flowercrops
Forced-air
coolingfor California
J. F.Thompson,
byD.S.Farnham,
A.M. Kofranek
R.F.Hasekand
FORCED-AIR COOLING is a method
of quicky cooling packed boxes of
blooms. It allows sttippersto use their
present ordering and packing procedures while ensuring that the blooms
leave their shed at proper shipping
temperatures.It is also a convenient
method of quickly removing field heat
from blooms that are to be stored.
Maximum quality can be maintained
during long storageby quickly cooling
blooms to proper storagetemperatures.
There are alternativesto forced-air
cooling that could be used by the industry. For example, employeescould
assembleand pack boxes in cold, refrigerated rooms, and the product
would be kept cool during the packing
process.Another alternative is to develop wind tunnels of cool refrigerated
air. The products might then be cooled
after the order is assembledand before
blooms arrive at a packing station.
Forced-air cooling of blooms after the
boxes are packed was investigatedbecause this system could be developed
with the least amount of capital investment, and many existing cold rooms
could be utilized for cooling.
ln January 1977, approximatelY50
percent of the floral products produced
in California were sent to distant markets by trucks. Insteadof the few hours
of transit time for delivery of blooms
to market by air, truck transport requiresseveraldays.When warm blooms
are placed on a refrigeratedtruck, they
cool very slowly and rarely reach the
desired temperature by the time they
reach their destination.Figure I shows
that in a nonprecooledload of blooms
the average bloom temperature does
not drop below 46 degreesFahrenheit,
and some blooms reach their destination at nearly 55 degreesF. Blooms
shippedat thesehigh temperaturesmay
suffer reduced quality and vase life.
Forced-air cooling helps ensure that
blooms transportedby truck are maintained at proper temperaturesso that
they will reach the east coast markets
in good condition.
Forced-air cooling is a method of reducing flower temperature by pulling
32-degree-F refrigerated air through
packed boxes of blooms. In a typical
system, vented boxes are placed in a
refrigerated room and stacked next to
an exhaust fan. The fan pulls refrigerated air through tlre blooms, which
cool by releasing their heat to the cool
air. Then, the stightly warmed air is
directed to refrigeration coils, where it
is cooled back to 32 degreesF. Figure
2 shows a schematicof a sYstemfor
cooling a small number of boxes.
OPERATION of a
EFFICIENT
forced-air cooler requires that the
boxes be vented on each end with
vents occupying 4 to 5 percent of the
end area. (The present2-inch diameter
vents occupy 2.5 percent of the end
area and reduce air flow by about 10
percent over properly vented boxes.)
The blooms must alsobe packedso that
no paper restrictsair flow. This means
that paper should not be placed over
the ends of the boxes. and, if blooms
are packedin a wedgeformation, paper
should not be placed over the entire
bottom wedge, preventing air from
flowing to the top wedge. (See figure
3.) Much of the paper currently packed
with blooms is designed to soak up
moisture. Blooms maintained at 32 to
38 degreesF produce very little moispotternsin o nonprecooledlood of blooms.Bloomswere ture,
Figurel. Temperoture
and no paperis neededfor moistruckfor the first eight hours.
tronsporledin o nonrefrigeroted
ture absorption.
Figure3. Poperplocementin box of cut flowers
Figure2. One type of forced-qirprecoolingunit
Carnations and roses shipped without proper cooling produce a great
deal of heat from respiration. Maxie
et aI (l) demonstratedthat heat production increasedrapidly as temperatures increased(table l). It should be
noted that the production of respiratory
heat is very similar for the two crops.
The temperaturerequired to successfully store carnations,rosesand mums
has been known by the industry for
many yearsto be at or near 32 degrees
F (2), (3), (4). Many of the bloom
temperaturesmeasuredon trucks during the past year were much abovethis
temperatureand may have contributed
to poor producequality. Proper cooling
of blooms before trucks are loadedcan
provide desirable storage conditions
over long distances.Orchids, gladiolus
and other tropicals have higher optimum storage temperatures. Recommendations in USDA Handbook 66
should be followed for them.
Moisture accumulationby blooms in
boxesshippedby truck may createconditions favorablefor botrytis and other
post-harvest diseases. When warm
blooms are placed on a refrigerated
truck, respirationcontinuesat a relatively high rate for many hours. The
water produced condenses on the
blooms.the plasticsleevesand packing
materialsas the bloomsgraduallycool.
One experimentwas conductedat Watsonville CA to evaluatethe moistureaccumulationproblem. The data obtained (table 2) show blooms cooled
u,ith forced air and shippedin plastic
sleeveshad much les moisturepresent
,rn rhe. sieevesthan srmrlar bloom.
placrd in the refrigerator while ther'
werr warm. Packed boxes of blooms
can rewarm rapidlf if placedin direct
sunlightor a warm environment.When
rewarmed, the respiration rates of the
However, recent laboratory studies on
floral products are drasticallyincreased, chrysanthemumsand carnations have
with the respiration rate being deter- shown that forcing air over blooms at
mined by the producfiempiiifure (ta- 10 times the recommendedvelocity and
ble 1). Moisture will again condense for more than 15 times longer than
on blooms,sleevesand packing material recomrnendedhad no detectableeffect
if the box is returned to refrigeration. on quality. If recommendedair rates,
Proper cooling methods and continu- cooling times, air temperatureand relaous refrigeration will prevent this tive humidity are adhered to, blooms
problem.
should not be damaged by forced-air
Blooms cooled with forced air and cooling.
allowed to rewarm do not accumulate
moisture during the rewarming process.
Some shippers are concerned that A FORCED-AIR COOLING SYS.
cooled blooms would acumulate.excess TEM-There .ue several requirements
moisture or sweat if sent to market by for a successfulforced-air cooling syv
air after being cooled with forced air. tem. Some of the elements are wellThe data in table 2 do not substan- known and have been sufficiently intiate that opinion. The vents used by vestigatedto date. Others require furCalifornia shippers (figure 2) only oc- ther developmentand evaluation.
The requirementsthat must be incupy about 2 percent of the box end
surface area, so there is little opportu- corporatedinto a forced-air cooling sysnity for warm, moist air to come into tem:
o The refrigeration capacity must
contact with blooms after the box is
returnedto a warm environment.Boxes be adequatefor the job. Data summarof blooms, however, should always be ized in table 3 illustrate the refrigerakept from exposure to high tempera- tion capacity required for shipping optures and direct sunlight.
erationsof various sizes.The refrigeraForced-aircooling doesnot appearto tion systemshould be designedto maindamagethe blooms.It might be thought tain temperature of 32 degreesF and
that forcing refrigerated air through a relative humidity of at least 90 perthe blooms would tend to dry them. cent.
Cornotions
Iemp
32
68
86
l0a
Btu/lon/hr
Btu/ton/hr
respirotory heof respirolory heol
89
2,191
4,730
?,653
| 4.718
95
2,685
4,858
7,990
t3,245
Boxesvenled Box nol vented
ond precooled or precooled
box
box
oox
refrigeroted rewormed refrigeroted
s un s hi n e
blooms
25
36
74
m i ni o l u r e
c o r n o t i o n s1 9 . 5
25.6
76.5
Toble L Rotesof respirotoryheot pro. Toble 2. Percentof plosticsleevescovd t . r c t i cbny l m p r o v e dW h i t e S i mc o i n o - ered with moisture,August31, 1976
fionsond ForeverYoursroses
Moximum
n u m b e ro {
boxescooled
oer hour
APproximole
refrigero.lion
r e q u i r e m e n "l t ( t o n s )
2to3
5
3 to 4
Io
6to8
20
12 to 16
40
l ) A c t u o l r e f r i g e r o t i o nr e q u i r e m e n l sf o r o
specificsystemshould be determined by
on engineer.
Toble 3. Refrigerotionrequirements
P r e s s u r eC o o l i n g
Air f low(r) inches time
lltlminibot (of woler) (min)
cornotions
chrysonthemu ms
60
0.5
2
100
40180
70265
5s
35
l) For more thon one box, oir flow equols
number of boxes x oir flow, pressure
remsins cons?ont,cooling lime ramoins
constont.
Toble4. Fonrequiremenls
Literoture cited
(l) Moxie, E. C., D. S. Fornhom;F. G. Mitchell,
ond N. F. Sommer.1974. Temperoture
Monogement Effects on Quolity of Cornotion Flowers ond Rosebuds,Colifornio Agriculture,Vol 28, No. I, pp6-7. Jonuory 1974.
(2) Holley, W. D., ond Boker, R. Cornotion
Production, W. C. Brown Co. Inc., Dubuque lA, 1953, p97.
(3) Arlostolerz,J. W, ond Longhons, R. W.
Roses,o Monuol on the Culture, Monogement, Diseoses, Insects, Economics ond
Breeding of Greenhouse Roses, pennsylvonio Flower Growers, New York Stoie
Flower Growers' Associotionond Roseslnc.
1969, ppl50-156.
(4) Lourie, A.; Kiplinger, D. C., ond Nelson,
K. S. Commerciol Flower Forcing, McGrowHill Book Co. Inc., 1958, pp458-459.
(5) Storoge Recommendolionsfor Cut Flow"
e r s , R o s e sI n c . , l l 5 2 H o s l e t t R o o d , H o s l e t t
Ml.
(6) USDA Hondbook '66. The Commerciol
Storoge of Fruits ond Vegetobles, ond
Florist ond Nursery Stocks
r The forced-airsystemmust have ties for cut flowers. The floral industry
should develop a systemof complete
sufficient air-flow capacity. The arr
flow and fan capacity required are refrigeration similar to that us€d by
the California fresh fruit and vegetable
summarizd in table 4. Frequently. the
industry.(Living plantsshouldbe hanquestion arises, "Can I speed up the
dled with a different system.)
rate of cooling by increasing the air
r Marketing practices that permit
flow through the packedflower boxes?"
proper cooling and temperature manRecentexperimentsat the University of
California at Davis and Salinas show agement of floral products must be
adopted. Forced-air cooling, in itself,
that air flow rates in excessof those in
table 4 will only decreasecooling times will not solve problems of poor hanslightly and require prohibitively large dling causedelsewherein the distribution channel.
fans to produce tlte pressureneededto
obtain higher air-flow rates.
o Packagingmust be adapted to fit
the total handling system.Standardized
box sizesand box strengthcriteria must
be developedfor forced-air cooling and
refrigerated truck transit. Standardized
box sizeswill allow loading patternsto
be developed to assure adequate air
flow through the entire truckload of
blooms.
. Blooms must be kept under continuous refrigeration after cooling.
Growers and shippers should strive fcr
completely refrigerated handling facili-
EDITOR'S NOTE: D. S. Farnham is
farm adviser,SantaCruz and Monterey
counties.I. F, Thompson is extension
specialist, agricultwal engineefing; R.
F. Hasek is extension specialist, floriculture, and A. M. Kolranek is professor.of lloriculture at the University of
California, Davis.
Partial funding of their proiect was
provided by the Northern Calilornia
Flower Shippers'Association.
The authors thank Roger E. Rig,
agricultural
marketing
specialist,
USDA, Fresno, for his advice and as_
sistanceon the proiect. They also thank
nurseriesand wholesaleflorists lor the
contributionsol bloontsand lor useol
their refrigeration antl packing shert
facilities: A. Nagamine Nursery,l,l,otronyille; Siri Bros. Nursery;BiIl Suvet,-
asu Wholesale Florist, Sunnyvale;
Mount Eden Nursery, Mount Eden;
Cut Flower Exchange,Sunnyvale;TST
WholesaleFlorist, Salinas,and the WiIliant Zappattini Co., Mountain View.
Reprinted from Floristsr
Review 161 (4L62): 36-8