What type of cooling system do I need for my greenhouse ?
NO COOLING
1. Inside temperature of greenhouse can exceed 140 degrees F.
2. Plants will die within a short period of time.
NATURAL VENTILATION
1. Roof vent opens to allow hot air to escape to outside.
2. Door or other opening must be left open to provide for incoming air from outside to replace exhausted air.
3. On hot summer days temperatures can rise 20 to 30 degrees above outside temperature.
4. Recommended for mild climate areas only.
FAN & SHUTTER COOLING
1. Outdoor air is introduced through motorized inlet shutters.
2. Hot air is exhausted by exhaust fans.
3.Temperature inside house can be maintained within 10 degrees of outdoor temperature with properly designed system.
4. Fans and shutters are controlled by thermostat.
FAN & SHUTTER COOLING with SHADE CLOTH
1. Outdoor air is introduced through motorized inlet shutters.
2. Hot air is exhausted by exhaust fans.
3. Shade cloth is placed over exterior of greenhouse or suspended from wires placed on inside.
4. Temperature inside house can be maintained within 3 to 4 degrees of outdoor temperature with properly designed system.
5. Fans and shutters are controlled by thermostat.
EVAPORATIVE COOLING (Positive Pressure)
1. Outdoor air is cooled by Evaporative Cooler (located outside) and discharged into greenhouse.
2. Hot air is exhausted through outlet shutters which operate automatically on pressure differential.
3. Temperature inside house can be as much as 10 to 15 degrees cooler than outdoor temperature with properly designed system.
4. Evaporative Cooler is controlled by thermostat.
5. System efficiency can be increased with the use of shade system. The fans will not have to work as hard to maintain the desired temperature.
EVAPORATIVE COOLING (Fan & Pad)
1. Outdoor air is drawn through pad cooling system located on one end wall of the greenhouse. This cool air enters into the greenhouse.
2. Hot air is exhausted by fans mounted on the opposite end wall of the greenhouse.
3. Temperature inside house can be as much as 10 to 15 degrees cooler than outdoor temperature with properly designed system.
4. Fan & Pad System is controlled by thermostat.
5. System efficiency can be increased with the use of shade system. The fans will not have to work as hard to maintain the desired temperature.
How does an evaporative cooling system work?
The heart of an evaporative cooling system is the pad where the water evaporates. This pad is manufactured of fluted cellulose sheets that are glued together. This material is chemically impregnated with special compounds to prevent rot and ensure a long service life.
A special water distribution system spreads water over the surface of the pad, ensuring a uniform supply of water to keep the entire air contact surface thoroughly wetted.
Fans on the opposite wall of the building create a negative pressure inside the building, causing air to be drawn through the pads.
Evaporation results from contact between air and water. A control system operates the water pump and turns the fan(s) off and on.
On a hot sunny day, the moisture content of the atmosphere remains virtually constant. This means that the relative humidity is lowest in the afternoon when the temperature is at its highest. And the lower the humidity, the better the evaporative cooling effect. In other words, the cooling effect is best when you need it the most.
Temperature reduction at pad at various conditions.
| HUMIDITY % |
TEMPERATURE ENTERING PAD F. (C.) |
TEMPERATURE LEAVING PAD F. (C.) |
| 5 |
113 (45) |
75 (24) |
| 5 |
104 (40) |
70 (21) |
| 5 |
95 (35) |
66 (19) |
| 5 |
86 (30) |
61 (16) |
| 10 |
113 (45) |
79 (26) |
| 10 |
104 (40) |
73 (23) |
| 10 |
95 (35) |
68 (20) |
| 10 |
86 (30) |
63 (17) |
| 20 |
113 (45) |
84 (29) |
| 20 |
104 (40) |
79 (26) |
| 20 |
95 (35) |
72 (22) |
| 20 |
86 (30) |
66 (19) |
How do I size my evaporative cooling system?
1. The first thing that you need to determine is the amount of air required. This is stated in CFM (Cubic Ft. of Air per Minute).
2. The total CFM required is based on several factors:
A) Light Intensity - determined by your geographic location and whether you use shade cloth
B) Length of Greenhouse - from air inlet to air outlet
C) Temperature Difference - from air inlet to air outlet
3. Use the following formula to determine the CFM required for your greenhouse:
CFM = Length x Width x 12
Example: Greenhouse that is 12' wide and 24' long requires 3456 CFM (12 x 24 x 12)
4. Increase or decrease the CFM amount calculated by using the following factors:
Shade Cloth Percentage Factor
Length of Greenhouse Factor
| 25 Ft or Less |
26 Ft. to 50 Ft. |
51 Ft. to 100 Ft. |
| 2.0 |
1.5 |
1.2 |
EXAMPLE:
12' x 36' Greenhouse with 50% Shade Cloth.
Determine basic CFM required using standard formula. 12 x 36 x 12 = 5184 CFM. We must now adjust this based on the Length Factor and Shade Factor.
5184 x .5 (Shade Factor) x 1.5 (Length Factor) = 3888 CFM
This is the CFM required to properly cool this greenhouse. If using evaporative coolers (swamp coolers) make certain that you size these units in accordance with their Actual CFM instead of the Industry CFM figures.
Remember, you must provide an adequate exit for the total CFM being supplied by the evaporative cooling units. You can use an open door, roof vents or exhaust shutters properly sized for the total CFM. The most efficient system utilizes exhaust shutters situated on the wall opposite from the evaporative cooler.
