South Carolina - Refrigeration

Key Concepts

Permits (§106.2, Item 7). A permit is not required for self-contained refrigeration systems that contain 10 pounds (4.5 kg) or less of refrigerant, or that are actuated by motors of 1 horsepower (0.75 kW) or less. Exemption from the permit requirement does not authorize work that violates other provisions of the code.

Change in refrigerant type (§1101.7). Prior notification to the code official — plus compliance with the provisions for the new refrigerant — is required where a circuit contains more than 220 pounds (99.8 kg) of Group A1 or 30 pounds (13.6 kg) of any other group.

Allowable quantities and occupancy limits. - Machinery rooms are not required for listed equipment containing not more than 6.6 pounds (3 kg) of refrigerant, regardless of safety classification, when installed per the listing (§1104.2, Exception 1). - Institutional: Table 1103.1 amounts reduced by 50 percent except kitchens, laboratories and mortuaries; total Group A2, B2, A3 and B3 shall not exceed 550 pounds in occupied areas or machinery rooms (§1104.2.1). - Total of all Group A2, B2, A3 and B3 refrigerants shall not exceed 1,100 pounds except where approved (§1104.3.3). - High-probability systems for human comfort shall use Group A1…

Key Concepts

Refrigerant classification and hazards - ASHRAE Standard 34 letter = toxicity (A = lower, B = higher); numeral = flammability (1 = no flammability, 2L = low flammability with slow burn velocity, 2 = low flammability, 3 = high flammability). B1 = higher toxicity, no flammability; B2L = higher toxicity, low flammability with slow burn velocity. (Ch. 2, "Refrigerants as Hazards," Page 22, Figure 2-8)

Cylinder safety (Ch. 2, Refrigerant Cylinder Safety, Page 21) - Refillable cylinders must be inspected every five years; the date is stamped on the cylinder. - Do not fill more than 80%; never heat with a flame; do not allow a cylinder to reach a temperature more than 125°F; store and transport vertically, valve at the top.

System layout and refrigerant state - The compressor and the metering device are the two dividers between low side and high side (Sections 8.1.1 and 8.2.1, Pages 126–128). - Some flash gas is acceptable in the evaporator because it cools the remaining liquid refrigerant; excess reduces evaporator efficiency, and flash gas in the liquid line ahead of a TXV can damage the valve (Section 8.3.2, Page 130).

Key Concepts

Compressors (Ch. 18) - In a fully hermetic compressor the compressor and motor are usually spring-mounted inside the dome (some units use external springs), and the discharge and suction lines inside the dome are flexible — Sec. 18.1.2, Construction. - Unbalanced loading of the compressor shaft from improper belt tension or drive shaft misalignment increases shaft seal wear; the shaft seal is a common failure point in open-drive compressors — Sec. 18.1.1. - Screw compressor oil injection seals the clearance between rotors and cylinder and helps cool the compressor — Sec. 18.2.4. - Pressure lubrication forces oil to all bearing surfaces; the compressor runs quieter even with greater bearing clearances because pressurized oil cushions the bearings — Sec. 18.3.4. - Rotary compressors serve window A/C, PTACs, and heat pumps up to five tons, and have high volumetric efficiency — Sec. 18.2.2. - A megohmmeter applies 500 Vdc to 1000 Vdc to windings — Sec. 18.1.7 (p. 365). Insulation of 20–40 MΩ = severe oil contamination: change oil and filter-driers, and if the oil has a burnt odor, check all system motors (including fan motors) for worn bearings — Fig. 18-11 (p. 367). - Wire wrapping to amplify…

Key Concepts

Range vs. differential adjustment - Range is the set of values between and including cut-in and cut-out; range adjustment raises or lowers both cut-in and cut-out by an equal amount, so the differential does not change (Section 17.2.1). - Differential is the difference between cut-out and cut-in. Differential controls may be cut-in control, cut-out control, or combination control (Section 17.2.2). Increasing a control's differential lengthens run time and the interval between cycles; decreasing it shortens both. - On a pressure motor control, range adjustment lowers both cut-in and cut-out when the screw is turned out (counterclockwise) and raises both when turned in (clockwise). Differential adjustment affects only the cut-out — turning it in (clockwise) increases spring tension and raises cut-out; the spring has no effect on cut-in (Section 17.4.4, Page 333). - High-pressure motor control is a safety device, not an operating control, "usually set to cut out at 20% above normal head pressure" (Page 334). - Low-pressure motor control: cut-out pressure should correspond to a temperature about 10°F below the desired evaporator outside surface temperature; cut-in should correspond to about the highest allowable evaporator temperature (Page 335).

Key Concepts

Tubing identification and sizing. ACR tubing is designated by its actual outside diameter; copper water tubing's nominal size equals the OD minus 1/8″ (MRAC 22nd ed., Section 5.1.1, Figures 5-1 and 5-3). Type K is a heavy wall, Type L is a medium wall, and Type L is the commonly used type. ACR tubing is charged and sealed with gaseous nitrogen, and coil ends should be plugged immediately after a length is cut from the coil (Section 5.1.1).

Soft vs. hard-drawn. Soft ACR tubing is sold in 25′, 50′, and 100′ rolls, most commonly 3/16″ to 3/4″ OD. Hard-drawn Type L or K ranges from 3/8″ to over 6″ and is supplied in 10′ and 20′ lengths. Hard-drawn tubing should not be bent, so flared connections cannot be used; its joints should be brazed, not soldered — solder should be used only on water lines (Section 5.1.1). Work-hardened copper may crack at stress points when flared and can be softened by annealing: heat to a dull cherry red, then allow to air cool slowly (Annealing Tubing procedure).

South Carolina Refrigeration Exam — 9 questions, 18% of exam

Key Concepts

Bend geometry (Pipefitter's Handbook, Pages 1-1 and 1-2) - Length of arc in any bend is measured along the pipe centerline, and the radius is also measured to the centerline: Length of Arc = No. of Degrees × .01745 × Radius. - Setback locates the beginning of a bend — the distance from the start of the bend to the point where the extended centerlines of the two straight legs would meet. Setback = Radius × Tangent ½ Angle of Bend. - For a 180° bend, setback measured to the leg intersection would be infinite; the bend is treated as two 90° bends and setback is taken as equal to the radius, with length of bend = Radius × 3.14 (Page 1-50). - For a constant radius, the length of pipe in a total of 180° of bend is the same no matter how the bending is divided or directed (Page 1-86).

Key Concepts

Fire protection (Subpart F). A fire extinguisher rated not less than 2A shall be provided for each 3,000 square feet of protected building area, or major fraction thereof, and travel distance from any point to the nearest extinguisher shall not exceed 100 feet — §1926.150(c)(1)(i). One 55-gallon open drum of water with two fire pails may substitute for a 2A extinguisher (c)(1)(ii); a ½-inch garden-type hose, not over 100 feet, discharging a minimum 5 gpm with 30-foot horizontal stream, may also substitute (c)(1)(iii). One or more 2A extinguishers on each floor; in multistory buildings at least one adjacent to the stairway (c)(1)(iv). An alarm system (telephone, siren, etc.) alerting employees on site and the local fire department must be established — §1926.150(e)(1) — with alarm code and reporting instructions conspicuously posted at phones and employee entrances, §1926.150(e)(2).

Definitions (Subpart C). Competent person: one capable of identifying existing and predictable hazards in surroundings or working conditions that are unsanitary, hazardous, or dangerous, and who has authorization to take prompt corrective measures to eliminate them — §1926.32(f). No degree, years of experience, or certificate is in that definition. Compare qualified (§1926.32(m)) and authorized person (§1926.32(d)).