Thermal comfort control on multi-room fan coil unit system using LEE-based fuzzy logic

Saving consumable energy and maintaining the thermal comfort level are two main topics in the heating, ventilating and air conditioning (HVAC) control field. The reliability of the controller is important as well. This paper proposes a least enthalpy estimator (LEE) that combines the definition of thermal comfort level and the theory of enthalpy into a load predicting way to provide timely suitable settings for a fan coil unit (FCU) fuzzy controller used in HVAC. According to the settings, including temperature and relative humidity, the fuzzy controller can make decisions and adjust the output of the FCU system. From actual experiments, the LEE-based FCU fuzzy controller can achieve the requirements of the FCU control system such as thermal comfort, energy efficiency and reliability.     

Modeling and optimization of HVAC energy consumption

A data-driven approach for minimization of the energy to air condition a typical office-type facility is presented. Eight data-mining algorithms are applied to model the nonlinear relationship among energy consumption, control settings (supply air temperature and supply air static pressure), and a set of uncontrollable parameters. The multiple-linear perceptron (MLP) ensemble outperforms other models tested in this research, and therefore it is selected to model a chiller, a pump, a fan, and a reheat device. These four models are integrated into an energy optimization model with two decision variables, the setpoint of the supply air temperature and the static pressure in the air handling unit. The model is solved with a particle swarm optimization algorithm. The optimization results have demonstrated the total energy consumed by the heating, ventilation, and air-conditioning system is reduced by over 7%.     

Maximising the energy output of a PVT air system

Simultaneously generating both electricity and low grade heat, photovoltaic thermal (PVT) systems maximise the solar energy extracted per unit of collector area and have the added benefit of increasing the photovoltaic (PV) electrical output by reducing the PV operating temperature. A graphical representation of the temperature rise and rate of heat output as a function of the number of transfer units NTUs illustrates the influence of fundamental parameter values on the thermal performance of the PVT collector. With the aim of maximising the electrical and thermal energy outputs, a whole of system approach was used to design an experimental, unglazed, single pass, open loop PVT air system in Sydney. The PVT collector is oriented towards the north with a tilt angle of 34°, and used six 110 Wp frameless PV modules. A unique result was achieved whereby the additional electrical PV output was in excess of the fan energy requirement for air mass flow rates in the range of 0.03–0.05 kg/s m². This was made possible through energy efficient hydraulic design using large ducts to minimise the pressure loss and selection of a fan that produces high air mass flow rates (0.02–0.1 kg/s m²) at a low input power (4–85 W). The experimental PVT air system demonstrated increasing thermal and electrical PV efficiencies with increasing air mass flow rate, with thermal efficiencies in the range of 28–55% and electrical PV efficiencies between 10.6% and 12.2% at midday.     

Neuro-optimal operation of a variable air volume HVAC&R system

Low operational efficiency especially under partial load conditions and poor control are some reasons for high energy consumption of heating, ventilation, air conditioning and refrigeration (HVAC&R) systems. To improve energy efficiency, HVAC&R systems should be efficiently operated to maintain a desired indoor environment under dynamic ambient and indoor conditions. This study proposes a neural network based optimal supervisory operation strategy to find the optimal set points for chilled water supply temperature, discharge air temperature and VAV system fan static pressure such that the indoor environment is maintained with the least chiller and fan energy consumption. To achieve this objective, a dynamic system model is developed first to simulate the system behavior under different control schemes and operating conditions. A multi-layer feed forward neural network is constructed and trained in unsupervised mode to minimize the cost function which is comprised of overall energy cost and penalty cost when one or more constraints are violated. After training, the network is implemented as a supervisory controller to compute the optimal settings for the system. Simulation results show that compared to the conventional night reset operation scheme, the optimal operation scheme saves around 10% energy under full load condition and 19% energy under partial load conditions.     

Rotational speed adjustment of axial flow fans to maximize net power output for direct dry cooling power generating units

The power consumption of axial flow fans may account for more than 1% of the rated power output of the power generating unit, so it is of benefit to the energy efficiency of the power generating unit to propose an operation adjustment approach to axial flow fans. On the basis of representative 2 × 600 MW direct dry cooling generating units, a computational model of air‐side flow and heat transfer of an air‐cooled condenser (ACC) combined with exhaust steam condensation is developed, by which the airflow rate, inlet air temperature of ACCs, the power consumption of axial flow fans, turbine backpressure, and net power output of power generating units at various wind speeds and in various wind directions are obtained. The results show that the net power output in the presence of winds always decreases when the rational speeds of the first upwind row axial flow fans increase from the rated speed of 79 rpm by 10% to 86.9 rpm. However, the net power output will increase in various wind directions if the rational speeds of all the fans except the upwind first row fans increase to 86.9 rpm. This can contribute to the optimal operation of the ACC by rotational speed adjustment of axial flow fans.     

300MW机组直吹式制粉系统通风量优化试验及分析

为解决直吹式制粉系统一次风机电耗较大、中速辊式磨煤机静环吹损较严重、煤粉细度偏小等问题,通过对磨煤机出口一次风速、磨煤机入口风压等关键点的控制,较系统的优化制粉系统通风量,达到降低能耗、提高锅炉效率的试验目的,对同类型机组的优化试验有一定借鉴意义。     

Development of a radial-flow multiple magnetically coupled fan system with one piezoelectric actuator

In recent years, piezoelectric fans and their feasibility for use in cooling electronic devices have been widely studied. However, there are few studies that address using a single piezoelectric actuator to generate radial air flow. In this study, a radial-flow multiple fan system (RMFS) was developed for the thermal management of high power LEDs. This system only used one piezoelectric actuator and a magnetic repulsive force to activate up to 20 fans, which featured low power consumption and a large cooling area. The RMFS was mounted in a circular heat sink to evaluate its thermal performance. To find the optimal design for the RMFS, the influence of some geometric parameters was investigated. The performance of different designs was compared with a commercially available axial fan. The results showed that design E had the best thermal performance among the designs because of its relatively large frequency and amplitude. The thermal resistance and percentage improvement under a 35 W heat flux were 0.86 K/W and 36.9%, respectively. In addition, a coefficient of performance (COP) was defined. The COP of design E was approximately 3.7 times that of the rotary fan. For the power consumption aspect, the RMFS is more efficient than the rotary fan.     

侧风条件下带消能导流装置的直接空冷岛冬季冻结风险模拟研究

哈密某电厂在其空冷岛中使用了一种新型消能导流装置来抵抗侧风影响、稳定机组背压。然而,该电厂冬季空冷单元散热管束冻结的情况依然存在。为了探究该装置对空冷岛冬季防冻的影响,利用Fluent软件对该电厂冬季大风时空冷岛的流动传热特性及各空冷单元的冻结风险进行了模拟研究。研究表明：空冷岛“消能导流装置”整体上对空冷单元的防冻起负面作用;在冬季大风条件下该装置迎风侧空冷单元的散热量平均超出警戒值27%以上,最高达到50%;消能导流装置主要通过提升轴流风机空气流速来增加对应空冷单元的换热量,该装置迎风侧空冷单元轴流风机的轴向空气流速甚至能达到与环境侧风相同的水平,这导致对应空冷单元换热量激增,更容易出现冻结事故;大风条件下该装置在空冷岛下方形成的高压区域分布并不均匀,临近主厂房与相邻空冷岛一侧的高压区域压力更高、面积更大,这些区域空冷单元的冻结风险更高。     

Operation strategies of axial flow fans in a direct dry cooling system under various meteorological conditions

For a direct dry cooling system, the turbine back pressure fluctuates with the meteorological conditions. Moreover, the operation of axial flow fans plays an important role in the cooling performance of air-cooled condensers (ACC). It is of significant use to study the operation strategies of axial flow fans under various ambient conditions. Based on typical 2 × 660 MW direct dry cooling power generating units, the ACC model coupled with the turbine thermodynamic characteristics is developed, by which the thermo-flow performances of the ACC are predicted in the dominant wind direction, and then the standard coal consumption is calculated. The results show that the increased ambient temperature and wind speed, or the reduced fan rotational speed leads to the high turbine back pressure. At the low ambient temperature and wind speed, the standard coal consumption rate of the unit can be reduced by reducing the speed of axial flow fans appropriately, with the maximum drop in coal consumption rate reached 0.734 g/(kWh) when the ambient temperature is 10°C without wind. If the wind speed exceeds 12 m/s or the ambient temperature reaches 25°C, 110% of the rated fan rotational speed is recommended.     

Performance enhancement of a subcooled cold storage air conditioning system

This article experimentally investigates the enhancement of thermal performance for an air conditioning system utilizing a cold storage unit as a subcooler. The cold storage unit is composed of an energy storage tank, liquid-side heat exchanger, suction-side heat exchanger and energy storage material (ESM), water. When the cooling load is lower than the nominal cooling capacity of the system, the cold storage unit can store extra cold energy of the system to subcool the condenser outlet refrigerant. Hence, both the cooling capacity and coefficient of performance (COP) of the system will be increased. This experiment tests the two operation modes: subcooled mode with energy storage and non-subcooled mode without energy storage. The results show that for fixed cooling loads at 3.05 kW, 3.5 kW and 3.95 kW, the COP of the subcooled mode are 16.0%, 15.6% and 14.1% higher than those of the non-subcooled mode, respectively. In the varied cooling load experiments, the COP of the subcooled cold storage air conditioning system is 15.3% higher than the conventional system.     

Numerical investigation on the flow field of an axial flow fan in a direct air‐cooled condenser for a large power plant

The flow field of an axial fan in a direct air‐cooled condenser for a large power plant is modeled numerically. In order to improve the efficiency of heat exchange of the air‐cooled condenser, methods of increasing the rotational velocity of the fan and laying out the guide blade at the outlet of the fan are adopted. Results show that increasing the rotational velocity of the fan can effectively increase the flux of the fan, and can improve the efficiency of an air‐cooled condenser; laying out the guide blade at the fan outlet can ameliorate the flow field in an A‐flame. This causes the rotational kinetic energy to change into static pressure at the fan outlet, so the ability of the heat exchange of the air‐cooled condenser is improved. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21027     

优化风机盘管设计 降低材料消耗

通过对风机盘管的主要技术指标和换热过程进行分析,结果表明,提高表冷器迎面风速与水流速可以提高风机盘管机组的制冷量、制热量。根据修改风机盘管的设计并实测得出,可以通过优化风机盘管的表冷器设计以保证风机盘管机组的制冷量与制热量,从而减少风机盘管的材料消耗与生产耗能。     

Chillers energy consumption, energy savings and emission analysis in an institutional buildings

Chillers consume more than 40% of the total energy used in the commercial and industrial buildings for space conditioning. In this paper, energy consumption by chillers and chilled water pumps, condenser pumps and fan motors has been estimated using data collected by a walkthrough energy audit for the 16 faculties of the University of Malaya. It has been estimated that chillers and motors and pumps used in chillers consume 10,737 MWh (i.e. 51% of total energy consumption) of electric energy for different percentage of loadings. As chillers are major energy users, variable speed drives are applied in chillers to reduce their energy consumption. It has been estimated that about 8368 MWh annual energy can be saved by using efficient chillers at different loadings. It has also been found that about 23,532 MWh annual energy can be saved for chilled water supply pumps, condenser pumps and cooling tower fan motors by matching required speeds using variable speed drives for 60% of speed reduction. About 1,274,692 kg of CO₂ emission could be avoided for using energy efficient chillers at 50% load. It has been also found that about 2,426,769 kg CO₂ emission can be reduced by using variable speed drives for 60% speed reductions. Payback periods found to be only few months for using variable speed drives in chilled water pumps, condensers and fan motors.     

防SARS抗菌型干工况运行风机盘管空调系统设计理念

提出了干工况运行风机盘管加大焓差处理新风机组空调系统的设计理念 ,分析了其原理、空气处理方案和关键问题 ,对于当前针对SARS掀起的抗菌空调研发设计工作具有一定的指导意义     

Numerical study of a hybrid ventilation system for single family houses

The main objective of this study is to develop and test hybrid ventilation systems and control strategies that are suitable for residential buildings. Two ventilation systems were modelled: a mechanical extract ventilation system (called the reference system) and a hybrid low pressure ventilation system that can support two different types of demand control strategies (occupancy detection and CO₂ concentration). The newly developed models were assembled with the existing thermal models of the SIMBAD Building and HVAC Toolbox developed by the CSTB.A single family house located in Athens (Greece), Nice (France), Trappes (France) and finally Stockholm (Sweden) was considered as the case study. Yearly simulations were performed to assess the performance of the hybrid ventilation control strategies. The assessment criteria used are related to indoor air quality, thermal comfort, energy consumption and stability of control strategies. The results show that the low pressure ventilation system can improve the indoor air quality and reduce the fan energy consumption compared to the reference system while maintaining the same building energy consumption for heating.     

固体吸附除湿技术用于民用建筑中央空调系统的经济性分析

针对传统空调冷却除湿方式的高能耗,提出将固体吸附除湿技术应用于民用建筑中央空调系统,并对采用这种除湿方式的干式风机盘管加固体吸附独立除湿新风系统与传统的风机盘管加新风系统在运行能耗方面进行经济性实例分析,结果表明干式风机盘管加固体吸附独立除湿新风系统较传统风机盘管加新风系统其夏季空调工况每天减少约14W/m2,有效降低建筑能耗。     

An air filter pressure loss model for fan energy calculation in air handling units

Air filters consume a significant part of the fan power in air handling systems. Due to lack of suitable models, the fan energy associated with the filter pressure drop is often estimated based on average airflow and average pressure drop across the filter. Since the pressure drop varies nonlinearly with airflow and the filter resistance varies with dirt build‐up, current methods often produce erroneous results. This paper presents a new air filter pressure loss model that has been developed and verified using experimental data. The model projects the pressure losses across the filter for both constant and variable airflows. The inputs to the model are the airflow rate, the time of use, the initial design and final pressure losses at the design flow rate, and the coefficient of a power law regression of pressure loss as a function of airflow rate. The air filter pressure loss model may be implemented in hourly building energy simulation programs that perform hourly simulation at the air handling unit level. Copyright © 2003 John Wiley & Sons, Ltd.     

Performance testing of an optimal photocatalytic mop fan air cleaning system

A novel photocatalytic mop fan air cleaning system has been developed. The novel mop fan system is optimized in terms of the pollutant degradation efficiency, energy consumption, appearance and cost reduction based on previous research. The fluid dynamic characteristic and energy consumption of the novel mop fan system has been identified by experimental testing. Pollutant degradation effect of the mop fan on a typical industry pollutant, diesel fume, has also been tested. It was found that the system has very low energy consumption and is very effective to destroy the diesel fume, a microparticulate pollutant. The system is suitable for any indoor environment to clean the air by removing the particulates, odors, virus, bacteria and volatile organic pollutants. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of neutral temperature on energy saving of centralized air-conditioning systems in subtropical Hong Kong

Higher room temperature can still let the occupants have a neutral thermal sensation if higher air speed is provided. With a suitable scheme of neutral temperature and comfort air speed, reduction of energy consumption of the central chiller plant may surpass the additional energy requirement of the air side equipment, then both energy saving and thermal comfort can be achieved for the entire air-conditioning system. To evaluate this, the energy consumptions of a centralized air-conditioning system using the common air side alternatives were studied for the subtropical Hong Kong. The alternatives are variable air volume (VAV) system, constant air volume (CAV) system and fan coil (FC) system. Each of them was associated to a central chiller plant to serve a high-rise office building. The studying range of the room air temperature was from 23 °C to 30 °C. It is found that the VAV and FC systems can provide both thermal comfort and energy saving for higher room temperature, but CAV system is not feasible when the room air temperature is above 27 °C. If the indoor air speed threshold is considered, the neutral temperature can be brought up to 26.5 °C, and the energy saving potentials of VAV and FC systems would be 12.9% and 9.3% respectively.     

高效喷雾通风冷却塔在循环水场中的节能分析

高效喷雾通风冷却塔通过通风蒸发、热传导形式带走热量来完成热水的降温过程,其主要特点是喷流雾化和利用循环水的余能来推动空气在冷却塔内的强制流动,从而代替轴流风机达到节电节能的目的。其核心部件是喷雾推进雾化器,其主轴采用高分子非金属耐磨材料制造,克服了用油轴承在水环境中易锈蚀、卡死等故障,减少了设备维修量。2008,中国石化洛阳分公司采用高效喷雾通风塔冷却技术对第三循环水场3号塔进行了改造,投用至今运行稳定,主要运行参数达到了预期的目的,冷却效果与使用轴流风机相当,循环泵电流与改造前相当,没有增加循环水的回水管路阻力。若洛阳石化循环水冷却塔轴流风机全部进行此技术改造,保守计算年可节电1500×10^4kW·h。