Abstract
Enhanced fabric performance is fundamental to reduce the energy consumption in buildings. Research has shown that the thermal mass of the fabric can be used as a passive design strategy to reduce energy use for space conditioning. Concrete is a high density material, therefore said to have high thermal mass. Insulating concrete formwork (ICF) consists of cast in-situ concrete poured between two layers of insulation. ICF is generally perceived as a thermally lightweight construction, although previous field studies indicated that ICF shows evidence of heat storage effects. There is a need for accurate performance prediction when designing new buildings. This is challenging in particular when using advanced or new methods (such as ICF), that are not yet well researched. Building Performance Simulation (BPS) is often used to predict the thermal performance of buildings. Large discrepancies can occur in the simulation predictions provided by different BPS tools. In many cases assumptions embedded within the tools are outside of the modeller's control. At other times, users are required to make decisions on whether to rely on the default settings or to specify the input values and algorithms to be used in the simulation. This paper investigates the “modelling gap”, the impact of default settings and the implications of the various calculation algorithms on the results divergence in thermal mass simulation using different tools. ICF is compared with low and high thermal mass constructions. The results indicated that the modelling uncertainties accounted for up to 26% of the variation in the simulation predictions.
| Original language | English |
|---|---|
| Pages (from-to) | 74-98 |
| Number of pages | 25 |
| Journal | Building and Environment |
| Volume | 131 |
| Early online date | 20 Dec 2017 |
| DOIs | |
| Publication status | Published - 31 Mar 2018 |
Funding
The authors gratefully acknowledge the Engineering and Physical Sciences Research Council and the Centre for Innovative and Collaborative Construction Engineering at Loughborough University for the provision of a grant (number EPG037272 ) to undertake this research project in collaboration with Aggregate Industries UK Ltd. Furthermore they would like to thank Dr Drury Crawley, Dr Jon Hand, Dr Rob McLeod, Dr Chris Goodier and Ms Maria del Carmen Bocanegra-Yanez for their help and advice. Appendix Table A.1 Building fabric construction details Table A.1 Construction Details Element (Outside – Inside) K (W/mK) Thickness (mm) Density (kg/m 3 ) Cp (J/kgK) U-Value (W/m 2 K) insulated roof panel system Roof Decking 0.14 25 530 900 EPS Insulation 0.035 300 25 1400 Plasterboard 0.16 13 950 840 Total 0.11 ICF & High Thermal Mass Floor Hardcore 1.8020 300 2243 837 Gravel Blinding 1.73 50 2243 837 Membrane 0.19 5 1121 1674 EPS Insulation 0.035 350 25 1400 Concrete Slab 1.13 150 1400 1000 Total 0.10 Low Thermal Mass Floor Stone Bed 1.8020 300 2243 837 Wet Lean 1.73 50 2243 837 Membrane 0.19 5 1121 1674 EPS Insulation 0.035 350 25 1400 Timber Flooring 0.14 25 650 1200 Total 0.10 ICF Wall Assembly Wood Siding 0.14 9 530 900 EPS Insulation 0.035 210 25 1400 Cast Concrete 1.13 147 1400 1000 EPS Insulation 0.035 108 25 1400 Plasterboard 0.16 12 950 840 Total 0.11 Low Thermal Mass Wall Wood Siding 0.14 9 530 900 EPS Insulation 0.035 210 25 1400 EPS Insulation 0.035 108 25 1400 Plasterboard 0.16 12 950 840 Total 0.11 High Thermal Mass Wall Wood Siding 0.14 9 530 900 EPS Insulation 0.035 210 25 1400 EPS Insulation 0.035 108 25 1400 Cast Concrete 1.13 147 1400 1000 Plasterboard 0.16 12 950 840 Total 0.11 Table A.2 Algorithms and input values used in equivalent models Table A.2 Simulation Solution (Loads, Plant, System Calculations): Simultaneous Calculations Time Step: 6/h (10mins) Warming up: 25 days Heat Balance Solution Algorithms: Surface and Air Heat Balance Equations Conduction Solution Method: Finite Difference Solution Internal Convection Coefficient: Fixed, User-defined value (hi = 3.16) External Convection Coefficient: Fixed, User-defined value (he = 24.67) Interior Surface Long-Wave Radiation Exchange: Calculated view factors (same values used in both programmes) Exterior Surface Long-Wave Radiation Exchange: Surface, Air, Ground and Sky Temperature dependent Direct Solar Internal Distribution: Calculated by the programme Solar Timing for solar data calculation: Midpoint of the hour Table A.3 Calculation methods and default solution algorithms used in the BPS tools. Table A.3 Tool A Tool B Simulation Solution (Loads, Plant, System Calculations): Simultaneous calculations Simultaneous calculations Time Step Resolution: Sub-hourly Sub-hourly Heat Balance Solution Algorithms; Surface and air heat balance Surface and air heat balance Conduction Solution Method; 1-dimensional 1-dimensional Conduction Transfer Functions Finite Difference Solution Internal Convection Coefficient Calculation: TARP Alamdari & Hammond correlations External Convection Coefficient Calculation: DOE-2 McAdams correlations Interior Surface Long-Wave Radiation Exchange: Script F(exchange coefficients between pairs of surfaces) Long-wave radiation exchange between all zone surfaces Exterior Surface Radiation Exchange: Surface, Air, Ground and Sky Temperature Dependent Surface, Air, Ground and Sky Temperature Dependent Direct Solar Radiation: Weather File Weather File Diffuse Sky Model; Anisotropic Anisotropic Solar Beam Distribution: Falling entirely on the floor Diffusely distributed within the zone Time Point for solar data: Solar timing at the midpoint of each hour Solar timing at the top of each hour
Keywords
- building performance simulation
- default settings
- impact of wind variations
- insulating concrete formwork
- modelling uncertainty
- solar timing