Eco Pelmet Modelling and Assessment. CFD Based Study. Report Number R1D1. 13 January 2015

Transcription

1 EcoPelmet Pty Ltd c/- Geoff Hesford Engineering 45 Market Street FREMANTLE WA 6160 Version:

2 Page 2 PREPARED BY: ABN Lincoln Street Lane Cove NSW 2066 Australia (PO Box 176 Lane Cove NSW 1595 Australia) T: F: E: sydney@slrconsulting.com This report has been prepared by with all reasonable skill, care and diligence, and taking account of the timescale and resources allocated to it by agreement with the Client. Information reported herein is based on the interpretation of data collected, which has been accepted in good faith as being accurate and valid. This report is for the exclusive use of EcoPelmet Pty Ltd. No warranties or guarantees are expressed or should be inferred by any third parties. This report may not be relied upon by other parties without written consent from SLR. SLR disclaims any responsibility to the Client and others in respect of any matters outside the agreed scope of the work. DOCUMENT CONTROL Reference Status Date Prepared Checked Authorised R1D1 Neihad Al-Khalidy Peter Georgiou Neihad Al-Khalidy

3 Page 3 Executive Summary (SLR) has been engaged by EcoPelmet Pty Ltd to perform a thermofluid study of a proposed Eco Pelmet utilising Computational Fluid Dynamics (CFD) analysis. The objective of this study is to demonstrate that the Eco Pelmet in combination with blinds can provide a benefit in reducing energy consumption from an air conditioning system while satisfying all codes and thermal comfort requirements. The following scenarios are analysed: Scenario 1: RA Pelmet, Blind Down Scenario 2: RA Pelmet, Blind Up Scenario 3: No RA Pelmet, Blind Down Scenario 4: No RA Pelmet, Blind Up The worst case solar heat gain scenario for a northern facade in Perth has been modelled for 15 June. The sun for a north-facing window will have a lower angle of incidence at midday in winter. The glazed façade is therefore exposed to a greater effective area of solar radiation and the window can transmit more solar heat in winter than in summer. A geometrically three-dimensional model of a proposed north facing office space and its ventilation system was assembled to capture the following: Solar access data including - transmission, radiation and reflection from the glass and associated blind; Re-radiation from the floor and walls; Air flow pattern; and Complex temperature profile including stack effect that occurs within the analysed office area. The ratio of transmitted, absorbed and reflected rays will vary according to the characteristic of the particular glazing. Double glazed low e glass is used for all analysed scenarios. The study compares the air flow temperature results with and without blinds. This study uses a generic blind to reduce solar heat gain. Further cooling load reduction may be achieved using blinds with higher reflectivity coefficients, etc. The following conclusions have been reached based on the results of CFD simulation: The blind is effective in reducing heat gain in the computational domain. The average temperature at typical chest level is reduced by ~0.7 C when the proposed blind is lowered to 0.9 m above the ground. The average air temperature and velocity at typical chest level for all analysed scenarios are summarised below:

4 Page 4 Executive Summary Scenario Average Velocity (m/s) Average Temperature - K 1 RA Pelmet, Blind Down (23.5 C) 2 RA Pelmet, Blind Up (24.2 C) 3 No RA pelmet, Blind Down (25.6 C) 4 No RA pelmet, Blind Up (26.2 C) On the basis of the above results: An RA Pelmet system can achieve a similar temperature profile inside the analysed office with a lower rated glazing system or reduced airflow rate in the domain The proposed RA Pelmet system will also help improving occupant comfort through reduced temperature range in the domain. Improving the thermal comfort will help achieving credits under green star rating tools mainly, IEQ 9. The green star rating tools encourage and recognise the use of thermal comfort assessments to guide a design option. The developed CFD model can be used to analyse a wide ranges of blinds plus Eco Pelmet configurations for the specific requirements of a particular commercial building design. Each building should ideally be separately assessed because of the varying building fabric, orientation, surrounding buildings, internal air conditioning details, shading devices, local weather data, etc.

5 Page 5 Table of Contents 1 INTRODUCTION 7 2 DESCRIPTION OF THE PROBLEM 7 3 MODEL DESCRIPTION Solar Model for the Indoor Ventilation Calculation External Glass Blind Air Conditioning Data Supply Air Return Air Outdoor Condition Lighting Heat Flux Floor Side Walls Other Boundary Conditions 9 4 DISCRETIZATION 11 5 RESULTS AND DISCUSSIONS Scenario 1: RA pelmet, Blind Down Scenario 2: RA pelmet, Blind UP Scenario 3: No RA pelmet, Blind Down Scenario 4: No RA pelmet, Blind Up 28 6 CONCLUSIONS 30

6 Page 6 Table of Contents FIGURES Figure 1 3D Model for the Base Case Scenario 9 Figure 2 Details of the Modelled Eco Pelmet 10 Figure 3 Grids for CFD Modelling 12 Figure 4 Scaled Residual History Scenario 1 13 Figure 5 Velocity Vectors at the Supply and Return Openings (m/s) Scenario 1 15 Figure 6 Predicted Solar Heat Flux on the Glazed Façade (W/m 2 ) Scenario 1 16 Figure 7 Predicted Solar Heat Flux on the Floor (W/m 2 ) Scenario 1 16 Figure 8 Velocity Profile at Various 2D Section a Typical Chest Level (m/s) Scenario 1 17 Figure 9 Path lines Coloured by Velocity Magnitudes (m/s) Scenario 1 18 Figure 10 Temperature Distribution at a Typical Chest Level (K) Scenario 1 19 Figure 11 Velocity Vectors at the Supply and Return Openings (m/s) Scenario 2 21 Figure 12 Velocity Profile at a Typical Chest Level (m/s) Scenario 2 21 Figure 13 Velocity Profile at 2D Vertical Section (m/s) Scenario 2 22 Figure 14 Temperature Distribution at a Typical Chest Level (K) Scenario 2 22 Figure 15 Temperature Distribution at a Typical Chest Level (K) Scenario 2 23 Figure 16 Predicted Solar Heat Flux on the Glazed Façade (W/m2) Scenario 3 24 Figure 17 Predicted Solar Heat Flux on the Floor (W/m2) Scenario 3 25 Figure 18 Velocity Vectors at the Supply and Return Openings (m/s) Scenario 3 25 Figure 19 Velocity Profile at a Typical Chest Level (m/s) Scenario 3 26 Figure 20 Path lines Coloured by Velocity Magnitudes (m/s) Scenario 3 26 Figure 21 Temperature Distribution at a Typical Chest Level (K) Scenario 3 27 Figure 22 Velocity Profile at a Typical Chest Level (m/s) Scenario 4 28 Figure 23 Path lines Coloured by Velocity Magnitudes (m/s) Scenario 4 29 Figure 24 Temperature Distribution at a Typical Chest Level (K) Scenario 4 29

7 Page 7 1 INTRODUCTION (SLR) has been engaged by EcoPelmet Pty Ltd to perform a thermofluid study of a proposed Eco Pelmet utilising Computational Fluid Dynamics (CFD) analysis. The objective of this study is to demonstrate that the Eco Pelmet in combination with blinds can provide a benefit in reducing energy consumption from an air conditioning system while satisfying all codes and thermal comfort requirements. 2 DESCRIPTION OF THE PROBLEM The problem considered is ventilation and thermal comfort of a north facing office at Perth. It is assumed that the front north facing wall of the office space is fully glazed from the ground to the ceiling. This study looks at the worst case solar loads in the middle of June heat gain scenario for a northern facade in Perth. The office is air-conditioned and designed to maintain 23±1 o C. The following scenarios are analysed: RA Pelmet, Blind Down RA Pelmet, Blind Up No RA Pelmet, Blind Down No RA Pelmet, Blind Up 3 MODEL DESCRIPTION A geometrically 3-dimensional model of a 4 m (length) X 3.6 m (Width) X 2.8 (height) of a north facing office space is assembled to capture the solar load, airflow pattern and complex temperature profile within the analysed office. 3.1 Solar Model for the Indoor Ventilation Calculation Direct and diffusive solar irradiations are predicted based on the global position for the project site, date and time of the day: Latitude, Longitude = 32 S, E Date & Time = 15 June at 12 noon. The sun for a north-facing window will have a lower angle of incidence at midday in winter. The glazed façade is therefore exposed to a greater effective area of solar radiation and the window can transmit more solar heat in winter than in summer. Fair Weather conditions are assumed for the Solar Irradiation Method calculation

8 Page External Glass All scenarios assume double-glazed low e glass with the following properties: Glass Density = 2,220 kg/m 3 Specific Heat = 830 J/kg.K Thermal Conductivity = 1.15 W/(m.K) Direct Visible Absorptivity Radiation = 0.49 Direct IR Absorptivity Radiation = 0.49 Diffuse Absorptivity Radiation = 0.49 Direct Visible Transmissivity Radiation = 0.3 Direct IR Transmissivity Radiation = 0.3 Diffuse Visible Transmissivity Radiation = 0.32 The airspace between the two layers is not modelled at this stage. 3.3 Blind This study assumes a generic blind with the following radiation properties: Direct Visible Absorptivity Radiation = 0.8 Direct IR Absorptivity Radiation = Air Conditioning Data Supply Air Two linear diffusers / Two slots per diffuser Air flow mass flow rate per diffuser: 75 l/sec Flow direction: 15 from horizontal Return Air Return air slots on the top of the proposed Eco Pelmet for Scenario 1 and Scenario 2 (refer Figure 2) Return slots over the banks of lights for Scenario 3 and Scenario Outdoor Condition Outdoor temperature of 22 o C is assumed. An external heat transfer coefficient of 4 W/m 2.K is used to capture conductive heat transfer from the outside of the building. 3.6 Lighting Heat Flux 10 W/m Floor A concrete floor is assumed. Radiant properties for a dark grey carpet are assumed.

9 Page Side Walls Solid walls are assumed to the south, east and west sides of the analysed office. 3.9 Other Boundary Conditions The following additional boundary conditions were used Turbulence quantities (kinetic energy and dissipation rate) were calculated from empirical relationships. Figure 1 3D Model for the Base Case Scenario Linear Diffuser Flow per linear diffuser = 75 lps 2 Slots per diffuser 1.2 m X 0.3 m light fitting Return Openings Eco Pelmet Blind-up Glazing Flow Direction = 15 deg from Horizontal

10 Page 10 Figure 2 Details of the Modelled Eco Pelmet Return Slots Removable Cover

11 Page 11 4 DISCRETIZATION The software package utilised in the current CFD analysis is the commercially available code Fluent. The CFD model solves continuity, energy and momentum equations in the computational domain to predict the steady state airflow and temperature inside the analysed office space. For the current analysis 3,518,789 nodes were used to cover the computational domain. Polyhedral and hexahedral elements were used for the computational domain (Refer Figure 3). The following techniques were used for discretization: Full buoyancy effects modelling RNG k-epsilon combined with wall function algorithm Surface to Surface radiation model A second order numerical scheme was used for discretization of pressure to obtain more accurate results. An iterative procedure was used to estimate the air velocity in terms of three directions, pressure profile and turbulence parameters. Figure 4 shows that the normalised residuals of continuity for all cases were reduced by between four orders of magnitude while the normalised residual of x-, y-, and z-velocity, k and epsilon was reduced between four and six orders of magnitude demonstrating a valid solution.

12 Page 12 Figure 3 Grids for CFD Modelling

13 Page 13 Figure 4 Scaled Residual History Scenario 1 * Valid numerical solution is obtained on a final mesh density utilising a 2 nd Order Numerical Scheme

14 Page 14 5 RESULTS AND DISCUSSIONS Detailed computational simulations of air flow distribution, turbulent flows and temperature profile have been carried out using the geometric model described above. The results are illustrated in Figure 5 to Figure Scenario 1: RA pelmet, Blind Down Results of simulations are presented in Figure 5 to Figure 10. The velocity vectors at the supply and return terminals shown in Figure 5 indicate the following: Air with a velocity of 1.7 m/s is provided at the celling level with a flow direction of 15 to the horizontal as per the giving boundary conditions. Air exits from the slots at the top of the Eco Pelmet. The solar load is reviewed on all surfaces and the contours of solar heat flux on the external glazing and the floor are shown in Figure 6 and Figure 7 respectively. One can see that the solar heat flux on the proposed glazing is ~400 W/m 2. Figure 6 shows higher solar flux in the order of 140 W/m 2 on the floor near the glazing where the blind is partially-up. Figure 8A shows air speeds through a 2D horizontal section at 1.5 m above the ground (Typical Chest Level). Velocity magnitudes are plotted on a colour coded scale between 0 m/s and m/s (dark blue representing still conditions at 0 m/s and red representing the strongest air speed at m/s). The average air speed is 0.2 m/s. Figure 8B and Figure 8C show air speeds through a vertical section through the linear diffuser. One can see that the CFD model captures the fluid flow characteristics very well. Airflow direction is 15 from the horizontal as per the given boundary conditions. Air then reaches the ground and circulates with lower velocities. Detailed air flow path lines from the slot diffusers are shown in Figure 9, which indicates that a portion of the supplied air can short-circuit toward the return pelmet. The location of supply/return terminals can be optimised using CFD. Figure 10A shows temperature profile through a 2D horizontal section at 1.5 m above the ground (Typical Chest Level). Temperature magnitudes are plotted on a colour coded scale between 293 K (20 C) and 300 K (27 C). The average temperature is K (23.5 C) Figures 10B and 10C plot the contours of static temperatures on tighter scales. The following conclusions can be reached from the above figures: Higher temperature is obtained near the glazed façade. The temperature difference in the majority of the room is within 2 degrees.

15 Page 15 Figure 5 Velocity Vectors at the Supply and Return Openings (m/s) Scenario 1 Supply Air Returned Air

16 Page 16 Figure 6 Predicted Solar Heat Flux on the Glazed Façade (W/m 2 ) Scenario 1 Figure 7 Predicted Solar Heat Flux on the Floor (W/m 2 ) Scenario 1

17 Page 17 Figure 8 Velocity Profile at Various 2D Section a Typical Chest Level (m/s) Scenario 1 A: Velocity Distrbution at Typical Chest Level (1.5 m above Ground) B:Velocity Distrbution at a 2D Vertical Section on m/s Scale C:Velocity Distrbution at a 2D Vertical Scetion on m/s Scale C:

18 Page 18 Figure 9 Path lines Coloured by Velocity Magnitudes (m/s) Scenario 1 Diffuser 1 Slot 1 Diffuser 1 Slot 2 Diffuser 2 Slot 1 Diffuser 2 Slot 2

19 Page 19 Figure 10 Temperature Distribution at a Typical Chest Level (K) Scenario 1 A: On K Scale B: On K Scale C: On K Scale

20 Page Scenario 2: RA pelmet, Blind UP Results of the Scenario 2 simulations are presented in Figure 11 to Figure 15. The velocity vectors at the supply and return terminals shown in Figure 11 indicate that the air flow velocities are similar to that in Scenario 1 due to the use of the same boundary conditions. Figure 12 shows air speeds through a 2D horizontal section at 1.5 m above the ground (Typical Chest Level). Velocity magnitudes are plotted on a colour coded scale between 0 m/s and m/s. The average wind speed is 0.17 m/s Figure 13 shows air speeds through a vertical section through the linear diffuser. One can see that the low velocity zone indicated by blue colour is larger than that in Scenario 1. Figure 14 shows temperature profile through a 2D horizontal section at 1.5 m above the ground (Typical Chest Level). Temperature magnitudes are plotted on a colour coded scale between 293 K (20 o C) and 300 K (27 o C). The average temperature is K (24.2 o C) Figure 15 plots the contours of static temperatures on tighter scale. One can see that the average temperature is at least 0.5 C higher than that in Scenario 1.

21 Page 21 Figure 11 Velocity Vectors at the Supply and Return Openings (m/s) Scenario 2 Figure 12 Velocity Profile at a Typical Chest Level (m/s) Scenario 2

22 Page 22 Figure 13 Velocity Profile at 2D Vertical Section (m/s) Scenario 2 Figure 14 Temperature Distribution at a Typical Chest Level (K) Scenario 2 On K Scale

23 Page 23 Figure 15 Temperature Distribution at a Typical Chest Level (K) Scenario 2 On K Scale

24 Page Scenario 3: No RA pelmet, Blind Down Results of the Scenario 3 simulations are presented in Figure 16 to Figure 21. The solar load is reviewed on all surfaces and the contours of solar heat flux on the external glazing and the floor are shown in Figure 16 and Figure 17 respectively. One can see that the solar heat flux on the proposed glazing and the floor is similar to that in Scenario 1. The velocity vector at the supply and return terminals shown in Figure 18 indicate that the air flow velocities at the supply opening are similar to that in Scenario 1 as per the given boundary conditions. Air is return via high level openings around the lighting fitout. Figure 19 shows air speeds through a 2D horizontal section at 1.5 m above the ground (Typical Chest Level). Velocity magnitudes are plotted on a colour coded scale between 0 m/s and m/s. The average air speed is 0.18 m/s Figure 20 show air flow path lines through the diffusers. One can see that the air flow path lines are different than that in Scenario 1 due to the location of the return terminals. Figure 21 shows temperature profile through a 2D horizontal section at 1.5 m above the ground (Typical Chest Level). Temperature magnitudes are plotted on a colour coded scale between 293 K (20 C) and 300 K (27 C). The average temperature is K (25.6 C). Figure 16 Predicted Solar Heat Flux on the Glazed Façade (W/m2) Scenario 3

25 Page 25 Figure 17 Predicted Solar Heat Flux on the Floor (W/m2) Scenario 3 Figure 18 Velocity Vectors at the Supply and Return Openings (m/s) Scenario 3

26 Page 26 Figure 19 Velocity Profile at a Typical Chest Level (m/s) Scenario 3 Figure 20 Path lines Coloured by Velocity Magnitudes (m/s) Scenario 3 Diffuser 1 Slot 1 Diffuser 1 Slot 2 Diffuser 2 Slot 1 Diffuser 2 Slot 2

27 Page 27 Figure 21 Temperature Distribution at a Typical Chest Level (K) Scenario 3

28 Page Scenario 4: No RA pelmet, Blind Up Results of the Scenario 4 simulations are presented in Figure 22 to Figure 24. Figure 22 shows air speeds through a 2D horizontal section at 1.5 m above the ground (Typical Chest Level). Velocity magnitudes are plotted on a colour coded scale between 0 m/s and m/s. The average wind speed is 0.23 m/s Figure 23 shows airflow path lines through the slot diffusers. Figure 24 shows temperature profile through a 2D horizontal section at 1.5 m above the ground (Typical Chest Level). Temperature magnitudes are plotted on a colour coded scale between 293 K (20 o C) and 300 K (27 o C). The average temperature is K (26.2 o C) Figure 22 Velocity Profile at a Typical Chest Level (m/s) Scenario 4

29 Page 29 Figure 23 Path lines Coloured by Velocity Magnitudes (m/s) Scenario 4 Diffuser 1 Slot 1 Diffuser 1 Slot 2 Diffuser 1 Slot 2 Diffuser 2 Slot 2 Figure 24 Temperature Distribution at a Typical Chest Level (K) Scenario 4

30 Page 30 6 CONCLUSIONS (SLR) has been engaged by EcoPelmet Pty Ltd to perform a thermo fluid study of a proposed Eco Pelmet utilising Computational Fluid Dynamics (CFD) analysis. The objective of this study was to examine a typical commercial building office layout for a worst-case solar heat loading scenario and assess the impact of the incorporation of an Eco Pelmet in combination with blinds on energy consumption from the office s air conditioning system. The following scenarios were analysed: Scenario 1: RA Pelmet, Blind Down Scenario 2: RA Pelmet, Blind Up Scenario 3: No RA Pelmet, Blind Down Scenario 4: No RA Pelmet, Blind Up The worst case solar heat gain scenario for a northern facade in Perth has been modelled for 15 June. A 3-D CFD model was developed for the typical analysed office capturing the following: Transmission, radiation and reflection from the glass and associated blind; Re-radiation from the floor and walls; Air flow pattern; and Complex temperature profile including stack effect that occurs within the analysed office area. The following conclusions have been reached based on the results of CFD simulations: The blind is effective in reducing heat gain in the computational domain. The average temperature at typical chest level is reduced by ~0.7 C when the proposed blind is lowered to 0.9 m above the ground. The RA Pelmet system can achieve a similar temperature profile inside the analysed office with a lower rated glazing system or reduced airflow rate in the domain. The developed CFD model can be used to analyse a wide ranges of blinds plus Eco Pelmet configurations for the specific requirements of a particular commercial building design. Each building should ideally be separately assessed because of the varying building fabric, orientation, surrounding buildings, internal air conditioning details, shading devices, local weather data, etc.

31 Appendix A Page 1 of 1