Zhizhong Huang

Measurement and simulation of indoor air quality and energy consumption in two Shanghai office buildings with variable air volume systems

Two modern office buildings in Shanghai with typical variable air volume (VAV) systems were selected for research. Four separate spaces on a standard office floor in each building facing different directions (north, south, east, and west) were selected for thorough site measurements of outdoor airflow rates and indoor air quality (concentrations of CO 2 and PM10) during typical days of the four seasons (summer, autumn, winter, spring). Computer simulations and calculations were also done of outdoor airflow rates and CO 2 concentrations in the four-test spaces on an hourly basis for the entire year. In addition to the site measurements, monthly electrical consumption for the two buildings was recorded or estimated. Simulations and calculations were performed of the buildings’ energy consumption and energy cost using two different outdoor air control strategies of a typical VAV system as well as a fan coil unit (FCU) system. The site-recorded data, or estimated data, and simulation results are compared and analyzed. The study reveals that in a VAV system, the outdoor airflow rate distributed to each zone varies greatly, especially during part-load hours, making it difficult to always ensure sufficient outdoor air in each zone and avoid indoor air quality (IAQ) problems. However, this problem can be prevented by using appropriate outdoor air control strategies—e.g. a fixed high level total outdoor airflow rate.

A new local pressure loss coefficient model of a duct tee junction applied during transient simulation of a HVAC air-side system

Most of the local pressure loss coefficient (LPLC) models for duct fittings used in heating, ventilation and air conditioning (HVAC) air-side system transient simulations are simplified. The LPLCs are defined as having a constant value at the rated flow condition or as having a polynomial function of the flow ratio (or velocity ratio). To determine the influence of these simplifications, this study used a diverging tee junction as an example. First, we performed CFD calculations to generate a new LPLC dataset and trained a data-driven model using feature weighted support vector regression (FWSVR) combined with particle swarm optimization (PSO-FWSVR). Finally, we compared this new LPLC model with the two traditional models at the level of both individual junction and air-side system. The results show that the accuracy of the new model is greatly improved and the LPLC model can have a significant impact on the system operation condition.

Emulation-Based Optimal Control of Chiller Plants

Chiller plants of HVAC systems usually operate in part-load conditions during most time of a year. Energy efficiency (i.e. energy input ratio, EIR) of chiller plant components such as chillers, pumps, and cooling towers are the functions of part-load ratio (PLR) and other variables. However, different chiller plant components have different functions of EIR to PLR and don’t reach their respective peaks at the same part-load ratio. Based on this fact, there are possibilities that overall efficiency of a chiller plant can be improved to and maintained at the maximum via optimal control of operating numbers and set-points of various plant components at various part-load ratios. An emulation-based optimal control strategy for chiller plants is introduced in the paper. The main idea of this control strategy is to set up a virtual chiller plant as a mirror of a real system. The virtual system is composed of mathematical models that are obtained through theoretical derivation, numerical calculation or off-line test. These models can emulate energy performances of the physical components in the real system. An optimization algorithm is first run on the virtual system to search for an optimal combination of the operating number and set-points of various components to achieve the highest overall efficiency of a chiller plant. An objective function of the optimization algorithm is the overall efficiency of a chiller plant, having real-time cooling load and meteorological data as inputs, and energy and mass balance and component capacities and restrictions as constraint conditions. Once an optimal combination is identified, it will be used to control the real system operation. A mockup system has been installed and operated in a 50,000 m2 office building in Shanghai, China in order to test and verify the optimal control strategy. Preliminary testing results show that the annual overall energy efficiency of the chiller plant (with constant speed centrifugal chillers) is from 0.7 kW/Ton to 0.75 kW/Ton, about 25% less than that of the same plant controlled by normal strategy.Copyright

DEVELOPMENT OF AN INTERACTIVE GRAPHICAL USER INTERFACE (GUI) FOR ENERGYPLUS

In order to make EnergyPlus easier to use in China, VisualEPlus, a Chinese graphical user interface for the program, has been developed. VisualEPlus is designed to be generic, so that it can be used in any country, as well as be linked to other modeling tools and interfaces for EnergyPlus. VisualEPlus has three main modules: (1) a Building Loads Module for defining the building geometry, envelope, and space conditions that has been adapted from an existing DOE-2 interface (DOE2IN); (2) a HVAC System Module with a drag-and-drop feature for defining the HVAC system; and (3) a View Report Module with a reporting and visualization tool for EnergyPlus reports and outputs. This paper presents the background and development of VisualEPlus, describes its main functions and features as compared to other existing interfaces for EnergyPlus, and discusses plans for the further development of VisualEPlus.Copyright