lenny flank
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I've begun working on the manuscript for the follow-up to my van-dwelling book, and one of the topics I want to cover are these alternatives to air conditioners. So here's what I got so far. I welcome any additions, subtractions, corrections anyone has. 
Fortunately, modern technology has invented a device that uses energy to pump the heat out of an enclosed area and actively cool it: “air conditioners” work on the basic physical principle that air gets hotter when it is compressed and gets cooler when it expands. They have revolutionized modern life.
Unfortunately, however, most van-dwellers will find it impractical to have an effective AC unit in their van. Even the smallest and most efficient models use a lot of electricity, and most vans will not have the space (and most van-dwellers will not have the money) for a sufficient solar panel capacity to run an AC long enough to be useful. It may be possible to power an AC effectively with shore power or with a generator, but that presents logistical problems of its own.
So some van-dwellers instead attempt to turn towards alternatives to the electric air conditioner, and two of these are the “ice fan” and the “swamp cooler”. In any van-dwelling forum, when the topic of “staying cool in the van” comes up, a number of people are certain to point to these devices. But while any number of people may suggest using one or the other, one finds very few people indeed who are actually using one in their van. And there’s a crushingly simple reason for that: they are not likely to work well for most van-dwellers.
Some sciencey stuff:
Water, like all matter, exists in three “phases”: solid ice, liquid water, and gaseous water vapor. These phases represent different levels of energy: to go from a lower phase to a higher one (such as melting solid ice into liquid water) requires that heat energy be added to the material, while going from a higher phase to a lower (such as condensing gaseous water vapor into liquid water) requires that heat energy be removed and released from the material.
We can illustrate this principle with the example of one of the simplest of all cooling systems (and the one that I happen to use during hot nights in the van): putting on a water-soaked t-shirt and directing an electric fan at you. As the moving air hits the water in the t-shirt, it causes the liquid to evaporate—i.e., to undergo a phase change from liquid to gas. This requires that energy be added to the liquid water to change it into a gaseous water vapor. The water molecules get this energy by extracting it from the surrounding air, which in turn lowers that air’s temperature and cools you off in the process.
The “ice fan” uses the same basic principle: in this setup, an electric fan blows over a container of ice, which produces cold air by extracting enough heat energy to change from a solid phase to a liquid, by melting. The fan then blows the resulting cold air over you to cool you down.
But the “ice fan” has severe limitations. It operates at a very low energy level and is therefore only capable of cooling the air in the immediate vicinity of the ice bucket: it has no effect at all on the temperature in the rest of the van’s interior (and thus you have to be sitting right next to it to feel any cold air from it). It also presents logistical difficulties in keeping the ice supply constantly replenished. All in all, it is simply not a practical solution—which is why virtually nobody actually uses it.
The “swamp cooler” also uses a phase change to extract heat from the air and cool it, but it is far more practical than the “ice fan”. Indeed, in many hot desert areas, large electrically-operated swamp coolers have largely replaced air conditioners as the preferred method of temperature control in suburban houses. But alas, they have severe limitations that make them unsuited for most van-dwellers.
In effect, the swamp cooler works on the same method as my “fan-on-wet-shirt” does, but on a much larger scale: by blowing a stream of air through a bank of wet material or a mist of water, the cooler produces evaporation which extracts heat from the air and chills it. A steady supply of water keeps the evaporation going continuously, while a fan system blows the cooled air around. Unlike my little fan and t-shirt, which only cools me, commercial swamp cooler units (also called, for reasons that are now obvious, “evaporative coolers”) are powerful enough to cool an entire house. And since they are essentially just a fan or blower and a water pump, they use a lot less electricity than a conventional air conditioner of similar size.
So, why isn’t everyone using evaporative coolers in their vans and RVs? Well, because there are crippling limitations to the system. The evaporative process works by converting liquid water into water vapor, which is absorbed into the air. The ability of a volume of air to absorb water vapor is indicated by its “humidity”—a concept many of us are familiar with from weather forecasts. Humidity is dependent upon many variables such as temperature and altitude, but at a very basic level, the higher the “percent humidity”, the more water vapor the air already holds, and the less it can additionally absorb. When it reaches 100% humidity, it is saturated and cannot hold any more water vapor.
For an evaporative cooler to effectively chill a large area, it must convert a large amount of liquid water into water vapor and extract a correspondingly large amount of heat energy from the air. But adding water vapor to the air increases its humidity, and that increase cannot go past the 100% limit. Further, the higher the temperature of the air, the greater the amount of water vapor it can hold before reaching saturation.
Swamp coolers are most effective, then, when the humidity of the air is already very low and the temperature is very high, allowing large amounts of water vapor to be easily evaporated. Ideally, the best conditions are humidity levels below 20%; they will work pretty well up to around 40%, and as the humidity rises above that they become rapidly less effective. At high humidity, they barely work at all.
And that is a crippling limitation. In areas with even moderate humidity, evaporative coolers simply cannot operate efficiently: in hot and humid areas like Florida, they are completely useless. Only the desert Southwest has the hot and dry environmental conditions that are needed for an effective swamp cooler. In the other three-fourths of the US, they are just not a workable option.
But even in the desert, swamp coolers present practical difficulties for the van-dweller or RVer. Most versions are simply not powerful enough: they produce a stream of cool air which chills the immediate area, but usually have no effect on the temperature in the rest of the van—making them no more effective in practice than my “fan and wet shirt” or an “ice fan”. Swamp coolers require a constant supply of water to operate, and the better they are at cooling the air, the more water they use. They also need a steady airflow to keep them supplied with the hot low-humidity air they need for proper evaporation. If this airflow is insufficient (as it often is in a small confined space like a vehicle), the cooler will be simply blowing humid moisture-laden air into the van, converting your indoors hot and dry desert environment into a hot and damp rainforest environment, making you more miserable and uncomfortable (and soaking everything in the van with condensation).
With its severe practical limitations, therefore, it’s not hard to see why virtually no RVs or camper vans are equipped with evaporative coolers, and why almost nobody uses them.
So how then does a van-dweller deal with day upon day of hot weather? There are, frankly, only two effective ways of beating the heat. If you are mobile, you can simply move to better weather. This will involve either going north to a higher latitude, or going up in elevation to a higher altitude, where it is cooler. If, on the other hand, you are tied to a fixed location and cannot move, your only choice is to not be in the van during the day when it’s hot—spend the day inside somewhere in the air conditioning, and don’t enter the van until evening when it has cooled off enough to be comfortable.
Fortunately, modern technology has invented a device that uses energy to pump the heat out of an enclosed area and actively cool it: “air conditioners” work on the basic physical principle that air gets hotter when it is compressed and gets cooler when it expands. They have revolutionized modern life.
Unfortunately, however, most van-dwellers will find it impractical to have an effective AC unit in their van. Even the smallest and most efficient models use a lot of electricity, and most vans will not have the space (and most van-dwellers will not have the money) for a sufficient solar panel capacity to run an AC long enough to be useful. It may be possible to power an AC effectively with shore power or with a generator, but that presents logistical problems of its own.
So some van-dwellers instead attempt to turn towards alternatives to the electric air conditioner, and two of these are the “ice fan” and the “swamp cooler”. In any van-dwelling forum, when the topic of “staying cool in the van” comes up, a number of people are certain to point to these devices. But while any number of people may suggest using one or the other, one finds very few people indeed who are actually using one in their van. And there’s a crushingly simple reason for that: they are not likely to work well for most van-dwellers.
Some sciencey stuff:
Water, like all matter, exists in three “phases”: solid ice, liquid water, and gaseous water vapor. These phases represent different levels of energy: to go from a lower phase to a higher one (such as melting solid ice into liquid water) requires that heat energy be added to the material, while going from a higher phase to a lower (such as condensing gaseous water vapor into liquid water) requires that heat energy be removed and released from the material.
We can illustrate this principle with the example of one of the simplest of all cooling systems (and the one that I happen to use during hot nights in the van): putting on a water-soaked t-shirt and directing an electric fan at you. As the moving air hits the water in the t-shirt, it causes the liquid to evaporate—i.e., to undergo a phase change from liquid to gas. This requires that energy be added to the liquid water to change it into a gaseous water vapor. The water molecules get this energy by extracting it from the surrounding air, which in turn lowers that air’s temperature and cools you off in the process.
The “ice fan” uses the same basic principle: in this setup, an electric fan blows over a container of ice, which produces cold air by extracting enough heat energy to change from a solid phase to a liquid, by melting. The fan then blows the resulting cold air over you to cool you down.
But the “ice fan” has severe limitations. It operates at a very low energy level and is therefore only capable of cooling the air in the immediate vicinity of the ice bucket: it has no effect at all on the temperature in the rest of the van’s interior (and thus you have to be sitting right next to it to feel any cold air from it). It also presents logistical difficulties in keeping the ice supply constantly replenished. All in all, it is simply not a practical solution—which is why virtually nobody actually uses it.
The “swamp cooler” also uses a phase change to extract heat from the air and cool it, but it is far more practical than the “ice fan”. Indeed, in many hot desert areas, large electrically-operated swamp coolers have largely replaced air conditioners as the preferred method of temperature control in suburban houses. But alas, they have severe limitations that make them unsuited for most van-dwellers.
In effect, the swamp cooler works on the same method as my “fan-on-wet-shirt” does, but on a much larger scale: by blowing a stream of air through a bank of wet material or a mist of water, the cooler produces evaporation which extracts heat from the air and chills it. A steady supply of water keeps the evaporation going continuously, while a fan system blows the cooled air around. Unlike my little fan and t-shirt, which only cools me, commercial swamp cooler units (also called, for reasons that are now obvious, “evaporative coolers”) are powerful enough to cool an entire house. And since they are essentially just a fan or blower and a water pump, they use a lot less electricity than a conventional air conditioner of similar size.
So, why isn’t everyone using evaporative coolers in their vans and RVs? Well, because there are crippling limitations to the system. The evaporative process works by converting liquid water into water vapor, which is absorbed into the air. The ability of a volume of air to absorb water vapor is indicated by its “humidity”—a concept many of us are familiar with from weather forecasts. Humidity is dependent upon many variables such as temperature and altitude, but at a very basic level, the higher the “percent humidity”, the more water vapor the air already holds, and the less it can additionally absorb. When it reaches 100% humidity, it is saturated and cannot hold any more water vapor.
For an evaporative cooler to effectively chill a large area, it must convert a large amount of liquid water into water vapor and extract a correspondingly large amount of heat energy from the air. But adding water vapor to the air increases its humidity, and that increase cannot go past the 100% limit. Further, the higher the temperature of the air, the greater the amount of water vapor it can hold before reaching saturation.
Swamp coolers are most effective, then, when the humidity of the air is already very low and the temperature is very high, allowing large amounts of water vapor to be easily evaporated. Ideally, the best conditions are humidity levels below 20%; they will work pretty well up to around 40%, and as the humidity rises above that they become rapidly less effective. At high humidity, they barely work at all.
And that is a crippling limitation. In areas with even moderate humidity, evaporative coolers simply cannot operate efficiently: in hot and humid areas like Florida, they are completely useless. Only the desert Southwest has the hot and dry environmental conditions that are needed for an effective swamp cooler. In the other three-fourths of the US, they are just not a workable option.
But even in the desert, swamp coolers present practical difficulties for the van-dweller or RVer. Most versions are simply not powerful enough: they produce a stream of cool air which chills the immediate area, but usually have no effect on the temperature in the rest of the van—making them no more effective in practice than my “fan and wet shirt” or an “ice fan”. Swamp coolers require a constant supply of water to operate, and the better they are at cooling the air, the more water they use. They also need a steady airflow to keep them supplied with the hot low-humidity air they need for proper evaporation. If this airflow is insufficient (as it often is in a small confined space like a vehicle), the cooler will be simply blowing humid moisture-laden air into the van, converting your indoors hot and dry desert environment into a hot and damp rainforest environment, making you more miserable and uncomfortable (and soaking everything in the van with condensation).
With its severe practical limitations, therefore, it’s not hard to see why virtually no RVs or camper vans are equipped with evaporative coolers, and why almost nobody uses them.
So how then does a van-dweller deal with day upon day of hot weather? There are, frankly, only two effective ways of beating the heat. If you are mobile, you can simply move to better weather. This will involve either going north to a higher latitude, or going up in elevation to a higher altitude, where it is cooler. If, on the other hand, you are tied to a fixed location and cannot move, your only choice is to not be in the van during the day when it’s hot—spend the day inside somewhere in the air conditioning, and don’t enter the van until evening when it has cooled off enough to be comfortable.
