"Applications" is a term used in this technology to identify or define the purpose for which the evaporative cooling equipment is selected. It is also sometimes used to define the method of application or installation.
A simple example would be the need to cool a 40,000 square foot warehouse in the Southwest. This is usually an application well suited for evaporative cooling, however some additional information is required to fully qualify the application. Some of the questions that should be answered are:
1. What is to be cooled? People, Equipment or other? If people, what are they doing. Office, production, warehousing, etc. If Equipment, what type and operation? Does the Equipment generate high heat loads, etc?
2. What kind of work is going to be performed? Certain kinds of operations can be better served than others. An example is printing processes. Color printing cannot dry too quickly or too slowly. Paper cannot be allowed to absorb too much moisture or it becomes too limp so humidity is very important.
3. What are the cost parameters? Can mechanical refrigeration be afforded even if it is desired?
4. What is the structure capable of supporting? Are there other structural considerations? Is it necessary to locate the equipment on the ground or roof or some other mounting method?
5. What are the climate conditions? Is the climate hot and dry or mild conditions?
Answering the above questions will go a long way in the determination of whether or not evaporative cooling will be the best type cooling system or not. Some of the following considerations will help to provide some answers to these questions:
1. People in production or warehousing type jobs are prime uses of evaporative cooling. Evaporative cooling not only cools by dropping the Dry Bulb temperature but it also cools by the chill factor of air passing over the body. For people in office type work, it is usually the practice to use mechanical refrigeration due to the need to maintain very low humidity levels. In addition to human comfort it is also important to maintain humidity control and cool equipment (like computers). Production and/or warehousing type jobs are usually best served by evaporative cooling. It is far easier to exhaust heat than it is to recirculate it and treat it. Perishable goods usually require mechanical refrigeration. Most mechanical equipment is best cooled by evaporative cooling due to the need for large volumes of air passing over the equipment and exhausting the air to the outside.
2. The type of work being performed influences the selection of cooling equipment. The example of printing on paper is a good case in point. Other types of work to be considered are those that require large volumes of air flow. Some types of work are just the opposite. High volumes of air flow may adversely affect the work (such as in some plastic film manufacturing)
3. Acquisition cost of mechanical refrigeration is usually about 3 times that of evaporative cooling for a similar structure. Costs vary widely due to type of structure, climate and other factors. Upkeep and maintenance costs are somewhat lower with evaporative cooling partially due to the technical expertise required. Operating costs are usually much higher for mechanical refrigeration. Sometimes 3 to 5 times higher in energy use alone.
4. Equipment selection must consider the ability of the structure to support it. It is not too unusual to have to locate equipment on the ground or some other mounting method because the roof will not support it's weight. Structural integrity is a serious consideration in selection and location of equipment.
5. The climate is a major consideration in the selection of cooling equipment. Evaporative cooling is especially effective in hot dry climates. Temperature drops of 30 to 40 degrees are rather easy to achieve. It is not too unusual to achieve lower temperatures with evaporative cooling than with mechancial refrigeration during very low humidity periods due the lowered performance of mechanical refrigeration equipment in these conditions. In the Southwest, it is a common practice to use both methods. Evaporative cooling can be used during the hot dry periods and mechanical refrigeration during high humidity periods. Most homes have an evaporative cooler and an air conditioner on the roof. I.E. in Phoenix, AZ., the evaporative cooler can be used at a cost of about $30.00 a month while the air conditioner would cost about $80.00 to $200.00 a month based on the size of the house and the equipment. Most commercial buildings are cooled with evaporative cooling in the warehouse/production area while refrigeration is used in the office area.
Evaporative cooling can be successfully used anywhere the wet bulb temperature is lower than the dry bulb which is almost everywhere.
Premier has shipped evaporative cooling to Louisiana, Florida, Mississippi, Alabama, Northeast and most other states (in the United States) as well as Korea, Japan, Mexico and other countries. The Middle East is an excellent example of the ideal climate for evaportive cooling.
The following methods of sizing evaporative cooling equipment is based on the best information available and some first hand experience. The "reality of results" rule has been a great teacher. The evaporative cooler technology is still plagued with what I call the "swamp cooler mentality". This mentality views this technology as if it had not progressed any during the past 60 or 70 years. The truth is that this technology has changed enormously during the past 15 to 20 years with the advent of the "Rigid Media" type cooling medium. Cooling efficiencies have increased from 45% to 50% with the "Swamp Cooler" to 90% to 99% with the new cooling medium. Today the best answer in selecting cooling equipment is evaporative cooling!
Step 1: Determine the Cubic Capacity of the structure or that portion of the structure to be evaporatively cooled. Formula = Width X Length X Effective Cooling Height* = Capacity in Cubic Feet. * = the actual height to be cooled. I.E. in a 25' tall building, it is the usual practice to cool only to about 16' to 20' based on the highest point the cooling is required. A heat stratification layer will form at the roof level which will not adversely affect the cooling process provided that space is not used. Remember cold air drops and hot air rises.
In example of Step 1. A structure that is 100' wide x 200' long with an effective height of 16' would equal 320,000 cubic feet.
Step 2: Determine the number of air changes per hour required to maintain desired indoor temperatures. This is an extremely important determination. Too many air changes will result in unnecessary cost while too few air changes will not acheive the indoor conditions desired. The best approach, short of a major engineering study of heat gains, etc., is a common sense approach of using the known conditions inside and outside the structure.
It is first necessary to know the climate design conditions of Dry Bulb and Wet Bulb for your location. This information is available from ASHRAE publications 1% scale (or from Premier's web site in section x) if there is a weather reporting station in your area. I.E. design conditions for Phoenix, AZ., is 109(f) Db and 69(f) Wb. This condition is only exceeded during 1% of the cooling season therefore the conditions are at the high end of the range. These conditions are "concurrent" meaning that they are present at the same time.
Using the formula to determine the predicted discharge temperature during these conditions you can know the temperature of the air you have available to use in the cooling of the building. ( Discharge temperature = (EDb - EWb) x SE or 109 - 69 = 40 x .9 = LDb 36(f) temperature drop. Db - LDb = 109 - 36 = 73 degrees (f) Dry Bulb discharge temperature. The air temperature of 73 degrees (f) is necessary to know for the next part of step 2. (Note: This procedure does not take into consideration the density ratio which would have to be considered in higher elevations).
Refer to following table to determine the proper number of air changes.
| Leaving Air Temperature | Temperature over ambient* | Air Changes/Hr** |
|---|---|---|
Above 78(f) |
20 degrees (f) |
30 to 60 |
76 (f) to 78 (f) |
15 to 20 (f) |
20 to 40 |
74 (f) to 76 (f) |
10 to 15 (f) |
15 to 30 |
72 (f) to 74 (f) |
5 to 10 (f) |
12 to 20 |
under 72 degrees (f) |
less than 10 (f) |
10 to 15 |
* Average amount indoor temperature exceeds the outdoor temperature when evaporative cooling is not in use at design conditions or interpolation/extrapolation of these conditions. *It is common practice to cool only to the height actually used and needs cooling. It is not bad to have a heat layer at the roof level provided the cool air coming into the structure does not flow through this layer. Most cooling installations will extend the discharge duct to the height above the floor where cooling is preferred and the capture area of the exhaust ducts likewise start at this level. This method does not disturb the heat layer.
Using the above table and a leaving discharge temperature (into the building) of 73 degrees (f) and determining that the indoor air temperature (ambient Db) and the outdoor temperature (ambient Db) is 120 and 109. The difference is 11 degrees (f) Referring to the above table, we see that we should plan approximately 12 to 20 air changes per hour. The reason for the range of air changes is to allow for other conditions not heretofore considered. Among these other considerations is human comfort cooling as compared to equipment cooing, etc. let's continue to size the equipment needed.
Let's summarize what we have determined so far. The cubic capacity to be cooled is 320,000 cubic feet. The discharge temperature required is 73 degrees (f). The number of air changes is between 12 and 20. Let's (I hate to say it) assume that this structure is heavily populated with people. We should than consider a greater number of air changes to assure the best human comfort level without increasing costs more than absolutely necessary.
To determine the total Cubic Feet per Minute of air flow required to cool this structure as indicated, multiple 320,000 (cubic feet) by 20/ 60 = 106,666 Cubic Feet per Minute (CFM). (Remember to express the requirement in the same unit of measure as the capacity. In this instance, that is Cubic Feet per minute rather than per hour and that is the reason I added the "divide by 60" into the formula). It is alright to round off this amount of CFM to 107,000 if you like round numbers. In fact if the number of air changes was reduced to, say 18 changes per hour, the amount of CFM would be 96,000 CFM. You can readily see why the number of air changes is so important.
It is common practice to refer to air changes as minutes of air change. I.E. in this instance, the 20 changes would be expressed as one (1) air change every 3 minutes. Another way to prove the process is to multiple the CFM X air changes (107,000 X 3 = 321,000 CFM which is close enough) Remember, we are not sizing a rocket ship and afterall, we are dealing with climate conditions that are exceeded only 1% of the time during the cooling season.
Next, we need to answer the question of how many individual coolers and the location of the equipment. Do we want to put ten (10 )10,700 CFM coolers across the roof of the strucure (on mounted on the side or ground) or do we want to install two (2) 53,500 CFM coolers or perhaps five (5) 21,400 CFM units? The answer to this question lies mostly in the consideration of costs. Cost of acquiring the five (5) units in this example would cost less than either of the other options.
The next step would be to click here to send e-mail to Premier Industries, Inc., and ask for a quotation and written specifications for any or all the sizes considered. Just tell us the CFM and External Static Pressure (pressure required to push the air through the duct system external to the cooler). From this simple information, we can quote you prices.
Important postscript: The air change method of sizing is a common sense approach. Since evaporative cooling quickly exhausts heat (in this case every 3 minutes), heat gain is considered in the above steps we took and is controlled by the number of air changes. It stands to reason that the indoor heat gain is reflected in the Dry Bulb difference between indoor and outdoor temperatures. This method automatically considers all the pertinent data by measuring the actual conditions in an existing strucure that must be dealt with. This method is also useful in new structures to design the cooling system except the heat gain has to be determined in advance of having the structure available to measure.
After going through the above detail to approach the sizing of evaporative cooling on a quasi scientific basis, experience tells us that 1 air exchange every 3 minutes is more than adequate for any conditions that would arise in Phoenix, AZ.
In new buildings, the Engineer would predict the outcome based on the known factors of discharge temperatures and outdoor Dry Bulb. Indoor heat gain would have to be determined to complete the process.
SENSIBLE HEAT REMOVAL SIZING METHOD:
To determine the amount of air volume (measured in CFM) required to remove indoor heat gain, the following formula can be used.
SCFM = Indoor Sensible Heat Gain (BTUH) 1.08 x (IDB-LDB) x Density Ratio
Where IDB = Indoor (Design) Dry Bulb LDB = Leaving Dry Bulb from Cooler
Example: An indoor heat gain of 144,000 BTUH at an altitude of 4000 feet. An Evaporative Cooler with 12" cooling media @ 500 FPM velocity is to be used to remove this heat gain. Outside design conditions are 94 Dry Bulb and 64 Wet Bulb with a design indoor temperature of 800 (f) Dry Bulb.
The discharge temperature (Db) must first be determined. Using the formula of ODb - (SE x (ODb - OWb)), the following result is reached. 94 - (.89 x (94 - 64) = 67.30 (f) LDb.
The Density Ratio is determined from tables available in the formulas and tables section. At 4000 feet elevation the Density Ratio is .87.
To determine SCFM to offset this indoor heat gain we can now utilize the formula:
144,000 BTUH = 144,000 1.08 x (80 - 67.3) x .87 11.933 = SCFM 12,067
This result indicates we need at least 12,067 Cubic Feet per Minute of air flow @ 67.30 (f) to offset the indoor heat gain of 144,000 BTUH.
Other types of applications:
A very effective and low cost application of evaporative cooling in a building such as the one described above could be cooled with a system we have named "Inviron Cooling". In it's simplest form, this type system uses cooling sections mounted in one wall and exhaust fans in the opposite wall. The exhaust fans pull the air through the cooling sections and exhausts the air to the outside. It is somewhat like making the entire structure into an evaporative cooler. Since exhaust fans are required, even with powered air systems, it is not an extra cost and since there is no expensive blower and motor, the cost is at the lowest possible.
This type cooling system is presently being used very successfully in several 40,000 square foot warehouse/production type buildings in Las Vegas, NV.
The Converta-Pak(tm-AZ) is a conversion and upgrade system that consists of a wet section and blank panels. It is intended to convert the old, existing Swamp Cooler to the new high efficient evaporative cooling technology. In the above example of 109Db and 69Wb conditions with a discharge temperature of 73 degrees (f) using 12" thick rigid media, the old swamp cooler would have discharged 91 degree ((F) air.
This simple and low cost upgrade/conversion system can also be very effectively used on Rotary Wheel type coolers. These type coolers are really archaic but many are still in use. It is a simple process of removing the "evaporative wheel" and replacing it with a properly sized Converta-Pak. Since the Rotary Wheel type unit blocks almost half the face area, the conversion also almost doubles the air volume in addition to much lower discharge temperatures.
Refer to the section on Converta-Pak(tm-AZ) from our home page for much more information about this system.
The Premier Precooler is a wet section with rigid media, usually 3" to 6" thick. This unit is used to pre-cool the air passing over/through heat exchangers or heat generating equipment. The best example is conventional air conditioners. The precooler is placed over the air intake of the condenser coil. The colder air passing over the condenser will increase the heat transfer rate considerably thereby allowing it to operate at a much higher efficiency and lower cost. It will also extend the useful life of compressors, etc.
The principle is simply to present an air intake temperature at the condenser coil that the equipment was designed for. All manufacturers specifications indicate that the hotter the air across the condenser, during cooling mode, the lower the efficiency. A 60,000 BTUH air conditioner at 80 degrees (f) ambient, may drop to only 45,000 to 50,000 BTUH when the ambient temperature rises to the 100 - 120 degree (f) level. In the Southwest, it is common for rooftop temperatures to reach 140 degrees or more during high heat periods.
Refer to this section from our home page for more information about Precoolers.
Premier specializes in custom designed and manufactured equipment. The "Make-Up Air Unit" or "Evaporative Cooling with Heat" type unit is a specialty with us. We can assist in the initial design of the Equipment and then produce the item to specifications required. This allows the customer to build the equipment to meet the need rather than have to change the need to accommodate existing equipment.
Refer to that section from our home page for more information.
Premier stocks large quantities of Rigid Media, . We can cut to size and ship next day. Click here to send e-mail to us for a price quotation or answer questions you may have about this media.
Refer to this section from our home page for more information about Rigid Media.
The Premier Mobile-Cool (c) unit is a portable evaporative cooler with 8" thick Rigid Media and Fan. This unit is designed to be moved to the area where spot cooling is needed. A water hose and 120VAC power supply is all it takes to be in operation. It also works very well as a "through the wall" permanent mount cooler!
Refer to this section from our home page for more information about the Mobile-Cool (c).
Refer to other sections in the Technical Data part of our web site accessible from our home page for other formulas, tables and written text regarding this technology to provide additional resources.