Reducing Simulation Performance Gap in Hemp-Lime Buildings Using Fourier Filtering †

Ljubomir Jankovic

doi:10.3390/su8090864

Abstract

Mainstream dynamic simulation tools used by designers do not have a built-in capability to accurately simulate the effect of hemp-lime on building temperature and relative humidity. Due to the specific structure of hemp-lime, heat travels via a maze of solid branches whilst the capillary tubes absorb and release moisture. The resultant heat and moisture transfer cannot be fully represented in mainstream simulation tools, causing a significant performance gap between the simulation and the actual performance. The author has developed an analysis method, based on a numerical procedure for digital signal filtering using Fourier series. The paper develops and experimentally validates transfer functions that enhance simulation results and enable accurate representation of behaviour of buildings built from hemp-lime material using the results of a post-occupancy research project. As a performance gap between design simulation and actual buildings occurs in relation to all buildings, this method has a wider scope of application in reducing the performance gap.

Highlights

Dynamic simulation is the only building design tool that enables reasonably accurate relative comparison between different design options
These differences between the actual and the simulated building are the main causes of the performance gap, in the case of hemp-lime bio-composite material, this is exacerbated by the absence of its accurate theoretical description in the simulation model
Extrapolation can often lead to unexpected errors, the rigour of the method presented here gives a reasonable expectation of its accuracy and a potential to reduce the performance gap between dynamic simulation and actual building performance in buildings built from hemp-lime material

Summary

Introduction

Dynamic simulation is the only building design tool that enables reasonably accurate relative comparison between different design options. Dynamic simulation is far less accurate in predicting the absolute performance of the chosen design [1] This inaccuracy is caused by differences between the actual building and the representation of its properties in the simulation model. The theoretical values of heat transfer properties of building materials may not correspond to the actual properties, due to different chemical composition and moisture content; behaviour of building users in the actual building may be oversimplified in the simulation model; and the build quality of the actual building, as it often happens, may be worse than the theoretical representation of the building in the simulation model These differences between the actual and the simulated building are the main causes of the performance gap, in the case of hemp-lime bio-composite material, this is exacerbated by the absence of its accurate theoretical description in the simulation model. The existence of the performance gap caused by inaccurate simulation leads to practical problems: over-specification of the heating or cooling plant, increased capital cost, prolonged part-load operation of the plant, increased running costs, increased energy consumption, and increased carbon dioxide emissions

Methods

Results

Conclusion