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House As a System
Published in Stan Harbuck, Donna Harbuck, Residential Energy Auditing and Improvement, 2021
Airflow is measured in cubic feet per minute (CFM), or ft³/min. A cubic foot is a little larger than the size of a basketball. Therefore, a flow of 100 CFM would be roughly the equivalent of the air in 100 basketballs flowing in one minute, Figure 3-6.
Airflow Analysis
Published in Kjell Anderson, Design Energy Simulation for Architects, 2014
Airflow that is not near objects tends to be smooth and directional, called laminar flow. When laminar flow is disrupted due to encountering objects or reaching higher velocities, it becomes turbulent flow. Direction and speed are very difficult to predict in turbulent airflow without CFD software or wind tunnel testing. For this reason, urban areas are prone to turbulent airflow from the combination of adjacent buildings with simulation required to determine the effects, see Case Study 9.4. The layer of air between the object and the outer edge of turbulent flow, where it subsides into laminar flow, is called the boundary layer.
Fundamental Principles of Aerodynamics (Subsonic)
Published in Rose G. Davies, Aerodynamics Principles for Air Transport Pilots, 2020
According to Bernoulli’s equation, static pressure of airflow increases with the decreasing speed along a streamline. When the air speed decreases to “0”, for example, at the leading edge of aerofoil, its static pressure reaches the highest value. The location, where the air speed decreases down to “0”, is called stagnation point, and the static pressure, density and temperature of air at this point are called stagnation pressure, stagnation density, and stagnation temperature respectively. For a level fluid flow, the static stagnation pressure, pstg, is equal to the total pressure P (pt).Example 2.3An airflow travels at v1 = 25 ms−1, p1=1.03 × 105 Pa, then its speed increases to v2 = 32 ms−1. Its density ρ = 1.225kgm−3. Find p2, and the stagnation pressure ps .Solution32 ms−1 = 16.45 kt, so air is incompressible. Use Bernoulli’s equation: p2+ρ2v22=p1+ρ2v12p2=1.03×105+1.2252×252−1.2252×322p2=1.028×105(Pa)The stagnation pressure pstg:pstg+0=p+ρ2v2=Ppstg=1.03×105+1.2252×252=1.034×105(Pa)
Effects of flow and heat transfer around a hand-shaped former
Published in Engineering Applications of Computational Fluid Mechanics, 2022
Kittipos Loksupapaiboon, Chakrit Suvanjumrat
A dimensionless quantity is used to represent the results of the airflow across a bluff body. Airflow causes drag forces, , which can be calculated by integrating the pressure and shear stress on the obstacle surface. The dimensionless drag force can then be calculated using Equation (3). The dimensionless heat transfer coefficient, the Nusselt number, is a parameter that defines the rate of heat transfer from the surface and involves the ratio of convection to conduction heat transfer. The average Nusselt number can be calculated using Equations (4)–(6). where is the heat transfer coefficient, is the hydraulic diameter, and and represent the wall and inlet temperatures, respectively.
Investigations on the dynamic characteristic and its influence factors of a transcritical CO2 automobile heat pump
Published in Science and Technology for the Built Environment, 2021
Xiang Yin, Anci Wang, Jianmin Fang, Feng Cao, Xiaolin Wang
Additionally, the airflow rate of the gas cooler also had much influence on the dynamic system performance. It is obviously observed in Figure 7 that the system COP decreased more quickly with a lower airflow rate. With the increasing airflow rate, this decreasing speed slow down, and the valley value of the COP grew dramatically when the airflow rate increased from 120 m3/h to 520 m3/h. On one hand, with the increase of the airflow rate, the convective heat transfer coefficient at the air side increased. On the other hand, the temperature difference between the supply air and the refrigerant was unchanged, but the temperature difference between the outlet air and the refrigerant slightly grew. Thus, the heat capacity increased, resulting in the larger COP. As for the stable value, the larger COP was also apparently obtained at the higher airflow rate. However, the airflow rate had an insignificant effect on the steady COP when the airflow rate exceeded 220 m3/h. For the relatively appropriate airflow rate of the HVAC, the higher airflow rate contributed to the better dynamic performance, but it had no apparent influence on the stable value. Therefore, for the automatic control system, it had better start at 520 m3/h at the first 1000s, and then worked at a relative low airflow rate for a more comfortable passenger compartment.
Opportunities and pitfalls of using building performance simulation in explorative R&D contexts
Published in Journal of Building Performance Simulation, 2019
R. C. G. M. Loonen, M. L. de Klijn-Chevalerias, J. L. M. Hensen
Using Fused Deposition Modeling (FDM), an Additive Manufacturing (AM) process based on material extrusion, the air channels are printed in wax so they can be placed in the formwork before casting the concrete and then be melted after the concrete is hardened (Figure 1). Consequently, the concrete is in direct contact with the convective airflow that circulates through it, and each air channel can be unique in form to optimize the performance of the system. The convection takes place with separate pipes on both sides of the concrete’s core to increase the charge/discharge of the thermal storage process. The airflow rate through the wall elements is controlled with the help of dampers and small computer fans with a power consumption of 0.5 W each.