Green Technology: Heat Recovery

ABOVE: Houses built of SIPs (structural insulated panels) are so airtight that whole-house mechanical ventilation is required. As a result, the houses are extremely well insulated and energy-efficient. Read more about this self-build.

What is it, and why do I need it?

We’re building houses that are better insulated and more airtight than ever — so why install standard ventilation that is open to the elements, such as trickle vents or airbricks? A mechanical ventilation and heat recovery unit (MVHR) extracts the stale and moist air from ‘wet’ rooms (kitchen, bathrooms) and, via ducting, puts it through a heat exchanger, usually situated in the loft. Incoming air (not the same air) from outside is then passed over this heat exchanger and fed through the ducts to living rooms. Oh, and it means no need for trickle vents or noisy extractor fans. Additionally, this type of mechanical ventilation is beneficial for those who suffer from allergies. Note that heat recovery is often an additional option for mechanical ventilation systems.

What do they cost?

Expect to pay in the region of £2-5,000 for a system of this sort. One option is to simply install the ducting at new build/renovation stage and add the kit later (indeed several suppliers provide the ducting for free).

It sounds noisy.

It isn’t. Most systems operate at between 20-30dB — the equivalent of a quiet whisper. Similar units have been installed in many homes in recent years without complaint.

What about in the summer — the last thing you want is warm outside air heated up?

Most systems feature a summer bypass that stops the system recovering heat in the summer, thanks to the use of temperature sensors within the ventilation unit.

Can you add a heating or cooling element to the systems?

Yes, by combining a heat pump (effectively an air-source heat pump) with the MVHR system. The high efficiency of these systems – such as the Neatafan HRD1 from Starkey Systems or the Genvex Combi 185 from Total Home Environment (totalhome.co.uk) – makes it an economical heating solution, particularly when combined with low-temperature underfloor heating.

A Sensible Option: An MVHR Installation

Builder Arthur Bland needed a solution to the ventilation, space heating and hot water requirement in his super-efficient Somerset homes — which are in fact twice as energy efficient as the German PassivHaus standard.

He opted for a Genvex Combi 185 from Total Home Environment — an all-in-one appliance that combines mechanical ventilation and heat recovery with a heat pump for space heating and hot water. The 185 changes the air in the properties once every two hours whilst using 95% efficient heat exchangers to recover heat – and the air-source heat pump – to further heat the homes. The system has a 185-litre integrated storage cylinder which can be upgraded to work with solar or biomass.
Total Home Environment: totalhome.co.uk, 0845 260 0123.

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More Green Technology:

• Solar PV
• Wind Turbines
• Solar Heating
• Biomass
• Water Recycling
• Heat Pumps

Further reading

• Ventilation: Your Options Explained
• Passivhaus: The Last Word in Green Building?
• How to build a no-heat home