Inherent correlation between the total output cooling capacity and equipment sensible heat ratio of a direct expansion air conditioning system under variable-speed operation (XXG SMD SHR DX AC unit)

Appropriately controlling indoor air humidity at a suitable level in buildings is important. To simultaneously control both indoor air dry-bulb temperature and relative humidity requires the match between the total output cooling capacity of an A/C system and the total cooling load in a space served by the A/C system, as well as the Equipment sensible heat ratio (SHR) of the A/C system and the Application SHR of the conditioned space. This paper reports on an experimental study on the inherent correlations between the total output cooling capacity and Equipment SHR of a DX A/C system. Experiments were carried out under different combinations of compressor speed and supply fan speed, and also under different inlet air conditions to the DX evaporator. The results obtained would lead to a better understanding of the operating characteristics of a DX A/C system under variable-speed operation, as well as the constraint of using these characteristics in developing appropriate control strategies, so as to better design, operate and control DX A/C systems for improved indoor thermal environmental control.     

Modeling the design and performance characteristics of solar steam-jet cooling for comfort air conditioning

A detailed mathematical model describing the performance of low-pressure low-temperature solar steam-jet cooling cycles for comfort air conditioning is presented in this paper. The model is based on the analysis of the cycle performance together with the supersonic flow conditions in the convergent divergent nozzle and the preceding supersonic and subsonic diffusers. The sets of simultaneous equations resulting from the model together with a subroutine providing numerical values of the thermodynamic properties of steam formulated a computer simulation program. The simulation program analyzes the performance of the solar steam-jet cooling system under different design and operating conditions. A set of design charts for the solar steam-jet cooling cycle and for the selection of the ejector dimensions were constructed. Finally, conclusions on the design considerations and limitations as well as the off design performance are discussed.     

大空间两种气流组织夏季热环境及其能耗实验研究

以某大空间实验基地为研究对象,针对喷口送风和柱状下送风两种分层空调的热环境及供冷量进行了实测研究.研究结果表明:因喷口送风空调区较大,在夏季室外气象参数基本相同的两种室外气象条件下,喷口送风空调系统供冷量比柱状下送风空调系统的供冷量分别高出20.8%、24.4%,且喷口送风空调系统抗干扰能力较柱状下送风强;喷口送风时工作区温度均匀性好于柱状下送风,头足温差较小,但其工作区风速超过标准,而柱状下送风时工作区风速则符合环境设计要求;两种不同送风量下喷口送风时吹风感指数分别为15.64%、11.23%,而柱状下送风时吹风感指数分别为4.17%、2.40%,柱状下送风要明显优于喷口送风.故从节能及热舒适性角度综合考虑,单侧回风的大空间建筑应尽可能采用柱状下送风分层空调,而对于干扰比较大,空调场地较小,无法布置柱状下送风口的场合,则选取喷口送风较好.     

Development of a method for calculating steady-state equipment sensible heat ratio of direct expansion air conditioning units

A complete set of calculation method for steady-state equipment sensible heat ratio (SHR) for a direct expansion (DX) cooling coil has been developed and reported. The method was based on the fundamentals of energy conservation and heat and mass transfer taking place in the DX cooling coil, and was experimentally validated using an experimental DX A/C rig. With the method developed, the effect of refrigerant evaporating temperature at fixed inlet air conditions on equipment SHR has been theoretically analyzed. The validated method can be useful in further studying the inherent operating characteristics of a DX air conditioning (A/C) unit and in developing suitable control strategies for achieving higher energy efficiency and better indoor thermal environment.     

Airflow maldistribution and the performance of a packaged air conditioning unit evaporator

The performance of an evaporator for a packaged air conditioning unit has been investigated. A heat transfer program ACOL5 validated in an earlier study, was used to predict the performance. Non-uniform velocity distribution measurements taken in a typical air conditioning unit were employed in the prediction of the evaporator performance. It was found that this maldistribution reduced the performance of an evaporator circuit, as compared to uniform flow. Circuits at the edges of the evaporator, where the velocity was low, did not perform well. With the refrigerants controlled by one thermostatic valve, the worst performing circuit affected the performance of the whole evaporator, the evaporator performance being reduced by as much as 35%. The performance of the evaporator, where the circuits had different numbers of passes, depended on the position of the circuit in the evaporator.     

热湿地区直膨式辐射顶板空调系统模拟分析

以广州地区某办公楼为例,利用Energyplus对直膨式辐射顶板空调系统进行模拟,并与风机盘管+独立新风空调系统、双冷源新风机组+辐射顶板空调系统进行能耗对比分析。结果显示,在直膨式辐射顶板空调系统中,辐射顶板承担系统69.2%的显热负荷;相对于风机盘管+独立新风空调系统,系统节能率为20.09%,相对于双冷源新风机组+辐射顶板系统,系统节能率为7.16%。     

某地铁项目空调送风道结构优化

在某地铁项目空调送风道方案设计完成的前提下,利用Catia三维软件进行M车空调送风道建模,然后,利用计算流体模拟软件Fluent对空调送风道进行CFD仿真分析,从而可以得出气流在风道、格栅和客室内部的流动状况。通过统计送风格栅各段的送风量,分析风道送风均匀性,从而最终确定最合理的送风道结构形式,以此改善此项目空调送风均匀及温度均匀性,提高客室空调整体舒适性。     

某火电机组汽电双驱引风机系统辅机故障控制仿真及试验分析

为了研究某火电机组风烟系统采用汽电双驱型引风机系统,不同设备故障条件下机组相应的控制策略,依据热力学原理及设备固有属性,并搭建了相应的动力学模型,对发电机跳闸、小汽轮机跳闸、引风机与小汽轮机同时跳闸3种故障下的控制策略进行分析。最后,通过3次实际试验验证了控制策略及模型仿真结论的正确性。研究表明：在发电机跳闸时,可以通过调门快速动作到一定开度来保证机组的安全运行;在小汽轮机跳闸或引风机与小汽轮机同时跳闸时,可以通过保证机组的水煤比、风煤比等参数实现机组的减负荷运行。     

MPPT of a PEMFC based on air supply control of the motocompressor group

In this paper, advanced control of the motocompressor group for Proton Exchange Membrane Fuel Cell (PEMFC) is addressed.     

Influence of air supply on the performance and internal flow characteristics of a cross flow turbine

This study attempts to improve the efficiency of a given type of cross flow turbine by supplying air from air suction holes. A newly developed air supply method is adopted. CFD analysis of the cross flow turbine is carried out to investigate the performance and internal flow characteristics of the turbine in detail. The air layer prevents shock loss between water flow and axis and suppresses recirculation flow in the runner passage. Hence, it is necessary to measure the amount of air layer in the runner passage and examine its effect on the performance of the cross flow turbine. The result shows that the turbine efficiency has improved more as the newly developed air supply method is applied effectively.     

洁净空调新风量的节能控制与运行

通过对洁净空调新风系统设计及运行的分析,探讨洁净空调变新风量的必要性和可行性,并利用自控相关理论,设计出在室内人员数量不定的情况下,通过实时监测室内二氧化碳浓度与余压状态来确定送入室内新风量的控制过程,最终达到系统节能的目的。     

Magnetic and thermal performance of a synchronous motor under lossminimization control

The steady state magnetic and thermal performance of a wound-field cylindrical rotor synchronous motor under loss minimization control is investigated. The calculated magnetic field waveforms are presented and it is shown that loss minimization control decreases the magnetic saturation. It is also proved that although the optimal stator current is increased, the temperature is decreased in all parts of the motor. Theoretical and experimental results are presented to verify the operational improvements     

Dehumidification effects in the superheated region (SPR) of a direct expansion (DX) air cooling coil

A DX air cooling coil may normally be assumed to have two regions in its refrigerant side, according to refrigerant status, a two-phase region (TPR) and a superheated region (SPR). Dry air side surface of the SPR in a DX air cooling coil has been normally assumed in lumped-parameter mathematical models previously developed without however being validated. Therefore, an experimental study has been carried out to examine such an assumption under different operating conditions. The experimental results suggested that the air side surface of the SPR in a DX air cooling coil was either fully or partially wet under all experimental conditions and assuming dry air side of the SPR could lead to an underestimated total amount of water vapor condensed on the entire DX coil surface. Therefore, it is recommended that the assumption of dry air side in a SPR be no longer used in future lumped-parameter models to be developed for improved modeling accuracy.     

Investigation of thermal performance of solar air heater having roughness elements as a combination of inclined and transverse ribs on the absorber plate

An experimental investigation has been carried out to study the heat transfer and friction characteristics by using a combination of inclined as well as transverse ribs on the absorber plate of a solar air heater. The experimental investigation encompassed the Reynolds number (Re) ranges from 2000 to 14 000, relative roughness pitch (p/e) 3–8 and relative roughness height (e/D_h) 0.030. The effect of these parameters on the heat transfer coefficient and friction factor has been discussed in the present paper and correlations for Nusselt number and friction factor has been developed within the reasonable limits. A procedure to compute the thermal efficiency based on heat transfer processes in the system is also given and the effect of these parameters on thermal efficiency has been discussed.     

基于金属毛细管网的新型温湿度独立控制辐射空调系统设计

传统空调系统存在如吹风感、冷表面滋生霉菌、能效比较低等一系列弊端。为了解决这些问题,提出一种基于金属毛细管网的辐射式热泵系统,利用敷设于建筑物围护结构内的金属毛细管作为室内侧换热器,由热泵系统控制室内温度。然而,热泵系统无法保证新风供应、存在室内结露等问题,因此提出在该系统基础上复合运行太阳能溶液除湿新风系统,利用太阳能集热板收集的热量对除湿溶液进行加热再生,室外新风经浓溶液除湿并经制冷剂冷却后,送入室内控制室内相对湿度。夏季供冷时,热泵系统和除湿系统共用1套制冷剂,达到同时实现室内供冷、除湿溶液再生和新风冷却的效果,保证室内舒适度及空气品质,避免室内结露。这种基于太阳能溶液除湿和金属毛细管网的新型辐射空调系统可实现室内温湿度独立控制,降低能源消耗,促进绿色建筑可持续发展。     

Measurement and prediction of the cooling characteristics of a generalized vibrating piezoelectric fan

Piezoelectric fans are thin elastic beams whose vibratory motion is actuated by means of a piezoelectric material bonded to the beam. These fans have found use as a means to enhance convective heat transfer while requiring only small amounts of power. The objective of the present work is to quantify the influence of each operational parameter and its relative impact on thermal performance. Of particular interest are the vibration frequency and amplitude as well as the geometry of the vibrating cantilever beam. The experimental setup consists of a piezoelectric fan mounted normal to a constant heat flux surface. Temperature contours on this surface captured via an infrared camera are used to extract the forced convection coefficient due to the fluid motion generated from the fan. Different fans, with fundamental resonance frequencies ranging from 60 to 250 Hz, are considered. Results show that the performance of the fans is maximized at a particular value of the gap between the fan tip and the heated surface. It is found that when a fan operates at this optimum gap, the heat transfer rate is dependent only on the frequency and amplitude of oscillation. Correlations based on appropriately defined dimensionless parameters are developed and found to successfully predict the thermal performance across the entire range of fan dimensions, vibration frequency and amplitude. An understanding of the dependence of thermal performance on the governing variables allows for improved design of piezoelectric fans as a method of enhancing heat transfer.     

Experimental assessment of heat storage properties and heat transfer characteristics of a phase change material slurry for air conditioning applications

A new microencapsulated phase change material slurry based on microencapsulated Rubitherm RT6 at high concentration (45% w/w) was tested. Some heat storage properties and heat transfer characteristics have been experimentally investigated in order to assess its suitability for the integration into a low temperature heat storage system for solar air conditioning applications. DSC tests were conducted to evaluate the cold storage capacity and phase change temperature range. A phase change interval of approximately 3 °C and a hysteresis behaviour of the enthalpy were identified. An experimental set-up was built in order to quantify the natural convection heat transfer occurring from a vertical helically coiled tube immersed in the phase change material slurry. First, tests were carried out using water in order to obtain natural convection heat transfer correlations. Then a comparison was conducted with the results obtained for the phase change material slurry. It was found that the values of the heat transfer coefficient for the phase change material slurry were higher than for water, under identical temperature conditions inside the phase change interval.     

Exergetic analysis of a double stage LiBr–H2O thermal compressor cooled by air/water and driven by low grade heat

In the present paper, an exergetic analysis of a double stage thermal compressor using the lithium bromide–water solution is performed. The double stage system considered allows obtaining evaporation temperatures equal to 5 °C using solar heat coming from flat plate collectors and other low grade thermal sources. In this study, ambient air and water are alternatively used as cooling fluids without crystallization problems up to condensation–absorption temperatures equal to 50 °C. The results obtained give the entropy generated, the exergy destroyed and the exergetic efficiency of the double stage thermal compressor as a function of the absorption temperature. The conclusions obtained show that the irreversibilities generated by the double stage thermal compressor will tend to increase with the absorption temperature up to 45 °C. The maximum value corresponds to 1.35 kJ kg⁻¹ K⁻¹. The entropy generated and the exergy destroyed by the air cooled system are higher than those by the water cooled one. The difference between the values increases when the absorption temperature increases. For an absorption temperature equal to 50 °C, the air cooled mode generates 14% more entropy and destroys 14% more exergy than the water cooled one. Also, the results are compared with those of previous studies for single and double effect air cooled and water cooled thermal compressors. The conclusions show that the double stage system has about 22% less exergetic efficiency than the single effect one and 32% less exergetic efficiency than the double effect one.