RETA CARO cheat sheet

Sensible heat changes temperature without a phase change (Q = m·cp·ΔT); latent heat is absorbed or released at constant temperature during a phase change.

Refrigeration capacity: 1 ton of refrigeration = 12,000 Btu/hr = 200 Btu/min = 3.517 kW.

Pressure–enthalpy diagram: the evaporator absorbs heat between the expansion-valve outlet and the compressor suction; the condenser rejects heat between compressor discharge and expansion-valve inlet.

Superheat = actual suction temperature minus saturation temperature at suction pressure; subcooling = saturation temperature at condensing pressure minus liquid line temperature.

Compressor displacement (ft³/min) = bore area × stroke × RPM × number of cylinders; volumetric efficiency falls as compression ratio rises.

Pressure ratio = absolute discharge pressure ÷ absolute suction pressure; high ratios raise discharge temperature and reduce capacity.

A thermostatic expansion valve controls evaporator superheat by modulating refrigerant flow; a flooded evaporator uses a float or level control instead.

Refrigerant lines: liquid lines sized to limit pressure drop and flashing; suction lines sized for minimal pressure drop to preserve compressor capacity.

Evaporator approach (TD) is the temperature difference between the refrigerated space or medium and the refrigerant saturation temperature.

Anhydrous ammonia is flammable at roughly 15–28% by volume in air and is classified as a 2.2 (nonflammable, toxic) gas under transport rules; it is toxic and corrosive to tissue.

Ammonia is lighter than air (vapor density about 0.6 relative to air), so it rises and accumulates at high points and ceilings.

The NIOSH IDLH for ammonia is 300 ppm; the OSHA PEL is 50 ppm as an 8-hour TWA; the ACGIH STEL is 35 ppm.

Ammonia is highly soluble in water; water is the preferred absorbent for vapor release, but never spray water into liquid ammonia pools because it adds heat and accelerates vaporization.

Ammonia ignites with difficulty; a direct ignition source plus high concentration is required, and oil-soaked insulation can be a fire hazard near leaks.

PPE for ammonia response includes full-face respirator or SCBA, chemical splash goggles, and ammonia-resistant gloves; butyl or neoprene is preferred over natural rubber.

Machinery rooms require ventilation, ammonia detection with alarm and shutdown interlocks, and emergency exits that open outward; the room must be separated from occupied spaces.

Emergency shutdown and isolation: close king valves and pump-down/isolation valves to limit release, and never enter a high-concentration area without SCBA and a backup person.

First aid for ammonia exposure: flush eyes and skin with copious water for at least 15 minutes, remove contaminated clothing, and seek medical attention; inhalation victims need fresh air and oxygen.