Small BLDC refrigeration compressors

[AntarcticPilot]

I posted this on a refrigeration thread, but it didn't attract any interest, but I'd be interested to know what people think.

I've seen various adverts for a mini compressor unit (like this: https://www.alibaba.com/product-deta...136562159.html). They look ideal for fitting to an existing cold box - most of the kits by Waeco etc. are complete overkill for what is required. Does anyone sell a complete kit incorporating these compressors? Filling a system isn't a DIY job, and sourcing and matching evaporators and radiators and control units isn't simple, either.

To me, these compressors look like the perfect answer to adding refrigeration to a smallish built-in cold box; low power, compact and efficient. But without there being a full kit like the Waeco ones, they aren't a practical solution.

 

[lw395]

Here's one in bits:
http://www.xtremesystems.org/forums...-What-s-inside-an-Aspen-1-9cc-mini-compressor
They've been around quite a few years.
It is, at the end of the day, a 12V motor and a compressor. Just a brushless motor running in the refrigerant presumably?
It seems there are similar things used in water coolers.

They are about 100W power in. I think my dehumidifier might be about 250W. Domestic fridges similar?

 

[pcatterall]

Also interested in locating a less expensive kit. The one described seems just a bit too small though. I did consider cannibalising a tatty working 220v fridge and sourcing some of those snap on connectors. It would be for a second cool box on board and to be used with shore power though operating at time through a transformer could be possible. It always seems that when 12 volts is needed the price trebles. I guess this is simply because so few 12 volts are made compared to 220?

edit..... we could cool off in the med by donning a space suit and wearing one of those mini compressors though!!

 

[AntarcticPilot]

Also interested in locating a less expensive kit. The one described seems just a bit too small though. I did consider cannibalising a tatty working 220v fridge and sourcing some of those snap on connectors. It would be for a second cool box on board and to be used with shore power though operating at time through a transformer could be possible. It always seems that when 12 volts is needed the price trebles. I guess this is simply because so few 12 volts are made compared to 220?

edit..... we could cool off in the med by donning a space suit and wearing one of those mini compressors though!!

It's actually of comparable capacity to much larger devices. For my purposes, though, it would be fine - my cold box is only a couple of cubic feet.

 

[superheat6k]

All hermetic compressors use brushless motors within the fridge circuit, because the refrigerant is a good dielectric (non conductor). These offer a cooling performance of up to 450 w, which would easily satisfy a small - medium cool box. The bigger issue is where that heat is going, and this means for optimum efficiency a water cooled condenser.

I'm not sure that despite its small size it isn't doing much less than a typical Danfoss 12v piston compressor. Its key advantage is its small size. But Alibaba sellers are looking to offer 300,000 pieces so not sure they will be the interested in a typical boater's requirement for 1 or at most 2 pieces.

 

[pcatterall]

All hermetic compressors use brushless motors within the fridge circuit, because the refrigerant is a good dielectric (non conductor). These offer a cooling performance of up to 450 w, which would easily satisfy a small - medium cool box. The bigger issue is where that heat is going, and this means for optimum efficiency a water cooled condenser.
.

So, is there more heat generated with these versus piston compressors ? would a small fan, and decent ducted airspace not suffice for cooling?

 

[lw395]

So, is there more heat generated with these versus piston compressors ? would a small fan, and decent ducted airspace not suffice for cooling?

Whatever compressor you have, the system is much more efficient pumping heat from -5 to +20 (?) of the sea than pumping heat into air at 40 degrees. In the Med, it's extra heat (and fan noise) that's unwelcome in the cabin. Less of an issue in the UK perhaps?

 

[AntarcticPilot]

Whatever compressor you have, the system is much more efficient pumping heat from -5 to +20 (?) of the sea than pumping heat into air at 40 degrees. In the Med, it's extra heat (and fan noise) that's unwelcome in the cabin. Less of an issue in the UK perhaps?

Just to clarify, I'm in the UK, so high air temperatures aren't a big problem!

There are suppliers who provide them in one-off quantities at around $100 each (haven't spotted a UK supplier). But what I'm looking for is a complete system like the Waeco ones, not individual bits. I'm not competent to fill such a system, and these small compressors are sensitive to the amount of oil, apparently.

 

[pcatterall]

Just to clarify, I'm in the UK, so high air temperatures aren't a big problem!

There are suppliers who provide them in one-off quantities at around $100 each (haven't spotted a UK supplier). But what I'm looking for is a complete system like the Waeco ones, not individual bits. I'm not competent to fill such a system, and these small compressors are sensitive to the amount of oil, apparently.

Yes, with you on this! lw395 makes a good point as we are in the med but it has to be balanced by issues and sea water cooling, more holes another pump, cost. with the unit outside the accommodation and a low power fan cost can be less and heat dissipated ok.

 

[superheat6k]

So, is there more heat generated with these versus piston compressors ? would a small fan, and decent ducted airspace not suffice for cooling?

The heat is not generated as such, the gas is compressed and the heat transfer occurs from the sensible heat of the compression (including the effect of the work done by the drive motor which is the energy in to the system), and considerably more so from the latent heat effect of the condensation (warm area heat rejection) and evaporation (cold area heat absorption) processes. Rotary compressors have less wasted mechanical movement than a piston compressor so will likely be slightly more efficient, so marginally more perhaps, but without data to compare difficult to be too precise.

An important consideration in any heat pump system (all fridges are heat pumps), is that in heating mode the input energy is added to the sensible and latent heat gains of compression, increasing the efficiency by one full EER point, whereas in cooling only the sensible and latent gains of compression are effective. In other words the condenser rejects the cooling energy plus the input energy, whereas the evaporator only absorbs the cooling energy.