CONSTRUCTION IN A DEMANDING CLIMATE
natural ground level. The 600 mm wide cavity was then filled in layers of 300 mm and tamped down from the middle to the edges. After curing for approximately seven days, the shuttering was stripped and the quality revealed. After some early teething problems, it became somewhat of a competition to see who could build the best wall.
To finish the walls, a breathable sealant was applied externally and a weak plaster mix internally. An in-situ cement window sill protects the walls beneath from water ingress, while a concrete ring beam forms a lintel over openings and carries the roof structure.
Importantly, the walls are low maintenance and require no paint. Local material was used, requiring less transport and the use of fewer kiln-fired bricks, achieving a reduction in embodied energy. The construction process was labour- intensive, and provided an opportunity for skills development. It is hoped that these newly acquired skills will be used again for other projects in the area. High-level chimneys and underfloor rock stores: Because air-conditioning consumes the greatest portion of electricity in the day-to-day operation of a clinic, it also presents the greatest opportunity for savings.
In the interest of airborne infection control, our clinic requirements were for 100% ducted fresh air, with a minimum of six air changes per hour (AC/h) in consulting rooms, and 12 AC/h in waiting areas.
In summer and winter, Beaufort West has long periods where it is necessary to temper any supply of fresh air in order to create the indoor conditions required for a comfortable and healing environment. To reduce the amount of cooling and heating energy required in this fresh air supply process, a system of roof stacks and underfloor rock stores was developed. The system works on the principle that, as air moves through a rock store, there is a transfer of heat between the air and the rocks. Heat transfer always occurs from hotter to cooler bodies, so hot air loses heat to cooler rocks, while hot rocks lose heat to cooler air. Given the large diurnal swing in outside air temperatures typical of Beaufort West, a rock store can be used to temper fresh air before it is circulated inside the building.
At the Hillside Clinic, fresh air is taken in through high-level chimneys and circulated through the underfloor bed of rocks, which tempers the air and reduces the burden on the mechanical HVAC system by reducing the temperature differential of the supply air.
Fresh air is taken in via chimneys that mimic those of the surrounding houses, and used air is expelled via another set of chimneys. The cowl design is based on an airplane wing, to create an updraft.
Sections showing high-level chimneys and underfloor rock stores.
HWC A
SOLAR PANEL
HWC A
SOLAR PANEL
CONSULT ROCK STORE
WAITING
Hybrid passive – mechanical ventilation. Air flow through chimneys, rock store,
and mechanical distribution system
Research indicated that we needed to find rocks that both had a high heat capacity, and sufficient surface area for efficient energy transfer. The optimal stone was described as round, with a diameter of 90-100 mm. Most fortuitously, the surrounding countryside is littered with rocks that match this specification perfectly.
After developing the model further, it was determined that the most economical and practical method for implementing the rock stores was to separate them into six individual local stores, each serving the area immediately adjacent to it. It was anticipated that a temperature moderating effect of +/–4˚C would be
Table 2. Measured temperatures. Location
Outdoor waiting Dec 2017 (shaded)
Jun 2018
Consulting room Dec 2017 Jun 2018
Staff room
Dec 2017 Jun 2018
Main waiting Dec 2017 Jun 2018
Green passage Dec 2017 Jun 2018
achieved, with a resultant reduction in energy consumption.
Construction of the rock stores: breeze walls were constructed inside the “basement pit”, parallel to the length of the foundation walls, and 600 mm away from them, to form a plenum on either side. These breeze walls were lined with wire mesh to further contain the rocks. After being cleaned to remove all dust and loose sediment, the rocks were closely packed between the breeze walls and covered with polystyrene insulation panels, followed by a reinforced concrete floor slab.
The air intake chimneys are directly connected to the intake plenum below
Air flow bypasses rock store CONSULT
ROCK STORE
WAITING
Date Max ˚C (time of day) Min ˚C (time of day) Range 32.3 (16:00)
19.9 (13:35) 27.3 (18:45)
20.9 (14:43 29.4 (14:24)
24.1 (16:16) –
16.5 (17:00) 28.4 (17:13)
22.1 (16:10)
16.2 (05:45) 4.6 (07:40)
26.6 (07:18) 14.9 (08:28)
22.1 (04:34) 12.6 (07:54)
–
10.8 (08:46) 21.4 (07:15)
14.8 (08:39)
16.1 15.5
4.7 6
7.3 11.5
–
5.7 7
7.3 Study conducted by CSIR May 2020 Health Estate Journal 31
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