Grantee Research Project Results
Final Report: Rice Hulls as Alternative Building (RHAB): Productive Use of Agricultural Waste
EPA Grant Number: SU835294Title: Rice Hulls as Alternative Building (RHAB): Productive Use of Agricultural Waste
Investigators: Williams, Michael , Feher, Stephen I.
Institution: Butte College
EPA Project Officer: Page, Angela
Phase: II
Project Period: August 15, 2012 through August 14, 2014
Project Amount: $81,612
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2012) Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Sustainable and Healthy Communities , P3 Awards , Sustainable and Healthy Communities
Objective:
The objectives of the Phase II project were to demonstrate the feasibility of RHAB concept as an energy efficient and cost effective building material when used in forms of proven building components, such as SIPS (structural insulated panels) and ICFs (insulating concrete forms). Considerable progress was made during year one of the Phase II project, from September 2012 through August 2013 as summarized in Annual Report Butte College, EPA-P3 Grant SU835095 of November 2013.
Summary/Accomplishments (Outputs/Outcomes):
The Annual Report for Year One of Phase II summarized the materials research phase of the project concluding with the selection of the best RHAB candidate material composition, the 2SRC2, consisting of 35% rice hulls, 50% Styrofoam and 15% cement by volume. This RHAB composition demonstrated the best overall physical, mechanical and thermal characteristics for the intended building system use. It has a density of approximately 35 lbs/cu.ft.
The basic design criteria established at the beginning of the RHAB project was that building components should be light enough to be lifted and placed by a single worker. Considering that 30 lbs /cu.ft. is the lowest practical density obtainable for the RHAB composite, it was decided to abandon the SIP (Structural Insulated Panel) application of RHAB for the time being in favor of focusing on the development of smaller RHAB ICF building components. However, the future use of RHAB composites in SIP application is not ruled out, if lifting and the placement of building components by the aid of crane or Other mechanical lifting device is acceptable.
The rest of the Phase II project was committed to designing and constructing a demonstration house module using the selected 2SRC2 - RHAB composition as an ICF building system. This requires the development of fabrication methods for full scale building components in a fast and economic manner. The structural and thermal properties of full size components need to be determined also in order to establish the design parameters for the demonstration house module.
Thermal resistance, R-value, measurements are required to determine the thermal performance of the selected RHAB composition (2SRC2) in full-scale ICF building components configurations in order to provide design parameters for thermal design of the demonstration house module.
The experiments performed to measure the thermal properties of RHAB started in the Phase I used small samples measuring 12 in x 12 in x 1.5 in. During the summer and fall of 2013 a test apparatus called the "Thermal Box" was fabricated. It is a 4 ft x 4 ft cube made of commercially available SIP panels with IOin. thick Styrofoam core and 1/2 in. O.S.B facings, as shown in Figure 1.
Figure 1. Thermal Test Box (left) and RHAB interns taking instrument readings (right)
The initial set of test using the Thermal Box were performed on simple flat slab specimens cast with the selected RHAB composite in blocks measuring 24 in. x 24 in. x 3.5 in. thickness. The tests begin with placing thermocouples to measure temperature on both faces of the test sample and at mid-thickness, as well as in the thermal box itself. The interior of the thermal box is heated by a 150 Watts incandescent light bulbs, which is controlled by a dimmer switch to reach and maintain the desired interior temperature. The exterior of the test specimen is either exposed to normal ambient temperature, or is cooled by ice to simulate winter design conditions.
From the data recorded over long period test running over several days the thermal properties of the test components are calculated for use in the design of the demonstration house module. The heat transfer measurement tests resulted in determining the thermal resistance value, or Rvalue, of the RHAB composite under simulated design conditions.
The average measured value Of R = 2.33 (O F-ft2—hr/BTU)/ in thickness.
This means that for achieving the target overall insulating value of walls, floor and roof/ceiling of 30 (O F-ft2—hr/BTU) these building components will need to be at least 30/2.33 = 12.87 in. thick. Considering that the walls and roof/ceiling will receive exterior waterproofing layers, and typically a layer of h in. gypsum board interior finish, both of which will add to the thermal resistance of the building envelope, it is deemed sufficient to design the RHAB, wall, and floor and roof/ceiling components thickness 12 inches including the reinforced concrete structural layers.
Measurement of the specific heat value of RHAB composite: This is a relatively simple test to perform, one that is thought in every freshman chemistry or physics class, known as the measurement of calorimetric value of materials. A large Styrofoam ice tub was filled with a known weight (mess) of water and a relatively large piece of RHAB was weighed and submersed in the water bath as shown in Figure 2.
Figure 2. Specific Heat Measurement Test Set-up.
Measurements of temperature changes in the water bath and the specimen allowed calculation of the specific heat value of RHAB as Cp = 0.30 BTU/Ib - OF.
Based on the thermal resistance measurements described above, the conclusion was reached that the RHAB wall, floor and roof/ceiling components should have 12 inches thickness, including the reinforced concrete structural components, in order to achieve the design criteria of average effective thermal resistance of R = 30 OF-ft2—hr/BTU throughout the solid components of the exterior building envelope, the equivalent of 6 inches thick Styrofoam insulation throughout.
That would mean that under the Northern California (our area at Butte College) summer and winter design conditions with maximum temperature differentials of approximately AT = 50 O F the average heat loss or gain through the exterior envelope of a RHAB building would be approximately U = 1.67 BTU/hr-ft2 (except for windows and doors). This value only applies under steady state heat transfer conditions, which in nature is seldom achieved. Under normal transient heating and cooling condition, when exterior temperatures change constantly from mid day high to nightly low, the effective heat transfer rate will be even lower due to the high thermal mass of the RHAB building system and the resulting phenomenon known as thermal lag. Actual thermal performance is hard to predict analytically and will be measured experimentally of full scale prototype RHAB wall, floor and roof/ceiling components using the Thermal Box and tests on the demonstration house module to be built next summer.
Figure 3. Conceptual design of the RHAB/SIBS building system.
Dark shaded areas in Figure 3, represent RHAB material and light shaded areas are reinforced concrete. The 9 in. thick flat slab of the floor panels is easily recognizable in the cross sectional view under the nominal 3 in. thick reinforced concrete floor slab, with the tapered side channels forming the reinforced concrete beams 24 inches on center.
The wall structure is a little harder to visualize and describe, but basically it consists of a lattice of 6 in. x 6 in. cross section reinforced concrete vertical columns and horizontal beams at 24 inches on center in both directions, encapsulated by the RHAB insulation.
Cost comparison of RHAB wall system with conventional construction methods was made based on the latest RHAB wall block configuration. The estimated cost of the RHAB wall is approximately S3.37/sq. foot, including the reinforced concrete fill. This compares very favorably with the cost of conventional 8 in. thick concrete block wall estimated at $6.04/sq. ft., which requires the addition of 4 in. thick rigid foam insulation to achieve the same insulation value of R=30. This preliminary cost comparison assumes that labor cost are approximately equal and are not included in the estimate. In reality, the RHAB wall construction may prove to save even on labor costs, considering its interlocking, mortarless design feature and simplified overall construction by eliminating the need for adding an insulation layer which not only adds to material cost, but also adds significant additional labor costs. Exterior finish costs are assumed to be equal using 0.50 in. thick stucco with elastomeric waterproofing paint at an estimated cost of $0.65/sq. ft.
Cost comparison with wood frame construction is more difficult, because the many different ways wood framed walls maybe assembled to reach the same R30 insulation value. However, for comparison purposes considered a standard wood framed wall using 6 x 2 studs at 16 inches on center with R19 fiberglass insulation of R=19, with 0.50 in. gypsum wallboard interior finish and 0.50 in. thick OSB exterior sheeting. This wall assembly requires an additional insulation layer of 2.00 in. thick rigid foam board and assumed to be finished with the same 0.50 in. thick stucco and elastomeric waterproofing paint assumed in the RHAB or concrete block wall configurations. The overall materials cost of this wall assembly is estimated at $5.88/sq.ft.
Considering that a typical 2,000 sq. ft. floor area house has approximately equal area of exterior walls, the cost savings using RHAB wall blocks would be approximately $5,000.00 on materials alone compared to wood-framed construction and more than that compared to concrete block.
As promising as these preliminary cost saving figures look, considerable additional cost comparison studies will need to be made as the actual construction design details and the actual manufactured costs of RHAB component are established based on further research and development, especially production technology development which remains to be done.
Exterior fire resistance is considered an important potential advantage of the RHAB system. The potential superior fire resistance offered by RHAB is judged simply theoretically based on the composition of the RHAB materials, which resembles ablative heat-shield composites used in the heat-shields of aerospace reentry vehicles.
Small samples of RHAB composites have been tested to evaluate its fire resistance performance as shown in Figure 4. It may seem simplistic, but an ordinary barbecue can serve to simulate the exposure to forest fire or brush fire for small material samples. The photo on the right illustrates the residual insulating properties of the 2 inches thick RHAB sample after about one hour of continuous fire exposure. The ice on top is melting "naturally" from the ambient air exposure and not from the heat of the fire transmitted through the sample. It is worth considering that the proposed RHAB wall design will be 12 inches thick.
Figure 4. Simplified fire test of RHAB material sample.
Physical construction of the RHAB Demonstration House commenced in early June on the Butte College campus near the Fire Safety Test site with the intent that the building will eventually be exposed to simulated wild fire tests.
Only two of the Phase Il RHAB student interns were available for this summer project, therefore additional Butte College students were recruited by John Dahlgren the Principal Investigator, who managed the construction project. The construction work was supervised by Stephen Feher, the inventor of the RHAB concept and Technical Director throughout the three year program, who is also a licensed general contractor.
Figure 5. RHAB Demo House under conStruction: starting with casting of RHAB insulation under the concrete slab (top row); temporary wood formwork in wall panels for casting RHAB and reinforced concrete elements (middle row); raising completed wall panel and finishing next.
Figure 6. RHAB Demo House under construction: tilting up final wall panels (top row); preparing for casting roof slab over RHAB insolating ceiling blocks (middle row); and completed building, awaiting final finishing and testing in next phase of RHAB projects at Butte College.
Future test program includes: nondestructive structural proof testing of roof system; thermal performance tests of the RHAB building envelope utilizing the built in instrumentations in the floor, walls and roof/ceiling structure. These tests are planned to start during the winter of 2015 and continued through the summer, thus they should verify the superior insulation properties of RHAB under the wide range of climate conditions experience in Northern California is a typical yearly cycle. Fire testing of the building may be performed during next summer.
Conclusions:
The RHAB technology, from here on called Sustainable Insulation Building System (SIBS) is a promising concept already demonstrated, at least on a laboratory scale, during three years of research and development effort under EPA-P3 sponsored project at Butte College in Oroville, California. Prototype full scale building components have been fabricated and successfully tested to demonstrate superior thermal and structural performance. The design and construction of a demonstration house on the Butte College campus has demonstrated the technical feasibility of SIBS in tilt-up construction application.
What remains to be accomplished will require SBIR and venture capital funding are the following:
- development of cost-effective mass production methods of SIBS;
- obtaining approval of SIBS under the Cal Green Building Code; and
- successful marketing to achieve wide scale use of SIBS
References:
1. Global Potential of Rice Husk as a Renewable Feedstock for Biofuel Production, Ali Abbas & Santos Ansumali, Published on line 14 April 2010.
Journal Articles:
No journal articles submitted with this report: View all 1 publications for this projectSupplemental Keywords:
Rice hulls, rice hull insulated rastra block, SIP's, concrete insulated formsProgress and Final Reports:
Original AbstractP3 Phase I:
Rice Hulls as Alternative Building (RHAB) Project | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.