Difference between revisions of "Fridge"
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# Heat exchanger at back. Requires rear ventilation, but no side ventilation.
# Heat exchanger at back. Requires rear ventilation, but no side ventilation.
# No external heat exchanger. These have cooling tubes built in under the outer skin, and require side ventilation for cooling.
# No external heat exchanger. These have cooling tubes built in under the outer skin, and require side ventilation for cooling.
# Less common is cooling underneath the fridge, with warm air expelled at the front at the base. Such fridges require no ventilation to sides or rear.
# Less common is coolingunderneath the fridge, with warm air expelled at the front at the base. Such fridges require no ventilation to sides or rear.
Revision as of 22:23, 29 June 2012
Most of the information here also applies to fridge freezers, and some of it to freezers.
Right: 1920s monitor top fridge
Larders & frost free fridges
Standard fridges have an icebox, which will ice up and require periodic defrosting.
Larders contain no icebox, and don't frost up, so are frost free.
Pretty much all brands of fridge have a good reliability record. (This is less true of fridge freezers.) Liebherr and Miele are generally reckoned to be among the best makes.
Damp and water splash cause case rusting.
Liquid oozes inside the fridge can penetrate interior lining junctions and saturate the insulation at the bottom, leading to external dripping, rusting, increased power consumption, inadequate cooling and sometimes smell.
This doesn't happen often, but fridges in tight spaces can overheat. Too high a temp at the rear causes overheating of compressor, with consequently reduced life.
An indoor/outdoor thermometer can be used to tell if the temp behind the fridge is getting too high, but its generally quicker to just place a hand on the hext exchanger at the rear. Warmth is to be expected, and hotness at one end, but if its hot all over then the compressor isn't getting the cooling it needs. In this situation, the refrigerant gas is delivered to the expansion line hot, so energy consumption increases, further increasing average compressor temp and reducing life expectancy.
The solution is more ventilation. Where its problematic to provide this, a quiet 3" or 4" fan can be used to move air upwards behind the machine (machines with side mounted cooling need side airflow). Such an arrangement will require an occasional clean to remove dust buildup.
Dripping & flooding
Modern fridges route interior condensation on the cooling plate down a pipe to a plastic tray on the compressor. The water evaporates from this due to the heat.
External dripping can be caused by the drainage tube becoming unattached from the plastic tray on the compressor. Some fridges have used metal evaporation trays, and these rust enthusiastically, eventually causing external dripping.
Interior dripping or flooding can be caused by blockage of the entry point of the pipe. Remove any debris and a poke the pipe with a bit of wire to clear it. If it blocks repeatedly, mould growth is the usual culprit. This can usually be stopped by cleaning the interior spotlessly. A bit of bare copper wire lying across the pipe entry can also help.
Exterior dripping can also be caused by saturated insulation This also causes the compressor to run continuously, and often the interior temp to be too high. Replacing the insulation is the only cure, which isn't worthwhile unless the appliance is of some value. Insulation saturation usually occurs at the bottom of the fridge, where many fridges have used a cheap saturatable insulation pad.
If the bottom insulation pad is the problem, its often possible to cut metal back to get the pad out and refill with a PIR or polystyrene foam building insulation, making it airtight with a little expanding foam (don't overdo the expanding foam!). Don't forget to leave the machine the right way up for 24hrs before plugging in.
With a bad thermostat the fridge either plays dead, or the compressor runs all the time, consuming excessive energy. Icing up of the cooling plate often occurs. A fridge running constantly can use about £70 of electricty a year, around £50 a year more than it should (exact figures vary).
Thermostats can be DIY replaced, and generic replacement stats are available. The temperature detecting capillary tube must not be cut or damaged. If its too long just coil the excess up.
Usually the stat needs no adjustment, other than the knob setting to give the correct temp, but if adjustment is needed, the 2 adjusting screws under the cover control set temp and hysteresis. If the hysteresis is set too small for the fridge, the compressor will stall on starting frequently.
Compressor runs but not cold
This is caused by loss of refrigerant, which is caused by a leak. A gas refill will only leak out again. Usually not worth repairing, unless the machine is valuable, because of the great difficulty in finding such a tiny leak.
Compressors can be replaced and the refrigerant gas refilled, but again most fridges aren't worth it.
A compressor with a partial short either blows fuses or overheats very quickly and cuts out. Its often possible to make these run by adding a high power series resistance to limit the short current, but the increased energy consumption and low cost of replacement fridges makes it not usually worthwhile. A 240v 3kW non-fanned heater makes a suitable series resistance.
Sometimes such compressors fail to start fairly often, so this should only be used as a temporary measure while a replacement fridge is obtained.
Fridge noise is usually caused by something touching the compressor or failure of the rubber suspension under the compressor. The latter can be fixed by inserting chunks of rubber under the compressor, making sure it can still move very slightly. Metallic clanking noise can be caused by loose mounting of piping or something touching the pipework.
When a gas leak occurs, repairers may offer to refill. However if it leaked out once, it will do so again, so this will only ever be a temporary repair. Locating a very slow leak to fix it is extremely difficult.
The situation is different with belt driven in-car compressors. These leak refrigerant as a normal part of operation, and eventually require refill. Ditto belt driven antique fridges.
Test effectiveness of the door seal by checking it will grip a till receipt all the way around. A failed seal allows air to leak through, which results in excessive condensation formation on the cold plate, more rapid icing of icebox models, and increased energy consumtion.
If the seal looks OK but isn't sealing, check the fridge is standing squarely and level on the floor with the feet adjusted correctly. The cabinent is easily jarred when not supported correctly on all feet, which can prevent the door fitting the frame. Secondly, check the door adjustment (where present). This should be correct when supplied, but can be misaligned when reversing the door.
Door seals can be replaced on some fridges. Peel the seal back to locate the screws. Unfortunately in some cases the only proper repair is a new door.
There is a cheap bodge that's sometimes the only economic option when the seal doesn't sit flat against the frame. Clean the face of the door seal well. Apply cling film onto the metalwork where the seal meets it. Apply clear silicone to the face of the door seal, and close the door fully. When fully set, open very gently & remove the cling film, and put clear tape over the surface of the silicone to give it a non-stick finish, trimming the tape. This method gives an effective seal, but the silicone's adherence to the seal is weak, and it must be treated gently. Sanding the original seal's surface would probably help.
Door sits ajar
If the door sits ajar rather than closing itself, adjust the front feet to tilt the machine back a few degrees.
Rapid interior icing is due to a door seal problem. See the above 2 sections
Be sure to avoid all scented cleaners. Avoid scourers which make the interior lining harder to clean in future. Avoid bleach too. Cream cleaner and a cloth are normally effective, with a brush for any residue buildup. Stubborn dirt should be soaked to loosen.
Plastic fittings in fridges & freezers are typically not dishwashable.
Where smells are persistent, wiping the interior with dissolved bicarb (and not rinsing) sometimes clears the last of the smell.
If the fridge is in such a state that stinking oozes have gotten into the insulation, nothing but a new fridge will remedy this. For a valuable fridge, replacement of the insulation is also an option.
Unused fridges should be stored with door ajar to avoid bad odours. When the door may get closed, placing a couple of clean dry teabags inside helps.
There are 3 common cooling arrangements:
- Heat exchanger at back. Requires rear ventilation, but no side ventilation.
- No external heat exchanger. These have cooling tubes built in under the outer skin, and require side ventilation for cooling.
- Less common is cooling underneath the fridge, with warm air expelled at the front at the base. Such fridges require no ventilation to sides or rear.
Its traditional to leave a small gap each side of a fridge. This gap makes moving the appliance easier, avoids the door catching, avoids vibration noise and increases rear ventilation. Newer fridges with no external heat exchanger need side ventilation for cooling.
There's also a condensation issue. You need enough ventilation at the sides to prevent the side panels dropping below the dewpoint and generating condensation, which would rust the fridge & run onto the floor. The other alternative is to seal the side gap so there's no flow of air to form condensation -- this is the approach used by linking kits for linking adjacent appliances.
Wire vs glass shelves
Glass shelves are wipe cleanable, and minimise spills of meat juices etc onto foods below. Glass and wire are both dishwashable.
Glass shelves can't always be retrofitted into a wire shelved fridge. Glass blocks air circulation, and this can sometimes result in inadequate cooling in fridges designed for wire. A fridge with a large cooling evaporator that extends most of the way down the fridge is much more likely to work with glass than one with an evpoarator at the top only.
If you do retrofit glass you need to check the temp on each shelf afterwards, to avoid risk of food poisoning.
The energy efficiency of fridges has improved substantially since the 1970s. A free 70s fridge will generally cost more in total over its lifetime than a new one.
A fridge with a compressor running continuously can eat £60-70 a year in electricity, costing much more over the years than buying a new machine.
Until 1993 nearly all fridges used the CFC refrigerant R12, also known as freon.
New fridges use any of several HC and HFC refrigerants, such as R134a. Some of these are believed to affect the ozone layer as well, some not.
Propane, Butane, Pentane
Third world fridges usually use propane (or similar gases) as the refrigerant. These gases are cheap and energy efficient, but leaked gas is explosive. Despite this, data indicates that real world risk is negligible.
Propane is also sometimes used by DIYers to repair fridges and a/c systems that were designed for R12, R-22 or R-134a. Its cheap, readily available, a plug-in replacement, and 9-15% more energy efficient than R12, but its also highly flammable.
Propane refrigerant is labelled as R-290. Note that bottled propane is a propane butane mix, not pure propane, and the 2 need to be separated, which isn't hard.
Butane is R-600 and works at low enough pressure to be contained in reinforced plastic hose.
Pentane is another low working pressure refrigerant gas.
Due to the good safety record, some British fridges are now using these gases. These come with a small warning sign on the rear. With these, one should ventilate well if gas is smelt.
Ammonia absorption cycle
Ammonia has long been used in a small percentage of fridges using the ammonia absorption cycle. These fridges are almost totally silent, with just the thermostat's click and the occasional quiet gurgle. They're easily spotted:
- the equipment on the rear looks quite different to compressor fridges
- They are completely silent when first plugged in
- They don't have a compressor
There are 2 issues with these fridges.
- Power consumption is relatively high, due to low thermal efficiency
- Even a mini fridge contains over 1kg of ammonia, which would be fatal if released.
One advantage of these fridges is they can in principle be run off any source of heat, such as 240v, 12v, bottled gas or paraffin. Hence they're standard equipment in caravans. The other is they're silent, so are used in bedrooms, hotel rooms, and so on.
The first fridges were little more than wooden cabinets, or sometimes metal. Ice was bought & placed inside to cool them. They tended to have several doors, sometimes drawers too, and wooden ones are readily mistaken for standard furniture. Gallery
These aren't practical or safe to use as fridges, due to lack of insulation and too high a storage temperature.
Pre- R-12 & Belt drive fridges
Early electric fridges used a separate motor and belt driven compressor. These are less efficient, and the compressor gradually leaks refrigerant, so needs refilling in time. The belt can slip or break.
These also used various nasty refrigerants. The refrigerants used are mostly toxic to very toxic, the non-toxic ones are explosively flammable. Such fridges were never well suited for use in inhabited spaces.
Refilling with modern refrigerants is usually not an option, as the working pressures of these old systems are often too far removed from those of modern equipment to produce a workable refrigeration cycle. The more toxic of the old refrigerants should be used in a location ventilated and isolated from the main building. Early machines using SO2 generated complaints of foul smells.
Butane and pentane work with lower pressures than R12, and may be usable in some cases.
Above is a double width version of the iconic monitor top fridge introduced in 1927, which used sulphur dioxide or methyl formate as a refrigerant. Some of these are still in service today.
Safe non-toxic non-flammable R12 refrigerant was introduced in the mid 1930s, and soon became universal. Old fridges using R12 and a sealed compressor unit will behave much like modern fridges, albeit with poorer energy efficiency, and without all the other modern refinements such as wipe clean linings, safe door latches, even interior temperature, frost free operation and so on.
Refilling R12 fridges that have leaked refrigerant is an issue. R12 refills will soon be banned by law. People have sometimes refilled these succesfully with HC fuel gas. Fuel gases are very cheap and available.
Foreign historic fridges don't all use R12 after the mid 1930s. Some countries preferred the much cheaper but highly flammable fuel gases.
New mini fridges usually use peltier heat pumps (old ones used the ammonia absorption cycle). Like ammonia, these are silent and have poor energy efficiency, but the very remote risk of ammonia release is not there.
These fridges don't generally have the same cooling power as standard fridges, with the ability to only cool by upto 15°C being normal. Thus they are not safe to use as a food fridge from a food poisoning point of view, as food stored at 10°C in a 25°C room spoils rapidly. This is why they're usually described as drink chillers only. If wanted to store food, the interior temp should be monitored and the machine only used for foods requiring refrigeration when the fridge is sufficiently cool. Foods that don't need refrigeration (such as wine, chocolate, and unopened tetrapaks) are safe to store in them.
The peltier pumps used in these are usually rated at 12v 5A, but can run on anything upto 16v for maximum cooling. Some of these mini fridges also have a fan or a second peltier, doubling power use.
5°C or below is the recommended fridge temp for food storage.
Temperatures in fridges tend to vary from one place to another. The salad crisper operates at high RH and slightly higher temp, keeping salads firm for longer and avoiding any risk of freeze damage. Enclosed spaces mounted on the door also run at slightly higher temp, and are good for keeping butter, making it not quite so hard.
Areas close to the cooling plate run colder, and salads can be frost damaged if put there.
Annual Total Cost of Ownership depends on purchase cost, life expectancy, energy efficiency and energy cost.
Fridges using fans often need a replacement fan fitted at some point in their life. This is a cost and reliability issue to bear in mind when purchasing.
News:uk.d-i-y and expert websites sometimes discuss TCO reduction strategies, but opinion remains divided. One thing is clear though: frost free fridge freezers have much shorter lives on average than traditional frosting ones.
- Check the fridge temperature is correct.
- Inspect contents regularly, removing anything that is beginning to spoil.
- Avoid arranging foods so that meat juices could drip onto other food types.
- Keep the fridge interior clean.
- Glass shelves reduce cross contamination by reducing drips.
- Don't pack a fridge full, this blocks airflow and results in unsafe temperature rise on some shelves.
- Don't store meat or fish above other food types, drips can contaminate.
Most local councils take fridges and freezers away free. Local dealers will purchase or collect the very few types of fridge they could repair and sell profitably, but this only applies to high ticket items.
Most other disposal options are now illegal for R12 fridges, since it is no longer permitted to release R12 to the atmosphere. There's R12 in the insulation as well as the coolant circuit of pre-1993 fridges.
Compressors removed from fridges have their uses. They provide compressed air at high pressure but low flow rate, and require an oil catcher if they're to last. A metal globe or other shape in the output pipe close to the compressor, filled with a copper scourer works to catch oil. When the compressor stops, the oil runs back in.
Its now unlawful to cut an R-12 filled compressor out, as this would release R12.
Fridge dials are usually marked with numbers unrelated to actual temperature. The only way to determine temperature is to leave a thermometer in the fridge.
A few fridges also have an insulation sheet between icebox and the main fridge space. The position of this can be adjusted in conjunction with the thermostat dial to achieve the desired temperatures in both fridge and icebox sections. The sheet is moved to adjust the relative temps of fridge and icebox; when blocking all airflow there will be maximum temp difference, and when opened there will be less temp difference.
Improving energy efficiency
The simplest way to improve energy efficiency is to replace a 1980s fridge with a modern A rated one.
Energy saver plugs
Energy saver plugs reduce energy consumption in older fridges, but are incompatible with a lot of new fridges, some of which have this technology built in. Energy saver plugs pass full power to the compressor during starting, then throttle the power back once running.
In most places a 10 year old fridge can be bought for the price of one of these plugs, and will deliver more performance improvement, so even for older fridges their use isn't popular. Maximum saving is obtained with large old fridges, such as original 1950s appliances.
More aggressive methods
People running fridges on small solar electric systems sometimes wish to reduce energy consumption further. Any of the following can help:
- Add more polyisocyanurate or polystyrene insulation on the outside of the fridge (watch for condensation on the metal cabinet, which can rust it)
- Use an energy saver plug when compatible
- Put frozen items in the fridge overnight when defrosting them
- Write the food contents on the front so decisions can be made with the door closed.
- Keep the fridge in a cold place eg garage - ensure its rated for such a temp range though
Domestic refrigeration is designed to operate indoors at around 20C.
Fridges will work at lower temps, unlike many fridge freezers. But cold rooms tend to cause condensation on the case, leading to rust and the risk of insulation saturation.
When put in a very hot room, such as a conservatory or shed in summer, a fridge is likely to fail to be able to cool enough to keep food safe. If any doubt, check the fridge's internal temp.
Fridges & freezers all have a room temperature range they're designed to work in. If your room will be far from 20C its possible to buy one rated to operate in that environment. Failing to do so can result in food poisoning.
RCDs can cause nuisance trips. If this occurs when out for the day the fridge will warm up, making some of the food unsafe to eat. Food poisoning claims orders of magnitude more lives than electrocution by fridge, so ideally a fridge should be run from a non-RCD circuit. This is even more true for freezers. Occasionally DIYers install a non-RCD feed for the fridge freezer when rewiring. The 17th edition wiring regs requires that any such socket be marked with its intended use, and not likely to be used for outdoor equipment, so not by the door.