Air-to-Water Nordic Heat Pumps

Download Resources

• ATW Series Brochure
• ATW Series Manual

Introduced in 2015, the Nordic ATW-Series heat pump is an air source heat pump that can heat or cool water for a hydronic heating/cooling system.  Applications include in-floor heating, heating through low-temperature radiators, pre-heating domestic hot water through the use of an indirect tank with hydronic coil, and heating / cooling through hydronic air handlers.

Nordic^® ATW-Series

Being an air source heat pump, the ATW uses an outdoor fan unit (rather than the ground loop used by a geothermal heat pump) to exchange heat with the outdoor air.  Unlike most or all other air to water heat pumps on the market, the Nordic ATW is a split system with separate indoor and outdoor units rather than a single unit monoblock system.

So unlike in competing units, there is an outdoor unit containing only an air coil, fan, expansion valve, and outdoor temperature sensor.  All other components, including compressor and electronics, are contained in the indoor unit.  This has several advantages: minimal installation and service work outdoors, components are in the conditioned space for longevity, antifreeze is not required in the water loop, no electric compressor heater is required, and directly heating domestic hot water is possible (through a desuperheater circuit) since the potable water lines are indoors and will never freeze.

The heat pump will be set up to heat or cool water in a buffer tank to a user-selectable setpoint temperature; when a zone thermostat requires heat or cooling, it will receive water flow from that tank by opening a zone valve or starting a zone pump.  (Two buffer tanks, heated and chilled, may be used instead where heating and cooling demands may occur simultaneously or close together.)  Water temperature control is usually performed by a built-in routine that maintains the buffer tank temperature without external sensors.  Optionally, BACnet or an external aquastat can be used.

In additional to the main hydronic water heating/cooling functions, there is a double-wall desuperheater for pre-heating domestic hot water with ~5% of the heat pump’s capacity.  This function is only active when the heat pump is running for space heating or cooling purposes.

The ATW uses a 2-stage scroll compressor.  The outdoor air coil is e-coated for corrosion protection, and the coaxial hydronic heat exchanger is copper / steel with optional CuNi inner tube available for applications where water quality may be an issue.  The cabinet is galvanized and powder coated.  Control is overseen by the Nordic GEN2 programmable control board, which has many advanced features like laptop connectivity via the free PC App software, data logging & graphing, and real time readout from electronic temperature & pressure sensors.

Here’s the product introduction video, from 2015:

And here’s a more in-depth ATW webinar, presented to Peel Passive House Consulting in August 2022:

Additional Resources