Thermal Testing of Refrigerated and Insulated Containers, Trailers and Van Bodies.
Heat leakage's of insulated containers, trailers, vehicles, or cabinets are determined in the CRT environmental test chambers.
In each test, the chamber air is maintained at a constant temperature in the range 0 C to +10 C. A metered quantity of electrical heat is fed continuously into the insulated test unit to maintain the internal temperature at least 20 C above the chamber temperature.
Once stable conditions are established, mean internal and mean external temperatures are calculated from twelve temperature sensors around and twelve inside the test unit. Dividing the measured heat input by the mean temperature difference determines the thermal heat leakage which is calculated in w/k.
The root mean area of the test unit is calculated from measurement of external and internal length, width and height. The overall heat transfer coefficient in W/m k is calculated from the thermal heat leakage divided by the root mean area.
Refrigeration Unit Capacity Testing
The performance of marine container and road transport refrigeration equipment, fitted to insulated containers or vehicles, can be determined in an environmental test chamber.
If not already known, it is first necessary to measure the heat leakage of the container or vehicle (see thermal testing).
The chamber temperature is raised to that specified (30 C for ATP, 38 C for ISO). The refrigeration unit is switched on with its thermostat set at its coldest setting. Thermostatic heaters control the test box interior specified test temperature causing the refrigeration unit to run continuously whilst attempting to reduce the temperature. The measured heat input balances the cooling effect to maintain the required test temperature.
The net refrigeration capacity of the unit on test, at the specified conditions, is the sum of the heat leakage + the balancing heat, provided by the heater, required to maintain the specified internal test temperature. Performance tests are normally conducted in a range of specified test temperatures.
CRT has two calorimeters available for refrigeration machinery capacity testing. These are in the form of insulated bodies with calibrated thermal characteristics. Test refrigeration units are coupled to the calorimeter similarly to those on insulated trailers. Refrigeration unit capacity testing is carried out in a CRT chamber in a similar way to refrigeration machinery testing as described for
Refrigeration Unit Capacity
Testing. Similar methods are used with both types of calorimeter.
Normal testing gives performance at 30 C air on condenser against specified air return to evaporator temperatures. Net refrigeration capacity is again the sum of the heat leakage + the electrical balance heat, though the heat leakage must be less than 35% of the sum.
Small Mobile Calorimeter
The mobile calorimeter unit can be towed to customer's premises where the test refrigeration unit can be attached. The combination may then be returned to CRT for testing. The CRT calorimeter is available for testing of transport refrigeration units with extraction rates of 3kw.
20' Picture Frame Calorimeter
This is available for testing all large vehicle refrigeration units and can be transported to customer's premises for refrigeration unit fixing. Alternatively the unit may be fitted at CRT.
For further details of any of the above subjects including testing, chamber hire and calorimeter hire please
contact CRT and we will be pleased to discuss your requirements.
Test chamber specifications
Prices will be sent on request.