Coupled simulation of convicton,radiation, and HVAC control for attaining a given PMV value

A new computational fluid dynamics (CFD) simulation for designing indoor climates is presented in this study. It is coupled with a radiative heat transfer simulation and heating, ventilating, and air-conditioning (HVAC) control system in a room. This new method can feed back the outputs of the CFD to the input conditions for controlling the HVAC system, and includes a human model to evaluate the thermal environment. It can be used to analyze the conditions of the HVAC system (e.g. temperature of supply air, surface temperature of radiation panel, etc.) and the heating/cooling loads of different HVAC systems under the condition of the same human thermal sensation (e.g. PMV, operative temperature, etc.) To examine the performance of the new method, a thermal environment within a semi-enclosed space which opens into an atrium space is analyzed under steady-state conditions in the summer season. Using this method, the most energy efficient HVAC system can be chosen under the same PMV value. In this paper, two types of HVAC system are compared: one is a radiation-panel system and the other is an all-air cooling system. The radiation-panel cooling is found to be more energy efficient for cooling the semi-enclosed space in this study.     

Field performance of a Japanese low energy home relying on renewable energy

This paper describes the construction and evaluation of an experimental low energy home assisted by a hybrid system using natural energy resources and unused energy. The home, for which a ground source heat pump (GSHP) system has been installed, was built on the campus of Hokkaido University, Japan in March 1997. The total floor area of the home is 192 m². This home is super insulated and airtight; the calculated coefficient of heat loss is 0.97 W/m² K. It has various passive strategies including direct solar heat gain and a ventilation system with an exhaust stack. Photovoltaic (PV) modules, wind power and solar collectors are adopted in order to achieve self-sufficiency in electric power and domestic hot water (DHW) supply. A GSHP is used for space heating and cooling. Two vertical steel wells are used as vertical earth heat exchangers (VHE). In summer, there is a floor cooling system using piped cold water from the VHE.Approximately 80% of the home’s total energy was provided by PV modules, solar collectors, as well as underground and exhaust heat. The annual amount of purchased energy during the test period was 12.5% that of a typical home in Hokkaido.     

Indoor cooling/heating load analysis based on coupled simulation of convection,radiation and HVAC control

A computational fluid dynamics (CFD) simulation for analyzing indoor cooling/heating load is presented in this study. It is coupled with a radiative heat transfer simulation and heating, ventilating, and air-conditioning (HVAC) controlling system in a room. This new method feeds back the outputs of the HVAC system control to the input boundary conditions of the CFD, and this method includes a human model to evaluate the thermal environment. It would be used to analyze the heating/cooling loads of different HVAC systems under the condition of the same human thermal sensation (e.g. PMV, operative temperature, etc.) even though the temperature and air-velocity distribution in the room are different from each other.To examine the performance of the new method, a cooling load and a thermal environment within a semi-enclosed space, which opens into an atrium space, is analyzed under the steady-state conditions during the summer season. This method is able to analyze the indoor cooling load with changes of target thermal environments of a room and/or changing clothing conditions of occupants considering the temperature and air-velocity distribution in the room. In this paper, two types of HVAC system are compared; i.e. radiation-panel system and all-air cooling system. The radiation-panel cooling system is found to be more energy efficient for cooling the semi-enclosed space. Changes of the level of thermal environment reduce cooling load effectively in case of the all-air cooling system while the radiation-panel system does not reduce cooling load even though the targeted thermal condition is relaxed. Energy saving effect is expected by easing the clothing conditions of occupants. In this study, the reducing effect of cooling load is quantitatively evaluated with clothing conditions also.     

混凝土空心楼板供热供冷的模拟分析

本文提出利用空心楼板中空部分作为空调系统的部分送风通道,并在楼板板面开孔的技术方案,一方面使楼板对室内具有一定的辐射供热供冷能力,另一方面也可使用送风直接对室内进行空气调节。本文利用有限元分析软件着重分析了空心楼板受一定参数的送风作用的结果,评估了以空心楼板为系统末端对室内进行空气调节的效果,初步论证了这种技术方案的可行性。论证结果显示,这种末端方案具备降低供热供冷能耗的潜力,可以极大地降低冷辐射表面结露的可能性,在新建建筑尤其是低能耗建筑中具有良好的利用前景。     

An analysis of stochastic properties of room temperature, cooling load and air-conditioning systems

Exact prediction of the heating and cooling load, proper sizing of the HVAC systems and the optimal control of the HVAC systems are essential to minimize energy consumption. Since external climates which are the main factors affecting cooling loads fluctuate randomly, calculation of the cooling load must take account of the stochastic nature of these processes.

This paper proposes methods of thermal calculation which give the density function of the HVAC system load considering the stochastic properties of the external climates. Simple HVAC systems are analysed for illustration of the applicability of these methods to many practical problems.     

广州珠江城项目建筑节能新技术应用综述

本文结合地区气候特点及建筑的体形、结构及功能,阐述了各种建筑节能新技术的应用,充分采用各种节能降耗措施,包括采用风力发电及光伏发电等可再生能源的利用、办公室采用冷辐射+需求化(VAV)置换送风的节能空调系统以及高效办公照明等措施,以达到节约能源的目的,为绿色节能建筑示范工程提供典范.     

A simplified correlation method accounting for heating and cooling loads in energy-efficient buildings

Simplified correlation methods are powerful tools to compare both the energy performance of buildings and the efficiency of different HVAC control systems. For buildings in which both heating and cooling loads contribute to the energy consumption, widely used methods, like the energy signature models, are not appropriate, since they cannot simultaneously handle both heating and cooling aspects. This paper proposes a new correlation method to overcome this difficulty. The ‘Eta method’ deals with internal gains, as well as solar gains, and can be used to calculate a utilization factor for free gains in the heating and cooling periods. Two examples to illustrate the method are given. The first one is a passive solar office room, on which different blind controllers were tested by simulation. The second example is a non-residential building in which two HVAC controllers were carefully monitored     

Modeling radiant heating and cooling systems: integration with a whole-building simulation program

One of the primary goals of the radiant heating and cooling community for the past two decades has been the fair and accurate comparison of radiant space conditioning systems with conventional forced air systems. The desire of the community was to give architects and engineers the ability to compare the energy consumption of different system types while requiring the systems to produce equivalent thermal environments. Unfortunately, radiant systems, though relatively simple in concept, are relatively complex from a modeling standpoint. A rigorous model must include fundamental laws of thermodynamics and properly account for heat transfer due to radiation, convection, and conduction. In addition, the model must do this in a generic way within a program that is capable of modeling buildings of any size and type and their associated HVAC systems. Such challenges are not easily overcome and require careful attention to detail as well as a solid foundation from which to build. This paper summarizes a model which addresses these concerns and provides a radiant system model within a popular building energy simulation program.     

地板辐射与置换通风组合空调系统的模拟

探讨了地板辐射供暖、供冷系统与置换通风系统的组合空调系统的流程,对组合空调系统进行了数值模拟。地板辐射供暖、供冷系统与置换通风系统相结合获得了良好的室内温度场和速度场,提高了空气品质,改善了室内的热舒适性。     

Application of an energy management and control system to assess the potential of different control strategies in HVAC systems

The significant and continuous increment in the global electricity consumption is asking for energy saving strategies. Efficient control for heating, ventilation and air-conditioning systems (HVAC) is the most cost-effective way to minimize the use of energy in buildings. In this framework, an energy management and control system (EMCS) has been developed to schedule electricity end-uses in the campus of the Universidad Politécnica de Valencia (UPV), Spain. This paper presents an evaluation performed by using the EMCS of different control strategies for HVAC split systems. It analyzed the effect of different schedules for a common air-conditioning device and demand response strategies are tested in several situations. The economic saving is calculated taking into account the electricity contract clauses. Finally, a test is made for the control of a group of similar devices in order to reduce the maximum peak power in consumption and to obtain a flexible load shape with the HVAC loads. The studies are then extrapolated to a larger system, the whole University campus, for which energy and economic savings are quantified.     

The impact of air filter pressure drop on the performance of typical air-conditioning systems

Filters are used in heating, ventilation, and air-conditioning (HVAC) systems for both commercial and residential buildings to protect the equipment and improve indoor air quality in conditioned spaces. Although there are many benefits of using the air filter in an air-conditioning system, the resistance associated with it can increase fan energy use and may adversely affect air-conditioning system performance and efficiency. The paper explores the impact of air filtration on energy consumption for a typical air-conditioning (AC) system with constant- or variable-speed fan. A whole building simulation model is used to simulate the annual energy consumption for various air-conditioning system capacities, different levels of filter cleanliness, and various filter minimum efficiency reporting values (MERV). The results indicate that with a constant-speed fan, the cooling energy use increases as the filter gets dirty over time and the energy use in the fan may increase but this depends heavily on the investigated fan performance curve. With a variable-speed fan, the fan energy use increases with a dirty filter but the cooling and heating energy uses are slightly affected. The fan energy use rise due to the dirty filter depends mainly on air system capacities, filter MERV ratings, and the degree of the filter cleanliness.     

Energy performance optimization of radiant slab cooling using building simulation and field measurements

Few field studies of energy performance of radiant cooling systems have been undertaken. A recently constructed 17,500 m² building with a multi-floor radiant slab cooling system in the tower was investigated through simulation calibrated with measured building energy use and meteorological data. For the very cold, dry region where the building was located, it was found that a typical floor of the tower would have had 30% lower annual energy use with a conventional variable air volume system than with the as-built radiant cooling-variable air volume combination. This was due to (1) simultaneous heating and cooling by the existing radiant cooling and air systems, (2) the large amount of free cooling possible in this climate, and (3) suboptimal control settings. If these issues were remedied and combined with improved envelope and a dedicated outdoor air system with exhaust air heat recovery, a typical floor could achieve annual energy use 80% lower than a typical floor of the existing building HVAC system. This shows that radiant thermal control can make a significant contribution to energy-efficiency, but only if the building design and operating practices complement the strengths of the radiant system.     

Optimal supply air temperature with respect to energy use in a variable air volume system

In a variable air volume (VAV) system with 100% outdoor air, the cooling need in the building is satisfied with a certain air flow at a certain supply air temperature. To minimize the system energy use, an optimal supply air temperature can be set dependent on the load, specific fan power (SFP), chiller coefficient of performance, outdoor temperature and the outdoor relative humidity. The theory for an optimal supply air temperature is presented and the heating, ventilation and air-conditioning (HVAC) energy use is calculated depending on supply air temperature control strategy, average U-value of the building envelope and two outdoor climates. The analyses show that controlling the supply air temperature optimally results in a significantly lower HVAC energy use than with a constant supply air temperature. The optimal average U-value of the building envelope is in practise mostly zero.     

Method for modelling space conditioning aggregated daily load curves: Application to a university building

Physically based load modelling methodologies have been widely developed and used because of their ability to predict the energy load dynamic response. Most building energy programs predict energy consumption and energy system performance through a whole building energy simulation as well as a global analysis of building thermal processes and heating, ventilation and air-conditioning (HVAC) system performance. A different approach is presented in this paper by introducing a new method for modelling the daily load profile of a group of air-conditioning systems. This method is based on the simulation of a single HVAC system, a set of end-use electrical measurements, and a detailed walk-through and energy audit. The basic methodology allows deducing the aggregated load of a group of space conditioning devices by the addition of the daily simulation of each individual physical system. As an application, the space conditioning daily demand curve of a university building is studied and results are presented.     

HVAC system optimization for energy management by evolutionary programming

Energy management of heating, ventilating and air-conditioning (HVAC) systems is a primary concern in building projects, since the energy consumption in electricity has the highest percentage in HVAC among all building services installations and electric appliances. Without sacrifice of thermal comfort, to reset the suitable operating parameters, such as the chilled water temperature and supply air temperature, would have energy saving with immediate effect. For the typical commercial building projects, it is not difficult to acquire the reference settings for efficient operation. However, for some special projects, due to the specific design and control of the HVAC system, conventional settings may not be necessarily energy-efficient in daily operation.In this paper, the simulation-optimization approach was proposed for the effective energy management of HVAC system. Due to the complicated interrelationship of the entire HVAC system, which commonly includes the water side and air side systems, it is necessary to suggest optimum settings for different operations in response to the dynamic cooling loads and changing weather conditions throughout a year. A metaheuristic simulation–EP (evolutionary programming) coupling approach was developed using evolutionary programming, which can effectively handle the discrete, non-linear and highly constrained optimization problems, such as those related to HVAC systems. The effectiveness of this simulation–EP coupling suite was demonstrated through the establishment of a monthly optimum reset scheme for both the chilled water and supply air temperatures of the HVAC installations of a local project. This reset scheme would have a saving potential of about 7% as compared to the existing operational settings, without any extra cost.     

Comparison of energy efficiency between variable refrigerant flow systems and ground source heat pump systems

With the current movement towards net zero energy buildings, many technologies are promoted with emphasis on their superior energy efficiency. The variable refrigerant flow (VRF) and ground source heat pump (GSHP) systems are probably the most competitive technologies among these. However, there are few studies reporting the energy efficiency of VRF systems compared with GSHP systems. In this article, a preliminary comparison of energy efficiency between the air-source VRF and GSHP systems is presented. The computer simulation results show that GSHP system is more energy efficient than the air-source VRF system for conditioning a small office building in two selected US climates. In general, GSHP system is more energy efficient than the air-source VRV system, especially when the building has significant heating loads. For buildings with less heating loads, the GSHP system could still perform better than the air-source VRF system in terms of energy efficiency, but the resulting energy savings may be marginal.     

低能耗技术在重庆绿色建筑中的应用

文章以绿色建筑工程——中冶赛迪研发中心项目为例,扼要介绍在设计中应用的低能耗技术。由于空调系统的能耗占建筑总能耗的比例很高,文章主要从空调系统方面作详细分析,包括地源热泵与低温热水地板辐射联合运行的采暖系统、地源热泵与热-湿分控空调末端联合运行的空调系统,以期对在重庆地区建筑中应用类似的低能耗技术有一定指导和示范作用。并推动低能耗技术在重庆地区建筑中的应用。     

低温地板辐射供暖系统在寒冷地区高大空间的应用

介绍了寒冷地区某高大空间地板辐射供暖系统的设计,并对其运行数据进行了测试.结果表明,在寒冷地区高大空间应用低温地板辐射供暖系统,可以满足供暖要求.     

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。     

某大型空调系统能耗分析

能源问题是决定我国能否可持续发展的关键因素之一。对某大型空调系统能耗进行了测试和分析，表明冷机实际COP低于其额定COP，并且空调箱能耗占到30％-50％；另外，对系统的负荷分析表明，造成系统的供需比下降的主要原因是该系统设计本身所造成。因此，对空调系统优化运行是节能改造必不可少的一个环节；同时，如何优化空调系统各级的设定参数以及系统的划分，将会从根本上提高系统冷负荷的供需比，从而大大减少系统能耗，可为大型空调系统的运行人员、设计人员提供参考。