The Village, Bramley

By Eamonn Ryan

EESCO was brought in to do the hot water system, for the seven blocks of both phases of a housing project called The Village in Bramley which is near completion. The project under review involves a 320kW heat pump, one of the largest EESCO has ever done.

Heat A commercial heat pump installed at The Village, Bramley.More people, more water, more saving EESCO (Elemental Energy) is a company whose core business is commercial heat pumps and hot and cold water reticulation. It is currently installing an indirect ‘district heating’ system at an affordable housing project called The Village in Bramley which is near completion. The biggest heat pump that it has manufactured and installed to date is a 500kW machine, while the current project under review involves a 320kW heat pump.

Andrew Lowe of EESCO says, “The Village, Bramley, is a two-year project that has been developed in two phases with Phase 1 of approximately 180 units already complete (at the time of the visit) and mostly rented out, and Phase 2 of 354 units under construction.”

EESCO’s brief was to design and supply an energy efficient hot water system to supply 534 flats housing approximately 1 350 people. The design was to include hot water storage, heating system, pressure pumps and ring main feed to each flat, primarily using the municipal water mains.

“Instead of putting in seven heat pumps and seven tanks – one for each block – we decided on a central plant which would distribute the hot water to each block via a ‘primary ring main’. The primary circuit exchanges heat with each block’s ‘secondary circuit’ via our imported ‘Alfa Laval’ double pass plate heat exchangers. The municipal water enters the BPHE (Brazed Plate Heat Exchanger) at a design pressure of four bar and incoming temperature of between 12°C and 20°C  and is instantly heated via the highly efficient ‘double pass’ unit, to the setpoint which is currently 58°C,” says Lowe.

“The primary heating circuit is a water / glycol mixture which is heated to between 65°C and 70°C by our locally manufactured heat pump via its BPHE condensing component. The primary heating liquid is stored in three  8 000ℓ steel glass flake epoxy lined low pressure storage vessels. The design pressure for the primary storage is only two bar making these tanks more economical than the standard four bar rated vessels. These storage vessels are stored on ground level, the heat pump however has been installed inside the roof plant room with a V-coil evaporator installed alongside in the open air where it achieves maximum heat absorption and has a lower noise impact.

“The reason for the ‘double pass’ type of heat exchangers is so that we can get the lowest possible return temperature from the primary loop. The lower the temperature of the water entering our heat pumps condensing unit, the more efficient the heat pump is – this is primarily due to the ‘de-superheating’ of the refrigerant when it is condensed in the heat exchanger. We can achieve water outlet temperatures 5°C to 7°C higher than the condensing temperature of the refrigerant which further increases the efficiency of the unit. The central heating plant is a more economical way of providing the entire complex with hot water. The 320kW heat pump is designed to heat 24 000ℓ of water twice a day in seven hours when the ambient temperature is down at 8°C,” says Lowe. 

The rooftop evaporator at The Village, Bramley.“The advantage of this alternative to a heat pump and tank in each block is that there is only one plant room, which uses less space and requires less maintenance. Then there are the additional benefits of less power supply needed for the entire complex and fewer main electrical cable supplies. Such a system isn’t more commonplace only because the concept isn’t better known in South Africa – this is only the second time we have done this, and as far as I know we are the only company doing this design. The circumstances of the site were ideal for it. We previously did the same concept at the Sierra Hotel in Randburg, which was of a smaller scale.

“The savings are huge, and the bigger a development the greater the savings in electricity consumption. It’s a function of more people, more water, more saving.” 

The system was designed and recommended to the developers by EESCO for the potential savings that could be achieved. The design team consisted of Lowe, who is a qualified plumber, the owner Bruce Thomas who has a background in commercial refrigeration, and Shaughn McRae who is the technical adviser. 

The expected COP for the heat pump is between 2.5 and 4.5 depending on the ambient temperature. 

One of the features of these heat pumps, primarily designed by EESCO, is that the evaporator has been separated from the condensing (heating) unit, which enables the product to be positioned more-or-less anywhere, because one of the issues with all-in-one type  heat pumps is that sometimes in a building there is nowhere to put it, because you have to reject and expel the cold air from the evaporator. 

“Separating the evaporator means it can be put anywhere – up to 50m away from the condensing unit. The design for these evaporators is also flexible – they can be either vertical or horizontal discharge, standing or hanging from the soffit. Fan motors are all fitted with speed control devices which not only help with electrical savings but also increase the lifespan of the motors. These units have also been designed with a wider fin spacing than the imports allowing us to run at lower ambient temperatures without having to defrost an iced-up coil,” 

says Lowe. 

Andrew Lowe, a qualified plumber at EESCO.“We have been experimenting with various additional energy-saving and efficiency increasing designs – one of which is the sub-cooling of the hot refrigerant using the evaporator coil – removing heat from the liquid line and transferring it to the evaporator is a win–win, increasing efficiency of the evaporator functioning and adding up to 35% capacity to the output of the heat pump. We have also replaced these air / refrigerant type evaporators with water/ refrigerant designs – this gives us the ability to install a fully self - contained unit in a basement boiler room and then have many options for harvesting heat from other sources – such as AC or refrigeration plants or solar heating systems.

“The heating component of these ‘split units’ have an exceptionally small footprint – a single unit that is 3m x 1m wide for units up to 500Kw, allowing us to find space in any building.” 

The Bramley system also requires a pressure pump set to boost the pressure of municipal water to the development, because of frequent pressure drops within the Bramley area. “The municipal water is fed into a holding tank, and then pumped out at the correct water pressure to supply both hot and cold water to the entire development. The capacity of the tanks at the moment is 12 000ℓ, but we are adding an additional 40 000ℓ outside. The 12 000ℓ is sufficient for the existing units, while the additional 40 000ℓ will provide for Phase 2 as well as reserves. This means if the municipal water supply goes down, the complex has 52 000ℓ litres to keep it going.”

The system brings a number of efficiencies to the development, says Lowe, primarily constant hot water at a considerably lower cost. 

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