Jul 14th 2011, 1:42:20
AC units inherently act as dehumidifiers unless the air moisture content is below to maximum the air can handle in contact with the coils (which is rare unless you live in a desert). They don't specifically drop the relative humidity of the air, but the drop in the moisture content in terms of water molecules to air ratio, and then the reheating of the air after it leaves the unit has the generally effect of reducing the relative humidity (which is the water being carried by the air divided by the total water carrying capacity of the air at the temperature and atmospheric pressure of an area, and also how we experience humidity - what feels humid at room temperature feels almost dry at 35 celcius).
In regards to the makeshift AC, you're taking advantage of a double phase change - ice to water, and then water to water vapor (your window AC typically relies on one phase change - liquid to vapor). However, since you are cooling by creating by using heat to warm and cause phase change in water/ice, and pumping the water vapor laden air back out into your environment you are introducing more moisture, and raising the relative humidity, which in turn lowers the temp you need to cool to to achieve comfort, so it isn't more efficient. Also, you are not getting as much air flow across through the cooler as you would with an AC, so while you are cooling some air, you aren't cooling enough to make a dent in a decent sized room.
Separating the air circulating in the room from the water vapor would create a more efficient system, especially by using a system of small pipes that the air is blown across, but we've just described half of an air conditioner.
The use of evaporation of water to cool air is an old and effective technique in dry climates, where the relative humidity can go up a long way before the effect becomes noticeable, but in the eastern half of North America, our heat comes with humidity, so systems that cool by evaporating water directly into the environment (like this cooler and our bodies) are less effective at increasing comfort.
Since evaporation consumes almost 10x the heat of melting, you're better skipping the cooler, small piece of pipe, and ice in favor of cold tap water, and spending more money on a larger fan, set in a window, so you are getting constant air changes - therefore lowering the amount, or even removing entirely the water vapor you are introducing into the air (I recommend setting the fan to blow out through a window, blanking off the the rest of the window around the fan with blankets and/or duct tape, and opening another window across the space 6-8 inches). Apply the water directly to your person, and stay in the air flow of the fan, which will speed the evaporation of the water, and in turn remove the heat from your person.
