建筑环境设计模拟分析软件DeST第9讲冷热源与水系统模拟分析(上)

冷热源系统是整个集中空调系统的核心，完全决定了系统能否保障用户的冷热需求，是投资和能源消耗的主要部分。因此冷热源的选择和运行方式直接关系到空调系统的运行效果，并影响到空调系统的运行能耗的大小。综述了目前模拟计算中的制冷设备的各种建模方法，并结合建筑能耗模拟计算的特点，详细阐述了DeST模拟软件中冷源和水系统模拟过程中所用到的制冷设备半经验模型以及冷源模拟分析方法，为冷热源和水系统的全工况优化运行设计计算奠定了基础。     

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 potential of solar air-conditioning systems for displacement ventilation

Solar air-conditioning can have higher application potential for buildings through the strategy of high temperature cooling. In recent years, displacement ventilation (DV), which makes use of the indoor rising plumes from the internal heat gains, provides a more effective supply air option than the traditional mixing ventilation (MV) in terms of both thermal comfort and indoor air quality. As it is possible to raise the supply air temperature to 19 °C for DV, it would enhance the competitive edge of the solar air-conditioning against the conventional vapour compression refrigeration. Through dynamic simulation, a solar-desiccant-cooling displacement ventilation system (SDC_DV) was developed for full-fresh-air provision, while a solar-hybrid-desiccant-cooling displacement ventilation system (SHDC_DV) for return air arrangement. The latter was further hybridized with absorption chiller (AB) to become SHDC_AB_DV, or adsorption chiller (AD) to be SHDC_AD_DV, in order to be wholly energized by the solar thermal gain. Benchmarked with the conventional system using MV, the SDC_DV had 43.3% saving in year-round primary energy consumption for a typical office in the subtropical climate; the SHDC_AB_DV had 49.5% saving, and the SHDC_AD_DV had 18.3% saving. Compared with their MV counterparts, the SDC_DV, the SHDC_AB_DV and the SHDC_AD_DV could have 42.4%, 21.9% and 30.3% saving respectively.     

江阴市某商业综合楼太阳能空调热水系统设计

给出了江阴市某商业综合楼太阳能吸收式空调的设计及计算方法,详细地阐述了该吸收式空调系统的运行原理、负荷计算、空气处理过程、太阳能集热器的设计计算和布置方式、空调系统冷热源的选择、冷水机组的选型及依据等,并分析了连续阴雨天生活热水的保障问题以及储热、储冷水箱选择的依据,阐明了该系统运行的可行性,并通过满负荷计算的方法比较了改造前传统空调系统的耗电量与改造后太阳能吸收式空调系统的耗电量,得出太阳能吸收式空调节能约42%,太阳能吸收式空调具有一定的发展前景。     

Modeling a solar-powered double bed novel composite adsorbent (silica activated carbon/CaCl2)-water adsorption chiller

During the past few decades, the growing demand for air conditioning has caused a significant increase in demand for primary energy resources. Adsorption cooling system is one of the technologies which could be powered by renewable energy. This study aims to improve the performance of a solar-powered adsorption chiller by applying a novel composite adsorbent, a mixture of activated carbon, silica gel and calcium chloride. Modeling is established to investigate the cooling performance of a composite adsorbent based adsorption chiller driven by flat-type solar collectors with three different configurations of glaze: (1) single glazed cover; (2) double glazed cover and (3) transparent insulation material (TIM) cover. The simulation results show that the coefficient of performance (COP) and the specific cooling power (SCP) of the adsorption chiller depend hugely on the solar collector temperature. It is found that a double glazed cover shows the best cooling performance and 30 m² is the most optimized solar collector area. Two to three hours of pre-heating time is required to initiate the desorption process of the adsorber in a day of operation. This newly developed silica activated carbon/CaCl₂ composite material as adsorbent used in the adsorption chiller could achieve a high mean COP_sc of 0.48. Its satisfactory performance suggests that this novel composite material has a potential to be used in the adsorption chiller system even if it is powered by unstable solar energy.     

Advancement of solar desiccant cooling system for building use in subtropical Hong Kong

The solar desiccant cooling system (SDCS) had a saving potential of the year-round primary energy consumption as compared to the conventional air-conditioning system for full fresh air application in the subtropical Hong Kong. In order to further enhance its energy efficiency, advancement of the basic SDCS was carried out through a strategy of hybrid design. Six hybrid system alternatives of SDCS were therefore proposed, three for full fresh air design while another three for return air design for the building zone. Year-round performance evaluation of each solar hybrid desiccant cooling system was conducted for typical office application under different climatic and loading conditions. All the six hybrid system alternatives were found technically feasible, with up to 35.2% saving of year-round primary energy consumption against the conventional air-conditioning systems. Among the hybrid alternatives, recommendations were made on the SDCS hybridized with vapour compression refrigeration for full fresh air design; and the SDCS hybridized with vapour absorption refrigeration for return air design, since they had the saving potentials of both primary energy and initial cost. These two hybrid system alternatives used evacuated tubes, a more economical type of solar collectors compared to the PV or PVT panels.     

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.     

Description and performance of an active solar cooling system,using a LiBrH2O absorption machine

The report describes the design, modelling and performance of an active solar cooling system in northern Italy. Various aspects related to active solar cooling, like energy storage, room comfort, modelling and the LiBrH₂O absorption cycle are discussed.The cooling system consists essentially of: an array of 36 m² of flat plate collectors with a black chrome selective surface; a LiBrH₂O absorption machine with a refrigerating power of 4 kW; and two storage devices of 0.3 and 2 m³ water. The system is installed in the JRC Solar Laboratory in Ispra.The results of one summer of operation are presented together with the results of the simulation model. The overall system efficiency, defined as the fraction of the solar irradiation which is converted into cooling effect, is calculated for the whole cooling season and is found to be 11%. This value lies close to the measured values for this parameter.     

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.     

Energy savings in a building using regenerative evaporative cooling

This paper explores the potential of reducing the annual energy consumption of a central air-conditioned building through advanced evaporative cooling systems. The building considered is a typical three floor library building of a University. The regenerative evaporative cooling technology is coupled with the liquid cooled water chiller system to accomplish the energy conservation objective. Comparisons of the regenerative evaporative cooling are made with simple evaporative cooling to bring out the importance such a system. The well-known building simulation software, TRNSYS is used to carry out the heat load calculations and the dynamic simulations of the building. Annual energy consumptions of different components of the air-conditioning system are estimated for the existing water chiller system as well as for both coupled evaporative cooling systems (simple and regenerative). The annual energy consumptions, the indoor temperature, the relative humidity and the thermal comfort index ‘PMV’ are compared for all the three different air-conditioning systems. The coupling of direct and regenerative evaporative cooling technologies with water chiller system has shown, respectively, 12.09% and 15.69% savings in annual energy consumption of the building, while maintaining PMV between ?1 and +1 for most of the hours in the year.     

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.     

Energy performance of a cooling plant system using the inverter chiller for industrial building

The purpose of this paper is to clarify energy performance of the cooling plant system in the industrial building using actual measured operating data and numerical simulation analysis. One aspect of industrial buildings is that they have large energy consumption for manufacturing and air-conditioning compared with office and commercial buildings. Some examples of high-efficiency technologies installed in this particular cooling plant system are inverter chillers, integrated cooling towers and a free-cooling system. The inverter chiller which has been put on the market recently is state-of-the-art technology. The maximum COP of the inverter chiller reaches about 18 under certain conditions and integrated cooling towers make lower temperature cooling water as the whole capacity is large. Actual operating data indicates satisfied values for chiller and system COP during the running period and the simulation results show that the cooling plant system can cut down annual electric power consumption by about 48% compared with conventional cooling system.     

太原地区用太阳能制冷及供暖综合系统的探讨

针对电力紧张、能源短缺的问题,提出了在太原地区利用太阳能吸收式制冷和太阳能地板辐射供暖综合系统的模式,介绍了该系统的工作原理,并列举了实际算例对太阳能的使用情况进行了说明,同时提出了有待进一步研究的问题,以达到节能环保的目的。     

Methodology for optimizing the operation of heating/cooling plants with multi-heat-source equipments

A methodology for optimizing the operation of heating/cooling plants with multi-heat-source equipments is proposed. The methodology decides the optimal combination of the running machines to minimize the energy consumption of a heating/cooling plant. The energy consumption, energy cost and carbon dioxide emission are simulated using a tool developed in the MATLAB^® Simulink^® environment, embedded with a module developed using MATLAB^® Stateflow^® that can automatically decide the on/off states of heat source machines corresponding to cooling and heating loads and an operational priority order of heat source machines. A case study is introduced to demonstrate the methodology, which is an actual heating/cooling plant located in Osaka, Japan. The plant consists of two absorption chiller/heaters, one centrifugal chiller, one ice chiller, and two air-source heat pumps. The proposed methodology is used to simulate the plant performance at six different operational priority orders of heat source machines. The best operational combination can reduce primary energy consumption by 19.7%, energy cost by 12.8%, and carbon dioxide emission by 29.6%, compared to present operation.     

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.     

A simulation appraisal of performance of different HVAC systems in an office building

The article reports on a simulation appraisal of energy consumption, energy costs and environment impact of three systems used for space heating, and space cooling of an office building in Kragujevac, Serbia. Three investigated systems are (1) a system with a natural gas boiler and convective baseboard heaters for water space heating and window air conditioners for air space cooling; (2) a system with a natural gas boiler and individual air reheaters for air space heating and a chiller plant for air space cooling; and (3) an air-to-air heat pump for air space heating, and cooling. The systems are modeled and simulated by using EnergyPlus software. After simulations, it is found that the first investigated system has the highest energy efficiency, the best economy, and the lowest environmental impact. That is because of the fact that the first system has water as a heating medium and uses predominantly natural gas as fuel. However, in future, when for generation the grid electrical energy requires less primary energy, and becomes decarbonized, the third system would be best to conserve energy resources and environment.     

Monitoring and analysis of an absorption air-conditioning system

In the last few years, high-energy consumption due to air-conditioning has led to a growing interest in the efficient use of energy in buildings. Although simulation programs have always been the main tools for analyzing energy in buildings, the reliability of their results is often compromised by a lack of certainty to reflect real conditions.The aim of this work is to monitorize and analyze the thermal behavior of an absorption-based air-conditioning installation of a university building in Tarragona, Spain. The existing monitoring system of the installation has been improved by implementing additional sensors and flow meters. The data has been stored during summer 2002 and used to assess the energy balance of the air-conditioning installation and the operational regime of the absorption chiller.     

遮阳系数对供暖与空调能耗影响差异的逐时解析

以中国福州为例,从当地逐时气象数据入手,分析了建筑空调负荷及供暖负荷的所有时刻对应的逐时太阳辐射,用特征温度法研究当遮阳系数减小时各时刻建筑的空调与供暖能耗及相对变化(节能率)情况。研究发现,由于冬季有太阳辐射各时刻的供暖能耗相对于无太阳辐射各时刻能耗比例很小,故遮阳措施对供暖总能耗的影响不显著,从而证明DOE-2关于冬季遮阳系数减小对供暖能耗影响的结论值得商榷;由于夏季有太阳辐射各时刻空调能耗远大于无太阳辐射各时刻空调能耗,故遮阳措施对空调总能耗及节能率的影响非常显著,DOP2软件与特征温度法的结果是正确的;通过对福州全年各时刻空调供暖能耗、建筑负荷及节能率进行解析,揭示了看起来很分散的各时刻能耗及节能率差异数据总体上遵循的某种共性规律,供同行参考。     

Classified identifications: the annual relative variation rates (RVRs) of energy consumption are approximate in different cities with the same shading coefficient

By research on the variation laws of annual heating and cooling energy consumption and their RVRs with sun-shading coefficient in all the hours with and without solar radiation in three cities (Tampa, Sterling of USA and Fuzhou of China) respectively, we can find that: in winter, the proportion of the heating energy consumption in all the hours with solar radiation in the annual heating needs is very small (less than 15%), the influence of shading measures on the annual total heating energy consumption and its RVRs is not so significant. And thus the predictions of DOE-2 on the effect of shading measures on the annual heating energy consumption deserve further study. However, in summer, the proportion of the cooling needs of each hour with solar radiation in the annual total cooling needs is very large (more than 95%), therefore the influence of shading measures on the annual cooling energy consumption and its RVRs is very great. And hence the predictions of DOE-2 and CTM are both reasonable. By comparative analysis on two representative cities, we can find out that under the same sun-shading coefficient, the annual heating RVRs and the annual cooling RVRs are both approximate in different cities. By further analysis on the distributions of the daily heating and cooling RVRs, the monthly heating and cooling energy consumption and its RVRs in Sterling with different shading measures, we can find out that sun-shading coefficient has a far less impact on the annual heating energy consumption than on the annual cooling needs.     

A low carbon cooling system using renewable energy resources and technologies

A simulation study to assess the performance of a renewable energy (solar-biomass) based single effect LiBr-water absorption chiller suitable for residential applications was conducted. The model took into account the characteristics of all the components of the system. Using Bangkok meteorological data and component specifications from manufacturers and other sources, the performances of solar collector, storage tank, biomass gasifier and boiler, and the absorption cooling system, as well as the overall system performance on a daily and monthly basis has been evaluated. The chiller and overall system coefficient of performances was found to be 0.7 and 0.55 respectively and the biomass (charcoal) consumption for 24 h operation was 24.44 kg/day. To validate the model formulation and its predictions, experimental observations of a similar system (same chiller size) were compared with the model results. The results of the study indicate that solar-biomass hybrid air conditioning for tropical locations for residential applications is feasible, and can replace conventional vapor compression systems, thus reducing the need for fossil fuel based energy systems for cooling purposes.