Refrigeration System Technology: Vapour Compression and COP

Industry study notes | Wednesday theme | 2026-07-29

1. The Core Cycle of a Refrigeration System

In every Yuanxian vacuum cooling machine, whether a produce pre-cooler or a food vacuum chiller, the core of the refrigeration system is the vapour compression refrigeration cycle (VCRC). The cycle is completed by four main components: compressor → condenser → expansion valve → evaporator (water catcher).

Cycle diagram

1 Compressor (low-pressure low-temperature gas → high-pressure high-temperature gas) ^ v 4 Evaporator / water catcher 2 Condenser (low-pressure low-temperature liquid (high-pressure high-temperature gas → low-pressure low-temperature gas) → high-pressure medium-temperature liquid) ^ v <- <- 3 Expansion valve (throttling and pressure reduction) <- <-

State parameters at each stage (R404A example):

Core principle: the refrigerant absorbs heat when it evaporates at low pressure and rejects heat when it condenses at high pressure, and compressor work moves heat from the low-temperature region (chamber / water catcher) to the high-temperature region (ambient air).

2. Compressor Types in Detail

The compressor is the heart of the refrigeration system, and three types are used in Yuanxian equipment.

2.1 Reciprocating compressors

Working principle: a crank and connecting rod drive a piston back and forth in the cylinder, and suction and discharge valves draw in, compress and discharge the refrigerant.

Brands we commonly use: Bitzer (Germany)

Typical matches:

Advantages: mature technology, easy to repair (valve plates are replaceable), suited to medium and low cooling capacities
Disadvantages: many moving parts, high vibration, limited capacity per unit
Applications: CVF-100 to CVF-4000 medium and large machines

2.2 Scroll compressors

Working principle: two scroll plates (a moving and a fixed one) mesh to form crescent-shaped compression pockets. The moving scroll orbits, shrinking the pockets from the outside towards the centre for continuous compression.

Brands we commonly use: Copeland (USA)

Typical matches:

Advantages: simple structure (few parts), smooth operation (no reciprocating motion), low noise, high reliability
Disadvantages: scroll plates cannot be repaired in place (a failure means replacing the whole machine), efficiency falls at high capacity
Applications: CVF-500 to CVF-1000 small machines, or parallel arrangements on medium and large machines

2.3 Screw compressors

Working principle: a meshing pair of male and female rotors turns inside the housing. Refrigerant gas is carried into the rotor grooves and the volume shrinks as the rotors turn, producing continuous compression. Both single-screw and twin-screw types exist.

Brands we commonly use: Hanbell (Taiwan), Bitzer screw

Typical matches:

Advantages: compact structure, small footprint, high capacity, good energy efficiency, stepless capacity control
Disadvantages: expensive (tens of thousands to a hundred thousand RMB per unit), not economical at low capacity
Applications: produce pre-coolers above CVF-3000, food vacuum chillers above CVF-800

2.4 Comparison of the three compressor types

2.5 How evaporating temperature decides compressor selection

When selecting a compressor, evaporating temperature is a more critical parameter than cooling capacity:

• Produce pre-cooling: evaporating temperature -5 to -15°C (only needs to reach 2–4°C), high coefficient of performance, easy selection
• Food vacuum chilling: evaporating temperature -15 to -25°C (loading hot at 90°C and finishing at 10°C), coefficient of performance falls significantly
• Freeze dryers: evaporating temperature -35 to -45°C (ultra-low temperature), extremely low coefficient of performance, requiring special selection

Bitzer compressor performance decay factors:

Example: a Bitzer 4PCS-10.2-30P with 32 kW at a -10°C duty has only about 25.6 kW left at -15°C, a 20% decay.

3. Condenser Selection

The condenser cools the high-temperature high-pressure gas discharged by the compressor into liquid. Three types are used on Yuanxian equipment.

3.1 Air-cooled condenser

Principle: a fan forces air across a finned tube heat exchanger, carrying away the condensing heat of the refrigerant.

Parameters:

• Typical condensing temperature: 45–50°C
• Dependent on ambient temperature: condensing temperature rises in hot weather and cooling efficiency falls

Advantages: simple structure, easy installation, no water source
Disadvantages: lowest COP, strongly affected by ambient temperature, fan noise
Applications: small machines (CVF-500 and below), water-scarce regions, mobile equipment

3.2 Water-cooled condenser

Principle: a shell and tube heat exchanger, with cooling water flowing through the tubes and refrigerant condensing in the shell.

Parameters:

• Typical condensing temperature: 35–40°C (10°C lower than air cooling)
• Requires: cooling tower + pump + piping system
• Cooling tower price reference (CVF-160 class): Lingji CT-40 about ¥2,200

Advantages: highest COP, low condensing temperature, high cooling efficiency
Disadvantages: needs a water source and cooling tower infrastructure, higher maintenance cost (water treatment)
Applications: large projects with ample water, projects with high energy efficiency requirements

3.3 Evaporative condenser (our main recommendation)

Principle: combines the merits of air and water cooling — water evaporating on the coil surface carries away heat while a fan accelerates evaporation.

Parameters:

• Typical condensing temperature: 38–42°C (wet bulb temperature plus 5–10°C)
• Water consumption: about 5–10% of an air-cooled tower (water-saving type)

Advantages: COP 12–15% higher than air cooling and 90% less water than water cooling, the best value between the two
Disadvantages: dependent on wet bulb temperature, scaling risk, needs regular cleaning
Applications: our main recommendation for medium and large machines (CVF-1000 and above)

3.4 Condenser TCO comparison

Counter-intuitive trap: water cooling is not necessarily cheaper than evaporative cooling. The infrastructure and running cost of a cooling tower plus pumps can be higher, especially in water-scarce regions.

4. Expansion Valves

The expansion valve is the throttling element of the refrigeration system, dropping the pressure and temperature of the high-pressure liquid refrigerant and controlling the liquid feed to the evaporator.

4.1 Thermostatic expansion valves

Principle: a sensing bulb detects the evaporator outlet temperature and the balance of forces between diaphragm and spring automatically adjusts the valve opening.

Brands we commonly use: Danfoss

Selection points:

• The valve capacity must match the compressor cooling capacity (err on the large side)
• The evaporating temperature range must fall within the valve's applicable range
• Food vacuum chillers see large water catcher load swings, so a large-diameter valve is recommended

4.2 Capillary tubes (for small machines)

Principle: a long thin tube provides flow resistance to throttle and reduce pressure. Fixed restriction, no adjustment.

Typical: internal diameter Φ2.5 mm, length 440 mm, 5 in parallel (CVF-160 class)

Advantages: extremely low cost, no moving parts
Disadvantages: cannot adjust the liquid feed, poor adaptability to different duties
Applications: very small refrigeration systems (CVF-50 and below)

4.3 Electronic expansion valves (the future direction)

Principle: a stepper motor controls the valve opening precisely with PID regulation.

Advantages: high accuracy, fast response, 5–10% energy efficiency gain
Disadvantages: high cost (3–5 times a thermostatic expansion valve)
Status: not yet used in volume by Yuanxian; worth considering on high-end export models

5. Refrigerant Selection

Recommendations:

• Standard domestic projects → R404A (best value)
• EU exports → R449A (GWP compliant)
• Small single-pallet machines → R410A (high efficiency)
• Extra-large vacuum chilling → R507 (higher cooling capacity)

6. COP Optimisation Strategies

COP (coefficient of performance) = cooling capacity ÷ compressor input power. These are the COP measures applied on Yuanxian equipment.

6.1 Lower the condensing temperature

Every 5°C reduction in condensing temperature raises COP by about 8–10%:

6.2 Choose a suitable evaporating temperature

• Do not lower the evaporating temperature more than necessary: going from -5°C to -15°C cuts capacity by 36% while energy consumption falls only 15%
• Produce pre-cooling: -10°C is the optimum balance point (best value)
• Food vacuum chilling: -15 to -25°C is needed (balancing cooling speed and energy consumption)

6.3 Compressor selection optimisation

• Small machines: scroll > reciprocating (lower cost, better efficiency)
• Medium machines: reciprocating > scroll (better reliability)
• Large machines: screw > reciprocating (higher efficiency, stepless capacity control)

6.4 Example comparison

The water-cooled solution has the lowest specific energy consumption, but cooling tower infrastructure and pump running costs must be included.

7. Common Misconceptions

1. A bigger compressor is always better

   • More power means more electricity, and the cooling capacity does not necessarily match. What counts is evaporating temperature + condensing temperature × the compressor performance curve.

2. Water cooling is always better than evaporative

   • Look at TCO: the infrastructure and electricity cost of a cooling tower plus pumps can be uneconomical where water and power are expensive.

3. Air cooling is the cheapest

   • Cheap equipment but high running electricity cost (COP about 70%), which may not be cheaper in the long run.

4. Scroll compressors suit every model

   • A single scroll unit has limited capacity (<30 kW), and large capacities need several in parallel, which complicates the piping and can cost more than it saves.

5. R404A is simply the best

   • Its GWP is as high as 3922 and EU F-Gas regulations have begun to restrict it. For European exports we should proactively recommend R449A, which is a point of differentiation.

Core Summary

References: knowledge base engineering models/compressor selection logic/, component parameters/, _INDEX_AI navigation.md, actual project system lists
Version: v1.0 | 2026-07-29