June 2022 - 42

technically speaking
BY ERIK RUNKLE
Evaporative Cooling,
Part 2: Maintenance
As discussed in the April 2022 issue of GPN magazine,
there are two major types of evaporative cooling used in
greenhouses: fan-and-pad or fog systems. The process of
evaporation absorbs energy from the air, which decreases the
air temperature. There are several factors that influence the
rate of evaporation (and thus efficacy of cooling), including
the amount of water vapor already in the air relative
to what it can hold (relative humidity or vaporpressure
deficit), air velocity and surface area of the
water being evaporated. These are all influenced
by the outdoor environment and the design and
maintenance of a greenhouse cooling system.
Evaporative cooling systems are only as good as
their design and maintenance. Even a well-designed
cooling system will be less effective without periodic
maintenance, especially for fan-and-pad systems. Part 1
of this article provided an overview of greenhouse
evaporative cooling methods. Here, general maintenance
guidelines of those systems are discussed.
First and foremost, follow the maintenance guidelines
for your system from the manufacturer or supplier.
Erik Runkle is
a professor and
floriculture
Extension specialist
in the department
of horticulture at
Michigan State
University. He can be
reached at runkleer@
msu.edu.
Regardless of cooling system type, the quality of water
has a large impact on maintenance frequency. Unless " pure "
water is used (reverse osmosis or deionized water), minerals
will accumulate in systems (pipes, pads, nozzles, etc.),
especially calcium.
Water evaporates as pure water and leaves the mineral
solids behind. Therefore, treating the water supply before
it enters the cooling system may be worthwhile. When your
water is moderately to highly alkaline, creating " pure " water,
or mixing it with your water to dilute its alkalinity, could be
worthwhile.
Fan-and-pad systems. Although these systems are
typically less expensive to install, they have more parts and
thus require more maintenance than fogging systems. The
following are some of the major maintenance suggestions:
* Routinely check that other greenhouse vents and doors
are closed when air is being pulled through the wetted
pads; otherwise, the efficacy of the system decreases
dramatically.
* Pads that are directly exposed to the outdoors may need
to be screened to prevent accumulation of debris (such
as cottonwood seeds). Clean these screens as needed to
ensure good air flow to the pads.
* Drain, flush and sanitize (using labeled disinfectants) all
parts of the water distribution system every three to four
months of use.
* Analyze the distribution of water released at the top of each
pad. There should be a thorough and uniform wetting of the
pad along its entire length. Adjust the water flow or make
other adjustments as needed.
* Control the growth of algae as much as possible by first,
operating fans without the pads for at least 30 to 60
minutes at the end of each day so that they dry out; second,
excluding light from the water tanks and distribution
systems; and third, ensuring fertilizer solutions do not enter
the system.
* Water collected at the bottom of the pads should be screened
before reuse. These screens need to be periodically cleaned
or replaced.
* A continuous, small amount of water should be discharged
from the tank and replaced with fresh water to control the
accumulation of minerals that leads to scale.
* Pads need to be periodically replaced because of the buildup
of salts in the water, algae or both. Inadequately maintained
systems will need more frequent pad replacement.
* Inspect all components of exhaust fans (blades, shutters,
motors, belts, etc.) to ensure they are clean and working
properly. Repair or replace as warranted.
Fog systems. Fog can be used for cooling in the summer
as well as during propagation in the winter. A well-designed
and installed system needs relatively little maintenance, as
outlined below:
* Every spring and with the pump on, inspect the pump area
and plumbing system to check for water leaks, paying special
attention to connections.
* After every few months of use, turn the system on and check
that each nozzle is properly functioning. Change the fineparticle
filter (if present) or replace nozzle as needed. Inspect
any other filters in the system and replace when warranted.
* Have a maintenance professional service pumps and water
purification systems (when present) every six to 12 months
of use.
Well-designed and maintained cooling systems create a cooler
greenhouse environment, which usually improves crop quality,
mitigates heat delay of flowering and creates more pleasant
working conditions. Poorly designed or maintained systems are
less effective and may be a waste of energy and water.
42 JUNE 2022 GPNMAG.COM
http://www.GPNMAG.COM
June 2022

Table of Contents for the Digital Edition of June 2022
