Medical Fridge - Made in China - Re-spec - R134a - R600a

[teemyob]

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

[mikeref]

Medical fridges are supposed to be fan forced at the evaporator, even product temperature required throughout. Then,not only is the assembly, (cabinet, inside and out) to be made of stainless steel, but the condenser is to be separate, as in the external static, but most commonly forced draft as well. Insulation also has a minimum thickness.Seems to me you have something like, (what Aussies call) a bar fridge. Small and handy fridge that motels have in the rooms :cool:
So correct me if i'm wrong and it looks nothing like this, however, a refrigerant charge of this size cannot make it very big in storage capacity, and the replacement of the compressor will do little to help with "skin" temperature. Might have better results with a compressor cooling fan. Outer limits for ,say, Vaccines is +2 to +8 degrees C.


Hope this can help you..Mike.

[chemi-cool]

[QUOTE=teemyob;254663 compact medical fridge built in China
. bad design all-around.

poor cooling efficiency.


The cheap chinese compressors are generating too much heat?
.

TM[/QUOTE]

Read your lines again, your answer is in your words.

[desA]

Looks like you have become the ?unpaid? designer for the Chinese manufacturer. :)

[monkey spanners]

Thermal imaging camera will show the size and shape of the condenser.

How important are the patients whos medicine will be stored in these things...

[teemyob]

Thanks for the replies.

The units are going out to Chemists, doctors surgeries and Nursing homes.

They are complaining of excessive heat on the sides (I think what makes the situation worse is that the end users think it is electrical energy and are shutting them off.

TM

[al]

Given that these fridges end up "built in", heat rejection through the sides is dopey, rear condenser (with or without fan), interior with small fan (frost free), run at 4c with 2c differential.

al

[mikeref]

The internal condenser pipe's contact to the outer skin is only a fraction of the pipe's potential to radiate heat.
So 355 of 360 degrees of the pipe exterior has no-where to radiate the heat except into the insulation. Pathetic! :(

[spimps]

Thanks for the replies.

The units are going out to Chemists, doctors surgeries and Nursing homes.

They are complaining of excessive heat on the sides (I think what makes the situation worse is that the end users think it is electrical energy and are shutting them off.

TM

Seems crazy to buy/supply cheap stuff when in my experience they can contain as much as £5000 worth of drugs per 7 ft cu capacity fridge,with drugs costing £3000 a month for some patients so a couple of those in a medical fridge high lights the value of a decent appliance being needed.
It's the recovery time as well that is an issue not to mention the core temp of items,open door whilst loading,
and searching for items in a high temp ambient plus they have the doors open listing and checking stuff for extended periods,not to mention the PANIC when they they check the temps shortly after nd it's high, so without an internal fan would be basically pants.
Had one similar to what you described built into a kitchen type cupboard (would have been great for proving dough) got them to free stand it until they could find a reliable one with electronic control and alarm ststem.

[mikeref]

Good post Spimps. Every time the door is opened, the cold air spills out and is replaced with warm air. More often than not, the air temperature sensor is placed in it's own "Box" to prevent short cycling of compressor.Before i get hammered on that point, the "box" is empty inside, only air is present ;) Small cabinets have a 100% air change when the door is opened and the person going in there will shuffle a few items around before obtaining what they are after :(