8 - Hemp plaster and passive cooling techniques for retrofit: A case study

Abstract

Energy consumption in the building sector is primarily driven by the consumption of existing buildings, while new buildings, which are generally more energy efficient, have a much lower share of the total. Although presenting several challenges such as cost control and preserving the appearance of existing buildings, the energy renovation of existing buildings offers an important source of energy savings that should be carefully considered. In this study, an existing office building representative of typical office buildings in Morocco, apart from thermal insulation, was monitored and modeled using TRNSYS, a building energy performance software tool, for the purpose of studying the impact of passive cooling and eco-material use in its retrofitting on reducing the overheating issues observed during the monitoring campaign. Additionally, a validated numerical model of the building was used to extrapolate the study to a typical version of an office lacking thermal insulation and double glazing, which is more realistic in the case of Morocco, since an insignificant number of office buildings are thermally insulated there. The results showed a significant improvement of the indoor air temperature of the south-facing rooms in summer (up to 2°C) when the building was simulated in free-floating mode. If we assume there is an HVAC system, the energy demand was also reduced significantly, especially with the use of automated Venetian blinds, reaching −16% of the cooling demand in the monitored building and −19% in the typical office building. Moreover, the thermal comfort, assessed using an adaptive thermal comfort index, was also improved, since the summer discomfort hours noticeably decreased in the typical office building thanks to the passive cooling techniques. However, economically speaking, the improvements to the existing building, namely adding hemp plaster to the roof and use of passive cooling techniques, are costly and have a very long payback period, which reflects the fact that these improvements are prohibitively expensive.