26 October 2018 Passive House Plus Jeff Colley: Study: extreme overheating not reflected in building simulations

Dangerous overheating in buildings may not be showing up in desktop studies, new research suggests.”
“Monitored operative temperatures of up to 47.5C recorded in a highly glazed apartment building in London were not reflected in software modelling of the same building, with temperature peaks in simulated scenarios between 18C and 30C cooler, depending on which weather files were used.”

If the dynamic simulations performed with IESVE is not predicting the overheating correctly in highly glazed buildings this is a significant issue for the building science community. This could be due to errors in the shading algorithm or perhaps the modelling setup was incorrectly chosen by the end user. This is one of the dangers of using dynamic simulations in that there’s so many knobs in the modelling packages that it’s very difficult to quality check those simulations. The Passive House Planning Package (PHPP) energy modeling tool that passive house designers use is much less precise in that it doesn’t look at hourly overheating but it does look at annual overheating levels and due to the simplicity the inputs can be fully quality checked. In our experience these building level can be more accurate reliable although they are less precise as to when (hourly) the overheating occurs.

The Passive House Planning Package (PHPP) energy modeling tool is a monthly energy blance tool that only provides a % of hours over 25C warning. This has been shown to work well for buildings with even temperatures throughout the building. Typically when the building has a portion that may be prone to overheating we will run a fully dynamic simulation to look at localized overheating with Energy Plus. This is considered to be the gold standard for building performance. IESVE is condidered to be equal although the calculation engine is not open source code like Energy Plus.

“when the peak external air temperature was 27.9C, the peak operative temperature in the unshaded room was 47.5C – while a room with external aluminium venetian blinds at 45° peaked at 29C, and rooms fitted with internal venetians and screen fabric recorded peaks of 34.5C and 32C respectively. On days nine to eleven, when external temperatures peaked at between 20.1 and 21.4C, operative temperatures in the unshaded control room peaked at between 42 and 45C – indicating extreme temperatures may be reached in comparatively mild summer conditions.”
“No g-value was given by the building developer but the glazing specifier advised that the glazing alone would be adequate to control the solar gains on all façades,”

Content by Passive House Plus.


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