teemyob
09-03-2012, 12:07 AM
Hello,
Can any of you clever folk help me out please?
Some time ago I was asked to inspect and report on a compact medical fridge built in China and supplied to the UK for distribution to UK pharmacies, doctors surgeries and rest homes etc.
Think table top fridge with a digital control and alarm.
The original was built with an R134a compressor, skin condenser. Was a bad design all-around.
I was asked for my opinions on the unit that was running to long and poor cooling efficiency.
I suggested many design changes and my main conclusion was that R600a should be adopted over R134a.
The unit has now been re-designed by the Chineses factory, including changing the compressor and system to R600a.
However, the factory have simply changed the compressor from R134a to R600a and kept the charge the same at 45g.
The first problems are that the systems, now charged at the same weight qt 45g is overcharged. This has resulted in a few major issues.
A Frosting on suction line
B Initial cooling, very efficient, cycle off time too long.
C High temperatures (in excess of +65c) on the side walls of the cabinet
I have attempted to optimise the refrigerant charge to that of an R600a system.
But the main problem that remains is that the surface temperature of the outside of the cabinet remains too high.
My thoughts are without testing is that......
The cheap chinese compressors are generating too much heat?
I am going to ask the client for permission to fit as test European compressor, for example a Danfoss TLES4.
But I am asking your advice first.
I am unsure without tearing one apart of how long the condenser run is.
Over to you?
Thanks in advance...
TM
Can any of you clever folk help me out please?
Some time ago I was asked to inspect and report on a compact medical fridge built in China and supplied to the UK for distribution to UK pharmacies, doctors surgeries and rest homes etc.
Think table top fridge with a digital control and alarm.
The original was built with an R134a compressor, skin condenser. Was a bad design all-around.
I was asked for my opinions on the unit that was running to long and poor cooling efficiency.
I suggested many design changes and my main conclusion was that R600a should be adopted over R134a.
The unit has now been re-designed by the Chineses factory, including changing the compressor and system to R600a.
However, the factory have simply changed the compressor from R134a to R600a and kept the charge the same at 45g.
The first problems are that the systems, now charged at the same weight qt 45g is overcharged. This has resulted in a few major issues.
A Frosting on suction line
B Initial cooling, very efficient, cycle off time too long.
C High temperatures (in excess of +65c) on the side walls of the cabinet
I have attempted to optimise the refrigerant charge to that of an R600a system.
But the main problem that remains is that the surface temperature of the outside of the cabinet remains too high.
My thoughts are without testing is that......
The cheap chinese compressors are generating too much heat?
I am going to ask the client for permission to fit as test European compressor, for example a Danfoss TLES4.
But I am asking your advice first.
I am unsure without tearing one apart of how long the condenser run is.
Over to you?
Thanks in advance...
TM