The energy and space-efficient centralised hot water solution designed for the multi-res complex Aroha

The elegant Art Deco apartments named Aroha in Avondale, Auckland, feature 117 stunning modern apartments encased in tall, slender towers. The three blocks are distinctly differentiated in coloured brick, and at the top of each tower, arches reflect the detail of early 20th century architecture. 

All of the services have been carefully resolved at the rear of the buildings, so that tenants can enjoy the beauty of the architecture and a clear outlook onto the suburb. It’s the fifth multi-residential project where Stiebel Eltron has partnered with Collins Plumbing in Ockham Residential project to deliver a centralised hot water plant system, providing energy-efficient hot water to all of the apartments from a centralised point on the site. 

A centralised system is ideal for multi-residential properties as it creates efficiencies in both space and power. Traditionally, multi-residential apartments would each have a hot water cylinder, which is less efficient than a hot water heat pump, and takes up a significant amount of space.

Another option that has been used in the past is individual heat pumps, but in a large-scale apartment complex like this, that is both expensive and potentially unsightly, says Stiebel Eltron Technical Manager Bhawesh Singh. 

“We decided it was far more efficient to have a centralised plant, so we designed a system with three  heat pumps outside with a total of 96 kilowatt output.  The heat pumps take the majority of the energy from the air  to produce hot water, which is then supplied to the tanks in the plant room, and distributed to the 117 apartments through a network of pipes.”

The efficiency of the system or the coefficient of performance (CoP) of the system is around three, which means it is 300% more efficient than a normal electrical hot water cylinder. This means running costs are a third of that of an electrical cylinder. 

"What it also means is you don't have to have a hot water cupboard in each apartment, which saves between half a square metre to one square metre of space per apartment.”

This is a huge amount of space to give up, particularly considering the per square metre cost of real estate in Avondale, which is around $12,000 per sqm. 

The centralised hot water plant itself only takes up around 15-20 sqm of space outside the building, and the hot water tanks take up only another 15 sqm inside the building.

The system is also compatible with solar PV, if it becomes more affordable down the track to add this as an energy source.

“In that case, the system could make even more power savings, as during the daytime when the sun is up, the heat pump can run using that energy as much as it can, and heat the water tanks for evening use.”

Bhawesh says Stiebel Eltron has monitored the power costs of the first four Ockham multi-residential apartments they provided a centralised hot water system for, and the results are incredible.

“For the measurements that we've done in the first four apartments, if we're looking at an apartment of somewhere between 50-70 sqm, with two - three people living in the apartment, we’re talking about hot water bills of  about $11-13 per month, which is insanely good.

“The cost savings are immense, and once you integrate solar PV, thepayback time of the initial system cost is much, much faster, and you run a much more efficient system.”

Stiebel Eltron worked with Collins Plumbing for the installation of the system, and trained the installers to maintain the system, which is now taken care of as part of the yearly maintenance schedule. 

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