Hydronic Underfloor Heating System – Case Study: BHP Billiton – Wolwekrans Colliery
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Every mineral processing facility knows that a rand saved on overheads is a rand gained towards the sustainability of the facility. Traditional methods of water heating, such as electrical resistance heating, have been used for years in the South African market with great success and reliability. With the rise in energy costs in South Africa over the last few years, consumers have become more innovative in their approach to energy efficiency and renewable energy.
Fortunately for BHP Billiton Wolwekrans Colliery their management team has established those improvements on the energy efficiency of their facility is a fantastic way of reducing overall operational costs. Thus, when Genergy was given the opportunity to partner with BHP Billiton on the newly built division, we jumped at the opportunity. The opportunity allowed Genergy to design, supply, install and commission an energy efficient hot water system and hydronic underfloor heating system making use of solar thermal technology as the primary source with heat pump as a secondary source.
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The energy efficient hot water system at the 4 change houses of the facility was designed to accommodate up to 1 000 users per day over three 8 hours shifts. This equates to approximately 120 000 litres of hot water at 60°C per day. From the 120 000 litres of hot water used per day approximately 15% is used in the nearby laundry for washing and 45% used for underfloor heating. The facility consists out of four change houses next to each other. The project was implemented in 1 phase, starting off with accommodating 500 users and the remainder of the users over a duration of 5 years.
A total of 216 flat plate solar thermal collectors, each covering an area of 2m², were installed at a tilt angle of 32° to ensure optimal year round performance of the solar thermal system. The orientation of the slab was north which allowed for maximum daily solar yield. The collectors were installed in 3 banks of 6 in series and 3 in parallel on the Tichelman’s reticulation principle to ensure uniform pressure and temperature of the solar collector array. Two inline circulating pumps, controlled by a temperature differential solar controller, ensured the optimal flow rate of the fluid conduit inside the closed loop. The fluid conduit exists of a 60% water and 40% food grade glycol mixture to prevent freezing and overheating of the closed loop. Expansion tanks were used to accommodate expansion and retraction of the fluid inside the closed loop. The internal heat exchangers fixed inside the hot water storage vessel were made of a corrugated flexible metal hose to increase surface area and promote better heat transfer to the water inside the vessel.
- Four off 92kW air source heat pumps were installed as a secondary form of water heating. The four heat pumps ensure sufficient hot water recovery between usage peaks even when no solar radiation is available
- The hot water storage vessels had a combined storage capacity of 40 000 litres, each one being 10 000 litre. The vessels and all associated pipework is lagged and cladded to reduce heat losses in storage and reticulation.
- Hydronic underfloor heating is one of the most economic forms of space heating. Each change house was fitted with an underfloor heating system which is heated by a 40kW internal heat exchanger in each one of the storage vessels.
A reduction of 90-95% in the energy used for water heating is achieved, thus a reduction in operational cost of the facility.
Work load of the heat pump water heaters are reduced ensuring longer lifespan and reduced maintenance/replacement cost 90-95% reduction in carbon emissions when compared to electrical resistance heating.
A payback period of less than 5 years and an effective lifespan in excess of 10 years.
Increased value of the facility.
Effective space heating reducing space heating cost and reduces hot water consumption of the facility.