No Heating bills, electricity bills or water bills (and free air conditioning)?


'Extracting and rejecting energy to/from the Thames is a viable technology, made easier with an indirect heat transfer device such as an energy blade'

We are told that it is a world first – a luxury residential property that is heated and cooled from the River Thames, with hot water generated by phase-change-material, PV & batteries sufficient to operate off-grid and has no need for a mains water supply.


In case you are wondering, a combination of factors have made this unique design possible. Perhaps most importantly a clever detailed engineering and architectural design coupled with a client who is not focused on the short term, and one who has been prepared to invest in energy saving technology whilst not compromising the aesthetic design or operation and comfort of their home.


Here are the key design features:


Winter time Electricity Generation:

We all know about PV and the benefits of generating electricity in the summer months when the sun is at high altitude. Most PV systems are sized in terms of kW(p), ie KW output at the peak generating condition, normally 21st June for a south facing roof.


However for this property the PV system has been sized to provide the desired output in mid-winter. This means a larger installation is required, covering most of the roof, but this will provide a surplus energy over the rest of the year that can usefully be deployed to save energy elsewhere.


In practical terms this has meant a 12kW(p) PV installation is proposed (considerably more than most properties that have panels fitted retrospectively).


Energy Blade thermal transfer device (Nuenta Ltd)

Water Source Heat Pump, with ‘Heat Blades’:

Water source heat pump technology has been around for some years now, most commonly used in ground source heat pumps. However the same equipment can also be used to transfer heating to and from a water source – in the form of water source heat pumps.

Clearly there has to be a local water source, and one which is flowing, has predictable temperatures and can be relied upon in terms of depth and flow throughout the whole year and will be available for many years to come.


Energy Blade thermal transfer device (Nuenta Ltd)

Fortunately this property is located on the Thames, with a boat mooring at the end of the garden, ideal for fixing heat blades which are suspended into the water.


These heat blades provide a heat transfer path to either take heat from the water into the property (via underfloor heating), and vice versa. (The system is also used to heat a hot tub via a separate circuit that will be approximately 5 times as efficient as the electric immersion heaters that are normally supplied with these units, and the electricity will again be direct from the roof PV system).


The water temperature in the Thames is ideal in the summer months for providing cooling to the property. The added benefit is that the heat pump does not need to do any ‘work’, merely just circulate the water/brine around the system to indirectly cool the floors. This form of cooling is extremely low energy, but also worth noting that this will be powered by surplus PV during the summer months anyway, so zero financial and carbon cost.


Free hot water from the sun – in winter?

In low energy modern properties with good levels of insulation, the energy required to generate hot water for washing and showers can be as significant as the heating energy for the house itself.


In order to maximise the surplus PV energy (and avoiding the poor return of exporting), this property uses electricity to heat the hot water - but not via a conventional immersion heaters.



Water to Water high efficiency heat pump (Viessmann 300G)

Sunamp heat stores are a modern technology that utilise phase change material to store thermal energy directly, and then discharges this extremely quickly when required, to generate instantaneous hot water.


The benefits? Thermal energy can be created for free from the PV surplus during the daytime (when hot water may not be required) and stored extremely efficiently until it is required (say in the evening or following morning).


Furthermore, if ever there is no surplus PV, the system will automatically hold off topping up the store until either free PV energy is available again, or until off-peak electricity time periods overnight.


Mains Water, not required?

The property will benefit from almost 10000 litres of rainwater storage, which is predicted to be sufficient to serve the property without any mains top-up, throughout the year.


The system includes both particulate and UV filtration, booster pump and buffer tank and serves all showers, WC’s, WHB, external taps and provides the feed to the hot water Sunamp units.


The tank capacity is anticipated to be sufficient to last throughout periods of no rain in the summer months, resulting in ‘billed mains water to just the kitchen tap.


Is this the future of housing?

We see a shift towards more electric only properties.


Why? Electricity is a flexible form of energy that can easily be generated (PV), stored (batteries) and converted to efficient heating (heat pumps), hot water (Sunamp), cooling (heat pumps) and of course powering lighting and our electrical goods.


Furthermore as our national grid becomes more carbon efficient, the planned new building regulations will also penalise grid supplied electricity less, promoting a move away from gas heating and making a SMART electrical home the likely way forward.


If you found this article of interest and would like further information or to raise any questions please feel free to contact the author:


John Grazebrook is a Chartered Building Services Engineer and design principal at BTP consultants.

Contact: johngrazebrook@btpconsultancy.com +44(0) 7450 026850