A house as well insulated and airtight as zero carbon house has to be well ventilated. Otherwise the air would quickly become stale and there would be a risk of condensation.
Heat exchanger and fan
We have a fan and a heat exchanger called a mechanical ventilation heat recovery system (MVHR). Warm humid air is extracted from the bathrooms and kitchen and discharged outside – but it doesn’t take the heat with it. Almost all the heat from the outgoing air (over 90%) is recovered and pre-warms the air that’s coming in, which is ducted to reach every room in the house. It also filters atmospheric grime from the incoming air. Although the MVHR uses some electricity, it saves several times more energy than it uses.
When it’s warm we ventilate the house naturally by opening the windows. Every room has at least one tilt-and-turn window. We don’t open them in the winter as that would let the heat out. But in the summer, when we don’t need to keep the heat in, we throw open the windows and save energy by turning off the fan. During the spring and autumn, we can combine the natural and the mechanical ventilation by opening the windows during the day, when the air temperatures are higher, and putting the fan on at night.
There are internal shutters from the bedrooms and stairs that can be opened or closed, to give a view into the living room below, creating an effect like an Elizabethan theatre. As well as being fun and offering the flexibility of changing the feel of the spaces, they provide additional light and ventilation when open.
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