Athanasios Tzempelikos

Review of modelling approaches for passive ceiling cooling systems

Passive ceiling cooling systems can lead to reduced cooling requirements, less fan energy and downsized ductwork, compared to conventional all-air systems. Additionally, radiant cooling of occupants allows for improved comfort while allowing for higher operating temperature, improving chiller efficiency. This paper presents a comprehensive review of current modelling approaches for passive ceiling cooling systems in order to document the state of the art and identify current research gaps and modelling development needs. Modelling methods are separated in three main categories, based on the domain of interest: component or “passive ceiling cooler” models, “indoor environment” models and “integrated” models. Simplified, detailed and empirical models are presented for each category. Different modelling approaches may be appropriate for different purposes (design vs. control analysis, and system simulation vs. whole building performance). The study summarizes useful findings, modelling limitations and applications, and presents needs for further modelling and simulation research, including passive chilled beams.

An integrated method and web tool to assess visual environment in spaces with window shades

The current article presents a synthesis of the most recent metrics (visual comfort autonomy, lighting energy use, and view clarity) for assessing the visual environment performance of spaces with window shades, in the form of an integrated framework—interactive web-based tool. A daylighting and glare simulation model is used to calculate interior daylight distributions, luminance mapping, and annual spatial visual performance metrics. Then, a decision strategy was developed for selecting fabric properties based on different priorities: maximizing outside view, maximizing energy performance, or a balanced approach with fixed or flexible criteria to avoid compromises, all under visual comfort constraints. The models and decision strategies were implemented into a web-based tool, which includes a database of different design configurations (climate, envelope configuration, orientation, glazing size and properties, comfort restrictions, occupant view directions, etc.) and either provides recommendations for selecting shade properties based on the variation of the three visual performance metrics, or compares different configurations with detailed output information. The tool, under further development, is currently available to the public and can be used to obtain preliminary information about the comfort, energy, and view clarity performance of spaces will roller shades, without the need of high expertise or complex simulations.

Comfort and energy performance analysis of different glazing systems coupled with three shading control strategies

Shading control strategies are often required to optimize the balance between solar gains, daylight availability, glare protection, and view to the outside. Automated shading operation, when properly designed, may avoid performance losses due to manual operation while maintaining indoor environmental comfort. In this work, the integrated performance of different glazing systems coupled with three control approaches for roller shades is presented for a typical office space. The first control is a standard open–closed operation based on a workplane illuminance range, while the other two are able to set intermediate shade positions according to the solar position to maximize daylighting. The third control addresses excessive daylight on the workplane by imposing a workplane illuminance threshold to reduce the risk of daylight discomfort glare. Daysim, based on Radiance and the daylight coefficient method, was used to calculate the annual illuminance profile over the workplane, and Evalglare was used to calculate glare indexes. EnergyPlus was used for thermal comfort and energy analysis. The results were processed through a MATLAB code for transferring required information from one tool to another. Moreover, to assess the global performance of the shading controls and fenestration configurations studied, visual and thermal comfort were evaluated through a set of metrics able to express both the availability (the fraction of time with acceptable comfort conditions at specific positions) and the spatial usability (the fraction of space simultaneously within comfort range at specific moments). The energy performance was also quantified in terms of primary energy demand for heating, cooling, and lighting. The results showed that it is possible to balance daylighting, thermal and visual comfort, and energy use. This can be achieved by simultaneously selecting shading controls that allow adequate daylight without causing glare, and glazing properties with good thermal performance that allow adequate daylight (high visible transmittance) but limit solar gains (lower solar transmittance or solar heat gain coefficient [SHGC]) for moderate and cooling-dominated climates.

Modeling high-performance buildings

We are extremely pleased to present this special issue of HVAC&R Research on “Modeling High Performance Buildings.” With ten original research papers related to different aspects of building performance, it represents an international overview (from almost every continent) of technological developments to enable better modeling of building systems and components with respect to energy and comfort—for homes, apartment buildings, and commercial buildings. While several papers are directly related to HVAC systems and components, other papers focus on predictive controls in solar houses, phase change materials, geothermal systems, airflow networks, and radiant/hydronic floor and ceiling panels. With such a wide variety of topics, it is easy to understand that modeling building systems and subsystems is a challenge and involves multiple disciplines and areas of expertise. The articles presented in this issue are significantly updated and expanded versions and were selected from papers presented at the 1st International High Performance Building Conference at Purdue, which was held in conjunction with the 20th International Compressor Engineering Conference and the 13th International Refrigeration and Air Conditioning Conference at Purdue in July 2010. With more than 300 papers presented, more than 600 total participants, and support from several organizations, including ASHRAE, these conferences are a major event for exchange of ideas, information, and presentations of cutting-edge research in the areas of compressors, refrigeration, and buildings. The conference covered several aspects of building design and operation, including HVAC systems, building envelopes and facades, building simulation and modeling, performance monitoring and diagnostics, renewable energy systems in buildings, building thermal systems and controls, indoor air quality, building materials, lighting and daylighting, natural and hybrid ventilation, thermal and visual comfort, solar energy systems, and net-zero energy buildings. The selected papers are aligned with the journal focus and present new developments on modeling building systems in order to achieve higher performance. Utilization of advanced building technologies and sophisticated control schemes is critical in order to approach net zero energy performance in homes. The first article by Candanedo and Athienitis presents a new predictive control methodology for a solar house with radiant floor heating (direct solar gains) and a solar source heat pump (building-integrated photovoltaic/thermal system). Transfer functions were developed between inputs (climatic conditions) and outputs (e.g., indoor air temperature) and used in a dynamic simulation tool with predictive control strategies to optimize the system for a higher level control strategy. The study showed that a supervisory predictive control algorithm, applied to schedule the set-point curve of thermal energy storage, can significantly improve the performance of a solar-source heat pump