Integrated assessment of indoor and outdoor ventilation in street canyons with naturally-ventilated buildings by various ventilation indexes: Fid-Bau Portal

Integrated assessment of indoor and outdoor ventilation in street canyons with naturally-ventilated buildings by various ventilation indexes

Yang, Xia / Zhang, Yong / Hang, Jian / Lin, Yuanyuan / Mattsson, Magnus / Sandberg, Mats / Zhang, Ming / Wang, Kai

Abstract

Abstract The integrated assessments of indoor and outdoor ventilation are still rare so far. As a novelty, this paper aims to quantify the influence of street aspect ratios (building height/street width, H/W = 0.5–5) and window sizes (1 m × 1 m, 1.5 m × 1.5 m) on indoor-outdoor ventilation in two-dimensional streets with single-sided naturally-ventilated buildings. Numerical simulations with RNG k-ε model are validated against experimental data and the grid independence are tested as well. Air change rates per hour (ACH, h⁻¹) are adopted for assessing indoor-outdoor ventilation by mean flows (ACH mean) and turbulent fluctuations (ACH turb) respectively. Age of air(τ), purging flow rate (PFR) and its corresponding ACH PFR are used to evaluate overall ventilation capacities. Shallower streets experience better indoor-outdoor ventilation. Outdoor ACH PFR drop from 14.69 to 17.55 h⁻¹ to 3.96–3.97 h⁻¹ as H/W rises from 0.5 to 3. In extremely deep canyon (H/W = 5), two-counter-rotating vortices produce much smaller velocity at low-level regions (U/U ref~10⁻³-10⁻⁵), resulting in small ACH PFR for outdoor (~0.76–0.91 h⁻¹) and indoor in 1–13th floors (~0.03–0.61 h⁻¹). When H/W = 0.5–1, leeward 5–6th floors experience smaller ACH PFR(e.g.~1.13–1.40 h⁻¹ as H/W = 1) than the other floors (e.g. ~1.54–9.52 h⁻¹ as H/W = 1). Particularly, as H/W = 2–3, leeward-side indoor ACH PFR in the middle floors (except the first and top two floors) are nearly constants (~1.02–1.69 h⁻¹) and much smaller than windward-side ACH PFR(~1.41–4.35 h⁻¹) which increase toward upper floors. Besides, the smaller window size reduces indoor ACH PFR by 19.38%~88.28%, but hardly influences outdoor ventilation. Moreover, both outdoor and indoor ACH PFR are greater than ACH mean but smaller than ACH mean + ACH turb. Although further investigations are still required, this paper provides an insight and scientific foundation on integrated indoor-outdoor ventilation evaluation with various effective ventilation indexes.

Highlights • It provides an insight to assess the coupled indoor and outdoor ventilation by CFD. • ACH by mean flows (ACH mean)/turbulence (ACH turb)/purging flow rate (ACH PFR) are adopted. • Outdoor ACH PFR are from 18 h⁻¹ to 4 h⁻¹ as H/W = 0.5 to 3 and only 0.8–0.9 h⁻¹ as H/W = 5. • Indoor ACHs is smaller than outdoor, and window sizes hardly affect outdoor ACHs. • Both outdoor/indoor ACH PFR are greater than ACH mean but smaller than ACH mean + ACH turb .