Warming up the student body

By Fiona Ingham

The Witbank Student Accommodation building has been completely refurbished, and houses a gobsmacking 50 000 litres of hot water used as the heating medium and features the latest in technology with the biggest heat accumulation system on the continent.

Witbank, which is Afrikaans for ‘white ridge’, is named after a white sandstone rim where wagon drivers used to stop. It is a coal mining town on the Mpumalanga highveld, 120km from Johannesburg and 100km from Pretoria. The town is at the epicentre of Africa’s largest coalfields, power stations and steel manufacturing industries. It lies on the eastern side of the Maputo Development Corridor. In 2006, its name changed from Witbank to eMalahleni, which is a Nguni name meaning ‘place of coal’.

It is here that Tshwane University of Technology has two satellite campuses, which naturally creates demand for student housing. The Witbank Student Accommodation building, comprising Blocks A and B, was not built as student accommodation. Before the refurbishment, Block B was used for residential purposes with a retail ground floor and Block A was used as offices. The building was converted to meet the pressing demand for student housing, explains Graham Elsey of AGE Plumbing Design Technicians. “Students were queueing up for this accommodation long before the building was finished,” he says.

The Witbank Student Accommodation building comprises 926 units and was previously heated by a series of dozens of 100 litre individual geysers. This antiquated system was removed to make way for a modern centralised hot water heating system, he explains. Elsey’s company was responsible for designing the heat pump and heat accumulator systems in the basement of the building along with the infrastructure pipework.

Energy efficiency

“The brief was to supply a central hot water supply system,” says Elsey. “The advantage of putting heat pumps in a basement is that it is like a cave: the temperature is constant and this means you get a better coefficient of performance [COP]. What we’ve done is to put ducts on the exhaust side of the air exhausts to take the cold air away from the unit, so you don’t get a short circuit with the air cycle in Block B. In Block A, the air exhausts directly out of the building via the basement exhaust fans.”

No dead legs

“We made sure that there is a constant flow of hot water, and so you never get a dead leg by putting in a return system, which conserves water. What we mean by a dead leg is a volume of water that grows cold in a pipe, which usually happens when the showerhead or mixer is far from the hot water tank. Naturally, it wastes water. With this system, there is never a dead leg. This system is also more efficient as it brings the unused water back here to be reheated.

“What has resulted is a Delta T, which is the difference between the hot water going out and the hot water coming back, of less than 5°C,” he says. 

The insulation is paramount, Elsey explains. “The pipework is all insulated — if we don’t insulate it properly with an R1-rated material, then all of this other work we do is useless. An R1-rated material means that you lose less than 1°C per hour in heat.

“So, it might be an older building, but we have installed the very latest in heat pump technology.”

Elsey explains that both Blocks A and B are gravity-fed systems from roof tanks. “Even engineers think that to equal out the pressure you can drop the line from the roof to the basement and then back up again, but you can’t do this.” He says that with this design, they borrowed a clever heating trick from the UK. “What you do is that you take your hot water line up with no branches off it, lay your pipes to the highest point, bring them down, and then branch off to ensure parity of pressure.”

Block A is served by two 10 000 litre heat accumulator tanks, which have been interlinked with Block B. This was done to ensure that if one of the systems go down then students can at least access some hot water, he explains. In Block A, they did not install exhaust ducts because exhaust fans are already installed in the car parks situated above the heat pumps, and this is responsible for drawing all the cold air outside.

“In Block B, we installed three 10 000 litre heat accumulator tanks to service about 400 students. This means we have 50 000 litres in total, for heating purposes only. The heat pumps warm up the water inside the tanks. Inside the tanks are a collection of coils, and the hot water comes from the coils. The heat pump is actually the heating medium and we never use that water, as it stays circulating in that tank. Block B also houses a retail section, but it is not connected to our system.”

Challenges

Elsey said that the original engineers submitted a design that the supplier knew wouldn’t work. Their contract was cancelled and AGE was brought into the project late.

The client should enjoy a 60–70% saving in electricity costs, Elsey says. AGE has a track record of this on other buildings, according to Elsey. This new system makes for happy students who can all get into hot water, in the nicest possible way.

Table 1. Cold water demand calculations   

Type

Type

Square metres

Population

Per litre

Total

Operating hours

Storage

Retail

F 1

4 666

22

125

2 750

15

1 650

Retail

F 2

1 494

150

14

2 100

15

1 260

Student

H 2

N/A

450

135

60 750

12

29 160

Flats

H 1

N/A

900

200

180 000

12

86 400

           

Total

118 470

               

Block

Min. ℓ/day

 

*Note these do not include Fire reserves.

A

29 160

           

B

86 400

           

Retail

2 910

           
               

LIST OF PROFESSIONALS

Owner  

Southern Storm Properties

Contractor

Dale Bannatyne

Wet services

AGE Plumbing Design Technicians

Architect and principal agent  

SW Design Architects

Infrastructure pipework and hot water

Langamanzi Technology

Supplier: Heat accumulators

Integrated Energy and Environmental Solutions (IEES)

 

 

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