In cold storage and refrigeration systems, understanding the relationship between the evaporator surface temperature and the cold room temperature is essential for maintaining product quality, energy efficiency, and system reliability.
Though both temperatures are part of the same cooling process, they serve different purposes and operate at different levels.
This article explains the key differences, reasons for the temperature gap, and its impact on system performance.
What is Evaporator Surface Temperature?
The evaporator surface temperature refers to the temperature of the surface of the evaporator coil inside a refrigeration or cold room system. It is the point at which the refrigerant inside the evaporator changes from liquid to gas, absorbing heat from the surrounding air.
- Typically, this temperature is lower than the desired room temperature.
- It ensures that enough heat is pulled from the room to maintain the set temperature.
- The difference between this and the cold room temperature is often called the “temperature differential” or TD.
What is Cold Room Temperature?
The cold room temperature is the air temperature inside the refrigerated space where products are stored. This is the target temperature that needs to be consistently maintained for food safety, pharmaceutical storage, or industrial applications.
- Usually set based on the product requirements (e.g., +2°C to +8°C for fresh produce, or -18°C for frozen goods).
- Controlled through thermostats and monitored via sensors.
Why is There a Difference?
The evaporator coil needs to be colder than the room air to absorb heat effectively. This temperature difference drives the heat transfer process, as heat always flows from warmer to cooler objects.
Key Factors Creating the Difference:
- Heat Transfer Efficiency: The colder the evaporator surface, the faster it can absorb heat from the room air.
- Thermodynamic Principles: A refrigerant evaporates at a lower pressure and temperature than the room air to extract heat.
- Frost Formation Consideration: A lower surface temperature helps condense and freeze moisture from the air, forming frost on the evaporator, which must be managed through defrost cycles.
Typical Temperature Differences
The temperature gap varies depending on the system and application:
| Application Type | Room Temp (°C) | Evaporator Temp (°C) | Difference |
|---|---|---|---|
| Cold Storage Room | 2°C to 8°C | -4°C to -8°C | 6°C to 10°C |
| Freezer Room | -18°C | -26°C to -30°C | 8°C to 12°C |
| Blast Freezer | -35°C | -40°C to -45°C | 5°C to 10°C |
Conclusion
The difference between evaporator surface temperature and cold room temperature is a fundamental principle in refrigeration systems. Maintaining the right temperature differential is critical for effective cooling, energy savings, and product preservation. Understanding and optimizing this relationship ensures that cold storage systems perform efficiently and reliably.