Less is more

Mike Hillard says industry and government are addressing the energy problem the wrong way round: “They continue to work on the principle: ‘this is how much energy we need and this is where we’re going to get it from.’ That’s totally ridiculous. The most economic and sensible course of action is to minimise the amount of energy we need in the first place. If we halved the amount we need now, even if we have the same mix of sources, we would halve the CO₂ emissions.”

It’s a simple point, and to prove it, Hillard is building his own house, which he boldly claims is the most energy efficient house in the world. In the picturesque setting of the Cotswolds the aptly named ‘Tranquility’ is taking shape. The difference between this eco-home and the other projects that have been built in the UK is that this still looks like a normal, conventional house. There are no external iconic features that scream ‘green’. Hillard’s project does its talking on the inside.

Tranquility is a 460 m², three-storey house, its facade a natural stone cladding in keeping with the region’s traditional style. “The bulk of the thickness of the walls is because it is built of natural stone,” says Hillard. “We could have built the same thermal efficiency through the walls if they had been 200 mm thinner, but we need to impress the world at large and we need people to say that if they could live with low energy in a house like this, they would choose to do it, because they wouldn’t be sacrificing anything.” Both the walls and the double glazed windows have a U-value of 1·1 W/m²K and, Hillard says, the heat loss through the floor is “as close to zero as you can get.”

The founding principle of the project is to is to minimise energy demand for a house, but without adding any energy generating equipment such as wind turbines. As Hillard explains: “If I produce x-amount of electricity and don’t use it, that will go onto the grid and will be used. The most important thing is to get domestic units down to almost no energy.”

The house is arranged in an L-shape with a 9 m x 9 m x 6 m high glass panelled ‘solar room’ nestled in between the two wings. This will act as the house’s main energy collector. The ground floor comprises living area, dining room, kitchen, office, cloakroom and sauna, which will be completely powered by heat from the solar room. On the first floor are four bedrooms, two with en-suite bathroom facilities and main bathroom.

The second floor loft space provides room for a relaxation area as well as Hillard’s writing office – he is currently working on a book on the survival of the planet.

The house is almost totally reliant on captured solar energy and rainwater and is designed to use the absolute minimum amount of power to operate its ventilation systems, heat exchange, water and energy storage. Hillard designed the building management system and approached Honeywell who have turned his design into reality. The system monitors 44 sensors inside and outside the house every 10 s. The system is hooked up to a pc on which Hillard is able to monitor temperatures, CO₂, CO, methane particulates, incoming solar radiation and relative humidity.

“One of the revolutionary ways the house works is that it’s hermetically sealed,” he says. “The computer manages the environment in the house and measures the air quality constantly. All the rooms have air circulating through them as and when they need to, but only when they need to.”

Pre-heated fresh air is taken from the solar room when available and distributed through the house, arriving in the main living spaces. Warm air is removed from bathrooms, cloakrooms, kitchen and sauna from where it is expelled through heat exchangers that can further heat the incoming air.

Underfloor heating is used throughout, but eight different specifications will be used and monitored to discover which one performs best. Hillard says: “We’ll measure the output from them at a later date and determine which was the most efficient way of doing it. A conventional underfloor heating system in a house puts out between 60 W/m² to 100 W/m², I think I’ve got that down to about 12 W/m².”

The same approach is taken in the solar room. Each of the four glass panels is a different specification which will be tested over time to find the best.

The solar room is the primary source of air for the house. It will be home to a large biomass consisting of a variety of fruit and plant life. Hillard estimates that the room’s temperature will be between 14°C and 20°C above the outside temperature. “In winter when the house is closed up, if the ventilation system decides it wants to change the air in the house, the air in the solar room is already pre heated, so instead of drawing the air from outside, the air being taken into the house is already warmer. As long as the temperature in the solar room is at 18°C, then the air going into the house is already at room temperature. The heat requirement in this house is so low that every time you cook, boil a kettle, put the tv on – we all emit heat, and we all put out 110 W anyway – you’re heating the space.” The fact that the room is growing this biomass also means the air is being heavily oxygenated, providing the house with unusually oxygen rich air. “The plants also act as bio filters so they’re going to be cleaning the air as well,” he says.

Also located in the solar room – to be hidden by soil and rocks on completion, is a 16000 litre water tank that stores all rainwater collected from the roof. The water comes through a pipe from the glass roof, 90% going into the tank and the other 10% being used to irrigate the plants.

There is also a 7000 litre tank, situated under the ground floor reception hall and close to the solar room which will supply the heat for the underfloor heating system and will also irrigate the plants in the summer when rainwater is less abundant. “We put it there for two reasons,” says Hillard.” One: it will output approximately 1 kW of heat energy passively, so once you’ve heated the water in there, you don’t need to run the pumps to get a kilowatt out of it and it will heat the floor and the surrounding walls. Two: this is potentially and psychologically the coldest part of the house because it connects to the solar room, which could in theory get cold.”

Hillard estimates the cost of filtering the rainwater will come to around £11 per year. “We have a 450 litre tank in the loft controlled by the computer. It tells the computer when it is running and when it is full, so every time it runs low, the computer turns the filter on and when the filter is up to temperature, the computer turns on the pump. That will run for about 14 minutes a day for the whole day’s supply of water.”

The building management system will measure exactly how much water is used in the house and it will also minimise the amount used, especially in the flushing of toilets, as Hillard explains: “All the toilets are dual flush, so for example: one will be 6:3 – six litres for a full flush, three litres for a small flush, but by monitoring it we will discover if we can flush them with less and they will be set to the exact amount.”

Hillard is confident enough about the performance of the house to claim that he has designed the most energy efficient home in the world.

“I doubt anyone can beat it for energy demand. This house has got 13 meters going into it, so we’ll be recording anything of any consequence. Those meters will be read every pulse. In the case of electricity, they will be measured every one thousandth of a kilowatt. We will time and date the use of that unit and know where it came from so we will know exactly how much energy this house is going to use, not just on heating, but on heating its water, cooking, lighting, how it handles its water, everything that’s material. We’re hoping we’re going to use less than £50 a year to heat it.”

It’s refreshing to hear a building designer put his money where is mouth is when it comes to energy targets, and you can’t help hoping that this building meets them.