uses ror coja Proteccic
University of Florida, Institute of Food and Agricultural Scien(
Central Florida Research and Education Center Apopka T
CFREC-Apopka Research Report RH-87-13
The use of a thin layer of ice to seal the openings in shade fac
during cold protection is becoming common in the Florida cut o.Lage
industry. This method is attractive because it is fairly inexpensive
requires little hand labor, avoids the use of expensive/special
hadehouses, only shades the crop temporarily, and is devoid of the
isposal problems that accompany the use of plastic films to seal
structures. Icing the top of shadehouses may enable the safe use of
educed irrigation rates applied to the crop and thereby save consid
water and energy while reducing operating costs. However, the effect
his practice have not been well studied and best management stratec
ave not been developed.
During the winter of 1973-'74 a preliminary field test was condL
daho in which water was sprinkled on an aluminum window screen cove
closure at the onset of freezing temperatures (2). The screen and
heet of ice formed on it effectively reduced heat loss from the enc
nd simulated twig temperatures were 2-100C warmer inside the enclose
During the winter of 1985-'86, temperatures were monitored in tb
commercial shadehouses located in Volusia County, Florida, which wez
quipped with overhead sprinklers that enabled icing of the shade fa
ata obtained in those studies is outlined below.
Copper-constantan thermocouples (ANG No. 20, Omega Engineering,
tamford, CT) were installed at a shadehouse in Pierson, Florida, ar
attached to a dataloacer (PD2064. Esterline Angus Instrument CorD.,
staggered pattern; w3in i/of' nozzles. vnen operate at r p.s.1.
Assistant Professor of Ornamental Horticulture, Central Florida Re
and Education Center. 2807 Binion Road. Anooka. FL 32703.
inside sprinkler system delivered about 0.21"/hr of water (97 gal/acre/min)
at the locations where the thermocouples were positioned.
Figure 1 illustrates the temperatures recorded January 27, 1986, during
an advective freeze with strong northwesterly winds (gusts over 25 mph) and
clear skies. As is often observed, temperatures inside the shadehouse
prior to sunset were cooler than outside (A). Testing of the overhead
irrigation system raised the temperature directly below the top but not
near the ground (B). Turning on the irrigation system inside the structure
raised temperatures above those outside the shadehouse (C). The
thermocouple directly under the roof of the shadehouse recorded an
immediate, drastic decline in temperature after the overhead irrigation
10 Inside 8' --& Inside 2' -B- Outside 2'
A A....a A
S. ....... ... ..... .... .. ....
ABOVE ON OFF ON OFF
BELOW ON A
-15 i I I i I I
5:00 6:00 7:00 8:00 9:00 10:00
Figure i. Effects of irrigation above and below the roof of a shadehouse
on temperatures during an advective freeze (1/27/86).
system was started (D); this illustrates the potential for disaster when
using irrigation for cold protection during advective freezes. Under windy
conditions cooling due to evaporation and convective heat loss may be
greater than the heat gain due to the sensible heat and heat of fusion of
water (4). Shortly after the initial drop in temperature, temperatures at
both levels inside the shadehouse increased to above those outside (E).
However, temperatures just below the roof were considerably higher than
those near the ground which indicates the iced top was trapping heat that
was rising from below. By about 9:30 p.m. the temperatures inside the
shadehouse were the same as outside (F) indicating that the heat gain due
to irrigation water was being offset by heat loss convectionall,
evaporative and radiational) in these areas of this shadehouse. Similar
results have been reported previously (6). The use of windbreaks and
shelterbelts could help reduce such heat losses (1, 3, 5), and increases in
RH-87-13, page 2
the water application rate near the perimeter would help maintain higher
Similar results were obtained the following night when temperature and
wind conditions were less extreme (Figure 2). Running sprinklers above the
Figure 2. Effects of irrigation above and below the roof of
on temperatures during an advective freeze (1/28-29/86).
shadehouse caused interior temperatures to increase above those outside
(A). The lower sprinklers near the perimeter of the structure were of only
slight benefit in raising the temperature (B), heat was trapped just below
the shadehouse roof (C), and temperatures at all locations rose rapidly
after sunrise (D).
The results at this site indicate the need to reduce heat loss or apply
greater quantities of water near the windward perimeter of shadehouses
during advective freeze conditions. Since the crop in this shadehouse was
newly planted leatherleaf fern, the diesel engine turning the well pump was
run at a low rpm that was adequate to provide enough water pressure to
protect the majority of the crop but did not provide enough water to
protect fern at the perimeter of the shadehouse. Changing the operating
speed of the diesel engines is one way of varying the amount of water being
applied for cold protection purposes.
DeLeMn Springs Study
This site consisted of a 2-acre shadehouse divided into two 1-acre
halves. Both halves were covered with 73% woven polypropylene shade fabric
and the north sidewall of the shadehouse was covered with a non-porous
material to act as a windbreak. One half of the shadehouse was 7.5' tall,
RH-87-13, page 3
had overhead sprinklers (Senninger 4023-1-3/4" IP, 5/32" nozzles) that were
spaced 60' x 60' to ice the top and lower irrigation sprinklers (Rainbird
20AH-3.5, 9/64" nozzles) spaced 36' x 36' in a square pattern. The other
half of the structure was 6.5' tall, was not equipped with an overhead
irrigation system, and had the same lower irrigation sprinklers and nozzle
sizes as the other acre. However, the sprinklers were spaced on 30'
centers (square pattern) so that at any given operating pressure the
application rate for the iced-top acre was about 25% less than that for the
non-iced acre. For example, when operating at a nozzle pressure of 25 psi
the application rate of the lower irrigation system on the side where
sprinklers were spaced 36' x 36' would be about 0.23"/hr (102 gal/acre/min)
as compared to 0.30"/hr (136 gal/acre/min) for the other side.
Temperature data were recorded as described for the Pierson studies.
wind speeds were monitored using an anemometer (Model 2535, WEATHERtronics,
Sacramento, CA), but were generally too low to register. Data recorded at
this site on March 1-2, 1987 are illustrated in Figure 3. As is often the
case during calm radiation freezes, temperatures inside the shadehouse were
colder than outside (A). Irrigating with the overhead system elevated the
inside temperatures (B) and for the early part of the morning of the 2nd
both lower irrigation systems maintained about the same temperatures (C).
However, from about 1:45 a.m. on the temperatures were lower by about 0.8C
(1.40F) on the side with the lower application rate.
ABOVE ON OFF ONOFF
4 -. O .- .. ... ....
0~~~ ~ 0-----f -
-0- Iced 8- Outside -0- No Ice
7:30 9:30 11:30 1:30 3:30
I PM I AM I
Figure 3. Effects of irrigation above and below the roof of a shadehouse
on temperatures during a radiation freeze (3/1-2/86).
These results suggest that the technique of using ice to seal
shadehouses may reduce irrigation system water application rates required
RH-87-13, page 4
using snauenouses 5uJ. L-aU LUL ULJLa .ULUL CUBJC 6LMW &UAL ;i.AMJ %AQaA
in these studies needs to be carried out before it can be determined under
what conditions and to what extent icing of shadehouses is beneficial
during cold protection. These preliminary studies suggest that icing may
require the concurrent use of windbreaks and/or shelterbelts (or icing of
1 Boone, C. C. and R. H. Stamps. 1986. Shelter belts and windbreaks:
Are they for you? Cut Foliage Grower 1(11):1-4.
2 Cary, J. W. 1974. An energy-conserving system for orchard cold
protection. Agric. Meteorol. 13:339-348.