Sanitary hot water & underfloor heating

The Challenge

When undertaking any new build heating is a key consideration. Undertaking such a project in the sun capital of New Zealand is no exception. The Abel Tasman region is itself a winter haven, with the average winter temperature as low as -2.8°C.

When embarking on designing/building a 268m², energy efficient home the homeowners wanted to include a hot water system capable of simultaneously providing sanitary hot water and underfloor heating without compromising efficiency.

The Solution

With outdoor ambient temperatures dropping below 0°C the heat pump chosen needed to have an inverter driven compressor and a microprocessor control capable of some very clever defrosting logic.

Utilising cutting edge technology a Mitsubishi Electric Hot Water System was installed, specifically a PUHZ-RP140VHA was chosen. With a heating capacity of 16kW this unit is ideal for larger underfloor heating applications. It also allows for water temperatures between 20 to 55°C for heating.

Being a split system this installation required the use of an external heat exchanger, an Alfa Laval ACH70-50H made of 316 stainless steel brazed plate. This system allowed the flexibility to position the heat exchanger right where the hot water is required. The addition of 30mm polystyrene insulation under the concrete slab improved heating response time as well as reducing running costs.

While a PAR-W21 LCD wall mounted 7 day timer/controller was installed, a specialised PAC-IF031 Water Flow Temperature Interface was also chosen allowing maximum control.

The use of this interface allows the hot water heat pump to heat sanitary hot water by intelligently switching between the heat pump and the electrical booster element in the hot water cylinder. It also ensures that the water is kept at the ideal temperature of 60°C in the hot water cylinder to kill bacteria such as Legionella.

Additionally, sensors are able to monitor the multiple hot water applications simultaneously to ensure maximum efficiency is achieved and that all applications are suitably addressed by the single heat pump.