GTRI Report: A5428/1

EVALUATION OF THE AURA VENTS
FOR HORTON HOMES, INC.

Final Report for Horton Homes, Inc.
12 August 1997

Preface

The work reported here was funded by Horton Homes.

The GTRI Principal Investigator was Dr. K. K. Ahuja. Horton Homes technical monitor was Mr. Carl Brorup.

The authors benefited significantly from discussions with Mr. Les Orenstein of Active Ventilation Products, Inc.

The authors are particularly grateful to Dr. Robert Funk for coordinating the smoke flow visualization, to Dr. Kevin Massey for his initiative of establishing the workability of the inlet of the flight simulation free jet facility for the present investigation and to Todd Elsbernd for his assistance in operating the test facility.

Special thanks go to Mr. Chris Downing of the EDI industrial outreach program of Georgia Tech for recommending this investigation team of Horton Homes, Inc.

Table of Contents

Section 1. VENTILATION CAPACITY OF FOUR VENTS

Section 2. VENTILATION CAPACITY OF A 4-INCH DIAMETER RELIEF VENT
WITH AND WITHOUT LOUVERED CAPS

2.1 Objective

2.2 Experimental Setup

2.3 Experimental Procedure

2.4 Results

2.4.1 Relief Valve With Caps; 10 Ft Inlet Duct

2.4.2 Relief Valve Without Caps; 10 Ft Inlet Duct

2.4.3 Relief Valve Without Caps; 21 Ft 3 In. Inlet Duct

2.4.4 Relief Vent Without Caps; 21 Ft 3 In. Inlet Duct

2.5 Conclusions

Section 1

VENTILATION CAPACITY OF AURA VENTS

1.1 OBJECTIVE

The objective of the study described here was to evaluate the ventilation capacity in cubic feet per minute (cfm) of the aura vents manufactured by Active Ventilation Products, Inc. for Horton Homes, Inc. Six Aura vents were tested: 6 in. Aura, 8 in. Aura, 12 in. Aura, 14 in. Aura, 14 in. Aura Commercial, and 18 in. Commercial. Volume flow measurements were made for each vent at five different wind speeds.

1.2 EXPERIMENTAL SETUP

Horton Homes, Inc. provided a simulated house, shown in Figure 1. The house measured approximately 4 ft 3 in. square by 5 ft high, with a sloping roof of about 15 degrees. A suitable hole was cut in the top of the house to allow mounting of the roof vents. Each vent was mounted over the hole in the roof and the edges were covered with duct tape to provide an air-tight seal.

A 16-in. diameter hole was cut on one wall of the house to allow a 16-in. diameter duct of be mounted. The duct provided an inlet of known area where the air intake velocity could be measured and mass and volume flow calculations could be made. With respect to the flow direction, the duct extended 4 ft to the left, and 6 ft to the rear with a right-angled bend.

The house was placed in front of the inlet of the GTRI Anechoic Free Jet Flight Simulation Wind Tunnel. This facility is normally used at GTRI to suck a significant amount f air for tasks associated with simulation of aircraft take-off and landing. The ambient air enters the inlet shown in Figure 1 and 2 and passes through a wind tunnel nozzle into a large, sealed, room on the other side of the inlet. The air from the room is removed by a powerful suction fan. This arrangement provides wind speeds over the house roof in the range 4-12 mph.

Fig 2aFig 2b

The inlet provided a controllable amount of wind to be passed over the house and the roof vents. A wind speed range of about 4 to 12 miles per hour was achieved. The 16 in. duct extended past the inlet of the wind tunnel, to prevent the wind from interfering with the air intake measurements. A schematic of this arrangement is shown in Figure 2a and 2b and a photographic view can be seen in Figure 3.

To measure the wind speed passing over the roof vents, an anemometer was mounted on the roof near the vents. To measure the amount of air exhausted from the house by the roof vent, another anemometer was mounted 24 in. downstream inside of the 16 in duct as shown in Figure 2b. This anemometer was calibrated to a lower limit of accuracy of 1 ft/sec prior to the test.

Except for the 18-in. vent, the open area of the inlet was greater than the open area of the openings in all of the vents. This allowed for the inlet to cause no restriction to the flow entering the house.

The data obtained is a at best of industrial quality, although extreme care was exercised in maintaining consistency and accuracy. For example, our best judgment was exercised in selecting a large enough inlet duct diameter to provide the most possible volume but no systematic study was conducted to optimize this diameter. Likewise, the minimum length of this inlet duct was used without conducting a detailed study on the effect of the inlet duct length.

1.3 EXPERIMENTAL PROCEDURE

Each vent was fastened and sealed to the top of the test house. The wind tunnel was then started and the desired wind speed was established. When the wind over the roof of the house was steady at the correct speed, a measurement was taken with the anemometer inside the 16 in. inlet duct. the anemometer averages the speed of the air inside of the duct over 16 seconds. Three successive averages were taken at the same wind speed. those three measurements were then used in the calculations of the mass and volume flow. this procedure was repeated for all six vents at five wind speeds of 4, 5.2, 7.5, 9.8, and 11.4 mph.

1.4 RESULTS

The 8 inch Aura and the 14 inch Aura vents were tested first. The results for these two vents are presented first.

1.4.1 The 8 in. Aura Vent

The following is a table of the volume flow exhausted from the house by the 8 inch Aura vent shown in the test configuration in Figure 4.

Wind Speed
Volume Flow
mph
cfm
4.3
81.45
5.2
98.20
7.4
142.88
9.6
163.71
11.1
185.70

The smoke flow visualization was performed for the 8 in. vent to ensure that air was being ventilated from the house at all wind speeds.

1.4.2 The 14 in. Aura Vent

The following is a table of the volume flow exhausted from the house by the 14 in. Aura vent shown in the test configuration in Figure 5.

Wind Speed
Volume Flow
mph
cfm
4.0
177.79
5.2
202.46
7.5
281.11
9.8
314.44
11.4
357.44

A smoke flow visualization was performed to ensure that air was being drawn into the house and blown out of the house through the vent at all wind speeds. Air was being withdrawn from the house interior at all wind speeds tested. A smoke flow visualization showing that smoke was indeed being ventilated out of the enclosure onto which the vent was mounted is shown in Figure 6.

Volume flow rates as a function of wind speed for the 8 inch and the 14 inch Aura vent are shown in figure 7. Almost a linear relationship appears to exist between the flow rates and the wind speed in the region of wind speeds tested.

1.4.3 The Results of other Aura Vents

Other four vents (6 in Aura, 12 in Aura, 14 in Aura Commercial, and 18 in Aura commercial) were tested using the methodology described above for the 8 inch and the 14 inch diameter vents. The following four tables provide the data for these four vents:

6 in. Aura Vent

12 in. Aura Vent
14 in. Aura Vent commercial
18 in. Aura Vent
Wind Speed
Volume Flow
Wind Speed
Volume Flow
Wind Speed
Volume Flow
Wind Speed
Volume Flow
mph
cfm
mph
cfm
mph
cfm
mph
cfm
n/a
n/a
3.5
116.82
4.0
177.79
3.7
148.93
n/a
n/a
5.1
165.22
5.2
202.46
5.2
205.25
7.5
86.57
7.4
228.52
7.5
281.11
7.5
296.94
10.0
115.42
9.9
269.01
9.8
314.44
10.0
475.66
11.1
128.81
10.8
307.88
11.4
357.44
11.6
419.34

A plot of volume flow rates versus the wind speed for these four vents appears in Figure 8. Once again, a linear relationship is found.

1.5 CONCLUSIONS

All Aura vents were found to provide ventilation. As expected, the larger vents provided larger volume flow rates. For example, the 8 in. Aura vent exhausted about half as much air as the 14 in Aura vent, at all wind speeds. For the two lowest wind speeds of 4.0 and 5.2 miles per hour, volume flow rates for the 6 inch commercial Aura were too small to be measurable. A ranking of the ventilation capacity at each of the nominal test speed is provided in Figures 9-13, respectively.

It should be noted that the curves of volume flow rates (X) versus the wind speed (Y) should pass through the zero or the origin of the X-Y axis as there should be no flow for zero wind speed. As seen in Figure 8 they approximately pass through the origin. The same is true for the 8 inch vent in Figure 7. However, the curve fit for the 14 inch vent in Figure 7, when extrapolated to zero wind speed shows somewhat positive ventilation for the zero wind speed. We believe it is a manifestation of the curve fit which has been made using a small number of data points. Additional test points should improve the curve fit. the data as measured (rather than extrapolated) should be considered reasonably accurate. To estimate volume flow rates at wind speeds other than those tested, one should be able to use linear extrapolation of the curves provided in figures 7 and 8. Some care should be exercised in using linear extrapolation of the data for the 14 inch vent to estimate the volume flow rates at wind speed below 4 miles per hour.

Continued (Section 2)