Title cooling performance test at set temp., -40C by use of TK, magnum plus
Name Admin Date 2021-06-29
 cooling performance test at set temp., -40ºC by use of TK, magnum plus:

We've tested the cooling performance actually under putting the container into test chamber with ISO test procedure as below: ambient temp: +38ºC, set temp:-39.40ºC


Total 24 sensors for temp checks ( interior: 12 places, exterior: 12 places


Running from 14:00 hrs of 25th June to 22:59 hrs of 25th June ( for about 9 hrs.

Average temp: exterior: +38.76°C; Interior:-34.30ºC during testing

The highest temp: +39.1ºC vs. the lowest temp: -36.5ºC during testing


♣ the container couldn't be reached up-to -40ºC actually

   Reason: container box is designed by -18ºC, +38ºC range: 56ºC

             U²º ( heat-leakage) : 38.13 Kcal/Hr.ºC

             Overall Heat transfer rate: 38.5 x 56=2,156 Kcal / hr. as undernoted:

     While, provided its design required at -40ºC, +38ºC, we can calculate its overall heat

     transfer rate like this: (-40ºC, +38ºC : range:78ºC)38.5 x 78=3,003 Kcal/hr.


Actual heat-leakage:U²º ; 38.13 Kcal/hr.ºC against 38.5 Kcal/hr.ºC noted above


Basically, historically, the reason why both cooling unit suppliers / reefer box manufacturers have clung to their design at -18C to +38C has been known that in general, the cargoes temp range ( frozen / chilled ) for usual requirement in the world under such set temp. level has been noted since from long times ago when Graff reefer factory in Germany, then Nippon Frauf in Japan, then Hyundai, Jindo in Korea, then CIMC, Maersk, Fuwa & DongFang in China now whereas the current reefer cargoes whose requiring set temp is variant widely and specially like super freeze and -40ºC required.


Nonetheless; such special cargoes required for lower set temp have been so little / rare that cooling unit capacity and reefer manufacturer's heat-leakage value haven't been more developed yet.


As you knew; the heat-leakage value is based on -18C( inside temp.) to +38C ( ambient  temp ); between +38C / -18C ( 20C 

÷ 2= 10C ( mean wall temp ), so called, it's U¹º, then we can convert it to U²º.

However, actually its heat-leakage test can't be carried out due to impossible test condition arrangement ( -18ºC interior: impossible during test )so that its heat-leakage value can be converted only from U²º test figure taken upon actually testing.


U²º : this heat-leakage test can be carried by both ATP & ISO test terms: eg., temp maintaining as a test term for ISO; inside temp: + 30° C, outside: 10° C mean wall temp : ( 30 + 10 ) ÷ 2= 20 ° C; ATP : inside temp: +32.5° C, outside temp : +7.5° C.

Of course; we can convert the heat-leakage value from U²º to U¹º by calculation: eg., U²º : 38 Kcal / hr° C, ( 38 ÷190 ) x 180= 36 Kcal / hr° C ( U¹º )


Note: the main reason why the conversion from U²º to U¹º is that actual operation condition of the reefer container at field has been proceed under U¹º condition mostly whereas the heat-leakage test can't be carried out actually.

In addition; at the time of calculation of U²º; in formula, a coefficient, 170, which is being applied for off-set of difference between U¹º & U²º; eg., as shown on the above diagram of Cyclopentane marked as ; U¹º is 39 Kcal / hr°C whereas U²º is 40.8 Kcal/hr°C ( 40.8-39 = 1.8 Kcal/Hr°C ; 4.5 %, which is the best suitable coefficient figure by 170 under formula research


Cooling unit ( TK) magnum rating: 7.3 Kw x 860=6,278 Kcal/Hr vs. 5,670 Kcal/Hr.(carrier)

  Please see the following TK Magnum cooling unit capacity:

As we can imagine on the basis of box design ( No change for foam density / thickness in this batch ); it's impossible for the box to reach the temp up-to - 40ºC due to critical point between box heat leakage & cooling unit capacity even though TK cooling unit capacity has been increased.

Besides, according to data record sheet; from 02:54 hrs to 09:00 hrs of 26th June; during which average temp was from -33ºC to -34ºC without being it reached even once up-to -40ºC under the compressor running, which meant the temp couldn't be possible to reach up-to -40ºC unless box design was enhanced by increasing of foam thickness and density technically.


In addition, please refer to this cooling unit function on the basis of the above data; according to cooling unit suppliers; in general, the capacity of the cooling unit per hour is to design to run by about 20 min. for a new empty reefer container at set point ( eg., -18ºC ) under being it reached while the remaining 40 min are dormant to save both electricity and compressor life. eg., ( 60 min x 2,135 Kcal hr. ( overall box heat transfer rate: actual heat-leakage: 38.13 Kcal x56C ) ÷ 5,670 Kcal/hr. ( carrier, Starcool, Daikin's cooling unit refrigerant equip rating ) = about 23 min. running, then 37 min dormant, which is ideal.


Besides, providing special TK magnum Plus is applied:

( 60 min x 2,974 Kcal hr. ( overall box heat transfer rate: actual heat-leakage : 38.13 Kcal x 78C ) ÷ 6,278 Kcal/hr. ( TK magnum plus refrigerant equip rating ) = about 28 min. running, then 32 min dormant


However, as noted above; from 02.54 hrs. to 09:00 hrs. (for about 6 hrs.) of 26th Jun., under set point at -40ºC required, the test reefer box whose temp could be reached only up-to -33ºC to -34ºC actually, but not at -40ºC as well as the cooling unit was running continuously without dormant due to as calculated above theoretically, higher overall heat-leakage rate of the reefer box under -40ºC set temp by different temp range 78ºC(-40ºC,+38ºC), but not 56ºC(-18ºC,+38ºC) designed in the spec even without being the box enhanced for-40ºC required specially this time, which could cause more electricity consumption, cooling unit fatigue and likely cargo claim eventually.

However, 20'Reefer container with the same TK cooling unit whose cooling performance at -40ºC set temp. has been achieved successfully.


Thus, in order to avoid this technical factor difference between cooling unit and reefer container box; the main factor relating to foam density and thickness to make less heat-leakage has to be matched with cooling unit capacity even though more production cost is essential. meanwhile, TK cooling unit capacity for 40' reefer container has to be re-surveyed to optimize this test together with consideration of the heat-leakage of reefer box.


Furthermore, as far as reefer box manufacturer has noted their design being possible for the cooling performance range from -40ºC to +80ºC in the spec. clearly, they should have fulfilled it for client's satisfactory through proto-type testing in advance.

Providing it is un-feasible, the box manufacturer is to discuss client and cooling unit maker to find a solution through reviewing of design in detail by use of mathematical engineering data, but not by a vague imputation to cooling unit's refrigeration rate.


Of course; any of parties among reefer box manufacturer cooling unit maker & buyer focuses as an economic principle, to minimize invest and maximize outcome to utilize it properly whatever they need it without overkill during producing. 

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