Thermoeconomic analysis and optimization of high efficiency solar heating and cooling systems for different Italian school buildings and climates

The paper investigates the energetic and economic feasibility of a solar-assisted heating and cooling system (SHC) for different types of school buildings and Italian climates. The SHC system under investigation is based on the coupling of evacuated solar collectors with a single-stage LiBr-H₂O absorption chiller; auxiliary energy for both heating and cooling is supplied by an electric-driven reversible heat pump. The SHC system was coupled with different types of school buildings located in three different Italian climatic zones. The analysis is carried out by means of a zero-dimensional transient simulation model, developed using the TRNSYS software; the analysis of the dynamic behaviour of the building was also included. An economic model is proposed, in order to assess the operating and capital costs of the systems under analysis. Furthermore, a parametric analysis and a subsequent mixed heuristic-deterministic optimization algorithm was implemented, in order to determine the set of the synthesis/design variables that maximize system profitability. The results are encouraging, as for the potential of energy saving. On the contrary, the SHC economic profitability can be achieved only in case of public funding policies (e.g. feed-in tariffs), as always happens for the great majority of renewable energy systems.     

Long term operation of a solar assisted ground coupled heat pump system for space heating and domestic hot water

This paper introduces a solar-assisted ground-coupled heat pump (SAGCHP) system with heat storage for space heating and domestic hot water (DHW) supply. The simulation results of the system's detailed operating performance are presented. The optimization of the system design is carried out by the TRNSYS and a numerical simulation is performed for continuous operation of 20 years under the meteorological conditions of Beijing. Different control strategies are considered and the operational characteristics of each working mode are studied. The simulating results show that the long term yearly average space heating efficiency is improved by 26.3% compared to a traditional ground coupled heat pump (GCHP) system because the solar thermal collecting system is used to elevate the thermal energy in the soil and to provide direct space heating with heat storage. At the same time, the underground heat load imbalance problem for a heating load dominated GCHP is solved by soil recharging during non-heating periods, while extra solar energy is utilized to supply DHW. The flexibility and high efficiency of the SAGCHP system could offer an alternative for space heating and DHW supply by heat pump technology and solar energy in cold winters of northern China.     

Case study of zero energy house design in UK

Possible solutions for zero energy building design in UK are discussed in this paper. Simulation software (EnergyPlus and TRNSYS 16) are employed in this study, where EnergyPlus simulations are applied to enable facade design studies considering building materials, window sizes and orientations and TRNSYS is used for the investigation of the feasibility of zero energy houses with renewable electricity, solar hot water system and energy efficient heating systems under Cardiff weather conditions. Various design methods are compared and optimal design strategies for typical homes and energy systems are provided.     

Energetic, economic and environmental performance of a solar-thermal-assisted HVAC system

A solar-assisted HVAC system was retrofitted in 2006-2009 onto an earlier (1980) energy-efficient building. A hybrid system of flat plate and vacuum tube solar collectors heats water in a large hot storage tank that is delivered to an absorption chiller in the cooling season or directly to heating coils in the heating season. Large chilled water storage tanks are charged off-peak and discharged during the day, cooling the building in parallel with the chiller. Measurements of the seasonal performance of the system are presented. Good overall agreement between actual measurements and earlier numerical modeling results is reported for our system, with one notable discrepancy attributable to the operation of the air terminal units, which requires tuning. In cold seasons, solar thermal energy can easily displace a large fraction of traditional heating sources. In the cooling season, the conversion of heat to cooling capacity incurs several parasitic losses, which if not accounted for properly in the design stage, have the capacity to completely offset any advantage gained from the solar system. The economics of building-scale solar thermal systems are strongly dependent on the cost of energy, and electricity in particular. The economics are favorable where electricity costs are high, and vice-versa.     

Application of night cooling concept to social housing design in dry hot climate

A passive night cooling system was developed and implemented for a new project of social housing. The passive cooling system incorporates a solar chimney in combination with high thermal mass in the building construction. The natural ventilation is enhanced with the help of the solar chimney and night fresh air cools the building structure. The design of this concept was calculated by balancing energy using basic thermal equations for a summer reference day and evaluated using two simulation tools, TRNSYS and TAS. The building has been constructed and actually in process of monitoring.     

直膨式太阳能热泵系统仿真

随着太阳能热利用和热泵技术的成熟及商品化,直膨式太阳能热泵技术将太阳能资源的清洁性、可再生性等特点和热泵系统的节能、高效的优点相结合,极具研究价值。但是目前直膨式太阳能热泵不能产品化推广的主要限制因素是系统设计不合理、运行不稳定、整体性能不佳等问题。现以直膨式太阳能热泵系统的优化和设计匹配为研究目标,同时,建立压缩机、集热器/蒸发器、热力膨胀阀、冷凝器及储热水箱的数学模型。从理论上分析集热器中集热面积、太阳能辐照度、环境温度、压缩机容积及冷凝温度等因素对直膨式太阳能热泵系统热工性能的影响,通过系统仿真及实验研究系统的整体热力性能,并在此基础上给出改善系统性能的建议。     

太阳能地板辐射供暖制冷系统模型仿真

近年来,我国北方地区新建住宅的采暖系统多数采用地板辐射供暖技术,而制冷系统仍采用传统的空调制冷技术,有必要对地板辐射制冷技术的应用进行研究,为此,针对一套实验用太阳房,搭建了太阳能地板辐射供暖制冷系统.通过计算确定了集热器面积、蓄热水箱体积、吸收式制冷机组的制冷量.利用TRNSYS仿真平台建立了系统仿真模型,并对控制策略进行了验证.仿真结果表明,该系统能有效地利用太阳能保持冬季室温18℃左右、夏季26℃左右的舒适温度.     

On the reliability-based design of structures including passive energy dissipation systems

This contribution presents a methodology for stochastic design of structures including vibration protection systems. The approach is then used to investigate the effect of uncertain model parameters on the reliability-based optimal design of structures with a class of passive energy dissipation systems. The uncertainty of structural parameters as well as the variability of future excitations are characterized in a probabilistic manner. The optimal design problem is formulated as a non-linear constrained minimization problem involving multiple design requirements, including reliability constraints related to the structural performance. Failure events defined by a large number of random variables are used to characterize the reliability measures. A sequential optimization approach based on global conservative, convex and separable approximations is implemented for solving the optimization problem. The effects of uncertain model parameters on the performance, robustness and reliability of protected systems is illustrated by two example problems that consider multi-story buildings under stochastic ground excitation.     

Optimal design method for building energy systems using genetic algorithms

In this paper, a new optimal design method for building energy systems is proposed. This method provides the most efficient energy system, best combination of equipment capacity and best operational planning for cooling, heating, and power simultaneously with respect to certain criteria such as energy consumption, CO₂ emission, etc. Specifically for this paper, the authors apply this method to a sample building as a case study. The “Genetic Algorithms (GA)” optimization method, which can resolve nonlinear optimization problems, is adopted for this optimization analysis. Also its applicability is analyzed in a case study. In order to validate the accuracy of this method, the correct optimum solution based on comprehensive inquiries is also calculated. A comparison of the GA solution with the correct solution demonstrates fairly good agreement. The results show that the proposed method is sufficiently capable of determining the optimal design and has the potential to be applied to very complex energy systems with appropriate modifications.     

TRNSYS simulation for solar-assisted liquid desiccant evaporative cooling

ABSTRACT

Recently, desiccant cooling systems are well thought of as a competent method for controlling the water content in the air. A solar flat-plate collector has been used as it decreases the dependency on non-renewable resources. Solar-aided liquid desiccant systems have been used to reduce the dependency of air-conditioning systems on non-renewable sources of energy. Manipal’s humid and searing climate provides certain benefits in setting up such a system. The suggested system has reliability and equipment life and also takes complete advantage of the available solar energy for the renewal of the liquid desiccant. TRNSYS simulation is used to predict the efficiency and feasibility of the system. The temperature and energy-load variations were successfully obtained. An effective simulation was developed whereby the solar air conditioning of a room was indicated.     

太阳能吸收——蒸汽压缩式空调系统的优化分析

通过对太阳能混合式吸收-蒸汽压缩式空调系统中能量转换过程的分析，建立了表征太阳能混合式吸收-范汽压缩式空调系统热性能特性的方程，指出了系统综合性能系数与系统内部不可逆系数以及太阳辐射参数之间的线性关系，并分析了各参数值对最优综合性能系数的影响。     

Numerical simulation and performance assessment of an absorption solar air-conditioning system coupled with an office building

To minimize environmental impact and CO₂ production associated with air-conditioning, it is reasonable to evaluate the prospects of a clean energy source. Solar energy, via thermal collectors can provide a part of the heating needs. Moreover, it can drive absorption chiller in order to satisfy the cooling needs of buildings. The objective of the work is to evaluate accurately the energy consumption of an air-conditioning system including a solar driven absorption chiller. The complete simulation environment includes the absorption chiller itself, the cooling tower, the solar collectors field, heater, storage devices, pumps, heating-cooling distribution, emission system and building. A decrease of primary energy consumption of 22% for heating and cooling is reached when using a solar air-conditioning system instead of classical heating and cooling devices. The modelling of each subsystem is detailed. TRNSYS software modular approach provides the possibility to model and simulate this complete system.     

Experimental study of a solar-assisted ground-coupled heat pump system with solar seasonal thermal storage in severe cold areas

This paper presents the experimental study of a solar-assisted ground-coupled heat pump system (SAGCHPS) with solar seasonal thermal storage installed in a detached house in Harbin. The solar seasonal thermal storage was conducted throughout the non-heating seasons. In summer, the soil was used as the heat sink to cool the building directly. In winter, the solar energy was used as a priority, and the building was heated by a ground-coupled heat pump (GCHP) and solar collectors alternately. The results show that the system can meet the heating-cooling energy needs of the building. In the heating mode, the heat directly supplied by solar collectors accounted for 49.7% of the total heating output, and the average coefficient of performance (COP) of the heat pump and the system were 4.29 and 6.55, respectively. In the cooling mode, the COP of the system reached 21.35, as the heat pump was not necessary to be started. After a year of operation, the heat extracted from the soil by the heat pump accounted for 75.5% of the heat stored by solar seasonal thermal storage. The excess heat raised the soil temperature to a higher level, which was favorable for increasing the COP of the heat pump.     

Modeling of a solar-assisted HVAC system with thermal storage

A numerical model of the solar-thermal-assisted heating, ventilation and air conditioning system in a 7000 m² educational building, situated in a high-desert climate, is used to predict performance and optimize control parameters. Heating, cooling and shoulder seasons are considered in the study. It is found that the solar assist can account for over 90% of the total heating requirements if certain energy conservation strategies are adopted. The solar cooling assist can reduce the total external cooling energy requirement by between 33% and 43%, the latter result achieved, surprisingly, at lower solar array operating temperatures. In the shoulder season, it is possible to operate the building without any external contribution, by heating the building in the coldest hours of the day, and using any excess heat to produce chilled water, to be stored and used when required. Operation of the solar-assisted system within a much larger district energy system makes it possible to achieve maximum performance.     

西藏地区太阳能采暖建筑热工性能优化研究

西藏地区太阳能资源非常丰富且冬季温度低,该地区非常适合大面积推广太阳能采暖系统,以达到节能减排的目的。但是由于实际大部分太阳能采暖工程,忽略了建筑围护对太阳能主动式采暖系统初投资与运行费用的影响,造成了太阳能主动式采暖系统初投资过高、太阳能保证率低。为了分析建筑热工性能对太阳能主动式采暖系统的影响,笔者利用数值模拟方法,将建筑热工性能与主动式太阳能采暖系统作为一个整体进行计算分析,利用初投资费用最低与全寿命周期总费用最低两个目标函数,对主动式太阳能采暖建筑热工性能的保温性能进行优化。结果表明,提高建筑围护结构热工性能,不仅可以降低太阳能采暖建筑的采暖运行费用,而且可降低整个系统的初投资。     

Feasibility of solar absorption air conditioning in Tunisia

Due to the high cost of fossil fuels and the environmental problems caused by the extensive use of air-conditioning systems for both residential and industrial buildings, the use of solar energy to drive cooling cycles becomes attractive since the cooling load is roughly in phase with solar energy availability particularly in Tunisia. In this paper, we present a research project aiming at assessing the feasibility of solar-powered absorption cooling technology under Tunisian conditions. Simulations using the TRNSYS and EES programs with a meteorological year data file containing the weather parameters of Tunis, the capital of Tunisia, were carried out in order to select and size the different components of the solar system to be installed. The optimized system for a typical building of 150 m² is composed of a water lithium bromide absorption chiller of a capacity of 11 kW, a 30 m² flat plate solar collector area tilted 35° from the horizontal and a 0.8 m³ hot water storage tank.     

基于TRNSYS的区域供冷能源站仿真控制研究

以泰州医药城区域供冷系统为研究对象,在TRNSYS中建立了区域供冷能源站模型。对能源站中的五台热泵机组采用组合式控制,模拟了冬夏季节的热泵机组联合运行时的供回水温度。     

Design of a solar absorption cooling system in a Greek hospital

Air conditioning of buildings is responsible for a large percentage of the greenhouse and ozone depletion effect, as refrigerant harmful gases are released into the atmosphere from conventional cooling systems. The need to implement advanced new concepts in building air conditioning systems is more crucial than ever today.Solar cooling systems (SCS) have the advantage of using absolutely harmless working fluids such as water, or solutions of certain salts. They are energy efficient and environmentally safe. They can be used, either as stand-alone systems or with conventional AC, to improve the indoor air quality of all types of buildings. The main goal is to utilize “zero emissions” technologies to reduce energy consumption and reduce CO₂ emissions.Amongst cooling technologies, absorption cooling seems to have a promising market potential.In this paper, the performance and economic evaluation of a solar heating and cooling system of a hospital in Crete, is studied using the transient simulation program (TRNSYS). The meteorological year file exploited the hourly weather data where produced by 30-year statistical process. The required data were obtained by Hellenic National Meteorological Service.The objective of this study is to simulate a complete system comprised of a solar collector, a storage tank, a backup heat source, a water cooling tower and a LiBr-H₂O absorption chiller. The exploitation of the results of the simulation provided the optimum sizing of the system.     

Solar powered absorption air conditioning

The design of buildings to provide a suitable thermal environment is discussed and the reasons for artificial heating or cooling introduced. The problem of sizing a solar-powered cooling plant is investigated. An iterative method of estimating heat flow and resultant temperatures in buildings subject to fluctuating heat loads is described. A model is developed to allow investigation of the performance of a solar collector and thermal storage system and some of the basic relationships between performance and physical parameters are determined.

An iterative method of predicting the cooling output from a lithium bromide-water absorption refrigeration plant having variable heat input is described.

The design of a solar collector/thermal storage) absorption cooler system, its performance on a particular building and its fine tuning are examined.     

深圳市福田科技广场建筑的环保节能设计

建筑环保节能设计是一种集成化、多元化和整体化的新型建筑设计方法。本文以深圳市福田科技广场建筑为例,主要叙述建筑环保节能设计方法及相应的技术支持,深化其中的多个关键环节,诸如建筑节能设计、建筑节水设计、太阳能系统综合利用、空调系统节能设计等;并突出建筑环保技能设计过程中人、建筑、自然(环境)三者之间的关系。