University of Pretoria – Boekenhout & Olienhout student residences
Holms and Friends: 52-kL low pressure metal vented storage system with 818m2 flat plate collector
TOTAL M2 Panels 818
Tank Storage 52,000
Year Commisioned 2012
Tank Construction Mild Steel, Vertical
High / Low- Pressure Storage Vented Low Pressure
Litre / m2 80
Energy Savings / Annum kWh 655,200
SHORT DESCRIPTION OF THE SYSTEM
Holms and Friends completed a solar water heating (SWH) project for the University of Pretoria (UP) – in 2012/13.
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 650 students with domestic hot water in both refurbished residences.
CHARACTERISTIC’S OF THE SYSTEM
The 409 x 2m2 collectors for this system were installed on top of the building roofs. The collectors are a total of 818m2 gross and linked to eight systems, each feeding a central duct. 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. Each array charges its own hot water storage vessel through a solar charging station.
The solar charging stations have a collective heat exchanger capacity of just under 600kWth which load the storage vessels in layers. This is to ensure optimum charging ilo of mixing the water.
The solar loops are charged with a water-glycol solution (20%), which is protection against freezing conditions. In addition the system is designed to handle full stagnation during the sunny summer holidays, when consumption might be very little. This is done through Membrane Expansion Vessels (MEV) with a total capacity of over 3,500-litre.
There are 2 x 1,600-, 4 x 7,200- and 2 x 10,000-litre buffer tanks. These are steel vessels without any internal protective coating. As no oxygen gets into the tank, no rust can occur. The vessels are well insulated with Rockwool of between 120 – 150 mm thickness. In addition, a galvanised metal sheeting protects the insulation from outside moisture & damage.
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 20 – 40 mm diameter, heavily insulated copper pipes. These are mounted inside the service ducts at each block, supplying instantaneous hot water to all hand wash basins, sinks and showers.
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.
Students have warm water in certain sectors for the first time since the residences were constructed.
Total warm water pipe length has been reduced by over 700 meter.
Systems are running for 1 and 1.5 years respectively and the client is satisfied with the performance.
Tel: 084 755 1524
Address: R511 ext, 26 Welgegund, 491 JQ, Hartbeespoort, 0216