New small-scale experiments are carried out to study the effect of groundwater flow on the thermal performance of water ground heat exchangers for ground source heat pump systems. Four heat exchanger configurations are investigated; single U-tube with circular cross-section (SUC), single U-tube with an oval cross-section (SUO), single U-tube with circular cross-section and single spacer with circular cross-section (SUC + SSC) and single U-tube with an oval cross-section and single spacer with circular cross-section (SUO + SSC). The soil temperature distributions along the horizontal and vertical axis are measured and recorded simultaneously with measuring the electrical energy injected into the fluid, and the borehole wall temperature is measured as well; consequently, the borehole thermal resistance (R_b) is calculated. Moreover, two dimensional and steady-state CFD simulations are validated against the experimental measurements at the groundwater velocity of 1000 m/year with an average error of 3%. Under saturated conditions without groundwater flow effect; using a spacer with SUC decreases the R_b by 13% from 0.15 m·K/W to 0.13 m·K/W, also using a spacer with the SUO decreases the R_b by 9% from 0.11 m·K/W to 0.1 m·K/W. In addition, the oval cross-section with spacer SUO + SSC decreases the R_b by 33% compared with SUC. Under the effect of groundwater flow of 1000 m/year; R_b of the SUC, SUO, SUC + SSC and SUO + SSC cases decrease by 15.5%, 12.3%, 6.1% and 4%, respectively, compared with the saturated condition.

A zero-energy building (ZEB) requires an innovative integration of technologies, in which windows play a paramount role in energy reduction, storage, and generation. This study contributes to four innovative designs of sliding smart windows. It integrates air-gap (AG), phase change material (PCM), photovoltaic (PV), and vacuum glazing (VG) technologies. These smart sliding windows are proposed to generate electricity along with achieving efficient thermal insulations and heat storage simultaneously. A two-dimensional multiphysics thermal model that couples the PCM melting and solidification model, PV model, natural convection in the cavity, and the surface-to-surface radiation model in the vacuum gap are developed for the first time. The model is validated with data in the literature. The transient simulations were carried out to investigate the thermo-electrical performance of a window with an area of 1 m by 1 m for the meteorological conditions of Kuwait city on the 10th of June 2018, where the window was oriented to south direction. The results showed that the total solar heat energy gain per unit window area is 2.6 kWh, 0.02 kWh, 0.22 kWh, 1.48 kWh, and 0.2 kWh for the double AG, AG + PV + PCM + VG, PV + PCM + VG, AG + PV + PCM, and the ventilated AG + PV + PCM + VG, respectively. The results elucidate the advantages of the integration of VG in this integrated sliding smart window. The daily generated PV electrical energy in these systems is around 1.3 kWh, 1.43 kWh, and 1.38 kWh for the base case with double AG, PV + PCM + VG, and the ventilated AG + PV + PCM + VG respectively per unit window area.

Heat advection caused by groundwater flow can potentially improve the performance of a borehole heat exchanger. However, the required flow velocity is not achieved under most natural conditions. This study focuses on artificial groundwater flow generated by pumping and investigates the associated effect in a lowland area near the Toyohira River alluvial fan, Sapporo, Japan. Thermal response test results are compared under natural and artificial groundwater flow conditions. A pumping well is constructed one meter from the borehole. Temperature profiles are measured in the U-tube during testing, using a pair of optic fiber distributed temperature sensors. The effective thermal conductivity is calculated from the profiles obtained in each 10-m sub-layer; this thermal conductivity is termed the stepwise thermal conductivity. Additionally, the upward flow velocity in the pumping well is measured to estimate the mean groundwater flow velocity at the borehole. The results show that effective thermal conductivity increases at depths less than 50 m, where the pumping creates mean velocities greater than 0.1 m d⁻¹ in each sub-layer (1.5 md⁻¹ on average). Thus, a borehole length of 50 m is more reasonable at the test site for its efficiency in a ground source heat pump system coupled with the pumping well than that used.