https://backend.orbit.dtu.dk/ws/files/218848684/qt85x6r3wv.pdf

A review of advanced air distribution methods - theory, practice, limitations and solutions

The task of HVAC systems is to offset indoor thermal and/or ventilation load. Indoor thermal load can be offset by either convective-dominant way or radiantdominant way. In convective dominant way, system recirculated air is thermally conditioned usually in terms of temperature and humidity. Indoor ventilation load has to be offset by convective dominant way, in which outdoor air is filtered, thermally conditioned and thus it becomes fresh air to dilute indoor pollutants such as CO2. Fresh air and recirculated air can be well mixed and supplied together from ceiling or upper space of indoor environments, which is mixing ventilation. The mixing ventilation system has been most widely used in engineering practice. Without making full use of fresh air, air with mediocre quality is inhaled by human occupants. To avoid energy wastage, thermally conditioned spaces without intensive human occupancy is unnecessary. The use of displacement ventilation was originated from Nordic countries, and this was mainly used in industrial workshops with high headroom. The concept has been used in other types of buildings. Design guidelines for these systems are relatively matured and established, and have been successfully applied in engineering projects. Air is mainly supplied from floor mounted displacement ventilation cylinders at very low velocity. Thermal buoyancy, instead of supply air momentum, is the major driving force to move air upwards from the air reservoir in the floor. Obvious vertical temperature gradient could exist in the indoor displacement ventilated space. However, air duct must be extended and connected with floor mounted displacement ventilation cylinders. Once fresh air and recirculated air are supplied together from displacement ventilation cylinders, large number of displacement ventilation cylinders must be installed to keep enough supply air to outlet area and to maintain a low supply air velocity. For spaces with large spans, hollow pillar or raised access floor must be used as connected air duct in core zones. Under floor air distribution can also achieve displacement mode ventilation by reducing supply air velocity. As a solution, Li presented the principle of vertical wall attached ventilation – the concept of wall attached air supply can be traced back to the early 1980s. The concept of vertical wall attached ventilation was originally named air curtain ventilation, later called attachment ventilation, which is based on the combination of mixing ventilation and displacement ventilation. A mixture of fresh air and recirculated air is first delivered and attached to vertical wall or pillar/column surface and is then moved downwards by the Coanda effect. As the air jet with high momentum approaches the floor, it impinges the corner, and is then separated from the vertical wall or pillar/column surface and reattached to the floor to generate air reservoir. Studies so far, have been mainly on the supply air velocity and the distance between vertical surface and centre of supply air diffuser. Compared with displacement ventilation, similar temperature and velocity fields can be achieved and big supply air flowrate problem can be solved. Therefore, a lot of successful engineering projects have been accomplished in buildings with high space height such as city halls, metro stations and hydro power stations along Yangtze River and Yellow River in China.

https://journals.sagepub.com/doi/pdf/10.1177/1420326X19833850

Xiang Wang

Papers

2D-PIV experiment analysis on the airflow performance of a floor-based air distribution with a novel mushroom diffuser (FBAD-MD)