Griffin Working With Van Wingerden
Greenhouse Company
Benefits of Horizontal Air Flow
 The Horizontal Air Flow (HAF) system has been proven to be the most efficient
method for good greenhouse air circulation. The benefits of more uniform temperature,
better growth and less disease help you to produce higher-quality plants.
The concept of HAF is that air moved in a coherent pattern in a building such as a
greenhouse needs only enough energy to overcome turbulence and friction losses
to keep it moving. In other words, it just has to be “kicked along”. The fans need to
be sized and placed properly to do this.
Air is also heavy. The air over each square foot of floor area in a typical greenhouse
weighs about one pound. A 30’ by 100’ greenhouse contains about 1 ½ tons. Once
the air is moving it will coast along like an auto traveling on a level road. That is why
HAF is so efficient.
Benefits:
Uniform temperature – as the air moves in a horizontal pattern down one side and
back the other in a free-standing greenhouse or down one bay and back in an adjacent bay in a gutter-connected house, mixing
occurs from side to side and floor to ceiling. We have instrumented a number of houses and seldom see more than 2 deg. F.
difference between any two points. Because of the constant movement of the air, heat supplied at one end is carried to all parts
of the greenhouse quickly. Stratification is also eliminated.
Less disease problems – research has also shown that air movement of 50 – 100 ft/min is adequate to keep nighttime leaf
temperatures almost identical with the surrounding air. When leaf temperatures are allowed to cool much below the air temperature,
the dew point is reached and condensation occurs harboring disease organisms. Radiant cooling on clear nights, especially
in non-IR poly covered houses will cool plant leaves several degrees below air temperature. HAF will reduce this difference.
Carbon dioxide – During daylight hours, photosynthesis depletes the carbon dioxide that is in the
boundary layer of air next to the leaf. Moving air will replace this depleted air with fresh air having
higher carbon dioxide content. If carbon dioxide is being added, a lower level is usually adequate to
get the same plant response, for instance, 800 – 1000 ppm rather than 1200 – 1500 ppm.
 Cooling effect – during warm days in the spring and fall, solar radiation warms exposed leaf surfaces
to as much as 15 deg. F. above air temperature. This can cause burning of the leaves, flowers or fruit.
HAF will remove this excess heat and increase plant growth.
These are some of the major benefits from HAF. To look at some of the installation techniques, refer
to Griffin’s 2003 catalog, page 213 for fan sizing, location, and the number of HAF fans you will need.
Both Acme and Schaefer HAF fans are listed along with variable speed controls. You can also find this information in Griffin's 2003 online catalog (in PDF format) by scrolling down to the Horizontal Air Flow System section.
Height of the fans is not critical but is best located above head height to get them out of the way. In
many greenhouses there is a truss or collar tie that can be used for support. If the house contains
hanging baskets, a location a couple of feet above or below them is best.
 One problem that can occur from a poor installation is a short circuiting of the air across the house
before it reaches the next fan. This will show up as cold spots or areas of poor growth and is caused
by not adding enough energy to the air or having the fans too far apart.
During fall or late spring operation, the HAF system should be shut off when exhaust fans are
operating. Some of the fans oppose the flow of the ventilation air. Several growers have reported
that HAF operation has increased the effectiveness of natural ventilation systems such as roll-up
sides and will also reduce hot spots.
Maintenance is also important for efficient operation. Dust and dirt should be cleaned from the
fans to increase air flow and reduce motor temperature.
Most of this information has been taken from a paper done by John W. Bartok, Jr., Agricultural
Engineer in May of 1996.
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All articles and material featured in this Gazette cannot be duplicated without written permission.
Copyright © 2004 by Griffin Greenhouse & Nursery Supplies.
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