extremely high pressures.
Low Pressure Switch – The low pressure switch is typically an automatically reset switch that will reset itself when the pressure on the low pressure side of the refrigeration systems returns to normal or above the setting on the switch. When a refrigeration system operates at lower than normal pressures the system can freeze up with the freezing beginning at the evaporator coil and working its way back to the compressor via the suction line. Freezing of the refrigeration system is bad and lead to liquid refrigerant slugging in the compressor which can lead to compressor failure. Things that can cause the low pressure switch to trip include:
Water towers maintain a ready limited supply of water for communities in the event the water main goes down. Many water towers are used for emergency situations for the fire department to have water for fighting fires and for water fire suppression systems to have a supply of water for the emergency if it should arise. Continue reading “Water Tower Pumps and Controls” »
This photo shows the boiler cabinet open exposing controls and basic components of the boiler. The module on the left is the ignition control module which controls the sequence of operation for ignition and burner controls of the boiler. When the boiler is enabled to run usually by a thermostat or controls the ignition control module begins the process of firing the burners. The process typically begins by having the ignition module check the safety circuit to ensure all safeties are normal and not in alarm. This includes energizing the inducer or forced draft fan motor and any limit switches and a flow switch to ensure the boiler has water flow. The inducer or forced draft fan motor causes some pressure switches to close proving that combustion air is available and that the combustion gases will be exhausted when the burners fire. After the safety circuit has been proven to be okay the ignition control opens the gas valve while simultaneously activating the spark ignition to ignite the gas now being supplied to the burner(s). Once the burners ignite the fire is proven, usually by a state of the art flame sensor, the ignition control module deenergizes the spark ignition. As the water heats up it is sense by an aquastat or temperature sensor. When the temperature of the water reaches the set point of main boiler controller the ignition control closes the gas valve and the main burners shut down. The inducer or forced draft fan motor continues to run for period of time so that all the combustion gases in the system are purged up the boiler flue or boiler stack.
Outside air louvers allow the ddc control system to open dampers and introduce fresh air into the building. Building automation system, or the energy management system as it is sometimes called, monitors outside air temperature and humidity and based on a calculation and opens the outside air dampers when this calculation determines a precise set point. Introducing outside air into the building not only makes common sense it is also required by the Mechanical Code in commercial applications. This is required mainly for health reasons as it rids the building of volatile organic compounds and CO2 which is naturally produced by humans. Large concentrations of CO2 can build-up inside the building and needs to be vented as too much CO2 negatively affects human health. It is therefore important that along with the intake of outside air into the building there needs to be an exhaust air damper to maintain good building pressure. Negative pressure inside a building is bad as it causes infiltration moisture issues which leads to mold and mildew. Too much pressure also creates its own problems so it is important, with an outside air damper system, to monitor and maintain building pressure. Enthalpy wheels add to the efficiency of a good economizer system. Continue reading “Outside Air Intake – DDC Outside Air Economizer System” »
Pump cavitation can cause severe problems to a pump if not addressed and corrected. To understand the cause of cavitation you need to understand the pressure temperature relationship of the liquid in the loop (typically water or water/glycol mix). As the water passes through the pump it changes pressure from the suction side to the discharge side of the pump. If the waters static pressure drops too much vapor is created causing tiny bubbles in the water or fluid in the loop passing through the pump. These bubbles are unstable and collapse causing severe turbulence inside the bearing assembly where the impellor is located and can damage the impellor. Cavitation is often occurring when one hears popping and crackling noises passing through pump. Cavitation can also sound like the pump is pumping rocks through the impellor. These abnormal noises are the result of these tiny bubbles collapsing. As these bubbles are forming the pump loses its ability to create the necessary head to continue circulating the fluid through the loop. Solve the problem of and the noises go away along with extended life of the pumping system. Continue reading “Hydronic Pump Cavitation” »
The boiler pressure relief valve is a safety valve designed to relieved an excessive build up of pressure inside the boiler. The is a pressure vessel designed to handle a safe amount of pressure. If the pressure were to build up beyond the safety limitations as set forth by the design specifications the boiler system needs a safe way to vent the pressure to prevent an explosion. The boiler relief valve is this safe way to vent excessive dangerous pressures inside the boiler. Continue reading “Boiler Pressure Relief Valve – Boiler Safety” »
R-134A is an inert gas used in air conditioner systems. R134A is used as a chemical refrigerant in automotive and domestic use air conditioners such as chilled water systems in both commercial markets and industrial markets. You are very familiar with R134A if you are either an automotive mechanic or a chiller mechanic. R-134A uses the names Tetrafluoroethane, Genetron, or Puron among other names depending on the manufacturer. The pressure temperature chart represents the average pressure temperature relationship of refrigerant R-134A.
On the left is a pressure sensor to tell a maintenance technician if the HVAC Furnace Filters and the right control is a low static pressure switch to trip the unit if the mixing box drops below the set point pressure the switch is calibrated to. The low static pressure sensor protects the fan and the duct work including dampers from damage if the economizer damper and the return air damper would fail closed or another possible scenario that would cause the unit to pull negative pressure in the mixing box.
Pressure controls typically either protect the unit from a catastrophic failure or are used to control a fan or dampers. Pressure controls are either switches that trip at a calibrated pressure set point or transmitters that can transmit an analog signal back to the controls systems to control other components that control air flow. On this air handling unit there are four pressure sensors. The pressure sensors shown in the photo (Filter Pressure Sensor and Low Static Pressure) and two additional pressure sensors.