ARCHITECTURE & DESIGN
continue to add unwanted heat in the summer. The internal energy gains from the use of appliances and lighting, from electronic equipment, or from hot water storage, therefore have to be accounted for to avoid excessive internal temperature rises in summer. Most significantly of all, however, windows that provide those beneficial passive solar gains during the winter then present an overheating risk challenge during the summer months. For this reason, the Passivhaus standard places a limit on internal temperatures of 25 ˚C that should only be exceeded for a small percentage of hours in the year according to its modelling design software. To remain below this temperature cap, designers need to carefully consider shading and ventilation strategies that will combine to keep the building interior cool during heatwaves. Passivhaus buildings eschew large extents of east and west-facing glazing in favour of windows orientated to the south, where the higher mid-day sun angles allow devices such as overhangs, brise-soleils, louvres, shutters, and awnings, to be deployed to avoid excessive direct solar warming of the interiors. Windows can be designed to be left open in a secure manner overnight, perhaps with fixed external decorative guarding, which allows cooler night air to replace warmer internal air escaping via high level clerestory window or rooflights.
TRADITIONAL OR HERITAGE RETROFIT
Visually inobtrusive refurbishment materials compatible with traditional construction – EnerPHit via components
top-up loft or ceiling insulation
retrofitted eaves
ventilation & contiguous thermal insulation
new raised deck for
access/storage
night purge ventilation in summer
supply air
vapour-open insulated linings create thermal
bridge-free envelope operable
secondary double glazing or replacement triple-glazed windows
sub-floor ventilation maintained
supply air draught-free
retrofitted linings with continuous air barrier
extract air
triple-glazed PH-standard replacement windows
external wall insulation with render or cladding finish
intake air extract air
whole house mechanical ventilation with heat recovery
add insulation between & under suspended floor
add floor insulation if levels permit
exhaust air
apron insulation reduces ground slab perimeter heat losses
compact building form
draught-free construction with continuous air barrier
thermal bridge-free construction
summer shading
optimum winter solar gains
triple-glazed PH-standard fenestration
Fig 1: An illustration of Passivhaus design.
High external temperatures Passivhaus also offers some advantages over conventional accommodation where external temperatures are high during the day – for example, the interior air at 21-24 ˚C can be used to cool down the fresh but warm incoming air. During late summer evenings, when external temperatures drop lower than internal ones, a summer by-pass can be engaged so that the cooler incoming fresh air directly lowers the temperature of the interior and its structures.
Other considerations include better planning and insulation of the hot water distribution network to avoid long, hot corridors, perhaps through shorter
horizontal runs with more vertical stacks. The use of reflective facing materials can help, and, for courtyards and large flat roofs, planted green areas will absorb much of the solar impact, as well as enhancing biodiversity and the roof’s visual aspect.
Lasting retrofit to Passivhaus standards
The benefits of Passivhaus design for new buildings are unequivocal, but much of the healthcare estate in the UK is now quite old, with large amounts of post-war stock to contend with. The answer lies in refurbishment, or, more specifically, retrofit, which is the term used in the
NON-TRADITIONAL OR POST-WAR RETROFIT
Opportunity to make transformational improvements in terms of architecture and energy efficiency – EnerPHit via performance
super insulation via a continuous thermal envelope
operable windows
supply air extract air
intake air exhaust air
whole house mechanical ventilation with heat recovery
supply air
extract air
super insulation via a continuous thermal envelope
night purge ventilation in summer
load-bearing insulation provides thermal continuity
Fig. 2: Retrofitting using Passivhaus design. 50 Health Estate Journal April 2017
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