Vertical Planar Liquid-Vapour Thermal Diodes (PLVTD) and their application in building façade energy systems

Abstract

Thermal diode; one-way heat transfer; switchable insulation; net zero energy buildings; building facade; solar collector; Highlights• Vertical planar thermal diodes realised & tested at realistic scales (0.15 & 0.98m 2 )• Reverse mode insulation (1.7<Ur<12 W•m -2 K -1 ) depends primarily on depth (22<x<70mm)• Forward mode heat transfer depends on temperature & heat flux (50<Uf<900 W•m -2 K -1 )• One-dimensional lumped parameter heat transfer model augmented & validated • Applications in solar collectors and climate control building envelopes discussed

BIPV/T facades – A new opportunity for integrated collector-storage solar water heaters? Part 2: Physical realisation and laboratory testing

“…Measured trends are in reasonable agreement with predicted performances which provides further model validation. Small discrepancies between modelled and measured results are primarily associated with the thermal diode conductance which was modelled as constant Uf,12 ≈ 38W•m -2 K -1 but varied in practice (95% of values varied in the range ±17 W•m -2 K -1 as reflected by the scatter in the measured data) owing to its temperature and heat flux dependence (refer to Pugsley et al, 2020). It should be noted that data on Figure 10 excludes transients during the first 30 minutes of each collection period when the rise in tank temperature occurs very much slower than the rise in absorber temperature owing to the lag introduced by the latent thermal mass associated with liquid-vapour phase change within the PLVTD.…”

“…One of the most unique aspects of the BIPV-PLVTD-ICSSWH concept is the thermal diode component. Whilst our experimental prototype functioned adequately during the laboratory tests, the pumped evaporator wetter mechanism was found to be problematic in respect of vacuum leakage, excessive power consumption, and uneven wetting of the evaporator plate which impaired the forward mode thermal diode performance (described in more detail by Pugsley et al, 2017Pugsley et al, & 2020. It was also found that the strut array support structure inside the PLVTD (see Figure 4) was difficult to fabricate.…”

“…Whilst ICSSWH systems suffer significant overnight heat losses (eg unavailability of stored heat for morning bathing etc) they offer a number of advantages in respect of cost, space, and inherent passive protection from overheating. Recent studies by Pugsley et al (2016Pugsley et al ( , 2017Pugsley et al ( , 2020 proposed the use of Planar Liquid-Vapour Thermal Diodes (PLVTD) to reduce problems of overnight heat loss in flat-form ICSSWH collectors.…”

BIPV/T facades – A new opportunity for integrated collector-storage solar water heaters? Part 1: State-of-the-art, theory and potential

“…Planar Liquid-Vapour Thermal Diodes (PLVTD) consist of two parallel plates of area A=yz separated by a cavity of depth x which contains a quantity of working fluid maintained in a thermodynamic state close to saturation (Pugsley et al, 2019(Pugsley et al, & 2020.…”

“…During reverse mode operation, the hottest plate is kept dry so that no vapour can be generated, no latent heat transfer occurs, and the partially evacuated cavity acts as an insulator (see Figure 4). Requirements, functions and interactions of the main PLVTD components can be summarised as follows, based on Pugsley et al (2017Pugsley et al ( & 2020:…”