The Bottom ‘Brine’

TV presenter and architectural designer Charlie Luxton has moved onto first fix now that his self-build is weathertight. Here, he explains how his mechanical ventilation system was installed — and how brine will help improve its efficiency!

It’s an exciting time as we now have a watertight building — the windows are in and the roof is pretty much on. No rooflights yet, but we’ve covered those openings over with insulation temporarily, so that we could move inside and start first fix plumbing, electrics and installing the mechanical ventilation with heat recovery (MVHR) system.

MVHR works by extracting warm, moist air from the kitchen, bathrooms and utility room, putting it through a heat exchanger to pre-heat filtered fresh air that is then introduced into the rooms.

So you are stripping the heat in the building to pre-heat fresh air as you ventilate it. It’s a really good system — and this one actually does a bit more than that… we’ll come to that later.

We’re using a semi-rigid ducting system — red oval plastic ducts that we’ve snaked around the house. They run in a continuous length from the various outlets and back to the main distribution box and into the MVHR unit, which means there is very little opportunity for air leakage. It also means it’s quite quiet as there are no junctions between flows of air.

We designed the building with a suspended ceiling, so that all of our services can be hidden. And the ability to install the MVHR – which has a whole host of ducting – and keep it hidden is the main reason we chose the suspended ceiling.

All of the various ducts wind their way through the building into the utility/ plant room. The ducts run back into large plenum boxes which are then routed off the Airflow MVHR unit. We’re using an Airflow system partly because the company makes this flexible duct system which I’m a big fan of, and partly because it’s a very high performance, Passivhaus-certified unit. It also has a CO2 monitor, so if it detects high levels of CO2, which can be a sign the house contains stale air, it will gently lift the level of ventilation.

The real jewel in the crown of this system, however, is the brine-to-air energy collector.

We put 100m of pipework underground in the garden which we pump brine round — this absorbs the heat from the ground. This is typically around 13°C yearround. As air comes into the building, it passes through the heat exchanger where the ground-heated brine

pre-heats the air (in winter) before it hits the MVHR system. This means you lose less energy when you’re shipping the stale air out of the house.

But it also has a role to play during the summer — the brine can actually help to cool the air that comes into the building.

It will use the bank of ground outside the house as a heat buffer — stopping very high and very low temperatures and evening out the

air temperature coming into the building at those extreme times to make the unit more efficient. It’s a pretty lowtech piece of kit really. It’s not using a refrigerant heat exchanger, it’s literally just pumping brine through the ground, but I think it’s pretty smart — and it is, in fact, the main reason why we’ve specified this system.