Fridge Loaded "Fully or Partly" Myth Debate
Submitted: Tuesday, Jul 18, 2017 at 10:12
ThreadID:
135274
Views:
6829
Replies:
12
FollowUps:
44
This Thread has been Archived
Allan B (Sunshine Coast)
.
The current stable ambients were a good opportunity for me to conduct further testing on the contention of keeping a fridge packed full in order to minimise energy input.
Using appropriate instrumentation, I firstly tested the fridge empty, then loaded it fully with plastic jars full of water at a temperature setting of 4 degrees. The Ah consumption was essentially identical in each case.
The compressor duty cycle changed but the total Ah remained the same.
I then removed the upper layer of contents and repeated the
test, again with the same result as before.
Then I placed several layers of bubble-wrap above the contents to fill the void and found that the Ah consumption was reduced by nearly 10% ----Eureka!!
I got to thinking hard about this. The only reason to put electrical energy into a stabilised fridge is to remove the heat ingress getting through the fridge insulation. Heat enters through the cabinet sides, bottom and top and first encounters the evaporator plates where it is absorbed before it can reach the contents. But look at those evaporator plates, they are not on the bottom or top, and at the sides they do not even reach all the way to the top. Heat is pouring in through the lid and the upper shoulders of the cabinet directly onto the contents. When I placed bubble-wrap on top of the contents I had placed further insulation in its path.
So I repositioned the bubble-wrap outside the cabinet, on top of the lid, leaving a void below the lid above the contents, and repeated the
test. The result was that the Ah energy was reduced to nearly as much as when it was inside the cabinet.
So the MYTH IS BUSTED on simply keeping the fridge full to save power.
But the MYTH IS PROVEN on adding insulation between the top of the contents and the heat source.
On trips, I usually add a folded towel above depleted contents to stop bouncing but have taken no note of fridge Ah change, but it seems to have that advantage. Putting a folded towel over the lid if no room inside with it hanging down over the cabinet shoulders could be a good idea if the fridge is chockers too. In fact even a mat of that 10mm HD foam on the inside bottom could be beneficial too. Few fridges have really adequate insulation after all.
Watch for me on the ABC Science Show. lol
Reply By: Les - PK Ranger - Tuesday, Jul 18, 2017 at 12:13
Tuesday, Jul 18, 2017 at 12:13
Fill fridge with food and beer.
Turn it on.
Enjoy the trip.
Not much seems to affect the efficiency that much, and what does it matter ?
You just drive daily touring, or have enough solar to keep
well powered.
There are just too many variables to worry about it.
Ambient temp in cab or rear tub, direction of travel (sun on fridge), putting warm cans of beer in each morning before travel, plug losing contact in ciggy plug for part of days drive (happens rarely), passenger not closing lid properly, etc etc.
AnswerID:
612587
Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 12:36
Tuesday, Jul 18, 2017 at 12:36
.
Ah Les, your a Troglodyte, lol.
I'm not troubled with worrying about variables but weren't you one of those promoting "filling the fridge" a while back. Maybe not Mate. I'm just putting a myth to rest.
But set it up right and then there are no troubles "to worry about".
You can't do much about ambient temperature, especially in a parked vehicle, but you can avoid positioning the fridge in the sun.
Mine is never in the sun, it's under the bed. Fridge cannot be stowed without closing lid... it's a snug fit under ned which reliably keeps lid shut too. "Ciggy plug"??.... What do you take me for? My cable is wired in with no plug except on the fridge. Do right what you can do right and accept what you can't.
This Troopy is set-up right Les. Pop up some time and I'll give you a hand.lol
FollowupID:
882863
Follow Up By: Les - PK Ranger - Tuesday, Jul 18, 2017 at 13:49
Tuesday, Jul 18, 2017 at 13:49
Lol, maybe a little more of a trog than I used to be, really the way I travel power consumption isn't a big issue.
My simple needs are the fridge and led strip light on the canopy tilt window to
cook / tend bar, etc under.
The techniice fridge is very low draw, maybe when I get the Waeco 11lt setup as a freezer I'll need to solar up more if camping 2 - 3 days etc.
This matter would be a little important to many people so good on you for doing some testing etc.
I really like your cdx11 mod with the drink bottles Allan, maybe one trip up with the
Ranger I'll pop up and have a look if you're in town.
I will be up there next week for a stint of work, and oh yeah, one weekender out Goomburra for a look, mate from
Gold Coast in his 'cruiser and me as pax in my brothers vehicle (a Jeep Grand Cherokee, wish us luck !).
FollowupID:
882868
Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 15:05
Tuesday, Jul 18, 2017 at 15:05
.
Les, my battery needs are not great either, but I was looking for something to do and was a bit scornful of "blind beliefs". It was interesting and convincing.
And yes, it could be useful for some people.
Techniice eh? Nice. Such low draw because of the good insulation. That is really what refrigeration is all about --- insulation.
I have tried to setup to have it all work with little fussing. I want to be enjoying my environment, not running around reading gauges. I can't even be bothered with 'tracking and waypoint logging'. Digital moving maps are only to keep me from getting hopelessly lost. I have spent my life in technology and enjoyed it but now I just want to enjoy living! Even hauling the camera out is a bit of a chore for me.
That CDX11 mod has been wonderful. I abhor warm water whilst driving and rotating drink bottles through the fridge is bothersome. Takes a little courage to whack a holesaw through the lid of your fridge though. I can imagine the reaction of some.
When run as a freezer, the CDX11 'parcel shelf' is of no value for storing frozen stuff and not even room for a couple of cans I think, so it was a worthwhile adaptation.
I would be really happy to see you up here. Stuck around bored until end August when off for a few weeks which includes
Hay River Track. I'm sure you have done it and could offer a few bits of advice. I'll keep my holesaw handy. lol
you can find my email in my Profile under "About Me". If unable, put your email up in a Post Followup and I'll come back.
Cheers Mate, and thanks for suffering my sophistical discourses.
FollowupID:
882871
Follow Up By: Les - PK Ranger - Tuesday, Jul 18, 2017 at 17:51
Tuesday, Jul 18, 2017 at 17:51
"the CDX11 'parcel shelf' is of no value for storing frozen stuff "
Absolutely right there Allan, and I personally feel (gut feel, fly by the
seat of your pants, 'real life experience' whole ' the vibe' thing :D) that even running as a fridge at say -2c it would have very little use, but the water bottle cooler would still be very good at the higher (than freezer) temps for some drink flasks.
I think I'd do the mod, pending ali bottle are the similar standard dia, and a rubber sleeve collar (or numerous wraps of 2" cloth tape) could be placed at the correct height to seal it off fairly
well.
Will catch up one day on a trip when I bring the
Ranger up for a spin.
For most trips it is far more economical to beek early and fly up ($98 return this trip !!) but I do love bring the 4WD up and doing a couple of trips to areas SEQ and northern NSW.
FollowupID:
882884
Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 22:28
Tuesday, Jul 18, 2017 at 22:28
.
Actually Les, I had to
shop around quite a bit to locate suitably sized SS bottles.
In order to fit within the recess of the shelf they needed to be 65mm diameter.
They are 150mm from bottom to shoulder which was ideal. They then sit almost fully within the cabinet with the shoulder still reaching the 'seal' and just sufficient protruding to easily grasp.
A piece of 2mm thick felt with snug holes acts as a seal. Works fine.
Draws only a couple of Amps as I recall and still cycles a bit at -10 degrees.
Naturally, being the freezer, it stays in service all the time.
FollowupID:
882896
Follow Up By: Les - PK Ranger - Tuesday, Jul 18, 2017 at 23:35
Tuesday, Jul 18, 2017 at 23:35
Cheers Allan, will
check the dozen or so bottles I have here when ready to mod.
FollowupID:
882898
Reply By: Frank P (NSW) - Tuesday, Jul 18, 2017 at 16:12
Tuesday, Jul 18, 2017 at 16:12
Nice little project, Allan, I will use that info in managing my car fridge.
The Vitrifrigo 130 litre van fridge is more problematic, being a front-opening cabinet type. It has a remote compressor and without breaking into the gas circuit I cannot pull it out far enough to improve side, back and top insulation.
We use storage containers the depth of each shelf to create "buckets of cold" to reduce the spill of cold air when the door is opened.
Before I converted the van to lithium batteries I was always looking to reduce 12V power consumption. I made a water cooled condenser to run in series with the conventional air and fan cooled one and had it installed to the refrigerant circuit by a fridge mechanic. Very simple - extra refrigerant line threaded through a metre of 12mm copper tube and a small pump supplying about 1 litre per minute of water from one of the van's tanks.
I got the idea from
these people. My understanding from them, IIRC, is that over a given period of time water can remove about 100 times more heat than air at the same temperature. I thought that if it could be done it may reduce compressor run times.
It did. I didn't do an amp-hour
test, but I did a roughly controlled before and after
test of compressor duty cycles. With the van parked in the same place, with the same fridge load and the same ambient temperatures (38+C - it was an obliging
Sydney heat wave:-)) the before cycle was 60% on, 40% off. The after cycle was almost the reverse - 40% on, 60% off, and that's after I wound the compressor speed down to reduce run-time current draw - 5 amps down to 3.5.
The small pump that Ozefridge supplies draws 0.5 amp and runs when the compressor runs.
Cheers
AnswerID:
612594
Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 17:07
Tuesday, Jul 18, 2017 at 17:07
.
Interesting setup Frank. Yes, as you say, water is far better as a transfer medium because of its greater specific heat value.
Way back as an apprentice I saw ther most amazing refrigeration machine. Picture this if you can........... It comprised a hollow shaft set in bearings and supported three 400mm copper spheres along its two or three metre length.
It was mounted through a wall with one sphere inside in an insulated room and carrying fan blades on its circumference. The outermost sphere dipped into an open top tank and had some shallow paddles on its circumference. There was a belt pulley on the shaft outside which was driven by an internal combustion engine. The centre sphere contained a compressor whose crankshaft remained stationary by an off centre gravity weight whilst the compressor rotated together with the whole assembly. The outer sphere contained the condenser while the inner sphere contained the evaporator. Pipes in the hollow shaft carried the refrigerant. The whole thing was a fully sealed-unit refrigerator to cool a butcher's cool room. It was no longer in use and with the premises being redeveloped it was headed to the scrapheap!
I was fascinated by it at the time but no-one appreciated its
heritage significance. I have never been able to find out more about this remarkable machine or any photo of it. Seems totally lost to any record. What a shame.
FollowupID:
882878
Reply By: CSeaJay - Tuesday, Jul 18, 2017 at 16:29
Tuesday, Jul 18, 2017 at 16:29
Allan
Why is it then that out in the bush and actually camping/using the fridge I draw far more power from a partially full fridge or freezer?
Time and time again; stock up, fill her up, and the battery SOC shows a marked difference, getting worse the lower it gets, stock up again when in civilisation and voila!
Just came back from a three month trip which again confirmed my previous experience, but this time with even more controlled environments (fully charged by full day driving, setting
camp in shade, steady weather conditions)
Not a 'scientific' measure by any means, but above happened time and time again, the freezer performed significantly better with a full load
Why would my experience be different to your findings?
AnswerID:
612595
Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 17:28
Tuesday, Jul 18, 2017 at 17:28
.
Hi CseaJay,
I honestly did not consider your "reply to be empty of meaning". I simply could not comprehend its significance. My failing, not yours.
I can give you no opinion for your observations. There must of course be reasons for the behaviour you witnessed but I could not even guess them. See, that is the perilous part, making guesses without careful observation and assessment. Sometimes we have to of course in the necessity of the moment but it can result in inadequate conclusions.
I don't know why your experience would differ from my
test results, but I do believe that there would be valid reasons for that difference. The usual explanation is that "We have missed something".
I will say that I do live by the view that "Whatever works, works".
FollowupID:
882879
Follow Up By: Sigmund - Wednesday, Jul 19, 2017 at 13:25
Wednesday, Jul 19, 2017 at 13:25
My limited understanding is this: SoC is a poor indicator in general of what current's been drawn and what capacity is left. At a minimum the battery needs to have had no inputs/outputs for several hours before the voltage measurement.
We can now get cheap inline power monitors that will record amps and watts, peak and total, and this is much more useful data.
FollowupID:
882920
Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 15:58
Wednesday, Jul 19, 2017 at 15:58
.
Not so sure just how useful in its simple form Sigmund.
Measuring Ah in and Ah out does not reveal near the true SoC due to transfer losses. You need to put significantly more energy into a battery than you can get out again. Most of these losses are variable with such things as battery age condition, charge/discharge rates, temperature etc. so the transfer ratio will change significantly with time and event. SoC indication on solar controllers will lead you up a garden path.
Some charging systems used on battery banks such as
fork-lifts have used such a system as 'charging controllers' but it was programmable for the transfer ratio and adjusted regularly. Such batteries also required a supervised 'maintenance' charge regularly to ensure good battery condition. I even now do that for my Troopy auxiliary batteries.
Voltage as a SoC indication is of some value. It gives some idea if the battery has useful SoC or is dead flat!!
Just charge the batteries with a good stage-charger and they will be filled.... reasonably so.
There is no easy way I'm afraid. Bantam has dealt with this in detail.
FollowupID:
882925
Reply By: member - mazcan - Wednesday, Jul 19, 2017 at 10:59
Wednesday, Jul 19, 2017 at 10:59
hi Alan B
an interesting read
i previously owned a very old s/h 29lt engel
grey sides with lite green lid
it kept things cold and was very reliable but I decided I may be able to improve its ability so while I had it completely stripped down and apart for a restoration job on it to get rid of rust as it use to be owned by a fisherman and had been on a boat most of the time
I decided to dismantle the lid there wasnt much installation in it so I put in as many sheets of polystyrene and alternative sheets of thick alfoil until I was only just able to clip the lid back together
I also removed the freezer unit from the box and did likewise sides and bottom then reassembled it
the difference was astounding if I turned it up just above 2 on the fridge setting I was freezing and busting stubbies of beer and cool drinks and the milk was also solid
I had to run it on 1 from then on so learnt from that experience that it is simply all about the thickness and quality of the insulation that makes a fridge highly efficient
I had previously pulled the outside cover of a rheem gas water heater and wrapped the tank in thick insulation which greatly reduced the gas consumption by keeping the heat in and reducing the burner time and my gas bill
that heater was installed at my current house in october 1989 and is still working perfectly by changing the anti corrosion rod regularly and running the house on mainly rain water and I also wrapped the copper pipes in the ceiling with insulation tubes as
well I get almost instant hot water even in winter
plumbers have told me its the oldest rheem heater they know of all the others have died long ago
so once again its all about the insulation for hot or cold and so that's what prompted me to try and better the old engels performance I sold the 29lt 4 yrs ago and upgraded to a 40ltr but I have to turn it up to high readings compared to the old one but they have made it impossible to get the lid etc apart on the newer models but i would like to better it too
cheers
AnswerID:
612614
Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 12:38
Wednesday, Jul 19, 2017 at 12:38
.
Hi Mazcan,
Yes, in thermal economy, insulation is everything.
Just think of it, given sufficient highly effective insulation, you would never lose any cold, errrr rather, you would never gain any heat, in a refrigerator.
However that of course is not sensible when considering practicalities and economics of manufacture and purchase. Compromises are necessary in most things.
There are some camping fridges available with much superior insulation but they are larger (for a given capacity) and considerably more costly. Lesser brands are endeavouring to prune every last cent from their manufacturing cost for profit and market competition. It seems in product marketing there is little favour for the middle ground..... it is either the Greatest or the Cheapest and those looking for a comfortable balanced product are left out. It was not always so. We are then left with the recourse of adapting to suit our purposes as you have done.
Quite some years ago, before
portable fridges, I chose to build my own icebox. I used a nice solid rectangular poly tote box enclosed in a cabinet of Masonite construction and
well painted. The all round insulation was some black commercial foam stuff that I scrounged somehow (not styrofoam) about 65mm thick. That damn icebox kept ice in it for a week! Don't know what happened to it... I seem to have left a lot of things in my wake! Probably loaned it to a mate.......!!! But it sure demonstrated the value of good insulation.
On the subject of hot water conservation, Our kitchen and bathroom are a little way from the HWS (heat pump type). Not too far for a shower etc. but it does take a little time and wastage of hot water to obtain just a small dose. So I disconnected from the HWS at these basin outlets and fitted under-bench 10 litre water heaters. We now have instant hot water at tap and do not leave a line of hot water decaying in the roof. I have no idea of the economics of it but the convenience is just great. My wife loves it and "A Happy Wife etc....."
The only thing that still confounds me is that signature of "quebbambiddybumtal".
Oh please email me with its meaning.
FollowupID:
882917
Reply By: The Bantam - Wednesday, Jul 19, 2017 at 14:27
Wednesday, Jul 19, 2017 at 14:27
Interesing observations ...... and realy to be expected.
Given no other inputs, the only thing a change in contents is going to do to a fridge is change its duty cycle ..... that alone may be a small benifit.
THE main issue with these and other fridges is insulation ....... apart from the eskies with a tacked on fridge units all the 12 volt fridges have piss poor insulation
If you feel the outside of your fridge and it is cool to touch it is leaking heat. .... yeh now pick it up and feel the bottom.
If the fridge is direct on a ute tray or on the floor of a vehicle, putting some sort of insulation under it can make a very big difference ...... I pretty much always travel with a large folded towel on to of my fridge or esky.
As for these fridge covers ...... yes they will offer a small insulation improvement ...... but consider the temperatures involved ........ if you wore it as a jumper would it keep you warm at -2C,
for significant insulation you need at least 3/4 to an inch of good insulating material to do a worthwhile job.
Having the fridge or esky inside an airconditioned vehicle will make a dramatic difference in performance as will ensuring that the fridge has a clear path to exchange air from the fridge unit.
There is a big difference between chest and front opening fridges ....... with a front opener all the cold air falls out every time the door is opened ...... a chest type retains a lot of it's cold air even if the top is left open indefinitely, this is how supermarkets get away with open top freezers
There is also a great difference between when running a given unit as a fridge and a freezer ....... losses that may not be significant are multiplied many times when the cavity temperature is dropped 20 degrees.
even the losses in items removed and replaced increases dramatically.
And yeh good fridge or esky managment can make a great deal of difference.
if you want to extend your run time from 2 days to 4 you will need everything going for you.
If you are dependent on ice .... good managment will get you ya 3 or 4 days ...... poor managment and the same esky and the same materials will be lucky to last a day.
cheers
AnswerID:
612617
Follow Up By: Member - graeme W (WA) - Saturday, Jul 22, 2017 at 16:47
Saturday, Jul 22, 2017 at 16:47
Hi Bantum. Not sure they all have piss poor insulation, have a look at Margarets trailblazers. My new one has 3inch insulation and bd50 compressor. In 30degree ambiant the other day it took 8 mins to get to minus 16 and had not got to the cut in again of minus 6 after an hour .It draws 6 amps but its all about total power use in my situation. Never been able to understand why people buy cheap fridges. Wish someone would do a comparison
test disregarding price on 12 volt fridges , I know which one would win.
cheers Graeme.
FollowupID:
882999
Follow Up By: The Bantam - Saturday, Jul 22, 2017 at 21:50
Saturday, Jul 22, 2017 at 21:50
The Trailblazers are hardly a high volume mass market fridge
FollowupID:
883008
Follow Up By: GREG T11 - Saturday, Jul 22, 2017 at 21:51
Saturday, Jul 22, 2017 at 21:51
The simple answer to why people by "cheap" fridges is some people can't justify outlaying $1500 + for something they use maybe 4 weeks in a year. However I do agree with you on the Trailblazers, very good for what they are , but the idea of portable is stretching it . They are big and heavy so not really an option for everyone.
My brother has one he bought second hand in 1997 to go around Oz. Wife and two kids and no second battery and knowing him no specific wiring to run it. Never heard any dramas but he would have been on the move after 2 days max.
He probably paid $1200-1500 back then and would get $900ish for it now maybe so pretty good resale. Maybe I might have first dibs at it when we sort our needs out in a couple of years, but one thing is certain it would be a reasonably permanent fixture in the vehicle.
FollowupID:
883009
Follow Up By: Member - graeme W (WA) - Saturday, Jul 22, 2017 at 22:38
Saturday, Jul 22, 2017 at 22:38
Cheers Guys. Just making a point really, my latest aquistion cost 2300 so about double the cost or a bit less than say a wacoe. By the time you replace the thermister in the wacoe not if but when it stuffs up at about 400 bucks and if you are lucky and nothing else fails, the fact that the trailblazer will use half the power or better and is not that much heavier or bigger for a given size, they should be a mass seller. Replacement cost of a thermostat in
mine is about 15 bucks and 10 minutes.
Mine will pass on to the kids in perfect working order whatever the year is.
Cheers Graeme
FollowupID:
883013