CONDENSATE FROM COOLING COILS

The present invention relates to an air conditioning system for cooling office buildings and other large structures, and, in particular, to an improved air conditioning system, one aspect of which recirculates condensate from the cooling coils to improve the efficiency of the system, thereby decreasing energy costs.

The use of air conditioners and evaporative coolers is well-known to those living in climates in which the outdoor temperature exceeds a comfortable range. Over the years, numerous patents have issued for air conditioning systems. Each system has a different method of keeping a room or building cool. A small sampling of patents in the air conditioning arts includes U.S. Patents Nos. 2,243,478; 3,200,608; 3,394,560; 3,691,786; 3,763,660; 3,766,751; 3,817,049; 3,864,929; 4,010,624; 4,203,302; and 4,827,733. In most of the inventions represented by these patents, the ultimate objective is to increase efficiency by providing increased cooling capacity while minimizing the need for electricity. Others, such as U.S Patents Nos. 3,394,560 and 3,766,751 are concerned with the removal of condensate which falls from the incoming air as it passes over the cooling coils.

One method of increasing efficiency has been to recirculate the cooled air within the building. See e.g. , U.S. Patent Nos. 2,243,478 and 4,827,733. Because the inside air is already cooler than the air outside the building, the air conditioner must do less work to cool the air in order to maintain a comfortable room temperature. Thus, it has been conventional wisdom to recirculate the cooled air to maximize efficiency and minimize cost.

Recently, however, it has become evident that recirculating air can have significant health consequences for people working or living in the

building. When the air is recirculated, most environmental contaminants which are in the room are also recirculated. If the contaminants are continually being formed, the level of contamination increases with each recirculation.

Common recirculated contaminants cover a broad range. For example, smoke from cigarettes or machinery is recirculated within the same room, or possibly to other parts of the building. The smoke can then build up from relatively harmless levels to those which pose threats to human health.

The contaminants which are recirculated, however, are not always man-made. Bacteria, viruses and other pathogens can also be recirculated, increasing the risk that numerous people in the building will come into contact with the microbes and become sick or otherwise incapacitated. During outbreaks of certain communicable diseases, excessive recirculation of air can lead to significant numbers of people becoming ill. Recognizing this threat, the Federal Government has recently propagated regulations concerning reasonable recirculation of air in the workplace. Among other things, the regulations allow employees to seek damages against their employers if the amount of air being recirculated exceeds set limits. The regulations place employers and the government in a difficult situation. On the one hand, excessive air recirculation will continue to cause health problems for employees, tenants and customers. On the other hand, decreasing the use of recirculated air will significantly increase energy costs, and will ultimately impact the environment as energy demands increase. These cost concerns will be of particular significance for those living in warm climates, as well as for businesses, such as grocery stores and shopping malls, which have large open buildings to be kept cool. Because of the costs associated with increased energy demands, limitations on

recirculating cooled air could potentially drive some companies out of business.

In order to limit the health risks from recirculated air and prevent large increases in the energy used to cool buildings, an air cooling system is needed which provides maximum cooling of the incoming air while minimizing the amount of energy required to do so.

SUMMARY OF THE INVENTION It is an object of the invention to provide an air cooling system which efficiently maintains comfortable room temperatures without recirculating indoor air.

It is another object of the invention to provide an air cooling system which uses low temperature air to maintain comfortable room temperatures in large buildings with high traffic flow.

It is an additional object of the invention to use condensate collected from incoming air to increase efficiency of the air cooler. It is another object of the invention to use air being exhausted from the building to cool the incoming air to increase efficiency.

It is still another object of the invention to use air being exhausted from the system to carry away condensate while cooling incoming air.

It is an additional object of the invention to use cooling coils which are positioned so as to maximize heat transfer with the incoming air by remaining substantially wet as the incoming air is drawn across the coils.

The above and other objects of the invention are achieved through an air cooling system which includes a heat exchanger with air flow channels or ducts through which cooler exhaust air is drawn from the building. Incoming outside air is drawn through channels in the heat exchanger and is cooled by cooler exhaust air in the air flow channels or ducts. The incoming air then

passes into a first plenum which contains cooling coils. As the air passes through the cooling coils, the cooling of the air causes moisture in the air to condense and fall to a collection pan below the coils. The cooled air passes into a second plenum (above the first) and is then forced into the building through a conduit by a fan or other blower.

In accordance with one aspect of the invention, the air is cooled to a temperature of between 35 and 44 degrees Fahrenheit. The low temperature air reduces the energy necessary to keep a building cool, because less air is required to cool the building and to maintain a comfortable temperature. Because less air is moved, a smaller fan may be used to move the air. Additionally, the low temperature air contains less humidity, making the overall air temperature feel more comfortable to those in the building.

In accordance with another aspect of the present invention, the cooling coils are disposed generally horizontally, rather than the traditional vertical or A- frame positions. The horizontal positioning allows most, if not all, of the coils to remain covered with condensate as the incoming air passes through them. The cold condensate increases the efficiency of heat exchange between the coils and the incoming air. The cooler incoming air, in turn, releases more moisture, keeping the cooling coils substantially wet.

In accordance with yet another aspect of the present invention, the cold condensate which falls from the cooling coils falls into a receiving pan in the first plenum. The cold condensate is then pumped to the air flow channels or ducts where it is released into the exhaust air. The cold condensate evaporates in the exhaust air, cooling the exhaust air. The cooling effect of the evaporation is further enhanced because the exhaust air is of low humidity due to the low temperature air blown into the building by the cooling

system. The colder the exhaust air becomes due to the evaporation, the more heat will be transferred from the incoming air to the exhaust air, thereby precooling the incoming air. When the various aspects of the invention are integrated, the air cooling system provides efficient cooling for buildings with high traffic flow. Further, the system simultaneously pumps fresh air into the building while exhausting heated air and airborne contaminants.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the invention will become apparent from a consideration of the following detailed description presented in connection with the accompanying drawings, in which:

FIG. 1 shows an elevated perspective view of a preferred embodiment of an air cooling system with recirculating condensate from cooling coils made in accordance with the teaching of the present invention;

FIG. 2 shows a frontal perspective view of an air cooling system as shown in FIG. 1, revealing the internal components of the system which enable the incoming air to be cooled to a satisfactory temperature; and

FIG. 3 shows a frontal perspective view of an air cooling system similar to that of FIG. 2 in which the flow patterns of the incoming air, the exhaust air, the condensate, and the cooling fluid are represented by directional lines to demonstrate the workings of the cooling system.

DETAILED DESCRIPTION Reference will now be made to the figures in which the invention will be explained in detail, and the various parts of the invention will be given numeral designations.

Referring to Figure 1, there is shown a front perspective view of an air cooling system, generally indicated at 2. The cooling system 2 has two heat exchangers 6, positioned on two sides of a central cooling unit, generally indicated at 10. The central cooling unit 10 typically consists of a first, lower plenum 14 and a second, upper plenum 18 positioned on top of the lower plenum and extending rearwardly from the lower plenum. In use, the air cooling system 2 is typically mounted on the roof of a large building, such as a grocery store or shopping mall. Two exhaust fans 20, positioned at or near the top of the heat exchanger 6, draw air out of the building and expel it into the outside air. Openings (not shown) are formed in the sides 24 of the heat exchanger 6 to draw outside air in so that the outside air (now incoming air) may be cooled and directed into the building. The expulsion of the exhaust air and intake of the incoming air allows for contaminated/heated air inside the building to be replaced with fresh/chilled air, thereby improving the temperature and quality of the air inside the building. The advantages of the arrangement shown in figure 1 will be explained in detail with respect to figures 2 and 3. Referring now to figure 2, there is shown a perspective view similar to figure 1, in which the internal components of the air cooling system 2 are visible. For the sake of clarity, some of the elements contained in the heat exchangers 6 are shown only in the left heat exchanger 6a to make other structures more visible in the right heat exchanger 6b. In the preferred embodiment, each heat exchanger 6 will have corresponding structures.

Both of the heat exchangers 6 have an opening 28 along the lateral side 24 opposite the central unit 10. Those skilled in the art of air cooling will recognize that the openings 28 could be placed on the forward and

rearward sides of the heat exchanger with minor modifications to the components described below. However, for the configuration shown, it is believed that having the openings 28 on the side will increase the cooling system's efficiency and will be simpler and less expensive to manufacture.

Each heat exchanger 6 has a plurality of air flow/heat transfer channels or ducts 30. As shown in figure 2, a first group of channels or ducts 34 are open on first ends 38a adjacent to the opening 28 and second ends 38b opposite the first end and adjacent to the central unit 10. The open ends 38a and 38b allow air to flow through the group of channels/ducts 34 in a generally horizontal path from the outside into the central unit 10.

Adjacent to the channels/ducts 34 is a second group of air flow/heat transfer channels or ducts 40. Unlike the first air flow channels/ducts 34, the second group of air flow channels/ducts 40 are closed on both horizontal ends. Also unlike the first group of air flow channels/ducts 34, the second group of air flow channels/ducts 40 are open at a top end 44a and a bottom end 44b. Thus, air or other fluids may travel through the second group of air flow channels/ducts 40 in a generally vertical direction, but may not travel horizontally. For the sake of convenience, the group of air flow channels/ducts which allow air to travel through the heat exchanger 6 vertically, such as 40, will be referred to as air flow ducts 40, and the group of air flow channels/ducts which, like 34, allow the air to pass through the heat exchangers 6 horizontally will be referred to as air flow channels 34. It should be understood that numerous different configurations could be used, such as using air flow tubes or similar arrangements rather than ducts. Those familiar with the air cooling arts will be aware of many alternatives which could be employed.

The vertical pathway provided by air flow duct 40 allows air from the building to be exhausted without mixing with the incoming air. The air flow channel 34 and air flow duct 40 are positioned next to each other so as to act as a heat exchange. In the cooling system 2 shown in figure 2, the air flow ducts 40 and air flow channels 34 are positioned so as to alternate between air flow ducts and air flow channels to maximize heat transfer between the exhaust air and the incoming air. Ideally, each air flow duct 40 and air flow channel 34 will be relatively thin, as thin ducts and channels provide an increased surface area volume ratio.

In an alternative to having the air flow channels 34 and air flow ducts 40, a similar result could be achieved by having a chamber running horizontally or vertically and having a plurality of air flow tubes traveling through the chamber in a direction transverse to the air flow through the chamber. Like the alternating air flow channels 34 and air flow ducts 40, the air flow tubes would allow for heat transfer between the incoming and exhaust air, while at the same time preventing airborne contaminants in the exhaust air from being recirculated in the incoming air. Such air flow tubes should be of a size which maximizes surface area without significantly interfering with air flow through the chamber.

The air flow channels, or ducts can be made of material which conducts heat extremely well or a suitable plastic if the surface area is increased to compensate for its lower heat transfer coefficient.

Regardless of whether ducts, channels or tubes are used, the exhaust air is drawn through the heat exchanger 6 by the fan 20 positioned at or near the top of the heat exchanger 6. Typically, the fan 20 will be a propeller fan of sufficient size to pull the exhaust air from the building. This is accomplished by drawing the air in the building through openings 48 into a

channel 50 near the bottom of each heat exchanger 6. The air is then drawn through the air flow ducts 40 or other heat exchange mechanism and is expelled by the fans 20 into the outside air. The fans 20 should be of sufficient strength to draw the air through at a rate of 0.15 to 0.25 cubic feet per minute for each square foot of floor space in the building being cooled.

While the fans 20 are pulling air from the building and exhausting it, air from outside is drawn through the heat exchangers 6, transferring heat from the incoming air to the air being exhausted. This results in air which has been precooled as much as 20 degrees Fahrenheit or more.

As the incoming air passes out of the heat exchangers 6, it passes into the lower plenum 14 in the central cooling unit 10. Positioned near the top of the lower plenum 14 is a plurality of cooling coils 54. The cooling coils 54 can carry virtually any agent commonly used for heat transfer in cooling systems. However, it is anticipated that an environmentally safe heat transfer fluid will be used, as international treaties have severely limited the use of chloroflourocarbons (CFCs) because of their destructive interaction with atmospheric ozone. When used in the present invention, the heat transfer fluid provides efficient cooling of the air, without the detrimental side effects of CFCs. When the coils are used for heating, the antifreeze solution provides freeze protection when the unit is in the heating mode. As is shown in FIG. 2, the cooling coils 54 are positioned generally horizontally. As the air travels upwardly through the coils 54, the air cools. Because cool air has a lower water retention capacity than warm air, condensate forms on the cooling coils 54. At the same time, higher levels of humidity in the incoming air increase the amount of condensate which is removed from

the air, thus increasing the work of the system 2 as damp air is harder to cool than dry air.

Traditional air conditioning units have positioned cooling coils either vertically or semi-vertically, like in an A-frame. (See the patents referenced above.) In such designs, the condensate usually forms on the portion of the coils furthest from the opening through which the air is drawn. The condensate usually forms on the cooling coils at this point because the cooling coils are arranged to have the coldest portion at the end opposite the opening. With this configuration, the air is continually cooled as it passes through the coils. The colder the air becomes, the less water it is able to suspend. Because the coldest coils are positioned vertically or semi-vertically, the condensate forming on the coil has a tendency to run off and is usually disposed of by a drain.

A primary advantage of positioning the cooling coils 54 horizontally is that the condensate falls from the upper (colder) coils onto the coils positioned below. In moderate to humid climates, this will result in the lower coils being wet most, if not all, of the time. Because of the thin layer of cold water, the wet coils are more efficient at transferring heat from the incoming air to the chilled fluid in the cooling coils 54. Thus, by positioning the cooling coils 54 horizontally, the cooling system 2 cools the air more efficiently as heat transfer between the air and the cooling fluid is increased. While many types of coils 54 can be used, it is anticipated that aluminum fin/copper tube coils will be used due to its durability and efficiency in exchanging heat between the incoming air and the cooling fluid.

It is anticipated that, in the future, other substances will be found or developed which are more durable and more efficient in heat transfer than finned

type coils. It is intended that the present patent cover use of such functionally equivalent materials.

In addition to the condensate coating the cooling coils 54, there will usually be excess condensate which will drip from the cooling coils and land in a lower part of the plenum 14. In the past, the condensate has usually been drained off, See e.g.. U.S. Patent No. 3,763,660, or the condensate has been sprayed against the condenser coils where it is evaporated by heat transfer. See U.S. Patent No. 2,243,478. As was noted above, the present invention takes advantage of the benefits of the latter methods of using the condensate without requiring energy to pump the condensate to the cooling coils 54. In the present invention, excess condensate falling from the cooling coils is collected in a collection pan 60 at the bottom of the lower plenum 14. Rather than disposing of the condensate, or spraying it against the cooling coils 54, a condensate pump 64 is positioned in the collection pan 60. The condensate is pumped through tubes 66 from the collection pan 60 to the heat exchange/air flow ducts 40.

The condensate is released into the exhaust air as the exhaust air is being pulled through the heat exchanger 6 by the fan 20. As the condensate falls down the air flow ducts 40, it evaporates in the exhaust air. The condensate can also be atomized, increasing the ability of the exhaust air to evaporate the condensate. Because the condensate is cold and the exhaust air has little humidity, significant heat energy is consumed in the process of evaporating the condensate. The consumption of the heat energy causes the temperature of the exhaust air to decrease. As the cooled exhaust air passes through the heat exchanger, it collects the heat contained in the incoming air, precooling the incoming air and lowering the energy required to cool the incoming air to a suitable temperature for release into

the building. Any condensate not evaporated in the air flow ducts 40 is collected and returned by a tube 68 to the collection pan 60 where it may be recirculated.

Returning again the incoming air being passed through the cooling system 2, the air is drawn from the lower plenum 14, through the cooling coils 54 and into the upper plenum 18. A fan 70 is positioned near an inlet 74 toward the back of the upper plenum 18. Rotating the fan draws the precooled air through the cooling coils 54, thereby chilling it. The fan 70 then forces the incoming air downward, through a conduit 78 and into the building below. The fan 70 must be of sufficient size and strength to direct about 0.3 cubic feet of air per minute for each square foot in the building.

The air released into the building is low temperature; typically between about 35 and 44 degrees Fahrenheit, and preferably between about 38 and 40 degrees Fahrenheit. The low temperature air is relatively dry, as cold air retains less moisture. Thus, a small amount of incoming air can significantly reduce the interior temperature and make the building environment more comfortable for those working or living therein. Referring now to figure 3, there is shown a view of the cooling system 2 similar to that in figure 2, but showing the flow pathways of the incoming air, the exhaust air, the condensate and the cooling fluid. To further illustrate the invention, approximate energy consumption will be discussed with the various flow pathways. The discussion assumes outside air conditions of 95 degrees Fahrenheit and a 75 degree wet bulb, correlating with 40 percent relative humidity. The desired space temperature in the building is between 72 and 74 degrees Fahrenheit with between 36 and 40 percent relative humidity.

Beginning at the top of the page, there is shown a dotted line 100 which represents the flow of the cooling agent which passes through the cooling coils 54. The cooling agent — in this case heat transfer fluid/anti- freeze — enters the cooling coils 54 at point 104. The typical temperature of the cooling agent is about 34 to 36 degrees Fahrenheit when entering the cooling coils 54. The cooling agent runs back and forth horizontally through the cooling coils 54 until reaching point 108 at which it exits the coils. As shown in figure 3, the entry point 104 of the cooling agent is higher than the exit point 108. With this configuration, the uppermost coils are the coldest and the lowermost coils are the warmest. Thus, as the incoming air rises through the cooling coils 54, each progressive row of coils further cools the air. In typical use, the cooling coils 54 will have between about 6 to 8 horizontal rows of coils.

After passing out of the exit point 108, the cooling agent is processed through an environmentally safe ammonia fluid chiller. A system pump (not shown) circulates the chilled fluid to the air cooling system. Those skilled in the art will be familiar with numerous different configurations which are commonly used with air cooling systems, and which could be used with the present system. It is anticipated that analogous cooling mechanisms yet to be developed would also be usable with the present invention.

With this configuration, cooling the heat transfer solution consumes approximately 1.5 to 1.7 watts per square foot of floor area under the conditions specified above.

As incoming air, represented by dotted line 120, is drawn into the system through heat exchangers 6, heat is transferred from the incoming air to the exhaust air, represented by line 130, which is drawn out of the building. As will be explained in detail below, the exhaust air 130 is typically between 78 and 80 degrees

Fahrenheit when entering the heat exchangers 6, and a temperature below that when leaving the heat exchanger. Passing the incoming air 120 through the heat exchanger results in the incoming air being cooled to between about 74 and 76 degrees Fahrenheit. The wet bulb drops to between about 68 and 70 degrees, and the relative humidity increases to around 76 to 78 percent.

As the incoming air 120 passes through the cooling coils 54 as it moves from the first, lower plenum 14 to the second, upper plenum 18, a significant amount of the moisture in the incoming air 120 condenses on the coils 54, thereby wetting the coils. Additionally, a significant amount of condensate also falls from the coils to the bottom of the first, lower plenum 14. The falling condensate is represented by a series of horizontal dashes 140. The condensate is collected in a collection pan 60 for reasons which will be discussed momentarily.

The cooled incoming air 124 is drawn through the cooling coils 54 by a fan 70 disposed in a conduit 74 toward the rear of the second, upper plenum 18. The fan 70 directs air through the conduit 74 and into the building. The air 128 arriving in the building is cooled to a temperature of between 35 and 44 degrees, and preferably between 38 and 40 degrees. Because of the air's low temperature, the fan 70 must only direct 0.3 cubic feet per minute per square foot of floor area. This requires only about 0.10 to 0.15 watts per square foot of floor space. Thus, based on the figures provided, a total of between about 1.7 and 2.1 watts per square foot of floor space is needed if the average user density is 0.015 people per square foot.

The air in the building eventually gains heat from the lighting, people and roof and raises the temperature from the space control temperature — typically 74 degrees Fahrenheit. This warmer, upper air 134 in the building eventually warms to between about 78 and 80

degrees Fahrenheit, and have a relative humidity of 30 to 35 percent, resulting in a wet bulb of about 60 degrees. This warmer, upper air 134 is drawn into the cooling system 2 through openings 48 and into channels 50 beneath the heat exchangers 6. The exhaust air 130/134 is directed upward through the heat exchangers 6. As the air rises, condensate 150 is pumped from the collection pan 60 to the exhaust ducts 40 by a pump 64. The cold condensate 150 is released into the exhaust ducts 40 where it evaporates in the low humidity exhaust air 130/134 as illustrated by the vertical dotted line 130a in the right heat exchanger 6b. The evaporating condensate cools the exhaust air 130/134, thereby cooling the incoming air 120 as described above. Any condensate 150 not evaporating in the exhaust duct 40 is recirculated back to the collection pan 60 where it may be used again. This recirculation is represented by solid line 152.

Drawing the exhaust air 130/134 through the heat exchangers 6 is performed by the fans 20 at a rate of about 0.15 to 0.25 cubic feet per minute for each square foot of floor area. The fans 20 and the condensate pump 64 consume about 0.075 and 0.10 watts per square foot of floor space. Thus, under the conditions described earlier, the cooling system 2 consumes between about 1.7 and 2.0 watts per square foot of floor space, considerably less than the cooling systems of the prior art. At the same time, the continuous in flow of fresh air prevents airborne contaminants from being recirculated.

In the manner described above, there is disclosed an improved system for cooling air using recirculating condensate to improve the system's efficiency. The above description is not intended to serve as a limitation of the invention, but rather a description of a preferred embodiment thereof. Those skilled in the art will recognize numerous modifications which can be

made to the structure and arrangement of the invention, including substitutions of structure, without departing from the scope or spirit of the invention. The appended claims are intended to cover such modifications and impart the scope of the invention.