Building a comfortable low-energy home is all about the fabric right? Everybody says that a ‘fabric first’ approach is what you need. Get that right and you’re sorted … or are you?
Getting the fabric right is undoubtedly a critical element of building a comfortable and efficient home … if you get that wrong, then it’s simply not going to work. However, once you’ve got the fabric – the thermal envelope – to the right standard, you need to think about the heating, hot water and ventilation systems and how you’re going to control them.
If you don’t get these elements designed carefully to match your carefully crafted low-energy envelope then you can quickly run into problems.
All too often, the services that are installed are left to the end, sometimes even without designing them and using the rules of thumb provided by the manufacturer..
So what are the common pitfalls?
Traditionally, M&E services in residential homes were designed by the installer using rules of thumb provided by the manufacturer of the relevant product and “doing what they’ve always done” and adding a bit of capacity, “just to be safe.” This doesn’t always provide the desired result.
Often, the heating system is over-specified. Not obviously a problem at first glance, but when matched with a very low heat demand and a standard control mechanism, this can result in temperature overshoot (too hot, too quickly) and the boiler (or other heat source) struggling to produce such low volumes of hot water whilst still operating efficiently. The net result is a higher capital cost than is necessary, an uncomfortable environment and higher heating bills. It needs some careful thought to decide on the right heating source (boiler, heat pump, biomass …) and match it to the right sort of heat emitter (radiators, underfloor, hot air …).
Ventilation is another area which is often overlooked, particularly in homes that aren’t designed to a low energy standard. We know that indoor air quality has a significant influence on the comfort and health of its occupants. Passivhaus (used here as the highest standards for comfort and energy efficiency) recommends providing 30m3 of fresh air per person every hour in order to deal with humidity and CO2 build up. Putting in a few extractor fans in the bathrooms and relying on the occupant to open the odd window simply isn’t going to achieve anywhere near this most of the time – so the lack of a ventilation strategy is effectively leaving the control of your indoor air quality to chance.
If you’re going to the expense of a major renovation or a new-build then a more robust ventilation strategy such as centralised extract, positive input or whole house ventilation with heat recovery is needed. Badly performing ventilation can be worse than none at all – noisy vents and incorrect flow rates are typical of poor ventilation designs, so having opted for proper ventilation, it’s vital to get it designed properly as well.
Control systems not only need to reflect the building’s characteristics, but need to suit the occupants. There are clever systems out there which use room and weather compensation to ensure a comfortable temperature output which need to be designed-in early as part of your whole house heating, hot water and ventilation design. You’ll probably want all this controlled from your smartphone – again, it’s all possible, but needs to be thought about as part of the overall design. All too often, the control systems for the various elements are not compatible with a low-energy building or with each other.
Finally, someone needs to be responsible for ensuring that all of these heating, hot water and ventilation (and electrical) systems work well together. We’ve seen many examples of different parties, handling each different elements, which in itself is no bad thing, but where there’s no-one in charge of co-ordinating the designs, it can lead to disastrous results.
Come visit us at the Home Building and Renovating Show at ExCeL London on 23-25 September and find out how we have incorporated better services design and installation into Enhabit’s offerings. We’ll have some design examples and a working sample Passivhaus certified Zehnder MVHR there.