• Energy Research

AbstractSwitchable exhaust air (SEA) window allows the exhaust air from HVAC system to be ventilated through the cavity of the window to ambient. It can be regarded as an exhaust air heat recovery device in buildings. The annual energy requirement of the window has been calculated in Wuhan, China. The energy requirements for conditioning fresh air with and without the total heat recovery ventilators (THRVs) are also investigated. Heat recovery performance of the SEA window and the THRVs is compared. Results show that the SEA window can potentially provide alternative solution for recovering the low-grade energy from air-conditioning exhaust air.

Abstract College buildings, especially college dormitories, have a high density of energy consumption. It is important to obtain the energy consumption characteristics and impact factors of college dormitories before implementing energy efficiency measures. However, few studies based on experimental data have been reported. This study attempts to analyze the energy consumption characteristics of college dormitories and determine the influential factors based on monitored data. Annual daily energy consumption data of 480 college dormitories with different orientations and floors were collected. The energy consumption characteristics and the impact of factors including the floor, orientation, and occupant’s gender are investigated and quantified through the statistical methods and covariance analysis. The results show that the energy consumption varies significantly between different dormitories, and the floor location is the most influential factor. The annual energy consumption of the dormitories on the top floor is 1015% higher compared with those on the other floors due to higher cooling or heating load resulting from the roof. Then, two floor-oriented electricity pricing strategies are recommended to balance the different energy bills caused by different located floors of rooms. The electricity tariffs for rooms on the middle/top floors should be increased/decreased by 3.5%/10.3% in the proposed floor-based electricity tariff. This study would provide a basis for energy efficiency improvement and tariff optimization for college dormitories.

The exhaust air glass unit (EAGU) can be treated as an integration of multilayer glazing unit and heat recovery device to utilize the exhaust air from conditioned space with a fresh air ventilation system to improve the thermal performance of window system. However, compared with the conventionally used mechanical ventilation with a heat recovery (MVHR) system, whether the use of EAGU is energy-efficient or not has not been estimated. In this paper, a numerical model, validated by experimental measurement, was used to calculate the hourly cooling and heating loads and annual energy demand of EAGU. This study compared the annual energy performance of EAGU and MVHR under various conditions, and further discusses the applicability of EAGU for different climates. The results indicate that the energy saving potential of EAGU ranges from 26.8% to 38.2% for different climate conditions. In the cooling season, the energy saving potential of EAGU performed much better than that of the commonly used MVHR. However, the EAGU was inferior to the MVHR in the heating season. Moreover, the EAGU is more suitable for application in warm climates, rather than cold climates. This study can provide some application guidelines about the selection of exhaust air heat recovery devices for maximizing the energy saving potential.

Abstract A new triple-glazed exhaust air window with built-in venetian blinds is described and investigated in this paper. In this type of window, the exhaust air passes through the air cavity between the glass panes before being released to the outdoor environment. Part of the heat or cold energy inherent in the exhaust air can be recovered. The temperature differential between the interior surface of window and indoor air can be directly reduced, which would benefit the indoor thermal comfort. To investigate the dynamic thermal behavior of the triple-glazed exhaust air window, an improved zonal model was built and validated by using the on-site experimental data. Temperature distributions of this window in both vertical and horizontal directions were analyzed. The influences of the airflow velocity in ventilated cavity and the slat angle of venetian blinds on the thermal performance of the window on a typical summer day were quantitatively investigated. The U-values of this window under different airflow velocities were also calculated. Results show that the temperature differential between inner glass pane and indoor air varies from 0.5 °C to 2.6 °C, and shows a relatively low fluctuation throughout the whole day. The heat gain through the window can be reduced as high as 42.3% in the cooling season, when the airflow velocity varies from the 0.1 m/s to 0.5 m/s. At an airflow velocity of 0.5 m/s, the U-value of the window can be decreased to 0.7 W/(m2 K).

An earth-to-air heat exchanger (EAHE) system utilizes the low-grade thermal energy of underground soil to warm up and cool down the flowing air within an underground buried pipe. Integrating the EAHE system with building ventilation can reduce the energy demand for conditioning ventilation air. The main purposes of this paper are to estimate the year-round energy-saving potential of the EAHE-assisted building ventilation system and provide its design guidelines in a hot-summer and cold-winter climate. A steady-state heat transfer model was proposed to calculate the outlet air temperature of an EAHE and further identify its ability to preheat and precool ventilation air. Influences of depth, length, and diameter of a buried pipe on the year-round thermal performance of the EAHE system were evaluated. The results show that considering the compromise between thermal performance and construction costs of the EAHE system, a depth of 5 m and a length of 80 m are recommended. The EAHE system can provide a mean daily cooling and heating capacity of 19.6 kWh and 19.3 kWh, respectively. Moreover, the utilization of the EAHE system can reduce by 16.0% and 50.1% the energy demand for cooling and heating ventilation air throughout the whole year.

Massive data can be collected from meters to analyze the energy use behavior and detect the operation problems of buildings. However, missing and abnormal data often occur for the raw data. Effective data filling and smoothing methods are required to improve data quality before conducting the analysis. This paper introduces a data filling method based on K-SVD. The complete dictionary is trained and then utilized to reconstruct incomplete samples to fill the missing or abnormal data. The impacts of the dictionary size, the data missing continuity, and the sample size on the performance of the proposed method are studied. The results show that a smaller dictionary size is recommended considering the computational complexity and accuracy. The K-SVD method outperforms traditional methods, showing a reduction in the MAPE and CVRMSE by 3.8–5.4% and 6.7–87.8%. The proposed K-SVD filling method performs better for non-consecutive missing data, with an improvement in the MAPE and CVRMSE by 0.1–4% and 5.1–6.7%. Smaller training samples are recommended. The method proposed in this study would provide an effective solution for data preprocessing in building and energy systems.

202407 bcch ; Accepted Manuscript ; RGC ; Others ; the National Key Research and Development Program of China ; Hong Kong Scholars Program ; Published ; Green (AAM)

Abstract The distributed energy system has attracted increasing attentions due to its high efficiency and low pollution emissions. The Chinese government has planned to promote the application of distributed energy systems using natural gas to address the atmospheric pollution problem. However, considerable uncertainties exist in energy market and policy, which would significantly affect the economic performance of distributed energy systems and make the promotion challenging. Therefore, this study attempts to investigate the impacts of energy market and policy uncertainties by evaluating the economic performance of a distributed energy system integrated with a district cooling system serving a campus in the cooling dominated area of China. Uncertainties in the following factors are taken into account: the natural gas price, the electricity price, the feed-in tariff, the incentive from the government and the carbon tax. The payback period of the distributed energy system under various uncertainties is analysed. Results show that the economic performance of the distributed energy system is satisfactory when the ratio of natural gas price to the electricity price is less than 3.. If the government plants to promote the DES, the incentive should be not less than 1300 CNY/kW or the carbon tax charged should be not less than 50 CNY/ton.