Kubili lodge – a geothermal work of art

Kubili lodge – a geothermal work of art

By Ilana Koegelenberg
The new Kubili private lodge required a seamlessly integrated, unobtrusive heating and cooling solution that wouldn’t detract from the natural environment in its surrounds — a challenge the professional team tackled head on with great success.

The Kubili site is located 30 minutes out of Hoedspruit, near the Klaserie River in the Thornybush private nature reserve, bordering on the Kruger Park. The total area of the establishment is approximately 3 000m2 and the lodge itself lays hidden away in the untouched Lowveld savanna vegetation surrounding it as the wildlife from the Kruger Park roams around freely.

The lodge can accommodate eight people in its various villas and offers a perfect tranquil, private getaway.

The scope of work included spacial heating and cooling via an underfloor heating and cooling system, heated towel rails, spacial heating and cooling through ducted hide-away fan coil units (FCUs), heating of the three swimming pools, and the domestic hot water supply. A misting system was installed in the covered outdoor area to cool in the summer.

The project was started in May 2016 and completion was in December 2017.

Client brief

The client required a system that “cannot be seen and cannot be heard”. The system needed to reduce the overall electrical load as compared with conventional systems. The client did not want multiple units due to the visibility and noise of multiple units, and the system had to be low maintenance. As such, it had to be designed to run “in the bush”. This particular “bush” also came with extremely high ambient temperatures.

The requirement was for:

  • Heating load: 175kW
  • Cooling load: 143kW.

The proposal was for a central plant that met all the demands for heating and cooling throughout the lodge. To eliminate the need for cooling towers or condensers (which would be quite visible), the suggestion was made to use ground as the energy source/dump.

The decision was then made to instead install a vertical geothermal loop field comprising 30m × 100m deep vertical ‘borehole’ loops, which would be used as the geothermal field for the plant.

Fondital 32kW condensing gas boiler. Image: Ilana KoegelenbergValsir multilayer pre-insulated pipe installed beneath the slabs. Image: Reliance Eco 
Storage tanks for backup water supply. Image: Ilana KoegelenbergConductivity test with test unit in progress. Image: Aqua Earth

System description

The system encompasses all of the lodge’s heating/cooling requirements and can be split into two sections: the central plant and the terminals.

Central plant

The heart of the plant is a heat pump-chiller, which transfers energy between the geothermal field, hot-water tanks, and cold-water tank. From these tanks, the terminals throughout the lodge are fed with hot/cold water as required to meet to the demand.

The heat pump then absorbs/rejects heat to and from the geothermal field as required, or it will transfer energy directly from the cold tank to the hot tank. The heat pump has built-in circulation pumps to meet the required duty of these primary loops.

Heat is also transferred from the hot water tank, via a coil and circulation pump, to the domestic hot water as a pre-heating device. This keeps the municipal water separate to the treated, closed-circuit of the HVAC system.

Hot or cold water is delivered to various terminals through a series of pumps. Large flows required by the FCUs are delivered with Wilo Giga variable speed pumps, and Lovato mixing group-sets supply the underfloor system and deliver water that is neither too hot in winter, nor too cold in summer. This control ensures a constant temperature of water supplied to the floors according to the design parameters.

The swimming pools are equipped with dedicated circulation pumps that supply the hot water required to heat exchangers in the pool circulation loops. Pools can be actively heated with energy from the heat pump when in heating mode or alternatively from rejected heat in cooling mode. This ensures that in cooling mode, waste rejected heat energy is rejected to the pools before the geothermal loops-field. There are also dedicated Lovato high-temperature group-sets for the heated towel rails.

The domestic hot water is critical for the lodge. There are 2 000 litres of storage with Boiler Nova high-pressure tanks. Domestic water is heated primarily with a transfer pump on the coil of the domestic tanks from the hot water buffer tank. This achieves a temperature of around 52°C.

Twelve Alpine easy flat plate collectors are installed in two arrays of six. The solar pump transfers energy from these panels to the domestic tanks and is then diverted to the hot water buffer if the tanks are on temperature. This is topped up with high-temperature water from the solar collectors. To provide for when the climatic conditions do not suit the solar, or when the water demand in the lodge is extremely high, a 32kW Fondital Itaca condensing modulating gas boiler has been installed on the top coil of the tank. This will ensure that the lodge never runs out of hot water.

Wilo inverter pumps, swimming pool heater pumps, and municipal booster pumps. Image: Ilana KoegelenbergGeothermal system layout. Image: AERSA
During a recent site visit… the project team and guests, front from left: Dennis Holden, Nino Agostinelli, and Ryan Scholtz. Back, from left: Henri van Niekerk, Ben Hefer, Albertus Lombaard, George Thomaides, Tinus Venter, Christiaan Delport, Mike Nel, Chris Elliot, and Mario de Freitis. Image: Ilana KoegelenbergHeader connection point in the control room. Image: Aqua Earth


All heating and cooling terminal units, underfloor, and domestic water are reticulated in an underground insulated trench that runs in the centre of the lodge.

The underfloor system generates most of the heat required in the spaces. Underfloor cooling provides additional comfort during scorching summer months and is carefully controlled via a hygrostat and mixing station to prevent condensation from forming on the floors if the temperature drops below dew point.

The swimming pools each have a Bowman stainless-steel shell and tube heat exchanger to provide the energy required to maintain the swimming pools at 28°C all year round, even though the pools have an overflow that acts as a ‘cooling tower’ and therefore requires a larger than usual amount of energy.

The heated towel rails, which only operate in a heating mode, are supplied with water that does not allow the temperature to burn the skin, but only heats up the towels and space to a comfortable temperature.

Equipment selection

The true beauty of the system installed at Kubili is the integration of the various services into a cohesive, sophisticated plant that runs efficiently and meets all the client’s needs. That is why it was crucial that everyone worked closely together on the design so that everything, from the domestic hot water to the FCUs, all ties in seamlessly and no energy is wasted.

An Aermec heat pump-chiller was installed in the plant room. This is a low noise; high-efficiency unit with a dual refrigerant circuit, electronic expansion valves, and onboard high-pressure circulator pumps for the heating and cooling circuits.

The domestic hot water system is backed up by a 32kW Fondital Itaca gas-fired direct boiler of the condensing, modulating type.

In terms of operating logic and controls, a fully integrated system like this can only be controlled and managed through a central controller. In this case, a PLC was custom built for the project and the controls integrated into a human media interface (HMI), which allows the client the control and visual operation of the entire system.

Valsir’s design software — Silvestro — was used to calculate the heat loads and the design piping and to incorporate this into the CAD drawings that the architects had generated for the building. Dwg-format drawings are uploaded into the software, and then various inputs are fed into the software. It then generates reports on the required heating/cooling capacity, flow rates, piping, and pressure drops.

Since the site covers a large area, and there are long pipe runs between the blocks, over 11km of Valsir Pexal multilayer pipe were used on this installation, ranging from 16mm to 63mm in diameter. Pipes from 16mm to 32mm were supplied pre-insulated and in rolls. This eliminated the need for elbows and joints on these smaller-sized pipes.

By using Valsir’s new Bravo-Press crimp fittings, available from 16mm to 75mm, it reduced the cost when compared to conventional joints, as it increased the ease and speed of installation.

“All of the suppliers were willing to go the extra mile and make a success of the project,” explains Dennis Holden of Reliance Eco, who designed the integrated geothermal HVAC system. “Since this was the first of its kind, there was a lot that needed to be designed and correctly selected for the application. Having the correct team was key, and the important factor was that each of these suppliers were part of the team that made it all come together.”

UFH pipe spaced at 200mm in one of the villa bathrooms. Image: Reliance Eco
Lovato mixing group-sets. Image: Ilana KoegelenbergThe central plant room. Image: Ilana Koegelenberg

Going geothermal

Aqua Earth in Randburg tackled the drilling for the geothermal system. A total of 30 boreholes were drilled to a depth of 100m each — meaning that a total of 3km was drilled into this site.

Once the hole was drilled, a vertical ground heat exchanger, in the form of a single U-Tube configuration, was placed in the 100m borehole. This successfully transfers between 4.4kW and 6.2kW of thermal energy in each hole as calculated from the site readings.

When it comes to pipe sizes, the loops consist of 200m × 32mm HDPE Class 16 pipe. As there are 30 loops in total, this meant that 6km of piping was installed in the system. Together with the header’s 200m, this adds up to a total of 6 200m of piping for the geothermal installation.

The fusion welding technique was used to connect HDPE pipes and HDPE pipe fittings to each other. A fusion welder is used to heat the inside of the pipe fitting and the outside of the pipe. Once the pipe and fitting reach the required temperature, the pipe is inserted into the fitting. The heated pipe and fitting fuse together before cooling down.

The pipe and fitting are joined without using any other form of material or equipment that can leak due to deteriorating material. For example, compression fittings contain rubber seals that deteriorate over time and start to leak.

All the loops were pressure-tested to four bar pressure before and after installation, to ensure the integrity of all the pipes and joints.

Only HDPE class 16 pipes are used for fusion welding due to the wall thickness that ensures a proper weld with the fitting. Thinner pipes deform when heated and inserted into the fittings.


The biggest challenge for this project was the distance to get to site — Kubili is about five and a half hours’ drive from Johannesburg.

In terms of setting up the geothermal field, the main challenge was timing. Also, because the teams were only allowed on site between 08:00 and 17:00 and not over weekends, this extended the drilling time somewhat. Still, the team managed to drill and equip at least one hole a day.

Another issue here was the fact that some of the boreholes had substantial water yields and diverting the water from the drilling area was challenging. There was also no Eskom electricity on site but luckily, this could be overcome with the use of a generator.

“There were no serious challenges, but planning was important,” explains Holden. “The project was simplified thanks to a great deal of assistance by the main construction contractor.”

List of professionals

Project manager

John Wicks

CIR Construction


Main building

CIR construction

HVAC and wet services

Reliance Eco

Geothermal drilling, testing, and installation of ground-loop system

Aqua Earth 

Product suppliers

Heat pump-chiller; FCUs, electronic thermostats, chilled water buffer tank, FCU valves, and actuators


Hot water buffer tanks, gas boiler, distribution manifolds, high temperature and mixing group-sets for all hydronic systems, three-way diversion valves, PLC control system, and HMI

Valsir Uneeq

Alpin Easy Flat plate solar collectors

Solar Energy

VS Giga variable speed pumps for FCU supply


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