12V v 240V refrigeration compressors

[Bro]

Two questions:-

1. For 12V dc refrigeration compressor (eg. Danfoss BD35F) v's 240V ac (eg. whatever unit is in Curry's "ESSENTIALS C61CF13 Chest Freezer") does anyone have real facts as to which compressor is most efficient and by how much?
2. Would Danfoss BD35F be man enough to handle a 60litres fridge?

I have a serviceable Danfoss (in a working LEC fridge with poor insulation value) that I might put into a second hand freezer cabinet then use with a different temperature controller as a fridge. Alternatively I might simply buy say, Curry's 240V "ESSENTIALS C61CF13 Chest Freezer" and run it off an inverter.

 

If I go the 240V ac route I shall adopt the control system proposed in an earlier thread by CaneyJ "Running an ac fridge efficiently" (thanks) and if I go the 12V dc route I shall use his suggestion of a digital temperature control (thanks again).

[BEngo]

COP data, at various condenser temperatures IIRC, for the Danfoss compressor is in the handbook, which was available on line. If you can find similar for the Curry's machine all you need to do is compare them. You might need to sneak up on a Currys compressor and see who makes it, and the model number- I would not be all that surprised if it were Danfoss.( Probably the Far East division or a Far Eastern sub-contractor with some Danfoss drawings or maybe just a unit to copy.) Google will then probably provide the data you want.

 

The BD35F is, I think actually just a standard size of normal Danfoss compressor, fitted with an electronics package to enable the motor to operate off 12/24 V and to provide voltage detection, over/under voltage protection/ fan control etc.

 

I see no reason why the Danfoss should not handle 60 l of fridge, provided the evaporator you have is suitably sized and the insulation of the cabinet is such that the heat inflow is less than the capacity of the compressor/condenser/evaporator to remove it, all in your operating conditions of course.

 

My refrigeration calculations are vv rusty so I won't even think of trying to make estimates of what these might be, but the U or K values for various sorts of insulation are readily available online so the heat inflow can be calculated. Unless you are sure otherwise, choose a fairly high condenser temperature and -18 C for the evaporator temperature.

 

Be aware that some pretty specialised equipment is needed to re-gas a fridge- the first problem is evacuating the air and moisture from the pipework before the gas can be put in. If you know someone with this kit he/she will probably be able to answer your question right off.

 

N

[Alan de Enfield]

I like to 'bodge-it' and mess about changing/mending/making things, but, sometimes the easiest way is the best way.

 

Just buy one 'ready made' - either 12v or 220v (whatever 'floats your boat')

[Bro]

I like to 'bodge-it' and mess about changing/mending/making things, but, sometimes the easiest way is the best way.

 

Just buy one 'ready made' - either 12v or 220v (whatever 'floats your boat')

 

Me too. Can't beat a bit of bodging. Snag is we can't buy a well insulated fridge at affordable price hence must bodge a freezer (roughly twice the insulation thickness of a fridge) into a fridge.

[Alan de Enfield]

 

Me too. Can't beat a bit of bodging. Snag is we can't buy a well insulated fridge at affordable price hence must bodge a freezer (roughly twice the insulation thickness of a fridge) into a fridge.

 

I was thinking buy a 220v one and run it off an inverter - it will use about the same as a 12v one except for the power used by the inverter itself.

I recently bought a 220v freezer and it is using 400 Wh per day (which via the inverter works out at about 40 Ah per day) and I can use the inverter for other things )hoover, toaster, electric drill etc)

 

My 'super-doopa' 12v fridge (bought last month at about £600) has a manufacturers stated 'average power consumption' of 45w, so if running 33% of the time, this would give a consumption of around 30/35 Ah per day

 

A typical (220v) A+ fridge uses 122kwh per year which comes out at around 33Ah per day (pretty much the same as a 12v fridge) at 1/5th of the price.

http://www.argos.co.uk/static/Product/partNumber/2663562.htm#pdpFullProductInformation

[OldGoat]

COP data, at various condenser temperatures IIRC, for the Danfoss compressor is in the handbook, which was available on line. If you can find similar for the Curry's machine all you need to do is compare them. You might need to sneak up on a Currys compressor and see who makes it, and the model number- I would not be all that surprised if it were Danfoss.( Probably the Far East division or a Far Eastern sub-contractor with some Danfoss drawings or maybe just a unit to copy.) Google will then probably provide the data you want.

 

The BD35F is, I think actually just a standard size of normal Danfoss compressor, fitted with an electronics package to enable the motor to operate off 12/24 V and to provide voltage detection, over/under voltage protection/ fan control etc.

 

I see no reason why the Danfoss should not handle 60 l of fridge, provided the evaporator you have is suitably sized and the insulation of the cabinet is such that the heat inflow is less than the capacity of the compressor/condenser/evaporator to remove it, all in your operating conditions of course.

 

My refrigeration calculations are vv rusty so I won't even think of trying to make estimates of what these might be, but the U or K values for various sorts of insulation are readily available online so the heat inflow can be calculated. Unless you are sure otherwise, choose a fairly high condenser temperature and -18 C for the evaporator temperature.

 

Be aware that some pretty specialised equipment is needed to re-gas a fridge- the first problem is evacuating the air and moisture from the pipework before the gas can be put in. If you know someone with this kit he/she will probably be able to answer your question right off.

 

N

 

 

I would take issue with some (highlighted) points above:-

The BF35F and larger BD50F is not a reworked A/C unit but has a variable speed DC motor - supposedly to make it more efficient.

 

My elderly Batts F/F has a total capacity of 160l but is probably tops in what you can go to

 

I'm worried about regassing fridge, AFAIK the BD units use R134 liquid whereas all modern domestic units use R600a. Some say it's OK - but I've not seen anything definitive.

 

There's plenty of information around for the BD and other Danfoss units - but I've found little in depth info: about 240V units from other maunfacturers.

 

For me the important considerations are:-

Standing power consumption of an inverter

Should it be a pure sine wave unit

What power capacity is needed to the 240 unit started.

[ditchcrawler]

A long time ago I posted how much power my 240v lec fridge with ice box + inverter uses. its basically the same cabinet as the 12/24 volt one. I have copied the information below.

 

I have been running another set of tests on our 240 volt fridge.

The fridge runs via a Mastervolt Mass Sine 24/1500 and all current

readings are take from a Sterling Battery Management unit.

The inverter + Fridge + fans =3.5 amps

The Inverter + Fridge = 3.4 amps

The Inverter = 0.4 amps

I have connected a RS hour meter across the refrigerator compressor to

record compressor run hours.

The refrigerator is a LEC Elan and sits under a work top with 25mm air

gap each side and 50mm between the top of the refrigerator and the

underside of the work top. The air space behind the refrigerator is

well over the recommended space as the hull side slopes from the floor to

the gunwale.

There are ventilation holes drilled in the floor behind and below the

fridge. Also there are 4 computer fans mounted in the floor connected in

series parallel that when running blow cool air from under the floor up

the condenser. All readings were taken with the fridge in normal use.

The fridge thermostat was set at 3 and had been running for a couple of

days to allow things to stabilise before readings were taken at 1700 hrs

each day. The thermometer inside the fridge was reading at the top of

the acceptable range.

At the end of the first day with the fans off and the fridge running as

normal the hour meter recorded 7.6 hrs in 24 hrs.

On the second day the fans were switch on and the reading at the end of

24 hrs was 7 hrs.

The next day the fans were switched off and the hours run were 7.1

This indicates to me that the fridge was adequately ventilated as

installed. That night I insulated the fridge on both sides and the top

with sheets of 25mm close cell insulation foam covered on both sides

with aluminium foil as used in the building trade. At this point things

got interesting which I can't explain. The running hours were slightly

less but the internal temperature of the fridge fell. Over the next 2

days I adjusted the thermostat setting to bring the internal temperature

back to its original level. This resulted on it now being set at 1.5 as

opposed to the original 3. I don't know why this happened as in my book

the thermostat should keep the inside of the fridge at a constant

temperature. I suspect it is a timer and not a stat.

Once this had settled down I started recording readings again which run

between 6.3 and 5.7 hours per day

11/8/06 1700hrs 1170.2

12/8/06 1700 hrs 1177.8 7.6

Fan on

13/8/06 1700hrs 1184.7 6.9

Fan off

14/8/06 1700hrs 1191.8 7.1

Insulation added and fans on

15/8/06 1700hrs 1198.5 6.7

reduced stat setting

16/8/06 1700hrs 1205.0 6.5

17/8/06 1700 hrs 1211.3 6.7

18/8/06 1700hrs 1217.0 5.7

19/8/06 1700hrs 1223.6 6.6

20/8/06 1700hrs 1230.0 6.4

21/8/06 1700hrs 1235.5 5.5

22/8/06 1700hrs 1241.2 5.7

[onionbargee]

The most high spec fridges now are using vacuum panel insulation. Off the shelf cabinets are not efficient insulation, and far below what is possible to achieve. Is it worth trying to get effecientcy from one ? I don't think so personally. I stuck 40mm kingspan board all over one of my gas fridges and it froze everything solid by the next morning.

 

I would start from the basis of constructing a cabinet with the maximum insulation possible, a double skinned stainless fabrication with a vacuum. In effect a giant flask.

[Bro]

The most high spec fridges now are using vacuum panel insulation. Off the shelf cabinets are not efficient insulation, and far below what is possible to achieve. Is it worth trying to get effecientcy from one ? I don't think so personally. I stuck 40mm kingspan board all over one of my gas fridges and it froze everything solid by the next morning.

 

I would start from the basis of constructing a cabinet with the maximum insulation possible, a double skinned stainless fabrication with a vacuum. In effect a giant flask.

 

If 40mm Kingspan had that effect then surely all you need to do is adjust the temperature setting and it's "Job done". Can't comment on practicality, cost or availability of vacuum panels but sounds good.

[ditchcrawler]

Interestingly I added extra insulation to my LEC 240 volt fridge and the compressor ran for the same length of time each day and the fridge got colder