Use of Numerical Modelling to Improve the Performance of Night - PowerPoint PPT Presentation

Use of Numerical Modelling to Improve the Performance of Night Ventilation Hayder. M. Khan, Dr. Gregory. F. Lane-Serff, Dr. Jonathan Dewsbury STAR Global Conference 2014 Vienna

Outline • Background: Energy efficient cooling in developing countries • Background: Challenges facing house design • Background: Passive cooling • Background: Night Ventilation • Background: The outline of my research • Background: Traditional Baghdadi house • Problem : Air quality and night ventilation • Solution: Simulation model • Solution: Mesh • Solution: Cases • Results: Effects of opening/closing windows • Results: Effect of fan • Results : Effect of exhaust fan • Results : Effect of ceiling Fan • Results : Effect of Wind catcher • References

Background: Energy efficient cooling in developing countries • Case example: Iraq (Middle East) • Suffering from a chronic energy shortage The demand is more than supply • Continues demand for new housing So the needs for energy will be more in future • Pollution problems And it is not a preferred building new energy plants to generate electricity • Solution: Re-design the house in way that makes them more efficient in energy use

Background: Challenges facing house design • Intensive solar radiation • Scarce water resources • High ambient temperature • Absence of building standards • Need for cooling system for house with low energy consumption • Passive cooling possible be the solution

Background: Passive cooling • They are many • They use renewable sources (wind, geothermal, etc ..) • Have a different thermal comfort criteria from conditioning building (i.e. different setting point temperature)

Background: Night Ventilation • Night ventilation is one of the passive cooling techniques . • It is common in hot arid areas where there is no need for water. • Discharge heat from building structure by natural ventilation during night. • Charging during day . • Need shading and close the openings during day time to reduce the heat loads [1].

Background: The outline of my research

Background: Traditional Baghdadi house

Problem : Air quality and night ventilation • The definition of night cooling shows that the openings need to be closed during the day time . • In same time courtyard reduces the air velocity in ground level to near zero which dramatically decreases the effect of infiltration and ventilation vents. • C02 is often used as indicator for air quality . Where it becomes dangerous not as a toxic agent but as asphyxiate condition when concentrations exceed 35000 PPM. • The accept limit is around 1000 PPM [3]. • The Problem : how we can balance between air quality and temperature during day time .

Solution: Simulation model • Exhaust fan was used to reduce the time required to ventilate. • The ceiling fan was used as an air mixer to decrease the local concentration of CO2 • Test room was located in ground floor. • K- ԑ realizable turbulence model • The fan was simulate as (Fan interface) • Courtyard dimensions are length, width and height = 5,4 ,8 meters . The dimensions , to increase the heat transfer coefficient and also enhance thermal comfort by • The operation of exhaust fan is controlled by CO2 sensor which was simulated by using • Multi component gas (Air+CO2) were chosen in accordance with survey for courtyard houses in Baghdad. increasing the air velocity. • The house has a two levels • Wind catcher is use to introduce fresh air to the courtyard through basement where it • The fan was simulated by using overset mesh . • Ideal gas Java code. with basement. • The simulation is for five hours from 10AM with time step equal to 300 seconds. • The CO2 was released by two manikins in sitting position, the releasing rate (G • Surface to surface Radiation model will become more cooler due to geothermal cooling. • Various radiation properties • Solar loads l/s)was calculated as: was set for wall ,roof and • Radiation temperature was set as a G= 4 * 10E-5 *M*A = 5 ml/s ( M(metabolic rate) =60 w/m2) and (A (human body floor. area =2.1 A2). sky temperature by using Swinbank • Soil temperature is decided equation[4] from an empirical equation 𝑏𝑛𝑐𝑗𝑓𝑜𝑢 ) 1.5 that depend on 𝑈 𝑡𝑙𝑧 = 0.0552 ( 𝑈 measurements from field • Inlet and outlet was set in way to location where its simulate atmospheric boundary layer temperature is changing with wind tunnel [5]. depth. • The air temperature at inlet was set to periodically change with time in line with weather data

Solution: Mesh • Mesh type polyhedral with prism layer. • The size of grid is ranging from 3.5 m to 4 cm with volume adaptation and by using Volumetric controls. • The number of cells (N) inside the rooms was chosen according to the relation [6]: N= 44.4E3*V 0.38 • The prism layer was decide to make the first cell in distance less than 5 mm from the walls .

Solution: Cases

Results: Effects of opening/closing windows 32.5 3.50E+03 32 3.00E+03 31.5 2.50E+03 Average temperature C 31 Average CO2 ppm 2.00E+03 Co2 30.5 Temperature 1.50E+03 30 1.00E+03 29.5 5.00E+02 29 28.5 0.00E+00 Close Open

Results: Fan Vs Open 32.5 3.50E+03 32 3.00E+03 31.5 2.50E+03 Average temperature C 31 Average CO2 ppm 2.00E+03 Co2 30.5 Temperature 1.50E+03 30 1.00E+03 29.5 5.00E+02 29 28.5 0.00E+00 Fan Open

Effect of exhaust fan 1,000 900 800 700 600 CO2 PPM 500 CO2 inside the room 400 300 200 100 0 0.1 1.2 2.5 3.7 5.1 Hours • The fan will be switch on (and also open the windows) only when the CO2 concentration inside in the room is over 800 PPM . • Time step is also change to 100s and it can decrease it or increase it . • The whole operation is done through the using of Java code.

Results : Effect of ceiling Fan 1.40E-01 3.00E-01 1.20E-01 2.50E-01 1.00E-01 2.00E-01 Mixing ratio 8.00E-02 Mixing ratio m/s 1.50E-01 6.00E-02 Volume average for Velocity inside the room (m/s) 1.00E-01 4.00E-02 5.00E-02 2.00E-02 0.00E+00 0.00E+00 Open Close Fan • With increasing the air velocity the thermal comfort get batter . • Mixing ratio = ((Highest concentration - Lowest concentration )/ Highest concentration ) Breathing zone

Results : Effect of wind catcher 45 40 35 30 Temperature C Average temerpature inside the 25 courtyard 20 Average temerpature inside the basement 15 10 5 0 Close Open Fan

References [1] Givoni B (1998) Climate Considerations in Building and Urban Design. Wiley. [2]Nicol J F (1974) An Analysis of Some Observations of Thermal Comfort in Roorkee, India and Baghdad, Iraq. Annals of Human Biology, 1(4), 411-426. [3]Awbi H B (1991) Ventilation of Buildings.E & FN Spon. [4]Richards P J, & Hoxey R P (1993) Appropriate Boundary Conditions for Computational Wind Engineering Models Using the K- ϵ Turbulence Model. Journal of wind engineering and industrial aerodynamics, 46 – 47(0), 145-153. [5]Richards P J, & Hoxey R P (1993) Appropriate Boundary Conditions for Computational Wind Engineering Models Using the K- ϵ Turbulence Model. Journal of wind engineering and industrial aerodynamics, 46 – 47(0), 145-153. [6] Nielsen P V, Allard F, Awbi H B et al (2007) No.10: Computational Fluid Dynamics in Ventilation Design.Federation of European Heating, Ventilation and Air Conditioning Associations.