Efficient heat pump project in Jewel City

Efficient heat pump project in Jewel City

By: Eamonn Ryan | All photos by Eamonn Ryan

Space and efficiency considerations and an optimised value proposition led to EESCO (Elemental Energy) winning the award for the water heating split system at a residential conversion of an existing building on Beacon Street called ‘Elevate’ in Johannesburg’s Jewel City adjacent to the CBD. Plumbcon Construction Plumbing did the remainder of the plumbing.

The EESCO design team consisted of Andrew Lowe, who is a qualified plumber, the owner Bruce Thomas who has a background in commercial refrigeration, and Shawn McRae who is the technical adviser.

“Beacon Road, which is now called ‘Elevate’, is a project that was developed by Ithemba Property Development (alone) for Divercity Urban Property Fund. The link to Jewel City is that Divercity is also the landlord/owner of Jewel City, and we think of all of these developments as part of a combined investment in improving this part of the city,” says Carel Kleynhans, Director: Ithemba Property Development.

Jewel City is a wider project which is changing the face of Johannesburg’s CBD and revitalising several city blocks that had been closed to the public for decades. This development is a mixed-use and amenity-rich affordable housing precinct. The Jewel City redevelopment initiative is a substantial investment in Joburg by Divercity, a new investment fund that is renewing and re-energising South Africa’s urban centres with unique inner-city precinct development.

The system

The brief EESCO tendered on was to ‘heat 30 000ℓ from 15°C to 55°C in six hours in winter conditions of 0°C ambient temperature’, winter being the worst-case scenario, according to Trinesh Chanka, a director at Izazi Consulting Engineers.

“The original tender was for an imported ‘all-in-one’ type heat pump that would have needed the evaporator cold air to be ducted out of the basement. We proposed our alternative locally manufactured hear pump. Our scope ended with the plant, and the plumbing company (Plumbcon) took over from there with the ring-main systems and sanitaryware,” says Thomas. The system was installed in November 2019 and the building has subsequently been populated floor by floor and wing by wing.

“This is an indirect heating system, but our system is different. There are other systems in the market which use a stainless-steel coil dropped into the inside of a square tank to heat the water. In our experience, that is an inefficient means of heat transfer. With our more modern double-pass brazed plate-heat exchanger. The efficiency is up to about 98%, because of the greater amount of contact area between the two mediums,” says Thomas.

The holding tank and pressure sets are designed to counter the risk of dips in municipal water pressure, he says. “In addition to the storage in the basement, there is storage up on the roof so the complex is not reliant on municipal water pressure but on its own system.

The hot water system itself is low pressure and unaffected by water pressure, which is why we can have more economical fibreglass tanks rather than steel pressure tanks.”

The three fibreglass tanks, 450kW heat pump and two 1 000kW heat exchangers are located in a plantroom in the basement, with a backup boiler (which has never yet been used). “The R134 A refrigerant used in our heat pumps enable us to heat water up to 80°C, which means you can use less storage (for instance, 20 000ℓ as opposed to 30 000ℓ at 60°C). “Another advantage of a plate heater exchange over a coil in a tank is that we can locate the plate closer to the delivery point, and with that higher temperature you can run smaller pipelines. Instead of a two-inch pipe running 60°C water, for example, you could have a 40mm pipe running 70°C water.”

Fresh water is pumped into the plate exchanger and once it is heated is transferred up to the two separate ring main feeds. The fresh municipal water is instantaneously heated by the primary water stored in the thermal fibre-glass storage vessels. The consulting engineers – Izazi Consulting Engineers – made the choice to split it into two systems.

As to the saving, Thomas points out that compared to the electric boiler back-up system it has, the savings are expected to be on average 65%. A minimum of 50% in winter and as much as 70% in summer.

Most systems are a combined unit which creates the problem that it cannot be located in a basement where it would recirculate cold air unless expensive ducting is provided which can also have an adverse effect on the heat pump’s performance due to back pressure on the fans. “When you have heavy tanks, as with the 30 tonnes we have here, engineers don’t want to locate them on the roof where additional load bearing costs would be incurred, but in the basement or ground level. That’s the attraction of the split system: the tanks can go in the basement with the heat pump, and the evaporators or ‘air coil’ can go wherever there is better air supply, such as the floor above or even the roof. Noise is another factor in placing the plantroom in the basement.

“The noise from the coils is a major consideration, they cannot be placed close to apartments. They must expel the cold air to the outside, and so in this project they have been located in the ground floor parking area.”

Features

The brazed plate heat exchangers (BPHE) operate by means of two separate mediums (water) exchanging heat with one another. Cold water (the secondary circuit) supplied from the building’s pressure pumps enters the heat exchanger and is instantaneously heated to 60°C. The hot water system (primary circuit) is a closed loop which never gets consumed, while the cold water after instantaneous heating goes on to be used in the residential units, or returned from the building to the system and re-heated to the required temperature by the BPHE and recirculated. The heat exchanger is a double-pass system which ensures that the return water – on the primary side is returned to the thermal storage vessels at as low a temperature as possible. The lower the entering temperature of the water for the heat pump, the more efficiently it operates.

“The three fibreglass tanks, 450kW heat pump and two 1 000kW heat exchangers are located in a plantroom in the basement, with a backup boiler (which has never yet been used).”

“The heat pump was manufactured to our specifications by SCM – a division of Metraclarck. We also use HC Heating Centre in Johannesburg, and also manufacture our own units. The software has been designed by us and the IP is ours. These commercial heat pumps are based on commercial ‘Multiplex’ refrigeration systems and have a number of safety features that other, more economical all-in-one types do not. These include:

  • Liquid Receiver – enables system to be serviced and filters changed without loss of refrigerant
  • Oil separator – ensures oil return to compressors
  • Oil management – for systems with multiple compressors; ensures all compressors oil levels are kept at optimum
  • Semi-sealed compressors – can be serviced and repaired and typically last 10-20 years
  • Variable speed drives – used on compressors and water pumps – increases overall efficiency

A web-based monitoring panel enables EESCO to keep tabs from its offices and respond timeously if anything goes wrong. This system also monitors and meters the KWH used to heat the water, the KL of hot water used and the water temperature. Historical Graphs are available and managing companies can easily access data such as cost per KL or building delivery temperatures.

“The system is as much an HVAC as a plumbing system, and compliance to standards is consequently challenging. There simply are no plumbing standards other than for domestic heat pumps. The piping, valves and electrical systems are compliant to standards with PIRB and SANS. Electrical CoCs are also a requirement. Installation of such a system consequently requires a team of plumbing, HVAC and electrical technicians, which are all inhouse at EESCO.

“The system typically requires three services a year, of which two are simply a visual inspection, cleaning of the evaporator coils and checking for refrigerant or oil leaks. The third is more detailed with among others, the liquid line driers replaced, oil condition evaluated, strainers cleaned, and electrical service. When it comes to evaporator coils, they can be custom designed for each site. There is a choice of vertical air discharge – flat bed or V-coil and horizontal discharge. In this case we designed them to fit existing louvres in the walls (to expel the cold air), and we decided to go with hanging, horizontal discharge types. We have also used different heating mediums for our evaporators – the norm is to use the typical Air-Water type evaporators – we have successfully used water-refrigerant evaporators. These ‘shell-in-tube’ type evaporators can be installed anywhere as they do not require any airflow,” says Thomas.

Water ring main system, plumbing, drainage and sanitaryware

This R9-million contract to reticulate hot and cold water from the plant room to the 404 units up to the eighth floor, as well as all the plumbing, drainage and sanitaryware, was allocated to Pretoria-based Plumbcon Construction Plumbing. Director Francois Dreyer explains that the firm was responsible for the complete plumbing installation: water piping, sewer drainage and sanitaryware installation.

With residential developments of this size, it becomes necessary to achieve almost instant hot water at the tap and so it is a good idea to install a main hot water supply pipe with a return pipe to the hot water cylinder and circulate the hot water around this pipe. All hot water piping is lagged with pipe insulation to minimise the heat loss.

“Our brief was to run the water supply in the soffit of the ground floor, rising to the units and to return the water supply back to the plant room. We also installed the sleeves and some of the waste piping system in the superstructure. The crimp piping was by Henco at the specification of the company’s internal wet services engineer – it was a design and supply plumbing project. The challenge, as with all projects, was the time frame.”

A ring main system is achieved by the installation of a circulating pump on the end of the flow line close to the hot water cylinder. The hot water is thus drawn around the ring type main and re-enters the hot water cylinder by way of the cold feed. The ring main is passed close by fittings requiring instant hot water and a pipe as short as possible is connected from the fitting to the ring main. It is this short distance that reduces the time it takes for hot water to reach the fitting. 

Supplier list:

Heat pump design:

EESCO

Heat pump manufacture:

SCM (Cape Town)

Fibreglass tanks:

Solar Heat Exchangers and IEES (Integrated Energy and Environmental Solutions)

Heat exchangers:

Alfa Laval (France) and Onda (Italy)

Compressors and Variable Speed Drives:

Danfoss (Germany)

Evaporator coils:

HC Heating Exchangers (Johannesburg) and Colcab (Cape Town), RefriComp

Plumbing company:

Plumbcon Construction Plumbing

Sanitaryware:

Italtile

Piping:

Henco (Belgium)

Construction company:

Naumann Construction (Cape Town)

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