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A field validation of the thermal performance of a passively heated building as simulated by the DEROB system
Energy and Buildings, 2 (1979) 65 - 75 © Elsevier Sequoia S.A., Lausanne -- Printed in the Netherlands
65
A Field Validation of the Thermal Performance of a Passively Heated Building as Simulated by the DEROB System* FRANCISCO ARUM'I-NOI~and DAVID O. NORTHRUP Numerical Simulation Laboratory, School of Architecture, The University of Texas, Austin, Texas (U.S.A.) (Received
Hourly thermal performance data for a passively solar heated house are compared with simulated data. The house, Solar Village 1, in Santa Fe, New Mexico, owned and occupied by the Douglas Baleomb family, has been instrumented and monitored since the 1976 77 winter. The data reproduced here were collected in February 1978, including on-site micro-climatic weather data. The simulation is carried out with the computer program DEROB as developed at the Numerical Simulation Laboratory o f the School o f Architecture o f the University o f Texas at Austin. DEROB is a fully dynamic program, capable in principle o f handling architectural designs o f arbitrary geometry and simultan. eously solving thermally coupled multispace structures. Solar Village I is a 2 storey, L-shaped, hybrid structure with a glasshouse occupying the front court (south-facing) 2-storey volume. Hourly data include, in addition to micro-climatic information, temperature readings o f the air in the glasshouse, o f the air in the various living quarters, the temperature readings across the adobe walls that separate the living quarters from the glasshouse, and also the temperature o f the two rock storage bins. The simulated model treats the house as having five thermally coupled spaces, one for each wing o f each floor or the living quarters, and one for the glasshouse. The output o f DEROB is
programmed to simulate the temperature readings at the places corresponding to the readings collected in the instrumented house. The agreement between simulated and observed values is sufficiently close to justify further validation o f the DEROB system and, subject to this additional validation, to offer it as a research simulation and design aid tool for the thermal performance o f passively heated and cooled buildings. INTRODUCTION This article reports on the first a t t e m p t to validate the simultaneous predictions o f the c o m p u t e r program D E R O B for a multizone, multicoupled structure. The results show that D E R O B is capable o f predicting the thermal performance of "complex" buildings consistently within 5% o f the measured temperature (°F) readings. The simulation results presented here came from the first pass of the program; no a t t e m p t was made to "calibrate" the model by changing any o f the parameters in the simulation data. The empirical data were collected by the Los Alamos Scientific Laboratory in the Balcomb residence (Unit 1, First Village) in Santa Fe, New Mexico.
DEROB *This work was supported by the Division of Solar Energy of the Department of Energy (Grant EM-78G-04-4236) as part of the project Integration and Validation o f the DEROB and PASOLE Computer programs for the Simulation of Passive Solar Heating and Cooling of Buildings.
D E R O B (Dynamic Energy Response of Buildings) is a-system of programs originally developed in 1972 - 1973 as instructional tools. Up until n o w its predictions had been tested only against simple experimental struc-
66 tures. It was written to describe the thermal response o f multiply coupled building zones [1]. In principle it can simulate buildings o f arbitrary geometries and arbitrary shading obstacles. The complexity o f the problems that can be addressed with DEROB is limited only by the core m e m o r y o f the computer being used and the budget for computer time. The flowchart o f the DEROB system as used in the simulation for this article is shown in Fig. 1. The core programs are DRBGF, DRBMT and DRBTL. DRBGF requires the digitized data for each surface of the model that is to be simulated. With this information it carries o u t a double numerical integration of the solid angles sustended by each surface pair in order to produce the radiation view factors. It also generates the transformation matrices for each surface from the building system to the local coordinate system of each surface. This permits the use o f 2~limensional geometry in all the geometrical calculations that follow. DRBMT requires the thermal DEROB
FLOW
properties of each wall as well as the output file from DRBGF. With this information it calculates the kernels for the dynamic solution of the heat diffusion equation of the opaque walls and it specifies the illumination tensors for each surface pair, one set of tensors for the visible frequencies and one for the infra-red. These tensors describe the distribution of radiation originating from any surface after all reflections and transmissions have been accounted for [1]. DRBTL requires information about the day-to-day use schedule of the building and the weather data in addition to the o u t p u t files from DRBMT. It then calculates, h o u r by hour, the temperatures of each of the rooms, the temperatures of the wall, a seven point rake for each opaque wall, and the surface temperatures for each glass "wall". It also calculates each c o m p o n e n t of the energy balance at each node o f the calculation. The o u t p u t from DRBTL are the final results of the simulation. For the simulation presented in this article
CHART
:~/Woll Description/ * Data / JWALGAMA] '¢::::=i~>/Wall Properties/ Data I n p u t /
B
D,OD.B
C ***
i ,Lo,EK I--,I
A
**
D 81E F G
Digitized Geometry of Building Thermal Properties of Materials Completed Geometric Calculations CalculationsIntegrating Thermal Properfiel with Geometric Properties
Weather Data
Building Schedule Data
~OoN
* See figure 2 ** See figure 3 *** S e e figure 4
Fig. 1. Flow chart of the DE_ROB (Dynamic Energy Respo~.se of Buildings) system showing the multiple peripheral programs and data interaction.
67 the output was set up to match the measurements taken by Balcomb and McFarland in the Balcomb residence. In addition to the core programs themselves, there are a number of peripheral programs that aid the user in preparing the data. Three of these programs were used in this simulation: W A L G A M A , DIGDRB and PLOTEK. WALGAMA receives the verbal description of the walls and it generates their thermal properties in the form needed to be used by DRBMT (Fig. 2), DIGDRB receives the shape, size, and orientation of each surface and it digitizes the surface in the form needed by DRBGF (Fig. 3), PLOTEK uses the output of DIGDRB to draw (in a TEKW~J.Cffi~ S ~ L E
INPOT
11. , N ~ b e r of walls Title 1 2• Number of sections •094 Fraction of area made of section I 5. Ntm~er of layers in eecticm i 6. Material of first I . ~ (stucco) 1.5 first layer ( i ~ ) 2. ~aterial of seo~-~ layer (gypaum board) .5 T h i c ) u ~ S S of second layer (inches) 3. Material of third laver (softwood) 7.5 Thickx~ss of third layer ( ~ ) 2. Material of fourth layer (gypsum board) .5 T n i r ~ m s s of f~*rth layer (inches) 6. Material of fifth layer (stucco) 1.5 __~Thic)~ess of fifth layer (inches) .906 6. 6. 1.5 2. .5 7. 2. 43. 5.5 2. .5 6. 1.5
Thickness of
TRONIX 4051) the actual shape that is being digitized. Figure 4 was taken from the screen output of PLOTEK.
THE BALCOMB RESIDENCE
The Balcomb residence, also known as Unit 1, First Village, was designed and built by Wayne D. Nichols. It is a 2500 ft 2 (230 m 2) 2~storey sun tempered dwelling in Santa Fe, New Mexico. The solar system is a hybrid, active/passive with a large 2-storey glassed-in atrium acting as a glasshouse and heat collection area. Heated air is taken from the top of the glasshouse by fan through two radiant rock beds and then back to the glasshouse. The house was funded in the first cycle o f the HUD Demonstration Program. It was also the first house in the program to sell [3, 4]. Dr Douglas Balcomb, its present owner, is the Director o f the Solar Energy Division of the Los Alamos Scientific Laboratory. As part of the LASL program of documenting the
t~kLC4~A S A ~ L E OI2rPUT
RUn Title 1 1 2 3 4
•
5
.125 .042 .625 .042 .125
C(I%EXJC=UVAI/E=
•430 •250 •063 •250 •430
132.000 78.000 27.000 78.000 132.000
.200 .260 .670 .260 .200
.354 .136 3.832 .136 .354
150.031 .430 132.000 .250 78.000 .205 •075 .022 2.000 .250 78.000 .430 132.000
.200 .260 •240 •170 .260 .200
.354 .136 •018 .657 .136 .354
.092 .088
DY~k ~ I G N =
.128 4.432
TIPE IAG=
15 •818 TIME C C N y ~ ? f = 1 .125 2 .042 3 .167 4 .458 5 .042 6 .125 CO~YJC= .044 •- UVALUE= .043 r~/NA ATTF~]UATION= T I ~ IAC~= T1%~
.814 1.785
O~GIN~
'
y
3 •919 24.339
Fig. 2. Sample input and output used by Program WALGAMA as part of the DEROB system• Verbal descriptions are required for input data, senerating thermal properties in the form needed by DRBMT.
Fig. 3. Sample input data and corresponding diagram for a planar wall surface to be used by DIGDRB in the simulation of the Balcomb residence.
68
VOLUME
Z
VOLUME
3
Numerals Represent Wall Number Used in the Simulation
VOLUME
4
G E O M E T R Y OF S I M U L A T E D B U I L D I N G
VOLUME
5
Wc C
8
I .18 2 .05 3 .16 4 .01 5 .35 6 .4 ? .54 8 1.0
3.34 2.03 1.8 66.26 2.98 2.34 1.33 .5
Walls in Thermal Classification 5 5,7,9,11,13,17, 25,33, 34 15 20,29,50 21,23,51,52 22,24 26,28 27
W© wall type according to thermal classification C conductance(BTU/hrftZ°F) U thermal inertia index Glass Walls 1,2,4, 6,8,10,14,16,18,19
Fig. 4. T h e v o l u m e s which m a k e u p t h e s i m u l a t e d version o f t h e B a l c o m b h o u s e a n d t h e walls w h i c h m a k e u p t h e v o l u m e s . E a c h is n u m b e r e d a n d classified as s h o w n .
thermal performance o f existing solar houses, he has instrumented Unit 1 with 36 sensors t h r o u g h o u t the house and connected them to an Acurex recorder. F o u r o f these channels record weather data, and the o u t p u t from these channels is used directly as input for DEROB. Of the remaining sensors, 28 were subject o f simulation b y DEROB, b u t because DEROB cannot describe stratification effects or two~iimensional diffusion phenomena, it simulates the remaining sensors with 18 outp u t ports. The location of the o u t p u t readings from DEROB and the location of the corresponding channel readings are shown in Fig. 5.
GEOMETRY OF THE SIMULATED HOUSE
The actual house is depicted in the isometric view shown in Fig. 5. The simulated geometry is shown in Fig. 4; it consists o f 32 "walls" enclosing five interconnected '"¢olumes". A "wall" can be a window, a door, the floor slab or the roof, as well as a
standard vertical wall. A " v o l u m e " is any space enclosed by a set of walls; it may or may n o t represent an individual room. In this case volume 1 represents the atrium as a single space, while the other volumes represent each wing o f each floor of the house even though some of these volumes contain more than one room. The openings such as windows and doors were centered on their corresponding walls. Although a more precise simulation can be carried out, we felt this model gave us enough information to study the salient thermal features o f the house without increasing the dimensions o f the arrays in DEROB. By not increasing the array sizes we were able to run the simulation in the interactive mode. The rockbeds were treated as independent entities with thermal contact only with the ground and coupled to the glasshouse by convection, either free or forced. The results o f the simulation show that this model was sufficient to reproduce the observed data within an overall 5% margin of error.
69
",,4..-_ _ _ PROBE
LOCATIONS
WITH
CHANNEL
l- r NO.s
Fig. 5. A n isometric of the Balcomb residence showing the probe locations of the channels where data were collected. This information was then compared to the D E R O B simulations. Sun tempered heating elements: 1, the south facing glasshouse 276 ft2 glass wall is composed of 16,34 ft X 76 in tempered double glazed P P G thermal glass units; 2, the north wall of the glasshouse is two storey high and is constructed of natural adobe bricks. This thermal storage wall takes in direct gain in the day, and stores for night time use. The wall is 14 in thick on the first floor, and 10 in on the second. Its mass is 114,625 Ib, and its heat storage is 227.250 Btus at 10 ° AT; 3, the vents in the glasshouse roof release summer heat. The active solar system: 1, fans draw air from the glasshouse roof, through rockbeds under the living and dining room floors. The rockbeds radiate and heat the slabs. The rockbeds are 436 ft3 with storage capacity of 90,000 Btus at 15 ° AT; 2, the solar hot water heater is shown separately; 3, auxiliary heat is provided by baseboard electricheaters in each room.
COMPARISON O F SIMULATION WITH EMPIRICAL DATA
The empirical data used here to compare with the simulation were collected on the site of Unit 1 in Santa Fe, N e w Mexico, between February 11 and February 14, 1978. The microclimatic data include the ambient temperature, the insolation on the horizontal plane (Fig. 6), and the wind direction. It did not include the wind velocity, the relative humidity or the barometric pressure. These three variables are used in D E R O B to simulate the film coefficients and the sky infra-red radiation. In order to complete the required data set, we used data available in our filesfor a winter period in Las Vegas, Nevada. Las Vegas was chosen because it has, like Santa Fe, low humidity and it is also located in high mountains. Glasshouse temperatures are shown in Fig. 7. Curve 1 (channel 20) represents the temperatures taken 10 in (25.4 cm) above the floor
on the east side, this register usually being in the shade. Curve 2 (channel 23) represents temperatures taken 158 in (4.01 m) above the floor in the center of the glasshouse next to an existing plant hanger. Curve 3 (channel 30) represents temperatures measured in the center of the glasshouse lOOin (2.54 m) above the floor. Curve 4 (channel 2 5 ) r e p resents measurements taken on the stairwell under the window. Curve 5 (channel 12) represents measurements taken on the west side 100 in (2.54 m) above the floor. Curve 6 (channel 17) represents measurements centered in the upper east vent inlet. It is clear from these data that stratification effects are present. The values calculated by DEROB assume a single value for the entire glasshouse since it does not calculate stratification effects. The simulated values are shown with the heavy solid curve. The agreement with the measured values is quite close. The greatest disagreements occur on the 4 5 Julian
70 , MIC~OCLIMATI(;
DATA
60-~.15
SO
I Ambient Temperature
.•.0 I
SO0,
40
• 250
700-
OF
600- .200
3of1° i
Imlolalion on a Horizontol Surface
• 150
20J"
-I00 .SO
42
!
43
44 JULIAN
45
46
DAYS
Fig. 6. Ambient temperature and insolation on a horizontal surface as recorded during the test period and used for the simulation by DEROB. GREEN HOUSE TEMPS
90
-/~%~i ~
l
52 80
I Green House- oh.20 2 Green House- ch.23 3 GreenHouse- oh.30 4 Green House- ch.2S S Green House- oh 6 Green House- ¢h.17 DEROB
!
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•~
6 6
,. / ~
66 ~ 6 6
666~
~
, 20
OF
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~4 4
so
'444., 14
44
t;
I
42
,-Io
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43
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44 JULIAN
¢
45
46
DAYS
Fig. 7. The temperatures actually recorded in the glasshouse of the Balcomb house as compared with the temperatures calculated by DEROB in the simulation. These data show some discrepancies due to stratification.
day (17%), and on the 42 Julian day (10%). It should be noted, however, that the measured radiation values may not be consistent with the temperature measurements in the glasshouse, and the wall temperatures. There is, o f course, a consistent disagreement between the
measured t e m p e r a t u r e at the inlet vent (top o f glasshouse) with the DEROB values. This disagreement is probabl y due entirely to stratification. An i m proved simulation o f the temperatures in the glasshouse m ay have
resulted if the total glass area and its config-
71 faces the glasshouse. The "outside" temperature was measured 3/4 in (1.9 era) from the surface facing the glasshouse (channel 31). Curve 1 in Fig. 9 represents the measured values, and the solid curve the values calculated by DEROB. The disagreement between the measured and observed values is never more than 10%, and usually less than 3%. The measurements in the "center" of the wall were taken 6 in (15.2 cm) from the outside surface; the measured values are contrasted with the DEROB calculated values in Fig. 10. The 'Snside" surface temperatures were taken 1 in (2.54 cm) from the surface facing into the middle east room. The measured values are contrasted with the calculated values in Fig. 11. In these last two figures the calculated values are never more than 3% off from the measured values. The discrepancy between the measured and calculated temperature values and their relative face may come from at least three sources: the output ports of DEROB do not match exactly the location of the experimental probes; the thermal properties of the adobe wall may be different from the standard values used in the calculation; and the fact that DEROB solves the one dimensional heat diffusion equation, consequently only one set of readings is generated
uration had been chosen to match more closely the real configuration. Rockbed temperatures are shown in Fig. 8. Curve 1 (channel 28) represents the air temperature in the middle of the east rockbed, and curve 2 (channel 24) represents the air temperature in the middle of the west rockbed. The east rockbed is 5 °F (2.8 °C) colder than the west rockbed, Since the DEROB simulation treated each rockbed the same as the other, no such differences appear in the results. The solid curve represents the air temperatures in the rockbed as calculated by DEROB. The simulated values are quite close (less than 2% off) to the west rockbed and consequently further off from the east rockbed. The rockbeds are simulated by assuming the rocks are spherical in shape and are closed~acked forming tetrahedron units. Thus, if V is the total vohtme of the rockbed container, the total rock surface is Sr = 2.34 V/r where r is the radius of the rock. In this simulation we use r = 1.5 in (3.8 cm). Also note that in this model the rocks occupy 78% of the total volume. Upper rake temperatures are shown in Figs. 9, 10 and 11. The measurements were taken on the 10 in (25.4 cm) east adobe wall that
ROCK
BEDS I Eost Rock Bed - c h . 2 8 2 West Rock B e d - ch.24 - DEROB
30 80
70 oF
2
2,=
~ -
~ "-,. ~
2 2
2
;
r
A
_ _
-20
2
"l
11111111
11111111
11
1
11
111
111
I 1,
°C
60
50-
-I0
I
42
43
44 JULIAN
45
46
DAYS
Fig. 8. The temperatures actually recorded in the rockbeds of the Balcomb house as compared with the temperatures calculated by DEROB in the simulation.
72
Dining room floor temperature is shown in Fig. 12. Curve 1 (channel 27) measured the temperature above the east edge of the rockbed. Curve 2 (channel 38) measures the tem-
for the entire wall; whereas for the real wall different locations on the wall surface will yield different readings.
UPPER
RAKE
I -
3/4" From Oulside Wall- ch.31 DEROB
IiO 40 IO0 11 90
"F
80
•C
?0
20
60 I0
5o I
42
I,
I
46
44
43 JULIAN
DAYS
Fig. 9. The upper rake temperatures actually recorded in the Baleomb house as compared with the temperatures calculated by DEROB in the simulation.
2-6"From Outside Wall-¢h.~ OEROB
4.0 I0O
2 90, 30
2"222
80OF
oC 70=
20
60. 50. |
42
'
43
I
44
'
I
"
I
45
I
-
46
,JULIAN DAYS
Fig. 10. The upper rake temperatures actually recorded in the Balcomb house as compared with the temperatures calculated by DEROB in the simulation.
73 VPPER
RAKE
3 I" From Outside-ch.33 - DEROB
.40 I
30
,~,,,,~,3~
oC 20
I0 I
42
!
I
43
JULIAN
I
44
I
44
45
DAYS
Fig. 11. The upper rake temperatures actually recorded in the Balcomb house as compared with the temperatures calculated by D E R O B in the simulation. DINING ROOM FLOOR I Dining Room Floor- ch.27 2 Dining Room Floor- ch.S8 3 0 i n l h g Room Floor-oh.29 -
DEROB
30 SO
70 L I I I 11 1_1_111 11 1 1 1 1
20
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"C V
60
50
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JULIAN
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DAYS
Fig. 12. T h e t e m p e r a t u r e s actually r e c o r d e d in three locations in the dining r o o m floor o f the B a l c o m b house as c o m p a r e d with t h e single l o c a t i o n t e m p e r a t u r e calculated by D E R O B in the simulation. Some error is due t o a lack o f direct thermal coupling with the rockbeds.
perature over the center of the rockbed; and curve 3 (channel 29) measures the temperature over the west edge of the rockbed. The solid curve represents the values calculated by DEROB. During this simulation the rockbeds
were not thermally coupled by conduction to the rooms immediately above them; therefore the calculated values do not reflect the influence of the rockbed. They only reflect the influence of the air temperature, the
74 auxiliary heater, and the radiation exchange with the other surfaces. The fact that the measured values (especially 2 and 3) are so close to the calculated values means that t o a first-order approximation we can indeed neglect this coupling. However, the calculated values are consistently lower than the measured ones, and from thermal b u o y a n c y arguments we should expect the opposite to occur. Better agreement between measured and calculated values may have been achieved if the rockbeds had been treated as "volumes" in thermal contact by conduction with the dining room ' ~ o l u m e " .
tion of the run. The entire house, including the rockbeds, are assumed to start at a temperature of 55 °F (12.78 °C). Figure 13 shows the relaxation of the temperature in the glasshouse for five combinations of the "fan speed" and the air infiltration rate. The results show that the presence of the storage rockbeds is more important than trying to reduce the infiltration rate to less t h ~ 1.2 volume changes per hour. A more extensive and systematic sensitivity analysis will be carried o u t in order to test the dependence of the accuracy of the predictions as the complexity of the model is increased or decreased.
SENSITIVITY RUNS
CONCLUSION No effort was made during this phase of the validation o f DEROB to make a systematic sensitivity analysis. The results of two parametric changes, however, are worth noting. The temperature relaxation rate of the glasshouse was calculated b y varying the infiltration rate and the speed o f the air going through the rockbeds. D R B T L was run for four days for each condition after "turningoff' the sun and fixing the ambient air temperature to 10 °F {--12.2 °C) for the duraTEMPERATURE
,°t
50
This first a t t e m p t to validate D E R O B with empirical data shows that this program is capable o f reproducing observed measurements consistently within a 5% margin of error, with occasional greater departures in the accuracy. Even these departures never exceeded 17%. There are many potential sources o f error in the calculation. These include: the approximation in the geometry of the glasshouse; simultaneous equations;
RELAXATION OF THE GREENHOUSE
Original Greenhouse Temp.- 55" F (12.8eC) (~'iglnal Rock Bins Temp.,, 70eF (21.1eC) Ambient Temp.-IO • F(-12.2eC) No Sun
--
I0
40eF
I
oC 0
30-~-
20-
Infiltration
vol/hr
Fo~Ce~ ve~
Bias to Greenhouse
-10
I 2 3 4 5
0.2 O.2 1.2 1.2 2.9 I
3000000ft3/hr (849.5 m3/hr)
30000 ooo
I
12
I
24
t--
t
i
i
36
48
I
60
HOUR8
Fig. 13. Temperature relaxation in the glasshouse showing the results of five combinations of "fan speed" and the air infiltration rate, starting at 12.8 °C (55 °F).
75 and the way in which families use a house which is n o t really a subject likely t o be simulated. Th e i m por t ance o f some o f these factors will need t o be studied using sensitivity runs.
ACKNOWLEDGEMENTS The authors gratefully acknowledge the help o f Ms. Margaret Sloan and Mr. Kelly McAdams.
REFERENCES
1 F. N. Arumi, The multispace thermal coupling algorithm of the DEROB system ; Heat Transfer in Energy Conservation, Winter A. Meet. ASME, 1977. 2 D. Balcomb and R. McFarland, personal communication (1978). 3 W. D. Nichols, Unit 1, First Village, Passive Solar Heating and Cooling, Proc. Albuquerque Conf. Workshop, LA-6637-C, 1976. 4 R. P. Stromberg and S. O. Woodall, Unit 1,Passive Solar Buildings: A Compilation of Data and Results, SAND 77-1204, 1977, p. 24.
65
A Field Validation of the Thermal Performance of a Passively Heated Building as Simulated by the DEROB System* FRANCISCO ARUM'I-NOI~and DAVID O. NORTHRUP Numerical Simulation Laboratory, School of Architecture, The University of Texas, Austin, Texas (U.S.A.) (Received
Hourly thermal performance data for a passively solar heated house are compared with simulated data. The house, Solar Village 1, in Santa Fe, New Mexico, owned and occupied by the Douglas Baleomb family, has been instrumented and monitored since the 1976 77 winter. The data reproduced here were collected in February 1978, including on-site micro-climatic weather data. The simulation is carried out with the computer program DEROB as developed at the Numerical Simulation Laboratory o f the School o f Architecture o f the University o f Texas at Austin. DEROB is a fully dynamic program, capable in principle o f handling architectural designs o f arbitrary geometry and simultan. eously solving thermally coupled multispace structures. Solar Village I is a 2 storey, L-shaped, hybrid structure with a glasshouse occupying the front court (south-facing) 2-storey volume. Hourly data include, in addition to micro-climatic information, temperature readings o f the air in the glasshouse, o f the air in the various living quarters, the temperature readings across the adobe walls that separate the living quarters from the glasshouse, and also the temperature o f the two rock storage bins. The simulated model treats the house as having five thermally coupled spaces, one for each wing o f each floor or the living quarters, and one for the glasshouse. The output o f DEROB is
programmed to simulate the temperature readings at the places corresponding to the readings collected in the instrumented house. The agreement between simulated and observed values is sufficiently close to justify further validation o f the DEROB system and, subject to this additional validation, to offer it as a research simulation and design aid tool for the thermal performance o f passively heated and cooled buildings. INTRODUCTION This article reports on the first a t t e m p t to validate the simultaneous predictions o f the c o m p u t e r program D E R O B for a multizone, multicoupled structure. The results show that D E R O B is capable o f predicting the thermal performance of "complex" buildings consistently within 5% o f the measured temperature (°F) readings. The simulation results presented here came from the first pass of the program; no a t t e m p t was made to "calibrate" the model by changing any o f the parameters in the simulation data. The empirical data were collected by the Los Alamos Scientific Laboratory in the Balcomb residence (Unit 1, First Village) in Santa Fe, New Mexico.
DEROB *This work was supported by the Division of Solar Energy of the Department of Energy (Grant EM-78G-04-4236) as part of the project Integration and Validation o f the DEROB and PASOLE Computer programs for the Simulation of Passive Solar Heating and Cooling of Buildings.
D E R O B (Dynamic Energy Response of Buildings) is a-system of programs originally developed in 1972 - 1973 as instructional tools. Up until n o w its predictions had been tested only against simple experimental struc-
66 tures. It was written to describe the thermal response o f multiply coupled building zones [1]. In principle it can simulate buildings o f arbitrary geometries and arbitrary shading obstacles. The complexity o f the problems that can be addressed with DEROB is limited only by the core m e m o r y o f the computer being used and the budget for computer time. The flowchart o f the DEROB system as used in the simulation for this article is shown in Fig. 1. The core programs are DRBGF, DRBMT and DRBTL. DRBGF requires the digitized data for each surface of the model that is to be simulated. With this information it carries o u t a double numerical integration of the solid angles sustended by each surface pair in order to produce the radiation view factors. It also generates the transformation matrices for each surface from the building system to the local coordinate system of each surface. This permits the use o f 2~limensional geometry in all the geometrical calculations that follow. DRBMT requires the thermal DEROB
FLOW
properties of each wall as well as the output file from DRBGF. With this information it calculates the kernels for the dynamic solution of the heat diffusion equation of the opaque walls and it specifies the illumination tensors for each surface pair, one set of tensors for the visible frequencies and one for the infra-red. These tensors describe the distribution of radiation originating from any surface after all reflections and transmissions have been accounted for [1]. DRBTL requires information about the day-to-day use schedule of the building and the weather data in addition to the o u t p u t files from DRBMT. It then calculates, h o u r by hour, the temperatures of each of the rooms, the temperatures of the wall, a seven point rake for each opaque wall, and the surface temperatures for each glass "wall". It also calculates each c o m p o n e n t of the energy balance at each node o f the calculation. The o u t p u t from DRBTL are the final results of the simulation. For the simulation presented in this article
CHART
:~/Woll Description/ * Data / JWALGAMA] '¢::::=i~>/Wall Properties/ Data I n p u t /
B
D,OD.B
C ***
i ,Lo,EK I--,I
A
**
D 81E F G
Digitized Geometry of Building Thermal Properties of Materials Completed Geometric Calculations CalculationsIntegrating Thermal Properfiel with Geometric Properties
Weather Data
Building Schedule Data
~OoN
* See figure 2 ** See figure 3 *** S e e figure 4
Fig. 1. Flow chart of the DE_ROB (Dynamic Energy Respo~.se of Buildings) system showing the multiple peripheral programs and data interaction.
67 the output was set up to match the measurements taken by Balcomb and McFarland in the Balcomb residence. In addition to the core programs themselves, there are a number of peripheral programs that aid the user in preparing the data. Three of these programs were used in this simulation: W A L G A M A , DIGDRB and PLOTEK. WALGAMA receives the verbal description of the walls and it generates their thermal properties in the form needed to be used by DRBMT (Fig. 2), DIGDRB receives the shape, size, and orientation of each surface and it digitizes the surface in the form needed by DRBGF (Fig. 3), PLOTEK uses the output of DIGDRB to draw (in a TEKW~J.Cffi~ S ~ L E
INPOT
11. , N ~ b e r of walls Title 1 2• Number of sections •094 Fraction of area made of section I 5. Ntm~er of layers in eecticm i 6. Material of first I . ~ (stucco) 1.5 first layer ( i ~ ) 2. ~aterial of seo~-~ layer (gypaum board) .5 T h i c ) u ~ S S of second layer (inches) 3. Material of third laver (softwood) 7.5 Thickx~ss of third layer ( ~ ) 2. Material of fourth layer (gypsum board) .5 T n i r ~ m s s of f~*rth layer (inches) 6. Material of fifth layer (stucco) 1.5 __~Thic)~ess of fifth layer (inches) .906 6. 6. 1.5 2. .5 7. 2. 43. 5.5 2. .5 6. 1.5
Thickness of
TRONIX 4051) the actual shape that is being digitized. Figure 4 was taken from the screen output of PLOTEK.
THE BALCOMB RESIDENCE
The Balcomb residence, also known as Unit 1, First Village, was designed and built by Wayne D. Nichols. It is a 2500 ft 2 (230 m 2) 2~storey sun tempered dwelling in Santa Fe, New Mexico. The solar system is a hybrid, active/passive with a large 2-storey glassed-in atrium acting as a glasshouse and heat collection area. Heated air is taken from the top of the glasshouse by fan through two radiant rock beds and then back to the glasshouse. The house was funded in the first cycle o f the HUD Demonstration Program. It was also the first house in the program to sell [3, 4]. Dr Douglas Balcomb, its present owner, is the Director o f the Solar Energy Division of the Los Alamos Scientific Laboratory. As part of the LASL program of documenting the
t~kLC4~A S A ~ L E OI2rPUT
RUn Title 1 1 2 3 4
•
5
.125 .042 .625 .042 .125
C(I%EXJC=UVAI/E=
•430 •250 •063 •250 •430
132.000 78.000 27.000 78.000 132.000
.200 .260 .670 .260 .200
.354 .136 3.832 .136 .354
150.031 .430 132.000 .250 78.000 .205 •075 .022 2.000 .250 78.000 .430 132.000
.200 .260 •240 •170 .260 .200
.354 .136 •018 .657 .136 .354
.092 .088
DY~k ~ I G N =
.128 4.432
TIPE IAG=
15 •818 TIME C C N y ~ ? f = 1 .125 2 .042 3 .167 4 .458 5 .042 6 .125 CO~YJC= .044 •- UVALUE= .043 r~/NA ATTF~]UATION= T I ~ IAC~= T1%~
.814 1.785
O~GIN~
'
y
3 •919 24.339
Fig. 2. Sample input and output used by Program WALGAMA as part of the DEROB system• Verbal descriptions are required for input data, senerating thermal properties in the form needed by DRBMT.
Fig. 3. Sample input data and corresponding diagram for a planar wall surface to be used by DIGDRB in the simulation of the Balcomb residence.
68
VOLUME
Z
VOLUME
3
Numerals Represent Wall Number Used in the Simulation
VOLUME
4
G E O M E T R Y OF S I M U L A T E D B U I L D I N G
VOLUME
5
Wc C
8
I .18 2 .05 3 .16 4 .01 5 .35 6 .4 ? .54 8 1.0
3.34 2.03 1.8 66.26 2.98 2.34 1.33 .5
Walls in Thermal Classification 5 5,7,9,11,13,17, 25,33, 34 15 20,29,50 21,23,51,52 22,24 26,28 27
W© wall type according to thermal classification C conductance(BTU/hrftZ°F) U thermal inertia index Glass Walls 1,2,4, 6,8,10,14,16,18,19
Fig. 4. T h e v o l u m e s which m a k e u p t h e s i m u l a t e d version o f t h e B a l c o m b h o u s e a n d t h e walls w h i c h m a k e u p t h e v o l u m e s . E a c h is n u m b e r e d a n d classified as s h o w n .
thermal performance o f existing solar houses, he has instrumented Unit 1 with 36 sensors t h r o u g h o u t the house and connected them to an Acurex recorder. F o u r o f these channels record weather data, and the o u t p u t from these channels is used directly as input for DEROB. Of the remaining sensors, 28 were subject o f simulation b y DEROB, b u t because DEROB cannot describe stratification effects or two~iimensional diffusion phenomena, it simulates the remaining sensors with 18 outp u t ports. The location of the o u t p u t readings from DEROB and the location of the corresponding channel readings are shown in Fig. 5.
GEOMETRY OF THE SIMULATED HOUSE
The actual house is depicted in the isometric view shown in Fig. 5. The simulated geometry is shown in Fig. 4; it consists o f 32 "walls" enclosing five interconnected '"¢olumes". A "wall" can be a window, a door, the floor slab or the roof, as well as a
standard vertical wall. A " v o l u m e " is any space enclosed by a set of walls; it may or may n o t represent an individual room. In this case volume 1 represents the atrium as a single space, while the other volumes represent each wing o f each floor of the house even though some of these volumes contain more than one room. The openings such as windows and doors were centered on their corresponding walls. Although a more precise simulation can be carried out, we felt this model gave us enough information to study the salient thermal features o f the house without increasing the dimensions o f the arrays in DEROB. By not increasing the array sizes we were able to run the simulation in the interactive mode. The rockbeds were treated as independent entities with thermal contact only with the ground and coupled to the glasshouse by convection, either free or forced. The results o f the simulation show that this model was sufficient to reproduce the observed data within an overall 5% margin of error.
69
",,4..-_ _ _ PROBE
LOCATIONS
WITH
CHANNEL
l- r NO.s
Fig. 5. A n isometric of the Balcomb residence showing the probe locations of the channels where data were collected. This information was then compared to the D E R O B simulations. Sun tempered heating elements: 1, the south facing glasshouse 276 ft2 glass wall is composed of 16,34 ft X 76 in tempered double glazed P P G thermal glass units; 2, the north wall of the glasshouse is two storey high and is constructed of natural adobe bricks. This thermal storage wall takes in direct gain in the day, and stores for night time use. The wall is 14 in thick on the first floor, and 10 in on the second. Its mass is 114,625 Ib, and its heat storage is 227.250 Btus at 10 ° AT; 3, the vents in the glasshouse roof release summer heat. The active solar system: 1, fans draw air from the glasshouse roof, through rockbeds under the living and dining room floors. The rockbeds radiate and heat the slabs. The rockbeds are 436 ft3 with storage capacity of 90,000 Btus at 15 ° AT; 2, the solar hot water heater is shown separately; 3, auxiliary heat is provided by baseboard electricheaters in each room.
COMPARISON O F SIMULATION WITH EMPIRICAL DATA
The empirical data used here to compare with the simulation were collected on the site of Unit 1 in Santa Fe, N e w Mexico, between February 11 and February 14, 1978. The microclimatic data include the ambient temperature, the insolation on the horizontal plane (Fig. 6), and the wind direction. It did not include the wind velocity, the relative humidity or the barometric pressure. These three variables are used in D E R O B to simulate the film coefficients and the sky infra-red radiation. In order to complete the required data set, we used data available in our filesfor a winter period in Las Vegas, Nevada. Las Vegas was chosen because it has, like Santa Fe, low humidity and it is also located in high mountains. Glasshouse temperatures are shown in Fig. 7. Curve 1 (channel 20) represents the temperatures taken 10 in (25.4 cm) above the floor
on the east side, this register usually being in the shade. Curve 2 (channel 23) represents temperatures taken 158 in (4.01 m) above the floor in the center of the glasshouse next to an existing plant hanger. Curve 3 (channel 30) represents temperatures measured in the center of the glasshouse lOOin (2.54 m) above the floor. Curve 4 (channel 2 5 ) r e p resents measurements taken on the stairwell under the window. Curve 5 (channel 12) represents measurements taken on the west side 100 in (2.54 m) above the floor. Curve 6 (channel 17) represents measurements centered in the upper east vent inlet. It is clear from these data that stratification effects are present. The values calculated by DEROB assume a single value for the entire glasshouse since it does not calculate stratification effects. The simulated values are shown with the heavy solid curve. The agreement with the measured values is quite close. The greatest disagreements occur on the 4 5 Julian
70 , MIC~OCLIMATI(;
DATA
60-~.15
SO
I Ambient Temperature
.•.0 I
SO0,
40
• 250
700-
OF
600- .200
3of1° i
Imlolalion on a Horizontol Surface
• 150
20J"
-I00 .SO
42
!
43
44 JULIAN
45
46
DAYS
Fig. 6. Ambient temperature and insolation on a horizontal surface as recorded during the test period and used for the simulation by DEROB. GREEN HOUSE TEMPS
90
-/~%~i ~
l
52 80
I Green House- oh.20 2 Green House- ch.23 3 GreenHouse- oh.30 4 Green House- ch.2S S Green House- oh 6 Green House- ¢h.17 DEROB
!
~'"~
~L~6
•~
6 6
,. / ~
66 ~ 6 6
666~
~
, 20
OF
"G 60
~4 4
so
'444., 14
44
t;
I
42
,-Io
:
43
!
44 JULIAN
¢
45
46
DAYS
Fig. 7. The temperatures actually recorded in the glasshouse of the Balcomb house as compared with the temperatures calculated by DEROB in the simulation. These data show some discrepancies due to stratification.
day (17%), and on the 42 Julian day (10%). It should be noted, however, that the measured radiation values may not be consistent with the temperature measurements in the glasshouse, and the wall temperatures. There is, o f course, a consistent disagreement between the
measured t e m p e r a t u r e at the inlet vent (top o f glasshouse) with the DEROB values. This disagreement is probabl y due entirely to stratification. An i m proved simulation o f the temperatures in the glasshouse m ay have
resulted if the total glass area and its config-
71 faces the glasshouse. The "outside" temperature was measured 3/4 in (1.9 era) from the surface facing the glasshouse (channel 31). Curve 1 in Fig. 9 represents the measured values, and the solid curve the values calculated by DEROB. The disagreement between the measured and observed values is never more than 10%, and usually less than 3%. The measurements in the "center" of the wall were taken 6 in (15.2 cm) from the outside surface; the measured values are contrasted with the DEROB calculated values in Fig. 10. The 'Snside" surface temperatures were taken 1 in (2.54 cm) from the surface facing into the middle east room. The measured values are contrasted with the calculated values in Fig. 11. In these last two figures the calculated values are never more than 3% off from the measured values. The discrepancy between the measured and calculated temperature values and their relative face may come from at least three sources: the output ports of DEROB do not match exactly the location of the experimental probes; the thermal properties of the adobe wall may be different from the standard values used in the calculation; and the fact that DEROB solves the one dimensional heat diffusion equation, consequently only one set of readings is generated
uration had been chosen to match more closely the real configuration. Rockbed temperatures are shown in Fig. 8. Curve 1 (channel 28) represents the air temperature in the middle of the east rockbed, and curve 2 (channel 24) represents the air temperature in the middle of the west rockbed. The east rockbed is 5 °F (2.8 °C) colder than the west rockbed, Since the DEROB simulation treated each rockbed the same as the other, no such differences appear in the results. The solid curve represents the air temperatures in the rockbed as calculated by DEROB. The simulated values are quite close (less than 2% off) to the west rockbed and consequently further off from the east rockbed. The rockbeds are simulated by assuming the rocks are spherical in shape and are closed~acked forming tetrahedron units. Thus, if V is the total vohtme of the rockbed container, the total rock surface is Sr = 2.34 V/r where r is the radius of the rock. In this simulation we use r = 1.5 in (3.8 cm). Also note that in this model the rocks occupy 78% of the total volume. Upper rake temperatures are shown in Figs. 9, 10 and 11. The measurements were taken on the 10 in (25.4 cm) east adobe wall that
ROCK
BEDS I Eost Rock Bed - c h . 2 8 2 West Rock B e d - ch.24 - DEROB
30 80
70 oF
2
2,=
~ -
~ "-,. ~
2 2
2
;
r
A
_ _
-20
2
"l
11111111
11111111
11
1
11
111
111
I 1,
°C
60
50-
-I0
I
42
43
44 JULIAN
45
46
DAYS
Fig. 8. The temperatures actually recorded in the rockbeds of the Balcomb house as compared with the temperatures calculated by DEROB in the simulation.
72
Dining room floor temperature is shown in Fig. 12. Curve 1 (channel 27) measured the temperature above the east edge of the rockbed. Curve 2 (channel 38) measures the tem-
for the entire wall; whereas for the real wall different locations on the wall surface will yield different readings.
UPPER
RAKE
I -
3/4" From Oulside Wall- ch.31 DEROB
IiO 40 IO0 11 90
"F
80
•C
?0
20
60 I0
5o I
42
I,
I
46
44
43 JULIAN
DAYS
Fig. 9. The upper rake temperatures actually recorded in the Baleomb house as compared with the temperatures calculated by DEROB in the simulation.
2-6"From Outside Wall-¢h.~ OEROB
4.0 I0O
2 90, 30
2"222
80OF
oC 70=
20
60. 50. |
42
'
43
I
44
'
I
"
I
45
I
-
46
,JULIAN DAYS
Fig. 10. The upper rake temperatures actually recorded in the Balcomb house as compared with the temperatures calculated by DEROB in the simulation.
73 VPPER
RAKE
3 I" From Outside-ch.33 - DEROB
.40 I
30
,~,,,,~,3~
oC 20
I0 I
42
!
I
43
JULIAN
I
44
I
44
45
DAYS
Fig. 11. The upper rake temperatures actually recorded in the Balcomb house as compared with the temperatures calculated by D E R O B in the simulation. DINING ROOM FLOOR I Dining Room Floor- ch.27 2 Dining Room Floor- ch.S8 3 0 i n l h g Room Floor-oh.29 -
DEROB
30 SO
70 L I I I 11 1_1_111 11 1 1 1 1
20
•F
"C V
60
50
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
I
43
?.,__~..~. . . . . .
,
!
42
_~
R
10
I
I
JULIAN
44
I
45
I
46
DAYS
Fig. 12. T h e t e m p e r a t u r e s actually r e c o r d e d in three locations in the dining r o o m floor o f the B a l c o m b house as c o m p a r e d with t h e single l o c a t i o n t e m p e r a t u r e calculated by D E R O B in the simulation. Some error is due t o a lack o f direct thermal coupling with the rockbeds.
perature over the center of the rockbed; and curve 3 (channel 29) measures the temperature over the west edge of the rockbed. The solid curve represents the values calculated by DEROB. During this simulation the rockbeds
were not thermally coupled by conduction to the rooms immediately above them; therefore the calculated values do not reflect the influence of the rockbed. They only reflect the influence of the air temperature, the
74 auxiliary heater, and the radiation exchange with the other surfaces. The fact that the measured values (especially 2 and 3) are so close to the calculated values means that t o a first-order approximation we can indeed neglect this coupling. However, the calculated values are consistently lower than the measured ones, and from thermal b u o y a n c y arguments we should expect the opposite to occur. Better agreement between measured and calculated values may have been achieved if the rockbeds had been treated as "volumes" in thermal contact by conduction with the dining room ' ~ o l u m e " .
tion of the run. The entire house, including the rockbeds, are assumed to start at a temperature of 55 °F (12.78 °C). Figure 13 shows the relaxation of the temperature in the glasshouse for five combinations of the "fan speed" and the air infiltration rate. The results show that the presence of the storage rockbeds is more important than trying to reduce the infiltration rate to less t h ~ 1.2 volume changes per hour. A more extensive and systematic sensitivity analysis will be carried o u t in order to test the dependence of the accuracy of the predictions as the complexity of the model is increased or decreased.
SENSITIVITY RUNS
CONCLUSION No effort was made during this phase of the validation o f DEROB to make a systematic sensitivity analysis. The results of two parametric changes, however, are worth noting. The temperature relaxation rate of the glasshouse was calculated b y varying the infiltration rate and the speed o f the air going through the rockbeds. D R B T L was run for four days for each condition after "turningoff' the sun and fixing the ambient air temperature to 10 °F {--12.2 °C) for the duraTEMPERATURE
,°t
50
This first a t t e m p t to validate D E R O B with empirical data shows that this program is capable o f reproducing observed measurements consistently within a 5% margin of error, with occasional greater departures in the accuracy. Even these departures never exceeded 17%. There are many potential sources o f error in the calculation. These include: the approximation in the geometry of the glasshouse; simultaneous equations;
RELAXATION OF THE GREENHOUSE
Original Greenhouse Temp.- 55" F (12.8eC) (~'iglnal Rock Bins Temp.,, 70eF (21.1eC) Ambient Temp.-IO • F(-12.2eC) No Sun
--
I0
40eF
I
oC 0
30-~-
20-
Infiltration
vol/hr
Fo~Ce~ ve~
Bias to Greenhouse
-10
I 2 3 4 5
0.2 O.2 1.2 1.2 2.9 I
3000000ft3/hr (849.5 m3/hr)
30000 ooo
I
12
I
24
t--
t
i
i
36
48
I
60
HOUR8
Fig. 13. Temperature relaxation in the glasshouse showing the results of five combinations of "fan speed" and the air infiltration rate, starting at 12.8 °C (55 °F).
75 and the way in which families use a house which is n o t really a subject likely t o be simulated. Th e i m por t ance o f some o f these factors will need t o be studied using sensitivity runs.
ACKNOWLEDGEMENTS The authors gratefully acknowledge the help o f Ms. Margaret Sloan and Mr. Kelly McAdams.
REFERENCES
1 F. N. Arumi, The multispace thermal coupling algorithm of the DEROB system ; Heat Transfer in Energy Conservation, Winter A. Meet. ASME, 1977. 2 D. Balcomb and R. McFarland, personal communication (1978). 3 W. D. Nichols, Unit 1, First Village, Passive Solar Heating and Cooling, Proc. Albuquerque Conf. Workshop, LA-6637-C, 1976. 4 R. P. Stromberg and S. O. Woodall, Unit 1,Passive Solar Buildings: A Compilation of Data and Results, SAND 77-1204, 1977, p. 24.