Test materials

3.2.1 The turbine ventilator

In Chapter 2 it was found that turbine ventilators with longer blades and a wider turbine base

diameter perform better than their counterparts. In this study, the best performing turbine ventilator was not tested. Instead, a more common, cost-effective and locally available turbine ventilator was selected.

Tests were performed on the 300 mm Windmaster Tornado® Turbine Ventilator, shown in Figure 18. The turbine ventilator is made of galvanised steel, and weighs 6.3 kg. It is reported to have an air removing capacity of 0.41 m3/s (1,489 m3/h) at an average wind speed of 4.17 m/s (15 km/h). Specifications for the Windmaster Tornado® Turbine Ventilator are provided in Appendix A.

Figure 18: A 300mm Windmaster Tornado turbine ventilator

3.2.2 Description of the low-income house

The low-income house used in this field study, hereafter referred to as the “reference house” and shown in Figure 19, is situated on the CSIR Built Environment Innovation Site at the CSIR’s Pretoria campus. A layout of the reference house is shown Figure 20 and architectural drawings are presented in Appendix B.

The reference house has a floor area of 39.6 m2, and a volume of 110.5 m3. It has two bedrooms, a living room, kitchen and bathroom. The external walls are made of 140 mm solid cement block, and the internal walls of 90 mm solidcement block. All internal walls have a cement slurry finish. The floor is a 75 mm concrete slab with a 75 mm power-floated concrete finish. The roof is made of 0.5 mm hard galvanised roof sheeting.

Figure 19: The reference house

Figure 21: North, south, west and east elevations of the reference house

Figure 21 is an illustration of each façade of the house. Windows are located on the northern and southern facades, and doors on the southern and western facades. The windows of the reference house are not efficient in delivering the maximum available air for natural ventilation to all areas of the house. The windows of bedroom 1 and 2, and the living room and kitchen are side-hung windows which open to the outside. The window in the bathroom is a top-hung window which also opens to the outside. The openable window area on the northern façade is 1.92 m2, and 1.62 m2 on the southern façade. Openable window area is an important parameter because it is directly related to the amount of air which can enter and leave the house. Side-hung and top-hung windows greatly reduce the effective openable area of windows. The northern and southern facades are 2.5 m high. The eastern and western facades have been inclined at 11˚, and peaks at the centre at a height of 3.08 m. The prevailing winds at the test site were from the North Eastern direction. Wind roses for Pretoria are presented in Appendix C.

3.2.3 Thermal considerations of the reference house

The thermal performance of the reference house (without the presence of a turbine ventilator) was studied by Osburn (Osburn, 2010). Using Energy Plus (v 3.0.0.028) (Osburn, 2010) was able to establish the temperature profiles inside the house as a function of outside temperature, in extreme conditions. (Osburn, 2010) assumed an accommodation schedule in the reference house which accounted for heat generation (due to occupants and appliances). (Osburn, 2010) also assumed that

air exchange was due to infiltration/exfiltration. During summer months, most of the low-income houses in South Africa are not heated or cooled, and the internal temperature changed according to the outdoor temperature (Makaka, Meyer, & McPerson, 2008). Figures 22 and 23 are temperature profiles of a hot and cold day, respectively. The “well insulated house” referred to in these figures is a newly proposed low-income house developed by the CSIR Built Environment which added carpeting, a ceiling and insulation to the reference house.

Figure 22: Temperature profiles on a hot day (Osburn, 2010)

From Figures 22 and 23, the internal temperature of the reference house varied with the outside temperature. The inside temperature was always higher than the outside temperature. This was attributed to the presence of the galvanised roof sheeting. The region closest to the roof would be warmer than the lower parts of the house (Osburn, 2010). Because heat always travels from warmer to colder regions, heat will move from the roof region to lower parts of the house. In this way the inside of the house is heated. While this may be acceptable in winter, it may be uncomfortable in summer. This is evident in Figure 22, where the internal temperature was up to 12˚C higher than the outside temperature. (Osburn, 2010) recommended that windows and doors be left open to increase the air exchange rate, thereby reducing the internal temperature.

Indoor Temperatures, Dec 10

0 5 10 15 20 25 30 35 40 0.00 6.00 12.00 18.00 24.00 Time Te m pe ra tu re (C el si us )

Reference House Well Insulated House

Figure 23: Temperature profiles on a cold day (Osburn, 2010)

Air in contact with the roof would be warmer, and subsequently less dense, than air of the rest of the house. By incorporating a turbine ventilator on the roof of the house, an escape port for the warm air would be introduced. While there is no scientific literature to indicate the temperature differential needed to cause free rotation of the turbine ventilator, one manufacturer’s specification sheet (Turbovent Data Sheet, 1996) indicated that a temperature differential in the order of approximately 14˚C is needed to obtain free rotation of the turbine ventilator.

If warm air was constantly being exhausted via the turbine ventilator, and being replaced by cooler air from the outside, the internal temperature of the house would then be lowered.