Cost Comparisons for Carbon Dioxide and

Mechanical Multi-Temperature Refrigeration Systems

On HJghway Trailers’

by

K. E. HokeAgricultural Marketing SpecialistU.S. Department of Agriculture

Office of TransportationInternational Division, Export Services Branch

Washington, D.C.

F. K. BuxtonU.S. Department of Agriculture

Offiqe of TransportationDomestic Division, Domestic Services Branch

Washington, D.C.

Abstract

Liquid carbon dioxide refrigeration offersa simple, reliable alternative to mechanicaltransport refrigeration for food delivery trailersoperated in an upper Midwestern area that couldbe cost effective when the refrigerant’s cost is$87 or less per ton. Operating and ownershipcosts were compared for both systems. Underthe conditions of the study, a carbon dioxidesystem was more economical than a mechanicalrefrigeration system when the cost of the liquidcarbon dioxide was $87 per ton or less. Thestudy indicated that a fleet of at least ten car-bon dioxide refrigerated units is needed to jus-tify use of a storage tank that can accept a 20-ton delivery of liquid carbon dioxide.

Introduction

The need to deliver economically frozenfoods, fresh meats, fruits and vegetables anddry groceries to convenience stores, institutionalfood service operations and restaurants in a

single vehicle has led to the development ofmulti-temperature refrigerated highway trailers.Distributors servicing the fast food and dairyindustries have been major innovators and usersof multi-temperature transport equipmentemploying new transport refrigeration tech-nologies.

The technology of using cryogenics tomaintain temperature control in food deliveryvehicles is not new. The U.S. Department ofAgriculture (USDA) in cooperation with cryo-genic suppliers and industry has conductedresearch and developed technologies needed toapply cryogenic refrigeration to the food trans-portation industry since the early 1960s [1,2,3].Karitas [4] recommended the use of multi-temperature trucks for institutional food deliv-ery systems. His studies show that the use ofsingle compartment trucks resulted in the high-est food delivery cost.

In 1984-85, the USDA’s Office of Trans-portation conducted field tests in cooperation

*The authors wish to acknowledge Liquid Carbonic Corp., Chicago, IL for Cryogenic refrigerationtechnical assistance in support of this research and Evans Bros., Waukesha, WI, for supplying refriger-ated transport equipment and basic cost data.

Journal of Food Distribution Research February 89/page 165

with a food distributor to evaluate the perform-ance of mechanical and cryogenic transportrefrigeration systems in multi-temperaturehighway trailers [5]. The cryogenic refrigera-tion system, based on the system patented byNielsen [6], injected carbon dioxide directly intoeach trailer compartment upon thermostaticdemand. A sketch of the liquid carbon dioxidefood delivery trailer is presented in Figure 1.The liquid carbon dioxide was carried in a1000-pound supply tank mounted under thetrailer behind the landing gear. Thermostatswere set to maintain O“Fin the forward, 35°F inthe middle compartments. No refrigeration wasprovided in the rear trailer compartment wheredry groceries were carried. The 45-foot Poly-urethane foam insulated trailers had thermalratings of 86 BTUS per hour per degree F. Themechanical refrigeration unit consisted of adirect expansion evaporator located in eachcompartment. The refrigeration capacity forthe front, middle and rear compartments was12,000,9,000 and 9,000 BTUS per hour, respec-tively. Bulkheads separating the trailer com-partments were constructed of two six-inchpolyurethane foam panels covered with nylonmaterial. Bulkheads were held in place withretaining bars locked into the trailer’s sidewallchannels.

Typically, trailer loading began around2:00 PM with palletized frozen items in thefront compartment, followed by fresh productsin the middle, and dry groceries in the rear.The mechanical refrigeration unit was startedupon completion of loading the frozen itemsand positioning the bulkhead separating thefrozen-fresh compartments. The cryogenicrefrigeration unit was started after the frozenitems and fresh products were loaded and therespective bulkheads positioned. Loading wasusually completed by 600 PM.

Before being dispatched at about 900 PMthe truck driver and his assistant reviewed theorders and special instructions for each store ontheir designated route. Each delivery routeincluded six to eight stops within a specifiedgeographical area. The trucks returned to thedistribution warehouse by 900 AM the nextmorning.

Results of the cooperative study showedthat the cryogenic refrigeration system rapidlyobtained the set temperature in each trailercompartment after door openings at stops tounload and maintained the set temperaturesalong the route within a very narrow range.Figure 2 depicts the air temperatures during afood delivery to a fast food store in a carbon

dioxide refrigerated trailer. Each door openingis characterized with a sharp rise in temperaturefollowed by a rapid lowering when the fooddelivery is complete and the unit is turned on.Since no refrigeration is required for the deliv-ery of dry groceries, the air temperature in thedry grocery compartment parallels the ambientair temperature. Temperature recovery rate isa critical factor in the delivery of frozen fooditems, particularly ice cream and prepared fooditems.

The temperature recovery rate withineach mechanical trailer compartment after dooropenings was considerably slower than the cryo-genic system. Also, the mechanical multi-temperature refrigeration system noise level washigher than the cryogenic system. For nightdeliveries to stores located near residentialareas, local ordinances require low noise levels.Mechanical refrigeration units are shut off dur-ing delivery. Cryogenic systems have littleoperating noise.

The economic feasibility of using a cryo-genic transport refrigeration system in multi-temperature highway trailers was not includedin the performance studies conducted in 1984-85. Purpose of the study was to compare thecosts between cryogenic and mechanical multi-temperature transport refrigeration systems usedto delivery food products.

Methodology

Cost information for 1987 was obtainedfrom the same food distribution company thatcooperated in the 1984-85 performance com-parisons. The cooperator’s cryogenic refrigera-tion operation is being run on an experimentalbasis to determine the operational and costcharacteristics of the system. The distributordelivers primarily to fast food restaurants, butalso to a few schools, colleges, hotels and hospi-tals. Operating costs were obtained from thefood distributor’s accounting records for 25refrigerated highway trailers (21 mechanical and4 cryogenic trailers) over the 1987 calendaryear. Values on the purchase price, salvagevalue, useful life, and interest rate for the trail-ers and refrigeration units as provided by thecooperator are shown in Table 1. Interest costsfor trailers and refrigeration units are computedby dividing purchase price less the salvage valueby two. This approximates the cooperator’saverage equity in the refrigeration units andtrailers during the “useful equipment” life. Thecooperator’s average equity plus a salvage valuewas multiplied by the current interest rate at theend of 1987 to estimate the interest cost. The

February 89/page 166 Journal of Food Distribution Research

Figure 1

A Liquid Carbon Dioxide Multi-Temperature Food Delivery Vehicle

Journal of Food Distribution Research February 89/page 167

(na

W-4&aJu

Uo

5s

i% T-11 I-I 1

40

2L4!-commaJm

;,

CLalNO0’=

L

I!llflllrtllllll

\

—’==.—.——. -.. -.—.4

Ill”llll 1]11111 ll”llj”ll”rl”l Tl”

N 6) K)N N

I(do) z121[lJ..v2IlIdNw

February 89/page 168 Journal of Food Distribution Research

Table 1

Variablm Used to Compute Interest and DepreciationIncluded in Ownership Cost for the Three-compartment Refrigerated Trailers

Purchase Salvage Useful Life Interest

Trailer $32,000 $2,000 10 11.5%

C02 Unit $10,800 $3,000 10 11.5%

Mechanical Unit $17,200 $250 7 11.5%

Table 2

1987 Total Costs Per Trailer for Fuel, Maintenance and OwnershipFor Carbon Dioxide and Mechanical Refrigerated Multi-compartment Highway Trailers

---------- Per Trailer ----------

Me-cal.

FuekCOZ -10 months @ $120/ton and

2 months @ $80/ton $5,923

Fuel oil, No. 2 @ $1.10/gal. $2,123

MaMenasceTrailer $1,737 $1,754

Refrigeration System s 315 $1,595

Ownership CostTrailer - Depreciation & Interest

@ 11.5% $4,955 $4,955

Refrigeration System - Depreciation& Interest@ 11.5% $1,574 $3,427

StorageR~nndcdc~mp (20 ton) -$990

TOTAL COST $15,494 $13,854

Journal of Food Distribution Research February 89/page 169

straight line depreciation method was used todetermine costs by expensing the purchase pricefor the trailers and refrigeration units minus thesalvage values over the useful life of the equip-ment. Variables used are shown in Table 1.

During winter operation in cold climates,the carbon dioxide trailers are heated in thenon-frozen compartments to prevent foods fromfreezing. The costs reported herein include thecosts associated with the purchase, operationand maintenance of a heating unit installed.The mechanical units were equipped with heat-ing provisions.

Results and Discussion

A comparison of the operating and own-ership costs for cryogenic and mechanicalrefrigeration systems used in three-compartmenthighway trailers during 1987 is shown in Table2, and lists the cost of fuel, maintenance, inter-est, depreciation, and storage tank rental. Thegreatest cost difference between the carbondioxide refrigeration system and the mechanicalsystem was in the ownership cost which aver-aged $1,853 lower for the carbon dioxide units.Refrigeration maintenance cost for the carbondioxide units also showed a substantial savingsof $1,280 per unit.

In this particular comparison, actual totalcost for the carbon dioxide refrigeration systemwas $1,640 per unit higher than for themechanical refrigeration system. This waslargely because the carbon dioxide price paid bythe cooperator was $120 per ton for the first tenmonths of the year and $80 per ton for theremainder. Had the carbon dioxide price been$80 per ton for the entire year, total cost wouldhave been $358 less per trailer than for themechanical unit. See the section on price scen-arios for carbon dioxide for the effect of dif-ferent price levels on total operating cost.

The carbon dioxide refrigeration systembecause of the few moving parts was less costly($1,280 per unit) to maintain and repair,Trailer maintenance costs were about the samefor both refrigerated systems. Rental of thecarbon dioxide storage tank (20-ton capacity)and transfer pump cost averaged $990 pertrailer.

Carbon dioxide fuel costs vary con-siderably throughout the United States accord-ing to demand and proximity to supply. Theprice the food distributor pays for carbon diox-ide is a major consideration when deciding toinvest in the carbon dioxide refrigeration sys-

tem. Also, the geographical location determinescarbon dioxide consumption--food distributorslocated in the cooler climates will not use asmuch of a cryogenic refrigerant as will fooddistributors located in warmer climates, Thesefactors are discussed in the following sections.

In Table 2 the actual total yearly costswere obtained from the food distributor’s 1987records. Maintenance costs for the cryogenicand mechanical trailers and refrigeration unitsare the total cost for labor, parts, lubricants,miscellaneous items and taxes.

Price Scenarios for Carbon Dioxide

Four price scenarios were developed toestimate cost of the system based on the pur-chase price of the carbon dioxide. The pricesused for carbon dioxide were $60, $80, $100and $120 per ton. Each of four carbon dioxideprices were combined with the cooperator’sownership and operating costs for the year 1987and are shown in Table 3. When liquid carbondioxide is priced at $120 per ton the yearly totalcost per trailer would be $1,679 above the costof operating a conventional mechanical trans-port refrigeration unit. At $100 per ton the costdifference is lowered to $664 per trailer. At$80 per ton, the liquid carbon dioxide unit totaloperating cost is $350 lower than the cost ofowning and operating a mechanical transportrefrigeration unit. At S60 per ton the total costfor operating the carbon dioxide unit isestimated at $1,363 lower than a comparablemechanical refrigeration unit. This illustratesthat the purchase price of the liquid carbondioxide is a major factor in determiningwhether a carbon dioxide system is cost com-petitive with a conventional mechanical system.Figure 3 also shows that the costs for a carbondioxide refrigeration system would be lowerthan a mechanical ref rigeration system when theprice of the liquid carbon dioxide is at or below$87 per ton.

The findings are based on the carbondioxide fuel consumption incurred by a singlefood distributor located in the northern midwestUnited States. The study does not reflect oper-ating costs of food distributors located inwarmer regions of the nation. The mean quar-terly temperatures and corresponding rate ofcarbon dioxide fuel consumption shown inFigure 4 illustrate the influence of climaticconditions on carbon dioxide consumption.Additional study and data would be requiredbefore conclusions could be made on operatingcryogenic transport refrigeration units inwarmer regions.

February 89/page 170 Journal of Food Distribution Research

Table 3

Projected Trailer Cost Comparison Between Carbon Dioxide (COZ) andMechanical Refrigeration Systems in Multi-Compartment Highway Trailers

At Different COZ Purchase Prices

---------- Purchase Price of COz/Ton ----------

Cost C02 per year* $6,088 $5,073 $4,059 $3,046

Total Cost COZ 15,553 14,518 13,504 12,491

Total Cost Mechanical** 13,854 13,854 13,854 13,8k

Cost Difference +1,679 + 664 -350 -l,36\

* Based on Co-operator’s 1987 consumption

** Cooperator’s 1987 maintenance and ownership cost

Table 4

Projected Total Fuel and Storage Tank Costs per TrailerFor 10 and 20 Trailers at Three Liquid Carbon Dioxide Prices

Using a 30- to 33-ton Horizontal Storage Tank

Number of Price of Total Annual Storage Tank C02 & Tank Cost perTrailers co2/to n Ost of c 02 ea Iv Rer ntal enta 1 cost Trailer

10 $60 $30,000 $12,600 $42,600 $4,260

10 $80 $40,000 $12,600 $52,600 $5,260

10 $100 $50,000 $12,600 $62,600 $6,260

20 $60 $60,000 $12,600 $72,600 $3,630

20 $80 $80,000 $12,600 $92,600 $4,630

20 $100 $100,000 $12,600 $112,600 $5,630

Journal of Food Distribution Research February 89/page 171

Figure 3

20000

15000

5iJoo

0

Per Trailer Cost Comparison for Multi-Temperature Carbon Dioxide 10And Mechanical Refrigerated Highway Trailers, 1987

(Based on Selected CO* Price Scenarios)

—. — -— ...—— —.——--— -.—.-. —-——.—..—

Carbon— Dioxide— ——————-—.—————_- ——.—.—.

/—————

$60

February 89/page 172

$80

/-”Mechanical

$100 $120

CARBON DIOXIDEDOLLARS PER TON

Journal of Food Distribution Research

Figure 4

50000

4000J3

cdnQoz~ 300000m=sI&o~ 20000

gCL

10000

n

Seasonal Consumption of C02 by a Multi-Temperature Food Delivery TrailerAnd Average Quarterly Temperature, 1987

45,656

“

JAN- MAR

25°

AVERAGE

APR-JUN JUL-SEP OCT-DEC

550 67° 38°

QUARTERLY TEMPEMTURES ‘F*

* Average quarterly temperatures for geographic area

where study was conducted. Source: “The WorldAlmanac Book of Facts, 1988’.’

Journal of Food Distribution Research February89/page 173

Storage Tank Size

The number of units being serviced is amajor factor in tank size selection. A trailertruck load of liquid carbon dioxide is 20 tons.A storage tank capacity of 30 to 34 tonshorizontal or 33 tons vertical needs to be in-stalled for the user to be able to take full trailerload deliveries and thus obtain the lowest car-bon dioxide price. Vertical storage tanks can beused when there is a minimum amount of spaceavailable at a facility. At 1987 monthly rentalprices a 30- to 33-ton horizontal storage tankand pressure vaporizer cost $1,050, and thevertical storage tank unit rent was $1,150 permonth.

Under the conditions of this study, it wasdetermined that a fleet size of ten or more cry-ogenic refrigeration units would be needed tojustify the rental of a 30- to 33-ton capacitytank. A horizontal storage tank this size rentedfor $12,600 per year in 1987. Table 4 projectsthe storage tank rental cost per trailer and othercosts factors associated with operating a fleet ofeither ten or twenty cryogenic refrigeratedtrailers, when liquid carbon dioxide is priced at$60, $80, and $100 per ton. The average unitoperating cost decreases considerably with anincrease in fleet size. For example, averageannual operating costs would decrease $630 perunit for a twenty-trailer fleet versus a ten-trailer fleet.

The food distributor had a twenty-tonliquid carbon dioxide storage tank. This storagetank does not have the storage capacity toaccept full truck load quantities of carbon diox-ide. However, it is sufficient to service thefour trailers presently contained in the coopera-tor’s fleet.

Conclusions

1. Based on the conditions of this study,when carbon dioxide costs less than $87 per ton,a carbon dioxide refrigeration system is a costeffective alternative to diesel/mechanical inmulti-temperature food delivery vehicles.

2. To purchase liquid carbon dioxide atthe lowest price, a twenty-ton delivery (fulltrailer load) needs to be ordered. To store fullloads on the premises, the food distributor needsa storage tank of 30 to 33 tons. Such a tank willaccommodate at least ten transport refrigerationunits. Additional fleet units would furtherlower the cost of operating carbon dioxide units.

3. Maintenance and ownership costs wereconsiderably lower for the carbon dioxiderefrigeration system than for the mechanicaltransport refrigeration unit.

4. Whether carbon dioxide refrigerationwould be economical in other areas of theUnited States would have to be determinedthrough additional cost studies designed to eval-uate (1) climatic conditions, (2) purchase priceof the carbon dioxide, and (3) trailer fleet size.

References

1.

2.

3.

4.

5.

6.

Doughtery, J. J., Jr. 1960. Test of LiquidNitrogen Refrigeration System Installed inFrozen Food Delivery Trucks. U.S. Dept.of Agriculture, AMS No. 426.

Guilfoy, R. F. 1963. Liquid CarbonDioxide Refrigeration in a Frozen FoodTrailer. 15 pp. U.S. Dept. of Agriculture,AMS No. 522.

Guilfoy R. F. and R. C. Mongelli. 1971.A Method for Measuring Cost andPerformance of Refrigeration Systems inLocal Delivery Vehicles. 16 pp. U.S. Dept.of Agriculture, ARS 52-64.

Karitas, J. J. 1978. Cost Comparison ofFive Institutional Food Delivery Systems.32 pp. U.S. Dept. of Agriculture, SEA,MRR 1092.

Tyree, L. 1985. “Future Trends inCryogenic Refrigeration for TransportVehicles,” Proc. Int’[. Institute of Refrig-eration, Commissions D1, D2, and D3,Orlando, FL, Nov. 17-21.

Nielsen, D, W. 1983, Refrigeration Systemwith Carbon Dioxide Injector, U.S. PatentNo. 4,399,658, August 23, 1983.

February 89/page 174 Journal of Food Distribution Research