What is the unit of refrigeration?

Short Answer:

The unit of refrigeration is “ton of refrigeration” (TR). It is defined as the amount of heat required to melt one ton (1000 kg) of ice in 24 hours at 0°C. One ton of refrigeration is equal to 3.517 kilowatts (kW) or 210 kJ/min. This unit is used to express the cooling capacity or rate of heat removal in refrigeration and air-conditioning systems.

In simple words, the unit of refrigeration helps to measure how much cooling a system can produce. Larger systems, such as air conditioners or cold storage plants, are rated in tons of refrigeration, while smaller units can be rated in watts or kilowatts.

Detailed Explanation :

Unit of Refrigeration

In refrigeration and air-conditioning, it is necessary to express the rate of heat removal or cooling capacity of a system in a standard form. For this purpose, the ton of refrigeration (TR) is commonly used as the standard unit. It represents the amount of heat energy required to convert a certain quantity of ice into water at the same temperature over a specified period of time.

The term “ton” in refrigeration does not mean the weight of the machine; instead, it is a measure of the cooling effect. It is based on the historical method of using ice for cooling before mechanical refrigeration systems were invented.

Definition of One Ton of Refrigeration

One ton of refrigeration is defined as:

The amount of heat required to melt one ton (1000 kg) of ice in 24 hours at 0°C.

When ice melts, it absorbs a certain amount of heat known as the latent heat of fusion. The latent heat of fusion of ice is 335 kJ/kg (approximately). Therefore, to melt one ton of ice, the total heat absorbed can be calculated as follows:

This is the total heat absorbed in 24 hours. To find the heat removal rate (per second or per minute), we divide by time:

 

However, by standard definition and practical usage, the rate of heat removal corresponding to one ton of refrigeration is taken as:

This small difference arises due to the approximation and use of practical values.

Conversion of Ton of Refrigeration into Other Units

To compare with other systems or calculate performance, refrigeration capacity can be expressed in different units:

  • 1 TR = 210 kJ/min
  • 1 TR = 3.517 kW
  • 1 TR = 3024 kcal/hr
  • 1 TR = 12000 BTU/hr

Here,

  • kW (kilowatt) is a unit of power used in SI system.
  • BTU (British Thermal Unit) is a unit of heat energy used in the British system.

Thus, refrigeration systems can be rated in TR, kW, or BTU/hr depending on the region and application.

Importance of Ton of Refrigeration

  1. Measurement of Cooling Capacity:
    The unit of refrigeration helps to easily measure and compare the cooling capacities of different systems. For example, domestic refrigerators may have a small capacity (less than 1 TR), while commercial systems like ice plants or large air conditioners may have capacities of several tons.
  2. Standardization:
    It provides a standard reference for engineers and manufacturers to design and rate refrigeration systems.
  3. Ease of Calculation:
    Using the ton of refrigeration simplifies the calculation of energy requirements and system performance.
  4. Relation to Real-Life Applications:
    Since the unit is based on the cooling effect produced by melting ice, it is easily understandable in practical terms.

Example Calculation

Suppose a refrigeration system has a cooling capacity of 7.034 kW. To find its capacity in tons of refrigeration:

 

Hence, the refrigeration system has a capacity of 2 tons of refrigeration.

Other Units Used in Refrigeration

Although the ton of refrigeration is the most common unit, other units like kJ/s, kcal/hr, and BTU/hr are also used depending on the field and country.

  • SI Unit: The SI unit of refrigeration is kilowatt (kW) since it represents the rate of energy transfer.
  • Metric Unit: The metric equivalent is kJ/min, as it shows the rate of heat removal per minute.
  • British System: Uses BTU/hr as the measure of cooling effect.
Conclusion

The unit of refrigeration is an important measure of the cooling capacity or rate of heat removal of a refrigeration system. The commonly used unit is the ton of refrigeration (TR), which equals the heat required to melt one ton of ice in 24 hours. It is equivalent to 210 kJ/min or 3.517 kW. This unit helps engineers, technicians, and users to compare and understand the performance of different cooling systems conveniently and accurately. In modern systems, both TR and kW are widely used to represent cooling capacity.