Andreas K. Athienitis

Investigation of the Thermal Performance of a Passive Solar Test-Room with Wall Latent Heat Storage

Abstract An experimental and numerical simulation study is presented of the application of phase change materials (PCM) in building envelope components for thermal storage in a passive solar test-room. Gypsum board impregnated with a phase change material was used. The experimental study was conducted in a full-scale outdoor test-room with the PCM gypsum board as inside wall lining. An explicit finite difference model was developed to simulate the transient heat transfer process in the walls. Reasonable agreement between the simulation and the experimental results was observed. It was shown that the utilization of PCM gypsum board in a passive solar building may reduce the maximum room temperature by about 4 °C during the daytime and can reduce the heating load at night significantly.

A methodology for simulation of daylight room illuminance distribution and light dimming for a room with a controlled shading device

This paper presents a methodology for detailed daylighting numerical simulation of an office space with an advanced window system and calculation of dimming levels for electric lights to provide the additional illuminance required so as to minimise electric energy consumption for lighting. The particular system considered is a double-glazed window with motorized highly reflective blinds between the two glazings installed in an outdoor test-room and operated by a custom-built computerised building automation system. The daylight transmittance equations for the window system were determined from experimental measurements. A major requirement for on-line control is the automatic determination of the blind tilt angle required in order to reduce glare and simultaneously allow the maximum possible amount of daylight into the room. Numerical simulations of blind control and light dimming are presented for a typical office.

Wind Driven Flow through Openings – A Review of Discharge Coefficients

Abstract This paper reviews the current literature on discharge coefficients (CD) of openings and compares different studies for wind-driven cross-ventilation. Considerable variation of discharge coefficients with opening porosity, configuration (shape and location in the façade), wind angle and Reynolds number is shown. Consequently, the use of a constant CD value such as that given in textbooks or other sources might be an invalid simplification. Scaling, upstream flow conditions, internal partitions and the assumptions of turbulent flow, sealed body and energy dissipation made for the application of the orifice equation should be considered in wind tunnel experiments of cross-ventilation.

The effect of solar radiation on dynamic thermal performance of floor heating systems

This paper presents a numerical investigation of transient heat transfer in floor heating systems using a three-dimensional explicit finite difference model. The study focused on the influence of the cover layer and incident solar radiation on floor temperature distribution and on energy consumption. Complete and partial (area) carpets were considered as well as hardwood cover layers over concrete or gypcrete thermal storage. Experimental and simulation results for an outdoor testroom reveal that solar beam radiation can cause a local floor surface temperature in the illuminated area 8°C higher than that in the shaded area. Partial carpet cover further increases floor surface temperature differences up to 15°C when solar radiation is absorbed. Solar radiation stored in the floor thermal mass was found to reduce heating energy consumption significantly (30% or more). Increase of thermal mass thickness from 5 cm to 10 cm did not lead to higher energy savings with conventional proportional-integral control. Advanced control algorithms need to be developed to maximize energy savings while maintaining good thermal comfort.

Numerical and experimental study of heat transfer in a BIPV-thermal system

This paper presents a computational fluid dynamics (CFD) study of a building-integrated photovoltaic thermal (BIPV/T) system, which generates both electricity and thermal energy. The heat transfer in the BIPV/T system cavity is studied with a two-dimensional CFD model. The realizable k-e model is used to simulate the turbulent flow and convective heat transfer in the cavity, including buoyancy effect and long-wave radiation between boundary surfaces is also modeled. A particle image velocimetry (PIV) system is employed to study the fluid flow in the BIPV/T cavity and provide partial validation for the CFD model. Average and local convective heat transfer coefficients are generated with the CFD model using measured temperature profile as boundary condition. Cavity temperature profiles are calculated and compared to the experimental data for different conditions and good agreement is obtained. Correlations of convective heat transfer coefficients are generated for the cavity surfaces; these coefficients are necessary for the design and analysis of BIPV/T systems with lumped parameter models. Local heat transfer coefficients, such as those presented, are necessary for prediction of temperature distributions in BIPV panels.

Predictive control of radiant floor heating and solar-source heat pump operation in a solar house

Solar radiation can supply a significant portion of the energy requirements of a house through the harmonized use of passive solar design and building-integrated active solar energy systems (e.g., building-integrated photovoltaic, photovoltaic/thermal systems, or solar thermal collectors). Given the variability of solar radiation, energy storage technologies, along with carefully planned control strategies, can offer significant benefits for the performance of these systems in terms of energy consumption, peak load reduction, and thermal comfort for the occupants. This article investigates the application of a predictive control methodology for a solar house. The case study is a room with a simple geometry with high insulation and air-tightness values and large windows (i.e., a typical room found in a passive solar house). Predictive control is applied at two different, but closely linked, levels: (a) local-loop control of a radiant floor heating system and (b) supervisory control of the temperature of a water tank—used for thermal energy storage—heated with a solar-source heat pump. The development of control strategies is facilitated by the use of simplified building models obtained from more detailed models appropriate for building simulation. This methodology provides insight into the relevance of different design and control parameters and makes it easier to apply software tools designed specifically for testing control algorithms.

Convective Heat Transfer Coefficients in a Building-Integrated Photovoltaic/Thermal System

This paper presents an experimental study for the development of convective heat transfer correlations for an open loop air-based building-integrated photovoltaic/thermal (BIPV/T) system. The BIPV/T system absorbs solar energy on the top surface, which includes the photovoltaic panels and generates electricity while also heating air drawn by a variable speed fan through a channel formed by the top roof surface with the photovoltaic modules and an insulated attic layer. The BIPV/T system channel has a length/hydraulic diameter ratio of 38, which is representative of a BIPV/T roof system for 30-45 deg tilt angles. Because of the heating asymmetry in the BIPV/T channel, two average Nusselt number correlations are reported as a function of Reynolds number: one for the top heated surface and the other for the bottom surface. For the top heated surface, the Nusselt number is in the range of 6-48 for Reynolds numbers ranging from 250 to 7500. For the bottom insulated surface, the Nusselt number is in the range of 22-68 for Reynolds numbers ranging from 800 to 7060. This paper presents correlations for the average Nusselt number as a function of Reynolds number; this correlation is considered adequate for the design of BIPV/T systems where forced convection dominates. Local Nusselt number distributions are also presented for laminar and turbulent flow conditions.

The relationship between net energy use and the urban density of solar buildings

There is a paradoxical relationship between the density of solar housing and net household energy use. The amount of solar energy available per person decreases as density increases. At the same time, transportation energy, and to some extent, household operating energy decreases. Thus, an interesting question is posed: how does net energy use vary with housing density? This study attempts to provide insight into this question by examining three housing forms: low-density detached homes, medium-density townhouses, and high-density high-rise apartments in Toronto. The three major quantities of energy that are summed for each are building operational energy use, solar energy availability, and personal transportation energy use. Solar energy availability is determined on the basis of an effective annual collector efficiency. The results show that under the base case in which solar panels are applied to conventional homes, the high-density development uses one-third less energy than the low-density one. Improving the efficiency of the homes results in a similar trend. Only when the personal vehicle fleet or solar collectors are made to be extremely efficient does the trend reverse—the low-density development results in lower net energy.

Investigation of thermal performance of a passive solar building with floor radiant heating

Abstract This paper presents a theoretical study of an integrated radiant floor heating–direct gain passive solar system. Thermal mass is utilized both for storage of auxiliary heating energy and direct solar gains incident on the floor. An explicit finite difference model is developed to accurately model nonlinear effects and auxiliary heating control. The numerical simulation model is employed to study the performance of a passive solar outdoor test-room with different amounts of thermal mass under various control strategies with constant and sinusoidal room thermostat setpoints. A satisfactory thermal mass is determined based on energy savings, reduction of room temperature swings, and prevention of floor surface overheating. Control of auxiliary heating based on a room effective (operative) temperature is shown to result in improved thermal comfort and higher utilization of passive solar gains as compared to room air temperature control.

Modeling, Design, and Optimization of Net-Zero Energy Buildings

Building energy design is currently going through a period of major changes. One key factor of this is the adoption of net-zero energy as a long term goal for new buildings in most developed countries. To achieve this goal a lot of research is needed to accumulate knowledge and to utilize it in practical applications. In this book, accomplished international experts present advanced modeling techniques as well as in-depth case studies in order to aid designers in optimally using simulation tools for net-zero energy building design. The strategies and technologies discussed in this book are, however, also applicable for the design of energy-plus buildings. This book was facilitated by International Energy Agencys Solar Heating and Cooling (SHC) Programs and the Energy in Buildings and Communities (EBC) Programs through the joint SHC Task 40/EBC Annex 52: Towards Net Zero Energy Solar Buildings R&D collaboration. After presenting the fundamental concepts, design strategies, and technologies required to achieve net-zero energy in buildings, the book discusses different design processes and tools to support the design of net-zero energy buildings (NZEBs). A substantial chapter reports on four diverse NZEBs that have been operating for at least two years. These case studies are extremely high quality because they all have high resolution measured data and the authors were intimately involved in all of them from conception to operating. By comparing the projections made using the respective design tools with the actual performance data, successful (and unsuccessful) design techniques and processes, design and simulation tools, and technologies are identified. Written by both academics and practitioners (building designers) and by North Americans as well as Europeans, this book provides a very broad perspective. It includes a detailed description of design processes and a list of appropriate tools for each design phase, plus methods for parametric analysis and mathematical optimization. It is a guideline for building designers that draws from both the profound theoretical background and the vast practical experience of the authors.