Field performance measurements of a heat pump desiccant unit in dehumidification mode

The variable refrigerant volume (VRV) air conditioning system needs to be operated in conjunction with a ventilation system, because the VRV system cannot provide any fresh air. The common ventilation unit used with the VRV system is the heat recovery ventilation (HRV) unit. In this study, a new ventilation unit, a self-regenerating heat pump desiccant (HPD) unit, was introduced and the characteristics of the HPD unit was experimentally investigated over a wide range of operating conditions in a field performance test. In addition, the energy saving contribution of the HPD and HRV units to the VRV system was compared. It was found that the HPD unit maintained the target indoor humidity ratio of 10 g/kg throughout the cooling season resulting in a better indoor thermal comfort than the HRV unit. Besides, it was found that the outdoor unit of the VRV system consumed 26.3% less energy for the operation in conjunction with the HPD unit as compared to the operation in conjunction with the HRV unit.     

冬季北方地区住宅建筑通风方式对比研究

随着住宅节能技术的广泛推行,对窗户的气密性要求越来越高,冬季冷风渗透远远不能满足室内人员对新风的最低需求。为了寻找节能、舒适的通风方式,本研究利用FLUENT对工程中较为常见的通风方式：自然通风方式、自然进机械排通风方式、带热交换的墙式通风器方式、带热交换的通风换气机组方式在气流组织、舒适性能、能耗特性及初投资方面进行了应用效果评价。最终得出：对于层高和装修标准较高的高级住宅中使用带热交换的通风换气机组,可以使通风系统在满足热舒适性和空气品质的基础上,更加节能,而对于一般住宅建筑,自然进机械排通风方式是相对最优选择。     

Simulation comparison of VAV and VRF air conditioning systems in an existing building for the cooling season

Performance of two widely used air conditioning (AC) systems, variable air volume (VAV) and variable refrigerant flow (VRF), in an existing office building environment under the same indoor and outdoor conditions for an entire cooling season is simulated by using two validated respective models and compared. It was observed that the indoor temperatures could not be maintained properly at the set temperature by the VAV no-reheat boxes. However, it could be maintained by the VAV boxes with reheat with a significant energy consumption penalty. It was found that the secondary components (indoor and ventilation units) of the VRF AC system promised 38.0-83.4% energy-saving potential depending on the system configuration, indoor and outdoor conditions, when compared to the secondary components (heaters and the supply fan) of the VAV AC system. Overall, it was found that the VRF AC system promised 27.1-57.9% energy-saving potentials depending on the system configuration, indoor and outdoor conditions, when compared to the VAV AC system.     

Integration of variable refrigerant flow and heat pump desiccant systems for the heating season

Integration of the variable refrigerant flow (VRF) and heat pump desiccant (HPD) systems was investigated in a field performance test for a heating season. The HPD systems use only the moisture in the outdoor air and return air to humidify the indoors during ventilation in the heating season. Three different operating modes: non-ventilated, HPD ventilation assisted and HPD ventilation-humidification assisted VRF systems were investigated. It was found that the VRF systems provided an average of 93.5% of the total heating energy for the HPD ventilation assisted mode. The remainder was the recovered heat by the HPD systems during ventilation. The VRF systems provided an average of 46.8% of the total heating energy for the HPD ventilation-humidification assisted mode. The remainder was covered by the HPD systems which provided additional sensible and latent heating. Overall, among the three operating modes, it is concluded that the HPD ventilation-humidification assisted VRF outdoor units consume less energy than the HPD ventilation assisted ones (about the same energy as the non-ventilated ones), while providing the best indoor thermal comfort and indoor quality conditions. For the total system, the HPD ventilation-humidification assisted VRF systems consume less energy than the HPD ventilation assisted ones.     

浅谈多联机空调系统的设计

简单介绍了多联机空调系统的工作原理,针对多联机空调系统在工程设计中应注意的建筑节能,室内机型选择,室外机布置等问题进行了分析探讨,指出了设计要点及注意事项,以促进多联机空调系统的推广应用。     

Use of Simulink to evaluate the air-quality and energy performance of HRV-equipped residences in Fairbanks, Alaska

Mechanical ventilation systems in residences usually serve a single purpose, providing only a relatively small benefit compared to the capital cost. Polluted areas use mechanical ventilation to filter incoming air, cold regions use it to be able to recover the heat from the stale air going out. However, both issues – energy and air-quality – can be beneficially addressed together using one ventilation system in cold climate regions with air pollution problems, such as Fairbanks, Alaska. This paper presents a dynamic model for evaluating indoor PM_2.5 levels and energy consumption associated with ventilation. The model was verified by comparing the model-predicted real-time indoor PM_2.5 level with the actual level measured in a Fairbanks home and a good agreement (r = 0.95) was found. Then, the model was used to study three ventilation scenarios of a typical home in Fairbanks—natural ventilation, using an HRV, and using an HRV with an additional particulate filter. The external cost associated with breathing the indoor PM_2.5 was also evaluated. The scenario with an HRV and an additional filter was shown to have about $380 lower annual energy cost than the scenario with natural ventilation and the saving in the PM_2.5 associated external cost was about $690 annually. The savings were shown to exceed the operational costs of the ventilation system.     

Variable refrigerant flow systems: A review

This review study presents a detailed overview of the configurations of the outdoor and indoor units of a multi-split variable refrigerant flow (VRF) system, and its operations, applications, marketing and cost. Besides, a detailed review about the experimental and numerical studies associated with the VRF systems is provided. The aim is to put together all the diversified information about the VRF systems in a single source. According to detailed review, it is observed that the compressor frequency and the electronic expansion valve opening should be controlled simultaneously for the control strategies, and it is concluded that VRF system not only consumes less energy than the common air conditioning systems such as variable air volume, fan-coil plus fresh air under the same conditions, but also provides better indoor thermal comfort as long as it is operated in the individual control mode. It is found that even though the main drawback of the VRF system is the high initial cost compared to the common air conditioning systems, due to the energy saving potential of the VRF system, the estimated payback period of the VRF system compared to an air cooled chiller system in a generic commercial building could be about 1.5 year.     

Energy simulation in the variable refrigerant flow air-conditioning system under cooling conditions

As a high-efficiency air-conditioning scheme, the variable refrigerant flow (VRF) air-conditioning system is finding its way in office buildings. However, there is no well-known energy simulation software available so far which can be used for the energy analysis of VRF. Based on the generic dynamic building energy simulation environment, EnergyPlus, a new VRF module is developed and the energy usage of the VRF system is investigated. This paper compares the energy consumption of the VRF system with that of two conventional air-conditioning systems, namely, variable air volume (VAV) system as well as fan-coil plus fresh air (FPFA) system. A generic office building is used to accommodate the different types of heating, ventilating, and air-conditioning (HVAC) systems. The work focuses on the energy consumption of the VRF system in the office buildings and helps the designer's evaluation and decision-making on the HVAC systems in the early stages of building design. Simulation results show that the energy-saving potentials of the VRF system are expected to achieve 22.2% and 11.7%, compared with the VAV system and the FPFA system, respectively. Energy-usage breakdown for the end-users in various systems is also presented.     

办公建筑热回收装置节能运行模式分析

当前新风负荷占建筑能耗的比重很大,而热回收可以有效减少新风负荷。为进一步细分空调系统中热回收装置的全年运行情况,提高热回收装置的节能运行效果,针对北京地区办公建筑,以研制的热管式热交换器为例,利用De ST软件构建了办公建筑模型。空调系统采用两管制风机盘管加新风系统。引入平衡温度的概念,划分了热回收装置的全年启停时间及对应运行模式,根据标准气象年的气象数据绘制能量回收效果图,得到相应模式下的热回收量,可节省62.6%~66%的新风负荷,节能效果明显。     

Coupling indoor airflow,HVAC, control and building envelope heat transfer in the Modelica Buildings library

This paper describes a coupled dynamic simulation of an indoor environment with heating, ventilation, and air conditioning (HVAC) systems, controls and building envelope heat transfer. The coupled simulation can be used for the design and control of ventilation systems with stratified air distributions. Those systems are commonly used to reduce building energy consumption while improving the indoor environment quality. The indoor environment was simulated using the fast fluid dynamics (FFD) simulation programme. The building fabric heat transfer, HVAC and control system were modelled using the Modelica Buildings library. After presenting the concept, the mathematical algorithm and the implementation of the coupled simulation were introduced. The coupled FFD–Modelica simulation was then evaluated using three examples of room ventilation with complex flow distributions with and without feedback control. Further research and development needs were also discussed.     

重庆农村住宅热环境调查与能耗模拟分析

通过对重庆地区农村住宅的实地调研和对农村典型住宅室内外温度的连续监测,获得农村住宅的主要围护结构类型及典型农村住宅供暖季与空调季的室内、外热环境状况,利用重庆地区自然通风适应性热舒适性评价模型进行分析。在现有农村住宅围护结构热工性能条件下,供暖季室内温度达到舒适范围的有0 d,空调季有73 d;室内热环境状况差,冬季保温要求比夏季隔热要求更高。在供暖空调设备典型运行模式下,以调研数据为基础,借助DeST-h软件对农村典型住宅供暖空调能耗进行模拟,获得了农村住宅单位建筑面积供暖空调设备耗电量。     

Effect of indoor buoyancy flow on wind-driven cross ventilation

Designing for wind-driven cross ventilation is challenging due to many factors. While studies have focused on the difficulty of predicting the total flow rate and measuring opening characteristics of cross ventilation, few have investigated the impacts on the distribution of indoor air. This paper provides insights on how local heat sources can generate significant buoyancy driven flow and affect indoor mixing during wind-driven cross ventilation scenarios. Measurements of air distribution were conducted by a tracer gas method for a multi-zone test building located in Austin, Texas, USA, along with cross ventilation flow at the openings. A computational fluid dynamic (CFD) model was also developed for this test building, which utilizes the measured flow properties at the openings as boundary conditions. Resulting air distribution patterns from the CFD model were then compared to the experimental data, validating the model. Further parametric analyses were also conducted to demonstrate the effect of interior heat loads in driving internal air mixing. Key findings of the investigation suggest a local heat source smaller than 35 W/m² can increase the indoor mixing during cross ventilation from less than 1 air exchange to as high as 8 air exchanges per hour. This result also suggests a typical occupancy scenario (people and electronics) can generate enough heat loads to change the indoor air mixing and alter the effect of cross ventilation.     

Optimization of indoor environmental quality and ventilation load in office space by multilevel coupling of building energy simulation and computational fluid dynamics

The fundamentals, implementation, and application of an integrated simulation as an approach for predicting the indoor environmental quality for an open-type office and for quantifying energy saving potential under optimized ventilation are presented in this paper. An integrated simulation procedure based on a building energy simulation and computational fluid dynamics, incorporated with a conceptual model of a CO₂ demand controlled ventilation (DCV) system and proportional integral control of an air conditioning system as the optimization assessment of conceptual model in the occupied zone, was developed. This numerical model quantitatively exhibits energy conservation and represents the non-uniform distribution patterns of airflow properties and CO₂ concentration levels in terms of energy recovery and indoor thermal comfort. By means of an integrated simulation, the long-term energy consumption of heating, ventilation, and air conditioning systems are predicted precisely and dynamically. Relative to a ventilation system with a basic constant air volume supply rate characterized by a fixed outdoor air intake rate from the ceiling supply opening, the optimized CO₂-DCV system coupled with energy recovery ventilators reduced total energy consumption by 29.1% (in summer conditions) and 40.9% (winter).     

Relating actual and effective ventilation in determining indoor air quality

Ventilation is both a mechanism for removing indoor air pollutants, and a potential energy load on the heating or cooling system of a building. Quantitative estimates of the ventilation rates, important for both of these applications, necessitate determining time-averaged quantities. The time-averaged ventilation rate appropriate for indoor air pollution, however, is different from that associated with energy load. We derive ventilation efficiencies for well-mixed, homogeneous, time-varying concentrations and corroborate findings with field data from a test house in Edmonton, Alberta, which indicate that monthly ventilation efficiency ranges from 79% to 92% with an annual average of 80%, and that hourly temporal ventilation efficiencies vary over a much larger range than time-averaged quantities.     

Evaluation of distributed environmental control systems for improving IAQ and reducing energy consumption in office buildings

Conventional heating, ventilation, and air conditioning (HVAC) systems are incapable of providing control over individual environments or adjusting fresh air supply based on the dynamic occupancy of individual rooms in an office building. This paper introduces the concept of distributed environmental control systems (DECS) and shows that improvement in indoor air quality (IAQ) and energy efficiency can be achieved by providing required amounts of fresh air directly to the individual office spaces through distributed demand controlled ventilation (DDCV). In DDCV, fresh air is provided to each micro-environment (room or cubicle) based on input from distributed sensors (CO₂, VOC, occupancy, etc.) or intelligent scheduling techniques to provide acceptable IAQ for each occupant, rather than for groups or populations of occupants. In order to study DECS, a numerical model was developed that incorporates some of the best available models for studying building energy consumption, indoor air flow, contaminant transport and HVAC system performance. The developed model was applied to a DECS in a model office building equipped with a DDCV system. By implementing DECS/DDCV and intelligent scheduling techniques it is possible to achieve an improvement in IAQ along with a reduction in annual energy consumption compared to conventional ventilation systems.     

中小型游泳馆无送热风暖通系统节能设计

以天津市某小型室内游泳馆为研究对象,计算了冬季带送热风的供暖通风系统的通风热负荷及其占总热负荷的比例。提出无送热风供暖通风系统方案,对室内空气设计参数的确定,围护结构、供暖通风系统的节能设计进行了探讨。为保证距地面2m以下空间内人员活动区的舒适度和防止围护结构结露,应采用散热器＋地板辐射供暖系统。围护结构结露可通过对金属构件施镀防腐层,设置墙体的保温、隔气层及涂抹防结露、防霉变的特种涂料等方法解决,设置通风系统仅是为了保证馆内空气品质。     

A combined system of chilled ceiling,displacement ventilation and desiccant dehumidification

Different types of heating, ventilation, and air-conditioning (HVAC) systems consume different amounts of energy yet they deliver similar levels of acceptable indoor air quality (IAQ) and thermal comfort. It is desirable to provide buildings with an optimal HVAC system to create the best IAQ and thermal comfort with minimum energy consumption. In this paper, a combined system of chilled ceiling, displacement ventilation and desiccant dehumidification is designed and applied for space conditioning in a hot and humid climate. IAQ, thermal comfort, and energy saving potential of the combined system are estimated using a mathematical model of the system described in this paper. To confirm the feasibility of the combined system in a hot and humid climate, like China, and to evaluate the system performance, the mathematical model simulates an office building in Beijing and estimates IAQ, thermal comfort and energy consumption. We conclude that in comparison with a conventional all-air system the combined system saves 8.2% of total primary energy consumption in addition to achieving better IAQ and thermal comfort. Chilled ceiling, displacement ventilation and desiccant dehumidification respond consistently to cooling source demand and complement each other on indoor comfort and air quality. It is feasible to combine the three technologies for space conditioning of office building in a hot and humid climate.     

华凯花园住宅小区供热空调设计

该小区为大型住宅小区,自建集中燃气锅炉房,作为暖通空调和生活热水热源,塔楼供暖系统分高低区,室内采用散热器供暖,分户热计量。冷源为水冷螺杆式冷水机组,住宅楼空调一期采用分体机,二期采用户式多联机,会所采用风机盘管加新风的集中空调方式,街面商业出租单元采用变频多联机。介绍了小区的暖通空调、自控和防排烟设计。     

某报告厅空调系统的设计及其能耗分析

介绍了西安某办公楼报告厅空调系统的设计。分别应用置换通风与混合通风两种通风方式，在室外和室内设计参数相同的情况下，充分比较了它们在送风量、新风量、能耗以及室内空气品质的不同。结果表明在某些应用场合，置换通风在空气品质提高和能耗降低上有明显的优势，同时这种优势不以牺牲热舒适性为代价，因此建议使用置换通风系统。     

空调系统节能技术在中国网通业务楼中的应用

从设计的角度,阐述了当今暖通空调节能技术的综合应用对于建筑节能技术推广的意义,详细介绍了变频冷水机组的节能特性以及变风量空调系统在建筑负荷调整中的关键作用,并重点阐述了排风能量回收系统和空调系统的结合,以及该系统对实现建筑节能目标的重要意义。