Fridge compressor cooling

Submitted: Friday, Dec 23, 2005 at 16:57
ThreadID: 122379 Views:2926 Replies:2 FollowUps:2
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Because we plan to be on the Roper again in April I decided to look at the possibility of adding another cooling system to the compressor side of the fridge. We seem to be one of the very few BT Owners who have any concerns about the continuous operation of the fridge compressor in high ambient temperatures. Those who have read my previous postings will know that we have insulated the sides & top of the fridge compartment and fitted two 6" computer fans at the top vent. All of this has meant that the fridge now cyles in the hot weather rather than run more or less continuously.

Yesterday I wondered what would be the effect of a 6" computer fan taking heat away from the compressor so rigged up a temporary setup. Although the day was fairly hot the van was in the shade in the shed. In each case the temperature was taken with the compressor running and the fridge close to end of cycle:

Compressor Bottom of coil bank

Fans @ top vent off 53 38
Fans @ top vent on 52 34
Addn. fan @ compressor on 50 34

All temps degrees C. Apparently the compressor will run 50-55 almost regardless, the effect of the fan at the compressor running continuously seemed to be cooling the unit quickly at the end of each cycle & so reducing the length of the next cycle.

I am mulling over whether or not to fit the compressor cooling fan as a permanent installation running continuously. Any advice/comments?

Andy
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Reply By: Bushtracker - Sunday, Dec 25, 2005 at 22:46

Sunday, Dec 25, 2005 at 22:46
Dear Andy, and more relating to other Boggers that might read this entry:
In all of our testing at BT, the reason we have not pursued this end, is that the results did not save power in the long run.... The added load of the muffin fans, ate up the power savings of shortened run times.

Now, in saying that, there is value if your are way up in Arnhem Land in summer and not plugged into 240, living in 50 degree heat in the van, as in the most extreme weather the fridge may not keep up. If this is the case, and I doubt that there is even one in one hundred that would summer over in the most extreme of weather, then you may need to look into this additional forced air cooling to increase the efficiency of the fridge... But as I say, too hot for me, and most others as well.... I have been caught out in hot spells out goat hunting on desert fringes, not pleasant. My fridge ran continuosly in the daytime, only shutting off once or twice in the night, and I had to evacuate the area after a few days... Also, if you are in that hot of weather, most will plug into air conditioning in 240volt, this will lift the loading on the fridge.. I really doubt even 1 in 100 will weather over in conditions so extreme the fridge could physically not keep up, but for those the muffin fan is a good addition to the cause..

Far more important than the muffin fan in those conditions is to park the van oriented so that the sun is not directly on that side of the van, as cooling is not a process of making cold, it is an engineering process of removing heat. Cold is just the heat removed from the box and transferred to the outside..

Kind Regards, from the ever experimenting Ranger at BT, and Merry Christmas to all, let us not forget what the Season is really all about...
AnswerID: 567630

Follow Up By: Andy1 - Monday, Dec 26, 2005 at 17:59

Monday, Dec 26, 2005 at 17:59
Steve

I remain amazed at the vehemence with which you oppose these fans. At no stage has the suggestion been made that the fitting of such become a BT option.

There seems to be no disagreement that the fitting of the fans is effective viz increasing cycling. The issue appears to be that of power consumption.

Lets look at cycling first, if a fridge runs continuously then it is not reaching the set (thermostat) temperature, that is the internal temperature is probably above 5 degrees - not really satisfactory, especially if it is closer to 8 degrees. A particular downside of this that the owner , in an effort to get the fridge temperature down, may keep moving the thermostat setting to colder and will get icing up on the back wall during the night.

With regard to power consumption, I suspect that you are correct in that fitting fans may in the end result in (slightly) higher power consumption although on a hot clear day with excess solar power available this becomes a moot point. We always turn the fans off at night. It is of course possible to connect the additional fan circuit to the circuit that runs the small fan on the electronics - this will keep the fan power consumption down.

The main drver for us has been to have the fridge cycle so that it runs at an internal temperature of about 4 degrees. I know a number of BT owners who have fitted some type of heat removal fan(s), in various configurations, to achieve cycling/internal temperaure setting.

Andy
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Follow Up By: Bushtracker - Monday, Dec 26, 2005 at 20:48

Monday, Dec 26, 2005 at 20:48
The point just remains, that these are not necessary for the 95-98%. I do not want the majority to feel they are missing out on something. And most would not have the technological background to build the system or to have the dicipline to quote: "switch the fans off at night" hence my notable point that the cost in power may outweigh the gains....

The problem we have is that not all people are gadget freaks and as technologically advanced as some like possibly you are. The BOG produces some unnecessary "Trends" as people think they might be missing out on something if they do not have all these little bits and pieces, so it is my job to let then know an overall perspective. And there are no muffin fans on either of the Directors vans... Don't take it so personally, my response is more for those that might think they are missing out... You obviously like to tinker with things to try and get better eficiency. I on the other hand, am here to moderate things a bit, and give the perspective that the majority are not likely to need this extra heat removal cooling. And unless the system is shut off overnight as you say, the power costs make it not worth while except as I say in the extreme north in summer..

Relax, I am not arguing with you, this is more for the rest. You of course may do what ever you like, but our tests did not indicate that it was a benefit for the majority, hence my response... Don't get your blood pressure up, this is not a contest. I am trying to look after the group as a whole...

Regards, the Ranger

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FollowupID: 845249

Reply By: Noosa Fox - Sunday, Jan 01, 2006 at 09:37

Sunday, Jan 01, 2006 at 09:37
Andy,

I have changed our fridge set up by blocking off the external vents and fitting internal vents. We only have a shelf above our fridge not a cupboard as a lot of vans do. I have raised the fridge about 20mm off the floor and by not having the angle seal strip across the bottom, this allows COOL air to flow under the fridge. On each side of the fridge cabinet at the rear I have also fitted a vent to allow COOL air to enter the rear at the level of the bottom of the fridge. At the top of the fridge cabinet directly above the condensor I have a vent right across the top to allow the HOT air to escape. While doing this I fitted a fan near the bottom of the condensor to push air upwards.

This system has been in place since September 2004, and the van has been used in all types of temperature ranges without any problems at all. For example, this week while returning home from Victoria the temperatures during the day in NSW were above 40C in many places.
The fridge continued to cycle on and off as normal, and didn't appear to be running any longer than normal, and there was NO noticable heat coming out the top vents of the fridge. I have never found it necessary to have the fan running to help out.

The temperature in the van was about 5C below the external air temperature and therefore I believe that the fridge has to operate more efficiently than by relying on the hotter external air to cool the van. Also most vans, including ours had the bottom external vent fitted just above the chequer plate, and as such is 150 to 200mm above the bottom of the fridge and therefore cooler air is not going across the compressor unit anyway.

It is my belief that the fridge is running more efficiently than what it was when it was using external vents, and there is no way that I would go back to having it exterally vented.

As Steve, has mentioned if 240 volt power is available then in above 40C temperatures most people would have the air conditioner running in the van. In those cirumstances the internal temperature in my van would be a lot more than 5C below external temperatures and therefore has to run more efficiently than external vented ones.

Another PLUS with Internal venting, is that there is NO dust build up on the condensor coil so the cooling affect has to be more efficient than a dusty one.

My fridge is set up in the manner as the instalation instruction described in the WAECO book with additional side vents at the bottom.

Brian
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