The passive-house standard, developed for cold central-European climates, faces a characteristic failure mode in subtropical regions: highly insulated, airtight envelopes can overheat severely in summer. A full-year monitoring study of the first passive house in Cyprus (Tseri, Nicosia) documented exactly this — the building met its design energy targets on paper yet failed the EN 15251 adaptive-comfort overheating criteria during heat spells, with individual remedies (night ventilation, increased cooling-plant capacity, low-emissivity coatings) each addressing only part of the problem. The open problem is to determine which combination of design and operational measures reliably prevents heat-spell overheating and secures comfort-criterion compliance while preserving the passive-house energy concept, with results shown to generalize beyond the single monitored Cyprus case.

Background

A passive house (PH) is a performance-based building-energy standard that achieves very low space-heating demand (typically ≤15\leq 15 kWh/(m2^2a)) through superinsulation, a highly airtight envelope (air-change rate at 50 Pa, n50≤0.6n_{50} \leq 0.6 per hour), high-performance windows, and mechanical ventilation with heat recovery (MVHR), which preheats incoming air using exhaust air and minimizes ventilation losses. Design compliance is verified with the Passive House Planning Package (PHPP), a spreadsheet-based design tool developed by the Passive House Institute; PHPP also sets a cooling-demand limit and a comfort-based overheating criterion (the indoor temperature may exceed 25 °C for at most 10% of occupied hours). The standard was developed for cold climates, and its transfer to warm regions raises a distinct problem: the dominant thermal challenge becomes excluding heat — solar and internal gains — rather than retaining it, while the same insulation and airtightness that save heating energy in winter can trap heat in summer. Summer comfort is judged against adaptive-comfort standards such as EN 15251 (superseded by EN 16798-1), whose overheating criteria for buildings without mechanical cooling limit (1) hours in which the operative temperature exceeds the upper comfort limit by 1 °C or more to at most 3% of occupied hours, (2) the daily weighted severity of exceedance, and (3) any excursion more than 3 °C above the comfort maximum. Fokaides, Christoforou, Ilic, and Papadopoulos (2016) reported the first full-year monitoring of a certified passive house in Cyprus: the PHPP design met the heating and airtightness targets and its annual cooling requirement stayed within the 15 kWh/(m2^2a) limit, but the calculated peak cooling load already exceeded the PH limit, and the monitored building failed the EN 15251 criteria in summer (in August 2015, indoor temperature exceeded 28 °C in 56% of hours in the living room, and weighted-exceedance days and 3 °C excursions occurred in all monitored zones). Simulation tests of single remedies showed night cross-ventilation (windows 50% open, 19:00–07:00) lowered the simulated bedroom operative temperature (the effective temperature combining air temperature and the radiant effect of surrounding surfaces) by only about 1.4 °C (predicted percentage dissatisfied, PPD — an index of thermal dissatisfaction — falling from 35% to 16%), increasing the HVAC cooling-plant capacity significantly improved the zone's simulated thermal performance, and a low-emissivity (low thermal-emittance) exterior coating changed simulated temperatures by a negligible 0.03 °C. The study thus left open how its single-building, single-climate findings generalize, and what combination of measures would actually work.

Problem Statement

For passive houses in subtropical (hot-summer, Mediterranean-type) climates, determine which combination of design and operational measures — envelope and glazing configuration, solar shading, night-ventilation and ventilation-control strategies, cooling-plant sizing, surface and material properties, and occupant-operational adaptation — reliably prevents summertime overheating and secures compliance with the EN 15251 adaptive-comfort overheating criteria (in their successor standard EN 16798-1) — assessed over the full cooling season, including the hottest episodes of the year, on the building-without-mechanical-cooling configuration for which those adaptive criteria apply, and therefore excluding active mechanical cooling from that compliance assessment, with any cooling-plant sizing in the combination instead accounted for against the passive-house cooling-demand limit — while preserving the passive-house concept and its low-energy heating and cooling demand limits. The question includes establishing how far single-building findings such as the Cyprus monitoring results generalize to passive houses in other subtropical settings, with the combination required to satisfy those adaptive-comfort criteria at least for the monitored Cyprus case and the generalization claim required to state explicitly the further subtropical settings and building or ventilation modes it is shown to extend to and those it is not, by whatever evidence the answer can defend.

References

  1. Paris A. Fokaides, Elias Christoforou, Milos Ilic, Agis Papadopoulos, "Performance of a Passive House under subtropical climatic conditions", Energy and Buildings 133 (2016) 14–31. DOI: 10.1016/j.enbuild.2016.09.060, https://doi.org/10.1016/j.enbuild.2016.09.060
  2. Ensiyeh Farrokhirad, Yun Gao, Adrian Pitts, Guo Chen, "A Systematic Review on the Risk of Overheating in Passive Houses", Buildings 14 (8) (2024) 2501. DOI: 10.3390/buildings14082501, https://doi.org/10.3390/buildings14082501
  3. Jürgen Schnieders, Tim Delhey Eian, Marco Filippi, Javier Florez, Berthold Kaufmann, Stefanos Pallantzas, Monte Paulsen, Elena Reyes, Micheel Wassouf, Shih-Chieh Yeh, "Design and realisation of the Passive House concept in different climate zones", Energy Efficiency 13 (8) (2020) 1561–1604 (published online 2019). DOI: 10.1007/s12053-019-09819-6, https://doi.org/10.1007/s12053-019-09819-6
  4. Kyriakos S. Xystouris, Paris A. Fokaides, Panagiota Antoniadou, Agis M. Papadopoulos, "Indoor thermal comfort conditions in summer under subtropical climate conditions", International Journal of Sustainable Energy 39 (4) (2020) 396–411 (published online 2019). DOI: 10.1080/14786451.2019.1701472, https://doi.org/10.1080/14786451.2019.1701472
  5. Mohamed Mahgoub, Tarig Ali, Mohamed Yehia Abouleish, Rabin Chakrabortty, Mansour Almazroui, Gowhar Meraj, "Passive house indicators in a hot desert coastal climate: PHPP v9 assessment of a Red Sea villa in Saudi Arabia", Theoretical and Applied Climatology 157 (2026), article 593. DOI: 10.1007/s00704-026-06509-z, https://doi.org/10.1007/s00704-026-06509-z