Zero Carbon House in the Shetland Isles uses Activair air source heat pump for energy-efficient heating and hot water

(10/03/2009)

The Zero Carbon House is the brainchild of product designer Michael Rea and his wife, Dot. The Zero Carbon House in the Shetland Isles chose Activair air source heat pump (ASHP) technology from Trianco to provide a cost-effective solution to energy-efficient heating and hot water.

To research ideas for the house, Michael visited companies in Scandinavia, Canada, England and Scotland looking at environmentally-friendly products and technologies. “We have tried to create a 21st century croft house that uses affordable green technologies” he said. He first saw the potential of air source heat pumps back in 1970 when he read a newspaper article about a project at the University of Salford. “A team had built an experimental house and used reconfigured refrigerators to heat water.”

The technology has been around for over 40 years but is only now being adopted more widely as a low-cost alternative energy source. The ASHP operates like a refrigerator in reverse, using a small amount of electricity to drive a fan and a quiet, low vibration compressor. From the surrounding air, it extracts large quantities of low grade, otherwise wasted, warm air and converts it using an exchanger and a fan into heat for domestic heating and hot water.

The electrical power needed is negligible so the homeowner creates a minimal negative impact on the environment. “I contacted a number of manufacturers and became an expert on air source heat pumps, as well as water-to-water and geothermal heating systems,” said Michael.

The cost of green technology is an important factor in developing the Zero Carbon House. “I thought ASHPs were too expensive until I saw Trianco’s Activair. It was a fantastic breakthrough for our project that this is such a low-cost technology.” The Activair costs from £1,000, making it more accessible to the average household keen to reduce energy bills and their carbon footprint.

“We wanted to show that anyone could consider building an eco-house – or achieve energy cost savings with retro fits. This is particularly relevant for ASHPs, which can replace gas or oil heating systems,” he said.

Trianco provided technical assistance to the Zero Carbon House to ensure the Activair’s potential was maximised. “This is not a standard installation so I came up with a design of what we wanted and Trianco’s technical specialist advised us,” said Michael.

The house features underfloor heating on the 180 square metre ground floor using hot water piped from a 5kW version of the Activair. But the Activair does much more than this, providing heat for two outside features as well.

“We had the idea to heat not just the house but also a 48 square metre hydroponic greenhouse that uses advanced light and heat technology to regular plant growth, as well as 25 square metre cold frame for growing produce,” Michael explained.

The harsh marine environment of Unst was unsuitable to locate the Activair on an external wall. Instead, it was installed in a cavity space under the ground floor, which would otherwise have been unused.

“We were amazed to discover that thanks to possible geothermal activity and the thick insulation under the floor, this under-build area has a constant air temperature of between six and 12ºC, making it ideal for an air source heat pump,” said Michael.

Water heated by the Activair is housed in a large, insulated 4,200-litre tank. Inside this, he has added a giant heating coil with its own water supply. While the Activair keeps the tank water heated to around 50-50ºC the water also warms the coil, which feeds in to the domestic hot water supply. This reduces the need to use traditional immersion heaters for hot water in the house by up to 60%, according to Michael.

The easy-to-operate controls on the Activair ensure temperatures can be carefully controlled. Heating the Zero Carbon House can even be controlled remotely using text messages or the internet.

Michael praised the Activair’s versatility. “We are in a remote location and can’t afford to have problems with our heating if we are to keep down our energy costs,” he said. “The Activair was easy to install, requires virtually no on-going maintenance and its modular construction makes it easy to replace parts if we ever need to,” he said.

The Activair is due to be fully operational in the Zero Carbon House from Spring 2009.

Related categories:  Energy saving technologies   Environmental technologies for Residential and Green homes   Ground and air source heating