Refrigerant Control in 1930's Refrigerators

[marx290]

A blog post with some pictures of refrigerators in the mid 1930s. Very cool stuff. The capillary tube was still kind of new and so was the thermostatic expansion valve. The Low side float gravity flooded evaporator was still around, but I think manufacturers were turning toward high side floats. Anyways...

1930s Household Refrigerators | musings on entropy

[NiHaoMike]

My friend Brittany Benzaia experimented with a low side float in her hybrid A/C that uses water as a refrigerant. I remember her saying that it worked just as well as or better than the high tech alternatives (electronically controlled expansion valves of various types) she tried and thus would most likely be what would be used in production. As an added benefit, it was easy to make it pose little resistance to flow when fully open which, when combined with the free-flowing centrifugal compressor, allowed it to have a very efficient bypass mode (turn off the compressor and let the refrigerant flow by gravity) that transitions smoothly to and from normal operation.

So amongst all the microchips, high voltage transistors, and an extremely fast and precise spinning wheel inside the compressor, there's that rather important part of the machine that operates exactly like the mechanism in a toilet tank...

[marx290]

That's very cool that someone is playing with low side floats. As far as I can tell, their use today seams limited to large industrial chillers. What exactly was her application?

Very cool to see a girl interested in refrigeration! Kind of a rarity for some reason, and going rogue with a float valve no less!

There are many advantageous features of a regulated, gravity flooded evaporator such as the low pressure drop as you noted. Also, most sources mention that they are more effective at absorbing heat because the heat transferring surface is very well wetted throughout. Of course, they ar fully flooded as well in the sense that implemented properly, they produce very little superheat and have the advantage of separating liquid refrigerant from being drawn into the suction line.

Drawbacks are the large refrigerant charge (which has positive effects depending on how you look at it), potential for oil logging in the evaporator and the lack of knowledge and equipment for implementing them. There are some reliability issues to overcome with a low side float too, but a mechanical float valve is not the only way to regulate liquid level in the evaporator.

Here's some more machines from the 1920s

[NiHaoMike]

From my understanding, she built an air conditioner that could operate as an indirect evaporative cooler or as a normal A/C with an evaporative condenser. What was notable was the use of water as a refrigerant, which had problems with needing a very high volume flow rate to get a usable capacity due to its low vapor pressure. The flow rate of a compressor increases with RPM, so her solution was to use a compressor that spins extremely fast (up to 100k RPMs or more, as opposed to 3600 RPM for a conventional compressor) in order to get the needed flow rate in a compact unit. Also notable was the use of a switched reluctance motor, which interestingly was invented over 150 years ago, but wasn't widely used due to limitations in control technology.

The large refrigerant charge is not an issue when even distilled water is dirt cheap. Lubrication is indeed one of the harder problems to solve, and it's one of her trade secrets. But still, 40 SEER equivalent with the most environmentally friendly refrigerant is setting a new future for energy efficiency, though mass producing that compressor is going to be a tough problem to solve...

[AC_Hacker]

Originally Posted by NiHaoMike

My friend Brittany Benzaia experimented with a low side float in her hybrid A/C that uses water as a refrigerant...

I did an Internet search for 'Brittany Benzaia'. Anytime I include such terms as:

• water
• refrigerant
• hybrid
• etc.

...the only hits I get are you telling this same story on other blogs.

Does this person actually exist?

Are there reports or diagrams or photos of her work?

-AC

[NiHaoMike]

She definitely exists. As for further details, I wasn't allowed to take pictures of the device due to IP concerns, but I am allowed to tell what I know and (of course) speculate about the details of how it works. I see the problem of manufacturing the compressor as being the hardest to solve (no doubt a lot of IP hiding inside it) so I actually plan to beat her to it by developing a hybrid A/C that uses a conventional compressor and refrigerant.

[marx290]

Yeah, NiHaoMike, that high speed compressor seems like quite the hurdle to overcome. I would love to see some DIY work on a hybrid system that uses more common components.

I don't have much need for AC here in the North West, but that hasn't stopped me from daydreaming about different schemes to cool a condenser. I would think to build an evaporative cooler would require a sensible source of water like rainwater catchment or some filtered waste stream of some sort. What are your thoughts on water source?

Also, are there issues with corrosion when dealing with water, copper and aluminum, or does such a device require more inert materials like SS?

[NiHaoMike]

Her unit just uses tap water, and so do most of the larger versions that are used in commercial and industrial applications. The interesting part is that it often takes a surprising amount of water to generate electricity, so chances are high that the overall water usage is much lower than for a conventional A/C. (Technically, the water isn't truly "used", since it just goes into the atmosphere to fall back as rain.)

[marx290]

I can appreciate your point about the quantity of water it takes to generate electricity. I'm sure it's quite large. With all the losses in generation, transmission and compressor motor coil windings, only reinforces the point that conventional AC wastes a lot of resources unnecessarily.

I don't have a any problem with using water in an evaporative sense; I know it is just going to condense somewhere else later. There are a lot of resources that go into producing a potable fresh water supply and since fresh water is becoming harder to come by, I would think utilizing a secondary source of water might be the responsible thing to do. That is why I suggested rainwater. But, in those large, thirsty operations, I can see why they use the potable water supply for the security, convenience and lower power consumption.

Have you done any work with evaporative cooling?

As I would understand it, water is very much a refrigerant in every sense of the word here. I guess that's fairly obvious, but it seems that it's rarely mentioned.