Water table depth data for use in modelling residential building ground-coupled heat transfer Melissa James a, * , Zhengen Ren b , Tim J. Peterson c , Dong Chen b a Energy, CSIRO, Melbourne, Private Bag 10, Clayton South, VIC, 3169, Australia b Energy, CSIRO, Melbourne, Australia c Department of Civil Engineering, Monash University, Clayton, Australia ARTICLE INFO Keywords: Residential energy efficiency Energy rating Water table depth Ground-coupled heat transfer ABSTRACT Water table depth influences ground-coupled heat transfer through the foundation of residential buildings and impacts energy consumption required for heating and cooling. Knowledge of water table depth in Australia is required to determine the extent of this impact on Australian housing. This study conducts a review of water table depth data in Australia and presents a case study indicating that 46% of Victoria’s Urban Growth Zone has water table depths estimated to be less than 5 metres. Houses built here with no insulation to the slab and on average soil type would have a 24%–54% higher heat loss than if there was no water table. The degree of impact varies with changing water table depth in different locations and over time. The uncertainty associated with estimated water table depth is large. Extending residential energy rating tools to account for water table depth would require the development of Australia-wide water table depth data. 1. Introduction Energy efficiency in residential buildings contributes to energy sav- ings, energy security, reduced greenhouse gas emissions, lower energy bills for households, and improved comfort and health of occupants. New residential buildings in Australia are subject to the energy efficiency (thermal performance) provisions of the National Construction Code (NCC). When designed and built they must meet a prescribed minimum standard. Since May 2016, 77% of new residential buildings demon- strated compliance with the NCC energy efficiency provisions by using a Nationwide House Energy Rating Scheme (NatHERS) accredited soft- ware tool, which estimates a home design’s potential heating and cooling energy use (CSIRO, 2020). NCC energy efficiency requirements have become more stringent over time and will continue to do so. In February 2019 the Council of Australian Governments’ (COAG) Energy Council agreed to the Trajectory for Low Energy Buildings, a national plan that sets a trajectory towards zero energy (and carbon) ready buildings for Australia. As above-ground components of the building fabric have become more energy efficient over time, heat losses through a building’s foundation have become relatively more significant. Nowadays, for a well-built house the ground-coupled heat loss can account for 30%–50% of the total heat loss (Deru, 2003). Incorporating detailed modelling of ground-coupled heat transfer (GCHT) in energy rating tools has become more critical. Ground-coupled heat loss can be significantly impacted by ground- water, soil thermal conductivity and ground surface conditions as shown in various measurement and modelling studies. A measurement study conducted by Ackerman and Dale (1988) investigated heat loss through the floor. The measurement duration was too short and information on key factors (such as soil conductivity) were insufficient. This situation was improved by a four-year site measurement of heat flow in slab-on-ground floors on wet soils by Trethowen and Delsante (1998). Several previous analytical studies investigated steady-state heat transfer for a slab-on-ground floor over a water table. Krarti et al. (1988) applied the interzone temperature profile estimation (ITPE) technique to model heat transfer in a slab-on-ground floor for different groundwater depths. Delsante (1993) used conformal transformation to solve the two-dimensional steady-state problem of the effect of water table depth and temperature on the total heat flux through a slab-on-ground floor. For an infinite groundwater flow rate, approximate expressions for the ground heat loss through the entire floor were derived by Hagentoft (1996) using linear superposition of three thermal processes. Chen (2013) developed explicit analytical solutions for two-dimensional steady-state heat transfer rates from a long-narrow slab-on-ground floor over a constant temperature water table at a finite depth. * Corresponding author. E-mail addresses: Melissa.James@csiro.au (M. James), Zhengen.Ren@csiro.au (Z. Ren), tim.peterson@monash.edu (T.J. Peterson), dong.chen@csiro.au (D. Chen). Contents lists available at ScienceDirect Cleaner Engineering and Technology journal homepage: www.journals.elsevier.com/cleaner-engineering-and-technology https://doi.org/10.1016/j.clet.2021.100096 Received 20 October 2020; Received in revised form 21 February 2021; Accepted 8 April 2021 2666-7908/© 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by- nc-nd/4.0/). Cleaner Engineering and Technology 3 (2021) 100096