Onderstepoort student residences, University of Pretoria
Holms and Friends: 40-kL low pressure metal vented storage system with 672m2 flat plate collector
TOTAL M2 Panels 672
Tank Storage 40 000
Year Commisioned 2003
Tank Construction Mild Steel, Vertical
High / Low- Pressure Storage Low- Pressure
Litre / m2 60
Energy Savings / Annum kWh 838,880
SHORT DESCRIPTION OF THE SYSTEM
Holms and Friends completed a solar water heating (SWH) project for the University of Pretoria (UP) – in 2012 the biggest glazed installation in Southern Africa. The company specialises in integrated energy strategies and EPC for large-scale, commercial solar water heating and photovoltaic systems. They are known for the training they present in the renewable energy and energy efficiency sector as well as education for sustainable development. The system supplies over 550 students with domestic hot water in both old existing and new residences.
CHARACTERISTIC’S OF THE SYSTEM
The 336 collectors for this system were installed on top of the campus carport and building roofs. The collectors are a whopping 672 square metres of collector surface. On the roof, 3 collectors are always connected in parallel. Two parallel strings are then connected in series, resulting in a thermal length of 12 m. One central feeder tube transports the warm water to a building especially constructed for the SWH-system, situated right next to the carport. This houses the heart of the system: Two giant 20 000 litre water storage tanks, an expansion tank, membrane expansion vessels (totalling 5400 litres) and 7 external heat exchangers amongst other.
The water heated by the solar panels is stored in the buffer tanks. Through external heat exchangers (i.e. they are not in the tank itself), a different continuous fresh-water supply is warmed and distributed to the individual residences. This results in an indirect loop system, having the advantage that the water in the large storage tanks, heated by the panels, automatically complies with health standards without major maintenance, since it will never be used for human consumption. It is merely the working fluid.
The water is distributed through pump-circulation, via 40mm diameter, heavily insulated pipes. These are mounted on steel frame structures, reaching each residence on campus. A safety measure is also in place for the period when the system is not in use – for instance over the December holidays. During that time, the whole system could get extremely hot and the water can expand – sometimes even reaching a gaseous state. Merely using open expansion vessels would result in continually having to top up the working fluid. That can lead to corrosion and contamination of the system, resulting thus in choosing membrane expansion vessels for this project instead. These and all other components are “Made in Germany” quality, directly imported or locally produced by Holms and Friends.
The project included energy efficiency & passive design on the building with the following objectives:
- Reduce the water (especially hot water) consumption,
- Reduce the energy losses on the complete system,
- Create better central control (i.e. remove the then uncontrolled horizontal electrical geysers distributed all over the buildings),
- Enlarge well insulated storage capacity to avoid peak demand electricity,
- Reduce running cost and deliver cheaper accommodation,
- Reduce the carbon footprint by using renewable energy,
- Create awareness amongst users (students), maintenance teams & management and
- Support the University of Pretoria brand.
We therefore could not just replace one energy system (electrical resistive) with a renewable (solar water heating) system. The water consumption had to be reduced. This was done by:
- Designing the building to have warmer bathrooms (avoiding heating the rooms with hot water and/or extended shower times),
- Provide an insulated hot water circulation pipe (avoiding long dead leg pipes with the associated cold water run),
- Using low flow showerheads and taps,
- Specifying timed taps (which need to be pressed again to dispense more water) and
- Creating awareness amongst end users.
The net effect was the reduction of design hot water consumption from 162 liter/person.day to 72,7 litre (i.e. a 55% reduction). It is now the most water efficient residence on the campus and 73% of SANS 10252-1 design standards.
CONTACT INFORMATION:Tel: 084 755 1524
Web: www.holmsandfriends.co.za Address: R511 ext, 26 Welgegund, 491 JQ, Hartbeespoort, 0216