A review of the performance of different ventilation and airflow distribution systems in buildings

Energy demand has been increasing worldwide and the building sector represents a large percentage of global energy consumption. Therefore, promoting energy efficiency in buildings is essential. Among all building services, Heating, Ventilation and Air Conditioning (HVAC) systems are significantly responsible for building energy use. In HVAC, ventilation is the key issue for providing suitable Indoor Air Quality (IAQ), while it is also responsible for energy consumption in buildings. Thus, improving ventilation systems plays an important role not only in fostering energy efficiency in buildings, but also in providing better indoor climate for the occupants and decreasing the possibility of health issues in consequence. In the last decades, many energy-efficient ventilation methods are developed by researchers to mitigate energy consumption in buildings. This paper reviews scientific research and reports, as well as building regulations and standards, which evaluated, investigated and reported the development of energy-efficient methods for ventilation in buildings. Besides energy-efficient methods such as natural and hybrid ventilation strategies, occupants’ behaviours regarding ventilation, can also affect the energy demand in buildings. Therefore, the influence of occupants’ behaviour on the energy use and the correlation between ventilation and the occupants’ health and productivity were also considered. The review showed that ventilation is interrelated with many factors such as indoor and outdoor conditions, building characteristics, building application as well as users’ behaviour. Thus, it is concluded that many factors must be taken into account for designing energy-efficient and healthy ventilation systems. Moreover, it should be mentioned that utilizing hybrid ventilation in buildings integrated with suitable control strategies, to adjust between mechanical and natural ventilation, leads to considerable energy savings while an appropriate IAQ is maintained.

Towards sustainable, energy-efficient and healthy ventilation strategies in buildings: A review

A Review on efficient thermal management of air- and liquid-cooled data centers: From chip to the cooling system

Challenges of future aircraft propulsion: A review of distributed propulsion technology and its potential application for the all electric commercial aircraft

A review of cavity-based trapped vortex, ultra-compact, high-g, inter-turbine combustors

Current CFD simulation studies of large data centers cannot model the detailed geometries of the perforated tiles due to grid size limitation. These studies often assume that the tile flow can be modeled as constant velocity based on a fully open tile. In this case, mass flux is enforced at the expense of under-predicting momentum flux; the error in momentum flux can be as high as a factor of four for a 25% open perforated tile. Since jet entrainment is a strong function of its initial momentum flux, this error can be significant with respect to predicting the mixing of the surrounding room air into the tile flow. Combined experimental and computational studies were carried out to quantify the importance of the detailed tile geometry, and it was found that proper prediction of the mixing process must account for the tile opening patterns. Suggestions of how to model the floor perforated tiles in data center CFD simulations are then presented.

Experimental and computational study of perforated floor tile in data centers

Aerodynamics of cross-flow fans and their application to aircraft propulsion and flow control

An improved CFD model is presented to predict the thermal field in a small data center test cell. CFD analysis reported in an earlier paper [19] tended to exaggerate hot and cold spots in a small data center test cell as a result of the inability of the CFD model to predict the correct level of mixing of the cold air emanating from the perforated floor tiles and the warmer room air. The same can be said about the mixing of the hot air stream exiting the rack and the surrounding room air. The overall RMS error in the earlier study was 4°C between numerical results and test data. Another indication of low mixing in the CFD results is illustrated in the comparison of the temperature profile along a vertical line in front of the rack between CFD results and test data. While the temperature of the cold flow from the under floor plenum entering the data center was measured to be 12.8°C, temperature measurement at the same location via a temperature mapping tool showed that it is 15°C at 6" above the floor and rising quickly to 17°C at a height of 4 ft. The present investigations yield several improvements to the CFD model, including modeling of the perforated tile flow and rack exhaust flow to conserve both mass and momentum, inclusion of the effects of buoyancy, and an improved thermal boundary condition for the floor. With these improvements, the overall RMS error was reduced to 2°C between numerical results and the same test data reported in [19].

Improved CFD modeling of a small data center test cell

A three-dimensio nal inverse method for the aerodynamic design of turbomachine blades using robust timemarching algorithms for the numerical solutions of the Euler equations is proposed. In this inverse method, the circumferential mass-averaged tangential velocity (or the blade loading) is the primary specified flow quantity, and the corresponding blade geometry is sought after. The presence of the blades is represented by a periodic array of discrete body forces which is included in the equations of motion. A four-stage Runge-Kutta time-stepping scheme is used to march a finite volume formulation of the unsteady Euler equations to a steady-state solution. Modification of the blade geometry during this time-marching process is achieved using the flow-tangency conditions along the blade surfaces. In this paper, the method is demonstrated for the design of two-dimensional infinitely thin cascaded blades ranging from the subsonic to the supersonic flow regimes, including cases with rotational flows and complex shock structures in the flow passage.

Thong Q. Dang

Papers

Experimental and computational study of perforated floor tile in data centers

Aerodynamics of cross-flow fans and their application to aircraft propulsion and flow control

Improved CFD modeling of a small data center test cell

Euler-based inverse method for turbomachine blades. I - Two-dimensional cascades

Mitigation of cross-contamination in an aircraft cabin via localized exhaust