By Tanya Olckers
Two gas generators get installed in student accommodation in Braamfontein at the forefront of heat harvesting.

30 000 litre heat accumulator. All images supplied by SA Heatpumps
Growth Point Student Accommodation Holdings needed a solution to their heating needs. An epic seven week nose- to-the-grindstone effort was made by Ingplan Consulting Engineers, SA Heat Pump Engineers, IEE Solutions, Dreycor Plumbing and EnerGas to get the system up, running and working satisfactorily.
This system was completely built from the ground up. Two gas generators will be installed to cater for the building daily energy use. The gas generators simultaneously generate electricity and use the heat from the engine jacket water and exhaust to heat water. The power output can be controlled between 50 and 100% of nominal rating which will proportionally affect the amount of heat output to be used for hot water heating.
The maximum thermal energy generated by each unit is approximately 240kW. According to the case study provided the generators will run on average only on 56% and provide approximately 5,700kW heat energy per day. The generator heat source will provide a constant flow of 10.6m³/hr (each) water at a constant supply temperature of 90°C. The system water will circulate to a low pressure domestic hot water tank, which will be controlled at approximately 55°C to 65°C. The hot water storage tanks are installed to be used as a battery for hot water generation to the building. Domestic cold water will flow through a coil system installed as part of the hot water storage tank, exit at minimum 55°C to cater for the hot water demand. Hot water will be circulated continuously to ensure immediate hot water at each supply point.

Wilo booster pumps and hot water return pumps.
For summer, it would require approximately 3,840kW/h heat recovery to heat 60kL to water from 18°C to 60°C per day. For winter, it would require 5,640kW/h heat recovery to heat 60kL water from 10°C to 60°C per day. It is envisaged that 100% hot water heating will be catered for by the gas generators.
Energy recovery from gas turbine generators fed on Egoli Gas to generate the 60 000L of hot water storage while generating all the electrical requirements of the building. That is the primary heat source. The secondary source is a gas heater bank, and the final third source if all else fails is a pair of air to water heat pumps. The whole plant room is run from a Program Logic Controller (PLC), which is a custom computer. It has colour touch screen interfaces for the whole plant system and all parameters and controls are monitored live via an online portal. So, authorised personnel can log in from anywhere in the world with an internet connection and see what all the statuses are and if they choose, they can send commands and change settings or start and stop certain equipment.
The client, Growthpoint, wanted to maximise energy efficiency from the gas energy source. While using gas to generate the power for the building, they did not want to lose the heat generated from the process. So, effectively water cooling the gas turbines and harvesting that heat energy to indirectly heat up the domestic water tanks is precisely what happened. The system is fully automated and will select which of the two tanks needs more heating than the other and proportionally modulate the heating supply to the tank that needs it most to regenerate the two tanks most effectively and as quickly as possible. Only when both tank systems are up to temperature will the system start to dump heat to the atmosphere.

Rinnai gas water heaters.
System design and specification were done in conjunction with the mechanical engineer.
- Generators went in by specialist
- Hot water tanks and heat pumps went in
- Tanks were assembled on site
- Booster pumps and circulators went in as did interconnecting piping, with insulation
- Then came the power distribution and signal cabling with control points then being installed
There was no room for any of the contactors to deviate from their allocated routing of pipe and cable or to reposition their equipment anywhere.
This portion of the contract was done mid to end of the last quarter of the year. That’s in the middle of the silly season for the building industry so materials were becoming scarce and certain items with expensive freighting had to be expedited while all other contracts on the books are in the same close out phases for the year it was. Extremely challenging to coordinate the labour, materials, and other elements.
The challenge was in designing the control logic and coordinating that with the gas generators which have their own logic. The two systems needed to talk to each other and work together. This type of plant/technology has only been done with one other similar installation in the country. The quality of the installation (commissioning and controls) must be top notch to ensure the system works optimally. The entire financial model (initial capital expenditure and payback) for the installation of the gas generators is dependent on the energy savings obtained by the heat recovery process.
- 80mm control valves, Energas generator.
- BWH40T soft start heat pumps.
Eco-friendly solutions.The insulation used is zero ODP (Ozone Depletion Potential). The hot water tank itself is made from fibreglass consisting of 40% recycled plastics. The insulation on the tanks is 95% recycled plastic bottles and is 100% recyclable at end of life. By harvesting heat from the generators, running dedicated heating for the hot water system is avoided. That negates the electrical energy that would have been required to be generated either by coal-fed grid power or burning additional dedicated gas heaters. So, the hot water is effectively 98% free energy of the building required electricity. |
The Tech
This tech makes the system reliable and automated, and there is no need to worry about maintenance staff not paying attention, or their level of understanding of the system. If something does go wrong, IEE Solutions will know immediately, and quite possibly why, too. Action can be taken remotely. |
Owner | Growth Point |
Architect/Engineer | Danie Bruyns |
Plumbing contractor | SA Heat Pump Engineers (Pty)Ltd and IEES |
Suppliers |
Wilo |
Energas | |
Rinnai |