GREENHOUSE AIR CONDITIONING
VENTILATION AND AIR MOVING

U.S. Global Resources is proud to distribute and design environmental control systems based on Air Conditioning and Ventilation Principles.

We supply equipment and systems from worldwide warehouses and factories.

All of our published literature contains data based on 60 cycle power. Conversions to international 50 cycle are available and are supplied on request. DC, DCA AND CDR FANS USE 50/60 CYCLE DUAL VOLTAGE MOTORS AND OUR DESIGNS INCORPORATE THE DIFFERENCES.

We request you advise us of your voltage and power requirements on all electrical systems and equipment requests.

Information and Help in Deciding on
Air Conditioning and Ventilation Needs

When considering Air Conditioning and Ventilation,.we are basically dealing with maximizing air flow by either natural or mechanical means - with the goal being cooling to or near wetbulb.

Deciding on Natural Ventilation

Natural Ventilation works well for some crops, and in moderate climates, in houses not so large that outside breezes cannot more enough air by force or convection.

Many talk of Natural Ventilation being the wave of the future and contributing to a reduction of cooling costs.


Retractable roof ventilation. Top retracted
for maximum sunlight and ventilation.

When depending only on Natural Ventilation, you are at nature's mercy - slow wind speed or no wind speed can cause the greenhouse to heat up. We can't turn the wind on and off. In most cases, natural Ventilations results by design to be a loose "air filtering facility" - a problem when winter temperatures are low. One of the reasons Horizontal Air Flow Fans (HAF) have become so popular is because Natural Ventilation does not take care of all of the plants ventilation needs.

It is important to know that, in many cases if not most, Natural Ventilation does not allow adequate airflow within the plant canopy and micro climate of the plant. In naturally ventilated houses with turbulence and various pockets of no air, then we have the possibility of disease, with the result of more chemical controls.

We have observed, particularly in the tropics and subtropics, facilities growing dense vegetables and cut flower crops where the greenhouses are 200 feet (60m), 270" (80m), and even 250' (100+m) wide by similar lengths - depending on small roof vents and 10' (3m) or 12' (3.66m) insect screened sidewalls - using natural ventilation. Crop quality generally suffers. It is recognized that Mechanical Ventilation may not be possible for a number of reasons, but smaller units, with larger vents, special insect screen walls and ends, will greatly increase air flow.

In Natural Ventilated houses such vents are better than gutter vents. Most feel gutter vents do not open as high as some advertise, they often leak in rainy season, and do not give the best ventilation. The higher the sidewall the better, but the higher the walls the weaker the structure. Sloped or Boxed Insect Screen helps internal air flow. Sidewall vents are always beneficial if you are not considering Air Conditioning at first. But whether you have house or 3 or 4 houses gutter connected, you still have two sidewalls. Roll up sidewalls leak a lot of air unless you buy the more state-of-the-art systems and they can be expensive. Leaking air decreases effectiveness of Air Conditioning and increases the winter heating costs. If you do not use roof vents in Naturally Ventilated houses, it is not generally recommended that air entrances and exits be more than 120' (36m) to 144'(44m) apart, but it depends on crops and natural air movement.

See our information on Fan-Jets in this website. This is an outstanding ventilation system created by Acme many years ago. The system utilizes air intake shutter, Blower Fan, Prepunched Tubing, and it evenly ventilates the house as air is pulled into the fan, distributed down the tube and out the holes, and then is exhausted out of the house by a properly sized fan. It works well with Unit Heaters to complete a heat system, and also is an inexpensive and ideal air circulation system to move air in the greenhouse and push warm air onto the crop in the winter. A great addition to the greenhouse industry.

Volumes have been written about Greenhouse, Poultry, Hog, Animal, and Agricultural Buildings. The benefits are many. Each system has to be designed to fit each clients' special needs.

Deciding on Air Conditioning

The object in Fan and Pad Air Conditioning is to cool the outside air to wetbulb or as close as possible. To do so properly, efficiently, and economically is another matter. We have implemented over 1100 projects worldwide under every climatic condition known in urban and rural areas - small and large projects for over 40 years.

In the tropics many feel that Air Conditioning simply will not work, and in some cases it is true, but generally some benefits can be derived. Madras, India has always been considered an impossibly humid, high temperature place where fan and pad systems will never work. At the Swaminathan Institute, we were able to cool the greenhouse from 98oF (37C) to 86oF (30C) when the wet bulb was 85oF (20C) immediately after a rain, and the system worked much better under lower wetbulb conditions.

In deciding on Air Conditioning, we must remember that high humidity and high temperature rarely occurs at the same time. High humidity generally occurs in the morning, the coolest time, and drops as the temperature rises. Under ideal conditions, when you increase temperature of air 20oF you lower humidity 50%.

Some important considerations in deciding whether to Air Condition:

  1. The House must be tight. Fans draw air from every direction. A loose or broken roof can mean that the fan will pull air into the hot gable and pull the warm air down across the crop. So, the greenhouse must be tight.
  2. Correct CFM is essential. Too few and the air moving through will heat up and you will have major differences between Pad temperature and Fan temperature.
  3. You must have endwall framing to support the fans and Pads (we supply when requested and offer information to subcontractors).
  4. What crop are you growing - in some cases or certain moderate climates, some crops do not require Pads - only fans and shutters.
  5. Elevation - the higher the elevation, the thinner the air, and the more volume required.
  6. Solar level - the higher the foot candle, the greater the temperature rise through the house, unless properly designed.
  7. Distance from Pad to Fan (length or width of House).
  8. Integration with Natural Ventilation, Air Circulation systems, Heating systems. Growers do not want efficiencies with one system overriding the other.
  9. Cost - costs vary depending on all the the above factors, plus quality of fans and pad systems. Pad systems come in aluminum, Galvanized, and Stainless Steel. Fans in steel, aluminum, and galvanized. Six, four, three, and two bladed fans are rated are various efficiencies.
If you would like us to quote on Air Conditioning, Fan, or Pad Systems, please supply the following information or answer as many questions as possible:
  1. Length of greenhouse?
  2. Width of greenhouse?
  3. Height of greenhouse?
  4. Number of gutter-connected houses?
  5. Type of covering?
  6. Crop to be grown?
  7. Average summer temperature at 2 pm (1400)?
  8. Highest average temperature of the year?
  9. Elevation above sea level?
  10. Highest maximum temperature in the last 5 years?
  11. Any humidity records available?
  12. Any obstructions, such as a greenhouse built with one end or side against a building?
  13. New construction or retrofit?
  14. If being installed in an operational greenhouse, what is the name of the greenhouse manufacturer?
  15. In some regions of the world, price is the sole consideration. We then offer our least expensive fans and materials with no walls or screens, some on site assembly, and smaller pad systems. Is price your only or main consideration (YES/NO)?
  16. Voltage requirements?

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This page was updated on:  February 11, 2008