Air Conditioning Nairobi, Refrigerating The Planet

Guest Post by Willis Eschenbach

I’ve mentioned before that a thunderstorm functions as a natural refrigeration system. I’d like to explain in a bit more detail what I mean by that. However, let me start by explaining my credentials as regards my knowledge of refrigeration.

The simplest explanation of my refrigeration credentials is that I have none at all. As with many trades I’ve pursued, I have no training in refrigeration. But the challenge was simple. When I was 37, a good friend of mine and I had taken the job of installing a blast freezer system in a 60′ (18m) steel sailboat in Fiji called the Askoy. I was sure we could do it … despite the fact that at that point in my life, neither of us had ever taken apart a refrigerator, or could even explain how a refrigerator worked.

Figure 1. The Challenge SOURCE

But we had two months before the job started, and one rule of thumb has never failed me—Do Your Homework …

I was laughing about this with my friend this afternoon. We’ve been partners in various oceanic ventures and adventures over the last forty years. He reminded me that I’d bought my refrigeration gauges and my Freon sniffer at the local flea market. I’d forgotten that detail. He was to do the metalwork, the piping and the soldering and such, while I had to design the system and charge it and get it working. We discussed our ignorance at the time, and he said “I never had any doubt that you’d do the refrigeration part.” I laughed and said “I never had any doubt that you’d do the metalwork part.”

I learned refrigeration the old-fashioned way. I taught myself.

WARNING—this post is a 50/50 mixture of science and autobiography, call it autosciography. If that makes your brain explode, DO NOT continue reading.

I went to a technical bookstore in San Francisco and bought a college refrigeration textbook, and a refrigeration technicians textbook. I started with the college refrigeration text, just like I was in college again. I read every word of every chapter, and then I answered all of the questions at the end of each chapter. I went back on the ones I missed until I understood them as well. At the end of the first month I could knowledgeably discuss superheat and the difference between the kinds of Freon and other refrigerants and how different types of refrigeration systems and heat pumps worked and what the units called “tons” measure in refrigeration (the cooling power equivalent to the melting of 2,000 pounds of ice starting at 0°C in 24 hours).

Then once I understood the theory backwards and forwards, I got out my refrigeration gauges and my sniffer, and I found some old refrigeration systems and I started working through the refrigeration technicians manual. By the end of the second month I could test and charge and repair a system, fine tune the setup, discharge the system and recapture the Freon, tear it down and build it again, whatever you wanted. I was ready to go. (Yes, there are other refrigerants besides Freon. But in 1981, for the kind of refrigeration I was doing, it was all Freon.)

So that’s how I learned about refrigeration, and my friend did the same regarding the metalworking and silver soldering and all the rest of the knowledge he needed. And after we finished the installation of the blast freezer, I subsequently made good money at various times diagnosing and repairing marine refrigeration systems. I’ll return to the question of my credentials and the lack thereof in a bit. But first, for those who like me couldn’t explain how a refrigeration system works, here’s my explanation.

A refrigerator cools things in exactly the same way that sweating cools your body—by evaporation. Of course instead of using water like your body does, a refrigerator uses Freon, or one of the modern refrigerants. But the principle is exactly the same regardless of the “working fluid”. You use an evaporating liquid to remove the heat from whatever you want to cool down.

Now, if the working fluid is actually boiling, you get the maximum evaporation. So for a particular refrigeration application, you might pick a liquid (one of the various Freons in the old days, now other liquids) that boils at say ten degrees below freezing.

Of course, your body uses up the water that cools us when we sweat. We don’t try to recapture that water, it condenses somewhere else.

But we don’t want to waste valuable Freon. We’d rather condense it back to a liquid. One way to do that, of course, is to pipe the vapor to some cold place, where it naturally condenses back into a liquid. In The Inventions of Daedalus, the eponymous author propounds another of his crack-brained but plausible schemes, this one for air conditioning Nairobi by running the vapor up to the top of Kilimanjaro, where it would condense and run back down by gravity. Here’s my sketch of his plan:

Figure 2. Daedalus’s plan for air-conditioning Nairobi (click to expand). The working fluid boils at say 5°C (41°F). The liquid return pipe is insulated so the fluid doesn’t boil on the return path to the evaporator.

The working fluid boils in the evaporator on the lower left. The evaporator is like a car radiator, and a fan blows through it, and the resulting cool air is used to air condition Nairobi.

The vapor then moves up to the top of Kilimanjaro, where a condenser (also looks like a car radiator) has icy natural winds blowing through it to condense the liquid. This liquid then flows by gravity down an insulated tube and back to Nairobi to start the cycle again. And like most of Daedalus’s inventions, there’s no reason you couldn’t actually build that.

Now, that’s the basic principle underlying how a refrigeration system works. A liquid turns to a vapor, absorbing heat in the process. This is called “latent heat”, because it doesn’t increase the temperature.

That vapor, containing the latent heat, is piped away from the object you want to refrigerate. Then somewhere else, it’s condensed back to a liquid, and in the process releasing the latent heat as sensible heat. Finally, the liquid is returned to the original location, to repeat the cycle.

Note the importance of the two phase changes in the process—evaporation (picking up latent heat) and condensation (releasing that latent heat elsewhere as sensible heat). Those two processes, evaporation and condensation, are the central part of the whole process of refrigeration. It’s just a very efficient way to move heat from A to B.

Now, consider Figure 3, which shows what a tropical thunderstorm is doing, and how it functions as a refrigeration system.

Down at the surface, the water is evaporating and refrigerating the surface. The thunderstorm forms over a local hot spot. The evaporation cools the surface, and the energy is transferred to the air as latent heat. The hot, moisture-laden air moves upwards.

Up at an elevation above the “lifting condensation level”, which is the elevation of the base of the clouds where condensation begins, the water condenses into larger and larger droplets. The latent heat is released back into the air as sensible heat. The water then falls as rain, to complete the cycle.

Figure 3. Natural refrigeration system. Just as in a domestic refrigerator, a working fluid (in this case water) is evaporated to remove heat from the surface, the area to be refrigerated. After rising up into the thunderstorm, the water is condensed, releasing the latent heat as sensible heat.

As you can see, this is the same system that Daedalus proposes to air condition Nairobi. It uses the same principle as your home refrigerator. Evaporation cools what you want cooled, and somewhere else, you condense the working fluid and get rid of the heat.

Now, let me start by making one thing crystal clear.

THIS IS NOT A FEEDBACK!!!

Instead, it is a natural refrigeration system, capable of cooling the surface well below its starting temperature. Treating it mathematically as a feedback is a huge mistake. It is nothing of the sort. It is a threshold-based emergent phenomenon which actively refrigerates the surface.

[UPDATE: In the comments, people have been confused by this question of feedbacks. Obviously I was not clear enough. When I say it is not a feedback, I mean it is not a simple linear feedback of the only kind considered by the IPCC. Instead, it is a control system which utilizes feedbacks of a host of kinds to maintain a constant temperature. -w.]

Not only that, but it selectively refrigerates the hot spots, forming just where it is needed. As a result, it is very difficult to represent by averages. This is especially true because its response time is minutes to hours, not days. The hot spot doesn’t really have time to get going before it is refrigerated into submission.

It gets better, much better. You see, up until now, I’ve just described the parts of the system that correspond exactly to manmade refrigeration systems. Let me point to some very clever wrinkles that thunderstorms use to increase their refrigeration capacities and to cool the surface more efficiently and more widely.

• Wind

The thunderstorm generates wind at its base, and evaporation is proportional to wind speed. If the wind underneath the storm cloud increases from say 5 knots to 20 knots, or say from 2 m/sec to 8 m/sec, evaporation goes up by a factor of 20 / 5 = four-fold. In other words, the self-generated wind alone multiplies the strength of the refrigeration by about four.

In addition, the wind increases the evaporative area by blowing water into the air as spray and fine droplets. These have a large surface area and evaporate rapidly. This also increases the strength of the refrigeration.

• Dual fuel

Thunderstorms run on both temperature and moisture. Moist air is lighter than dry air. The four-fold increase in evaporation yields a proportional increase in the vertical speed of the air moving through the thunderstorm, because it is much lighter. It also keeps the thunderstorm from dying out if the temperature drops, because once the wind starts, the moist air is light enough to keep the thunderstorm going until the surface temperature falls to well below the temperature required for initiation.

• Direct surface refrigeration by cold working fluid.

In most manmade refrigerators, evaporation is the only mechanism for cooling the objects to be refrigerated. The working fluid is not used directly to cool down what is being refrigerated. Instead, it’s brought to the evaporator in an insulated tube and immediately evaporated to carry away the heat.

But in addition to the evaporation, a thunderstorm also delivers large quantities of chilled water directly to the surface. This is a separate and distinct refrigeration mechanism, one not generally utilized in manmade refrigerators.

• Refrigeration via entrained wind.

You’d expect that the rain would warm as it fell through the warmer lower atmosphere, and to some extent it does. But it also entrains the air around it as it is falling, carrying it along. This sets up a vertical entrained wind that falls right along with the rain. That wind is constantly cooled as it falls by the evaporation of the rain that it is mixed in with. And since the rain and the chilled air fall together as a package from aloft, they both arrive at the surface much cooler than the surroundings. Often when standing out on the apartment deck in the Solomon Islands at night, the first sign of the approach of a thunderstorm would be the arrival of the cool entrained wind.

The entrained wind falls vertically with the rain, but unlike the rain it’s not absorbed by the surface. So it blows out cold air horizontally in all directions from the base of the rainfall. This blast of cool air is quite distinct. It smells of the upper atmosphere where it originated, and it is very refreshing on a hot night. It is also a separate and distinct refrigeration mechanism.

• Re-use of heat of condensation.

This one is sometimes done in manmade installations. In the thunderstorm, the heat is used to drive and sustain the building of the “tower”, the tall vertical part of the cumulonimbus cloud. This in turn increases the speed of the upward flow through the core of the thunderstorm, and allows for the possibility of another phase change.

• Increased Radiative Heat Loss

Each thunderstorm is surrounded by an area of descending dry air. The moisture has been removed from the air, first in the form of rain and then in large thunderstorms in the form of ice. Because little water vapor remains, much more of the upwelling surface longwave (thermal) radiation will escape to space.

• Additional phase change

It would certainly be possible for humans to design a system using a second phase change in the working fluid. Right now, our refrigeration systems utilize the phase change from gas to liquid and back again. But there’s another possibility, to go from gas to liquid to solid and back again.

The advantage is that you can move more heat that way. Instead of just the heat from one phase change, you could move the heat from two phase changes as latent heat.

So why don’t humans utilize both phase changes for extra efficiency? Well, we haven’t figured out an easy way to get the solid working fluid from wherever it was frozen, back to the evaporator to start the story over. I mean, we could freeze the Freon after it’s condensed into a liquid … but then how do we move solid Freon back to the evaporator to continue the cycle? With wheelbarrows?

Nature doesn’t mind these small problems, however. Nature continues to cool the water past the point where it condenses, and all the way to where it freezes … and then it uses gravity to return the solid working fluid back to the surface as frozen water. I can only bow my head in awe, what a clever setup. At the surface the ice will first melt (cooling the surface) and then warm up to the local temperature (further cooling the surface) and then evaporate to continue the cycle.

• Inter-storm coupling.

When the need for surface refrigeration gets high (anomalously warm surface temperatures), a new emergent pattern appears. The thunderstorms start to align themselves in long rows, called “squall lines”. These in turn have long canyons of descending air between them. This is a type of Rayleigh-Bénard circulation that greatly increases the throughput, and thus the refrigeration capacity, of the mass of thunderstorms.

CONCLUSIONS

• At all times and all around the planet, thunderstorms are constantly refrigerating tropical hot spots to prevent the globe from overheating. This constant refrigeration is what controls the surface temperature of the planet, not CO2. If this refrigeration system failed even for a week, we’d fry.

• The thunderstorm refrigeration system utilizes the same familiar principles of manmade refrigeration—evaporation removes the heat from what you want to refrigerate, and condensation gets rid of the heat somewhere else.

• In addition, the thunderstorm refrigeration system utilizes some unfamiliar processes, all of which combine to greatly increase the refrigeration capacity of a given thunderstorm.

• The refrigeration is selective, responding to local temperature—the hot spots get refrigerated until they confess, and the cold spots get nothing.

• The current generation of climate models deal with feedbacks. This is nothing of the sort. It is an emergent mobile self-sustaining refrigeration system, not a feedback of any kind. It needs to be analyzed as such, and it is very difficult to do so by means of parameters or averages.

• The system responds to temperature. It is not driven by the forcing, nor does it respond to areas of high forcing. Instead, it actively responds to surface temperatures. The formation of a local hot spot is quickly followed by the formation of a corresponding refrigeration system to cool the hot spot down.

• The system is extremely sensitive to the formation of local hot spots. It puts a refrigeration unit right to work on the problem. On the other hand, it is indifferent as to the cause of the hot spot. It chills them all the same.

• In addition, the surface temperature of the system is relatively insensitive to the number of hot spots—you just get more or less refrigerators to match the number of hot spots, and that keeps the temperatures within bounds. And this in turn means that the surface temperature of the system is relatively insensitive to the forcing.

• As a result, the system doesn’t care about CO2, or about small variations in the sun, or about the effect of volcanoes. The threshold for refrigerator formation is based on surface temperature, not on CO2. If there are more hot spots, the system simply makes more refrigerators, whether the hot spots are from CO2 or from a clearing of the aerosols or from a 5% increase in sun strength over a billion years.

• In such a system, the idea of “climate sensitivity” doesn’t go anywhere or mean anything. The system is relatively insensitive to the forcing, not sensitive. The system responds to hot spots by building refrigerators … and as a result the surface temperature is maintained despite variations in the forcing. The problem is not that the relationship is non-linear. In a thermostatically governed system such as the climate there often may be no relation all between forcing and temperature.

• This is a relatively simplified (but very accurate) explanation only one of a host of interlocking emergent phenomena that maintain the surface temperature within ± half a degree in a hundred years. Yes, there are lots of details I’ve left out, and manmade refrigeration systems have other valves, bells and whistles … if you’re interested lets discuss them, but please don’t bust me for leaving them out.

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That’s what I wanted to say about refrigerators and thunderstorms. When you are analyzing our climate, which contains powerful emergent refrigeration systems like thunderstorms, you can’t analyze them as a feedback. It’s very difficult to parameterize them. You have to get out your refrigeration tables and analyze them as what they are, huge natural refrigeration units, and very efficient ones at that.  My takeaway message is this:

The surface temperature of our amazing planet is set and maintained by the constant refrigeration of the surface hot spots as they form, not by the forcing, whether from CO2 or anything else. 

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To close, earlier I said I’d return to the question of my credentials for talking about refrigeration. Well, before we went to Fiji my friend and I researched the available marine refrigeration systems. We went and talked to the people freezing the product and saw what they used. Harlow, the owner of the boat, wanted to be able to purchase and process what they call “crayfish”, the tropical ocean lobster. To do that, you want to flash-freeze them with a wind colder than 40° below zero or so (either -40°C or -40°F, they’re the same). They need to be snap-frozen, an ordinary freezer won’t do it.

So my friend and I located a killer packaged refrigeration unit, all assembled, self-contained, ready to go. We could bolt it in and go processing in a couple weeks, because that was the dream. We’d finish the freezer and go processing crayfish around the tropical South Pacific … what’s not to like? So we went down to Fiji. Harlow was going to buy the packaged unit and bring it down.

But Harlow decided he knew better. So he shows up in Fiji with a refrigeration compressor, and an evaporator, and a condenser, and some fittings and valves and pipe, and tells us he wants it built from scratch. Oh, and he wants it water-cooled, not air-cooled. Oh, and not driven electrically, but run off a “lay-shaft”, a separate shaft driven by the main engine which drives other machinery in turn.

Ooooooh kaaaaay … we can do that, Harlow, but it’s gonna take a while.

So for my very first refrigeration project, my friend and I got to design and build an entire marine engine-driven commercial-type blast freezer system with a water-cooled condenser … from scratch, from the individual pieces. Might as well set the bar high, I figure …

So I got out my texts and tables and designed it up, and we got started, nothing else to do. We built the lay-shaft, and installed the refrigeration piping from the engine room up forward to the freezer room, belt-drove the lay-shaft off the main engine, and then got the water pump and the refrigeration compressor to run off the lay-shaft, and laid out and cut and soldered and tested all of the piping, and that’s only a tiny fraction of all of the tasks … in a foreign country, with not a whole lot of refrigeration parts available, and no instruction manual.

Like we warned Harlow, it took a while, just about six months to do it, with my gorgeous ex-fiancee serving as the ship’s cook and nurse and general hard worker. But finally, after scraping Suva dry of various refrigeration parts and pieces, one fine day I charged up the system, and we gave it the first test … and the wind off of that blast freezer was at -50°F (-46C) just like we planned. Indeed, the blast freezer worked like a champ. As long as the main engine was on it could be clutched in or out to run it, and the lay-shaft could also be driven by the auxiliary engine to keep the freezer hold and the seafood frozen if the main engine died. It was a sweet rig.

So naturally, Harlow decided that we should have a party to celebrate, and we were all up for the plan. We’d been anchored right offshore from the Royal Suva Yacht Club the whole time, so we invited everyone.

There was a trimaran owned by a friend at the Yacht Club at the time, so we tied her up alongside the Askoy. That was for the big wide stable dance floor, we hung speakers from the rigging on each side. Our friend Doc Lowry used his 28′ open skiff as the shore boat, to bring out loads and loads of people from the Yacht Club dock. He spent most of the night moving folks from the Club to the party and back again … then out to the party again …

As each person arrived, we took them a couple at a time down into the blast freezer. You entered through a hatch in the deck, and down below it was cold, cold, cold. I had put a number of bottles of vodka into a basket right in front of the blast of the freezer. I stuck a thermometer through the cap in one of them, it registered minus thirty degrees … I still have a picture of it around here somewhere. [UPDATE—found the picture. You can see the red indication.]

So as each person came down into the freezer, we’d prop them up in front of the wintry blast. The wind was strong, and blowing at minus fifty degrees F. Most of these folks were Fijians, who had never seen any place that was as cold as plus 50°F (10°C), much less minus 50°F. They started shivering as soon as they got inside, they’d never in their lives felt a wind at minus fifty. So I or their other host of the moment would pour each person a reasonable glass of pure vodka at minus thirty degrees.

Vodka at that temperature hardly has any taste, and the folks were in a hurry to get out of that damned freezing cold, so they’d drink it down straight like it was water … then we’d take them back out into the balmy tropical night. They’d get about ten steps across the Askoy deck, maybe somebody would pull them onto the dance floor, maybe not, but in either case, a few steps later, the combination of the initial freezing cold wind, the vodka, and the subsequent heat would make their knees wobbly and their eyeballs jiggle, and the Askoy Freezer Party got just that much merrier. The Yacht Club Bar eventually closed, and the bar guys and the Club office ladies joined the party. People kept arriving. Big Jenny showed up at three AM and shouted “Am I late?”

“No, party just starting, girl!” We took her into the freezer and gave her a double shot, and indeed the party restarted when she came back out.

I’ve not been to too many parties like that one. Rumor had it that it resulted in one marriage and a couple of divorces. Both a wallet and a set of eyeglasses committed suicide by jumping into the Suva Harbour sometime during the night.The amount of debris on the deck and the dance floor was overwhelming. And me, I proved it was a magical party. By the end of the night I was so drunk that shortly before dawn I went to sleep on a nice, soft pile of rope I’d discovered up front near the bow of the boat. It was covered by some gunny sacks, and I nestled in and got comfortable and was gone.

When I woke up, though, I sadly concluded that some ungrateful bastard must’ve replaced the rope while I was sleeping, because I found I was nestled on the usual pile of Askoy anchor chain … in its usual spot up in the bow … covered up as always with dirty gunny sacks …

Sleeping on chain, I found out, makes a man say very bad words upon awakening. If you are given an alternative mattress choice, say a bed of nails, or a small barnyard stall with two chickens and a rabid goat, I’d advise taking it. Plus it seemed that the entire Fijian mosquito tribe had taken advantage of the party to do some in-flight refueling. My body was royally whupped in the morning, big anchor chain marks and dents in my hips and side, covered in mosquito bites.

But I didn’t care a bit. The freezer was done, the icy blast off the evaporator was at minus fifty, the vodka had been at minus thirty to forty all night long, the party was a success, and my gorgeous ex-fiancée and I had danced away the night.

And that’s all there is to my refrigeration credentials. Well, except for several times after that, when I made money fixing various non-operating sailboat refrigeration systems.

Regards to everyone,

w.