Refrigeration – Using electrical or magnetic effect – Thermoelectric; e.g. – peltier effect
Reexamination Certificate
2000-05-10
2002-07-16
Doerrler, William (Department: 3744)
Refrigeration
Using electrical or magnetic effect
Thermoelectric; e.g., peltier effect
C062S310000
Reexamination Certificate
active
06418728
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally concerns evaporative coolers, and particularly concerns evaporative coolers in which water or air that is used by the cooler is itself pre-cooled, particularly by use of electricity and more particularly by action of a thermoelectric cooling element.
2. Description of the Prior Art
2.1 Evaporative Coolers and Cooling Systems
The following discussion is taken in substantial part from the paper
Evaporative Cooling System for Aquacultural Production
by C. D. Baird, R. A. Bucklin, C. A. Watson and F. A. Chapman appearing as Fact Sheet EES-100, a series of the Florida Energy Extension Service, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida (publication date: March 1993).
2.1.1 What is Evaporative Cooling?
For a simplistic understanding of evaporative cooling, the air may be though of as being like a sponge. Similar to a sponge, air has an ability to absorb moisture that it comes in contact with. The amount of moisture that the air will absorb depends on the condition of the air, or specifically, (i) how much moisture the air already contains and (ii) the temperature of the air. If the air is warm and contains only a small amount of moisture, then it will more readily absorb moisture. As air cools, its volume decreases, and with it, its ability to absorb moisture decreases. After all, how easily you can clean up a spill depends on the capacity of the sponge that you are using.
The term “relative humidity” describes the quantity of water in the air in relation to its total capacity. Any volume of air at any given temperature has an ability to hold a certain quantity of moisture. If the air contains 20% of its total capacity to hold moisture, the relative humidity is said to be 20%. A relative humidity of 100% indicates that the air at this temperature and pressure is holding all the moisture it can. If the air has a low relative humidity when entering an evaporative cooler (explained in the next section), then it has the ability to hold more moisture, and will thus evaporate more water and cool more effectively.
When describing the amount of moisture in the air, the term relative humidity is used because the “sponginess” of air changes relative to air temperature. The warmer the air, the more spongy it becomes, and the more water it can hold. That is to say that if air at any temperature has a 100% relative humidity then it can hold no more water vapor (at that temperature). However, if the air is heated, it expands, and as a result the relative humidity decreases even though the total amount of water vapor in the air has not changed. As a result, we must describe the level of humidity relative to the condition of the sponge we are talking about. Is it a 50° F. sponge or an 80° F. sponge? An 80° F. sponge will hold more water at 50% humidity than will a 50° F. sponge.
Evaporative cooling works on the physical principle that in order to evaporate water, heat (energy) is required. In fact, the evaporation of one gallon of water requires almost 8,700 BTU's of heat. Where does this heat come from? It come from whatever the water is in contact with as it evaporates. This could be a hot sidewalk, a human body, a tree, from the air itself, or a wet cooling pad. As the heat is removed from an object, the temperature of that object is decreased—in this case, the air.
It is important to realize that the temperature of the water does not have a great effect upon the cooling produced through the evaporation. If one was to place a gallon of 50° F. water on a warm sidewalk, it would produce 9,000 BTUs of cooling by consuming the heat to perform the evaporation. A gallon of 90° F. water would produce 8,700 BTUs of cooling, only a 3 percent difference. After all, if you were sprayed with water at either of these temperatures on a hot day, you would still feel much cooler.
Typical BTUs removed from the air based on a given amount of water consumed in an hour are as follows: Ten (10) U.S. gallons (37.8 Liters or 8.3 Imperial Gallons) of water suffices to remove 87,000 BTU's. Twelve (12) U.S. gallons (45.4 Liters or 10.0 Imperial Gallons) suffices to remove 104,400 BTU's. Fourteen (14) U.S. gallons (53.0 Liters or 11.7 Imperial Gallons) suffices to remove 121,800 BTU's.
In simple terms, evaporative cooling is nature's way of cooling.
2.1.2 Humidity and Evaporative Cooling
As previously stated, a cubic volume of air at a certain temperature and pressure has the ability to absorb and to hold a certain amount of water vapor. If a volume of air contains 50% of the amount of moisture that it is capable of holding, it is said to be at 50% relative humidity. The higher the temperature of the air, the higher the amount of moisture it is capable of holding. Any change in the temperature without a corresponding change in the pressure results in an increase or decrease in the ability of the air to contain water vapor.
If the temperature increases without an increase in the pressure, the result is a decrease in the relative humidity, and thus an increase in its ability to hold more moisture. That is to say that in the morning the humidity may be high, but as the day passes and the temperature increases then the relative humidity will naturally decrease.
The extent to which relative humidity decreases through the day can be affected by local weather systems and proximity to large bodies of water. If an increase in temperature is accompanied by a weather system containing moisture, the decrease in humidity will not be as great. But, the fact remains that relative humidity does drop as air temperature increases. In fact, for every 20° F. rise in temperature, the moisture-holding ability of air doubles. For instance, if the temperature of the air was 70°F. and the relative humidity was 100% at 5 a.m., and the temperature increased to 90° F. at noon, the moisture holding ability of the air would double.
As a result, the air would now be holding only half of the moisture it is capable of holding, and the relative humidity of the air would drop to 50%.
The hotter the day, the drier the air becomes, and the more cooling that can take place through the evaporation of water. This means that when the day gets hot enough to require cooling, the relative humidity will be much lower than in the morning and allow an evaporative cooler to work well.
Since any evaporative cooling device must evaporate water to achieve cooling, more water vapor is put into the air. As the abient relative humidity increases, it becomes more difficult to put moisture into the air. The efficiency of any evaporative cooling device is directly related to its ability to evaporate water (a cooling process) at a given relative humidity. A unit with low efficiency will cool only at low relative humidity levels, while a unit with high efficiency can achieve effective cooling at much higher humidity levels.
Evaporative coolers are extremely energy efficient because there is no compressor or refrigeration cycle involved. Evaporative coolers can replace an air-conditioning system in hot, dry climates. Ventilation is increased and cooling costs reduced.
2.1.3 How Evaporative Cooling Works
Evaporative cooling occurs when water is brought in contact with air that has a wet bulb temperature lower than that of the water. As the air and water remain in contact, the heat required for evaporation is taken from the water and the air causing both the water and the air to be cooled. Therefore, evaporative cooling can be used to cool water (e.g., cooling towers for commercial air conditioning) or air (e.g., evaporative pad cooling for greenhouses) . For the system of the present invention, evaporative cooling is used to directly cool water, which in turn cools air. Therefore system may be considered to cool both water and air.
The amount of cooling that can be accomplished through the evaporative process depends on the humidity level of the air—the dryer the air, the greater the evapor
Doerrler William
Fuess & Davidenas
Jiang Chen-Wen
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