..... ,,

d.~.fiR-81-2162

TITLE: LOS ALAMOS NATIONAL LABORATORY PASSIVE SOLAR PROCRAM

AUTHOR(S): Donald A. Neeper

SUBMllTED TO: 1981 passive and Hybrid Solar Energy pro8ramUpdate Meeting

Washington, D.C.August 9-12, 1981

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(sl!liRLOS ALAMOS SCIENTIFIC LABORATORYPoet Off Ice Box 1563 Los Alamos, New Mexico 87545An AffFmaUvaAction/Equal -W -

Form No, S39 R3St.No. 283Swn

LOS ALAMOS NATIONAL LABORATORY PASSIVE SOLAR ?ROGRAFP 3159A

(

Los Alamos Nattonal LaboratoryP.O. BOX 1663, MS/571Los Alamos, NM 8754S

U-7405-ENG-36

Donald A. Neeper

ABSTRACT

Progress in passive solar tasks performed at theLos Alamos National Laboristo~yfor FY-81 isdocumented. A third volume of the Passive SolarOesi n Handbook is nearly complete.~

TwenQ -efghtons of sunspaces were studied using our

solar load ratio method of predicting performance;the configuration shwing best performance isdiscussed. We have noted and measured themininwmlevel of insolation needed to generate convectiveflow in our thermosiphon test rig.

We also include information on test roanperformance, off-peak auxiliary electric heating fora passive hoine,free convection experiment,monitored buildings, and technical support to the USDepartment of Energy.

SUMMARY

The Los Alamos National Laboratory performedwork on eight passive tasks for the Department ofEnerg, Office of Sol~r Applications for Buildings,during FY-81.

A third vol~e of the Passive Solar OesiHandbook is being ccsnp;led~isnda draft will~fore the end of Fy-81,

Using the solar load ratio (SLR)** method forpredicting performance of sunspace-type passivebui?dings, we studied 7 different geometries eachwith 2 configurations of storage wall and thepresence or absence of night insulation. Thecomparative performances of the variousconfigurations were obtained,

Previous Los Alamos work in free convectionconfirmed the validity of the similarity approach.Having already established the importance of doorwayair convection to h~at transfer in passive solarbuildings, we are ncu simulating larger roans andstudying the effect of room length and width,transoms, and vents on heat transfer by freeconvection.

Thermosiphon collector experiments performed onour convective loop suggest that a certain thresholdof solar energy is required tn operate convectiveflow. This measured level ofm nimum insolation is

Japproximately 40 to 50 Btu/h ft ,

In FY-81 we studied 14 test cell configura-tions. A set of these experiments led to the dis-covery that a masonry Trombe wall can *e used as aheat flux meter. This technique enables us todetermine the U-values of the outer surface andglazing during night periods,

As part of our program of instrumented build-iIIgS, we have completed a comprehensive analys~s ofthe Balcomb house. Our conclusion is that the over-all performance of the house has been exceptionallygood.

We are currently &nalyzing and evaluating datafrom our study of off-peak auxiliary heating for apassive solar house, The control system has per-formed fairly well; hcwever, excessive andunexpected heat losses suggest that additional insu-lation should be installed during home constructionto isolate the ground storage in order to insuregreater heating efficiency.

1. INTRODUCTION

The Los Alamos National Laboratory began itsstudies of passive s~lar systems in early 1976 withthe idea that such historically sound methods forresidential heating were most appropriate for theimperatives of today’s energy-saving society. How-ewer, modern times and technology dictated that theperformance of passi~e solar systems be optimized,the behavior be well understood, and the technologyitself placed on a firm engineering foundation,

The Laboratory began passive systems studieswith the use of small test boxes and larger testrooms, The purposes of both the boxes and the roomswere the same: to provide a simple, inexpensivemethod of evaluating individual passive concepts,techniques, geometries, and materials and to provideaccurate experimental results agai~st which to vali.date theoretical num?rical modeling and simulationmethods,

The following four interconnected elments havecontinued to form the cornerstone of the Laborato-ry’s passfve solar program:

o Laboratory experime,ltsconsisting of carefullycontrolled evaluations of one or more passive

%~h f rk was performed undet’th@ auspices of the US Departnwnt of Energy, office of Solar Applications forBuil:if is.

**Sol?:”load ratio (SLR) is defined as solar radiation absorbed in the solar system divided by buildingheating load,

o

0

0

techniques through the use of physical modelsor test rocms (special ~ structures);

Evaluation of various passive techniquesthrough year-round, hour-by-hour monitoring ofthe performance of a nunber of residential andlight ccxmnercialpassively heated buildings inNew Mexico and elsewhere;

Development of theoretical and nunerical modelsfor predicting the thermal performance ofbuildings mploying passive tec!nfques, and theuse of these models to evaluate their utilityin various latitudes and climates and theirsensitivity to variations of design parameters;

Di5semfnation of useful information on passivesolar heating to the architectural and buildingcommunity in the form of handbooks and computercodes,

II. PASSIVE SOLAR DESIGN HANDBOOK (R. W. Jones)

The Passive Solar Design Handbook, Vol. 3, isIn preparation as a sequel to Vol. 2. It willsupplement Vol. 2 by the addition of extensive newdata, There will be chapters on the optfmwn mix ofconservation and solar, direct gain, and sunspaces.Also tncluded will be appendices containingextensive new data on thermal-storage walls andsolar radfation.

The optimum-mix chapter will presentinformation on the optimum mix of conservation andpassive solar strategies in building design.Guidance will be available within this section onselectfng the appropriate conservation level for agiven locatlon.

The direct gain chapter will contafn extensivenew information relative to the Vol. 2 coverage.;here will be SLR correlations for nine high-massreference designs (as opposed to two in Vol. 2).Analysis methods will also be presented for alow-mass, sun-tempered design, and numerous newsensit~vity curves will be p~esented.

The sunspace chapter will present SLRcorrelations for 28 reference designs. An extensiveset of sensitivity data will also be included.

We will present 57 solar load correlations (asopposed to the4 inVol. 2), including 15waterwall, 21 vented Tr’ombewall, and 21 unvented Trombewal! correlations.

The solar r~diation data wI?l be more a~curateand comprehensive than in Vol. 2* A secondcorrelating parametef, the averags monthly clearnessratio. will be added to relats rad’;ationincident onand transmitted th~ough tilted surfaces to theradiation incident on a horizontal surface, TtlerewI1l also be data to rel!ts absorbed solar radiattonto transmitted solar rad{ation, a feature notpresent in Vol. 2 (see Ref. 1),

111, SOLAR LOAD RAT:O FOR SUNSPACES (R. D!McFarland, G, Lhzarus)

It is vital that we understand and can predictthe behavior of the sunspace- or reenhouse-type of

!passive desi n, It is fast becomng the most?popular pass ve design with homeowners because of

the amenities it offers in extra living space andplant growing. in addition to collecting solarenergy. ....— ..

We continued develo&ent of performancepredictions for sunspace types l~f~~~ive solarheated buildings. Me basedtkse #edit.ti.onsnohour-by-hour computer simlations using comput,ermodels developed in tie frdmemork of the lns Ahoospassive Solar energy sinMlation-prqram lPASOLE).We determined SLR correlations for a total of 28sunspace configurations, These are comprised offour geometries for attached sunspaces (Fig. 1) andthree geometries for semi-enclosed sunspaces, allwith and without night insulation and for twowall/storage types. “Semi=enclsed’’.is a term usedfor geometries in which the residence encloses thesunspace on three sides--the east and west ends andthe north wall.

The two basic geometries for attached sunspacesare shown in Fig. 1. We studied these basicgeometries with opaque, insulated end walls and withglazed end walls for a total of fourattached-sunspace geometries,

Figure 2 shows the three semi-enclosedgeometries selected for development of SLRcorrelations, East, west, and north walls of thesunspace incorporate provisions for naturalcirculation of warmer sunspace air into theresidence.

--—

-s

GcofwtryB.—--

Ffg. 1, Attached sunspace geometries.

QEOMETRY

(cl

GLAZING 9uNSPACE

s MASS WALL

p—- 12ft +

(D]

p— t2ft—?

(E)

GL,AZING 19ft

6f+I

Fig. 2, Sectton through semi-enclosedsunspace geometries.

Annual simul?t’~ns were made for each of theconfigurations for 5 heating load coefficients foreach of 24 US cities usin Typical Meteorological

?Yedr weather data, b tots of 3360 simulations.

He found that Gemetry D, w~th a single planeof tilted gliszfng,gives the best performance of theseven geunetries investigated. It should be notedthat Geometry D also presents the worst potentialoverheating problem.

The monthly solar savings fractfon* (SSF)results of the simulations were used to Grtermineleast-squares correlations of monthly SSF as afunction of a modified monthly SLR (SLR’). Thesecorrelations were determined to minimize thestardard deviation in annual SSF. The correlationsare of the forir

SSFM ~ 1 - a exp (-b * SLR’), and

SLR’ ■ (S-L)/(DD*LCR),

where S is the solar radiatton absorbed fn thesunspace per unit collector area; L is the lWIS frmtho sunspace per uni’ collector area, approximatedby L ■ LCR * 00 * H, ~here LCRS fs the sunspaceload coefficient per unit collector area; ODis themonthly nunber of heating degree-days; LCR ts thebuilding load coefficient per ullttcollector area;and H, a, and b are empirical constants found foredch of the 23 configurations.

The tible belcud &pares the bnnual performance”of tio cbsncpdce 5Y5-SZ wlt4 *t ef wwen@d, —double-glazed Trombe b&all+yttems wlthmwithout aSelect{ve Surtace. #reed tbe Cystms has nightinsulation. -. . --- -------

..—..— --.— .

---–~E4-——. _..-.— .—- .-

ccuPAuIsGicfAtwALmwiwcEoFSUUSPACEAUD-E UALL6VSTEMS

~LcQ SSF{1) (2)— (3) (4)—— ——

Albuquerque, Wf4 0.60 9.72 0.52 0.69Caribou, ME . - --X- -0,22-- Q.Z6 0.17 0.33Madison, WI 24 0.27 0.33 0,22 0,39Nashville, TN 24 0.43 0.56 0.40 0.57Santa Maria, CA 60 0.64 0.77 0.50 0.64Seattle, WA 24 0.36 0.40 0,30 0,45

(1) Sunspace Geometry A with opaaue ends(2) Sunspace Geometry D(3; Unvented Trambewal) with no selective surface(4) Unvented Trambe wall with selective surface

Iv, SIMILARITY STUDIES OF INTERZONE CONVECTION (J.E. Perry)

The understanding of how passive buildingsbehave depends, in larae part, on understanding theheat transre: within the structure, For thisreason, we have, for the past 2 years, investigatedth{s phenonwnon,

In the computation of heat transfer withinmultiroom structurc$, and especially in thequantitative cmnputer modelin of this heat

!transfer, it is particularly mportant to understandthe heat trmsfer by free convection through opendoorwdys b:tween rooms that are at differenttemperatures. We can calculate, by well knowntechniques, heat conduction through walls, andradiation energy flw through openings. But thecalculation of this kind ot convection in anyconvenient and quantitative form has remainedintractable since Navier and Stokes published their

}original equa ions of fluid nmtion in 1827 and 1845,respectively,

Recently, doorway convection has been fo~JfIdtobe an important mechanism for heat transfer, Peferto the enerv-flow study of the Balcomb house inSection VI-B of this paper,

The problem can be bpproachsd throughsimilarity studies, but evws this technique has nothad wi e applicability to fnter-room or inter-zonecases~~3 In this similarity mthod, the fluidflow equations are set Up in nondimensional formwith two nondimensional groups of corst&ntsap earing as cuefficlents in the equations. The1’so utlons of the equatlcns are simflar for those

flulds and equivalent geometries for which the twocoefficients have the same values, In the case ofconvection, the “similar” solutions are the flowvelocity fields and the temperature distributions,

The tw coeffic~ents pertinent to freeconvection are the Grashof (Grj and Praodtl (Pr)

%aTar savings fraction (SSF) is defined as 1 - aUX~liarY heat!ng raquired, divided by building hedttnq load,

numbers. Given tm connected romns (r) and a scalemodel of these rouns (m), the convection betweenrocrnscan be calculated by studyin the convection

!In the model provided Gr(r) ■ Gr(m &nd Pr[r) =Pr(m). To achieve these equalities, assuning air inthe roans and a given temperature difference betweenrocsns,AT(r), it is necessary to use a different gasand an altered LT(m) in the mociel,

T. ~shof nunber, which expresses therelat ,)sbetween buoyancy and viscous forces in thegas and establishes the similarity of the twvelocity fields, is given by

Gr ❑ gH3AT/(v2T) ,

where g is the gravitational constant, H is acharacteristic length (e.g., the height of thedoorway), AT is a temperature difference (e.g.,between roans or between the top half of the doorand the bottom half), T is the average absolutetemperature of the gas, andvis the kinematicviscosity of the gas, The latter is v ■ u/o, whereIiis viscosity and ; is density. The Prandtlnunber, which establishes the similarity ofttsnperaturedistributions between model and rooms,is gfven by

Pr=v/a=~x~=uCp/k ,

where a 4s the d;ffusivity of the gas g<k/(dCp), with k the conductivity and CPheat at constant pressure.

ven by a ■

the spec”fic

The current experiments are en extension ofthose u d rtaken recently by Dennis Heber at LosAlhmos~,~ The model js an insulated box ofInside dimensions 100 tn. long, 48 fn. wide, andin, deeD. An electrically heated end Dlate

24

simulates a Trctnbewall, ~ water-cooled end platesimulates a north building wall, and a l-in.-thickStyrofoam sheet with doorway simulates the east-westram-divider wall. To insure equality of Grashofand Prandtl nunbers, a dense gas, Freon 12, is usedin the model, and :)T(m)■ 3,2 LT(r). Under theseconditions, the roan linear dimensions are 5.65times those of the model.

To discuss convection heat transfer, it ‘necessary to invoke a thirJ similarity nunberNusselt Nunber (Nu). This is given by

NU ■ hH/k ,

wh~re.h is a heat transfer coefficient (Btu/h

sthe

offt2),3 In this case h is the natural convectionheat transfer coefficient averaged over the dooniayuraa.

Analysis shows that for inter-rocm convection,the thr.e similarity nunbers are relRted by theexpression

Nu.CPrGrl/2 ,

where C is a discharge coefficient related CIthesharpn~ss of the d es of the door opening.

!I

Empirically this re ation has been found to hold forC in the range of 0.65 to 1.0.

From hissoodel and also frcm–& ~~s in acwlbuildings, Ueber foundUu ■ 0.26 Pr12r . Bysubstituting in the appropriate values far ●ir, thecorresponding convection has~ fl- t.hrw$ a dea-wayis givenby dQ/dt ■ 4w(khTa) ~ ,nhere the heatflow is in Btu/h,rnds thewidthof. &ba daor U ft,H its heightdn ft,ti AJaA .%&4bem?ecureddifferencehetween the ●irkqmratu.m ia41ne upperhalf of the &or~ree and thatia th-kmwrbalf ofthe ar~. – ....... ---------—------ -------

Weber’s results confirmed the validity of thesimilarity approach. His formula For convectiveflow as a function of the air temperatures in adooway is an important result for calculating heatflws in multire~buildi~gs.- +itiever,h4s work wasfor a lfmited set of room-door geometries. Thepresent experiments will undertake to confirm andextend his results, Whereas his model applied totwo rooms 8 ft high by 13.5 ft square, the presentmodel can represent rom,s up to 11 ft high, 22 ftwide, and a total of 45 ft long, The followlngvariables can be studied: room lengths, widths,heights, and different heights room-to-room, docrheights, transoms, upper and lower vents, and doorsthat are off-center in the dividing walls, As withthe previous experiments, the objective 1s to derivean empirical algorithm or algorithms that can beused for mathematical modeling.

V, THERMOSIPHON COLLECTOR EXPERIMENTS(F. Biehl)

The goal of this program is to devise designguidelines for afr thermosiphon heatir,gsystems tobe used in large building retrofit applications.The results of a test system will be compared withanalytical results in order to verify the analyticalapproach, This method will perm~t us to evaluateperformance of system conf~ urations not actuallytested. 7Additionally, we w 11 use the analysis togenerate the optimum configuration for var:ouslocalities.

He test two parallel, side-by-side test loopssim:lltaneouslyso that a selected design parametermay be evaluated relative to a referenceconf~quration. Details regartiingthe test setup areavailable in Ref. 5,

Test data were obtained for the three channeldepths of3.5, 6.5, and10,5 in. Channel depth isthe narrw dimension for zir flow behind th~absorber of a flat plate collector. The testresults for the 3.5-in, and 6.5-in, depths arepresanted in Figs, 3 through 6 and show thecollector efficiency and flow Reynolds numbers forthe 3.5-in, and 6,5-in, channels, Figure 3 depictsthe collector afficlency as a function of stressfactor (defined as the difference between collectorinlet t~perature and ambfent temperature, dividedby the incident solar insolation). Test oints and

!analytical predictions are fndicated in a 1 fourfigures, Constant ambient temperature, solarincidence angle, and optical properties wereemployed in the analysis, The majority of test datawere obtained at ambient temperature! between 40 and5ooF, Analytical calculations at both 40 and500F ar~ sh~n for the ~est~olle~tor (6,5.fn,channel) to ~llustrate the impact upon collectorperformance of the assunwd ambient temperature,

‘0 ~50

-P-AMBlENT~40” F

7>40 # AMBIENTs50” F

> **vz 30

*$+””.~u +*G +++L 20

+u

‘k!K____do 005 0.10 0.15 020 0.2!! 030

(TIN-TAMB)/I(”F FT2H/Bfu)

Fig, 3. Collector efficiency vs stress factor.West collector, 6.5-tn. channel depth.

I 1.

!ir----A-

{

‘o~joo 005 010 015 020 025

(TIN-TAMB)/l(”F FT2H/BiU)

Fig. 6. Reynolds number vs stress factor.Fast collector, 3.5-in. channel depth.,.. —

‘r--—— ‘1 I -1

dZ2

t

+ TEST VALIJES

E0---0 ANALYSIS

ol—~ ~005 010 030

(TIN-TAMe)/I (“F FT2 H/8~U)

Ffg. 4. Reynolds nunber vs stress factor.West collector, 6.5-fn. channel depth.

‘Or~-

,

I

( ~p’ti:L

t

+~ 20

++

$++ 1ES7 VALUES

‘:C:. J I ,0 005 010 015 020 025 030

(TIN-TAMOUI(’FFT2 H/8fu)

Fig) 5. Collector efficiency vs stress factor,East collector, 3.5-in. channel depth,

An examination of the figures reveals that thepredictions are more accurate for the 6.5-in, chan-nel than for the 3.5-in. channel. Further inspec-tion of Figs. 4 and 6 show that the Reynoldsnumber is considerably higher for the 6.5-in. chan-nel, Sihce the heat transfer between the collectorplate and airstream depends on the flow Reynoldsnumber, the simulation requfres an acceptable ana-lytical model for this relationship. The modelemployed in ‘he analysis was extrapolated from meas-ured data in neated flow channels operating athigher Reynolus numbers and, therefore, the greaterthe extrapolation frcm the reference values, themore likely it is that the extrapolation will de-viate from the correct value. Nusselt number exper-imental results are absent in the low turbulent-flowregime (or transition regime) for asynwnetrically~~~ed rectangular ducts in thermally developing

. The collector plate t?mployedconsisted of asheet metal panel with attached extended surfacesperpendicular to the collector surface (fins). Inorder to achieve correlation between test and analy-sis, a factor of 0.7 was used for fin efficiency.

The three previously discussed collectors areall 15 ft {n length. The length of the 3,5-in, deepcollector was changed to 7.5 ft in order to evaluatecollector length uDon performance. An analysis thatsimulated the proposed length change showed a sub-stantial attenuation in flow Reynolds nwnber accom-panied by a corresponding loss in performance.Since the analysis is suspect at IIlow Reynoldsnumber (less than 3000) and a poorly p~rformingcollector would yield little infornstion, a fewdesi n changes were incorporated into the shorter

!conf guration. Remodified the bottom of the air-flow channel from square corners to quarter-roundcorners and painted the interior of the collectorflow channel. The former ~hange reduces tho cornerflow resistance from 40 to 10% of the total systemresistance, whereas the paint improves radiant heattransfer from the absorber plate to the rear of thechannel, which is also exposed to the air stream.

The weather pattern that prevailed during thetests of the short collector included few clear-skydays, These weather conditions provided an

opportunity to evaluate collector response to lowinte~,sitysolar radiation. Unfortunately, theinsolation tended to change frcrnlow to moderatelyhigh intensity over relatively short time periods sothat the collectors rarely reached steady-stateconditions. However, we did observe a threshold ofinsolation below which no energy is extracted fromthe air stream. This suggests that a certain levelof solar energy is required to generate convectiveflow. This measured level of minltnwnsolarradiation is approximately 40 to 50 Btu/h ft2(where the diffuse radiation ccmponent predominates)and has been confirmed by the computer simulation.Computer results are depicted in Fig. 7 showing theper cent energy loss (heat losses in the systemdivided by the collector section heat gain) as afunction of ificiclentsolar radiation and collectorinlet temperature.

I I I 1 I I I I I I 1 I

lNSOLATION(Btu/hft2)

Fig, 7, Per cent energy loss vs insolation,

VI, COMPONENTS AND BUILDINGS (R. D. McFarland)

A. Test Roomslnce 976 the Laboratory has been using small,

side-by-side test cells, designed to bereconfigurable, to evaluate passive heatingtechniques and to obtain thermal performance datafor validating ccmputer codes and models. In FV-81,we studied 14 test cells designed as follows:

Description

Unvented masonry wall, flat black.

Unvented masonry wall, selective surface,

Double-wide sunspace, glazed apertureslopod at 600 from horizontal,

Commercial water wall, selective surface.Crimsco, Inc., heat wall module.

Texxor con$ of phase-change calciunchloride thermal storage with felect~vesurface,

Double-wide sunspace, glazed aperturevertical, with qlazed roof sloped ~t 300fr~ horizontal,

Sun-tapered building model of Navyhousiag, with adjustable parameters.

10 Sun-tempered building model of Navyhousing, reference cell with fixedparameters.. . ..

11 Direct gain, unpaintec!/paintedmasonry.

12 Unvented ~sonry will witho~t-thermostatper internation~l agreement of-theConsnitteeon Challenges of MQd?rn 50C

13 NOnsol~e~ererice”cejl for”load--determination,

14 tleat-pipewall (developed in the passprogram) supplied by Battelle Columbu.Lab!matory...-- -. - - -

ety.

ve

All of tttetest rooms have been revised and were inoperation with 180 channels of data working well onour new data logging system. This system hasalready detected and helped eliminate errors thatwould have been difficult to find in previousyears, With the new system, the laboratory operatorcan obtain a plot of any parameter upon consnand.

The glazed aperture has been standardized onmost of the rooms to increase the LCR to about 26,using patio door glass, See Ref. 6,

The heat-pipe wall in Test Room 14 proved to bescmwhat troublesome. The five-heat-pipe unit fromBattelle was too large for the test-room aperture,leaving one heat pipe partially covered, $hippfngdamage to Los Alamos rendered one pipe useless;subsequently, a second heat pipe failed. In spiteof these problems, we collected data fran this testroom during the heating season. The resultsindicated that,the heat-pipe concept would probablywork well with all heat pipes in operation,

ThF cell showing best performance in termS Ofcollection efficiency was Cell 5, the water wallwith selective surface, The phase change cell (Gell6) performed well, but tended to overheut once thephase-change salt was melted, The performance ofthe direct gain cell (Cell 11) was improved markedlyby the addition of night insulation,

During the winter, comparative tests were runbetween Cell 1 (unvented masonry wall with flatblack paint) and Cell 2 (unrented masonry wall withselective surface toil), Table II summarizes thegeneral results. Cell thermal performance ismeasured by the collection efficiency during aselected two-week period in each month listed on thetable. Also comp?red is the performance of Cell 5,the wdter wall,

TABLE 11

COMPARATIVE PERFORMANCE OF CELLS 1, 2, AND 5

Number of Night Thermal Perf,Glazings Insulation Cell 2 Cell 5

(All 3CP11S) ._.Period __ (Cell 1) ~~ ~

1:;:; No 1,18 ;,11: Yes 0.88 1,26

2/81 1 Yes 0,91 1,323/81 1 No 1.43 1,27

We have discovered that a masonry Trombe wallcan be used as a heat flux meter. Fran tefnperaturesmeasured at the two surfaces of the masonry wall,one can determine the heat fluxes by applying thediffusion equation. This technique enables us todetermine the effective U-values of the outersurface and glazing during night periods, when thereis no insolation on the wall. This is cnerging as avery nice analysis tool. The U-values given inTable III were determined by this method andillustrate the advantage of a se)ective surface asccsnparedwith double glazing. Measurements at thetop, middle, and bottom of the wall shcw temperaturestratification. The stratification would lead toerroneous results if one attempted, for example, todetermine an effective emiss{vity of the surfacefrom temperature measurements at a single level.

TABLE 111

EFFECTIVE U-VALUES

Nwnber of Night SelectiveGlazings Insulation Surface ~.— —.

2 No No 0.46No No 0.80

i No Yes 0,262 NO Yes 0,29

lor2 Yes No 0,14

B. Instrumented BuildingsFor he past several yeers, we have studied 14

privately cwned passive solar buildings to I“ecordthe thermal comfort and energy savingsch~-acteristics and to provide validation data forcalculations of the behavior of the monitoredportions of the buildings.

We have completed a ccsnprehensiveanalysis ofthe @alconb house and will do a review of otherhouses.

Tha Balcanb solur house is located in Santa Fe,Newhiexico, at an elevation of 7200 ft and alatitude of 35,LloN, lt is a tw-stry building

!with a total living area of 1950 ft of floorarea, The solar heating is primarily passive butalso incorporate an active system for supplementalheat storage. Warm air is drawn throuSh ducts fromthe top of the greenhouse and forced by two 250 Wfans through rock beds located beneath thedovmtairs living area floors; distribution ispassive by conduction up through the floor. Thehouse is very well insulated, with an overallmeasured heat-loss coefficient of 14,300Btu/oF-day (counting the greenhouse as an unheatedspace), There is ample mass for heat storage in themasonry (adobe) wall that separates the reenhouse

!from the house, the rock-on.dirt floor o t’mgr~enhousc, the rock beds, and a partially bermednorth wall,7

?~rfnrmance data on the house havQ beenevaluated for the period Novwnber 1, 1978-April 24,1979, and more detailed information was obtainedover b 6-week period In spring 1980, Daily eoergyflows have been calculated for the followingelements:

Heat flow throughjthg adobe wall that sepiratei”the house .frqnthe.greenhouse; .._ .. ... ....

- ....--..-—.. ..Convection through the doorways fih.at.~eparatethe house frcm the..greenhOusgi__________ ,. .

.—..— -. . .... .Heat generated M1.~.l.J_y@W4Urn.@.StOVc(was estimated);

Heat required for t~e evaporation ofwatw’ t’rwplants and othc, sources of water within thehouse (was estimated);

ie~t-”t>a~s~,ort<d-b~~h<~a~s-~~&~h~” - “ -greenhouse to the rock beds, heat flow upthrough the floor slabs covering the rock bedsinto the dining room and living room, and heatflcnvinto the ground underneath the rock beds;and

Heat flow fram the water heater to the ho’)se(h’aS estimated as 11,780 Btu/day plus 25% ofthe electrical energy into the wilterheater).

The overall performance of the house has beenextraordinary. It has provided good comfortc~)ditions in a cold climate with very smellrequirements for auxiliary heat. Solar heatingfraction is 89%; operation is simple and reliable,

The greenhouse is an efficient solarcollector, Approximately 31% of the solar radiationtransmitted into the greenhouse is subsequentlytransferred to the house. In addition, thegreenhouse is adequately heated, maintainingconditions WCII above freezing, without auxiliaryheat, A critical design feature that leads togreenhouse effectiveness is the ability to thermallyisolate the house from the greenhouse by clmingdoors

The predominant mode of heat transfer betweenthe greenhouse and the house is by convectionthrough doorways that are opened during thedayt~me. The fact that the greenhouse serves as amajor traffic area is important to the effectivenessof this control mechanism, Typical convectionthrough a doorway is 50,000 Btu on a sunny day forthe upstairs bedrooms and 23,000 Btu for thedownstairs; this difference is due to the slightlycolder room temperatures and hi her greenhouse

!temperatures u stairr. The typ cal driving ATupstairs ts 158F, Much of this heat goes tosatisfying daytime loads, but about 40% is stored inplaster walls, wood-beamed ceiling, and housefl,enishings,

The prima~y importance of the massive adobewall between the house and the greenhouse is fordirect-gain storage +n the greenhouse, Most of theheat absorbed by the ‘all is released back to the~r~enhouse atnight~r,d is essential to maintainingreasonable ternerature conditions in the greenhouse,

rThe amount of w t transmitted through the wall tothe house is 1,1 mtll!on Btu for the year, Th{seffect is larger upstairs due to less shading of thewall, slightly lcwer room temperatures, and athinner wall (10 in, vs 14 in. downstairs),

I

Heat storage in the plaster walls, wood-beamedceiling, and furnishings of the house issignificant. Carryover heat frcm one day to thenext is observed on 89 of the 176 days of theanalysis period, averaging 49,200 Btu per day.Diurnal heat storage (heat stored and releasedduring the same day) occurs nearly every day andaverages 89,000 Btu/day.

The effecc of water evaporation in thegreenhouse is significant in improving the livingqllalityby increasing the hunidity into the 20 to50% ccsnfortrange; this hfsnidityincrease is at theexpense of about 57,000 Btu or 10% of clear-daysolar gains.

The rock bed definitely appears to have apositive effect on the heating of the house andespecially on the ccmfort characteristics, althoughthese effects are less than originally estimated.About 53% of the heat deposited in the rock bed Isconducted up through the floor slab into the livingarea, The remaining 47% is conducted into theground underneath the rock bed (the perimeter of therock bed is insulated with 2 in. of foam, but it is

not insulated underneath). The averagefloor-surface temperature above the rock bed is69.2oF, which compares with 600F measured on thefloor, well away frcwnthe rock bed. The beneficialef~’actof this increase in floor temperature allowsa ducrease in air ~crnperatureof the rocxnof about2oF in order to maintain equivalent cwcfortconditions. It is also important to note that heatwould be lost from the floor, even if the rock bedswere not present. The net benefit of the rock bedto the house is estimated as 30,000 Btu per day or5.3 million Btu per year, canbi,lingthe direct andtwo indirect effects. Another benefit of the ~ystemis the 10-15° reduction fn greenhouse temperaturesobserved when the fan is operated. Reversethennosiphon from the rock bed to tilegreenhouse cansignificantly impair the effective performance ofthe system; backdraft dampers prevent thisdegradation.

Sumner weather in Santa Fe is mild with largediurnal swings. Maximum house temperatures are820F upstairs and 78°F downstairs without airconditioning. Overheating thdt might be caused bythe reenhouse is prevented by sun control, good

fvent lation, and night-vent cooling of the largehouse mass, The reenhouse roof and second-floor

fbalcony effective shade the adobe wall. Crossventilation and stack ventilation remove excess heat.

Excellent agrement was achieved using themonthly SLR method to estimate auxiliary heat basedon the actual observed solar radiation and netheatlag requirements. The house was treated as amixture of semi-enclosed sunspace (to account forthe reenhouse) and direct gain (to account for the

!SE, U, NH, andNE house windows). See Ref. 8.

VII. COOLING (R. D. McFarland)

We are in the process of determining thecooling Implications of solar gains and thermalstoraqe as the first step In integration ofresid~ntial cooling, heating, and daylighting. Wevt;I go on to review climate data for the broadpotmtial of reducfn residential cooling loads by

?suitable use of pass ve architecture. He sent aletter to DOE Headquarters in June 1980 including

data showing some of the cooling load impacts ofpassive heating systems, ._ . -

At tb!s time we have just btiun ~ork on accmiprehensivestudy of the total energy savings ofvarious schemes of.preventing wlarmmkmting--astudy that we hope Mill =ultti.uenmlmetbodsfor design. Figure Bfiows 4YPicAl nwlb nbtainedfor SiI’IIUliitiOnS Mith south ulAzing 0!JerhM3S nod

water wall passi~eheatlng SYstm. -Lb.ese are linesof constant energy savings relative to the samesystem with no overhang. The numb rs on the lines

$represent thousands of Btu/year/ft of collector.This particular graph Is for a heatingload-collector area ratio of 28 Btu/DD ft2 and acooling system COPOf UO.-The averhang ratio isthe width of the overhang, X, divided by the heightof the aperture being shaded, H; the separationratfo is the distance between the top of theaperture and the bottom of the overhang, Y, dividedby H.

Fig. 8,

VIII. STUDY

OVERHANG RATlO

Effects of overhangs on a water wallpassive heating system inAlbuquerque, NM.

OF OFF-PEAK AUXILIARY HEATING FOR 4PASSIYE SOLAR HEATEO RESIOENCE (H. S. Murray)

IntroductionThe auxiliary energy for passive solar heated

structures may be provided by storing energy in theground underneath the structure during utilityoff-peak hours. Thts approach is attractive t~builders of passive solar heated homes due to ...erelative ease with which electrical resistance matsmay be placed on the ground during excavation forthe foundation, and due to fmproved aestheticsachieved by eliminating baseboard electricalheaters, This auxiliary heating method isattractive to the electrical utilities because thesystem uses only off-peak power for heating andwould thus allay concerns that passive solar heatedhomes would aggravate utility load peaking problems.

The use of off-peak storage released passivelyto the heated enclosure leads to significant controlproblems, Energy must be expended before it is

1.’

needed to heat the structure due to the thermal lagof the storage mediun. The success of this approachdepends upon the development of a control systathat regulates the roan temperature sufficientlywhile using energy at a cost lower than that for aconventional electrical backup system. .“,-

Project History and Objectives-----.—-.-—

This 1s a Joint project between the Los AlamosNational Laboratory; the Public Service CcrnpanyofNew Mexico (PNM), the electric utility cunpany; andCommunico, Inc., a bu+lder of passive solar heatedhmnes in Santa Fe, New Mexico. The objective of theproject is to determine the feasibility of apassive, off-peak electrical auxiliary heatingsystem, The role of Los Alamos is to provide systemanalysis, instrumentation support, control systemdesign, and performance analysis.

The house under study is a 1200 ft2 passivesolar house with direct gain and Trcanbewallcomponents, located in the La Vereda subdivision ofSanta Fe, New Mexico. Construction of the house wasundertaken in late 1979. A number of temperaturemeasurements are made in the ground heating system,interior of the house, and in the Trombe wall todetermine system performance. Ccsnpletehourlyelectrical load data for the entire system, heatingsubsystem, and hot water subsystem are provided byPNM. We took data on the system from October 1,1980, through April 30, ?981. During this period,control system operation was studied using differentmodes of operation.

~ r or to installation of the heating system,simulation studies were performed on the-systsmusing actual solar and weather data to determinedesign parameters and to examine the ef ect ofcontrol stratec~ on system performance.J Theperformance of an intelligent controller that knwsthe weather the follwing day but operates theheating system only off peak (10:OIJp.m. to8:O0a.m.) was ccmpared to conventional thermostatcontrol of baseboard heaters. The findings of thesimulation studies were as follows:

1. Optimun depth of the mats should be 9 in. belowthe floor slab.

2. The optimally controlled ground heating systemuses 17% more energy than the baseboard systembut at an 18% cost savings due to the off-peakrate differential (approximately one-half ofthe on-peak rate),

The simulation analysis was performed for a wideran~o of system parameters, such as ground and fillconductivity. We assumed that ~eripheral losseswould be ~inimal due to the use of rigidinsulation. We calculated that the ground therms?storage system losses should be less than 24% forthe system to be clearly economically superior to aconventional system.

w ecause he simulation analyses indicated aneed for an intelligent controller, amicroprocessor-based control systm was specifiedand installed, The controller is quite flexible,allowin for the study of different control

!strateg es. The use of this controller during the1980-81 winter illuminated a nunber of problem areas

pertaining to microprocessor control of advanced-–”-”heating systems; the ”$pecl~ic”problemswfth which Wedealt were sensor Failure, system response to power-failures, and IrnpFovVngoperator Tnterfacei-””-””-–---”.. . ...... ...._-.— _- .._.-........ .

Perfor%sanceAnalysTi --””--” ‘—”–- ““”””-The system was operateil~e~e~cofitrol “-”-

modes during ”the exper~iiental”~=.~e spec7TTc——..-.-.

results of the effect ‘o?co7itrhTZt-rite_______ ..s

7are not

complete; kswever, the system uiea “cons de”rably ‘moreelectrical‘beatingenercjylhan expected.

-—— ....-.

Temperature measurements in the grou~d and floorslab were used to calculate heat flw into theheated enclosure; the heating system was activatedon November 27, 1980. The monthly performance ofthe system from December 1980 th~ough April 1981issummarized in fable IV. _Ytie-totalof heating “- -degree-days for October through April was 5504oF-days.

TABLE IV

LA VtR[DA HEATING SYSTtM

IKAN DAILY ENtRGV

cl~ct,ical F\cml- Hmti .“Solar (Dfrect HQatin~ “--

...inergy Heat{ng SYSIG

+ Trcmbe Nail) Enerw -eelIvere6 DC9re:;&$~(650r) [ff!ciencyMonth kUh k!dhkUh Y %—

k . 47.7JaII. 46.7Feb. 51.6b.. 34.0Apr. 30.6

Seasonal 42,oAveraqt

23.7 12.327.S 11.734,9 17.240.3 22.422.0 10.029.6 14.1

9131012806871391

3993(Tot.11)

51.942.549.35S.645,550.0

We observed that only 50% of the electricale~ergy used is delivered to the heated enclosure.The losses are thus far greater than expected.Heat-flow calculations for the soil below theelectrical mats indicate that 8% of the heat is lostdownward. This loss is well within the limit foreconomical operation, as found in the simulationanalyses. However, an additional 42% of the heatappears to be lost peripherally, and this loss leadsto poor system performance.

Average enclosure temperatures are summarizedin TableV. The control system was set to controlthe interior temperature at 700F.

TABLE V

LA VEREDA AVERAGE ENCLOSURE TEMPERATURES

oct.* 74.8 81.4 69.0 46.9:;.* 69.9 75.6 64.8 35,?

71.5 77.2 66,9 33.3Jan; 69.9 75.1 65.7 32,4Feb. 69.9 75.6 65.2 36.2Mar. 67,8 71.6 64,1 36,9Apr. 71.9 75.5 68,6 52.0

* ——Unheated

Conclusionbreakdown of heating cost--adjusted for the

off-peak rate differential--compared to the heatingcost for a conventional system--also adjusted forthe off-peak rate differential--has not yet beenmade, The low system-heating efficiency of 50%suggests, however, that the comparison will

probably not be favorsble. The control systanperformed reasonably well; it appears that thenorml passfve heating system overheating problemwas not aggravated, and the nuninal interiortemperatures were kept near the desired setpolnt.The h~se was unoccupied a great deal of tie tlmso that normal interior heat loads were notprese,lt,and nomal operation would not require the70% setpoint. These factors incraased the heatload. The question of whether this systm can bemade to operate economically Is being examined. Inorder ‘hot a pc;sive ground-storage systm befunctional beyfid question, a great deal of careiiwstbe taken during construction to lSOlatethermally the grourldstorage reservoir.Specifically, sufficient rigid insulation should beextended to a depth of at least two ft belw theelectrical-mat level.

IX. SUPPORT TO DoE HEADQUARTERS (J. E. Perry,ii.O. Way)

Los Alamos technical support work consists offour general aspects: (1) responses to specificrequests for information frun the DOE Passive SolarDivision, (2) the intercanparison of passive solarnetwork canputer calculations, (3) participation inmeetings for the generation of a multiyear plan fordata acquisition in Class A monitored passivebuildings, and (4) monitoring of the University ofCalifornia at San Diego (UCSO) contract on the“Impact of Controls in the Passive Heating ofBuildings.”

In the first category, multiyear passive solarplans for passive solar heating and cooling andpassive solar prorhcts were read and extensivereviews were provided.

As the second aspect o: our support work, wedirect the activities of national and internationalworking groups on passive solar simulationanalysis. Simulation exercices are defined by LosAlamos and distributed to working group mmbers.Results are later submitted to the Laboratory,where a canparative analysis is conducted. Theresults of the comparative analysis are reported atperiodic meetings of the two worit:nggroups. TheNATO-sponsored Camnittee on the Challenges ofModern Society is an international working groupthat last met on Decanber 10, 19B0, In Nice,France, to discuss rerults. The next meeting isplanned for August 22 in Brighton, England.

The System Simulation and Econanic Analysis(SS/EA) working group was organizd by DOE andfunctions at tilenatforlallevel. rhe SS/EA grouplast met in Philadelphia on May 27, 19B1, duringthe AS/ISES conference. Another meeting istentatively plann~ to coincide with the6thNational Passive Solar Energy Conference inPortland, Oregon, September 8-12, 1961.

Considerable time has been spent discussingwith mmbers of the Energy Center of UCSO theirpassive controls work; we have also studied thei~papers, He are monitoring this excellent work forthe Chicago Operations Office of 00E, which fundspassive contracts.

REFERENCES

1.

2.

3.

4.

5.

6.

7.

8.

9.

J. D. Balccah, et al., Passive Solar DesignHandbook, 2 (US DOE, 00~-OIZl/Z, Jan. 1~0).

H. Schlichling, “Boundary-Layer Theory,”McGraw-Hill (1%9).

D. O. Heber, “Similitude Modeling of NaturalConvection Heat Transfer Through an Aperturein Passive Solar Heated Buildings,” Ph.D.Dissertation for the University of Idaho, LosAlamos National Lab: ‘ory Report LA-8385-T(19BO). Seealso U. O. Uray and D. D. Heber,“LASL Similarity Studies, Part 1, HotZone/Cold Zone: A Quantitative Study ofNatural Heat Distribution Mechanisms inPassive Solar Buildings”; and D. D. Heber, W.O. Hray, and R. J. Kearney, ‘LASL SimilarityStudies: Part II, Similitude Modeling ofInterzone Heat Transfer bv NatdralConvection,” Proc. of 4th-National PassiveSolar Conference, KanSa5 Citym MO ,~-D 919.

D. D. Heber and R. J. Kearney, “NaturalConvective Heat Transfer Through an Aperturein Passive Solar Heated Buildings,” Proc. of5th National Passive Solar Conference,liiilierst,M4, Ottober 19-Z6,_.

U. S. Morris, “Development of an ExperimentalTest Apparatus for Natural Convection SolarCollectors,” Proc. of the 5th National PassiveSolar Conference, Ottober 19-26Amherst, MA Z (American Section of’theInternation~l~ar Energy Society, Newark,OE, 1980) pp 1CI32-1036.

“Energy Technology: October-December 1980”Los Alamos National Laboratory ReportLA-8797-PR, (April 1921)

J. D. Balcomb, J. C. Hedstrom, andJ. E.Perry, ‘Performance Evaluatiwl of the EialcombSolar House,” Colloque Solaire International,Nice, Frws, Secember 11-12, 1980.(LA-UR-BO-3453)

J. D. Balcmb, J. C. Hedstrom, andJ. E.Perry, Jr., “Performance Sunsnsryof theBalcnmb Solar Home,” Solar Rising 1981 AnnualISES Meeting, Philadelphia, PA, May 26-30,19B1. (LA-UR-81.1039)

H. S. Murray. J. L. Melsa. andJ. D. Balcomb.“Control Sy~~em Analysis”for Off-Peak “Auxiliary Heating of Passive Solar Systems,”2nd Annual Systems Simulation and EconomicsAnelysis Conference, San Ciego, CA, January23-25, 1980.

PASSIVE PAPERS PUBLISHEO OURING FY-81

J. O. Balcomb and J, C. Hedstrom, “Oetennining HeatFluxes frmn Temperature Measurements Made inAassive Halls,” The Fifth National PassiveW#rence, Amherst, Massachusetts, October 19-26,

. (LA-UR-80-2231)

R. W. Jones ard R. D. McFarland, “Attached SunSpace J. E, Perry, “Rock Bed Behavior and ReverseHeating Performance Estimates,” 5th Passive Thermosiphon Effects,” 5th Passive Conference,Conference, Amherst, Massachusetts, October 1?-26, Amherst, Massachusetts, October 19-26, 1980.1980. (LA-UR-80-2236) (LA-UR-80-2429)

W. O. Wray, N. M. Schnurr, andJ. E. Moore,“Sensitivity of Direct Gain Performance to DetailedCharacteristics of the Living Space,” 5th PassiveConference, Amherst, Massachusetts, Octobe, !9-26,1980. (LA-UR-80-2266)

W. O. Wray, “A Quantitative Comparison of PassiveSolar Simulation Codes,” 5th Passive Conference,Amherst, Massachusetts, October 19-26, 1980.(LA-UR-80-2267)

J. C. Hyde, “Performance of Night Insulation andSe”lectiveAbsorber Coatings in LASL Test Cells,”5th Passive Conference, Amherst, Massachusetts,October 19-26, 1980. (LA-UR-80-2268)

O. D. Weber and R. J. Kecrney, “Natural ConvectiveHeat Transfer Through an Aperture in Passive SolarHeated Buildings,” 5th Passive Conference, Amherst,Massachusetts, October 19-26, 1980. (LA-UR-80-2328)

W. S, Morris, “Development of an Experimental TestApparatus for Natural Convection Solar Collectors,”5th Passive Conference, Amherst, Massachusetts,October 19-26, 1980, (LA-UR-8C-2329)

J. 0, Balcc+nb,“Conservation and Solar: WorkingTogether,” plenary for 5th Passive Conference,Amherst, Massachusetts, October 19-26, 1980. /(LA-UR-80-2330)

D. D. Weber, “Similitude Modeling of Natural

/

Convection Heat Transfer Through an Aperture inPassive Solar Heated Buildings,” Ph.D.Dissertation, University of Idaho, 1980.(LA-8385-T)

S. K. Reisfe?d and D A. Neeper, “Solar EnergyResearch at LASL: O~tober 1, 1979 -March 31,1980,” Los Alamos Scientific Labor&tory ReportLA-8450-PR. (November 1980)

W. 0. Wray, “An International Comparison of PassiveSolar Simulation Codes,” Colloque SolaireInternational, Nfce, France, December 11-12, 1980.(LA-UR-80-339?)

J. D. Balccunb,J. C. Hedstrom, and J. E. Perry,“Performance Evaluation of the Balcomb SolarHouse,” Colloque Solaire International, Nfce,France, December 11-12, 1980. (LA-UR-80-3453)

J. D. 8alcomt# “Development of Simplified DesignAids Based# the Results of Simulation Analysis,”Colloque 3olaire International, Nice, France,December 11-12, 1980. (l,A-UR-80-3473~

J. D. Balcomb, “Physfcs of Passfve SolarBuildings,” Amerfcan ;ociety for Engineering

~Education 1981 ,!WIUd~ Conferel,ce,Los Angeles, CA,<June 22, 1981. (LA-uR-81-903)

W. O. Wray, “Performance of Low-Mass, Sun-”remperedBuildings,” Solar Rising 1981 Annual ISES Meeting,Philadelphia, PA, May 26-30, 1981. (LA-UR-81-988)

J. D. Balcomb, J. C. iiedstrom,and J. E. Perry,Jr,, “Performance Summary of the Balcomb SolarHome,” Solar Risfng 1981 Annual ISES Meeting,Philadelphia, PA, May 26-30, 1981. (LA-UR-81-1039)

J, D. Balcomb, “Passfve Solar or Superinsulation?,”A, T, Times, National Center for AppropriateTechnology, Butte, MT, April, 1981, (LA-IJR-81-1133)