Theoretical analysis on efficiency factor of direct expansion PVT module for heat pump application

Abstract

Direct expansion solar assisted PVT (photovoltaic/thermal) heat pump is a combination of PVT technology and heat pump technology, which can improve the comprehensive conversion efficiency of solar energy, and it is suitable for solar heating applications. In this paper, the efficiency factor of direct expansion PVT module employing roll-bond panel has been theoretically derived, modified, and validated by experimental results. Moreover, the efficiency factor could be used to design, evaluate, and optimize the thermal performance of direct expansion solar assisted heat pump systems. In addition, parameter analysis of four evaporator unit types has been conducted, and the recommendation values of each parameter have also been presented. The simulation results show that the roll-bond evaporator (fluid channel width: 10 mm) with hexagon and rectangle patterns have better temperature distribution uniformity than grid and linear types, and their temperature differences are both 0.038 ℃ while their dimensionless pressure losses are 0.109 and 0.230, respectively. To specifically design different kinds of PVT collector/evaporator or direct expansion evaporators, a novel design method for roll-bond evaporator is proposed, and a combination of hexagon and grid types is recommended for PVT module. Moreover, the recommendation fluid channel width of the roll-bond panel is 8 mm to 13 mm while the scaling ratio is 0.8 to 1.2. The modified efficiency factors are 0.521, 0.564, 0.549, and 0.342 of hexagon, grid, rectangle, and linear types when the fluid channel width is 10 mm, respectively.

Blended Ag nanofluids with optimized optical properties to regulate the performance of PV/T systems

“…With the increase of world population and the aggravation of energy crisis, most countries have devoted themselves to utilizing renewable energy (Shen et al, 2020;Wei et al, 2020). As a sustainable and environment-friendly energy, solar energy has advantages like large reserves, wide distribution and no pollution (Zhang et al, 2020b), and therefore has captured great attentions of researchers and developers (Yao et al, 2020).…”

Performance and application boundary analysis of a solar PV/T heat pump system

“…U L can be expressed aswhere h cv,p-g and h rd,p-g are the thermal conductivity and radiative heat transfer coefficients between the photovoltaic cell and glass cover, respectively, W (m −2 K −1 ); and h cv,g-a and h rd,g-a are the convective and radiative heat transfer coefficients between the glass cover and environment, respectively, W (m −2 K −1 ). The four coefficients can be calculated using the following equations: 20 h rd,p-g = ε p · σ ·( T p + T g )·( T p 2 + T g 2 ) h cv,g-a = 2.8 + 3· v air h rd,g-a = ε g · σ ·( T g + T a )·( T g 2 + T a 2 )where δ g is the thickness of the glass cover, m; λ g is the thermal conductivity of the glass cover, W (m −1 K −1 ); ε p is the emissivity of the PV cell; σ is the Stefan–Boltzmann constant, W (m −2 K −4 ); T g is the temperature of the glass cover, °C; v air is the wind speed, m s −1 ; and ε g is the emissivity of the glass cover.…”

Performance improvement of vapor-injection heat pump system by employing PVT collector/evaporator for residential heating in cold climate region

“…The calculation expression of each heat transfer coefficient could refer to the authors' previous work [34]. The heat transfer rate of the PVT panel equals the heat transfer rate of the assimilated thermal energy minus the total heat loss, calculated by:…”