A new operating strategy for economizer dampers of VAV system

The paper proposes a new operating strategy for the outdoor, discharge, and recirculation air dampers of the economizer in VAV system, called split-signal damper control strategy. The strategy controls the outdoor air by only one damper while keeping the remaining dampers full open. The discharge or recirculation air damper is modulated to control the amount of outdoor air introduced into the system while keeping the two remaining dampers full open. Since at least two dampers are always kept fully open during the occupied times, the strategy can provide a minimum static pressure drop in economizer dampers and results in minimum energy use in return and supply fans. An additional advantage is that the proposed strategy prevents reverse airflow through the discharge air damper of a VAV system that uses a volume matching control strategy. The proposed strategy along with the existing strategies such as the three-coupled dampers used in most existing system and the two-coupled dampers are evaluated on an existing system using 1-year long measured data set, along with an economizer damper model developed and validated in this paper. The simulation results show that the annual energy savings in supply and return fans of an existing system, compared to the traditional strategy of three-coupled dampers, are 12% and 5%, respectively.     

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.     

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-saving estimation model for hypermarket HVAC systems applications

Energy saving estimation model (ESEM) use normal distribution (Gaussian) probability theory to predict potential savings for previously determined system improvements. Those improvements are low/high cost investments based on data gathered during one year monitoring of typical hypermarket facility HVAC system. The consumption of electrical energy and natural gas has been monitored and system segments with largest amount of energy consumption have been marked. Gathered data pointed out to fan units as the biggest energy consumers and suggested that system energy-saving improvement must be focused on fans energy consumption control. This paper deals with ESEM inputs and outputs in order to provide correct financial estimation of specific investment.     

Influence of building parameters and HVAC systems coupling on building energy performance

The performance of different HVAC systems varies when coupled with different buildings. This paper examines the relationship between building heating and cooling load and subsequent energy consumption with different HVAC systems. Two common HVAC systems in use throughout the UK office building stock, variable air volume (VAV) system and fan coil (FC) with dedicated outside air system, have been coupled with a typical narrow plan office building with and without daylight control and for both cellular and open plan.The results presented in this paper clearly indicate that it is not possible to form a reliable judgment about building energy performance based only on building heating and cooling loads. For the two investigated systems, variable air volume system and fan coil with dedicated outside air system, the difference between system demand and building demand varied from over −40% to almost +30% for cooling and between −20% and +15% for heating. If a heat recovery unit is used, the difference in heating performance is even greater, rising to −70%.     

A review on buildings energy consumption information

The rapidly growing world energy use has already raised concerns over supply difficulties, exhaustion of energy resources and heavy environmental impacts (ozone layer depletion, global warming, climate change, etc.). The global contribution from buildings towards energy consumption, both residential and commercial, has steadily increased reaching figures between 20% and 40% in developed countries, and has exceeded the other major sectors: industrial and transportation. Growth in population, increasing demand for building services and comfort levels, together with the rise in time spent inside buildings, assure the upward trend in energy demand will continue in the future. For this reason, energy efficiency in buildings is today a prime objective for energy policy at regional, national and international levels. Among building services, the growth in HVAC systems energy use is particularly significant (50% of building consumption and 20% of total consumption in the USA). This paper analyses available information concerning energy consumption in buildings, and particularly related to HVAC systems. Many questions arise: Is the necessary information available? Which are the main building types? What end uses should be considered in the breakdown? Comparisons between different countries are presented specially for commercial buildings. The case of offices is analysed in deeper detail.     

用变速泵和变速风机代替调节用风阀水阀

通过５个工程实例，探讨在供热空调系统中利用变速风机和变速泵代替调节用风阀水阀实现风和水系统的调节的可能性，分析表明，这样做可以节省运行能耗，同时改善系统的调节品质，系统的初投资一般也不会增加。水泵和风机能耗约占供热空调系统总能耗的４０％，这些能耗中的１／３左右被各种调节阀门所消耗，但这样大的代价并没有换来好的调节效果，反而导致系统中许多问题发生。     

Energy optimal control of a residential space-conditioning system based on sensible heat transfer modeling

Nowadays most HVAC systems for residential building in the Unites States use a single-zone, two-position control system which is simple and easy to manage. However, this two-position control system has its disadvantage for its unsatisfactory thermal comfort and energy efficiency. This paper presents a proportional control system for the residential building by seting up the dynamic simulation for the building and the control system. The state-space method is used to model the building system and the simulation code is implemented on MATLABTM. Under this model, optimization of the controller is possible and implemented. The thermal comfort and energy efficiency are compared under the different schemes. It has been found that proportional control is advantageous to the two-position control for the thermal comfort while there is not much difference in energy consumption between two control schemes. However, in this work the furnace was operated without any minimum run time and under continuous data sampling.     

济南某住宅楼空调系统运行状况测试及能耗分析

对济南市某住宅楼空调系统夏季运行过程中冷冻水供回水温度、冷却水供回水温度、冷冻水流量,机组负荷率等参数进行调研和测试,根据实测数据分析该空调系统用能状况,运行效率,为空调系统的实际运行优化和该住宅建筑节能提供基础数据。     

Real-time determination of optimal indoor-air condition for thermal comfort,air quality and efficient energy usage

For building, “surroundings” that effect on indoor-air condition change with respect to the time. Without proper determination of the desired indoor-air condition to heating, ventilating and air-conditioning (HVAC) system, it may not be feasible to provide simultaneously occupants with thermal comfort and acceptable air quality with efficient energy consumption all the time. This paper presents an alternative methodology of real-time determination of optimal indoor-air condition for HVAC system in order to achieve such total requirements. Predicted mean vote (PMV), CO₂ concentration and cooling/heating load are used as parameter indices for thermal comfort, indoor-air quality and energy consumption respectively. The performance index of the HVAC system is then defined by summation in terms of square errors between those actual parameter indices and their desired values. This performance index is to be systematically minimized by a gradient-based technique in order to yield optimal indoor-air condition for HVAC system. A case study was chosen in 24 h operating HVAC system of a single-storey building by determining indoor-air temperature, indoor-air humidity, indoor-air velocity, and air-ventilation rate. The experiment results show that the proposed methodology can be efficiently implemented in the real-time determination of indoor-air condition to HVAC system that maintains PMV and CO₂ concentration close to the desired levels with less energy consumption when compared to those from the conventional approach.     

空调系统能效提升及运行管理系统技术集成与示范应用

重庆某商场全年能耗较高,中央空调设备运行效率低,缺少智能调节手段,具有很大的节能潜力。该文根据商场能耗特点和运行模式制定了空调控制系统节能改造方案,应用适宜的节能产品和实际运行效率优化控制策略,包括中央空调节能专家群控、水泵变频、风机变频等策略。在同样的工况下,分别进行常规模式运行和节能模式运行,实测数据表明,空调系统单项节能率达到30%。     

Evaluating performance indices of a shopping centre and implementing HVAC control principles to minimize energy usage

Heating, ventilating and air-conditioning (HVAC) systems in buildings must be integrated with an efficient control scheme to maintain comfort under any load conditions. Efficient HVAC control is often the most cost-effective option to improve the energy efficiency of a building. However, HVAC processes are non-linear, and characteristics change on a seasonal basis so the effect of changing the control strategy is usually difficult to predict. The present study aims to reduce energy consumption by defining new HVAC control strategies and tuning control loops in a shopping centre. First, an energy audit was performed to investigate the potential for energy savings and to redefine the control scenarios, while a methodology for the shopping centre was developed. Performance indices were then calculated and compared with the yardsticks. Next, normalised performance indices were computed to reach out a better understanding of the building’s efficiency. Finally, new strategies were implemented with the help of the existing building management system (BMS) and about 22% of energy saving was achieved.     

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.     

Performance of temperature and humidity independent control air-conditioning system in an office building

The temperature and humidity independent control (THIC) system, which controls indoor temperature and moisture separately, may be an attractive alternative to existing conventional HVAC systems for its prominent improvement on the overall system performance and utilization of low grade energy resources. In order to verify the effectiveness of THIC system, a pilot project has been implemented in an office building in Shenzhen, China. In the system, liquid desiccant fresh air handling units driven by heat pumps are utilized to remove the entire latent load of outdoor air supplied for the whole building, and chilled water at the temperature of 17.5 °C from chiller is pumped and distributed into dry fan coil units and radiant panels to control indoor temperature. This paper presents the results of field test of the system, which shows that the system can provide a comfortable indoor environment even in very hot and humid weather. The COP of the entire THIC system can reach 4.0. According to the energy usage data recorded from the year 2009, the energy consumption of the THIC system in the tested office building was 32.2 kWh/(m² yr), which demonstrates magnificent energy-saving potential compared with the conventional air-conditioning system (around 49 kWh/(m² yr)).     

HVAC systems for the fire protection engineer

Engineers concerned with smoke control often specify the use of the building HVAC system in a special mode of operation for controlling smoke. However, depending on the type of system and its set of components and controls, HVAC systems may be easy or difficult to adapt for use in controlling smoke. The various types of HVAC systems such as multizone systems, induction unit systems, fan coil systems, VAV, etc. are described relative to their ease of adaptability for controlling smoke. Also, the role of system components and controls in HVAC system operation and adaptability of the system as a smoke control system are described.     

过渡季节应用自然冷源的设计方法

在计算通风空调切换温度基础上,提出过渡季应用自然冷源的设计及节能评估方法,通过采用过渡季通风量控制策略减少风机运行能耗.上海地区某高大厂房采用此方案,与过渡季空调方案相比,负荷率0.8时,空调主机年节能率为29.3％,卸载控制策略时的风机能耗为风机满载运行时的41％～56％.提出以日期作为通风空调运行切换依据,并定量分析不保证率与节能率的关系.     

Energy savings modelling of re-tuning energy conservation measures in large office buildings

Today, many large commercial buildings use building automation systems to manage a wide range of equipment. This paper investigates the energy savings potential of several common heating, ventilation, and air conditioning (HVAC) system re-tuning measures on a typical large office building using the EnergyPlus software. Individual re-tuning measures simulated include automatic schedule adjustments, damper minimum flow adjustments, thermostat adjustments, as well as dynamic resets to static pressure, supply-air temperature, condenser chilled- and hot-water temperatures, and chilled and hot water differential pressure set points. All individual measures and combinations were simulated in 16 locations representative of different climates in the USA. Many of the demand-side individual measures were capable of reducing annual HVAC energy consumption by over 20% in most cities. Supply-side measures affecting HVAC plant conditions were only modestly successful (less than 5% annual HVAC energy savings). Some of the combinations revealed between 35% and 75% HVAC energy savings.     

Intelligent system based on wavelet decomposition and neural network for predicting of fan speed for energy saving in HVAC system

In this study, a heating, ventilating and air-conditioning (HVAC) system with different zones was designed and tested. Its fan motor speed and damper gap rates were controlled by two controllers (i.e. a PID controller and an intelligent controller) in real time to minimize its energy consumption. The desired temperatures were realized by variable flow-rate by considering the ambient temperature for each zone and evaporator. The PID parameters obtained in our previous theoretical work using fuzzy logic were utilized in this study. The experimental data used in this study was collected using a HVAC system built in a laboratory environment. The fan motor speed and damper gap rates were predicted using wavelet packet decomposition (WPD), entropy, and neural network (NN) techniques. WPD was used to reduce the input vector dimensions of the intelligent model. The suitable architecture of the NN model is determined after certain trial and error steps. According to test results, the developed model performance is at desirable level. Efficiency of the developed method was tested and a mean 95.62% recognition success was obtained. This model is an efficient and robust tool to predict damper gap rates and fan motor speed to minimize energy consumption of the HVAC system.     

暖通空调节能设计探究

改革开放以来,我国的经济高速发展,与此同时,各类能源被大最消耗,所以对于我国来说节能具有重大的意义。而目前,建筑能耗在我国的整体能耗中所。叶的比例比较大,而其中暖通空调系统则义可以说是建筑能耗中的主要耗能之一,所以实现暖通空调的节能具有非常重要的意义。木文我们将通过对暖通空调系统中节能的一些主要途径的研究,指出暖通卒调的节能设计方面中存在的一些主要问题并进行分析,提出了暖通空调节能设计的具体措施,这对降低暖通空调系统中的能耗,提高能量的使用效益具有积极有效的促进作用。     

Optimal and robust control of outdoor ventilation airflow rate for improving energy efficiency and IAQ

Combining demand-controlled ventilation (DCV) and economizer control can achieve adequate and even better indoor air quality with minimum cooling/heating energy consumption in buildings. The control instability during the transition processes between different control modes is among the major difficulties faced when combining DCV control with economizer control in applications. The practical energy benefit is another concern when using free cooling in the subtropical climate like Hong Kong. A robust control strategy, using “freezing”, gain scheduling, I-term reset and feedback transition control for different transition processes, is developed addressing the instability problems. The energy benefit of using economizer control is evaluated by over one year's comparison tests on two air-handling units in a building.