Optimization of Solar Thermal Fraction in PVT Systems

AbstractOver the last years there has been a growing interest in hybrid Photovoltaic-Thermal (PVT) collectors for their applications in building integration. The hybrid systems integrate the features of the photovoltaic and the solar thermal (water or air) systems in one combined product/system. The PV electricity production in a hybrid system could be significantly different from the one of a standard PV module because, mainly, cells temperatures change according to the amount of heat removed by the absorber of the PVT system and, moreover, to the insulation level of the PVT system. This last factor is related to many parameters, among which it is possible to identify water flow rate and temperature, which are directly related to PVT plant configuration and size as a function of users heat demand. Starting from these considerations, the aim of this paper is to calculate the optimal value of solar fraction f for hybrid PVT systems, under energetic end economic point of views, and to find a correlation between the percentage of heat demand covered by the PVT system and photovoltaic cells temperature. In fact, changes in solar fraction imply different average cells operating temperatures and consequently, variation in total energy efficiency. For this purpose, simulations of liquid-based PVT systems for domestic application have been performed through TRNSYS energy simulation tools, carrying out subsequently a detailed energetic and economic analysis

Solar Heating and Air-Conditioning by GSHP Coupled to PV System for a Cost Effective High Energy Performance Building

Abstract Energy requirements for new buildings show the strong direction given by UE Directives to improve energy performance in buildings according to economic feasibility. Nowadays it is possibile to const ruct new buildings reaching a substancial reduction in energy consumption containing prices and time for the construction. In architectural competitions are always included architectural, energy and economic parameters of quality which are decisive in the success of the project design. A Housing Contest to collect projects with high performance and low cost for residential buildings for the Municipality of Comune di Milano, Italy, and the future construtions in the local area was launched by the to involve architects and professionals on the future development of the urban landscape giving specific requirements to achieve high performance. These requirements were focused on energy quality, acoustic quality, quality of the building site, guaranteed time schedule, prefabrication, economic affordability in comparison with the market trend of costs. The project presented in the paper is one of the chosen building by the Municipality to represent a pilot project for possible future constructions. In the Contest all the design group were in team with a builder to verify and guarantee the costs of the construction. The high energy performance required coupled to the low cost assured by the projects gave the Municipality a good example of how is possible to fulfill quality levels recommended by EU Directives and national regulations. In the Contest a high energy performance for heating was compulsory. The project described in the following paragraphs not only fulfill this energy requirement but also is almost self-sufficiency since it provides the energy for heating, cooling and common electrical demand

An Algorithm for Designing Dynamic Solar Shading System

Abstract The present study aims to define and validate an analytical procedure for determining the optimal movement profile for dynamic shading system based on the horizontal mobile blinds for high level of illumination and visual comfort in indoor environments. The algorithm is developed to design a dynamic solar shading system for an office building (Ergo Tower) situated in Milan, Italy. The calculations take into account variables such as geographic location, date, time, surface orientations and geometrical and functional characteristics of shading system. In the first step the solar coordinates and the variation of solar incidence angle on the building surfaces have been defined. Using the equations of solar geometry the typical solar path (sun position e.g. solar altitude, azimuth etc.) corresponding to the specific location for the entire year and also the variation of the incidence angle with which the direct radiation affect the building surfaces are described. Based on the geometry of shading system, the optimal values of inclination of the profiles can be calculated. Finally, due to the technical limitations of the systems, the feasible configuration has been determined corresponding to an angle close to the optimal values of inclination for ensuring appropriate shading. This test system allows the definition of the movement of dynamic solar shading systems based on a specific location and geometrical/mechanical characteristics of a certain technical solution

Photovoltaic-thermal solar-assisted heat pump systems for building applications: Integration and design methods

Abstract The photovoltaic-thermal collector is one of the most interesting technology for solar energy conversion, combining electric and thermal energy production in a single device. Vapour-compression heat pump is already considered the most suitable clean technology for buildings thermal energy needs. The combination of these two technologies in an integrated "photovoltaic-thermal solar-assisted heat pump" (PVT-SAHP) system allows reaching a high fraction of the building thermal needs covered by renewable energy sources and to improve the performances of both the photovoltaic-thermal collector and the heat pump. The first is cooled down increasing its energy conversion efficiency, while providing low-temperature thermal energy to the second, which benefits from a higher evaporation temperature. The review study presents the state-of-art of photovoltaic-thermal solar-assisted heat pump systems intended to cover thermal energy needs in buildings, with a particular focus on the integration methodologies, the possible configurations, the use of different sources and the design of sub-system components. These issues are addressed by much scientific research, to improve the reliability and applicability of this technology, as an option for the building decarbonization. This study aims to present PVT-SAHP systems in an organic and critical way to propose a useful tool for future research developments. More in detail, the work highlights the fact that the integration of photovoltaic-thermal collectors as evaporator of the heat pump in direct-expansion systems allows the highest heat recovery and performances. However, the distinction of the two circuits lead to more reliable, flexible and robust systems, especially when combined with a second heat source, being able to cover both heating and cooling needs. The implementation of real-time control strategy, as well as the continuous development of the compressor and refrigerant industries is positively influencing this technology, which is receiving more and more attention from scientific research as a suitable solution for nearly zero energy buildings

IEA ECES Annex 31 Final Report - Energy Storage with Energy Efficient Buildings and Districts: Optimization and Automation

At present, the energy requirements in buildings are majorly met from non-renewable sources where the contribution of renewable sources is still in its initial stage. Meeting the peak energy demand by non-renewable energy sources is highly expensive for the utility companies and it critically influences the environment through GHG emissions. In addition, renewable energy sources are inherently intermittent in nature. Therefore, to make both renewable and nonrenewable energy sources more efficient in building/district applications, they should be integrated with energy storage systems. Nevertheless, determination of the optimal operation and integration of energy storage with buildings/districts are not straightforward. The real strength of integrating energy storage technologies with buildings/districts is stalled by the high computational demand (or even lack of) tools and optimization techniques. Annex 31 aims to resolve this gap by critically addressing the challenges in integrating energy storage systems in buildings/districts from the perspective of design, development of simplified modeling tools and optimization techniques

Adaptive-predictive control strategy for HVAC systems in smart buildings – A review

Abstract High share of energy consumption in buildings and subsequent increase in greenhouse gas emissions along with stricter legislations have motivated researchers to look for sustainable solutions in order to reduce energy consumption by using alternative renewable energy resources and improving the efficiency in this sector. Today, the smart building and socially resilient city concepts have been introduced where building automation technologies are implemented to manage and control the energy generation/consumption/storage. Building automation and control systems can be roughly classified into traditional and advanced control strategies. Traditional strategies are not a viable choice for more sophisticated features required in smart buildings. The main focus of this paper is to review advanced control strategies and their impact on buildings and technical systems with respect to energy/cost saving. These strategies should be predictive/responsive/adaptive against weather, user, grid and thermal mass. In this context, special attention is paid to model predictive control and adaptive control strategies. Although model predictive control is the most common type used in buildings, it is not well suited for systems consisting of uncertainties and unpredictable data. Thus, adaptive predictive control strategies are being developed to address these shortcomings. Despite great progress in this field, the quantified results of these strategies reported in literature showed a high level of inconsistency. This is due to the application of different control modes, various boundary conditions, hypotheses, fields of application, and type of energy consumption in different studies. Thus, this review assesses the implementations and configurations of advanced control solutions and highlights research gaps in this field that need further investigations

Optimal Balance between Heating, Cooling and Environmental Impacts: A Method for Appropriate Assessment of Building Envelope’s U-Value

In Europe, the recent application of regulations oriented to zero-energy buildings and climate neutrality in 2050 has led to a reduction in energy consumption for heating and cooling in the construction sector. The thermal insulation of the building envelope plays a key role in this process and the requirements about the maximum allowable thermal transmittance are defined by country-specific guidelines. Typically, high insulation values provide low energy consumption for heating; however, they may also entail a risk of overheating in summer period and thus negatively affect the overall performance of the building. In addition, the embodied energy and related emissions caused by the manufacturing and transportation processes of thermal insulation cannot be further neglected in the evaluation of the best optimal solution. Therefore, this paper aims to evaluate the influence in terms of embodied and operational energy of various walls’ thermal insulation thicknesses on residential buildings in Europe. To this end, the EnergyPlus engine was used for the energy simulation within the Ladybug and Honeybee tools, by parametrically conducting multiple iterations; 53 variations of external wall U-value, considering high- and low-thermal-mass scenarios, were simulated for 100 representative cities of the European context, using a typical multifamily building as a reference. The results demonstrate that massive walls generally perform better than lightweight structures and the best solution in terms of energy varies according to each climate. Accordingly, the wall’s thermal transmittance for the samples of Oslo, Bordeaux, Rome and Almeria representative of the Continental, oceanic temperate, Mediterranean, and hot, semi-arid climates were, respectively: 0.12, 0.26, 0.42, and 0.64 W/m2K. The optimal solutions are graphically reported on the map of Europe according to specific climatic features, providing a guidance for new constructions and building retrofit

development of an interactive building energy design software tool

Energy efficiency is one of the most important topics worldwide, nevertheless, each region has its own specifics, which have to be considered. This is especially important for online tools that deliver comprehensive information on energy efficiency and renewable energy for average consumer as well as for municipalities and governments. These tools are essential for energy retrofit of existing building for energy saving as well as designing of new energy-efficient buildings and also for designing and sizing renewable energy technologies such as solar home system. A dynamic interactive building energy design software tool has been developed especially tailored taking care about main features required for Sub-Saharan African context, under a joint agreement (research project) between Politecnico di Milano and UN-Habitat. In this chapter, the results of testing of the software tool for building geometry have been presented