Supercheap 42 litre compressor fridge/freezer – LianFa LF8042

Supercheap 42 litre compressor fridge/freezer

LianFa LF8042

 background     

    Some testing and experimenting has been done to see if there was any way of improving the efficiency of the fridge without making any major modifications. The restriction of no major modification to the fridge prevented some avenues from being investigated further.

test environment

      The testing was done with the fridge set to 0 degrees, approx 80% full of drinks and inside a habitable room. The room temperature was not controlled and impacted on absolute results however adjacent testing ( ie tests either side of each other ) would not have had any significant changes in environment so should be indicative for comparison purposes. The duty cycle was measured by utilising a data logger sensing the load current with a sample period of 10 seconds. Results were monitored until 3 successive results were stabilised and then recorded.

observations/ modifications     

      1. The DC plug and cable were changed to utilise a standard ‘ARRID’ style plug. This is very similar to the supplied plug/ socket combination however it required that the DC socket on the fridge be replaced as the diameter of the socket was fractionally smaller than the more common ARRID plug and it wouldn’t fit.

      2. Testing was then done to see if the ‘off’ time of the fridge could be increased.

      The compressor unit was identified as a significant heat source near the fridge compartment. Various forms of insulation were tried to see if they impacted on the ‘off’ time for the fridge. No significant improvements were found however the insulation does effect the cooling ( or ‘on’ time ). See the test data. The material used is similar to ‘bubble wrap’ packaging material with a foil skin on the outsides. It was chosen as being readily available and flexible enough to be manipulated into place.

      3. What may be worth investigating is if the insulation is acting as insulation or as an air baffle.

      4. Experimentation with the fan placement and number of fans produced some significant improvements in the duty cycle of the compressor. The original fan is located in the approximate centre of the motor compartment, blowing air horizontally from the middle of the compartment through the condenser.

      The problem with this location is that the hot air from the compressor, directly below the fan, is blown through the condenser. By relocating the fan so that cooler outside air is first blown over the condenser the efficiency of the fridge is dramatically improved. As an indication the standard fridge, as tested, had a duty cycle of ~59%, ( Test 1 ). With insulation and the relocated fan the duty cycle is ~39% ( Test 6 ). The on time has been reduced by nearly 50%.

      5. The fan location was not particularly critical however the proximity of the fan intake to the outside casing was critical. Initial testing was done by relocating the original fan to within 10-15mm of the outside of the compressor compartment, then a flexible air baffle was added to seal the fan intake to the outside of the compartment. The compressor run times improved from ~233 Seconds ( Test 4 ) to ~203 Seconds ( Test 5 ).
Results with a fan on the side or on the top of the compartment made minimal difference to the duty cycle.

      6. The final fan location was on the side of the compartment and fixed to the outside of the case ie no air gap between the fan intake and the outside.

      7. The modifications were undertaken to have minimal impact on the fridge to allow for easy removal and restoration of the original configuration. As a result the air intake for the fan Is not optimal. A significant amount of fan noise is produced because of the restrictions to the inlet causing the air to be sucked in the existing ventilation slits. And some mechanical vibrating noise as a result of the fan being mounted onto the case.

      8. Some experimentation was done with a 50degC thermal switch (mounted onto the compressor) to switch the fans on/off. This appeared to have a slight detrimental effect on the duty cycle.

      9. Further investigation into switching the fan on/off with the compressor would be warranted if only to reduce the noise and current consumption.

test results

Test 1

Standard
  run 1 run 2 run 3
On time (sec) 323 320 320 330
Off time (sec) 223 220 230 220
Duty Cycle 59%      

 

 Test 2

With insulation only, no fans at all
  run 1 run 2 run 3
On time (sec) 323 310 340 320
Off time (sec) 187 190 180 190
Duty Cycle 63%      

 

Test 3

With standard fan, insulation
  run 1 run 2 run 3
On time (sec) 343 340 360 330
Off time (sec) 223 220 220 230
Duty Cycle 61%      

 

Test 4

Insulation, internal fan (near side of case, sucking in cool air)
  run 1 run 2 run 3
On time (sec) 233 220 240 240
Off time (sec) 250 250 250 250
Duty Cycle 48%      

 

Test 5

Insulation, internal fan (near side of case, sucking in cool air) plus fan baffle
  run 1 run 2 run 3
On time (sec) 203 210 200 200
Off time (sec) 250 250 250 250
Duty Cycle 45%      

 

Test 6

Insulation, small fan (80mm) bolted inside of case, blowing across radiator
  run 1 run 2 run 3
On time (sec) 170 170 170 170
Off time (sec) 270 270 270 270
Duty Cycle 39%      

 

[postscript] This fridge eventually died and was replaced with a Waeco CF50 vera. So far, after several years, we’ve had no problems. Once it is out of warranty I may look at adding / modifying the fans inside the Waeco fridge. The concepts regarding fan placement and ducting are relevant regardless of the fridge brand.