The Thermal Resistivity of SB construction

The Thermal Resistivity of Straw Bales for Construction Joseph C. McCabe 

ABSTRACT

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INTRODUCTION

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History of Straw bales used for construction

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History of Straw Thermal Analysis

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Method for thermal analysis of Bales

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Bales (used in this project)

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Conditions and type of bales used for testing

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Moisture in the bales

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Results

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Use of this insulation value

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Discussion

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Conclusion

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REFERENCES

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Appendix I (Problems encountered during testing)

A Project Submitted to the Faculty of the DEPARTMENT OF NUCLEAR ENGINEERING In Partial Fulfillment of the Requirements For the Degree of Master of Science In the Graduate College THE UNIVERSITY OF ARIZONA Various Copyrights (c) 1993 All rights reserved. Statement by author: This thesis has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgement of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or impart may be granted by the head of the major department or the Dean of the Graduate College

when in his judgement the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. Acknowledgements: I would like to thank the following for help in this thesis: Lou Thompson for his brains, Matts Myhrman for his movement, University of Arizona Environmental Research Laboratory for the facilities, Dr. Nader Chaulfoun for his data, Dr Alphonso Ortega and Dr. Coates for their knowledge, Dr. Rocco Fazzolari, Dr. William Fillipone and Dr. John Peck for their review and their assistance. And, mostly, thank you Dr. Cynthia Erickson for everything! Dedication: This thesis was written for all those who can benefit from the use of straw materials for buildings, everyone.

ABSTRACT This thesis describes the procedure for obtaining an insulation value for straw bales for construction. A modified hot plate was placed between two bales and temperature readings were taken at various locations in and on either sides of the straw bales, this is referred to as a "modified guarded hot plate procedure". An R-Value of 52 (H-FT^2-F/BTU-Bale) was determined for wheat bales. Rice straw bales have similar insulating value. This R-value was used to demonstrate the energy requirements of a residential building constructed with straw bales. The use of this value has wide ranging implications on energy use for buildings. In order to compare straw bale insulation to more traditional insulation materials the Arizona home energy rating program, CalRes, was used. An average residential building energy usage decrease of 12.4% per year was determined by using straw bales. Straw is an anisentropic material. Insulating values of bales varies with position. Heat flow against the grains has a higher insulating value (R=3.15/inch) than heat flowing with the grains (R=2.38/inch). Moisture content and bale density also effect insulating values.

INTRODUCTION This thesis attempts to explain the history of straw bale construction; the problem of no known values for the thermal resistivity of straw bales for construction; how experimentally a value of the thermal resistivity was determined; and what this insulating value can do for typical building designs.

History of Straw bales used for construction

The history of straw bale construction is an important portion of this thesis because it removes the "Three Little Pigs" attitudes to this building technique.

Information from Out On Bale, Unlimited, a straw bale construction consulting firm located in Tucson indicates the use of grass as a building material dates back to the Stone Age, by which time humans were making extensive use of the enormous grassland areas of the African and European continents. The next logical progression toward bale buildings would be the use of such bundles of stems as units to build a wall. Out On Bale, Un-Limited is presently trying to confirm the existence, in Great Britain (Cheshire), of a slightly more than twohundred year old residence reportedly constructed by laying up long, tied bundles of straw with an earthen mortar. Nebraska residents have used straw for a building material for over 100 years. Although there was a negative social stigma attached to living in a building made of straw, these homes were practical, inexpensive efficient and sturdy. In fact several are still standing today. Nebraska Historical Society located in Lincoln Nebraska has a file on straw bale buildings in various counties in west and north Nebraska. Pictures #1-3 show various views of these existing structures in Nebraska.

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Photos courtesy of Nebraska Historical Society, Lincoln Nebraska. Straw bale construction flourished in the Sandhills of Nebraska more than any known location. Straw was one of the only indigenous materials available to the sandhills area of northwest Nebraska. Bale construction was an appropriate, sometimes necessary, response to a unique combination of legislative, geologic, natural resource and socio-economic factors that prevailed in that region in the early 1900's.

The Kincaid Act of 1904 opened up the part of Nebraska that includes the Sandhills to homesteading under new rules. Applicants could claim a full section (a one mile square) rather than the quarter section previously allowed. This act brought large numbers of financially pinched homesteaders into a nearly treeless, semi-arid region characterized by vast areas of roadless, rail-less, grass-stabilized sand dunes. Many inhabitants said that they, or others, had built bale houses as a temporary, stopgap measure to get the family under roof in the shortest possible time for the least possible money. Many of them planned to build a "real" house as soon as enough money could be saved. Such houses were often left exposed on the outside, while plastered on the inside to enhance tidiness and prevent drafts. When the owners finally believed that they were living in a "real" house, a process that sometimes took as much as ten years, the outside walls would finally get a thick coat of mud plaster or cement stucco. .1 As of this date (3/18/93), Out On Bale Un-Limited has solid documentation on eightyfive bale structures built since 1940, in Mexico, the United States, Canada and Finland. Climatically, the range of building sites includes semi-arid, southern Sonora, Mexico; rainy, humid Alabama; wintry northern Alberta, Canada; and the coast of Maine. The buildings run the gamut from a 10' by 12' storage shed, built by a 5th grade class with

rice straw bales, to an art gallery, to a 40' by 80' grocery store, to elegant homes, to a 26,000 square foot hog barn with a straw-insulated roof..2 Building of Railroads through the midwest is one factor that added to the reduction of straw use. Railroads and merchandizing enabled wood products to replace Nebraska's indigenous materials for buildings needs. There has been a renewed interest in straw bale material because of environmental interests and changing social values. Recent renewed interest in straw bale construction makes engineering properties associated with the material a necessity. What insulating value should be applied to the straw bale wall? Energy designs can be compared with this important characteristic. Sophisticated computer programs such as Calpas and DOE2 as well as state energy rating programs such as Arizona's CalRes can predict the energy consumption of a building using the known R-values. It is believed that this information has not been available for straw bales previously. The Department of Energy (DOE) estimates are that the home heating and cooling energy usage in this country is 11% of the total U.S. energy consumption..3 Total U.S. consumption was 74.2 Quadrillion BTU's in 1983..4 The straw bale insulating material has great potential to reduce the residential sector building energy usage. Houses built with straw bales have been constructed at costs of $20 to $75 per square foot depending upon the sweat equity and extravagance of design compared to $45$75 of conventional home costs. Photographs 4 and 5 show the before workshop and after views of a recent wall raising just south of Tucson downtown. This wall raising took 3 hours to accomplish with the help of about 25 workshop participants.

[172k] [179k] {A post thesis note here, this bale structure burnt to the ground a few weeks after this picture was taken. Located in the barrio district of Tucson, it highlights the need for immediate stucco for fire proofing and precautionary steps.}

Bales don't provide great reductions in construction costs compared with conventional building practices; however bales provide society with a reduced cost associated with the environment and health. Agricultural wastes are typically burned; the straw bale construction creates a demand for this material and reduces the burning. Recent proposed California legislation will prohibit the burning of rice straw material. It is possible that other states will enact similar legislation for other materials posing threats to the environment. The high thermal efficiency of straw bales reduce the energy requirements for heating and cooling thus reducing pollution associated with energy to heat and cool dwellings. This is an inexpensive high insulating material which does provide cost economies in comparison with conventional high insulation costs. Bales can be a pollution abatement program; the sequestering of yesterdays pollution in todays straw material. Other value is to our old growth forests; trees can remain standing if the biannually, renewable crop of straw is used as a replacement building material. The structural capabilities of straw bale walls has been addressed in a 1993 paper by Galen Bouali a civil engineering graduate student at the University of Arizona.

History of Straw Thermal Analysis An extensive review of published materials uncovered articles on straw and straw board materials in relation to the thermal and sound absorbing properties. Published thermal properties of paddy straw particle boards were available in a paper Mechanical and Thermal Properties of Particle Boards Made from Farm Residues. Low- density particle board specimens with the following specifications were made using ureaformaldehyde resin 6% (w/w) as the binding material, hot pressed under 1.47 MPa pressure and 170 C temperature for 15 minutes. Board Size 0.225 X 0.25 X 0.016 m = 8.86" X 9.84" X .63" Moisture content 11- 14 % Particle size 5 - 10 mm long Density 190 kg m^3 = 11.86 lbs/ft^3 The thermal properties were: Porosity 55 % Thermal Conductivity 226.0 Jm^-1h^-1C^-1= .0363 BTU/h-Ft-F= R value of 27.57/Ft (R=2.29 h-Ft^2-F/BTU-in, similar to mineral fiberboard) Specific heat 753.5 J kg^-1 C^-1 = 0.1799 BTU/lbm-F Diffusivity: 44.46 10^-8 m^2 s^-1= 0.1724 Ft^2/h .5 These values include the bonding material and are not exactly representative properties of the bales. The procedure for the testing to determine these numbers is not known. Actual testing results from this project indicate that this R=2.29 h-Ft^2F/BTU-in value is close to the insulating value of bales with heat flowing with the grains of the straw of R=2.38 h-Ft^2-F/BTU-in. The Canada Mortgage and Housing Corporation, Housing Technology Incentives Program, in Ottawa, Ontario, Canada has information on an innovative straw/bale mortar wall system which describes the results of testing done in Canada on a sample wall created by laying up straw bales (460mm or 18- 1/2" wide) with a cement-limesand mortar. A mixture of the same materials was then plastered onto each side to create a layer 20mm (3/4") thick. These results indicated an average moisture content of 13.36% and an insulative quality (RSI 6.17 or R-35)..6 As with the previous article the procedure for this testing is not available.

Method for thermal analysis of Bales Testing has followed to my best ability the guidelines set out by the American Society for Testing and Materials ASTM, 1991 Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission properties by Means of the GuardedHot-Plate Apparatus. This test method covers the achievement and measurement of steady-state heat flux through flat-slab specimens using a guarded-hot-plate

apparatus..7 It is used for board insulation, batt insulation and flat-slab specimens. The testing was modified such that there was no cold plate. The cold plate was replaced by sheet metal surfaces providing room temperature across the surface. There was also no guard; the hot plate was surrounded by the insulating materials. A special opportunity was available for me to use an adobe building at the Environmental Research Laboratory near the airport in Tucson. A beautifully landscaped facility provided a comfortable atmosphere for testing as well as appropriate monitoring capabilities. Adobe mass provides a constant temperature room to conduct testing. Temperature swings from 71.3 to 68.7 F dry bulb ( delta temperature of 3.1 F) on March 18th and 19th were typical for the small temperature swings throughout the beginning testing periods. Temperature swing of 2.6 F was obtained during steady state conditions for the bundle on March 28th. The adobe building came equipped with wet bulb, dry bulb and room radiant monitoring equipment. These data points, bale thermocouple and heat flux sensors were wired into the Omega portable datalogger, Model OM-372. This was linked via RS-232 to an IBM-XT terminal where information was logged using Procomm communications software running under DOS. Data was transferred to spreadsheet using Lotus and computations and graphing performed by QuatroPro. Average reading values were used for computations and graphing.

U of A Environmental Research Labratory[93k] Thermocouple are T-type, blue and red insulation. Calibration of thermocouple was performed using a calorimetric thermometer graduated at .2 degrees from 0 to 214 degrees F, a corrections table generated and applied to the data logger. Heat flux sensors are Hycal Engineering B1- 7-120. Computations for insulating properties was performed using ASTM Designation: C 1045 - 90 Standard Practice for Calculating Thermal Transmission Properties From Steady-State Heat Flux Measurements..8 Testing was performed on blue polystyrene as a control (R-value of 5/inch) which was compared to rice and wheat straw bales. Bale bundles were the heart of the testing, for bales making up a bundle. Bundles were produced in a systematic procedure. Plastic milk cartons were used to elevated the bundles from the conduction of the adobe building brick floor. Banding straps were placed on top of the milk cartons and taped in place for future banding requirements. White painted 44" X 45"- 26 gauge sheet metal was place on top of the milk cartons and straps. This standard white paint gave the surface an emissivity of 0.9. The first two bales were placed on the sheet metal. The heat source wrapped in aluminum foil to distribute the heat and was centered upon the two bales. Four thermocouple were Elmers glued to the heat source aluminum foil, two on the top and two on the bottom at 6" away from the center lengthwise. The particular bale which would have its internal temperature was placed on top of the first bale and the portion of the heat source under it. This bale was carefully measured for thermocouple placement. A pair of thermocouple was placed at the levels of 2", 5" and 10" from heat source, . Thermocouple were also place on the internal surface of the bale to determine the heat flow in the crack between the bales. The last bale was placed to make the bundle. Three thermocouple were placed on the top surface of the bales. For

the wheat straw bundle a heat flux meter was placed on the top surface in the center of the bundle. One piece of sheet metal was placed on the top, and the bundle was banded together with 4 straps. Sheet metal was placed on the 4 sides remaining and banded in place. Corners of the bundle had portions of straw materials showing through the sheet metal. This was required so the bundle could be compressed by the banding procedure. All thermocouple wires were exiting the bundle at the same location while following constant heat flux paths in the interior of the bale bundle. Pictures # 7 shows actual testing in the adobe building.

[168k] Additional information obtained during testing was the volume of bales weight of bales, the density and the percent moisture of bales being tested. Not in the original report but for the net here we have animations of the testing. Click on these images if you have FLI capabilities or Quicktime.

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[120k FLI animation] Temperature readings were at the heat source, bale surface, and at different levels in the bales, 2", 5", and 10" from the heat source. Other testing included thermocouple placed at the 1", 2", 3", 4.5", 6", 10" and surface positions. Heat flux metering was placed at the heat source, 4.5" 10" and surface levels. Room temperature, room wet bulb and dry bulb temperatures as well as room globe temperatures were obtained.

Steady state operation was determined when the hot plate heat source did not vary more than 1 degree F for a one day period. Voltage and current measurements were obtained to the heat source. The test procedure was to examine bales for consistency, record bale external characteristics, and to measure the bale dimensions and weight. The bales were positioned for cubic configurations such that the heat source is sandwiched between two bales. The dimensions of the end of the heat source and the bale surface dimensions were confirmed. This were used in edge loss and shape factor corrections analysis. The main goal was to obtain constant temperature readings through out a sample test area of the bale. This was accomplished in steady state form after days of heating the interior of the test module bundle. Testing indicated steady state operation was obtained many days and in the case of the rice straw, weeks after the heating began. Thermocouple were placed on the heat source and at various levels of the bale, and at the bale surface. The placement of thermocouple was suggested by ASTM C 1045909 with at least 2 thermocouple at each level. The energy to the heat source was regulated so the temperature remains constant. This was done with a DC power supply. The heat source is a radiant heat panel by Aztec. This normal 200 watt rating 15" X 23.5" panel was attached to a 25 volt DC power supply to regulate power to the heating device. The voltage and current is measured with a Fluke model 8012A and a Hewlet Packard model 6215 A. The DC power supply regulated the power into the hot plate for straw high temperature testing at Voltage=25.3 Volts DC Current=0.341 Amps For a wattage of (V*I)=8.63 Watts=29.4 BTU/hr Power was reduced for the polystyrene testing and low temperature bale testing. The heat flux metering was used for determination of actual heat flow in the bales and polystyrene tests. Thermocouple were calibrated before using. Voltage corrections for specific thermocouple were programed into the Omega data logger. Temperature readings were logged on 10 minute intervals. When the hot plate temperature no longer varied more than 1 degree for the day average steady state condition was assumed. A delta temperature across the bale was measured and applied to the equations for insulating value.

Background on bales used in this project Bales from farms have varying volumes and banding schemes. New Mexico bales are typically 2 band, Yuma bales are 3 plastic wraps. 3 plastic wrap norther California rice straw bales were shipped for this experiment. Bales of various materials are

available. Straw comes from rice, oats, wheat, etc. The bales used for this project were rice straw bales and wheat straw bales. Bales range in size from 50 to 80 lbs and sizes 35"-47" long, 14-16.5" high and 18"23" wide..10 Drawing # 1 illustrates these dimensions. These dimensions orientation the fibrous material of the bale horizontal. Bales have been oriented in various positions in building construction. Testing the properties was done in the horizontal and vertical positions. If the bales of a wall are vertical straw materials the wall thickness (16.5" heat flow against the grain) is less than if the straw is horizontal (23" heat flow with the grain) and there is less insulating value per inch. The heat flow during comparison testing was perpendicular to the strands of straw, the 16.5" dimension or height of bale. Testing was also performed on the bales to determine 23" length insulating value, called "on end" testing. Typical building practice uses either orientation.

These bale tests were compared with the same test method performed on pieces of 4" thick polystyrene, having a known insulating value of R=5 h-Ft^2-F/BTU-in. These pieces of polystyrene were positioned for a cubic arrangement of 48" X 48" X 32", similar to the bale cubic arrangement. These comparisons provide similar edge and corner loss comparisons.

Conditions and type of bales used for testing This thesis used two different types of straw materials. Wheat straw bales were obtained from a warehouse in Tucson. Rice straw bales were shipped from Northern

California. All bales had been unused, 3 string bales dimensions and weight of the bales used as shown in Table # 1. Weight of bales and density were measured in an attempt to follow the ASTM Thickness and Density of Blanket or Batt Thermal Insulations..11 This method had applicable guidelines for proper apparatus, however the batt insulation expansion procedure was not applicable because of the varying surfaces of the bales; the bale length is shorter where the ties are, the bales bend and have pockets of straw sticking out. To the best extent accurate measurements were performed, however all dimensions should have a + or - 1/2" discrepancy because of difficulty in measurements. The method for bale moisture has not been addressed with standard procedural process. It is a unique measurement for our applications.

Conditions and type of bales used for testing This thesis used two different types of straw materials. Wheat straw bales were obtained from a warehouse in Tucson. Rice straw bales were shipped from Northern California. All bales had been unused, 3 string bales dimensions and weight of the bales used as shown in Table # 1. Weight of bales and density were measured in an attempt to follow the ASTM Thickness and Density of Blanket or Batt Thermal Insulations..11 This method had applicable guidelines for proper apparatus, however the batt insulation expansion procedure was not applicable because of the varying surfaces of the bales; the bale length is shorter where the ties are, the bales bend and have pockets of straw sticking out. To the best extent accurate measurements were performed, however all dimensions should have a + or - 1/2" discrepancy because of difficulty in measurements. The method for bale moisture has not been addressed with standard procedural process. It is a unique measurement for our applications.

Moisture in the bales Testing performed for this thesis represents a small sample of bales. Bales used for construction should have the driest possible conditions for greatest insulating value. Dry bales have higher insulating values than bales with moisture because the moisture migration transfers heat. Wheat straw has 28% moisture content when fresh cut weight, rice straw 20%..12 Typical bales have 14% moisture. However the industry does not track statistics for moisture percentage values. Two types of moisture values are important to the agricultural industry. First is the quality, dry bales last longer and don't rot. The second is marketing. Marketing is important because of the value of the straw not the water. Bales are penalized for being wet..13 The moisture content is important in determining the insulation properties of the bale material without the effect of water, moisture. The method for determining water content or this thesis was to break open the center of a bale, and obtain a representative sample of the interior straw. This

straw was weighed, and heated for days at 100 C, then weighed again. The difference of the weights is the moisture removed. The bale was banded together and used in the test bundle. Percent moisture of bales were obtained before and after the testing of the wheat bales. Percent moisture tests of a the rice straw bales which were dried on a sun porch at a temperature of 103-110 F during sunny days provided an 8.4% moisture content. The percent moisture test of the rice straw used in the thermal testing was determined after the testing of the test bundle bales. TABLE # 1 Straw Bale Characteristics Bale Type # 1 Wheat 2 Wheat 3 Wheat 4 Wheat Average St. Dev. 5 Rice 6 Rice 7 Rice 8 Rice Average: Std. Dev. Bale # 1 2 3 4 5 6 7 8 Wheat Ave Rice Ave:

Dim (in inches) Weight % hgt wth length lbs Moisture 16.7 22.5 44.4 84 8.4% 16.7 22.5 44.5 80 8.4% 16.0 23.5 47.0 83 8.4% 16.3 23.0 46.7 84 8.4% 16.4 22.9 45.6 82.7 8.4% +.34 +.48 +1.39 +1.89 16.5 23.0 45.5 77 8.2% 15.5 23.5 44.5 76 8.2% 16.5 23.0 45.5 79 8.2% 16.5 23.0 44.5 71 8.2% 16.2 23.1 45.0 75.7 8.2% +.5 +.25 +0.6 +3.4 Volume Density ft^3 lbs/ft^3 19.68 8.68 9.71 8.24 10.23 8.12 10.14 8.28 10.03 7.68 9.42 8.07 10.03 7.88 9.80 7.24 9.94+.29 8.33+.24 9.82+.29 7.72+.36

Percent moisture was one of the biggest problems in obtaining a steady state condition. This problem provides information regarding the typical bales used for construction. Materials are cut in the field and laid out to dry. The length of time material stays in the field depends upon the weather; ideally it is collected and baled in its driest possible state. Wheat bales tested 8.2 to 8.4 % before and 5.9% after the bundle thermal testing; this shows that drying out during the testing. It has been the findings of this experiment that the straw samples do not dry out more than 5% moisture when the heat is applied for extended periods. Bales could have been placed in ovens and dried at extreme temperatures, but this would not provide typical building material information. It was assumed that the material reaches an equilibrium of moisture content dependent upon relative humidity and temperature. See Appendix for more information on problems during testing.

Results

The steady state condition took a long time to achieve because of moisture problems in the bales. The rice straw had considerable moisture, taking two weeks to reach a steady state condition. The values of temperature readings for the horizontal position of the rice and wheat straw bales are: TABLE # 2 3_28_93 Horizontal after steady state, rice straw, average temperatures of thermocouple readings: Hot Plate 2" Ave. 5" Avg. 10" Avg.Surf Average: 142.9 123.7 108.3 89.5 70.5 Minimum: 142.6 123.5 108.2 89 68.3 Maximum: 143.2 123.9 108.5 89.7 72.7 Room W.B. Room D.B Average: 59.3 67.8 Minimum: 58.8 66.3 Maximum: 60.1 68.9

4_6_93 Horizontal after steady state, wheat Straw average temperatures of thermocouple readings: Hot Plate Ave 144.4 Max 144.8 Min 143.8

2" Ave 131.1 131.5 130.5

5" Avg 109.0 109.5 108.3

10" Ave 90.0 90.3 89.8

Surf Ave. 76.0 77.2 74.9

Room W.B. Room D.B. Ave: Min Max:

61.1 62.4 59.9

69.9 71.6 68.3

These tests are illustrated in the Graph # 1 "Rice Straw, Horizontal Steady State 3_28_93 Ave Temps" and Graph # 2 "Wheat Straw Horizontal Steady State 4_6_93 Average Temperatures".

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It was found that a temperature versus distance graphing of the test provided near straight line relationship from the hot plate to the 6" level in the straw bundles. This can be seen in the graph Temp vs Distance 4_18 Wheat Low Temp, Graph #3.

[5.6k] Polystyrene insulation with a known insulation value of R=5/inch was tested in the same manner as the bales. An R- value of 4.9 was experimentally determined in the bundle configuration using heat flux measurements at the 4.5" level and a delta temperature of hot plate minus the 4.5" level. This same method was used on wheat bales in the horizontal, low and high delta temperature and "on end" positions. Graphical representation of these comparative tests are shown in Graph #4, #5, & #6. The results for these tests are as follows:

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TABLE #3 Results of Bale Bundle Testing Compared With Polystyrene Type q Delta u R for of Temp 4.5" Bale Wheat 2.33 31.0 0.075 13.3 Wheat 1.39 19.7 0.071 14.2 Low Temp Poly- 1.44 31.9 0.045 22.2 styrene Wheat 1.59 17.0 0.09 10.7 on end

R for R for 1" Bale 2.96 3.15

48.8(16.5") 52.0(16.5")

4.93 2.38

54.8(23")

Units are: q-(BTU/FT^2-H), u-(BTU/FT^2-H-F), R-(H-FT^2- F/BTU-inch) Graph # 7, R-Value per inch illustrates these results.

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Use of insulation value Typical building design analysis information is available to compare conventional building techniques with the straw bale. For this thesis I have performed computer energy simulations of existing designs which are presently being built and meet current Arizona energy use requirements. These simulations are done with a program called CALRES/Arizona, a computer program developed for the Arizona Energy Office by Berkley Solar Group Software for the Arizona Home Energy Rating System. CALRES/Arizona is a design tool used to compare design strategies. For this project the high insulation properties of the straw bale is compared with the typical R-11 and R-19 wall insulation used in todays buildings. The exterior convection, interior and exterior surface materials remain unchanged. These data files were obtained from a study for Southwest Gas performed by Dr. Nader Chaulfoun at the University of Arizona Department of Architecture. The names of the construction designs have been withheld because of their unimportance to this thesis; the important information is the energy usage comparison of existing building techniques to that of the straw bale construction. Building designs were chosen at random for small to medium size structures. Tucson Arizona is the weather file used, the worst case orientation to the sun was used with the largest window facing west. There were no stucco or adobe surfaces applied to the simulation, only the inside and outside convection with an R=52 insulation value. A review of the results are: TABLE # 4 Calres Arizona Comparison of Homes

Weather Data Tucson AZ. Calres Arizona Comparison of Homes House # SQ. FT. 1 1211 2 1132 3 1400 4 1305 5 1596 6 1504 7 1523

Original (kBtu/ft2-yr) Heating Cooling Total 23.02 23.78 46.8 28.81 69.32 98.13 17.57 38.12 55.69 16.54 34.62 51.16 14.32 36.13 50.45 14.28 39.38 53.66 23.6 23.17 46.77

Weather Data Tucson AZ. House With # Heating 1 18.33 2 23.49 3 14.83 4 14.71 5 12.87 6 12.44 7 18.06

Straw (kBtu/ft2-yr) kBTU/yr Cooling Total Savings %savings 21.21 39.54 8791 15.5% 60.82 84.31 15644 14.1% 34.34 49.17 9128 11.7% 31.59 46.3 6342 9.5% 33.73 46.6 6144 7.6% 36.21 48.65 7535 9.3% 19.79 37.85 13585 19.1% Average: 12.4%

This is a significant decrease in energy usage.

Discussion Insulation value of straw bales for construction has great implications for reducing residential energy consumption. The Department of Energy predicts that energy end use in U.S. residential and commercial buildings for space heating and cooling was 9.5 quadrillion BTU's in 1990 and will be over 11 Quadrillion Btu's in the year 2010. In Tucson Arizona the percentage of residential energy usage for cooling is much higher than the national average at 49%, lower for heating at 16%. This energy usage is what straw bale construction can reduce without reducing comfort or air changes per hour. Recently there have been laws created to ban the burning of field straw. This material is currently a waste product for the farmers. Along with these laws, high disposal costs will increase usage of straw for construction.

Conclusion Straw bale construction has high insulating value of R=52 for a 16.5" bale width with typical home temperatures. Rice straw is similar to wheat straw in its insulating value. The positioning of straw bale does have an effect on the insulating value of the bale. Heat traveling against the grains of the straw has a greater insulating value that heat traveling with the straw grains. Home energy usage can be reduced by 12.4% by using this building material. This project demonstrates the great impact straw bales can have on the residential energy usage heating and cooling usage. Utility companies can benefit from this reduction in conduction of heat when the need to reduce energy usage is greatest,

when it is hot out. Typical demand side management DSM programs look for opportunities to reduce the peak energy usage of the year so that new power plants don't have to be constructed for this peak energy usage. Straw bale construction can help to reduce this peak energy usage, as well as bring the whole yearly demand curve down. The Thermal Resistivity of Straw Bales for Construction Joseph McCabe

References 1 Myhrman, Matts, interviewed by Joseph McCabe, Tucson, AZ., 2 P.M., April 6, 1993RETURN 2 Myrman, Matts, April 22, 1993 Architecture and the Great Plains: The Built Environment, Past and Present symposium. Work in progress.RETURN 3 Mcpherson, E. Gregory, "Benefits and Costs of Energy- Conserving Site Design", American Society of Landscape Architects, 1984RETURN 4 U.S. Department of Energy/ Energy Information Administration (1992) Annual Energy Outlook 1984 (DOE/EIA-0383(84)) Washington, D.C.: U.S. Government Printing Office II.RETURN 5 A. Sampathrajan, N.C. Vijayaraghavan & K.R. Swaminathan, "Mechanical and Thermal Properties of Particle Boards Made from Farm Residues", Bioresource Technology 0960-8524/92 p 249-251RETURN 6 Canada Mortgage and Housing Corporation, Housing Technology Incentives Program, Ottawa, Ontario, Canada, K1A OP7. 1984. An innovative straw/bale mortar wall system. NHA 577 84/08.RETURN 7 ASTM, Designation : C 177 - 85 1991 Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission properties by Means of the GuardedHot-Plate Apparatus. Volume 04.06 p. 20RETURN 8 ASTM Designation: C 1045 - 90 Standard Practice for Calculating Thermal Transmission Properties From Steady-State Heat Flux Measurements. Vol, 04.06, p 538 RETURN 9 Ibid, ASTM C-1045-90 Vol 04.06 p. 542 10 MacDonald, Stephen O., "Straw Talk & Tech Tips", The Last Straw, Tucson, AZ Fall 1992 p. 7RETURN 11 ASTM 1991 Thickness and Density of Blanket or Batt Thermal Insulations. C 167 p. 11 Vol.04.06RETURN 12 Risser, Paul G., "Agricultural and Forestry Residues", Biomass Conversion Processes for Energy and Fuels, Plenum Press, NY., p. 36.RETURN

13 Larson, D.L., interviewed by Joseph McCabe, University of Arizona, Agricultural Engineering, Tucson, AZ., 2 P.M. 3/30/93RETURN

Appendix I Problems encountered during testing This section is included to help those who wish to further the study of the thermal properties of straw bales. The intent is to have learned from the mistakes made during this study.

Straw is an anisentropic material. The insulating value is different if heat is flowing with the grains of the straw or against it. For the testing this provided problems in determining constant heat flux lines. The heat flux would radiate out from the heat source in a 3-dimensional pattern. Heat flux was not constant at different levels in the bale or polystyrene materials. A cold surface was installed to force the flux in a specific direction with no additional beneficial effect, in fact it made the heat flux in the center of the bale less than it had been without the cold surface. The straw sample was surrounded by polystyrene having twice the insulating value, however the heat continued to flow from the insulation up to the cold plate as well as from the heat source out to the insulation giving very low heat flux measurements in the center of the straw sample. The radiant heater panel had slight fluctuations across the face. This is a conducting, resistive material with positive power lengthwise on the ends and negative in the center. Aluminum foil was wrapped around the flat heating material to increase the consistent heat distribution at the heating source. The placement of thermal sensors was difficult. Straw is a nonhomogeneous material. To get the best measurements a temperature sensing probe placement should be exact. The area surrounding the thermocouple needed to be the same density of material as the total bale. A placement of sensor in between, or on the surface of the bales was not an accurate representation of the temperature in the bale. After conducting numerous weeks of testing it was determined that 3" into the bale seemed to provide a good representation of temperature. Bale dimension measurements are difficult to within plus or minus one half an inch. The solution was to produce a probe which would not effect the measurements but allow for exact placement. I used a bamboo skewer which had the 24 gauge T type thermocouple glued to it every 2". The skewers were pushed into the bale, horizontally. The long stick enabled the horizontal placement at a vertical placement required. The skewer was broken at the point the bale surface was reached; sacrificed for exact placement of the thermocouple. The skewer appear to be similar to the straw material; placed along constant heat flux lines. Four thermocouple were placed directly on the heating source, two on top and two on bottom, two thermocouple were placed at the 2", 5" and 10" levels both 4" of center line and 6" off center line, then 3 thermocouple were placed on the surface of the bale bundle just under the sheet metal, once again at 4" off center line, 6" off center line and one directly at the center of the heating panel below. Water content of the bales was a difficult parameter to determine. Tests on the rice bales left on the hot sun porch indicated a 8.4% moisture. Rice bales used for steady state thermal testing conditions had a 8.2 % moisture. Wheat bales tested 8.2 to 8.4 %

before and 5.9% after the bundle thermal testing; this shows that drying out during the testing. After testing of the Rice bale bundle the compression bands were removed, water had condensated under the sheet metal face, the rice straw bales were "wet" with moisture there. This moisture was less than 1" deep into the bale. Apparently this did not affect the steady state condition of the testing because steady state was maintained for the horizontal and vertical testing. Horizontal versus vertical placement of the bales changed the temperature readings. This is evident in the graph # 9 "Vertical Rice Straw Bales, 3_29_93 2", 5", 10" levels". The probes didn't move; temperature readings changed directions depending upon if they were on the top of the vertical center line or on bottom. The higher placed thermocouple had correspondingly higher readings. This was also the case at the heat source as seen in the Graph # 10 "Vertical Rice Straw Bales 3_29_93 Hot Plate Temperatures". The temperatures were higher at the top of the hot plate than at the bottom, and temperatures throughout the bale were correspondingly lower the lower the thermocouple placement. Bale bundle exterior temperatures were not as constant for the top of the horizontal bundle as for the bottom. An Omega Radiant Heat gun temperature reading device showed that the top of the bundle was 75-76 degrees while the bottom was 70-71 degrees. This demonstrates the effect of moisture in the bale and possibly the effect the colder floor had on the heat transfer of the bale bundle. It was seen from the vertical testing that there are convection effects in the bales at the heat source. When turned on its side, the hot plate temperatures are drastically effected. This can be seen in the differences in two graphs, Rice Straw, Horizontal Steady State for 3_28_93 Graph # 1 thermocouple readings in layers and the "Vertical Rice Straw Bales 3_29_93 2", 5" 10" levels" Graph # 10. When turned on its side, the physically lower thermocouple readings were a lower temperature than the physically higher temperature readings. This is illustrated in the graphs. A guarded hot plate apparatus was used without reduction of the heat flux losses. A polystyrene box was constructed which surrounded a straw sample with an R=80 wall insulating value. An ice bath was used as a cold surface. The heat flux still varied at different levels throughout the sample indicating a loss of flux to the polystyrene box. A hot wire technique was tried. This provided good results for polystyrene samples as well as styrofoam, however, the contact between the straw and probe provided wrong results for the insulation value of the straw. This technique was abandoned. Corner and edge loss factors as well as three dimensional effects make the theoretical analysis of the cubic bundle arrangement difficult. A shape factor can be used to account for these effects. These calculations indicated an R value of R=58 for the horizontal bales. The previously determined method is more reliable.