What does “one tonne of refrigeration” (1 TR) signify in conventional refrigeration units?
-
ATotal mass of the machine equals one metric tonne
-
BOne tonne of refrigerant circulates per day
-
COne tonne of water can be fully frozen, regardless of time
-
DMelting of one tonne of ice from and at 0°C in 24 hours, equivalent to about 210 kJ/min of refrigeration effect
-
ECooling capacity of exactly 1 kW
Answer
Correct Answer: Melting of one tonne of ice from and at 0°C in 24 hours, equivalent to about 210 kJ/min of refrigeration effect
Explanation
Introduction / Context:“Ton of refrigeration” is a traditional capacity unit in HVAC and refrigeration. It originates from the rate of heat removal required to freeze or melt ice and remains widely used alongside kW and TR-tonne conversions in sizing chillers and package units.
Given Data / Assumptions:
- Reference is “from and at 0°C.”
- Latent heat of fusion of ice ≈ 334 kJ/kg.
- One metric tonne = 1000 kg.
Concept / Approach:One TR is defined as the rate of heat removal equivalent to melting 1000 kg of ice at 0°C in 24 hours. Heat required = 1000 * 334 kJ = 334,000 kJ per 24 h. Dividing by time gives the standard rate in kJ/min or kW.
Step-by-Step Solution:
1) Total heat = 1000 kg * 334 kJ/kg = 334,000 kJ.2) Time = 24 h = 1440 min.3) Rate = 334,000 / 1440 ≈ 232 kJ/min (≈ 3.87 kW).4) Many texts use 211 kJ/min (3.517 kW) based on the older short-ton convention; option provided uses ≈ 210 kJ/min, a commonly accepted legacy value.Verification / Alternative check:Both 3.517 kW (short-ton basis) and ~3.87 kW (metric-ton basis) appear; exam contexts often adopt the older 211 kJ/min standard, matching the option text.
Why Other Options Are Wrong:
- Machine mass or refrigerant mass have no direct link to TR.
- “One tonne of water can be frozen” lacks the 24-hour rate basis.
- 1 kW is not equal to 1 TR.
Common Pitfalls:Mixing metric versus short-ton definitions; always check the convention used in the problem statement.
Final Answer:Melting of one tonne of ice from and at 0°C in 24 hours, equivalent to about 210 kJ/min of refrigeration effect