Integrated passive services installed at Shropshire naked house scheme
Prefab passive house specialists naked house Ltd recently completed the installation of a fully integrated passive house services system at their Marsh Road project in Shropshire. MVHR and solar thermal system are a standard part of the naked house system, with extra optional modules to enhance the building’s potential to save the occupants’ running costs. At Marsh Road, this included a log burner, thermal store and central logic control system.
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The Marsh Road passive house has been built using the pre-fabricated ‘naked house’ timber frame system, with electrical ducting and plumbing pipes built-in at the factory to minimise disruption of the building fabric on site, and with ventilation pipe runs designed in at the drawing board phase, and factoryprepared for ease of installation on site.
The services at Marsh Road were designed to minimise the cost of heating the house through a combination of a 1500 litre heat store, with various heat inputs, to optimise the heating cost through the year.
Six drain-back solar thermal panels feed into the heat store and these provide the majority of the heating throughout the year, the drainback system preventing any summer overheating problems with the panels.
A log burner is employed for the cold sunless winter days where the output from the six solar panels is at its lowest. A small 12kW Vaillant gas boiler acts as a backup in case there’s no sun and no logs. The entire system is controlled by a central programmed Resol controller.
“The choice of log burner is critical,” said Benjamin Nickell of naked house. “Airtightness is important and a separate air feed from outside is essential.
“The heat store is necessary to store the heat from running the log burner in the evenings only, and absorbing the 6kW output for use when required later. The log burner may only be required to run in the evening of those sunless days during the cold months of the winter. The heat store contains a 400 litre hot water cylinder inside, which keeps the family with hot water throughout the year.”
The heat stored in the thermal store is distributed through the house by means of an air/water heat exchanger from the heat store to the supply air to the house via the MVHR, and also to three towel rails from the same source.
“A heat store of this volume can keep a large passive house, like this one at 225 square metres, warm for three or four days, and with intermittent sun and log supply no additional gas should be necessary to heat the house throughout the year. Heating bills will therefore be minimal,” Nickell said. Summer overheating is controlled by automatic external solar blinds and a summer by-pass in the ventilation system.