Evaporative Cooling System
Evaporative Cooling System Proposal
Evaporative cooling differs from typical air conditioning systems, which use vapor-compression or absorption refrigeration cycles. Evaporative cooling uses the fact that water will absorb a relatively large amount of heat in order to evaporate (that is, it has a large enthalpy of vaporization).
Many poultry houses today are equipped with cooling systems that consist of some arrangement of cool cell pads at one end of the house and large tunnel exhaust fans at the other end.
Evaporative Cooling System Installation Drawing:
| Ambient Dry Bulb Temperature Degree ( Cْ ) | Humidity | ||||||||
| 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% | |
| 10 | 4 | 4.5 | 5.5 | 6 | 7 | 7.5 | 8 | 9 | 9.5 |
| 15 | 7.5 | 8.5 | 9.5 | 10.5 | 11 | 12 | 13 | 13.5 | 14.3 |
| 20 | 11 | 12 | 13 | 14.5 | 15.5 | 16.5 | 17.5 | 18.5 | 19 |
| 25 | 14.5 | 16 | 17 | 18.5 | 20 | 21 | 22 | 23 | 24 |
| 30 | 17.5 | 19.5 | 21 | 22.5 | 24 | 25 | 26.5 | 28 | 29 |
| 35 | 20 | 23 | 25 | 26.5 | 28.5 | 30 | 31.5 | 32.5 | 34 |
| 40 | 23 | 26.5 | 29 | 31 | 32.5 | 34.5 | 36.5 | 38 | 39.5 |
| 45 | 26 | 29 | 32.5 | 35 | 37.5 | 40 | 42 | N/A | N/A |
| 50 | 29 | 32.5 | 36.5 | 40 | 44 | N/A | N/A | N/A | N/A |
How to make the evaporative cooling system more effective:
- Increasing surface area of evaporation
- Choosing different evaporative media
- Adding air movement/wind
Factors That Influence Fan and Pad Evaporative Cooling Systems Operational Considerations It is very important to keep the building as tight as possible to push entering air through the pads. Make sure that all doors and other openings are kept closed when not in use and that any gaps in the greenhouse coverings are sealed. If not, air will be pulled through these openings rather than through the cooling pad. The efficiency of a fan and pad cooling system depends on air moving through the cooling pads
Location of Fans and Cooling Pads
It is not practical to separate the pad and exhaust fans by more than 200 feet. A distance of 150 feet or fewer is preferred.
Cooling Pad Area
Pad area is typically based on velocity of 350 feet per minute through a standard six-inch pad and 225 feet per minute for a four-inch pad. Another way to look at it is that for a six-inch pad you should have one square foot of pad for every 350 cubic feet per minute (cfm) of exhaust fan capacity or for a four-inch pad one square foot of pad for every 225cfm of exhaust fan capacity.
Using these sizing guidelines, the pressure drop across the pads will be approximately 0.05 inches and the cooling efficiency will run between 70 and 75 per cent.
In our case
The area of the cooling pads which we installed is 387.5 Sqf which means these area require 387.5*225= 87.187.5 CFM
We installed 10 fans with around 4700 CFM which means the total CFM provided by the 10 fans are 47000 CFM
Example: The air cooler ( MC25000) comes with cooling pad size 11 sqf and considering that this cooling pad is 4 inch then they require (11*225=2475) CFM while the actual CFM of this air cooler is 13000. Why the fan size is not proportional with cooling pad size in this air cooler? The answer is to get more air flow
Design Conditions:
| Tunnel fan capacity (cfm) | 47000 |
| Outside temperature (C) | 50 |
| Outside relative humidity (%) | 30 |
| Pad height (ft) | 6.0 |
System Performance:
| 4″ Pad | |
| Design pad velocity (ft/min) | 225 |
| Minimum recommended pad area | 209 sq. ft. |
| Minimum recommended pad length | 35 ft. |
| Pad static pressure | 0.05 in |
| Evaporative cooling efficiency | 73% |
| Wet bulb / pad temperature | 33.22 C |
| Incoming air temperature | 37.77 C |
| Incoming Rh | 74 % |
| Pad water usage | 2.9 gals/min |