Probabilistic assessment of overcooling risk for a novel extra-low temperature dedicated outdoor air system for Hong Kon
- PDF / 1,667,943 Bytes
- 16 Pages / 612 x 808 pts Page_size
- 40 Downloads / 144 Views
Probabilistic assessment of overcooling risk for a novel extra-low temperature dedicated outdoor air system for Hong Kong office buildings
1. Department of Building Services Engineering, The Hong Kong Polytechnic University, Hong Kong, China 2. Department of Built Environment and Energy Utilization Engineering, Taiyuan University of Technology, Taiyuan 030024, China
Abstract
Keywords
Overcooling causes thermal discomfort and wastes energy. Effectiveness of a novel dedicated outdoor air system (DOAS) consisting of a multi-stage direct expansion coil to generate extra-low temperature (XT) outdoor air to handle the entire space cooling demand for better energy and humidity control has been confirmed in previous studies. In these studies, the terminal system was assumed using variable air volume (VAV) without reheating. The conventional VAV system without reheating has overcooling problem. This is associated with uncertain fluctuations of operating characteristics. However, virtually no study has been done to investigate its overcooling risk, and how it is compared with XT-DOAS. In this study, a rigorous probabilistic approach is proposed to account for the uncertain fluctuations of operating characteristics to assess their overcooling risks. Monte Carlo simulations with 10,000 interactions was used for risk analysis. A morphing method was employed to develop 10,000 weather files that could give an accurate prediction of future variations in yearly weather conditions. Reliable datasets were used to develop the probability distribution functions to account for the daily variations in use patterns. The most probable operating characteristics were input to EnergyPlus for hour-by-hour simulations. The annual cooling load profile formulated by the probabilistic approach was successfully validated by in-situ measurements. The probabilistic assessment results show that XT-DOAS has far less overcooling hours and lower long-term percentage of dissatisfied than the conventional VAV system. The results also indicate that the proposed probabilistic approach is useful for a robust system performance evaluation.
overcooling risk,
Introduction
Overcooling causes thermal discomfort and wastes energy. This problem is particularly prominent for the conventional VAV system without reheating. The conventional VAV system varies the supply airflow rate at a constant temperature in response to the space cooling demand for maintaining the desired temperature. The minimum air flow fraction (MAFF) of supply air (SA) should be set and can be as low as 30% of the peak flow to satisfy ventilation requirement (ASHRAE 2017). Overcooling occurs when the space cooling demand drops further after reaching the minimum airflow setting (Gangisetti et al. 2016). However, a literature search E-mail: [email protected]
Monte Carlo simulation, uncertainty analysis, extra-low temperature system, VAV system
Article History Received: 12 February 2020 Revised: 20 May 2020 Accepted: 22 June 2020 © Tsinghua University Press and Springer-Verlag GmbH Germ
Data Loading...
