Northland DHB Heat Pump Diesel Boiler Replacement

Northland DHB were able to save hundreds of thousands in annual energy costs and maintenance costs along with significant reductions in carbon emissions through the replacement of diesel boilers with unique Aquanex heat pump water heater technology.

Kaitaia, Dargaville and Bay of Islands Hospitals were heated with centralised diesel fuelled boilers. Temperzone was approached by Airzone to apply newly developed heat-pump technology to replace the boilers which have high operating and maintenance costs. The hospital heating systems were set up in a primary / secondary loop configuration, with both space and domestic hot water being supplied to various parts of the building. 

The first key decision was to separate the domestic hot water from the space heating circuits.

This allows the targeting of the most appropriate heat-pump technology for the temperature range and seasonal demand of the water being heated. With the Hospitals located in Northland, the heating season is relatively short, allowing much of the system to be switched off during the winter months. This was not possible with the boiler system with heating systems combined.

The challenge was the space heating systems.

With the distribution networks having been added to over the years, it was not realistic to adopt a balanced flow distribution system, so the Temperzone R&D Department decided to trial commercial variable speed (inverter) compressor technology for this application. This approach would allow the compressor to operate at a speed to maintain a unit outlet water temperature of 55 deg C. Each heat-pump water heater contained at least two inverter compressors, allowing the compressor speeds to be maintained at the peak of the efficiency curve.

Such a system requires the heating distribution system to be converted from a fixed flow system to a variable flow system, with the building heating load controlled by the system flow rate. In practice, this is a straightforward design change, and is supported by high efficiency variable speed pumps.

The Bay of Islands Hospital was converted first, followed by the Dargaville Hospital. In early 2019 the Kaitaia Hospital upgrade was completed. The Dargaville site contains numerous separated buildings, so a distributed heat-pump water heating system approach was used, with the heat-pumps located around the site close to each area of heating demand. At Kaitaia, the buildings are more concentrated, so the heat-pumps were connected to a common flow / return manifold. 

The upgrades were funded under the EECA Crown Loans Scheme. Dargaville and Kaitaia Hospitals collectively saved over $200,000 on annual energy costs, over $100,000 on annual maintenance costs and a reduction of 794 tonnes of CO2 emissions each year. With numerous old boilers due for replacement around New Zealand, these projects have demonstrated the application and cost effectiveness of Inverter In-line heat-pump technology in commercial applications and are a key technology as we begin the transition to a low carbon future.

Temperzone has now mainstreamed these in-line inverter heat pumps under the brand Aquanex. These in-line inverter variable speed systems maintain a constant leaving water temperature under any conditions and do not require water buffer tank storage.


Dargaville Hospital MWS and MWH units


Kaitaia Hospital MWS and MWH units