Fridge, you'll kill us all.... :o)

[knighty]

industrial fridges (and I'm assuming heat pumps) have an accumulator just after the condenser (hot bit) as somewhere for the refrigerant to collect up as a liquid and to help collect the oil - the liquid refrigerant comes in the top and and out of the bottom - so if you loose a bit of refrigerant the pressure drops and there's a bit of gas at the top of this small tank/bottle but there's still liquid at the bottom and going out to the evaporator (cold bit) (there's normally a very small oil return pipe going to back to the compressor too)

it's a bit like a small reservoir so as you loose a bit of gas, and as a buffer so as the weather changes and changes the pressure in the gas side of things changes it doesn't effect the way the system works... (but they're never great.... they need quite a bit gas pocket at the top for the changes in weather, so there's not enough liquid in the bottom to make up for loss or gas)


but I've always thought.... there should be another (bigger) tank between the high pressure side and low pressure side, with pressure valves connecting it to each... too much pressure in the high side and refrigerant is let in..... too little pressure on the cold side and some is let back out into the system....

that way you could have a decent amount of refrigerant in it..... and the system would stay at the right pressure for years.....

I have to have mine at work gassed up every year.... could maybe get away with every 2 years but it's not worth the loss in efficiency.... and that's with pretty new systems, 2 of them are less than 3 years old and still need it !

[Eccentric Dyslexic]

Ok next job for ya... remove and weigh all the gas from a 12kw Heat PUmp to check if the right amount is still in there...
Steve

I know you're just taking the p*ss 

Who sed i was jesting  

My HP takes 1.3Kg of R407c and 1l of oil.  I suppose i could refill the system via a filter/dryer to make sure the gas is nice and clean and dry....?  I can buy bottles of R407c off of eBay

Steve

[Heinz]

it's a bit like a small reservoir so as you loose a bit of gas, and as a buffer so as the weather changes and changes the pressure in the gas side of things changes it doesn't effect the way the system works... (but they're never great.... they need quite a bit gas pocket at the top for the changes in weather, so there's not enough liquid in the bottom to make up for loss or gas)

so there's a wee tank, liquid in the bottom, gas in the top. Couldn't you use one of those cheap magnetic thermal strip gas cylinder level gauges to "see" the level of the liquid in the reservoir and top up if it's low?? Or is the temp change between the gas/liquid not great enough?

Heinz

[knighty]

yeah it's all the same temp (quite warm!)

another thing I forgot to say is, industrial compressors (and I guess heat pumps?) "pump down" just before they turn off - the solenoid letting liquid through to the evaporator (cold bit) closes but the compressor keeps pumping and sucks the gas side empty pumping everything into the accumulator and high pressure side...

they do that so there's no chance of any of the refrigerant in the gas/cold side condensing back down to liquid and being sucked into the compressor and damaging it

in domestic fridges when they compressor shuts off, the pressure equalises around the system and all the liquid refrigerant drops down to the lowest point.... which is in the bottom of the compressor - they only have enough refrigerant in to fill the bottom of the compressor (where the motor is) the top of the compressor is above that level and in gas


as you might have guessed..... refrigeration engineers charge a fortune so I've done a lot of reading up on the subject !!

[Heinz]

and a Land Rover  though anyone who keeps goats must have a screw loose anyway 

Cheers, Paul

A LandRover? I wasn't aware that you could only have one?! I thought they were herd animals???
1966 109 GS canvas top - my wheels general workhorse,  Lpg
198? 109 FFR Canvas top - sleeping
1973 88 hard top - long term project
1953 86 series1 hard top - awaiting rebirth one day if I ever have the time.
1991 127 RAF ambulance - current favorite, v8 Lpg camper, doesn't go far and not nearly as thirsty as you'd expect.
1990 110 RAF station wagon - not sure what to do with this one but it's eating no grass.
197? 88 pickup - spares.
some others being recycled into other things (that's real recycling, not "recycling") and slowly being reclaimed by the earth...

Just in case someone jumps on the anti 4x4/gas guzzler bandwagon. We really do need a 4x4, a Ford KA would not make it up the 750 foot hill dirt track for long, would not be able to bring the firewood out of the forest, would not get us home in the winter and would not get the kids to school in all weathers. A (real) LandRover does all this and will probably still work for the kids when I'm long dead... 

Heinz

[Stevie D]

A LandRover? I wasn't aware that you could only have one?! I thought they were herd animals???

 

I must tell the wife that one, I've just bought a 3rd.

Love the home made mill as well - excellent work on the fridge too!

Steve

[Heinz]

Well, that's about 10 months and the butane fridge hasn't missed a beat  although by saying that, I've probably jinxed it 
I do have a small problem with it though. The condensation dish on top of the pump no longer gets warm enough to evaporate the accumulated water, dish overflows and the water run out onto the floor. Any bright ideas to avoid me getting abuse from the rabble and having to dry up the mess once a week? Best I can come up with is a bit of tubing shoved in the drain hole and a milk bottle beside the fridge..... not sure how well that will go down with the woman though.  My other idea is a wick dipped in the dish, which goes up to the warm condenser, but it would probably just end up mouldy.

Heinz

[Justme]

Well, that's about 10 months and the butane fridge hasn't missed a beat  although by saying that, I've probably jinxed it 
I do have a small problem with it though. The condensation dish on top of the pump no longer gets warm enough to evaporate the accumulated water, dish overflows and the water run out onto the floor. Any bright ideas to avoid me getting abuse from the rabble and having to dry up the mess once a week? Best I can come up with is a bit of tubing shoved in the drain hole and a milk bottle beside the fridge..... not sure how well that will go down with the woman though.  My other idea is a wick dipped in the dish, which goes up to the warm condenser, but it would probably just end up mouldy.

Heinz

Our fridge was like that from new. In the end I piped it through the floor to a drain. Not easy to move the fridge now but better than a spill.

[Eccentric Dyslexic]

The wick idea is best, maybe an old cotton rag with the bottom in the dish and the top against the condensor, its heat will keep it dry at the top, encouraging more water to be drawn up into the rag.  i wouldnt worry about the mold, it shouldnt cause much of a problem as it will be mostly dry, try it and see.

I'm wondering why your pump is not getting hot, maybe the new gas is so much more efficient the pump isnt running long enough for it to get hot:-)  The pipe coming from the pump gets hot though doesnt it? 

Another point to improve efficiency, try running a little pc fan to blow on the condensor when the motor runs....have a play with that and re do your kw/h test...

Steve

[Heinz]

OK, added a rag to the fridge. About a foot long bit of denim, inch and a half wide, dipped in the dish and woven up the condenser bars. The PC fan is a good idea, but I think they are normally 12 volts? Suppose I could use an adapted cheap plug transformer from the pile of cast off chargers in the shed, going to reduce the efficiency though...

Heinz

[Eccentric Dyslexic]

I would have thought efficiency should improve, normally, the condensor relys on convection to cool the rails on the back, but if you use a fan to aid convection it should help.  Our A++ rated Samsung yankie FF has no rails on the back...it uses a fan to cool the output from the condensor.

One simple way to see if it helps is to monitor the temp of the pipe at the far end of the condensor rail before it goes into the back of the fridge, if its cooler with the fan, the fridge will be more efficient....nice little experiment anyway! 'Leccy consumption will go up a tad due to the fan, but run time should reduce...

Steve