Alternative Technology Assn Forums

1. 

   axess
   Member

   Hi Everyone,

   We are thinking of re-vamping our kitchen and wonder what posters think about having a separate cool compartment with a compressor outside.

   Our existing Fisher & Paykel fridge has run without any problems for over 15 years so far, but adds to the heat load in summer due to the venting of heat through the side panels. If the compressor unit was outside then that heat load would be gone and the cabinet might perform better if well insulated and constructed.

   The alternative of dedicated air circulation for the existing fridge might be difficult to achieve because of the rammed earth walls.

   Ideas anyone?

   Posted Thursday 11 Feb 2016 @ 5:15:42 am from IP #
2. 

   Bushwalker
   Member

   Most fridges these days use the sides and back of the fridge to dissipate the heat extracted from the fridge rather than the old style coils that were at the back of the fridge. You'd need to find a fridge that would run efficiently with the compressor removed some distance. Maybe a commercial model, but would it be as efficient?

   Also, moving the compressor outside would reduce heating the room in summer at the cost of running the compressor in a hotter environment. Should work better in winter except the room wouldn't benefit from the heat. Maybe it would balance out?

   Posted Thursday 11 Feb 2016 @ 5:36:57 am from IP #
3. 

   maelgwn
   Member

   These guys sell a kit for DIY fridges with separate condensers and cool boxes:

   http://www.ozefridge.com.au/

   BUT - lets think about this. When at equilibrium (e.g. most of the time), the heat you pump out the back is equal to the 'coolth' that leaks out from the fridge and into your house. Therefore the only heat you actually generate is to cool down things that go into the fridge (which is roughly equal to the coolth generated taking things out) and from the compressor and motor inefficiency. Compressor and motor heat is equal to the power consumption of the fridge.

   Assuming 500kWh per year, this is actually pretty minor. Would take about 150kWh of AC to remove the heat. But you probably only actually run the AC like 5% of the time, leaving you bugger less than 10kWh per year. Hardly seems worth the trouble!

   Posted Thursday 11 Feb 2016 @ 6:16:28 am from IP #
4. 

   wlb
   Member

   Ours is outside. It uses an Ozefridge system. We're off-grid, and have been since 1998 after buying an off-grid property built in 1980. We originally had a large Electrolux gas fridge which died inexplicably in 2008. They're usually bulletproof. I've now had a lot of practical experience with off-grid refrigeration and know what works in our situation and what doesn't, and why. I have a background in refrigeration, but not the conventional type.

   We're currently planning a new kitchen and refrigeration is one of the things I'm focussing on. The aim is to store enough cold during the sunlight hours to carry the fridge and freezer through the night without calling on the battery bank to run them. The problem with my Ozefridge system is not its fault. It's designed for marine use, with superior insulation and ideally, a top-opening cabinet. We have none of these things. The cabinet is an ancient conventional upright Kelvinator fridge-freezer with less than ideal insulation. The intention was to build it in to kitchen cabinetry, adding external insulation on all sides but the front. This would have been easy given that the compressor/condenser unit is outside on the other side of the wall. But due to space constraints, this never happened and the fridge's ice tanks aren't big enough to carry it right through the night.

   In the new kitchen, the freezer will be a chest freezer built into a bench and 'powered' by the relocated Ozefridge system. The compressor/condenser unit will be in the adjacent laundry this time around, rather than outdoors. It will be cleaner. No dust and spiders. If heat becomes a problem I will switch it from air-cooling to water-cooling and circulate the water outdoors. These units have this option as standard.

   For the fridge I have a modern Fischer & Paykel '3-door' upright fridge. Freezer above, fridge below, and externally accessible vegetable crisper drawer beneath. It is one of the models with the condenser built into the external walls. A stupid idea purely based on misguided aesthetics. Makers promote the smooth, clean lines of the cabinets. No unsightly wire-mesh thingies hanging off the back to collect dust. Marketing claptrap. Anyway, it's going to be modified.

   The condensers in the walls will be bypassed and replaced by a water-cooled condenser. The cabinet will be built into insulated kitchen cabinets but with ventilation where the compressor is. The fan-forced freezer (no longer required) will be used to freeze several permanently installed, large, flat tanks of brine. The fridge compartment below will be chilled by air or antifreeze solution (probably the latter) recirculated through the freezer compartment, and thermostatically controlled. The fridge's compressor will be powered during daylight hour and function normally, but at night the compressor will be switched off and the stored frozen brine will be used. Initial experiments using three 5L containers of water frozen during the day and transferred to the fridge in the evening resulted in only 2/3 of the ice melting over 12 hours; so I'm reasonably confident. The biggest drain by far on our batteries overnight is the fridge. Changing this will greatly improve their life.

   So in answer to your question, you could have yours modified to be water-cooled and just run that part outside, if the heat is a problem for you.

   Posted Thursday 11 Feb 2016 @ 9:51:56 am from IP #
5. 

   johnmath
   Member

   For some reason fridges are designed/sold in Australia are made in such a way that some of the heat extracted from inside the cabinet is allowed to soak back into the cabinet. This is because the compressor/condensor is usually located at the bottom of the fridge and heat rises of course.

   In Japan, the compressor is at the top of the fridge and fan cooled. That means Japanese fridges, even big six-door fancy Panasonic ones, use less than ⅔ of the electricity of the most efficient fridge you can buy in Australia. My in-laws in Kyoto have a monster Panasonic fridge that is rated at about 180 kWh per year.

   If you are going to design a fridge with outdoor compressor (great idea BTW) then I suggest looking a eutectic fridge components such as used in boats. They are designed to be very efficient and suit custom installation.

   Alternatively, if you build in your fridge, you can have an earth pipe venting to the bottom of the fridge and a flue exiting to the ceiling space. Warm air from the fridge will rise up the flue into the ceiling, drawing cool air from the earth pipe to makeup the lost air around the fridge. I improved the efficiency of a conventional fridge by about 40% by using a flue to extract waste heat.

   An earth pipe is simply a length of PVC stormwater pipe buried in the ground and open to the air outside of the house, with the other end open in the space you want to see cool. To cool a fridge cavity, the pipe would need to be about 10 meters of 90 mm stormwater pipe and buried at least a couple of meters deep where the ground temperature is stable.

   An earth pipe is a great way to keep a pantry at around 20 degrees in a house without air conditioning. They can be scaled up to cool a whole house.

   Posted Friday 12 Feb 2016 @ 1:42:06 am from IP #
6. 

   Flying high
   Member

   Haven't seen the Oz Fridge thing before..

   Wow a 15 yo fridge, suggest that this would pump some heat out.

   We have an Electrolux Aussie made fridge rated at 356 kWh per year, very efficient, R600a gas...don't notice any heat in summer.

   Using the KISS principle I'd be getting the most energy efficient fridge I could afford..and get rid of the old clunker you have.

   Posted Saturday 13 Feb 2016 @ 1:20:51 am from IP #
7. 

   gazmo88
   Member

   Here is the executive summary on marine fridges:

   When it comes to marine fridges Eutectic designs couple with the need to charge batteries at least once a day. One runs the propulsion motor (usually without the prop turning) to charge batteries and fridge. The fridge is charged by freezing down a "holding plate" which is a sealed box containing brine (although far more sophisticated eutectic solutions are available). These devices use quite a bit of current when running - more than most boat sized solar panels can provide.

   The total lowest power consumption per amount of cooling over 24 hours however is provided by sealed compressor units such as the Danfoss BD-35F. These will require a duty cycle of approx 40% over 24 hours in the tropics - depending on heat load on the box.

   The BD35F generally comes with a cooling coil and a fan like a regular fridge, which requires two motors - one for the compressor and one to drive the fan to pass air over the coils. It runs on both 12 and 240 volts, which can be handy.

   There is however a variant that requires no cooling fan but rather uses a "keel cooler" which is essentially a metal block attached to the outside of the hull through which the refrigerant passes. If your house does not float on water then a water tank, swimming pool or dam will suffice as long as its really close to the compressor.

   This latter variant is the lowest energy consumption fridge you can construct. But it requires 24 hour feeding, albeit at a lower than 50% duty cycle. This may impact on the rest of your energy strategy.

   A top loading box with seals which are under positive pressure (think old style ice box door handles) performs best. The rule of thumb last time I did it the sweet spot was 4 inches of foam insulation for a fridge box and 6 inches of foam for a freezer box. Same foam requirement for the lids of course. You need to use closed cell foam so it does not absorb moisture so EPS is generally out. Optimum cold box panels are lined with aerogel but are silly money.

   Don;t forget to skin the outside of the foam in alu foil to reflect radiant heat.

   Throw away the awful bimetallic strip "thermostats' and get some digital electronic ones with proper temperature sensors. You will save a heap of amps.

   Then never run it empty - put in bottles of water to keep it topped up to exclude as much air as possible.

   All this stuff is out there if you search.

   Be aware however that this will cost more than a nice shiny store bought fridge. Possibly much more.

   If you are living on a boat with limited battery capacity and surface area for panels all this is critical. It is less so in an environment where adding panels is an option.

   Good luck

   Posted Saturday 13 Feb 2016 @ 12:56:26 pm from IP #
8. 

   johnmath
   Member

   Thanks for a great description gazzmo88

   Posted Saturday 13 Feb 2016 @ 10:28:22 pm from IP #
9. 

   axess
   Member

   Thanks for all the interesting replies so far.

   The heat effect of the outside skin of our existing fridge has produced an interesting side effect on our adjacent food storage cupboards. This has created an ideal environment for weevil production amidst our grains and other food items.

   We have removed all items several times, and added the affected items to the compost bin, but only realised today that the infestation revitalised itself by hiding in the "System 32" shelf holes during the weevil pogroms. We are loath to use chemicals in the food cupboard so used filler to fill the unused shelf bracket holes. A point to consider when the kitchen is remodelled.

   We are leaning to keeping the fridge in the kitchen but in a different location. We will also try to introduce dedicated venting but locating the enclosed space next to a partition wall.

   Thanks again for all the replies.

   Posted Sunday 14 Feb 2016 @ 2:37:23 am from IP #
10. 

    Phil A
    Member

    Remotely mounting the compressor wont remove all of the heat. The heat created at the compressor unit is only for the short time the compressor is running the rest of the cycle is heat from the condenser.
    The further from the fridge the compressor, the more energy losses as well,
    The most practical point is to at least get the condenser on the outside of the fridge. Fitting the condensers inside the cabinet is a brain dead arrangement.
    How the hell can this be legal?
    Energy conservation.... what a joke....
    Gram make fridges with condensers on the rear, (1970s style) outside of the cabinet.
    Thicker cabinets and better quality insulation also help considerably.
    Air can then be ducted to and from if you wish to get the heat outside.
    Our Australian made fridge freezer used 1600 watts per day. The new gram fridge and separate elcold freezer (double the size) uses less than 600 watts combined.
    The elcold freezer is 100mm thick, and will keep below zero without running, for days. The Australian fridge was 30mm!! with poor quality insulation.

    Posted Sunday 14 Feb 2016 @ 10:39:01 pm from IP #
11. 

    Benny
    Member

    Why would anyone ever consider a shop display type fridge Mathew ? They don't have "remote compressor" as the OP wants and they are incredibly inefficient - with poor insulation and often open fronts. And try to find the technical info' on these units. I can't understand why commercial equipment doesn't seem to need energy rating labels.

    Posted Thursday 31 Mar 2016 @ 9:58:55 am from IP #

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