Refrigeration System Components and Installation Practices
The star of the freezer means * = -6 ºC.
Refrigeration System Components
Evaporators
- Types: Visible or buried.
- Temperature Conservation: Limited space and evaporator size.
- Apparatus Combination: Network hose and multiple computers (e.g., 2 evaporators, 2 tabs).
- Single Computer Evaporator: More coils for the freezer, less cooling capacity.
- Circuit Perimeter: Extended around doorways to prevent frost (highest leak potential).
- Loop: Circulates oil from the crankcase for cooling.
The vacuum is up to 30 inches.
Fridge-one behavior = **
- Split System: Party system.
- Capacitor: One capacitor can serve multiple evaporators (indoor units).
Heat Pump
The evaporator, instead of drawing cold, becomes the condenser, heating and then removing the capacitor, which also changes the evaporator.
Load-Loss: Influences speed; cannot exceed 3 psi (due to friction in small pipes).
Pipe Laying Conditions
- Lines should be as short and direct as possible (reduces cost, lower pressure drop).
- Minimize accessories (reduce leakage).
- Avoid placing pipes in extreme temperatures (operational problems).
- Lines should not interfere with building use or be susceptible to damage.
- Pipes should have a slope (2% higher than water) in the direction of fluid flow to the condenser, aiding oil return to the compressor; staple every 1 meter.
- When crossing walls, floors, or ceilings, protect pipes with lined tubes (10-15cm thickness).
- Insulate lines requiring it with flexible material (noise reduction).
- Ensure minimum velocity for oil return to the compressor and suction line (vertical section: min. 6m/s; horizontal section: min. 3m/s).
- Insulate suction lines; fluid load loss should be 3psi (1ºC) and 6PSI in the discharge pipe (insulate only in heat pumps).
- Place suction or discharge traps 3-5m apart (not at evaporator outlets).
- Select line diameter based on pressure loss (3psi) and gas velocity (max. 15m/s).
- Liquid Line: Not isolated.
- Gas Line: Isolated.
- Heat Pump: Both lines are isolated.
Pressure Loss
Results from gas friction against tube walls, causing volume increase and coolant density decrease (increases with line length and smaller diameter). Pressure loss should be below 3psi.
Pressure-Loss Test
Use a pressure gauge at each end and subtract the pressure valve reading or a rapid test (drill pipe loaded) if diameter allows. Alternatively, measure pressure at the evaporator outlet using a T-fitting with an output for the manometer.
Each pumping cycle uses 1-4% by weight of refrigerant + oil.
- Degree of Miscibility: Depends on pressure, temperature, and phase of the refrigerant gas (vapor-liquid is not miscible).
Suction and Discharge Pipes (Vertical)
Subject to load variation and gas volume. Double brackets are used with a smaller rise than the other (ensures refrigerant gas velocity for oil drag).
- Load-Variation: The small tube is sized for oil return at minimum capacity, and the second tube is sized for pressure losses at full load (siphon between the two is advisable).
- Design and Installation Choice: Up to 6 psi.
- Refrigerator Performance: Up to 3 psi.
Discharge line coupled with liquid to prevent liquid in the condenser.
Discharge Line
Should not be isolated unless running inside the conditioned space within a conduit, if it recovers heat from hot gases, or for safety reasons (operates at 60-80ºC, burn risk).
Liquid Line
Not isolated unless passing through a high-temperature area to prevent auto-evaporation (flash gas). The liquid line leaves the condenser to the expansion valve (fewer problems). Liquid enters the expansion valve at 100%.
- Suction and Liquid Lines Together: Mechanically join and isolate as a single tube section not exceeding 15m.
- Subcooling between 5-10°C is good, with maximum yield at 10-13°C.
- Subcooling decreases by 1°C every 3.5m.
- Maximum flange length: 15m.
Heat Pump
Requires more refrigerant charge and cooling liquid line. Liquid line subcooling is downward; if height exceeds 10m, use a pressure equalizer (regulator) at the bottom for cold-only systems. A manual valve is used in heat pumps, along with a check valve; pressure loss should not exceed 10psi.
Units
- Outdoor unit above the indoor unit.
- Outdoor unit below the indoor unit.
- Two units at the same height.
Cold-Only Systems
Indoor unit operates as an evaporator, and the outdoor unit as the condenser (including compressor).
- Suction Line-Up: Higher gas velocity of 6m/s.
- Flexible Unions: Copper and bronze; vibrations from the compressor or pipes require a dampening sleeve firmly attached to one side of the tube for vibration absorption. Install a discharge silencer for gas resonance.
- Mute Download: Dampens pulsations (pipe noise and vibration).
Evaporators (Heat Exchangers)
Transfer heat absorbed by the fluid from the environment to change its state to LV (do not operate more than 24 hours).
- Heat-Sensitive: Evaporator absorbs air heat; low air temperature.
- Latent Heat: Evaporator absorbs air heat; frost condenses water vapor from the air (20% in summer).
- Working time: 16 hours for cooling, 18 hours for freezing.
- Defrosting: Skip expansion to the evaporator or heat the ice with electric heating.
Evaporator Types
- Air cooling (natural and forced circulation).
- Liquid cooling (immersion, double pipe countercurrent, rain, fire-tube, special).
- Freezers.
Leak: Low pressure and temperature; warming increases suction line temperature, and frost is no longer cool but the fan is.
- Evaporator temperature between -18 and -30°C for food preservation.
- Simple Tube Evaporator: Hanging tube-shaped coil (s-shape) through which refrigerant passes, transferring cold.
- Finned Evaporator: Fins crossed by serpentine coils.
- Embossed or Formed Evaporator: Plates cooled with cooling coils.
- Flooded Evaporator: Uses a float dispenser to maintain the liquid level as high as possible in the evaporator (if not flooded, the evaporator is dry or direct expansion).