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Building thermal load prediction through shallow machine learning and deep learning
Building thermal load prediction informs the optimization of cooling plant and thermal energy storage. Physics-based prediction models of building thermal load are constrained by the model and input complexity. In this study, we developed 12 data-driven models (7 shallow learning, 2 deep learning, and 3 heuristic methods) to predict building thermal load and compared shallow machine learning and deep learning. The 12 prediction models were compared with the measured cooling demand. It was found XGBoost (Extreme Gradient Boost) and LSTM (Long Short Term Memory) provided the most accurate load prediction in the shallow and deep learning category, and both outperformed the best baseline model, which uses the previous day's data for prediction. Then, we discussed how the prediction horizon and input uncertainty would influence the load prediction accuracy. Major conclusions are twofold: first, LSTM performs well in short-term prediction (1 h ahead) but not in long term prediction (24 h ahead), because the sequential information becomes less relevant and accordingly not so useful when the prediction horizon is long. Second, the presence of weather forecast uncertainty deteriorates XGBoost's accuracy and favors LSTM, because the sequential information makes the model more robust to input uncertainty. Training the model with the uncertain rather than accurate weather data could enhance the model's robustness. Our findings have two implications for practice. First, LSTM is recommended for short-term load prediction given that weather forecast uncertainty is unavoidable. Second, XGBoost is recommended for long term prediction, and the model should be trained with the presence of input uncertainty
Characteristics of homogeneous charge compression ignition (HCCI) combustion and emissions of n-heptane
This paper reports the outcome from a systematic investigation carried out on HCCI (Homogeneous Charge Compression Ignition) combustion of a diesel type fuel. The n heptane was chosen in this study to study the premixed diesel HCCI combustion characteristics with port fuel injection. Measurements were carried out in a single-cylinder, 4-stroke and variable compression ratio engine. Premixed n-heptane/air/EGR mixture was introduced into the cylinder by a port fuel injector and an external EGR system. The operating regions with regard to Air/Fuel ratio and EGR rate were established for different compression ratios and intake temperatures. The effects of compression ratios, intake temperatures, Air/Fuel ratios and EGR rates on knock limit, auto-ignition timing, combustion rate, IMEP, and engine-out emissions, such as NOx, CO, and unburned HC, were analysed. The results have shown HCCI combustion of n-heptane could be implemented without intake charge heating with a typical diesel engine compression ratio. The attainable HCCI operating region was mainly limited by the knock limit, misfir, and low IMEP respectively. Higher intake temperature or compression ratio could extend the misfire limit of the HCCI operation at low load but they would reduce the maximum IMEP limit at higher load conditions. Compared with conventional diesel combustion, HCCI combustion lead to extremely low NOx emissions ( less than 5 ppm) and smoke free exhaust. But HCCI diesel combustion was found to produce higher HC and CO emissions. An increase in intake temperature or compression ratio helped to reduce HC and CO emissions.
The progress on the study of land surface heat fluxes over heterogeneous landscape of the Tibetan Plateau
Examining exotic structure of proton-rich nucleus Al
The longitudinal momentum distribution (P_{//}) of fragments after one-proton
removal from ^{23} Al and reaction cross sections (\sigma_R) for
^{23,24} Al on carbon target at 74A MeV have been measured. The ^{23,24} Al
ions were produced through projectile fragmentation of 135 A MeV ^{28} Si
primary beam using RIPS fragment separator at RIKEN. P_{//} is measured by a
direct time-of-flight (TOF) technique, while \sigma_R is determined using a
transmission method. An enhancement in \sigma_R is observed for ^{23} Al
compared with ^{24} Al. The P_{//} for ^{22} Mg fragments from ^{23} Al breakup
has been obtained for the first time. FWHM of the distributions has been
determined to be 232 \pm 28 MeV/c. The experimental data are discussed by using
Few-Body Glauber model. Analysis of P_{//} demonstrates a dominant d-wave
configuration for the valence proton in ground state of ^{23} Al, indicating
that ^{23} Al is not a proton halo nucleus
An integrated wind risk warning model for urban rail transport in Shanghai, China
The integrated wind risk warning model for rail transport presented has four elements:
Background wind data, a wind field model, a vulnerability model, and a risk model. Background
wind data uses observations in this study. Using the wind field model with effective surface
roughness lengths, the background wind data are interpolated to a 30-m resolution grid. In the
vulnerability model, the aerodynamic characteristics of railway vehicles are analyzed with CFD
(Computational Fluid Dynamics) modelling. In the risk model, the maximum value of three
aerodynamic forces is used as the criteria to evaluate rail safety and to quantify the risk level under
extremely windy weather. The full model is tested for the Shanghai Metro Line 16 using wind
conditions during Typhoon Chan-hom. The proposed approach enables quick quantification of real-
time safety risk levels during typhoon landfall, providing sophisticated warning information for
rail vehicle operation safety
Candidate chiral doublet bands in the odd-odd nucleus Cs
The candidate chiral doublet bands recently observed in Cs have been
extended to higher spins, several new linking transitions between the two
partner members of the chiral doublet bands are observed, and
intensities related to the chiral doublet bands are presented by
analyzing the coincidence data collected earlier at the
NORDBALL through the CdN, 4nCs reaction at a beam
energy of 65 MeV. The intraband and interband
ratios and the energy staggering parameter, S(I), have
been deduced for these doublet bands. The results are found to be consistent
with the chiral interpretation for the two structures. Furthermore, the
observation of chiral doublet bands in Cs together with those in
Cs, Cs, Cs and Cs also indicates that the
chiral conditions do not change rapidly with decreasing neutron number in these
odd-odd Cesium isotopes
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