Florida Scientist, QUARTERLY JOURNAL of the FLORIDA ACADEMY OF SCIENCES VOL 39-3-1976

Miller,Editor Academy Symposium SOLAR ENERGY Bruce Nimmo, Chairman Collegeof Engineering, FloridaTechnologicalUniversity,Orlando,Florida32816 The 1976 Academy Symposium topic, Solar Ener

Testingof Flat Plate SolarCollectors

Commercialization DelbertB Ward andPaul

J.Nawrocki 173

Energy and EnergyConversion Laboratory

HerbertA.Ingleyand George W. Shipp 181

ofTechnology AlbertP.Sheppard andJ.RichardWilliams 188

SolubilityStudies of Refrigerant-CarrierFluidPairsfor

R D.Evans andJ. K.Beck 199

FLORIDA SCIENTIST

QuarterlyJournalofthe FloridaAcademyofSciences

Editor:HarveyA.Miller

Departmentof BiologicalSciencesFloridaTechnologicalUniversity

The Florida Scientistispublishedquarterlybythe Florida AcademyofSciences,

indi-viduals or institutions interested in supporting science in its broadest sense.

receive a subscription to the Florida Scientist Direct subscription is available at

Originalarticlescontainingnewknowledge,ornewinterpretation ofknowledge,are

welcomedin anyfield of Science as representedbythe sections of theAcademy, viz.,Biological Sciences, Conservation, Earth and Planetary Sciences, Medical Sciences,Physical Sciences, Science Teaching, and Social Sciences Also, contributions will be

waymaterial thatis publishedelsewhere Contributionsfrommembers oftheAcademy

810East Rollins Street

Florida Scientist

HarveyA Miller,Editor

Academy Symposium

SOLAR ENERGY

Bruce Nimmo, Chairman

Collegeof Engineering, FloridaTechnologicalUniversity,Orlando,Florida32816

The 1976 Academy Symposium topic, Solar Energy, is indeed a timely one for the State of Florida and the nation as a whole The

truly difficult problems will be facing us in the near future Solar energy, outstanding in extent and environmental acceptability,

Summary papers were presented at the symposium covering the historical development and present state of the solar industry, the importance of equipment testing and standards, the activities

of the internationally known Solar Energy Laboratory of the versity of Florida, the role and scope of the newly formed Florida Solar Energy Center, and finally a survey of projects under way at

Uni-the Georgia Institute of Technology and theirrelation to majorlarresearch and development projects around the world.

so-Hopefully, the exchange of information, the bringing together

and summarizing of the literature and the opportunity for

discus-sion will help bring the date for large scale utilization of solar

energy a little closer for the State of Florida, the United States and

TESTING OF FLAT PLATE SOLAR COLLECTORS AND

SOLAR HOT WATER SYSTEMS

Bruce Nimmo

Collegeof Engineering, FloridaTechnologicalUniversity,Orlando,Florida32816

Abstract: The introduction to themarketplace ofsolarequipment which does not meet

ex-ecutedsolarequipmenttestingprogram Thispaperreviewssomeflat plate collectorandsolarwater

manufacturersofsolarequipmentisthe testing ofsolarcomponents andsystems

The emergingsolarindustry inthe State of Florida,aswell as in therest ofthe

suchtesting Asa result,shoddyorinoperative equipmentofpoormaterials,

de-sign,or both,has founditswaytothemarketplace(Schwartzman, 1975)

The equipment whichthe industryproducesmust be efficientandwell

thermallyandstructurally, inameaningfulmannersothathewillknowafterthe

equipmenthasbeeninstalledwhat hecan expectofit.

If a set of standard test criteria is not developed, there is great potential

for user disappointment with consequent destruction of trust and confidence

The result, ofcourse, isunfavorable impact oncurrent andfuture markets and

collector, thesingle most common solardevice forboth pastandpresent

appli-cations

Component and System Test Procedures Prior to 1974— Developmentof a

HottelandWhillier(1958).Theseauthorshave appliedbasic techniquesof

the collector

of fluid

By measuring the individual items on the right handside of this equation it is

beexpressedas

FR=heatremovalfactorwhichaccountsforthefactthattheenergylosses

arebasedonthe differencebetweenfluid inletand ambient

I=totalincidentsolarradiation

Ta= ambientairtemperature

Tf i=fluid inlettemperature

Tf , =fluidoutlettemperature

radiation,a usefuland commonlyusedcollectorefficiency,17, results.

xi= qu/A = FR [(T«e

)

II

pickuporthe collectorefficiency

solar water heaters were by Robinson and Stotter (1959) and Whillier and

Richards (1961) Thefirst paper discusses fourparameters which it is suggested

1) Thermalefficiency ofthecollector.

2) Aerial efficiency of the collector to reveal efficiency of space utilization

(calculatedasAactive/Atotal ).

3) Orientation efficiency determined from the angle between the incoming

con-tinuously"faced"thesunwouldhave anorientation efficiency ofone).

coeffi-cientfromthe tank

The paper by Whillier and Richards made a strong plea for international

adoption of a standard test procedure for rating the performance of solar flat

testingtechnique called for appears to have had considerable influence on the

NationalBureau of Standards testprocedure (Hill and Kusuda, 1974) Whillier

andRichardsmake thesuggestion that (ra)eand ULcanbe determined fromthe

appara-tuswhich wassetup as part ofthe basic facilitiesofthe South African Council

forScientificandIndustrialResearchinPretoria

Numerousexperimentaltest results forbothcollectorsandsolarwaterheatersystemswerereportedintheliteratureduringthe 1950's, 1960's,andearly 1970's

with widely varyinglevelsofsophisticationintheexperimental work.The works

ofKhanna (1968), Czarnecki (1958) and Whillier and Saluja (1965) are

totalwater heater systems(the formerunderactual "inuse"conditionsin India,

thelatterunder simulatedconditionsin Australia) Khanna'spaperlacks

collectors These collectorshadlife times of 2-4 yrdepending upon theheaders

detri-mentaleffectsoncertain selective surfaces

Doron(1965), in a brieftechnical note has described twotest methods

(iso-thermal andvarying temperature) used in the National Physical Laboratory of

Israel in the early sixties. He points out that there are two possible operationmodes for collectors; the "boiling" mode when the collector is essentially iso-

thermalandthe "heating"mode whenthe collectorfluidentersatone

tempera-tureandexits at ahigher temperature Ofcourse, in large collector arrayseach

modeled by the "boiling" mode even though, in fact, no phase change takesplace

TheStandardsInstitutionofIsrael(1966) establishedandpublished(S.I. 609)

a standardfor solarwater heater testmethods whichledtocollectorefficiency,

and

NO 1976] SOLAR COLLECTORS 133

Nevins(1974)has describeda variety ofapproaches usedinAustraliaforing solar collectors These include simple comparative testing against a "stan-

test-dard" unit,detailed testingtodeterminecollectorlosscoefficientsandradiation

absorptioncoefficient1

andtotalsystem performancetests.

The results of a series of 3 wk solar hot water system tests, under a variety

ofsimulatedpracticaldomesticconditionswasdescribedby Chinnery(1971)

Recent Solar Test Procedure Developments— A number of testing

pro-cedures were discussedat the National Science Foundation Workshop onSolar

pro-poseda dailyheat capacityratingin lieu ofefficiencytestsinordertoprovidean

collec-tionisneeded,at thegenerallocality atwhichthe collector istobeused

The National Bureau of Standards (NBS) recommended test procedures, as

developed byHillandKusuda(1974)anddiscussedbyHill (1975),lead to

consist of determining the average collector efficiency for 15 min periods by measuring the flow rate through the collector and the temperature rise acrossthecollector Foreachtestperiodconstraintsaregivenforcloudcover,ambient

temperaturevariation,minimum insolationrate,incidentanglebetweensunand

anormal tothe collector andinstrumentationerrorlevels. KellyandHill(1974)

havepresentedtestprocedureswhich were developedatNBSfortestingof

fortheunitandtheresponse tostepincreasesanddecreasesintheenteringfluid

temperature Anexcellentreviewofthebackgroundforthe NBS workistedinHill etal. (1976)

difficultiesand instrumentation costs experienced with the mass

procedure is based on a closed system in which the heat from the collector is

temperature inthe tank is measuredtodetermine theenergyratepickup ofthe

collector The primary operational advantage ofthe technique isthat onlyone

theNBS techniquewhichrequiresmeasurement offlowandtemperature.A

po-tentialdrawbacktothe calorimeterapproachIsthatonenever achievesasteady

state forfluidtemperature.Aresultofthisis,ofcourse, that thethermal

capaci-tanceofthe collectormust betakenintoaccountinthedatareduction

Simon (1974) has described a program carried out at the NASA Lewis

radi-ation The advantage ofthe indoor solarsimulator approach is that true steady

state is achieved under controlled conditions of environment The drawbacks

areexpenseand potentialmismatch between the trueandsimulated solar

NASA-Lewis simulator has good spectral qualities and the indoor data are well

Twosystem-oriented mobiletest facilities have beendescribedin the

litera-ture The Honeywell (1974) transportable solar laboratory was designed and

builtprimarilyasameansofevaluating"onboard"solarheatingandcooling

sys-temsunder various climatic conditions It also servedasa traveling

demonstra-tionunittoacquaint thepublicwithsolar systemsandcapabilities Nimmo and

Larsen(1976)havedescribed the design and development ofamobilesolaringandrecording systemtobe usedinthemonitoringof"inuse"solarhot watersystemsinthe State of Florida.Thedesigncallsforcapabilitiesofmakingappro-

pumpedsystems

main-tainability) which must be considered in collector specification A document whichaddresses itselftomanyoftheseother aspects isthe NBSreport"Interim

PerformanceCriteriaforSolarHeatingand CombinedHeating/ Cooling Systems

andDwellings" (NBS,1975)

Finally, mention should be made of the fact that commercial collector test

Fromthissummaryoftesting activities,it isapparentthatthe largenumber

ofthermalperformancetestsreportedintheliteraturemay be groupedasshown

inTableI.Althoughother relatedcomponentssuchasauxiliaryenergysupplier,

com-ponent list, these devices typically are commonin conventional heating, lating and air conditioning design work and have been subjected in many in-

solar or

solar simulator -In situ testwith

-Storage

3, 1976] SOLAR COLLECTORS

a thermal performance specification2

which has been written for a given

sys-tem, thenthe amountof usefulheatoutputorthe collector efficiencyasationofenvironmentalconditionswouldgenerallybesatisfactory.If,ontheother

func-hand,thetestisbeingperformedtoobtaininformationfora prescriptive

de-sign, the greaterdetailisusuallyrequiredintheconductofthetestsand

ofequation 2 whichisuseful in obtainingdiagnosticinformationfrom collector

the average fluid temperature and the ambient temperature the following

Streed (1975)has pointed out that by plotting the measured efficiency as a

can becharacterized asshown inFigure 1. The yaxisinterceptis related to an

experimental value of (ra)e and the slope related to an experimental value of

:The phrases performance specification and prescriptive specification have the following connotation. A

prescrip-tive specification describes themeansto achieve desired results such as use of antireflective coatings (Hartman, 1974).

surface were at the average fluid temperature, is termed the collector efficiency factor F'maybe determined

However, it is recognized that in reality UL isnot a constantbut rather a

func-tion of the collector and ambient temperatures In addition, the product (ra)e

expectedfrom to30degrees).For commonflatplate collectordesigns,the

non-linearity ofthecurvewilltendtoshow upathigheroperangtemperatures

sub-systems(components)andsystems.Hepointsout thattestscoveringmostaspects

func-tional applications Streedhas suggested the listing shown in Table 2 as

sub-systemtestparameters

System Design Requirements SubsystemTest

Energy Collection

test isuniquely suited to answer the ultimate question, "Is thissystem a sound

choicefromtheeconomicpoint ofview."Naturally, ifthesystem isa prototype,

allowances must be made for the inherent additional costs. This would be true

for essentially all solarsystemsexcept solarwaterheaterswhicharebeyondthe

prototype stage

Two major efforts are presently under way by technical societies in the

UnitedStatestoassistinevolvingstandardsfor solartestingandcooling.Thefirst

is the work ofthe American Society for Testingand Materials (ASTM) carriedoutunder subcommittee E21.10 Solar Energy Utilization Thiswork was insti-

and

1976] SOLAR COLLECTORS 137

ofHeating, RefrigerationandAirConditioning Engineers (ASHRAE) The

subcom-mittee 93-Pandthe standardsfor solarthermalenergystorage arebeingstudied

by subcommittee 94-P A report will be made to the ASHRAE standards

com-mitteeinmid 1976.There appearstobea feeling thatASHRAE'sresponsibility

shouldbelimited to thermal testingof collectors while ASTM shouldhave sponsibility fordurability and reliability of materials The latter shouldincludethebehaviorofthe collectorunder"stagnation", ornoflowconditions

mar-ketplace is urgently inneedof standardsandthat the professional-technicalcieties and the federal government are moving to meet the need Meanwhile,

re-quiredwhenoneassociateswithanewproduct

LITERATURE CITED

Chinnery, D.1971 Solarwaterheating inSouthAfrica.CSIR(Pretoria) Res Rept 248:8-24.

Czarnecki, J. 1958. Performance of experimental solar waterheaters in Australia SolarEnergy

,andT.Kusuda.1974. Methodof Testing forRatingSolar CollectorsBasedonThermal

Performance.NBSRept.NBSIR74-635.Washington

E.Streed, G Kelly,J. Geist, andT. Kusuda 1976.Development ofProposed

Washington

Honey-wellSystemsandResearchCenter Minneapolis.

64:91.

Kelly,G.andJ.Hill 1974.Methodof Testing forRatingThermalStorageDevices Basedonmal Performance.NBSRept.NBSIR74-634.Washington

Coolingof Buildings.NSF-RANN75-019:373-379.

Coolingof Buildings.NSF-RANN75-019:349-358.

Nevins,R 1974.CSIROandAustralianExperiencein Testing Solar Collectors.Areport to the U S.

Rorinson, N.and A. Stotter 1959. A proposed standard test codefor thedetermination of the

Simon,F 1974 Status of theNASA-Lewisflat-plate collector testswith a solar simulator.

Work-,andP.Harlament 1973 Flat Plate CollectorPerformanceEvaluation:TheCasefor a

Streed, E 1975. TheRelationshipsBetween TestsonComponents Separatelyand Testson

Per-formanceof Solar TotalSystemsonInstallations. Presentedat theConference on Standards

Whillier,A 1966.LowTemperatureEngineeringApplication of SolarEnergy.AmericanSociety

,andS.Richards.1961.Astandard test for solarwaterheaters Proc Conf.NewSources

ofEnergy.Rome.Paper5-97:111-113.

EngineeringConsultant,AppliedSolarEnergy,16 InterlakenRoad, Orlando,Florida32804

Abstract: Promotion of cheap electricityandgas formass-produced waterheaters in the post

WorldWarII era led to thedemiseof thesolarenergyindustry in Florida.TherecentOPECoil crisis

limitations of eachtype Flat plate collectorshave advantagesover concentrating collectors for

house hutthese uses are not yet cost-competitivewithfossil fuels.Recovery ofpotablewaterbysolar

solarenergyholdspromiseforexpandedexploitation ofouronly continuously renewednatural

re-source—thesun.

marketfor solarhardware Some ofthem manufacture components, some totalsolarsystems

In some ways this activity conjures up visions of times past, for during the

ways,the currentre-emergencebearsnoresemblancetothepast,forthe reasons

which have led to renewed activity in solar manufacturing, research and

de-velopmentarebroaderinscopeand morepersuasiveinnaturethanthe pressures

whichledtothesolar activitiesof1900to 1960

'Copyright 1976 Douglas E Root, Jr., Orlando, Florida All rights reserved.Nopart of this articlemaybe

fallofprevioussolar activities inFloridawhichreachedtheirpeakinthe 1950s.History—Inland Florida of the early 1900's was largely rural and agricul-

much ofthe year because ofseasonal inundation of the many and broad flood

and navigable river corridors until the Florida land boom of 1925-27 Natural

barbershop signswhichread "Bath—10^(first water—20$)" wouldbeginto

dis-appear "Hot water in every room" appeared on billboards advertisingFlorida

accommodations and it became fashionable to bathe more often than once a

week These changes in social customs required a source of low temperatureenergy andFlorida's citizens had more sunshine thanmoney available tothem

EarlyPatents: A patentperipheral tothe basic principle involving the

trans-parency ofglass to the solar spectrum andits opacityto longwave length heat

Davis ofPasadena, California, "inventedcertain new anduseful improvements

in solar water heaters," according to records in the U S. Patent Office Many

II. Theseearlypatents included:

PatenteeandAddress

Wm.J.Bailey, Monrovia,Calif.

T.F.Nichols, Bay,Ariz.

F.A.Skiff,Pakta,Mass

Wm.J.Bailey, Monrovia,Calif.

D.A.Harrison,LosAngeles,Calif.

E.D.Arthur, Arcadia,Calif,andW.G

Carther, Arcadia,Calif.

W.Christiansen, Miami,Fla.

F.

J.Bentz, Miami,Fla.(storagetank)

Miami,Fla.

W.F.Clark, Philadelphia, Pa

Pollstoren,Pa.

H M.Carruthers,Miami,Fla.

^Patents marked by an asterisk (°) are of the type of construction generally used in conventional solar water

2,122,821° July5, 1938 O.H.Mohr, Oakland,Calif.

2,133,649 Oct 18,1938 C G Abbot, Washington, D.C

2,141,330 Dec.27,1938 C.G.Abbot,Washington, D.C

2,202,019 May28, 1940 O.H Mohr, Oakland,Calif, (cooler)

2,205,378 Jan 25, 1940 C.G Abbot, Washington, D C

2,202,756* May28, 1940 S.Cline, Miami,Fla.

2,208,789* July23,1940 B.H.Cally,Miami,Fla.

2,213,894° Sept.3, 1940 E.J.Berry,OrlandoPark,Fla.

2,247,830 July,1941 C.G Abbot, Washington, D.C

2,249,642 July 15,1941 E.T.Turner

populationliving inFloridaduringthefirstquarter of the20thcentury,by

wherethesunprovidedtheonlyreadilyavailableoraffordablesource ofthermal

deckswere housedin thickwoodenboxeswhich wereusuallycovered withglass(Veltfort, 1942) A collectorarea ofabout 12 sqftper personwasrequired.3

The wholesouth-facingsystemwas ground mounted andconnectedtoa largestorage

arrangement of the connecting piping allowed natural circulation of the sunheated water Internal convection causedthe stratification ofthe hottest water

hot water to house

gate valve

air inlet drain cock

hot water from collector

gate valve

cold water to collector

water drain cock

Fig 1.Sketchof athermosyphonsolarwaterheater (after Partington, et al., 1975).

Early Manufacturers: Soon, roofing and plumbing contractors discovered

that the making of"storeboughten" solar water heaters added a lucrative new

product line to their shelfitem hardware During the 1920's and 1930's dozens

ofthem begantomanufacture andtorefineflat plateheatcollectors.A few

which copper tubes weresoldered at about 6 in intervals They still depended

hot andcoldlegsoftheirpiping,but theywere moreefficient than their

prede-cessors The wooden box had given way to a more durable one made of metal

which contained insulation in the form of sheeting such as "Celotex" or even

mineral wood or sawdust (Hawkins, 1947) In the northern part of Florida, the

to operate at acceptably high temperatureseven in winter Large solar storage

incorporatedintosome new housing, and commercialunits beganappearingon

earlier, the solar heat collectors were moved from the yard to the roofwhere

grow-ing shrubs and treeswas less of a problem The solar storage tanks were

some-times housed in an imitation chimney structure or in the attic of thebuilding

itself. Figure 2 shows such an installation which hasbeen in use for more than

25 years Figure 3 shows a ground mounted solar water heater whichhasbeen

inuseformore than50years Figures4and5arefromillustrationscontainedin

Fig 3.Agroundmounted4X14 ft solar heat collector.Thestorage tank ishousedin thewooden

Bentel's SolarHeaterInc.

BollingerCompany

Lake Worth,Florida

HotSpotSolarHeaterCompany

DixieHighway

West PalmBeach,Florida

2Avenue andJacksonSt.

Tampa,Florida

Pan-AmericanSolarHeater,Inc.

SolarWaterHeaterCompany

SolarWaterHeater Co.ofTampaTampa,Florida

DaytonaBeach,Florida

No 3, 1976] ROOT—APPLICATION OF SOLAR ENERGY 143

installation often used where

boiler to be placed under

gable, as shown at left.

SPECIFICATIONS

between box androoi.

RECOMMENDATIONS

Typ* of Building Size Sun Coil Storage Boiler

Small bungalow No 8 or 10 40 gal.

Residence

2-bath residence No 12 80 gal.

3-bath residence 2 No 10s 80 or 120 gals.

Extra large residence 2 No 12s 120 gal.

Day fc- Niqht Water Heater Co., Ltd.

Early Literature: Mangon (1880)in France, Ericcson (1884), the designer ofthe steel ship Monitor, and Willsie (1909) were among those who made early

ROCKWOOL-^ ^HORIZONTAL TANK

DOUBLE GLAZED,

WITH AIRSPACE KFLATCOPPERTUBING

CORRUGATED BACKING

REYNOLDSMETALLATION WITH

the 1930's, 1940sand 1950's. Many ofthem wereinstalled in government housingprojects

estab-lished forlow incomegroups.

(1942)

Institute of Technology received the financial support of the Godfrey Cabot Foundationduringthe mid-1930's,atwhichtimetherewereonlytwoothersuchprograms One was conductedinAlgeria,theotheratTashkentinRussia (Hottel

and Howard, 1971) The University of Florida and the University ofWisconsin

initiatedresearchprogramswithinthenextfewyearsanditlookedasifthe

than 50,000solarwaterheatersinuseintheMiamiareaalone(Hottel, 1955)

BUT, something went awry—

By the mid-sixties public interest in purchase ofsolar waterheaters hadall

but disappeared throughout the entire United States and the marketplace no

longer supported the industry Accordingly, innovation for product ment ceased as companies failed or reverted to previous product lines such as

improve-plumbing androofing Interest in solarenergy continuedamong afew scientists

such asFarrington Danielswho wasdirectingmuch of hisattentionto solarstills

de-mands on our fragile and limited aquifers intensify with exploding population

Energy held in Phoenix, Arizona, in November, 1955 In any event, as popular

interest in applied solar energy declined in the U S., scientific and popular

in-terestdeveloped abroad, especiallyinAustralia,Israel, France andJapan

Table 1.

Condition

Absolute PercentFrequency Frequency

Damagecausedbytankleaks

Insufficient hotwater

Replacedbefore failure, unit

considered too old

Poorposition,shading

Notsafe,worrisome

Toomuchrust orsediment

Damagedbystorms

Alreadyhadconventional unit

Other

Tanks mounted aboveceilingswere generallyset indrip panstowhichdrain

lineswereconnected However,the drainlinesoftenbecameclogged withtrash

duringtheir10-20 yr ofdormancypriortotankfailure.Thismeant wet andoften

falling plaster was the first warning many home owners had that their attic

mountedsolartankhadsprungaleak.AsScott'ssurveyreports, thisturnedmany

solar water heater owners toward electric or gas units Eric Farber, long time

addi-tionally that the mass purchase offully automatic washing machines and

dish-washers during the late 1950's and into 1960's put too much demand on many

solarhot watersystems(Farber, personalcommunication, 1974)

They remainedbatch produced by relatively small manufacturers, but electric

and gaswater heaters, as demandgrew, became mass produced by majorfirms

Thesolarsystems stayedexpensive whilethe electricandgasunitsbecameveryinexpensiveduringthe 1960's

The power of advertising may have been a contributor to declining public

interest, too During the sixties, electrical energy became so abundant that

power companies spent millions urging the public to buy "gold medallion all

electric homes" or to "live better electrically." The power companies offered

power

Probablybecause of the combined negative effects ofthe problems caused

change exertedby theutilitycompanies and conventional water heater

manu-facturers, few solar water heaters were sold in Florida from 1960 until about

1975and mostofthemanufacturingcapabilitywaslost.

appeared at the time to be a safe and nearly inexhaustible source of

power-lightwaternuclearreactors.By 1965, onlyahandfulof universitylevelresearch

scientists continuedtheir interest in thesolar field. Farber at the University of

andTelkesin New York(laterDelaware)werenotableamongthese

France helpedkeep scientific investigation alive Theactivity in Australia was

themid-1950's in Phoenix, Arizona, asthe AssociationforAppliedSolar Energy and it had sponsored the First World Symposium on Applied Solar Energy in

thatcityNovember1-4, 1955.)

Asthe 1960s passed,solarwaterheatersdisappearedfrom theroofs in

Flor-ida—and in Arizona, New Mexico and southernCalifornia, too, for thatmatter

Somethingelsewasalmostgone by 1970,too,butfew recognizedthedanger

signals

Thatfactiswellunderstoodnow.In aspeechdeliveredinWashington, D C,

January 30, 1976, to the American Institute of Aeronautics and Astronautics,

Robert Fri, Deputy Administratorfor ERDA, stated that proven petroleum

will cause shortages in Western bloc nations to occur far short of that time

in-formationavailableonthatsubject.It isnotlikelythatpetroleum can everagain

belookedto asasourceofcheapenergy

in an articleon atomic power whichappears in the February 16, 1976, issueof

U S. News and WorldReport Supplementalelectrical energyfrom thatsource

isgoingtoamounttoconsiderablylessthanhad beenexpected

ERDA's NationalEnergy Researchand Development Plan isexcerptedand

1975 It is apparent from thispublication that thehomeownercan expect little

relieffromconstantly increasing powercostsbefore at least 1985 Thatis to say,littlerelief intermsofthenewtechnologywhich ERDAexpectsto developand

market.Hotteland Howard(1971)haveanalyzed,indepth, most suggestedlongrangesolutionstothegrowing worldenergydemand.

A Near Term Prospect for Relief— Whatabout anold technology?What

about the solar water heater? What about solar building heating? What about

solaroperated air conditioning? In Floridahomes 85%ofthe energy consumed

By way ofanswering those questions, letus review the SolarConference of

February 13-14, 1976, sponsoredby the Associated Plumbing and Mechanical

ContractorsofFloridainOrlando.Thatitwasattendedbypeoplefrom 22states,

sur-prising There was somethingsurprising aboutthat conference, however Some

42 manufacturers displayed solar devices rangingfrom differential thermostats

tocompletesolarheating systemsforbuildings.Thethreelargest manufacturers

ofconventionalwaterheatersin theworld displayedsolarstoragetanks.Twoof

and respected aerospace firms displayed flat plate collectors and systems for

waterheatingandhydronicbuilding heating

Thelargest plumbingsupplyhouse in Floridadisplayedsolarheatcollectors

and complete solar water heating systems which it manufactures One of the

aluminumpanels with integral tubingsystems made exclusively for use insolar

heat collectors One of the largest glass manufacturers in the world displayed

com-ponents displayed a tracking solar collector which utilizes a rectangular nellensandissaid toproducewaterorsteamattemperaturessuitableforpower-

These were not handmade prototypes on display These were production

modelsreadyfordeliverynow.

Consideredcollectively, these displays indicate that those planningthe

eco-nomic future of some very large companies, with widely divergent interests,

have reacheda similar conclusion Their conclusionwould seem tobe that the

Availability of Solar Energy— Even superficial study of insolation data

(Fig 6, 7andTable2)establishesthatsufficient solarenergyisavailable, inmost

ofthe UnitedStates, to heat a house andits hot wateror to power its air

collec-tion Insolation data measured on a horizontal surface tends to give the

quantity of solar energy impinging on the surface However, if the insolation

figuresarecorrectedto reflectthe quantity ofenergywhichimpingesona

prop-erly sloped surface, the apparent locational differences are smaller Figures 6

Thesolid line indicates levels for a horizontal surfacebaseduponmeandaily solar radiation for 1964.Thedottedline indicates levels for a south facing surface elevatedfromhorizontal toanangle equal

to the latitude plus 10° 4

The solarclimate hasnot changedsince the "old" solarindustry diedin the

1960's Whatis to preventthe renewed interest in thesun's energyfrom dying

changed—markedly

Energy in the 1950's and 1960's was so cheap it wasbasically free. Energy consumption wasnot even consideredin most manufacturingoperations Gaso-

moreelectricityandnatural gasatgiveawayprices.That wastheenergy climatesurroundingthewaningFloridasolarwaterheater industryofyesteryear

Thereis simply no hope thatsuch a situation will occur again Oil rich

na-tions have realized they are custodians of an exhaustible asset which requires

power plants have turned up about as many problems as they have solutions

timeandthecost ofoperationisexpectedtobehigher than the currently able oil and gas fired generating plants Environmentalists are less than over-

oper-joyedattheprospectofrenewedstripminingofcoalto fuelthem Windpower,

oceanthermalgradients,bioconversionanddirectproductionofelectricityfrom

sunlight—all ofthese things offerpromise inthe future,butthehardware is

1976)

4

Thevalues given represent a first approximation approach to the actualamountof insolation received

Geo-metrical considerations dictate that a sloping surface interceptsmoredirect orbeamradiation than a horizontal

insolation is direct Because of rain showers, however, muchof thesummerinsolation any surface receives is

reflected radiation when cumulus clouds abound and ground reflected radiation from lakes and fields. Many

investigators have suggested methods for evaluating both the beam and diffuse radiation received by variously oriented surfaces.Amongthemare:Moon(1940), Hottle&Woertz(1942), Brooks (1952), Becker andBoyd(1957),

No 3, 1976] ROOT—APPLICATION OF SOLAR ENERGY 149

os CM 1-1 M HPOHNHH H H CO rH r-i r-irM

H ih cm tomCO rH in t~ 00HOHHIlOCMCMCMCMTlOrHtoCM r-i CO tOO Or^r^^ ^ n

150 FLORIDA SCIENTIST [Vol. 39

CO CO CO CM CO

tO rH CDOXOM^flif

CM CO rH t>OCO t^ to c-o

oo co too *

CO CO CTl r« Tf

'j"mcm cm in t« in cd t- tt

No 3, 1976] APPLICATION OF SOLAR ENERGY 151

mto t-oooCIHlOOf

TT TT TJ< Tf Irt

CM*CO* *

to toOt^ Ol

•<r co 'tf <r co oo

«-Economic Parameters: The displays in Orlandoestablish that solarheat lectorsandcompletesolarwater heating systemsareavailable,butaretheyeco-

col-nomically competitive? Opinions vary Florida Power's managerofenergy

1975) Onthe otherhand,some consumers maysubscribetotheeconomic

Whilesolarbuildingheatingwouldhardlybe consideredsensible in most of

research-ers tobe competitive with electricheatin manyparts ofthe UnitedStates

(Fal-termayer,1976;Hotteland Howard, 1971)

recognizedresearchers inthe solar fieldseeno reason why hardware cannotbe produced now which will satisfy the physical and economic requirements forsolarpoweredairconditioningsystems(Farber, etal., 1966)

CurrentProduction: In 1974 only 136,540sqftofmedium temperature heat

collectorsarethoughttohavebeen producedinthe UnitedStates.Thefirsthalf

of1975 broughtincreasedproductionto276,466sqft (F.E A., 1975).Theannual

Sys-temSales,Glass Division, PPGIndustries

tempera-ture heat collectors from January through June, 1975—up from 1,137,196 sq ft

ERDA'scatalog ofsolar energy heatingandcoolingproducts (ERDA, 1975)

lists over460 manufactured components currentlybeing offered Their list, by

theirownstatement,isvery incomplete

So— even thoughthe solarclimatehasnot changedsincethe 1960's,the

eco-nomic climate is more favorable for the development of solar devices Major

marketplace After spendingless than $100,000 peryr onsolarresearchand

de-velopment from 1950-1970 (Hughes, 1974), the federal government spent $86

TimeisNear."

Available Hardware— With such a profusion of products being offered for

arebeing usedinsolarcomponents,especiallywaterheaters

shouldbenotedthatvery longtermstorage isnot easyto justify intermsof

eco-nomicfeasibility—noris itoften required ErichFarber reportedtotheAP&MC

per KWH for electricityusedto heatdomestichot water, in a citywithatemperateclimate (for

Earnings Investment Total Tax Expenses Annual

elsewhere.

weatherdatacoveringmanyyearsand concludedthatveryrarely are there three

consecutive days with less than 1/3 of the maximum insolation available

any-where in the 48 contiguous United States At most, two orthreedays supplyof

energy mayreasonablybe usedas the sizingcriterion Economic considerations

easytohandleandcontainandcapableofstoringacceptablequantities ofenergy

mag-present, manyinvestigatorsthink thatthe problemspresentedoutweighthe

ad-vantagesofferedbysuchaheatstoragesystemforthe practicalheatingandingof buildings

have approximately twicethe volumeofawater tankforequalstorage capacity

(ATbeing equalinbothcases).Aswateristhemostwidely usedstoragemedium,

letusexamineitsusemoreclosely

Comparatively few thermosyphon solar systems are being installed at the

of flow rate and required little attention except for freeze protection, but the

Most modern solar water heating installations include a small circulatingpump and a differentialsensor system tocontrol the on-offmode of thatpump

(Fig 8.) Ifwateris circulated throughaheatcollectorin locationswhere

freez-ingtemperaturesareencountered, provisionsmustbemade to protect the pipes

from freezing Some manufacturers recommend using valves to isolate the

re-membered that some tubing systems are not designedto drain completely and

theymust beprotectedbyothermeans(Fig.9).In areaswherefreezing

tempera-tures are only occasionally encountered, some circulating pump controls are

equipped with"freeze-sensors"which turnthem on intermittentlyduring

tank prevents freezing automatically (as long as no power failures are

solar heat collector

gate valve

air inlet drain cock (boiler drain)

•solar storage tank

rculating pump

Fig 8. Conceptualdrawingof a forced circulation solar waterheater (after Partington, et al.,

Fig 9 Various configurations of pipe grids in solar collectors: upper left, parallel horizontal;

upperright, sloped horizontal;lowerleft, tube-in-sheet;andlowerright, vertical tubeswithheaders.

heat exchanger which, in turn, transfers it to the storage tank Because many

heat exchangers are used to guarantee double walled separations from what is

collec-torsbeingsold in Floridaat this time are offered with one ofthese three types

toallowuntreatedwatertogravitydrainwhenthepump isturnedoff.

Concentratingvs. Flat Plate Collectors: Concentratingparabolic troughsand

absorbing surfaces to produce higher temperatures than can be obtained with

Parting-Fig 11.Concentratingsolar collectors: left, reflecting trough;andright, section of Fresnel lens

Concentrat-ingcollectors,onthe otherhand,moreoftentrackthesunfrom morningtonight

varia-tions in solar altitude

short-comings Flat plat collectors arecapable ofconverting diffuse solar energy into

heatandthus work about20% as wellon a cloudy dayasa sunnyone

Unfortu-nately, concentratingcollectorsdonothavethiscapability, soeven though they

collect energy at a higher temperature (200°-1200°F) and often absorb moreenergy permin ofsunlightexposure, theyseldom collectmuch moreenergy per

hurricaneforcewinds), collectorswitheven modestconcentration ratiosof3-10

Becauseoftheir relativelylowcostandtheir ability to collect diffuse aswell

asbeam radiation, flatplatecollectorsare theworkhorses of thesolarindustry

Eventhoughvariations(Fig 13) aremanufactured whichuseairas aheat

circulates (Fig 14).

tempera-tureheatcollectors(ca. 90°F) usedforswimmingpoolheatingsometimesutilizeplastic heat decks Largeareas are requiredfor adequate pool heating andun-glazed plastic collectors are less expensive than conventional flat plate collec-

un-uncovered

Inthelowtemperature (180°F) collectors,copper,aluminum andsteeldecks

dark-enedwith organiccoatings or electrically depositedcoatings with equal ease sothe choice of deck material involves evaluating its resistance to corrosion, theeasewithwhichitmay befabricated,anditsrelative cost Someheatdecks con-

tain fluid passages which are an integral part of their fabrication Aluminum

decks withintegralpassages arefashionedfromallthree metals Mostoftentheir

results inhighmaterialcostsbecauseofthe thicker-than-necessarywebs between

muchas 100% copperdecks

n

flat black paint clear glass

Fig 13 Cross-section of a solar collector for usewithair as the heat collecting fluid.

sol-dered to the sheet continuously or intermittently, clamped to the sheet or

bondedtothe sheetwith thermally conductiveadhesives

easyto solder, acceptedfor contactwith potable waterby all known code

juris-dictions, corrosion resistant andit isan excellentheat conductor The factthat

it is such a goodheat conductorleads Hottel (1955) toconclude that "The use

theblack absorberplate."Theexcellent heat conductionofcopperledHawkins

will cost half as much to construct per square foot ofsurface." Itmatters little

whichauthority is accepted in that, with goodthermal contact between pipes

spacedat 6in and arelatively thin deck, above 93% ofthe potential heat drain

from thedeckisrealized

Continuous soldering is reported to be 30% better than clamping (Whillier,1967) Ifthermallyconductiveadhesives prove to bedurable whensubjected to

the tremendous thermal stressesencountered onsolarheat decks, theirthermal

ofabout20 BTU/(hr)(sqft) (°F perft). Solderingisexpensive; gluingwith

ther-mally conductive adhesives is much cheaper, so iftheydo prove durable, their

use may reduce fabrication costs. Linear cylindrical troughs stamped into the

isasmuchas 1/8inwide,the conductanceofthatbondissogoodthatthe

limit-ingheat transfer coefficient in the overall series occurs in the static liquid film

ontheinsidesurfaceofthecontainingtube(Whillier, 1964)

Figure 9 shows severalstyles ofpipe gridbeing manufactured Theyare all

1976] APPLICATION OF SOLAR ENERGY 159

No smaller than 1/2 in I D

tube except on closed loop

systems Boiler scale can

Not less than

3/8 in if two

covers used

4 - 8 in between soldered tubes.

Minimum deck thickness:

thickness of edge insulation reduces edge losses, it also reduces heat collection area and thus heat gains. 1/2 in of good quality foam is a rule of thumb compromise for most climates when insula- ting metal housing boxes.

Fig 14 Cross-section of a flat plate heat collector indicating designparameters(after Root, 1976).

and completeinternal wettingresults in maximum heattransfer evenifthe

Soldered pipe connections within the heat collector housing box deserve

jointsinvolved.Wenotethat afamilyoffourwillrequire agoodquality40-48sq

good measureof success Heattransferis furtherencouraged bythe application

ofthermally conductive adhesive tothe interfacebetween the rectangulartube

Becauseofthe corrosive nature ofmuch of Florida's drinking water,

alumi-num andsteel tubes areseldom put intodirect contactwith it. More often they

are employedin conjunction with heat exchangerstoform a closedheat

silicone oilsorother non-corrosiveliquidsmaybe usedforheattransport

Because ofthe dilemma causedby thehigh cost ofcopper on one hand, but

inwhich coppertubes or pipes areaffixed toaluminumorgalvanizedheat decks

Therearetwoproblemstobedealt withinthese cases The coefficients of

ther-mal expansion ofthese materials differby roughly one third (steel0.114X10"4

;

copper 0.166x10 4

; aluminum 0.224X 4

) (Perry, 1941) As a consequence of

deformation or it may "work" back andforth if it is not continuously soldered.This"working"soonleadstoreduced thermalcontactbetweentubeanddeck

A secondproblemwith hybrid decks involvesthedifferingpositionsof their

metal components inthe galvanic series Ifmoisture containinganyconducting

at hybrid decks because of potential galvanic corrosion problems Costs are a

Everythingwhich goes into the construction of heat decks is relatively

re-duce their functional efficiency by 20% mayreduce their cost by 15% or evenmore In such acase, the cheapercompromise wouldbenefit the consumer and

heatcollectors, the use of materials or constructionmethods whichreduce their

lowtemperature heatcollectorsisthattheir units willlastat least20yr.

energywhich impingeson itssurface Unfortunately, mostblack paints re-emit

more than 90% of that energy at a relatively long wave length— 3-15 microns

fora200 °Fdeck Becauseit ispossibletointerrupt theoutflow ofthelongwave

be-comecenteredaroundtheirlongtermadhesion, surfacedurability,ease of

appli-No 3, 1976] 161

For years, researchers have been investigating selective surfaces which

it even at a very long wave length At least four methods accomplish this and

theyhave beendescribedindetailbyFarber(1959), McDonald(1975), Merriam

(1973),Tabor(1958, 1961, 1967)andDuffieand Beckman(1974).Sufficeittosay

degree ofselectivity and some collectorsbeing marketedarebeing coated withthem Numerous electroplated selective coating systems have been developed

Heat decks with surfaces which have been electrolyticallyproduced are being

marketed byseveral manufacturers Atleast one collectormanufactureris

thermaldiode

Ifselective coatings have shortcomings, they are related to their high cost

reducereradiation ofheat energyisamajoradvantageandwillbe examined from

a slightly different standpoint in subsequent paragraphswhich deal with

trans-parentcoverings

sun,it will cometo equilibrium withits surroundingsat a temperature not

use-fullyaboveambient.7

dam-aged byweatheringina short time However,if it issurroundedontheback and

sideswithinsulationandcovered withaweatherproof,light transparentsurface,

isflowingtodrainheataway fromtheheatdeck, itmay risetoavery high perature onawarm sunny day Theinsulatingmaterial mustnotbreakdown at

encountered with freon blown polyurethane foams used in heat collectors On

occasion theyhave expandedirreversibly andtheirexpansion hasdamagedlectors(EngineeringNewsRecord,Nov. 20, 1975).Goodhigh temperaturetoler-

col-anceofC02blownpolyurethanefoam hasbeenreported(Moore, 1974) Insome

instances, polyurethane has out-gassed a low molecular weight material which

hasrecondensedontheinside ofthe transparent collectorcoverandcutdownitssolar transmittance Water vapor in contact with very hot urethane foam sur-

hydro-floricandhydrochloricacid

However, freon blown polyurethane is a readily available, relatively

col-lectors, care should be exercised to separate it thermally from the potentially

Theuse of uninsulated, uncoveredswimmingpool heating decks is in apparent conflict with this statement,

very hot heat deck surface Anair gap willaccomplish the desiredthermal

un-coupling

as polyurethane at about the same price—$0.31 per sqft for 1 in foam sheets

No known field tests made on the isocyanurates have shown up the problems

Styrofoam will not stand thehigh temperatures produced when no heat is

being takenoffthe deck, so if it is tobeused itmust beprotectedbyathermal

ofthevery long life expected ofan expensive heat collector, itmust be

antici-pated that constant expansion and contraction of the transparent surface may

exposedtowater, it absorbs itinto itsmatrix bycapillary action This does not

meanthatfiberglass should notbeused; itdoesmeanthatboxeswhichuse such

bottomdrain holestoallowany accumulatedmoisturetoescape

Asbestos concrete has been used to build ground mounted heat collector

boxes inAustralia foryears(CSIRO, 1964).Itsuse offersthe opportunityforthe

collec-tordecksforbuildingheatingandcoolingmay bedeployed

With the exception of asbestos concrete, all the insulating materials

struc-tural support for the heat deck and insulation and protects both from the

weather.Foryears, 18to24 guagegalvanizediron or aluminum have been used

forboxesforheat collectors(Hawkins, 1947).Theyarestronganddurable.They

may be paintedand they are easytowork with andform Unfortunately, these

metalsare also excellentheatconductors, soanyenergy whichescapes through

losttotheatmosphere

Asaconsequence ofthisshortcomingofmetalboxes, several manufacturers

Fiber-glassreinforced polyesterresinmay beusedin thismanneraslongasit isberedthatanyunreactedpolyester resinmayout-gasiftheinside surface ofthe

remem-box reaches very high temperatures At least one manufacturer uses an violetshieldedplasticextrusionincombination withseveral insulating materials

bat-tens

Whateveritsbasicconstruction, the chiefrolethe boxservesistohouse the

provideadditional insulationwithoutlosingsignificantdurabilityor strength, so

much thebetter Once the heat deck is insulated and housed, the transparent

covermaterialmust beselected Inaccordance with thegreenhouseeffect,solar

hotdeckwillnot(Fig 15). Thatisonly half the story,unfortunately.Whilelong

of the solarspectrum witha solar flux expressed inBTUperhrpersq ft vs.wavelength of light.

absorptionheats the glazing pane.The outside surface of thehotpaneisin

con-tactwiththe ambientairandit losesheatby themechanism ofupwardtion—and reradiation to the sky under clear conditions The effective tempera-

(Whil-lier, 1967) Since water does not normally flow through the heat collector atnight, the fact that the effectivenight sky temperature isthought tobe-100°FH

for purposes ofradiation loss calculations, is of no great concern except in the

col-lectors are reported to have frozen upon rare occasions at air temperatures of

38°-40°F!

By whateverseriesofmechanisms,iftheheatdeckradiatesheattothe

trans-parentcover,some ofthatheatisgoingtobelosttotheatmosphere Thisiswhy

selective coatingshave adistinctadvantage overnonselective coatings They do

decks allow heatcollectors tobe operatedat high temperatures with low losses(Fig 16). Some effortshave been made tocoatglass andtransparent plastic sur-

than to absorb it (Johnson et al., 1975) The procedure also reduces reradiationlosses.

two major glass manufacturers are makingevacuated tubular glassheat

worksfine but the costs range upto $70 per sqft ofcollector surface Another approachtoreducinginternalconvectionisbeingtried.Flat plate collectors are

beingfitted with honeycombs tobreak up the air space separating heat decks

losses. Atthistimethere are nosystemsofthistype thoughttobeeconomicallycompetitiveintermsofdollarsof collectorcostperBTUcollected.

A secondglass cover is sometimes added to reduce upward losses from flat

aboutthe latitude of Gainesville, Florida,incold weather

Figure 14showssatisfactorycovertodeckspacingforbothsingleanddouble

appli-cations Hail breaks untempered glass and even tempered glass is subject to

breakage whenhitwith heavyobjects Exceptfor itstransparencyto solar

morn-ing andlateafternoonasa glasssurface does But 4 mil Tedlarrequires support

Fur-ther, it is transparent to 30% ofthe long wave length heat radiation to which

glass is opaque (Duffie and Beckman, 1974) Polycarbonates are very strong

though quite expensive Like glass, they are opaque to longwave length

(Kirk-patrick, 1974)

Productswhich contain 15%-40% fiberglassfilamentsbondedtogetherwith

been developedfor use in buildingandgreenhouse construction The

molded or sheet form Covers made of these materialsmay be molded in such

awayas tooverlapthesidesoftheheatcollectorbox and produce a highly leak

resistantjoint.

pro-videforabout90%ofthe hot water needsof a familyoffour inmostof Florida

10% Manyofthem recommendthe retention anduse ofanexisting electrichotwater heaterif it isrelativelynew(Fig 17).

forcedbyaverylow power(30 watt)electricpump Theoperationofthepump

No 3, 1976]

pressure&temperaturereliefvalve

hot water from

solar storagetank

hotwatertohouse

tankdownat groundlevelwhereit'seasiertosupportand whereleaksarenotas

harmfulwhen theyfinallydevelop The heatcollector may stillbe placedon a

sunnysouth facing roofwhereit'sfairlywellprotectedfromaccidentalbreakage

Other Applications—Solar water heaters are still expensive So are solar

complete units Arkla doesproduce a limitednumberoflithium bromide-water

absorption units modified for use with 190°—220° water or steam Private

solarwaterheatingfieldinthefewyears sincethe oilembargo madeusawareofthefragilityofAmerica'senergy supplysources.Asenergyreservesdwindlefur-ther, Florida m^y suffer more than many other states since virtually all ofher

rise andthe combination will move the state in an unenviable position

likely to occur Florida's fresh water supply is limited Salt intrusion in deep

an abundance ofveryhumid air—especially during the summer when demands

on thewater supply areapparentlyat theirmaximum.Solidabsorbentslike

A

of this scheme was used in 100 BC in Theodosia, Crimea Nocturnally cooledrockpileswereusedto collectdew which was pipedtocommonwatering spots

through sandstonepipes (Daniels, 1964)

Conventionalsolarstillswereusedtoproduceallthefreshwaterforthe

Chil-eannitratemines near Las Salinasfrom 1872 toabout 1910 The 51,000 sqftof

wasabout 33%

Animal andplant life beingtotallydependent onusable water, it isnot

of solarstills. MariaTelkespresenteda reporton themtothe World Symposium

anda team from Batelle Memorial Instituteheadedoriginally by Locklin

com-bined efforts tostudy the subject at a thoroughly instrumentedlarge facility at

Ponce de Leon inlet (Strobel, 1957; Bloemer, et al., 1964) In 1970, a "Manual

Laboratory (Univ ofArizona 1970-71 Annual Report) Severalarticleshave

ap-pearedrecentlyin SolarEnergy onsimilarthemes

covermay be glassorplasticbut itsinside surfaceshouldbetreated sothat the

condensingfilm will not "bead" on the surface (Daniels, 1964) The cover may

beattachedtoarigidframeoritmaybeinflated likea sausageskinwitha small

pump. Farrington Daniels, another pioneer in solar distillation, devotes a full

chaptertothe subjectin hisbook"DirectUseofthe Sun's Energy"(1964)

A novel approachto improvingthe efficiency of solarstills with heat pipes

isshown in Fig 19 (Lowe, 1975) Output ofdistilled water wasreported tobe

The main problem with using solar energy to distill water is that because

solar flux density is low, large expensive areas are required to harvest enough

energyto produce useful quantities ofwater But, as conventional energycosts

solar energy in the corn and wheat producing states but it does not consume enough energy in Florida to be of primary interest Protection of ornamental

largestindependentlyowned commercialplantgrowerinFloridaused $140,000

worth offuel at a cost of$0,104 persqft ofgreenhouse space toprevent frost

damage