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101 Collins St, Melbourne

Heat pump installation to supply domestic hot water by Thermal Energy Solutions and Energy Smart Water

Picture of a tall commercial building.
Image: 101 Collins St

A prominent fifty-storey office skyscraper in Melbourne’s central business district required the replacement of one of its existing gas hot water plants. The plant in question supplied domestic hot water to 23 levels. The project involved the conversion of domestic hot water generation from the original building calorifiers (which were connected to the buildings natural gas-fired heating hot water plant) to a system featuring highly efficient commercial heat pumps, thermal storage calorifier tanks and solar PV collectors to provide off-grid

direct current (DC) electrical energy production as the primary form of heat generation.

Separating the domestic hot water system from the central heating hot water plant enables the gas fired heating hot water plant to be able to shut down during summer periods to further reduce gas consumption, pumping energy consumption, plant operating costs and associated plant maintenance.

Three installed heat pump units.
The heat pump units. Image: Energy Smart Water

A.G. Coombs Advisory was commissioned by the building management at 101 Collins St to prepare a design-and-construct tender package and provide technical and installation administration services for a retrofit solution for conversion of the high-rise DHW plant. Thermal Energy Solutions provided technical input to the tender concept and were subsequently successful in being awarded the project to design and supply Enermax tanks, heat pumps and solar PV elements and controls.

This project was awarded the 2022 National Energy Efficiency Award for Integrated Clean Energy. This award recognises projects that have demonstrated excellence in integrating high levels of energy productivity and renewable energy considering aspects of performance, leadership and innovation. The project was also selected as a finalist for a 2022 AIRAH Award in the Innovative Use of Renewable Energy in HVAC&R.

System requirements:

• Reliable and uninterrupted hot water delivery over 23 levels

• Use electric heat pumps to efficiently heat water without gas

• Use solar PV system to maintain water temperature (when solar is available)

• Be separated from the existing heating hot water plant

• Inclusion of a business management system (BMS) interface to the heat pumps and solar PV

• Meet minimum first-hour hot water demand of 1060 L to supply 132 hand washing basins, 22 service sinks and pipework heat loss.

The original domestic hot water plant comprised of an ageing 7000 L calorifier heated by the building’s heating hot water plant which operated at 70% efficiency. By separating the domestic hot water plant from the heating hot water system, the heating hot water system can be completely shut down during the summer months.

Image of four commercial thermal storage tanks.
The highly insulated thermal storage tank reduces energy waste from heat loss. Image: Energy Smart Water

The new Enermax system is designed to reduce the building’s carbon footprint and energy costs while ensuring the reliable delivery of hygienic hot water. Further, the plant boasts a smaller footprint and improved durability. It was essential to the clients that the system replacement be conducted at low cost and with minimal disruption to the buildings hot water supply.

Solar panels installed on a tall building with Melbourne CBD in the background.
Part of the 8 kW solar PV array on the 101 Collins St building. Image: A. G. Coombs Advisory.

A high efficiency heat pump solution reliably delivers primary domestic hot water requirements in addition to an existing solar PV system connected to the building’s electrical supply. A dedicated 8 kW solar PV system was installed to provide primary energy for heating the four 500 L Enermax storage tanks via electric immersion heating elements. The system is designed to integrate fully into the building’s existing systems and was delivered to site as a ‘plug-and play’ package ready to be plumbed and commissioned by the commercial plumbers for the facility, Regional Plumbing.

New system components

The ENERMAX solution consisted of: • 4 x Enermax 500 L SMARTcube Tanks

- Heat exchanger tank

- Dual stainless-steel coils providing DHW heat transfer and required deliverable flow rates.

- Highly insulated thermal storage tank (1.4 kWh-th/day heat loss)

• 3 x Enermax 19 kW high temperature commercial heat pumps

- External

- COP = 3.58 at 20° C ambient and 60% RH

• 4 x my-PV 2 kW SC20 immersion elements

- Powered by DC energy from dedicated PV panels without the need of inverters

- The heat pumps and solar PV elements are interfaced with the BMS to monitor and measure the system’s operation and performance.

An engineering line drawing of a solar PV and heat pump water heating system.
The system design drawing. Image: Energy Smart Water.

System performance


During a 25-day test period following final commissioning, the solar PV system had generated 3.78 GJ (1050 kWh) of solar energy. The heat pumps had delivered an estimated thermal output of 17.01 GJ (4725 kWh-th) for a total thermal output of 20.79 GJ (5775 kWh-th) while only consuming 5.67 GJ (1575 kWh).

The previous plant, with convention natural gas-fired heating hot water boilers operating at 70% thermal efficiency, would consume approximately 29.7 GJ of gas to meet the same hot water demand.

During this period the new plant reduced energy consumption by 80.91% at the plant level, with a similar reduction in associated greenhouse gas emissions. The heat pump systems offered significantly improved energy efficiency, providing up to 358% of the energy consumed compared to 80% for most gas systems. The solar PV heating further reduced energy consumption and combined with high temperature, fit-for-purpose commercial heat pumps has removed natural gas as an energy source for water heating purposes at this site.

This innovative project in a high-profile existing building showcases a scalable and practical technology solution using available technology to degasify to remove Scope 1 emissions in existing buildings while improving energy efficiency.

Service delivery

Consistently delivering up to 1257 L at 65 °C in the first hour with a recovery rate of 893 L/hour.


The total footprint is less than the original system. Heat pumps are in a previously unused outdoor area with only the tanks located in the plantroom.


The Enermax SMARTcube allows for hygienic hot water delivery. Water intended for consumption is never stored in the tank, as it flows through the tank’s stainless-steel coils it draws heat from the surrounding hot water. This avoids the build-up of sediment and residue.


The modular system was prefabricated then disassembled and brought on site without the need for external cranes or lifts. It was reassembled and installed on site with minimal disruption to the building’s domestic hot water supply.


Piping between the tanks and heat pumps is unpressurised, which reduces wear and tear for improved durability and less ongoing maintenance. The solar PV boosting reduces heat pump operation, further improving durability.


• This Enermax solution led to a significant reduction in energy consumption and removed natural gas as the building's DHW supply energy source.

• Heat pump hot water systems improve energy efficiency three-fold.

• Heating from dedicated solar PV as the primary energy source can further significantly reduce energy consumption on days with high solar gain.

• Heat pumps and solar heating elements provide valuable and actionable data to facility managers through BMS integration.

• Heated water is reliably and consistently delivered over 23 levels from a centralised fit-for-purpose commercial system.

• Installation occurred with minimal disruption to water supply with a reduced plant room footprint.

• The unique Enermax system design delivers improved long-term durability and lower maintenance costs via combination of heat pump technology and direct solar PV energy contribution.

Client/owner: 101 Collins Street Management

Client's advisor: A.G. Coombs Advisory

Designer: Thermal Energy Solutions (TES)

Supplier: ENERMAX by Energy Smart Water (ESW)

Installer: Regional Plumbing


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