Design of Room Cooling Facilities(With Plan)

8/9/2019 Design of Room Cooling Facilities(With Plan)

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Design of Room Cooling Facilities:

Structural & Energy Requirements

Contents

Why Cool

Planning Before You Build

Types of Produce, Quantity and Movement of Produce,

Storage Capacity, Produce Packages, Location and Layout

Design and Contruction

Foundation and Floor, Insulation, Doors, and t!er "ard#are Items

Calculating the Heat Load

Sizing the Refrigeration System

Reducing the Refrigeration Load

Other Factors to Consider

Condensation and "umidity, Sanitation and Maintenance,

Temperature Control, Container Design and Positioning

Summary

Plan for a Refrigerated Storage Building

Proper temperature control is essential to protecting the quality of fresh produce. By

constructing and maintaining their own cooling facilities, farmers, packers, and roadsidevendors can substantially reduce the overall cost of owning one of these useful structures. This

publication describes how to plan a postharvest cooling facility of modest size and how todetermine its structural and energy requirements.

Why Cool?

Most fruits and vegetables have a very limited life after harvest if held at normal harvesting

temperatures. Postharvest cooling rapidly removes field heat, allowing longer storage periods.Proper postharvest cooling can:

Reduce respiratory activity and degradation by enzymes;

Reduce internal water loss and wilting;

Slow or inhibit the growth of decayproducing microorganisms;

Reduce the production of the natural ripening agent, ethylene.
http://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#whyhttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#planninghttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#designhttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#calculatinghttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#sizinghttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#reducinghttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#otherhttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#summaryhttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#planhttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#planninghttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#designhttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#calculatinghttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#sizinghttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#reducinghttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#otherhttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#summaryhttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#planhttp://www.bae.ncsu.edu/programs/extension/publicat/postharv/ag-414-2/#why


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!n addition to helping maintain "uality, postharvest cooling also provides mar#eting fle$ibility by

allowing the grower to sell produce at the most appropriate time. %aving cooling and storage

facilities ma#es it unnecessary to mar#et the produce immediately after harvest. &his can be anadvantage to growers who supply restaurants and grocery stores or to small growers who want to

assemble truc#load lots for shipment. Postharvest cooling is essential to delivering produce of

the highest possible "uality to the consumer.

Planning Before You Buil

'lthough small, commercial, contractorbuilt cooling rooms are available, they are often much

more e$pensive than ownerbuilt structures. !n addition to avoiding a substantial amount of the

construction cost, you can tailor a cooling facility to your individual needs by designing andbuilding it yourself. (hether the cooling facility is built or bought, you can ensure its

effectiveness by giving careful thought to the topics discussed in the following sections.

!y"es of Prouce. )ifferent types of produce have different cooling re"uirements. *or e$ample,

strawberries, apples, and broccoli all re"uire nearfreezing temperatures, whereas summer s"uashor tomatoes can be in+ured by low temperatures &able -. !f small "uantities of produce with

different cooling re"uirements must be cooled or stored together, the temperature will have to be

set high enough to prevent chill in+ury of susceptible produce. &his temperature, however, willnot provide optimum "uality and storage life for other types of produce.

!a#le $% Proucts !hat Sustain Col n'ury

Chill sensitive Freeze Sensitive(below 40-45 F) (below 32 F)

Beans all ty!es" #!!les

$gg!lant #s!aragus

O%ra Bram&les

Pe!!ers Ca&&age

Potatoes Peaches

Pum!%ins S'eet corn

S(uash summer" Stra'&erries

S'eet!otatoes S(uash 'inter"

)omatoes

Watermelons

Some fruits and vegetables produce ethylene gas as a natural product of ripening and respond to

this gas by accelerating their ripening. /thers do not produce ethylene but are very sensitive to it&able 0. *or sensitive produce, minute "uantities of ethylene gas will greatly accelerate the

ripening process even at low storage temperatures. !t is very importantnot to store items

sensitive to ethylene with those that produce this gas.

!a#le (% Proucts !hat Prouce Ethylene or )re Ethylene Sensiti*e%


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Ethylene Producers Ethylene Sensitive

#!!les Broccoli

Cantalou!es Ca&&age

Honeyde' melons CarrotsPeaches Cucum&ers

Pears Cut flo'ers

Plums $gg!lant

)omatoes *reen &eans

Leaf greens

O%ra

Peas

Pe!!ers

S(uash

S'eet!otatoes

Watermelons

!n addition to ethylene sensitivity, some types of produce generate odors that are readilyabsorbed by other items. &he odor of apples and onions in particular are easily transferred to

other produce items. 1onse"uently, care should be e$ercised when storing other products with

either of these items.

Most conflicts in storing mi$ed produce are avoidable, but serious problems may develop if theuni"ue re"uirements of each commodity are not #ept in mind. 1omplete information on

postharvest cooling and storage re"uirements of most types of 2orth 1arolina fresh produce may

be obtained from 3$tension Publication '45-5-,Introduction to Proper Postharvest oolingand !andling "ethods.

+uantity an ,o*ement of Prouce. 'lthough the primary function of any cooling facility is

to remove field heat, an important secondary function is to provide cold storage space. 1ooling

capacity and storage capacity are separate characteristics, but together they determine the size ofthe facility. 1ooling capacity and, to a lesser degree, storage capacity depend upon the size of the

facility and the capacity of its refrigeration system. &herefore, it is important to determine the

amount of produce you are li#ely to cool and store.

' refrigeration system can be thought of as a pump that moves heat from one place to another.Refrigeration capacity, a measure of the rate at which a system will transfer heat energy, is

normally e$pressed in tons. ' ton of refrigeration capacity is the ability to transfer the amount of

heat re"uired to melt - ton of ice in a 05hour period 066,777 8tu. Said another way, arefrigeration system of -ton capacity is theoretically capable of freezing - ton of water in 05

hours. &hat is, it can transfer 066,777 8tu in 05 hours or -0,777 8tu per hour.

&he correct size for a refrigeration unit is determined by three factors, the first of which is the

weight of produce to be cooled. Since most produce is sold by volume by crates, bo$es, orbushels you may have to determine its weight per unit of volume. /bviously, the more produce

to be cooled, the larger the refrigeration unit must be.


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&he second factor is the minimum time re"uired from start to finish of cooling. !deally, cooling

should ta#e place fast enough to prevent serious degradation of the produce but no faster.

1ooling produce faster than necessary is unduly e$pensive because the refrigeration system mustbe larger and the demand cost for electrical energy is greater. &o cool a load of produce in 0

hours instead of 5 may re"uire twice the refrigeration capacity, and the cost of electricity may be

three times as high.

&he third factor is the nature of the refrigerated space: its size, how well it is insulated, and howit is to be operated. 8ecause as much as onehalf of the refrigeration capacity in a typical facility

is used to overcome heat gained through the floor, walls, ceiling, and doors, it is important to

minimize these gains. Selecting a refrigeration unit of the proper size will be discussed in a latersection.

Storage Ca"acity. &he decision to cool and ship produce immediately or to store it for a time

often depends not only on the type of produce and mar#et conditions but also on the availability

of space in the storage facility. &he type of produce you grow will determine, in part, how much

storage space you need. /bviously, highly perishable produce re"uires less storage space thanless perishable items simply because it cannot be held for long periods without losing "uality.

!f the construction budget will allow, it is advisable to construct enough storage space for at least

one day s ma$imum harvest of the most perishable commodities and even more for the lessperishable items. !t is much easier to build ade"uate storage space initially than to add space

later. 1ost per s"uare foot decreases and energy efficiency increases with the size of the facility.

'de"uate storage space should not be overloo#ed, since one of the ma+or benefits of apostharvest cooling facility is the mar#eting fle$ibility it allows by providing short term storage.

/n the other hand, e$cess unused storage space is a waste of energy and money.

&o determine the amount of refrigerated space to build, use the following formula:

+ , -./ 0 C 1 S"

(here: + , 2olume of the refrigerated s!ace in cu&ic feet

C , ma3imum num&er of &ushels to &e cooled at any one time

S , ma3imum num&er of &ushels to &e stored at any one time

'fter you have determined 9, divide it by the ceiling height in feet to obtain cooling room floor

area in s"uare feet. eep in mind that the ceiling height should be no more than -6 inches greaterthan the ma$imum stac#ing height of the produce you intend to cool. *or produce pac#aged in

bul#, volume must be converted to bushels before applying the above e"uation.

Prouce Pac-ages%&he fresh produce industry uses a bewildering array of pac#agingcontainers, such as fiberboard cartons, bul# bo$es, bas#ets, wirebound cartons, and trays *igure-. &he types of pac#age you select should always conform to the standard type used by the

wholesale mar#et. Produce mar#eted in nonstandard containers often does not sell easily.


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Figure $% Common "rouce "ac-ages%

8e sure to allow enough space in your floor plan for aisles and wal#ways. &hey must provideready access to all the produce stored in the room. *or small to medium cooling rooms, devoting

0 percent of the total floor space to aisles and wal#ways is not e$cessive. Since produce

containers should never be allowed to touch interior or e$terior walls, reserve at least an

additional < inches of space for good air circulation.

&here are also limits as to how high produce containers may be stac#ed. &he ma$imum height

varies with the commodity and type of pac#age but should not e$ceed a safe level nor damage

the produce. &o allow for good air circulation, produce should never be stac#ed closer than -6

inches to the ceiling. (hether or not you anticipate the use of forcedair cooling, allow sufficientspace for active cooling. &hat is, allow space to install forcedair fans or to spread the produce

out for rapid cooling.

!f the produce volume is sufficient to +ustify the use of a lift truc# and hence palletized loads,their dimensions should be considered in the design of the facility. )oors and aisles should be no

less than - -=0 times the width of the lift truc#s. Ramps leading to floors above grade should be

inclined at a slope of no more than - to . !t is also convenient to include a raised doc# for

loading truc#s and trailers.

.ocation an .ayout%&he location chosen for the cooling facility should reflect its primary

function. !f you plan to conduct retail sales of fresh produce from the facility, it should be locatedwith easy access to public roads. ' retail sales operation located away from the road, particularly

behind dwellings or other buildings, discourages many customers. 'de"uate par#ing forcustomers and employees, if any, must be provided. !f the cooling facility is used in connection

with a pic#yourown operation, it is best to locate it near restrooms and retail sales areas.

!f, however, the primary function of the cooling facility is to cool and assemble wholesale lots,ease of public access is less important. !n this case, the best location may be ad+acent to the


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pac#ing or grading room. !n addition to housing grading and pac#ing e"uipment, the space could

be used to store empty containers and other e"uipment and supplies when it is not needed for

cooling. 'll cooling and pac#ing facilities should have convenient access to fields or orchards toreduce the time from harvest to the start of cooling.

Regardless of how it is used, the facility will need access to electrical power and water. *orlarger cooling rooms re"uiring more than about -7 tons of refrigeration in a single unit, access to

threephase power will be necessary. &he location of e$isting utility lines should be carefullyconsidered, as connection costs can be prohibitive in some rural areas. 1onsult your local power

company for details. !n addition, it is a good idea to anticipate any future growth when locating

and designing your facility.

8efore you begin construction, familiarize yourself with any applicable laws, regulations, and

codes pertaining to construction and electrical systems, wor#er health and safety, and the

handling and storage of food products.

Design an Construction

Plan number ,577 cubic feet of

refrigerated space with a design storage capacity of appro$imately ?,777 bushels. &he nominaldesign cooling capacity is ?77 bushels per day with a ? -=0 ton refrigeration unit. 's e$plained

earlier, however, the re"uired refrigeration capacity cannot be accurately determined unless the

types and amounts of produce to be cooled are #nown.

&hese plans illustrate only one of many wor#able designs. (hat may be ideal for one operation

may not be suitable for another. !n developing the overall design, therefore, give seriousconsideration to how the produce will move throughyourfacility. )oors, loading doc#s, and

ad+acent wor# areas should be conveniently located to accommodate the flow of material.Remember the cardinal rule of industrial engineering, 'lways ma#e it easy to do the right thing.

&he construction of a produce cooling and storage facility is an investment in "uality

maintenance. &herefore, the materials and wor#manship of the facility itself should be of the best

possible "uality. Many different construction materials are suitable for such a pro+ect. &hedifficulty is deciding which ones are the most appropriate and cost effective for your application.

Many problems can be avoided by paying particular attention during the construction phase to

the items discussed in the following sections.

Founation an Floor%'lmost all postharvest cooling facilities built nowadays are constructed

on an insulated concrete slab with a reinforced, loadbearing perimeter foundation wall. &he slab

should be built sufficiently above grade to ensure good drainage away from the building,

particularly around doors. &he floor should also be e"uipped with a suitable inside drain todispose of wastewater from cleaning and condensation.


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&he floor of a refrigerated room must support heavy loads and withstand hard use in a wet

environment but still provide an acceptable measure of insulation. &he slab floor should be at

least 5 inches of wiremeshreinforced concrete over 0 inches of waterproof plastic foaminsulation board such as )/( Styrofoam or e"uivalent. *ive or even < inches of concrete may

be necessary for situations where loads are e$pected to be unusually heavy.

&he need for floor insulation is often poorly understood and therefore neglected to cut cost. &his

is false economy, however, since the insulation will pay for itself in a few seasons of use. !f theroom is to be used for longterm subfreezing storage, it is essential that the floor be well

insulated with at least 5 inches of foam insulation board having a rating of R07 or greater to

prevent ground heave.

'ny framing lumber in contact with the concrete floor must be pressure treated to prevent decay,

especially the sill plates and lower door frames, which may be in longterm contact with water.

'lthough no produce would normally come into contact with it, the lumber must be treated with

an approved nonto$ic material. !nformation on the to$icity of treated lumber should be obtained

from the building materials supplier. 'dditional information is available in 3$tension publication'4@@-,Pressure#Treated $outhern Pine% $ome &uestions and 'nswers.

)uring construction, the interface between the underside of the sill plate and the floor must be

sealed to prevent the movement of water. &his is easily done by completely coating the undersideof the sill plate with a heavy layer of suitable sealant before securing it to the foundation pad

with anchor bolts. &he sill plate mustbe ade"uately secured to the floor to prevent the building

from moving off the foundation in a high wind.

'lthough the plan shows a treated 5by5inch bumper guard ad+acent to the sill plate, a 5by


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Figure (% Bum"er guar

nsulation%&hermal energy always flows from warm ob+ects to cold ones. 'll materials, even

good conductors li#e metals, offer some resistance to the flow of heat. !nsulation, however, isany material that offers high resistance to the flow of energy. %undreds of different materials

have been used at one time or another for thermal insulation. Since selecting the properinsulation is one of the most important building decisions you will ma#e, it is important that the

material be not only cost effective but also correct for the +ob. &he characteristics of insulationmaterials differ considerably. Suitability for a particular application, not cost, should be the

deciding factor in choosing a material. Some of the important characteristics that should be

considered are the product s Rvalue, its cost, and the effects of moisture on it.

R/0alue%' measure of an insulation s resistance to the movement of heat is its Rvalue. &he R

for resistance number, is always associated with a thic#ness; the higher the Rvalue, the higher

the resistance and the better the insulating properties of the material. &he Rvalue can be given in

terms of a -inchthic# layer or in terms of the total thic#ness of the material.

&he total resistance to the flow of heat through any insulated wall is simply the sum of the

resistances of the individual components. &hat is, in addition to the thermal resistance of the

insulation, the inside and outside sheathing, layers of paint, and even the thin layer of air ne$t to

the surface contribute to the wall s overall thermal resistance. 'lthough they are highly weatherresistant and re"uire little up#eep, metal sheathing materials are very poor insulators. (hen

specifying building materials, be sure to select those with the best combination of economic

value and thermal resistance. &he Rvalues of common building materials are listed in &able ?.

!a#le 1% nsulation R/0alues for Common Builing ,aterials

-!"lueFull thic#ness

$"teri"l % inch thic# o& '"teri"l

"tt "nd l"n#et nsul"tion*lass 'ool4 mineral

'ool4 or fi&erglass 5./6

Fill-*y+e nsul"tion Cellulose 5./6

*lass or mineral

'ool -./675.66

+ermiculite -.-6

Wood sha2ings orsa'dust -.--

i,id nsul"tion Plain e3!anded e3truded

!olystyrene /.66

$3!anded ru&&er 8.//

$3!anded !olystyrene

molded &eads 5./9

#ged e3!anded


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!olyurethane :.-/

*lass fi&er 8.66

Polyisocyranuate ;.66

Wood or cane fi&er

&oard -./6

Fo"'ed-in-Pl"ce nsul"tion S!rayed e3!anded

urethane :.-/

etal siding ?6.6=

5@;7inch !ly'ood =.-/ 6.89

=@-7inch !ly'ood =.-/ 6.:->asonite !article&oard =.6:

-/@5-7inch insulated sheathing -.6:

=@-7inch Sheetroc% 6.8/

=@-7inch 'ood la!siding 6.;=

Cost%&he cost of insulation varies considerably with the type, whether e$pressed in dollars per

s"uare foot per inch of thic#ness or dollars per s"uare foot per unit of thermal resistance R. *ore$ample, even though the Rvalue per inch of polyisocyranuate &able ? is more than twice that

of loosefill cellulose, the cellulose may actually be less e$pensive in terms of insulating value

per dollar.

/f the insulation materials commonly used for refrigerated rooms, loosefill cellulose is usuallythe least costly, followed by batts and blan#ets, then various foam sheet materials, and finally

sprayed or foamedinplace materials, which are the most e$pensive. Sprayedon and foamedin

place insulations have the added advantage of sealing an otherwise lea#y structure and thereby

greatly reducing infiltration. Sprayedon foam also significantly reduces labor and material costsbecause an interior panel wall is not re"uired. 1ertain types of foam insulation may constitute a

fire hazard if carelessly handled, and care should therefore be e$ercised. 1hec# local fire and

building codes. !n selecting any insulation material, carefully consider the cost associated withinstallation and any additional material costs.

Effects of ,oisture%!n most types of insulation the flow of heat energy is impeded by smallcells of trapped air distributed throughout the material. (hen the insulation absorbs moisture, the

air is replaced by water and the insulating value is greatly reduced. *or this reason, insulationshould be #ept dry at all times.

(ith the e$ception of most plastic foam insulations, which are essentially waterproof, all

insulation materials must be used with a suitable vapor barrier. ' 5mil polyethylene sheet is

normally installed on the warm side outside of the insulation, the opposite of the normal


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practice for house construction. &his placement prevents the formation of condensation on and

within the insulating material. &he vapor barrier sheet must be continuous from floor to ceiling.

(here two sheets +oin, they should overlap -0 inches and be positively sealed for e$ample, withduct tape.

)oors and /ther %ardware !tems. &he door is a critical part of a cooling facility. !mproperlybuilt or maintained doors can waste large "uantities of energy. )oors should have as much

insulation as the walls and should be well weather stripped to reduce the infiltration of warm air.)oor gas#ets should always provide a good seal.

)oor seals can be chec#ed by inserting a thin sheet of paper between the door and the seal area

and then closing the door. &he seal is acceptable only if resistance is felt when the paper is pulledout. Remember that a large single sliding or swinging door is much easier to #eep tight than a set

of double swinging doors.

'll large doors have a tendency to sag over time unless they are diagonally braced and well

supported. Ase only the best grade of hinges and latches. 8e sure that the door can be openedfrom the inside. Plastic strip curtains are often added to reduce energy loss when the door must

remain open for long periods. &hese curtains allow free entry and e$it by people, produce, and

for# truc#s but bloc# the mi$ing of inside and outside air, which can waste a substantial amount

of energy. 'lthough there are many acceptable designs, three door section details that have beenproven in actual use are shown in *igure ?.


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Figure 1% !hree acce"ta#le oor esigns%

Calculating the 2eat .oa

&he optimal storage temperature must be continuously maintained to obtain the full benefit of

cold storage. &o ma#e sure the storage room can be #ept at the desired temperature, calculate the

re"uired refrigeration capacity using the most severe conditions e$pected during operation.&hese conditions include the mean ma$imum outside temperature, the ma$imum amount of

produce cooled each day, and the ma$imum temperature of the produce to be cooled. &he total

amount of heat that the refrigeration system must remove from the cooling room is called theheat load. !f the refrigeration system can be thought of as a heat pump, the refrigerated room can

be thought of as a boat lea#ing in several places with an occasional wave splashing over the side.

&he lea#s and splashes of heat entering a cooling room come from several sources:


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2eat Conuction heat entering through the insulated walls, ceiling, and floor;

Fiel 2eat heat e$tracted from the produce as it cools to the storage temperature;

2eat of Res"iration heat generated by the produce as a natural byproduct of its

respiration;

Ser*ice .oa heat from lights, e"uipment, people, and warm, moist air entering

through crac#s or through the door when opened.

E3am"le. &he following e$ample illustrates the method for calculating the amount ofrefrigeration needed to operate a cold storage facility.

&wo thousand bushels of summer apples are loaded into a storage room 0? feet s"uare and -5

feet high inside dimensions at the rate of 077 bushels per day. &he walls have an insulation

value of R-


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conduction, %1, through the walls is found by multiplying the area of the walls by the

temperature difference and dividing the product by the Rvalue.

Wall area s( ft" 0 )em!. Difference F"

HC Btu@hr" , 7777777777777777777777777777777777777777

R72alue s( ft F@Btu"

=4-;; s( ft 0 8; F

, 777777777777777777

=: s( ft F@Btu

, 54;:8 Btu@hr

%eat conducted through the ceiling is calculated using the same e"uation. %owever, since

the ceiling usually has a more direct e$posure to sunlight and hence a higher temperature,more insulation is installed in it, and the temperature difference in the calculation is

increased by -7 * that is, 67 * C -7 * D @7 *. !f applicable, the installation of an attic

fan will reduce the temperature considerably, but the cost of the fan and the electricity to

run it should be weighed against the saving in heat conduction.

/- s( ft 0 /; F

=4/58 Btu@hr , 7777777777777777

-6

%eat conducted through the floor is also calculated with this e"uation. %owever, since the

ground has an average yearround temperature of appro$imately * in most parts of

2orth 1arolina, less insulation is put in the floor, and the temperature differential used inthe e"uation is decreased to 0? *.

/- s( ft 0 // F 7 5- F"

=4=6: Btu@hr , 7777777777777777777777777==

&he total amount of heat conducted through the walls, ceiling, and floor is the sum ofthese three calculated values:

54;:8 Btu@hr 1 =4/58 Btu@hr 1 =4=6: Btu@hr , :4/68 Btu@hr

'alls" ceiling" floor" total"

0. Fiel 2eat%&he second source of heat is the warm produce brought into the coolingfacility. &he heat energy it contains is calledfield heat. &he amount of field heat is

usually calculated from the mean ma$imum monthly temperature in this e$ample, 67 *.&he apples are to be cooled from a field temperature of 67 * to the optimum cold storagetemperature of ?0 * within 05 hours.

*ield heat, *%, is the product of the specific heat, S%, of the crop the amount of heat

energy it holds per degree, the difference, )&, between the field temperature and the

storage temperature, and the weight, (, of the produce.

FH Btu@hr" , SH Btu@l&@F" 0 D) F" 0 W l&"


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&he specific heat of water is - 8tu per pound per degree *ahrenheit. Since fruits and

vegetables are mostly water, their individual specific heat is directly related to their water

content and can for practical purposes be estimated as -. *or actual specific heat values,see &able . *or this e$ample, we will use the actual value of 7.6>. &his means that 7.6>

8tu of heat must be removed to cool - pound of apples - *.

!a#le 6% S"ecific 2eat an 2eat of Res"iration for 2orticultural Cro"s 7ro8n in

5orth Carolina

Res!iration

7777777777777

S!ecific Heat Cool Warm

Commodity Btu@l&@F" Btu@l&@hour"

#!!les4 summer 6.;9 6.6=; 6.586

#!!les4 fall 6.;9 6.6=- 6.-86#s!aragus 6.8 6.-8/ -./-5

Beans4 &utter 6.95 6.=-5 6.9=:

Beans4 string 6.= 6.=:= 6.;;/

Beets4 to!!ed 6.6 6.6-; 6.6-

Blue&erries 6.;: 6.6-; 6.98;

Bram&les 6.;9 6.6- 6.9==

Broccoli 6.- 6.6- =.59:

Ca&&age 6.8 6.6-5 6.-/9

Cantalou!es 6.8 6.6-/ 6.56/

Cucum&ers 6.9 6.== 6.=96

*ra!es 6.;: 6.6=8 6.=9

*reen onions 6.= 6.6: 6.968

Leafy greens 6.6 6.=66 =.658O%ra 6.- 6.-/9 =./;5

Peaches 6.= 6.6-5 6.8::

Peas4 garden 6.9 6.=99 =.:/=

Peas4 field 6.95 6.=:6 =.//8

Pe!!ers 6.8 6.68: 6.-/-

Potatoes 6.;8 6.6-; 6.6//

S(uash 6./ 6.=:= 6.9/=

Stra'&erries 6.- 6.6: 6.;9-

S'eet corn 6.9 6.=;: =.:88

S'eet!otatoes 6.9/ 6.6:8 6.=66

)omatoes4

mature green 6.8 6.656 6.=9

)omatoes4 ri!ening 6./ 6.6:9 6.=;;

)urni!s 6.5 6.658 6.=56Watermelons 6.8 6.658 6.==6

'lthough a bushel of apples weighs about 5 pounds, we will assume a weight of 7

pounds to ta#e into account the weight of the container, which must also be cooled. &he

amount of field heat that must be removed is:


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7.6> 8tu=lb B 67 * ?0 * B 077 bu B 7 lb=bu D 5->,,,577 8tu per hour.

?. 2eat of Res"iration%&he third source of heat is the respiration of the crop itself.%orticultural crops are alive and give off heat as they respire. &he amount of heat

produced depends on the temperature, the crop, and the conditions and treatment the crop

has received. &he heat of respiration at various temperatures for horticultural crops grownin 2orth 1arolina is given in &able . &he amount of heat given off appro$imately

doubles for each -6 * increase in temperature. &herefore, less refrigeration is re"uired to

remove the heat of respiration when produce is cool than when it is warm.

/n the last day of harvest, the storage facility will contain -,677 bushels of cool applesand 077 bushels of field warm apples. 't this time the respiration heat load generated by

the stored crop will be the largest. &able shows that fieldwarm summer apples pro

duce about 7.?57 8tu per pound per hour, whereas properly cooled summer applesproduce only 7.7-6 8tu per pound per hour. &hus fieldwarm apples produce nearly -@

times as much heat by respiration as do cool apples. Since the freshly harvested warm

apples will be cooled to their proper storage temperature within one day, the heat of

respiration used in the calculation will be the average of the values. &he average is:

6.586 1 6.6=;

7777777777777 , 6.=9 Btu@l&@hr

-

&he weight, (, of the -,677 bushels of cool apples is appro$imately:

W , =4;66 &u 0 /6 l&@&u , 64666 l&

&he heat of respiration of the cool apples, %Rc, is:

HRc , 64666 l& 0 6.6=; Btu@l&@hr

, =4:-6 Btu@hr

&he weight, (, of the 077 bushels of warm apples is appro$imately:

W , -66 &u 0 /6 l&@&u , =64666 l&

&he average respiration rate, as given previously, is 7.->@ 8tu per pound per hour.&herefore the heat of respiration for the warm apples, %Rw, is:

HR' , =64666 l& 0 6.=9 Btu@hr

, =496 Btu@hr

&o obtain the total heat of respiration, %Rt, we add the value for cool and warm apples:

HRt , =4:-6 Btu@hr 1 =496 Btu@hr


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, 548=6 Btu@hr

5. Ser*ice .oa%&he fourth source of heat comprises a number of miscellaneous items and

is called theservice load. !t includes heat given off by e"uipment such as lights and fans

and by people wor#ing in the storage room, heat brought into the storage area by warmair when the door is opened, and heat that enters by air infiltration past faulty door

gas#ets and through other crac#s. &he amount of heat contributed by these sources is

usually very difficult to determine accurately. Service load is therefore dealt with

collectively and estimated to e"ual -7 percent of the heat from the other three sources:conductance, field heat, and heat of respiration. &he service load, SE, is therefore:

/. SL , 6.=6 0 :4/68 1 =94866 1 548=6 Btu@hr"

, -495= Btu@hr

&he total heat load is the sum from all four sources, as shown in &able


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R1, for a unit that would +ust handle the heat load in the previous e$ample under the conditions

describedwould be:5646:= Btu@hr

RC , 77777777777777777

=-4666 Btu@hr ton

, -./= tons' 0.-ton refrigeration unit would need to run continuously to #eep the temperature in this

storage facility at ?0 * under the conditions listed above. !f the conditions used in this calculation

were changed, a 0.-ton unit could be either too large or too small to maintain the desiredstorage temperature. &he capacity needed to maintain a temperature of ?0 * would increase if:

&he refrigeration system were to run only part of the day,

More than 077 bushels of fruit were stored every day,

&he building were larger,

&he incoming fruit were warmer than 67 *,

&he outside temperature were higher than 67 *,

&he amount of fruit in storage were greater.

*or e$ample, if harvesting were increased to 577 bushels of apples per day, the total heat load

would increase to nearly -,777 8tu per hour. ' 5 -=5ton unit running continuously would bere"uired to maintain a storage temperature of ?0 * under these conditions.

!n practice, it is advisable in selecting a refrigeration system to add reserve capacity to the

calculated rating as a protection against overloads. /f particular interest is the fact that

refrigeration systems, for reasons to be discussed later, are operated for a total of only -< to 07hours per day. &he total capacity of the system must be increased, therefore, to compensate for

the Foff time.F *or e$ample, if the system described in the e$ample were to operate for only - tons instead of 0.-

tons.

*urthermore, it is good practice to increase the capacity of the system by a chilling rate factor.

&he rate at which heat is removed from the produce is not constant during the cycle but is

greatest at the beginning. !f the capacity of the system is not sufficient to overcome the thermalinertia of the produce, cooling time may increase above the specified limits for the product. &o

compensate, a chilling rate factor of -. is applied to most fresh fruits and vegetables. &his factor

is applied in addition to the ontime factor. &hus the actual refrigeration system capacity, R1,

re"uired for the e$ample facility would be:

RC , -./= 0 =./ 0 =./ , /.:/ tons


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Reucing the Refrigeration .oa

!n the e$ample, field heat accounts for 6.@ percent of the total heat load. /nce field heat has

been removed from the crop, much less refrigeration capacity is re"uired to maintain the storagetemperature. (hile .


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Conensation an 2umiity. &he cooling coils of the refrigeration system *igure 5 must be

colder than the air in the room if the air is to be cooled. &he larger the temperature difference, the

greater the rate of heat transfer and the smaller and less e$pensive the cooling coils. %owever,the colder the coil surface, the more water vapor from the air will condense on the coils, either as

a li"uid or as ice. 3vaporator coil condensation represents wasted refrigeration capacity and

should be minimized. 'llowing hot, humid air to enter the cooling room is particularly costlybecause the refrigeration system must not only cool the air but also condense the additional water

vapor.

Figure 4% E*a"orator coils insie a cooling room%

8esides substantially reducing the energy efficiency of the system, condensation of water

reduces the relative humidity of the air. Since the optimum storage humidity for most produce is

@7 percent or greater, either moisture must be added with a humidifier or the difference betweenthe air and coil temperatures must be minimized. &he temperature difference can be reduced by

increasing the size of the coils enough that the airtocoil temperature differential is * or less.

2ot all refrigeration contractors are aware of the special needs of produce cooling, so whenpurchasing a system be sure to specify a * ma$imum airtocoil differential. &he system will be

slightly more e$pensive, but the benefits will soon pay for the difference in cost. &able 6 lists the

recommended ma$imum coiltoair temperature differential for various relative humidities.

!a#le >% ,a3imum E*a"orator Design !em"erature Differential

esired el"tive esi,n *e'+er"ture .u'idity i&&erenti"l


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(+ercent) ( F)

; /

/ ;

-

6 =6;; ==

;: =-

;8 =5

;- =8

;6 =/

9: =:

96 =;

!f the cooling room temperature is below ?< *, the coil temperature must be below freezing, and

ice will therefore accumulate on the coil surface. &he ice acts as an insulator, greatly reducing thecoilGs capacity to absorb heat from the air. &his ice must be removed periodically by some type of

defrosting mechanism, such as electrical resistance heaters, a warm water spray, or themomentary reversing of the refrigerant flow. !f the refrigeration system has sufficient capacity, it

may be allowed to remain off for < to 6 hours to let the ice melt naturally without addingsupplemental heat. Mechanisms designed specifically to aid defrosting introduce heat into the

room to melt evaporator ice, thus adding to the total cooling load. &he amount of heat added,

although small, should be ta#en into account when calculating refrigeration unit size.

Sanitation an ,aintenance. !t is essential that storage rooms and containers be clean and

sanitary. 'll accumulations of condensation water should be piped outside. 1lean all storage

rooms thoroughly before filling them. !f molds are found growing inside the room, disinfect the

surfaces with a 7.0 percent solution of sodium hypochlorite - gallon of household chlorine

bleach in 07 gallons of water applied with a highpressure washer. 'llow the room surfaces toair dry for several days. Refrigeration coils, fans, and ducts should be inspected and cleaned

regularly. Refrigeration coils in particular can become clogged with dust and dirt, substantiallydecreasing their thermal efficiency.

!em"erature Control. !n controlling a cooling facility, the most important temperature is that of

the produce, not the air. Measuring the air temperature will not correctly indicate produce

temperature because the heat of respiration alwaysraises the temperature of the produce abovethat of the surrounding air. Put thermometers and thermostat sensing elements into the produce

or at least into the produce container. )irectly measuring the temperature of the pulp interior of

the product is the only accurate way to determine the produce temperature. !t is good practice to

use several pulp thermometers in various locations to obtain an accurate temperature reading.&hermostats and wetbulb thermometers should be recalibrated from time to time with an

accurate mercury thermometer. %umidistats can be chec#ed for accuracy with a slingpsychrometer. !f possible, avoid positioning the sensing elements of controllers on the e$terior

walls or ceiling. &ypical temperature controllers are shown in *igure .


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Figure 6% !em"erature controllers%

&he produce temperature and the humidity must be monitored fre"uently during cooling and

storage to prevent undercooling and chill in+ury. 'lso, maintaining the proper temperature and

humidity becomes more important with increasing time in storage. *or the proper cooling andstorage temperature and humidities, refer to 3$tension publication '45-5-,Introduction to

Proper Postharvest ooling and !andling "ethods.

Container Design an Positioning. &he movement of air inside the cooling room helps conduct

heat away from the produce. Produce containers should be designed and stac#ed to allow

sufficient air circulation to enhance the cooling rate and #eep the crop at the optimum storagetemperature. 3vaporator coil fans may be positioned to aid air circulation inside the cooling

room. *or the rapid cooling re"uired by many horticultural crops, it may be necessary to movecool air past the produce with additional fans. *ans designed and operated specifically to force

cold air through produce containers can reduce cooling time by more than 67 percent if sufficient

refrigeration capacity is available. *or more information, refer to 3$tension publication '45-5

?,*orced#'ir ooling.

Summary

'lthough cooling increases production cost, it is essential to maintaining high product "uality.

2o amount of cooling, however, will improve poor"uality produce. !f you wish to have high"uality produce after cooling and storage, you must start with high"uality produce. Maintaining

"uality re"uires harvesting the crop at the correct stage of maturity; handling it with tender,

loving care; and "uic#ly cooling it to the proper storage temperature.

Many factors must be considered when planning and building a cooling facility. 'mong them arehow it is to be used, the types and amounts of produce to be cooled and stored, and the desired

refrigeration capacity. &he correct size of a cooling facility cannot be determined strictly on a


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Fs"uare foot per acreF basis. Similarly, the capacity of the refrigeration system needed cannot be

accurately determined solely on the basis of the floor area or volume of the facility. 8y ta#ing the

time to follow the design procedures described in this publication, you can assure yourself thatthe facility you build will be ade"uate to meet your needs under all foreseeable conditions.

Plan 9$46: Refrigerate Storage Builing


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Prepared by

". +. Boyette, )tension 'gricultural ngineering $pecialist

-. . /ilson, )tension !orticulture $pecialist. '. stes, )tension "arketing $pecialist


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This publication was produced by the (orth arolina ooperative )tension $ervice withsupport provided by the nergy +ivision, (orth arolina +epartment of conomic and

ommunity +evelopment, from petroleum violation escrow funds. The opinions, findings,

conclusions, or recommendations e)pressed herein are those of the authors and do not reflect theviews of the nergy +ivision, (orth arolina +epartment of conomic and ommunity

+evelopment.

Published by

!2E 5=R!2 C)R=.5) C==PER)!0E E!E5S=5 SER0CE

2orth 1arolina State Aniversity at Raleigh, 2orth 1arolina 'gricultural and &echnical State

Aniversity at 4reensboro, and the A.S. )epartment of 'griculture, cooperating. State AniversityStation, Raleigh, 2.1., R.1. (ells, )irector. )istributed in furtherance of the 'cts of 1ongress of

May 6 and Hune ?7, -@-5. &he 2orth 1arolina 1ooperative 3$tension Service is an e"ual

opportunity=affirmative action employer. !ts programs, activities, and employment practices areavailable to all people regardless of race, color, religion, se$, age, national origin, handicap, or

political affiliation.

:@=7->7)WE7-=65=; Re2ised" #*78=87-

Design of Room Cooling Facilities(With Plan)

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