Zoltán Pásztory, Zoltán Börcsök Innovation Center
University of Sopron
4. Bajcsy Zs. str. Sopron 9400 Hungary pasztory.zoltan@uni-sopron.hu
Abstract:. Multiple reflecting insulation material was developed and built into a pilot building in the frame of four year research project called Mirrorpanel. The thermal insulation system used effectively the reflection of radiated heat the reduced convection effect of small air gaps, and the good thermal resistance of still air. Recycled paper were used for the material of reflecting layers with a special coating for reflect higher ratio of radiation. The distance between layers was set to 5 mm. Laboratory size panel thermal conductivity was 0.029 and full size panel was 0.038 W m-1 K-1.
Keywords: Thermal insulation materials, heat reflection, Mirrorpanel
1. Introduction
Researchers found, that in the European Union, buildings account for 40% of the total energy consumption (Report on the Green Paper on Energy or Doing More with Less, European Commission, 2005, Directive 2010/31/EU). In residential homes, about 82% of the total energy is used for heating and hot water production (Gordon and Holness 2008, Linder, S. & Bhar 2007). At the same time, in Europe at the temperate climate often cooling of the building is required during the summer due to heat which amount of heat could partially or completely cover the heating demand during the winter. The energy used can be reduced by increasing the thermal insulation of the buildings and by storing the summer heat for space heating purpose at winter (Magyar et al. 2017, Faitli et al. 2015, Dincer and Rosen 2011, Agyenim et al.
2010, Dincer 2002, Ismail and Stuginsky 1999). The natural based, environmentally friendly products are gradually gaining ground between the thermal insulation materials. To examine these two way together, an environmentally conscious, energy efficient test building was built. The building was environmentally friendly by its thermal insulation was solved by multiple reflecting of thermal radiation and was made of natural based material (Pásztory 2013). This study summarizes the experiences of this pilot building concerning the reflecting thermal insulation system which was tested for years to get experience of effectivity.
2. Materials and methods
2.1 Mirrorpanel thermal insulation
The concept of the formation of narrow air layers with the help of heat-reflecting foils within the wall structure was used to build the insulation of the house by minimalizing the heat bridges and slowing down the heat flux by multiple heat reflection layers trough the wall. This Mirrorpanel system was designed for wood frame structure buildings, where there is an air gap between studs. Normally these gaps are filed with traditional insulation materials such as, rockwool glasswool or cellulose fiber. The frames provide the fixing places of the new developed insulation system and the cover plates were OSB both side for protecting the system from mechanical stress.
The material of the reflecting layers was recycled paper which was coated special nanopigment to reduce the original surface emission value from 0.93 to 0.35 and to preserve the vapor permeability of the layers.
The layers was coated both sides for having higher thermal resistance of the system. According to preliminary studies, the 5 mm gap was economically and technically optimal between layers. Small, 1.5×0.5 cm cellulose distance holders were used to keep the distance between the layers and they were fixed to the edge of the layers by stapling. Because of the small surface and the relatively low thermal conductivity of the distance holders, they have little heat bridge effect to the overall heat conductivity of the whole structure.
The framework was made of 6×16 cm spruce laths and the frame systems were covered with fiber-reinforced gypsum boards on both sides (Figure 1).
There were built a laboratory sized small panels and the life size panel for testing. The small panel was 300 mm by 300 mm with a thickness of 30 mm and the air layers was 5 mm insight the panel. The life size panel was 2 m by 1.25 m the thickness was 16 cm. In case of small size panel the frame element was only 15 mm because the purpose of these samples was to determine the thermal conductivity of the pure Mirrorpanel system without frame’s effect. In the large panel the frame was built in as a normal wall structure and the purpose of the measurement was the examination of thermal conductivity of the whole system.
Figure1 The Mirrorpanel wall system a) full panel surface, b) panel cross section
By means of the special form and material of Mirrorpanel thermal insulation system could reduce the thermal transmittance trough the wall in three ways. The low emissivity layers reflect thermal radiation multiple times; the 5 mm air gaps provide a significant thermal resistance for thermal conductivity and because of the narrow air layer and the small temperature difference between the boundary layers the convection effect can be neglected according to the Prandtl and Grashof dimensionless numbers. The structure was designed for having the minimal surface contact perpendicular to the surface of the wall which causes minimal thermal loss by heat bridges.
2.2 Test building
120 m2 residential home was built in western part of Hungary for testing the system (Figure 2). The orientation of the building was toward south with larger windows for increase the solar gaining and no window was set to the north which was the ruling wind direction too. The house was very well insulated for minimize energy demand for heating and cooling purpose. The whole building was sit to a foundation surrounded by 20 cm extruded insulation boards reduce the heat loss toward the ground. The roof has also high thermal resistance, the thickness was 40 cm and cellulose insulation fibers filled the gap between rafters. Three glassing windows were chosen with a thicker frame structure and with plastic distance holder between glasses. It was devoted high attention to the air tightness for reducing the heat loss by filtration.
By the effort of the high insulation elements of the pilot building the thermal energy demand was quite low, around 1 kW in case of 22 degree Celsius temperature difference.
Figure 2. Experimental building in West-Hungary
3. Result and discussion
3.1 Mirrorpanel thermal insulation
The heat conductivity of a completed, large panel was measured by the Hungarian Building Material Certification Institute (ÉMI), it was 0.038 W m-1 K-1, including the thermal bridges of the distance holders, and the fiber-reinforced gypsum boards on the sides, which is better than the light frame walls made of commonly used insulating materials [5]. This result is significantly better than that of the traditional light frame panels which consist rock or glass wool having thermal conductivity about 0.04 W m-1 K-1.
The results of the small size laboratory panel was 0.029 W m-1 K-1 which value is really low taking into account the thermal conductivity of still air (0.025 W m-1 K-1).
Both experiment proved that the multiple reflection of radiation and the small air gaps and the reduction of the numbers and surfaces of heat bridges can result lower thermal conductivity than the fiber and foam based insulation materials. Proved that it is possible to build a system and the reduction of surface emissivity is a key element of the low thermal conductivity.
4. Conclusion
New insulation system was build and tested in laboratory size and also in building size. For space heating seasonal thermal energy storage system was designed and built into the test building and a finite element simulation was run for determination the elapsing time of the thermal storage block.
• Multiple thermal reflection can be used as an effective insulation system and the insulation value is competitive relates to the traditional insulation materials. The best value in laboratory size was 0.029 W m-1 K-1, and the full size panel reach the 0.038 W m-1 K-1 value.
• Space heating of reduced thermal loss building can be supplied of seasonal thermal storage system.
• Insulation thickness of the thermal storage block has slight effect to the elapsed time.
• The withdrawn energy dominantly influence duration of the operation time of the seasonal thermal storage system.
• Transient model could not be compare to the steady state situation unless the average value of the transient model is calculated for longer time.
As the energy consumption has increasing importance the improvement of the building envelope produce building with reduced energy demand. By this process the seasonal thermal storage system will be investigated and to build different model will be necessary for the future for the better thermal design of the building.
5. Acknowledgement
The work was carried out as part of the ”Sustainable Raw Material Management Thematic Network – RING 2017”, EFOP-3.6.2-16-2017-00010 project in the framework of the Széchenyi 2020 Program. The realization of this project is supported by the European Union, co-financed by the European Social Fund.
6. References
Report on the Green Paper on Energy or Doing More With Less, European Commission, Brussels, Belgium, 2005.
Directive 2010/31/EU of the European Parliament and of the Council of 19 May 2010 on the energy
performance of buildings. Online.
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:32010L0031:EN:NOT
Gordon, V.R. & Holness, P.E., Improving Energy Efficiency in Existing Buildings. ASHRAE Journal, 50(1), pp. 12-26, 2008.
Linder, S. & Bhar, R., Space conditioning in the residential sector in Europe, Deliverable 1 Ground Reach EU project. Ecofys. pp. 1-38, 2007. Online.
Pásztory Z. (2013): Improved heat insulation system (Mirrorpanel) for construction of wood buildings.
Holzforschung 67(6): 715-718. DOI 10.1515/hf-2012-0198
Dincer, I. & Rosen, M.A., Thermal Energy Storage: Systems and Applications, 2nd ed.. Chichester: Wiley, pp. 83-190, 2011.
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Dincer, I., On thermal energy storage systems and applications in buildings. Energy and Buildings, 34(4), pp. 377–388, 2002.
Ismail, K.A.R. & Stuginsky Jr., R., A parametric study on possible fixed bed models for PCM and sensible heat storage. Applied Thermal Engineering, 19(7), pp. 757-788, 1999.
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Faitli J., Magyar T., Erdélyi A., Murányi A.: Characterization of thermal properties of municipal solid waste landfills. WASTE MANAGEMENT 36: 1 pp. 213-221., 9 p. (2015)
III. RING – Fenntartható Nyersanyag-gazdálkodás Tudományos Konferencia 2019. október 10-11 - Sopron