Compressor Basics
This classification of compressor works by physically capturing gas in a measured space and then reducing that space to force the gas out.
What is a positive-displacement compressor?
The three physical changes refrigerant undergoes in a condenser are desuperheating, subcooling, and this primary state change
: What is condensing?
: This hard, insulating deposit forms on condenser and cooling-tower surfaces when dissolved minerals precipitate out of the water.
What is scale (or scaling)?
This style of fan pushes air across the condenser coil, with the cup of the fan blade facing the condenser.
What is a forced-draft fan?
: At outdoor temperatures of 65°F and lower, this type of control is required to prevent condensing pressures from dropping too low for the metering device to feed properly.
What is low ambient control (or head pressure control)?
: This is the most common problem with water-cooled equipment, indicated by a high discharge pressure and a higher-than-normal temperature difference between saturation and leaving water.
Answer: What is liquid floodback?
In a scroll compressor, this specific compliance relies on centrifugal force to hold the moving scroll against the fixed scroll to seal the flanks.
What is radial compliance?
This specific process accounts for approximately 80% of the heat removal within the condenser.
What is condensing (or the change of state from vapor to liquid)?
This is the periodic, intentional release of water from a cooling tower sump designed to reduce the mineral concentration.
What is blowdown?
: These highly efficient aluminum coils are made from ribbons containing small passages, allowing them to use about half the refrigerant charge of a traditional coil.
What are microchannel coils?
This electronic control chops part of the sine wave to reduce fan RPM but should never be used on fan motors with sleeve bearings
: What is fan speed control?
This is the absolute first step a technician must take when servicing water-cooled equipment, before checking any other operating characteristics
What is checking the water flow?
This value is calculated by dividing absolute discharge pressure by absolute suction pressure.
What is the compression ratio?
For every 1 degree Fahrenheit of subcooling achieved in the condenser, the total cooling capacity of the system increases by this percentage
What is 0.5%?
These systems send city water through the condenser only once before discharging it down the drain, making them prohibitively expensive to operate.
What are wastewater systems?
These coils look prickly and are manufactured by wrapping thin, slit strips of aluminum around aluminum tubing
What are spine-fin coils?
Condenser-flooding systems typically use these two specific valves: one to restrict liquid drainage and one to bypass discharge gas to the receiver.
What are the ORI and ORD valves?
: A three-phase scroll compressor that starts with a loud rattling noise, equalized pressures, and fans turning backward is experiencing this electrical fault
What is reversed phase rotation?
This dynamic-displacement compressor behaves somewhat like a very fast fan, using an impeller to throw refrigerant outward and convert velocity into pressure.
What is a centrifugal compressor?
In an air-cooled condenser, you calculate the heat of rejection (in BTUH) by multiplying the temperature change by the CFM and this specific convenience constant.
: What is 1.08?
This deadly bacteria can grow in untreated cooling-tower water and be spread through the mist, as discovered during a 1976 convention outbreak.
What is Legionella?
This application keeps the compressor inside the building out of the weather while moving the air-cooled condenser outdoors.
What is a remote air-cooled condenser?
This single, non-adjustable valve simplifies condenser-flooding by combining the functions of the ORI and ORD valves into one control
What is the OROA valve?
A three-phase scroll compressor that starts with a loud rattling noise, equalized pressures, and fans turning backward is experiencing this electrical fault.
: What is reversed phase rotation?
This is the space between the piston top and the cylinder head at the end of the compression stroke, which traps gas that must reexpand on the downstroke
What is clearance volume?
This phase occurs in the very first portion of the condenser and accounts for roughly 15% of the total heat removed.
What is desuperheating?
This piping design routes water and refrigerant through the condenser in opposite directions so the coldest water contacts the coldest liquid refrigerant.
What is counterflow?
: If you have more than 20% mechanical damage to these on an air-cooled coil, the condenser’s efficiency will be too low to survive heavy summer loads.
What are the condenser fins?
This method of restricting condenser airflow uses mechanical louvers but should only be used on centrifugal-type fans, never propeller fans
What is damper control?
: To safely recover refrigerant from a water-cooled condenser without freezing and bursting the tubes, you must do one of these two things with the water.
: What is continuously circulate the water or completely drain the water?