Cool concept

A domestic boiler that generates heat by applying the process of refrigeration backwards has been developed.

A UK firm has unveiled a domestic boiler that generates heat by applying the process of refrigeration — backwards.

The micro combined heat and power (CHP) boiler from Chester-based Energetix — operating on the Organic Rankine Cycle (ORC) concept — weighs six times less than other CHP boilers and will produce better energy savings for UK homeowners, claimed chief executive Adrian Hutchings.

Energetix plans to make its product commercially available late next year.

Most CHP boilers use gas or oil to power an engine, which drives a generator that produces electricity. The heat is then used to generate hot water for heating or washing.

These boilers work almost like a mini power station inside a home. However, whereas the primary purpose of a power station is to produce electricity, the installation of a CHP boiler is intended for the production of heat as more heat energy is produced than electricity. Therefore, a CHP boiler is determined to be efficient when there is sufficient demand for all the hot water it produces.

Hutchings said he and his team at Energetix took this into account when deciding on a design for their boiler.

’Effectively it works like a fridge running backwards,’ said Hutchings.

Practical advantages

The ORC begins when an organic liquid is pressurised by a pump and then evaporated using heat from the boiler. The pressurised vapour then passes through a scroll expander and drives the scroll. As the vapour decompresses, it turns a generator that produces electricity.

Afterwards, the low-pressure organic vapour passes through the heat exchanger to produce useable hot water. Finally, the organic vapour condenses to a liquid and then repeats the process.

Hutchings said the system has practical advantages over CHP boilers that use fuel cells or Stirling engine designs. For example, he said, ORC boilers have much simpler start-and-stop procedures. ’A stirling engine might take 20 or 30 minutes to warm up, and during that time it is using power,’ he said. ’It uses a similar amount of power when shutting down.’

He added that fuel cell systems aren’t much better. ’With a fuel cell, you can’t turn them off because you lose efficiency,’ he said.

The ORC boiler’s lightweight and low thermal mass makes it a faster responding device. ’Our module weighs about 20kg including the support frame, whereas a Stirling engine is more like 120kg,’ said Hutchings. ’We’re producing power in 30-90 seconds and it takes the same amount of time to shut down.’

Quick turn-on

While other CHP boilers give homeowners the option to feed excess electricity back to the National Grid, Hutchings said this is a waste of energy. The ORC boiler turns on and off so quickly, there is no need to run it all the time and generate excess electricity. ’I can’t see why it’s viable to have our system running at 3am trying to sell electricity back to the grid,’ he said. ’I won’t be using a kilowatt of power in my home at that time in the morning.’

Another advantage of the ORC is that it operates at lower temperatures and pressures than other CHP boilers. Therefore it can take advantage of low temperature heat sources such as solar thermal energy.

Energetix has been trialling its boiler in an empty test house outside Chester since January. From the results, Hutchings said the company has determined that a modest sized, semi-detached property could make annual savings of £150 to £200 on utility bills compared to a home with a brand-new condensing boiler. ’You would also save between a tonne and a tonne and a half of carbon dioxide,’ he claimed.

The technology behind these boilers means they won’t be cheap. Energetix could not provide any figures, but estimates a unit price of £650 for the ORC.

However, Hutchings said that with their energy savings, customers would see payback in three to five years.

Currently, the company is looking for a UK boiler manufacturers to work with. Its role will be to produce and fit the ORC module inside traditional boilers.

Hutchings said it is unlikely that the boilers will make their commercial debut in the UK. Instead, it is likely be Holland late next year. Energetix has already signed up a Dutch boiler manufacturer to work with them.