A novel portable cooling unit with air purification for displacement ventilation: Parametric study with zonal model and field experiment

• Published in: Building and environment Vol. 244; p. 110657
• Main Authors: Essa, Aya, Yamanaka, Toshio, Choi, Narae, Kobayashi, Tomohiro, Kobayashi, Noriaki, Komori, Miharu, Matsui, Nobuki, Okamoto, Tetsuya, Arakawa, Takeshi, Yamoto, Yuki, Otaka, Shogo
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2023
• Subjects: Air purification; Cross-infection; Displacement ventilation; Droplets; Portable cooling unit; Temperature gradient; Displacement ventilation; Portable cooling unit; Cross-infection; Droplets; Air purification; Temperature gradient
• ISSN: 0360-1323; 1873-684X
• DOI: 10.1016/j.buildenv.2023.110657

Displacement Ventilation (DV) has been known as an energy saving system as it relies on buoyancy force to draw hot air upwards to be displaced by cool air. The main strength of DV that recommends it nowadays is that a well-designed DV system prevents mixing of contaminants as they are dragged along the hot air upward flow leaving the occupied zone, breathing zone in particular, clean. However, the system's effectiveness is lowered in large rooms due to design problem such as difficult balance between sufficient supply flow volume and low inlet velocity, furniture arrangement acting as obstacles, or room geometry. Hence, DV feasibility is limited to small and mid-size rooms. In order to expand the DV potential and applicability to all space types and sizes, this study proposes a portable DV air purifying unit. The unit is designed to be mobile consisting of air recycling unit with no duct connections which widens the range of use to cover a variety of indoor spaces as well as small to medium sized room. The unit has two main functions, one is reinforcing the temperature gradient as stratification crucial for DV, and the second is purifying recycled air. To investigate the effectiveness and feasibility of the proposed DV unit, block model calculations and full-scale experiment were conducted. In a small room, multiple cases were calculated and assessed in terms of temperature distribution and stratification height. In addition, exhalation droplets were simulated and the particulate matter count was used as an indicator for the air quality. Observations on the proposed unit’ s performance and design aspects were highlighted. •To enhance DV performance in large spaces, novel portable DV unit is proposed.•The novel PDVU strengthens the temperature gradient to improve air quality.•PDVU supplies the exhaust hot air at high levels and cool filtered air near floor.•PDV unit can be compensatory to the ventilation system supplying cool clean air.•Using PDV unit reduces the PM count in the room in occupied zone.