System 24 – Sunknown: lodge, training centre and office



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Sunknown: lodge, training centre and office - Hartebeespoort

Holms and Friends: 3,500-litre storage system with 41m2 vacuum tube collector

TOTAL M2 Panels 41
Tank Storage 3,500
Year Commisioned 2014
Tank Construction Stainless steel, vertical
High / Low- Pressure Storage High Pressure
Litre / m2 85.2
Energy Savings / Annum kWh 51,120




SUNKNOWN is a Bed-&-Breakfast which will eventually have 9 bedrooms (total of 15 beds) for weekday business people travelling between the North West province and Gauteng province, as well as weekend holiday travelers (including the mountain bike riders traversing the site). In addition, the building houses a multi-purpose event hall which can house 150 people (cinema layout). This hall is mainly intended for training of professionals and end-users in the build- and energy industry. In addition it houses the offices of Holms and Friends, the local energy consultancy (
The whole development is designed and constructed with sustainable principles in mind and is completely off-grid in terms of services. It demonstrates practical solutions for energy efficiency and renewable energy within the built environment. The development is on the same estate as the well-known Holm-residence, which has become a South African landmark for being the first modern house which is completely autonomous. This site is annually visited by many interested architects, engineers and developers.
Phase 1 of SUNKNOWN (500m2 floor area under floor space heating and 5 bedrooms maximum 10 beds and kitchen) was completed in October 2013, while phase 2 soon to follow thereafter. This write-up is for the system for phase 1.


 The system is designed to demonstrate different technologies and building integrated solar water and space heating. The requirements for the winter space heating are very limited; partly due to the relative mild and short winter, but mainly due to the passive design and good insulation of the building.

The under floor space heating system has a 2,500-litre buffer tank (with no pressure), which supplies the UFH manifold for both the ground floor (training centre) and the upper floor (Lodge, as well as office space). The buffer tank is loaded with a solar collector which has a true north orientation, but very high tilt angle (75°). The idea is that it is well integrated with the architectural design and that it harvests mainly the lower winter sun and very little summer sun.

The same buffer tank is used to pre-heat the water in the domestic hot water vessel. The solar collector has an area of 36.75m2 and designed as a low flow system with 15kg/m2.hour flow. The maximum temperature in this system is set at 80°C. The collector is managed by a AT UVR 61-3 differential solar controller which runs high efficiency WILO pumps. The water supplied to the UFH manifold is pre-mixed to max 45°C. This manifold has different zones in the total 500m2 floor area, which are managed by two separate temperature sensors. The individual zones can be balanced to avoid over-heating of certain rooms.

The domestic hot water vessel is somewhat over-sized, as it is important to have spare capacity. The whole site is run by solar energy and backup energy needs to be generated during the best possible sunshine hours. The 1,000-litre tank will be charged with a 4,34m2 high flow SUNDA vacuum tube collector (4 x Seido2-8 collectors). The absorber plates within these vacuum tubes can be set at any angle. Therefore the tilt angle will be 75°. These collectors double up as railing on the balconies. The flow is calculated at 25kg/m2.hour through a spiral pipe heat exchanger (calculated to be 12kWth) in the lower part of the vessel. The solar loop has a 24-litre MEV, while the storage vessel has a 200-litre MEV (allowing for stagnation temperatures at 95°C within the vessel). In addition there is a 270-litre MEV for the expansion on the storage vessel. The domestic water heating system has a 7,2kWth backup heat pump which can manage temperatures up to 65°C (at a lower CoP of 2,8). The water is supplied to the consumer through a fresh water station by LME (LME-WW26) and controlled by a controller from Technische Alternative. This supplies five (5) bathrooms, a guest bathroom and kitchen.
The complete thermal heat requirements will be covered with renewable energies through a combination of efficient design, low consumption, large storage capacity and backup with a heat pump driven by a photovoltaic array.



Tel: 084 755 1524
Address: R511 ext, 26 Welgegund, 491 JQ, Hartbeespoort, 0216





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