A methodology for evaluating the ventilative cooling potential in early-stage building design

As a result of the new initiatives and regulations towards nearly zero energy buildings, designers are more frequently exploiting the cooling potential of the climate to reduce overheating and improve indoor well-being of people. At early stage of design, climate analysis is particularly useful for determining the most cost-effective passive cooling methods, such as ventilative cooling. However, besides the external climate conditions, building energy uses are characterized by occupancy pattern and needs, envelope characteristics and internal loads. Therefore, the climate analysis cannot be abstracted from building characteristics and use.
Within the IEA Annex 62 project, national experts worked on the development of a ventilative cooling potential tool, which aimed at assessing the potential of ventilative cooling by considering building envelope thermo-physical properties, internal gains and ventilation needs. The calculation methodology has been further developed within CEN/TC 156/WG21 TG on “Ventilative cooling systems - Design”. The main development regards the application of thermal balance calculation method from EN ISO 52016-1:2017 to calculate free-floating temperature, heating and cooling loads with and without ventilative cooling contribution, which considers also lumped thermal capacity.
The analysis is based on a single-zone thermal model applied to user-input climatic data on hourly basis. The tool predicts the percentage of hours when direct ventilation with minimum airflow rate required for indoor air quality or increased airflow rates can potentially ensure indoor thermal comfort.
Moreover, such methodology could provide building designers useful information about the level of ventilation rates needed to maintain acceptable indoor thermal comfort conditions.
The paper aims at presenting the new calculation methodology and at validating the calculation results on a reference room according to the guidelines reported in the ASHRAE Standard 140-2020.
In particular, the influence of using dynamic loads, adaptive thermal comfort model, building thermal mass and ventilation needs in the thermal balance calculation of the building are analysed. Despite the methodology is simplified, the overall goal is to provide engineers a tool for predicting in preliminary design phase and with a limited degree of uncertainty whether the building can exploit ventilative cooling to maintain indoor comfort conditions.