Refrigeration Operator B flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Compressor function

Raises refrigerant pressure and temperature, moving vapour from the low-side evaporator pressure to the high-side condensing pressure. It is the primary energy consumer in a vapour-compression cycle.

Condenser heat rejection

Rejects heat absorbed in the evaporator plus compressor work. Q_cond = Q_evap + W_comp. Air-cooled condensers typically reject 1.2 to 1.3 times evaporator load.

Evaporator superheat

Difference between suction line temperature and saturated suction temperature at the same pressure. Thermostatic expansion valves maintain stable superheat, commonly 5 to 10 K at the evaporator outlet.

Liquid subcooling

Difference between saturated condensing temperature and liquid line temperature. Subcooling ensures solid liquid reaches the metering device and prevents flash gas at the valve inlet.

Oil return requirements

Suction line velocity must be high enough to carry oil back to the compressor, typically 4 to 7 m/s in horizontal runs. Oil separators and traps assist return in low-temperature systems.

Scroll compressor

Uses two interleaved spiral scrolls; one orbits while the other stays fixed, trapping and compressing gas pockets. Common in mid-range packaged and split air-conditioning systems with few moving parts.

Pressure-enthalpy diagram

Plots refrigerant pressure against enthalpy. The four processes are compression, condensation at constant pressure, isenthalpic expansion, and evaporation at constant pressure; used to calculate COP and capacity.

Ammonia refrigerant properties

R-717 has zero ODP and GWP under 1. It is toxic and flammable at high concentration, detectable by odour near 5 ppm, and attacks copper and brass, so steel piping is used.

R-410A characteristics

Near-azeotropic blend of R-32 and R-125 at 50/50. Operates at higher pressures than R-22, requires POE oil, and must be charged as a liquid to avoid fractionation.

Refrigerant glide

Temperature difference between bubble point and dew point at constant pressure in a zeotropic blend. Glide affects superheat settings and requires liquid charging and careful servicing.

Coefficient of performance

COP = Q_evap / W_comp, the ratio of cooling delivered to work input. COP increases with higher evaporating temperature and lower condensing temperature.

Montreal Protocol and Kigali

The Montreal Protocol phased out CFCs and HCFCs such as R-12 and R-22. The Kigali Amendment phases down HFCs; Canadian regulations restrict high-GWP refrigerants and require leak reporting.

Refrigerant leak testing

Use electronic detectors, UV dye, soap bubbles, or dry nitrogen pressure testing. Never use oxygen or compressed air to pressure-test because of fire and explosion risk.

High-pressure cut-out

Safety switch that stops the compressor when discharge pressure exceeds a set limit below design pressure. It usually requires manual reset after tripping to force investigation.

Low-pressure cut-out

Switch that stops the compressor on low suction pressure, protecting against loss of charge or freezing. May be automatic reset for normal cycling or manual reset for safety trips.

Oil pressure safety switch

Trips the compressor if net oil pressure (oil pump pressure minus suction pressure) does not build within a set time, typically 30 to 120 seconds after start.

Relief valve piping

Relief devices protect against overpressure. Discharge must be piped to a safe location; ammonia relief valves vent to atmosphere through a vent line sized to prevent back pressure.

Ammonia room safety

Machinery rooms require ammonia detectors, mechanical ventilation, and emergency ventilation interlocked with detection. Alarms and evacuation procedures must be posted and tested.

Pump-down cycle

The compressor runs until a low-pressure switch evacuates the evaporator, then stops. It prevents liquid migration to the compressor during off cycles and is common in larger systems.

Lockout tagout

Energy-isolation procedure before servicing: disconnect power, lock the disconnect, tag it, and verify absence of voltage. Required before electrical or mechanical work on equipment.

Shift log readings

Record suction and discharge pressures and temperatures, condensing and evaporating temperatures, superheat, subcooling, oil pressure, motor current, and sight glass condition each shift.

Sight glass indicators

Bubbles indicate flash gas or low charge; a colour change in the moisture indicator signals moisture, requiring drier replacement. Check during steady operation, not right after start.

Condenser cleaning

Dirty or scaled condenser tubes reduce heat transfer and raise condensing pressure, increasing power use. Water-cooled condensers need periodic tube cleaning and cooling tower water treatment.

High discharge pressure causes

Common causes are a dirty condenser, overcharge, non-condensable gases, high ambient temperature, or restricted airflow. Investigate in that order before adding or removing charge.

Low suction pressure causes

Common causes are a restricted metering device, low refrigerant charge, blocked or frosted evaporator, or restricted suction line. Check superheat and sight glass to narrow the cause.

Preventive maintenance schedule

Includes electrical connection checks, condenser cleaning, charge verification, oil and filter changes, safety control testing, relief device inspection, and running-hour records for overhauls.

TSSA and Operating Engineers

The Technical Standards and Safety Act, 2000 governs pressure equipment in Ontario. TSSA administers O. Reg. 219/01, which sets plant classification and the required operating engineer class.

Plant log book

Record of operating readings, maintenance, tests, and unusual events. Entries must be legible, dated, and signed by the operator, and retained as required by regulation.

Certificate of qualification

Issued by TSSA and required to operate a plant of a given class. It must be valid and current, and the operator may only operate plants within the certified class.

CSA B52 scope

Mechanical Refrigeration Code covering design, installation, and operation of refrigeration systems in Canada, including safety devices, machinery rooms, and refrigerant limits.

Refrigerant record keeping

Federal halocarbon regulations and Ontario rules require tracking refrigerant purchases, use, leaks, and recovery, with certified technicians for certain handling and leak reporting above thresholds.

Bypassing safety devices

Never bypass a safety control without written authorization and compensating controls. The operator must report defects promptly and restore protection before returning equipment to service.