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During the regulation process of VAV systems, the supply air volume changes with the real time load changes, which will cause the fresh air volume to deviate from its set value. Insufficient fresh air results in poor IAQ, whereas an excessive fresh air increases energy consumption. Therefore, an effective method to control the fresh air volume is essential for VAV systems. Based on the differential pressure control theory, two improved control methods—the fresh air section static pressure control method and the critical air volume control method—are proposed herein. Three control methods were compared through experimental study. The results indicate that differential pressure in the first improved method is higher than that in the differential pressure control method, which increases the ease of measurement. However, both these methods have approximately 15% to 25% errors when the supply air volume is small. The critical air volume control method provides more precise control of the fresh air volume, and eliminates deviations at small supply air volumes. Furthermore, the fan power is reduced as well. Investigation has demonstrated that the critical air volume control method is energy-efficient, and can provide new insights into optimized energy-saving control methods for VAV systems. This work proposed a fresh air volume control method of VAV system, the critical air volume control method. This method improves the control accuracy and the convenience of differential pressure measurement of VAV system. The reliability of the method was verified on the test rig, and it is similar to the engineering situation. Therefore, this method has practical application value. Also this method reduces the fan energy consumption of VAV system, thereby improving energy efficiency and reducing operating costs.

The extraction and analysis of electricity consumption changing patterns are increasingly important, as they can guide in energy management and efficiency retrofitting. Consequently, it is necessary to extract the laws governing building electricity consumption characteristics. This method should be on an hour-scale and successfully applied online to various buildings. Under these conditions, the method should be as simple as possible to ensure excellent online applications. A matrix model method was developed based on the conventional K-nearest neighbour clustering algorithm, which introduced the concept of electricity intensity levels. This method used the slopes of the power consumption curve as the grading standard for the extraction and assessment of the electricity consumption laws. The validation results for seven different buildings with various functions and climate zones, including the mean absolute error, mean absolute percentage error, mean square error, root mean square error, and coefficient of variance, showed that this method met the aforementioned requirements. Moreover, this method can be used for power consumption prediction, which integrated a process of filtering historical data, leading to better accuracy and less data volume than that of other methods that use historical data for prediction. Practical application This paper proposed a matrix model method based on the conventional K-nearest-neighbour clustering algorithm, which introduced the concept of electricity intensity levels. This method was applied to various buildings online, which coupled the process of filtering historical data and flexible selectivity of models when used on different buildings. This method was used for assessing energy-saving potential, energy-saving retrofit priorities, and power consumption forecasting, which will benefit researchers and engineers.

The outstanding combination of high strength, fracture toughness and low mass makes the metastable β titanium alloy an ideal material for aviation application. Machining of the metastable β titanium alloy remains a challenge due to their poor machinability. In this study, the high feed milling of a novel metastable β titanium alloy M28 is investigated to evaluate the performance of a potential high-efficiency-machining approach for the next generation titanium alloy and promote the understanding of high feed milling. The cutting force and the wear mechanism of carbide tool coated with TiAlN-Al2O3 are investigated as well as the influence of high feed on machined surface microstructures and microhardness. Due to the chip thinning effect of high feed milling, a proper high feed maintains a sufficient chip thickness to prevent the ploughing. Cutting edge degeneration induced by the carbide matrix fracture accelerates the tool wear. Mechanical stress induced cracks lead to the uneven delamination of the TiAlN-Al2O3 coating. Slight effect of high feed can be found on the microstructures and microhardness of the machined surface. While the tool wear leads to significant grain fragmentation and distortion at the surface. Since no white layer is found in the cutting of M28, high feed milling shows the advantage of preventing the heat induced surface injury.

In order to design the vertical falling film evaporators applied in the sewage source heat pump systems, a numerical study employing the VOF (Volume of Fluid) method has been carried out to determine the thickness and the wave behavior of falling liquid film outside a vertical tube. The effects of the annular gap, tube diameter, tube length, spray density, viscosity and surface tension are discussed. The simulation results demonstrate that spray density and the fluid viscosity are the two most influential factors affecting the film thickness. Besides, when spray density is larger than 0.100 kg/(m∙s), the film thickness decreases slightly with the increase of the flow distance. So the influence of tube length on film thickness cannot be ignored and it also should be considered in the film thickness prediction model. On the other hand, the tube diameter and the surface tension have little effect on the film thickness. It mainly have a significant impact on the wave amplitude of the liquid film at low flowrate. Besides, the annular gap provides a limited effect on the outlet section of the falling film. On the basis of the simulation results, a new correlation incorporating the tube length is developed to effectively predict the falling film thickness. Compared with the experimental data, it is found that the prediction accuracy of the correlation can be controlled within ±15%. The present research provides a theoretical basis for designing falling film evaporators.

The dispersion of the coronavirus pandemic has caused immense damage worldwide, and people have begun to ruminate epidemic prevention strategies for public places. Airport terminals with a high number of occupied passengers have become potentially high-risk regions for aerosol transmission of coronavirus disease 2019 (COVID-19). In this study, the Eulerian-Lagrangian approach and realizable

Systematic and random errors for working sensors in building systems can seriously affect the operation performance and have a significant negative impact on energy efficiency and indoor comfort. H...

The temperature of domestic drain water is relatively high, but its flux is sometimes insufficient as a heating source. Thus, the conventional wastewater source heat pump water heater is incapable of meeting user heating demand given the limited sensible heat temperature difference in many situations. To address this problem, a novel in–house heat pump water heater with a freezing latent heat evaporator and assisted by domestic drain water was proposed. A prototype of the system was first constructed to determine the performance of the system. An experiment was then conducted, in which a parallel helical coil tube evaporator was designed and developed to extract freezing latent heat from domestic drain water. Experimental data was obtained in different experimental conditions. Results of the investigation show that the heat pump water heater with a freezing latent evaporator recovers 3.4 times more energy than the conventional wastewater source heat pump water heater, and saves 60% energy compared with the traditional electric water heater. Furthermore, an interesting result is that the heat transfer coefficient increased significantly at the moment the wastewater was just frozen. This paper provides a reference for the wastewater source heat pump water heater to extract freezing latent heat from domestic drain water.

Among sub-items of energy consumption in public buildings, lighting sockets play an important role in energy-saving analysis. So, the energy consumption data quality of lighting sockets is important. However, limited by the initial cost of energy monitoring platform, it is difficult to install electricity meters covering all branches and to retrofit the incompact classification electricity branches, which results in a mixture of the lighting socket energy consumption and other components. In this study, a separation methodology is proposed. First, the abnormal data in the energy monitoring platform are cleaned and screened using a clustering algorithm. Second, the average outdoor air temperature partitioning model (OATPM) method and the k-nearest neighbor (KNN) clustering algorithm method are proposed for identifying and separating the abnormal data. These two methods have complementary advantages in the best applicable scenarios, including calculation accuracy and other aspects. The verification results for three buildings show that the relative error of this separation methodology is less than 15%. Finally, this paper presents the optimization parameters of the KNN method. Through this methodology, building managers need only historical data in an energy monitoring platform to separate the combined power consumption of the lighting sockets and air-conditioning online, independent of detailed information statistics.

The process of the constructing and operating building energy consumption monitoring platforms (BECMPs) has last for more than a decade in China. In the meantime, a lot of problems occurred, such as data loss and data anomaly. However, there is lacking method to automatically measure the data quality of BECMPs. Most data problems can only be discovered by human checking, which is often delayed, and the severity is often unclear, resulting in restriction to further data utilization. Based on previous research on the causes of data loss and data anomaly, this paper put forward an index system to evaluate the data quality of BECMPs. The index system targets the data quality itself as well as the designing, constructing, debugging, operating and maintaining process of BECMPs, which enable the maintenance personnel to have a clear knowledge of the data quality and help them keep the system in an optimal state.

The correct data or information from the building sensing networks plays a vital role in the operation algorithms. The sensor errors usually show a negative effect on the performance of control, diagnosis, and optimization of building energy systems. Thus, the physical working sensors periodically need to be removed to be calibrated by the reference sensors, which will disrupt the normal operation of building systems from time to time. The virtual in situ sensor calibration (VIC), based on the Bayesian inference and Markov chain Monte Carlo methods (MCMC), is an effective approach to handle the systematic and random errors of various working sensors simultaneously. This technology uses the distance function and system models to estimate the true measurements and addresses most of the practical problems in a traditional calibration process. However, the sensitivity coefficient in the definition of distance function is one of the determining factors in the calibration accuracy and how to define it still remains uncertain. Therefore, this study employed the genetic algorithm (GA) to optimize this parameter in a LiBr–H2O absorption refrigeration system. The results revealed that the systematic and random errors of temperature and mass flow rate were reduced considerably with the help of optimized sensitivity coefficients and most of the measurements approached to their true values after the calibration.

Fouling growth in pipes is a basic problem in the design and application of sewage source heat pump systems. After investigation, in the design of the operating parameters of the sewage source heat pump actual project, the flow rate of the sewage in the industrial sewage source heat pump is 0.2–1.8 m/s, the sewage inlet temperature is 18–23.5 ℃, and the condensation temperature is 30–35 ℃. Aiming at the basic problem of fouling growth in sewage pipe, a fouling growth test bench in heat exchanger tube under condensation condition of sewage source heat pump was built. Based on the actual collected urban sewage, the effects of fouling growth on the flow and heat transfer characteristics of the heat exchanger were studied under the condition of equal wall temperature. The experimental results show that the larger the initial Reynolds number, the smaller the thermal resistance of the pipe fouling, and the longer the time for the stable growth of the dirt. In terms of heat transfer, pipe fouling growth affects the overall heat transfer coefficient of the pipe, but the initial Reynolds number also affects the overall heat transfer of the pipe. At the initial Reynolds number between 7150 and 16,091, there is a point that minimizes the effect of pipe fouling growth on the overall heat transfer of the pipe. The research results in this paper can provide guidance for the optimal design of sewage source heat pump system.

With the gradual advancement of energy-saving work in public buildings, the number of energy monitoring systems continues to increase. However, due to the low level of information management, quality problems are common in monitoring data; there are cases where data is missing or abnormal, which hinders the well progress of energy conservation. Therefore, the method for quickly and accurately repairing problem monitoring data needs to be studied. The core part of the power consumption of HVAC is the freezing station, in which the power consumption of the chiller occupies a major part, needs to be concerned. This paper proposes to repair the data by establishing energy consumption model. The research object is the chiller of a campus education office building. Firstly, the factors that affect the power consumption of the chiller are mastered. Then, the operating parameters are simulated by e-Quest software, and a multivariate regression model of power consumption with meteorological parameters is established. Finally, the model is used to repair the problem data. The results show that the correlation coefficient between the leaving supply temperature of water and power consumption is about 0.9, which has the greatest impact and is of great significance to the retrofit of the systems. And, the repair accuracy for missing data reaches 2–3%, indicating that the method is fast and effective and can be applied online.

To maximize the recovery of heat energy from bathing wastewater, a two-series-connected bathing wastewater source heat pump hot water unit (SCBWSHP) with large temperature difference was proposed. Its rated design parameters are: the inlet and outlet temperatures of the bathing wastewater are 30 °C and 6 °C, respectively. The tap water inlet temperature is 10 °C, and the hot water outlet temperature is 45 °C. The effects of the mass flow rate of the tap water and the bathing wastewater on heating performance of the SCBWSHP were investigated experimentally. The results showed that the COP of the whole unit is 4.5 at the ratings. When the tap water mass flow rate increases from 600 to 900 kg/h, the whole unit COP increased by 18.7%, from 3.20 to 4.88. And the COP of the whole unit increases from 4.03 to 4.83 as the bathing wastewater mass flow rate rises from 600 to 1000 kg/h, increased by 16%.

With the problem of environmental pollution becoming more and more serious, people pay more and more attention to indoor air quality, because more than 80% of the time spent in the indoor environment. This paper designs an indoor air quality monitoring system based on Internet of Thing cloud platform, which adopts modular design idea and realizes the development process of the system quickly. The architecture design of perception layer, network layer and application layer of the system is given. Sensors can be connected to the communication gateway as long as they conform to Modbus communication protocol. The WYSIWYG (What-You-See-Is-What-You-Get) method is used to develop the interface of the monitoring system. Finally, the system is tested and analyzed. The test results show that the system runs stably and accurately, and supports remote monitoring of web and mobile versions.

An intensive study on the heating temperature aimed to create a satisfying indoor condition that should meet the residents’ thermal requirements in accordance to their daily behavior pattern. Unlike urban residents who stay indoors for a long time, rural residents constantly live in a dynamic environment: they often leave their residences and get busy with numerous labor activities. Therefore, the thermal sensation questionnaire survey performed in a steady environment is not suitable for them. To study the rural heating temperature in a dynamic environment, a three-years field investigation was performed in South Liaoning province. During the investigation, a continuous tracking method was adopted to record the residents’ behavior; objective environmental parameters test and subjective thermal sensation surveys were rigorously recorded. The results indicate that the residents behavior pattern exerts an influence on the heating temperature by influencing the residents’ clothing insulation. Heating temperature in auxiliary rooms can be directly determined by the residents’ thermal sensation, with the reasonable value of 11 °C. The influence of residents’ behavior on clothing should be considered when determining heating temperature in the master bedroom, the reported value of which is 13 °C. The heating temperature obtained by the thermal sensation fuzzy comprehensive evaluation model in paper reflects the rural residents’ real-life requirements on thermal environment, and it provides a reference for designing rural residences.

Road tunnels have recently become prevalent in urban areas of China. In areas adjacent to these tunnels, air quality and human health are important public health concerns. As such, assessing pollut...

The main objective of the present study is to investigate the heat transfer characteristics of vertical falling film evaporation of refrigerant R-134a outside of a single smooth and enhanced tubes. The experiment was carried out under the conditions that spray density in the range of 0.058–0.44 kg m−1 s−1, corresponding inlet Reynolds number from 1000 to 6800. The evaporation temperature ranges from 6 to 12 °C and heat flux is between 10 to 40 kW m−2. Variations of heat flux, spray density and saturation temperature were analyzed. The obtained results revealed that the saturation temperature has little influence on enhanced tube, but it can improve the performance of the smooth tube markedly. Moreover, it was found that as the heat flux increases, the heat transfer coefficient of the smooth tube increases, while that of the enhanced tube significantly reduces. Nevertheless, the heat transfer performance of the enhanced tube still outperforms that of the smooth tube up to 2∼12 times. Besides, it was also found that spray density is an important factor for vertical falling film evaporation. The increase of the spray density appropriately can improve the heat transfer coefficients in both smooth and enhanced tubes, but the supply that is too much or too little both has adverse effects. Accordingly, the spray density should be kept in a optimum range, especially the minimum must be reached in order to prevent liquid film break and the dry-out patch. The present study provides a basis to investigate the application of enhanced tube in the vertical falling film evaporator.

Electricity consumption in university dormitories deserves more attention owing to its constituting a large proportion of total electricity consumption in university buildings and the enormous electricity conservation potential. This research proposes a methodology comprising aggregated and segmented analyses to provide an in-depth understanding of electricity consumption in university dormitories from multiple perspectives. Aggregated analysis provides global perspectives for electricity consumption by resolving a novel and practical problem of setting free electricity consumption quotas for student dormitories. Segmented analysis provides partial perspectives for electricity consumption by discovering electricity consumption patterns according to the academic calendar. The actual daily electricity consumption data of 2434 undergraduate dormitories, 542 graduate-MS dormitories, and 583 graduate-PhD dormitories collected by smart meters from a Chinese university are analyzed to demonstrate the application of the proposed methodology. The main results of the research include the following: (1) different modes of setting free electricity consumption quotas have different effects on electricity conservation, and the monthly mode seems to be a more efficient alternative to stimulate energy-saving behaviors than the annual mode; (2) there is no significant linear correlation between outside temperature and electricity consumption against the background of limited electric power and nonusage of air conditioning systems; and (3) the representative electricity consumption patterns in the three types of dormitories are explored according to the academic calendar. The university administrators can devise good electricity use policies and implement electricity network planning and operations according to the patterns. The implications of the results and several recommendations for promoting energy conservation are provided simultaneously

Saving energy in rural residences is of great importance. In this paper, a field investigation of the basic physics information and thermal environment of rural residences was carried out, using a rural residence in Dalian as an example. Based on the analysis of this investigation, we find that the thermal performance of the building envelope, the living habits of the occupiers and the household economy have a close relationship with unsatisfactory residential thermal environment. Therefore a new perspective regarding optimization of rural residences is provided in terms of building plan layout, shape and properties of the building envelope. This paper presents rural residential optimization methods in which orthogonal numerical test and rules for integrated balancing methods are combined. Through numerical simulation with TRNSYS, the significance of different factors influencing indoor temperature has been given, and the optimal thermal parameters of the building envelope and plan layout of a rural residence are determined. The results show that south window-to-wall ratio is the most significant factor influencing indoor temperature and therefor this is the primary parameter requiring optimization. The south window-to-wall ratio of a rural residence in a cold region should be 45%. In addition, it is demonstrated that the optimal rural residence, when compared to traditional rural residences, has a satisfactory social benefit in terms of improving the indoor thermal environment and protecting the atmospheric environment during a heating season. This paper will offer a theoretical reference for the construction of modern rural residences.

Super-long urban road tunnels have become prevalent in China recently. This study established a three-dimension CFD model containing two adjacent super-long urban road tunnels to estimate characteristics of pollution dispersion outside the tunnels. The results indicated that crossflow between two adjacent tunnels was quite severe, which contributed to carbon monoxide concentration was almost 50 ppm exceeding the 10 ppm limit of National Standard in China for 1h exposure level when exhaust shafts were absent. When the shafts exhausted 80% pollutants from the tunnel portal, crossflow between two adjacent tunnels could at least decrease to 20% of the conditions without shafts. The simulation results could not only demonstrate the importance of shafts for super-long urban road tunnels, but also provide a fundamental and guideline for evaluation of urban environment and design of the tunnel exhaust shafts, including locations and types.

Generally, the temperature of domestic waste water is high above 30℃. However, when dealt with by common sewage-source heat pump system, temperature difference between inlet side and outlet side is small as 5℃. It leads to manifold cycles and energy waste. To acquire a unit of heat pump water heater of sewage dealing with large temperature difference with high energy utilization rate, through which the cold water (about 5℃) can be heated once to hot water (about 45℃) to reach the temperature for daily use and waste water (about 30℃) can be rapidly dropped to cold water (about 6℃) to satisfy the standard of waste water emissions. In this paper, two staged series of heat pump water heater dealing with large temperature difference is proposed. And performance factor of system is analyzed through simulation by MATLAB so as to find the optimum middle operating point. This method ensures pattern operating in large temperature difference but in small flow at both the hot and cold sides. At the same time, it avoids the lasting elevation of condensing temperature and the constant reduction of temperature in evaporation, which helps to facilitate the stability and optimal performance of the operating unit.

In this paper, a heat pump hot water unit with the dual-source evaporator using air or water as the heat source is proposed. The idea is firstly to use the heat from the bath wastewater to heat the domestic hot water. If the stored wastewater is insufficient, the ambient air will be applied for assisting the heat pump. The structure of the dual-source evaporator is simpler and compacter compared with the traditional form of two evaporators arranged in parallel. For testing it, the heat pump hot water unit with the evaporator is established. The performance of the unit and the dual-source evaporator are investigated experimentally when the bath wastewater is used as the heat source. Experimental results show that the coefficient of performance (COP) of the heat pump can reach 5.02 when the wastewater temperature is 32℃, and the heat transfer coefficient of the evaporator can reach to 1003.56 W/m2 K. And the temperature of wastewater can be decreased to 8℃ by cyclical utilization. So the effect of heat recovery is remarkable for the heat pump hot water unit with the dual-source evaporator. When air is used as the only heat source, the performance of the heat pump is about the same as that of a conventional air-source heat pump, and this paper does not research on it.

Heat pumps are a part of the environmentally friendly technologies using renewable energy and have been utilized in HVAC systems. A heat pump water heater unit with frozen type evaporator was designed and developed. And a test bed was constructed to determine the performance of the unit. In the experiment, a parallel helical coil type evaporator was used in the unit to extract latent heat from the sewage. The data (dynamic COP and other parameters) was obtained in three processes(including the first freezing, melting, and the second freezing) at different water temperatures (8.2℃ and 13.8℃). Results show that compare with traditional water source heat pumps, the newly designed unit with the frozen evaporator can reduce the required water amounts as a heat source by more than 90%. The higher initial temperature of hot water and sewage, the higher temperature of sewage after melting. Meanwhile, with the increase of the initial temperature of hot water and sewage, the comprehensive COP was greater. This paper will provide a reference for the sewage source heat pump system to extract the latent heat from the sewage.

The data quality of building energy consumption monitoring platform is generally not high and there are a lot of problem data. This paper proposes an identification method of implicit error energy consumption data based on the overall usage characteristic. In this method, we connect hourly energy consumption data into lines. According to the influencing factors of the building operation, we classify the energy-usage mode. By using the clustering method, we identify partial abnormal data. Then we count the slopes of historical energy consumption data characteristic lines and compare the time-varying characteristic lines of real-time with the historical characteristic lines under the same energy-usage mode. By using the energy consumption data of an office building, we verify the reliability of this method in identifying the abnormal energy consumption data of lighting and socket. This method improves the quality of data and will make the energy monitoring platform more efficient in building energy conservation.

Correlation models between human behavior and energy consumption of teaching buildings are crucial for devising energy efficiency strategies. Especially in teaching buildings in campus, on one hand, the investment is limited and the level of operation and maintenance is low. On the other hand, the certain management system exists, and the flow of occupant in campus is also regular obviously. So, it is difficult for large-scale technical retrofits and possible for management retrofits. In order to the low-cost management retrofits, the model between human behavior and energy consumption are studied in this paper. According to the models, on the one hand, managers of campus can predict energy consumption based in historical, for matching energy consumption supply and demand each other. On the other hand, managers can judge future human behaviors based on historical energy consumption, for conducting management to reduce energy consumption. In this paper, first, correlation models between the energy consumption and human behavior are proposed and the lighting management level coefficient K is defined to evaluate the lighting management level. With the aid of the correlation models and K, managers can obtain management strategies to increase energy efficiency without large-scale technical retrofits. The verification results show that the proposed strategies could bring a 13.96% economic benefit ratio. Second, correlation models between human behavior and influencing factors of human behavior are proposed for predicting human behavior. Finally, a technical route of energy efficiency retrofit by management is suggested and validated. Although the energy-saving ratio is not conspicuous, the cost is low and the operation is easy. It means that the technical route is worthy for research and promotion.

Targeting at rural residence in south Liaoning province, a continuous test on indoor temperature and atmospheric temperature is made and a questionnaire survey about residents’ thermal sense is conducted. Combined with local residents’ mode of life, living habit, psychological demand, economic situation and so on, heating design temperature of south Liaoning province is given. It shows that the temperature demand of residents that live in traditional house is lower, which of master bedroom is 12 to 14 centigrade. To newly building, the heating temperature demands of different rooms are different. The heating design temperature of frequently used room ranges from 12 to 14centigrade, and occasionally used room ranges from 10 to 14 centigrade. However the heating design temperature of room which is hardly used is from 9 to 13 centigrade. This paper will offer theoretical basis for new rural construction in south Liaoning province.

The public bath is the emphasis target of energy-saving renovation of existing public buildings in China. In that case, the integration of the hot water supply system according to the characteristics of heat sources should be studied and optimized to improve the comprehensive energy efficiency and the hot water production of the system. This paper analyzed and remedied the deficiencies of several common hot water supply systems with multi-heat-source, introduced a novel hot water supply system with multi-heat-source based on PVT (photovoltaic and thermal) heat pump and water source heat pump, and then carried out the integrated optimization research of this new system. The main studies include: (1) Established the novel hot water supply system with multi-heat-source and the calculation model of system heating characteristic. (2) Introduced the evaluation method of the comprehensive energy efficiency and economic performance for the hot water supply system with multi-heat-source. (3) Aiming at reducing the total cost of hot water supplying, the integration optimization ideas of system were proposed. By above methods, the integrated optimization of the existing North Mountain Public Bath in Dalian University of Technology was conducted. On one hand the daily production of the existing hot water supply system in the public bath is increased from 80 t to 146 t, the supply capacity of hot water is significantly promoted. On the other the total cost of hot water supplying decreases from 9.6 RMB/(t year) to 4.9 RMB/(t year), the comprehensive energy efficiency and the economic performance of system is improved.

Although the integration of photovoltaic-thermal (PV/T) heat pump systems on buildings can assist in reducing the electricity demand of high-energy consuming buildings, the large occupation area of PV/T modules hinders its popularization. To overcome this problem, a novel PV/T evaporation roof coupled with a heat pump system composed of electronic expansion valves, a condenser and a compressor is proposed, which serves as an electric generator, evaporator for the heat pump system and the external surface of a building roof. This paper investigates the actual operating performance of the direct-expansion roof-PV/T heat pump system under different seasonal conditions. The structure and design of PV/T evaporation roof and the whole system are first presented, followed by the construction of an experimental platform and finally the operation of the system is analyzed through performance evaluation indices and field-testing. The experimental results indicated that the system performed better in the summer than in the winter, with the electrical efficiency, thermal efficiency and overall efficiency averaging at 11.23%, 64.25% and 83.32%, respectively. The average COP was 5.9, with a maximum value of 8.9. Additionally, it took 2 h to heat the water within a 1.5 m3 heat storage tank from 25 °C to 60 °C, which was twice as fast as under winter conditions. Meanwhile, a significant decrease in system performance resulting from changes in environmental parameters in the winter was observed. The average electrical efficiency, thermal efficiency, and overall efficiency were 11.67%, 60.17% and 78.84%, respectively, while the average and maximum COP were 3.7 and 5.24 respectively.

In multi-zone variable outdoor air (OA) volume air-conditioning systems, there is often a mismatch between OA volume flow supply and demand, because variable air volume (VAV) systems exhibit nonlinear, multivariable, and long delay characteristics. Traditional methods ensure indoor air quality (IAQ) by increasing OA volume flow, which leads to a waste of OA flow energy. To address this problem, an optimal control method for determining discrete variable OA volume flow setpoints, based on differential pressure control, is proposed in this study. In this method, changes in indoor CO2 concentration and the total air volume flow demand of terminals are regarded as constraints of OA volume flow setpoints. A Proportional-Integral (PI) calculation method and trial-and-error method are used to discretize continuous OA volume flow setpoints to increase system stability. Two types of experiments were conducted to compare the characteristics of the two discrete OA volume flow setpoint determining methods, and to verify the feasibility of our new approach. The results show that the OA volume flow control loop can be well fitted with other control loops of VAV systems, and ensure OA volume flow demand for a target area. The proposed method provides greater energy savings than maximum OA ratio control strategy (7%–22%) and typical on-demand ventilation method (6.1%), and better control performance than continuous OA volume flow setpoints control system. The PI calculation method is suitable for conditions with high IAQ requirements, while the trial-and-error method can be used for comfort air-conditioning systems to adjust the indoor environment.

In order to increase the efficiency of solar collector, a methodology is proposed based on the analysis of its influencing factors, such as thermal conductivity of filled layer, structure forms of filled layer and heat loss coefficient. The results of analysis show that the heat transfer between pipes in evacuated tube is one of the most important factors, which can lead to the decrease of the outlet temperature of working fluid. In order to eliminate the negative influence of the heat transfer between pipes, the hollow filled-type evacuated tube with U-tube (HUFET) was developed, and the heat transfer characteristics of HUFET were analyzed by theoretical and experimental studies. The results show that the thermal resistances decrease with the increase of the thermal conductivity of filled layer. When the thermal conductivity is over 10 W/(m·K), the change of thermal resistances is very little. Furthermore, the larger the thermal conductivity of filled layer, the less the rate of the energy transfer between the two pipes to the total energy transfer, which is between the absorber tube and the working fluid. There is a little difference between the efficiencies of HUFET and UFET, with the efficiency of HUFET 2.4% higher than that of UFET. Meanwhile, the validation of the model developed was confirmed by the experiment.

This paper describes the development of a new type hybrid photovoltaic/thermal (PVT) solar collector. The test setup of the photovoltaic/thermal performance of the PVT solar collector filled with graphite was established to compare the conventional PV module and the PVT solar collector filled with graphite. The output power, backplane temperature, the inlet temperature, the outlet temperature and the tank temperature were tested in this study. The photovoltaic/thermal performance of the PVT solar collector filled with graphite was evaluated by the thermal efficiency, electrical efficiency and primary energy saving efficiency. The results show that the electrical efficiency of the PVT collector can be enhanced by cooling down to the backplane temperature. Lower inlet temperatures result in higher thermal efficiency. The inlet temperature increased with increased tank temperature. As the inlet temperature increased to some point, the outlet temperature gradually stabilized. The mean value of electrical efficiency of a PVT collector filled with graphite and conventional PV module were 6.46% and 5.15% between 8:00 a.m. and 4:00 p.m. The highest electrical efficiency of a PVT collector filled with graphite was 7.2%. The highest Primary Energy Saving efficiency of PVT collector filled with graphite was 48% at 10:35.

This paper firstly define most unfavorable thermodynamic loop to reflect the dynamic situation of terminal cooling load distribution, then present its online identification method that can easily applied for optimal reset of differential pressure. We use the optimal domain of maximum valve position among whole braches in chilled water system to calculate the variation of differential pressure setpoint, and control the pumps according to the optimal setpoint. We applied presented method to a VWF retrofit project in a Suzhou factory building and evaluate its energy saving effect through its equipped building energy management system. Experimental results showed that presented method can achieve 22%-53% pump power consumption savings compared to traditional control method. During the test period, the average level of valve position of presented method was highest among all tested control strategies. The optimal reset method of differential pressure presented in this paper is an energy efficient, high stability and easily online applied control method.

A gas–liquid separated solar collector system was developed. The operating temperatures are in the range between 100 and 150 °C. The boiling collector can be used for process heat supply in the industry and for solar cooling applications as well. This gas–liquid separated solar collector system can use flat-plate solar collector and heat pipe solar collector to generate mid-temperature steam. This system can reduce the usage of the heat pipe solar collector and heat the working medium to the saturated liquid by the flat-plate solar collector, which can reduce the cost of the system. R245fa, also known as 1,1,1,3,3-pentafluoropropane, was used as the high temperature working medium in this system. The simulation results show that this system can work normally. When the mass flow of working fluid was reduced by half of general condition, the collection time was cut by 25%. In contrast, when the mass flow of working fluid was kept the same and the collector area was doubled, the operation time was cut by 35%.

The heat transfer efficiency of solar collector tubes is a crucial factor for the application of solar heating and cooling systems (SHCS). How to enhance solar collector efficiency has become a hot topic. In this paper, a new type of collector tube – filled-type evacuated tube with U-tube (UFET), was presented to increase solar collector efficiency by eliminating the thermal resistance between the absorber tube and the copper fin of the conventional evacuated solar collector. First, a UFET heat transfer model was built with different U-tube structures and the universal UFET model in uniform boundary condition. Furthermore, the thermal performances of three types of UFET were compared theoretically and experimentally. The results show that the maximum solar collector efficiency of UFET with three U-tubes reaches 0.82 and is higher than other types with the same heat transfer surface area. In addition, the theoretical result is 4% higher than the experimental result, indicating that the developed model is validated by the experimental investigation in this study.

Untreated urban sewage contains large amounts of thermal energy; and its temperature is suitable as a heat source in heat pumps for the heating and cooling of buildings. However, it is not widely used in heat pump systems due to the problem of filth. This paper presents an untreated sewage source heat pump (USSHP) system in which auto-avoiding-clogging equipment is used to continuously capture suspended solids in the sewage. Thus, the block problems caused by filtration and fouling in the heat exchanger tubes can be efficiently resolved in this system. In an actual engineering application, the characteristic parameters of USSHP system are tested under typical operating conditions for heating status. Based on the test results, the performances of the USSHP system are examined. The results indicate that the thermal resistance of the convective heat transfer and fouling on the sewage side in the sewage exchanger is 80% of its total thermal resistance. The COP of the heat pump unit and the COP of the USSHP system are 4.3 and 3.6, respectively.

Building energy consumption statistics is an important part of building energy saving, which has a great number of data to be processed. It is essential to evaluate the validity of building energy consumption statistics by using scientific method. However, the traditional method by using energy consumption per unit is very difficult to confirm the reasonable ranges, such as power per unit area, because these indexes generally varies in a large range for most sorts of buildings. Based on the building energy consumption bill, this paper firstly puts forward two new evaluation indexes, ratio of practical energy consumption expense to energy consumption (RREEE) and multiple of standard coal for building and heating ventilation and air-conditioning system. Then this paper finishes the evaluation and analysis for the government buildings, shopping mall buildings, top grade hotel buildings, etc. in Dalian, by using this evaluation method. The results show that it is very easy for the evaluation method of RREEE to adjust the validity and reasonability of the building energy consumption statistics, and easy to finger out the reasonable range of the building energy consumption indexes, which means the evaluation method will have an important practicality in building energy consumption statistics.

This paper presents an optimal design method for heat exchangers in a dual-stage circulating high-temperature heat pump (HTHP) system. The paper first presents a series of steady-state models of components and a simulation platform of whole system; the output of the simulated system is verified by the operational data of a real heat pump plant. The method is investigated and implemented by the simulation platform based on these models, and it consists of four steps: 1) the selection of an optimal condenser and evaporator (the C-E plant), 2) the optimization of the total heat transfer area of the C-E plant, 3) the optimization of the condenser-to-evaporator heat transfer area ratio ( AR ) and 4) a matching scheme for the AR and heat transfer area of the regenerator. The method adopts the coefficient of performance (COP) as the optimization target and employs the heating capacity, water velocities and water-side pressure drops and the compressor discharge temperature as constraints. The case studies demonstrate that the presented method is effective at solving the problem of mismatches among single components. The optimal design scheme provides the same heating capacity with a 13% decrease in the total area of the exchangers.