Piping, Fittings, and System Installation

Piping, Fittings, and System Installation

Chapter Introduction

This chapter covers all the knowledge required for the Red Seal exam concerning piping, fittings, and the installation of refrigeration and air conditioning systems. You must master materials, joining techniques, safety rules, expansion calculations, and the requirements of Canadian national standards. Mastering this content is essential, as questions on this topic typically represent 10 to 15% of the exam.

Piping Materials and Their Applications

Copper Tubing

Copper is the predominant material in refrigeration for liquid, suction, and discharge lines. You must know the three types of hardness:

Nominal copper tubing dimensions are based on the outside diameter (O.D.). Wall thickness varies by type (K, L, M), which affects the inside diameter (I.D.) and therefore the flow capacity. For refrigerant lines, Type L or K is generally used.

Rule of thumb: Refrigerant velocity in suction lines must be maintained between 4 and 10 m/s to ensure oil return. In liquid lines, velocity must be below 1.5 m/s to avoid noise and erosion.

Steel Pipe

Black steel (Schedule 40 or 80) is used for ammonia (NH₃) systems and for large R-22 or R-134a installations. Stainless steel is reserved for special applications (food industry, corrosive products).

The schedule indicates wall thickness. Schedule 80 has a thicker wall than Schedule 40 for the same nominal diameter. For ammonia, Schedule 80 is generally required for diameters under 2 inches.

Plastic and Other Materials

Fittings and Joining Techniques

Brazed Fittings (Soldering)

Brazing uses a filler metal whose melting point is above 450 °C. In refrigeration, silver brazing is used with silver alloys (15%, 35%, or 45% silver).

Approximate melting temperatures:

Correct brazing procedure:

Trap to avoid: Heating the tube directly instead of the fitting. The filler metal will be drawn toward the hottest zone, creating an incomplete joint.

Mechanical Fittings

Arc-Welded Fittings (Steel)

For steel, arc welding (SMAW) or TIG welding is used. TIG is preferred for ammonia because it produces a clean bead without slag. Full penetration is essential to avoid oil pockets and corrosion.

Thermal Expansion Calculations

The thermal expansion of copper is 0.0000167 m/m·°C (16.7 × 10⁻⁶ m/m·°C). For a 30-meter line with a ΔT of 50 °C:

ΔL = L₀ × α × ΔT

ΔL = 30 m × 0.0000167 /°C × 50 °C = 0.025 m = 25 mm

This 25 mm expansion must be absorbed by expansion loops or natural changes in direction. The minimum length of an expansion loop is calculated by:

L = 2 × √(3 × E × D × ΔL / S)

Where:

Example: For a 28.6 mm O.D. tube with 25 mm of expansion:

L = 2 × √(3 × 110,000 × 28.6 × 25 / 70) = 2 × √(3,367,857) = 2 × 1835 = 3670 mm ≈ 3.7 m

Slopes and Oil Return

Recommended Slopes

Oil Traps (Siphons)

An oil trap must be installed at the base of any riser in the suction or discharge line when the vertical height exceeds 2.5 meters. The general rule:

Important: In variable-capacity systems (variable-speed compressors), double traps or double-rise traps are sometimes necessary to ensure oil return at low flow rates.

Pipe Insulation and Protection

Types of Insulation

Minimum thickness: Suction line insulation must be thick enough to prevent condensation. The rule of thumb: for a surface temperature of -10 °C and 60% relative humidity at 24 °C, at least 25 mm of cellular rubber is required.

Vapor Barrier

The vapor barrier is mandatory on the outer surface of insulation on cold lines. It prevents moisture vapor from migrating toward the cold surface. Vapor barrier joints must be sealed with an appropriate adhesive. A tear in the vapor barrier negates the effectiveness of the insulation.

Supports and Anchors

Support Spacing

Important rule: Supports must never compress the insulation. Use clamps with insulating inserts or double-shell supports. Rigid supports (without insulation) create thermal bridges that cause condensation.

Fixed Anchors

Fixed anchors (anchor points) divide the piping into independent expansion sections. They must be placed:

Canadian Electrical Code, Part I Requirements

The Canadian Electrical Code, Part I (C22.1-21) governs the electrical installation of refrigeration systems. The relevant rules for piping:

Rule 8-200 (Section 8): Conductor Sizing

The ampacity of conductors must be determined according to the Code tables. For compressors, the conductor must be sized at 125% of the full-load current (FLA).

Rule 26-252: Motor Disconnection and Protection

Each motor must have an accessible disconnecting means and overload protection. The disconnecting means must be visible or lockable.

Rule 28-110: Overcurrent Protection

The circuit breaker or fuses must be sized according to the motor's starting current. For a hermetic compressor, use the rated load current (RLA) and not the FLA.

Trap to avoid: Confusing RLA (Running Load Amps) and FLA (Full Load Amps). RLA is used for sizing overload protection, while FLA is used for sizing conductors.

CSA B149.1 Code (Natural Gas and Propane)

CSA B149.1 applies to gas heating systems, but also to refrigeration installations using gas burners. Key points:

CSA Standards for Refrigeration Piping

CSA B52 (Mechanical Refrigeration Code)

CSA B52 is the reference standard for the installation of refrigeration systems in Canada. Essential points:

Pressure Testing per CSA B52

Nitrogen test procedure:

Important: Never use oxygen or acetylene for pressure tests. Use only dry nitrogen or CO₂.

Installation of Valves and Accessories

Service Valves

Service valves (Schrader valves) must be installed:

Filter-Driers

The filter-drier must be installed in the liquid line, between the condenser and the expansion valve. It must be:

Sight Glasses

The sight glass must be installed in the liquid line, after the filter-drier. A sight glass full of clear liquid indicates a correct charge. Bubbles indicate a refrigerant shortage or excessive pressure drop.

Welding and Safety

Personal Protective Equipment (PPE)

Ventilation

Brazing copper produces zinc oxide fumes and cadmium fumes (if the alloy contains it). Adequate ventilation is mandatory. Cadmium-free alloys are preferred for health reasons.

Fire Risk

Complete Installation Procedures

Suction Line Installation

Liquid Line Installation

Discharge Line Installation

Pressure Drop Calculations

Pressure Drop in Refrigerant Lines

The total pressure drop (ΔP) in a line consists of:

Simplified formula for static loss:

ΔP_static = ρ × g × h

Where:

Example: Liquid R-134a (ρ = 1200 kg/m³) in an 8-meter riser:

ΔP = 1200 × 9.81 × 8 = 94,176 Pa ≈ 94 kPa

This 94 kPa loss corresponds to approximately 3 °C of saturation for R-134a. It is too high and requires additional subcooling or a larger diameter.

Equivalent Length of Fittings

Each fitting adds an equivalent length of straight tubing. Typical values in equivalent diameters:

Example: A 90° elbow on a 28.6 mm O.D. tube is equivalent to 30 × 28.6 = 858 mm of straight tubing.

System Purging and Dehydration

Nitrogen Purging During Brazing

When brazing copper lines, a nitrogen purge (flow of 0.5 to 1 L/min) must be maintained inside the tube to prevent the formation of copper oxide (black scale). This oxidation forms at high temperatures and can clog expansion valves and damage compressors.

Vacuum Dehydration

After installation and the tightness test, the system must be dehydrated under vacuum:

Micron: Unit of pressure used in dehydration. 1 micron = 0.001 Torr = 0.133 Pa. Standard atmosphere = 760,000 microns.

Triple Evacuation Method

For systems containing moisture, triple evacuation is recommended:

This method is more effective than a single vacuum because it removes moisture by successive dilution.

Specific Safety Rules

Refrigerant Handling

Confined Space Work

Cutting and Opening Circuits

Before cutting a tube containing refrigerant:

Traps to Avoid

Summary

Final Exam Tips

Good luck with your Red Seal exam preparation. Mastering piping is fundamental to passing the exam and to your career as a refrigeration and air conditioning mechanic.