To give an idea what to do to make an efficient fridge or cooler I am going to run through the notes I have taken over the years, but also explain the why's and wherefore's of each part, because knowing why can help you make informed decisions about each step.
First I will define what a fridge or coolbox is...
A coolbox is an openable heat insulated box, a refridgerator is simply a coolbox that adds some means of removing heat from the inside to the outside.
What are we trying to achieve? to keep certain items cool/cold. It is very important to understand that cold is merely the abscence of heat and that heat is energy.
Consider air at 100 degree C and water at 100 deg C they both have the same temperature but contain entirely different amounts of heat energy
Put your hand in boiling water and you will be scalded, air at that temperature will just be uncomfortable, you may be wondering what the hell this as to do with fridges and coolboxes? actually everything because air contains so little heat energy, it takes very little energy to remove it from the box, however the solids in our fridge/coolbox would take masses of energy to remove.
Lets take a few figures to heat (or cool) 1 KG (1 KG = 1 Liter) of water by 1 degree C takes 1.15 Watts
as an average
generally the contents of a fridge have a specific heat capacity of 75% of water
say we are putting warm contents in at 31 C and of course we actually want them to be 4 C (reccomended temperature for fridge)
lets say we have a 60 Litre fridge 2/3 rds full thats 25 KG of food and drink
we have (25 x 75%) X 31 X 1.15 = 668 Whrs
Thats how much power we would need to get the food cool, the 1/3 rd air space takes that little energy to cool its not worth mentioning.
This is why we should always put food/drink into the fridge/cooler that is as cold or colder than required, big energy saver stage 1
Now to show the effects of insulation....
If how 60 Ltr fridge/cooler had 2" of insulation it would allow 320 Watts of heat back in per day, with 3" of insulation that would be 213 Watts per day and with 6" insulation only 107 watts per day for efficiency Insulation is of Major importance....
The maths will come in handy later ( I will be making a spreadsheet up to do all the maths required including the later Insulation and fridge/cooler size maths ) for a cooler it will show how long the contents will stay cool for a fridge it will show the energy required to keep the temperature down.
I will try to do one in Imperial (American weights and measures too, should not take to much converting)
btw although it takes energy to cool things do not forget there are free sources of energy out there, the ambient temerature is also a source of energy....
The Easicool Returns.
Cooling units powered by natural evaporation, clean & eco-friendly.
First built in 1962 the Easicool is an environmentally friendly coolbox,
which works on the evaporative principle,the transfer of latent heat by
absorption. No gas or electricity is required just a cup full of water
added daily to keep the liner moist. The water is then carried around the
inner cabinet & as it evaporates the interior is cooled.
It is not a refrigerator but it will continue to work long after an ice
pack has melted in a standard coolbox.
They are ideal for camping, caravanning, boating & all outdoor pursuits.
The Easicools are independent of any power source & therefore more
versatile than an ordinary coolbox.
Fitted by motor caravan manufacturers as original equipment in the 60’s.
Dimensions (cms) : H51 x W36 x D31
Capacity: 32 Litres
Features: Wine rack & shelf
Price: £65 plus £7.50 for UK p&p
You can buy one here
In a normal fridge a compressed gas is circulated, this absorbs the heat and radiates the heat out of the back.
an Absorbtion fridge (absorbtion fridges were invented and patented by Einstein) like the electrolux 3 way relies on the circulation bought on by heat constantly turning the amonia to gas which circulates absorbs the heat the which is radiated out the back, the amonia is in a constant cycle of turning to gas then reforming as a liquid.
The Easicool works on a total loss evaporative principle, the water evapourates taking the heat energy with it, in hot dry countries this method is still used to keep food cool.
You will notice a significant drop in temperature if you ever stand beside a waterfall, the water is attracting heat energy from the surrounding air.
Another easy test is damp a clean piece of cloth and then breath through it.
Depth of cooling can be up to 12 degrees or so below the ambient temperature.
To see how it works you could place a milk container in a bowl of water, damp a piece of cloth, drape it over the milk container and make sure the bottom edges are in the water in the bowl. Place it in the airing cupboard, when checked several hours later you will find.
1. the water level as dropped
2. the milk will still be cool
There is a fair bit more to come, hopefully thats wetted your apetite a bit....