Three Golden Rules for an Energy Efficient House
The number of energy saving methods and technologies currently available can be daunting when considering how to tackle the design of a new house. Understanding the basics therefore is everything otherwise the detail can become overwhelming. So, for the sake of simplicity I’ve distilled things down to just three golden rules.
Rule No. 1: Insulate
This might sound obvious, but we live in a climate where heating is the main issue when it comes to domestic energy consumption. The UK building regulations require a decent standard of insulation which we should be thankful for. Anything better than standard compliance must be considered as a plus, especially with windows.
Rule No. 2: Air tightness
This is an interesting one, as how can a healthy house be airtight? It’s a bit counter-intuitive, but when put into context with the third golden rule it starts to make sense. Airtightness is all about quality construction. Buildings have many potential weak points. Take the joints between walls and windows, penetrations for services, and junctions where roofs meet walls. And bizarrely, we are encouraged to create ‘leaks’ with rudimentary bathroom and kitchen extract fans and trickle vents in windows.
Extract fans and trickle vents are just low tech solutions to counter the build-up of moisture inside buildings, which would otherwise cause condensation. The side effect of trickle vents and extract fans is simply heat loss. We pay a lot of money for our winter heating and are then forced to throw a lot of it away. Condensation in buildings is of course not good. Cold, wet surfaces are hazardous in any indoor environment.
This is where rule no. 3 comes in and completes the holy trinity.
Rule no. 3: Heat recovery ventilation
AKA mechanically ventilated heat recovery (MVHR), this is a low tech, low energy way of keeping a highly insulated, airtight building healthy, dry and warm (or cool) at any time of year. For the uninitiated, understanding heat recovery ventilation requires further explanation.
Having worked with mechanical engineers for decades on many different building types, I’ve often struggled to get common sense explanations of how certain technologies actually work. So I continued to probe until I became comfortable with a simple explanation that actually made sense.
Heat recovery ventilation works like this.
Imagine a box or chamber divided down the centre with a membrane of thin metal foil. On one side of the foil, all the warm, moist air from the kitchen, bathrooms and utility passes through and is extracted from the building. On the other side of the foil, fresh outside air is brought into the building and distributed to living areas and bedrooms. As the fresh air passes the foil separating the two chambers, as much as 80% of the heat from the warm, stale air is transferred across the foil membrane to the fresh air. So simple, yet so efficient. All it takes is a couple of fans to keep the air moving. Of course the real thing looks nothing like this. It is much more compact and efficient but this is just an easy way to explain the principle. The average domestic MVHR unit is a bit larger than a typical boiler.
Once the three golden rules are applied it then comes down to detail. Exactly how much heat is needed? How will it be generated? How will it be distributed? This is where it can become confusing.
Theoretically, if the three golden rules are implemented, then very little energy will be needed to keep a house comfortable in the colder months.
Humans, winter sun and appliances (cookers, light fittings, fridges etc.) all create heat, and if controlled can be sufficient to create a comfortable environment and you can always throw in a wood burning stove for some cosiness.
Beyond the overriding principles there are limitless options. We now enter the world of heat pumps, geo-thermal heat exchangers, photo voltaics and solar thermal systems. Each individual project will have its own specific idiosyncrasies so some technologies will be more appropriate than others. I hope to expand on these more in future articles, but for now, embrace the three golden rules and don’t get bogged down in the detail until the time is right.
Related Articles: What Exactly is ‘Self Build’?