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Pasted in below are some comments from Richard on the article that
describes converting a chest freezer into an efficient refrigerator.
Some of the comments might also apply to making your own fridge from
something like the Danfoss units.
Comments from Richard:
Just thought I would drop a line because I
enjoyed reading your PDF about building a chest fridge.
I think you are probably quite right that fridges
are optimised for convenience and not performance. My father used to
design fridges (industrial ones) and I know what he would be saying
that a freezer compressor used to run a fridge could be running
inefficiently although your figures suggest that if that is the case
the result is still very good. The other warning he would give is that
if the compressor is designed to run for an hour per day running it for
just ten minutes a day might reduce its life because of things like
lubrication. The proof is in the pudding as it were so if it is running
sweetly then that demonstrates the formula works.
A couple of points came to mind as I read the
article and so I hope you do not mind if I mention them. You never know,
they might be useful.
I think one limitation of a chest fridge might be
the lack of movement of air in the fridge. I understand that while in a
freezer one would want the air to be largely static this is not what is
needed for a fridge. For the freshest (best kept) food I think an
internal fan would help. I would guess that the fan should also cut-off
when the door is opened.
Talking of fans I suspect that in many cases a
fridge (or freezer) would become more efficient if a fan is added to the
condenser. It depends on how and where the unit is mounted but a small
fan using very little power might well have the same effect as a
turbo-charger on a petrol engine consuming some power but increasing
the overall energy efficiency of the cycle. Having said that; with such
short on cycles for the compressor I wonder if it would make any
improvement here.
I think taking an incandescent bulb out of the
unit made sense. However there is an ecological advantage to lighting in
a fridge. If you can see what you want faster then you are out of the
fridge sooner and the lid is closed earlier. The trend toward LED
lighting is a real advance for me. Higher quality lighting with quite a
bit less heat and energy consumption.
Finally I wanted to mention the grading of energy
use. In Europe we have A, B, C and so on categories to indicate energy
efficiency. I think these are very effective and I will explain why. A
unit that consumes 102kWh/annum is more efficient than one that consumes
143kWh/annum of course. When faced with 20 refrigerators in a shop the
consumer can make use of these numbers IF they are simply looking for
the lowest consumption. They could but most people are really
uncomfortable with numbers. If they are looking for anything else (and
they should be) then it turns out to be really very difficult for most
people in practice. I know this because part of my job boils down to
explaining stuff like this to people. The great thing about this
simplification is that people understand an A unit is better than a
B and if they are interested will look at the 8 A rated fridges in
the shop rather than all 20 units. They can then still look for their
other needs like capacity, features and so on. They can get efficiency
and everything else they want. If you leave it to the numbers then in
practice pretty much only those simply looking for the lowest
consumption end up making proper use of the numbers.
Anyway; just some thoughts. Hope they are useful.
Best regards,
Richard
Gary May 1, 2012
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