Summer free cooling ventilation potential of rock bed heat storage

In many mild climates, during most part of summer, night-time temperatures are much lower than comfort temperatures. That is the case of most parts of Italy, where monthly mean temperatures in July and August are lower than 28°C. Nonetheless, daytime temperatures are higher, thus air-conditioning is widely used even in buildings with low inner gains, like dwellings. It is obvious that it would be possible to have free cooling by storing night-time "cold" in order to provide it during daytime. On the other hand, as dwellings are usually occupied during nights, indoor temperature cannot be lowered as much as possible, without limiting comfort. So, rock-bed heat storage will let time shifting of temperature peak. Yet, even though it is not brand new, no design procedure is readily available. Moreover, the heat storage is very bulky so its integration in the architecture is a barrier. Rock-bed heat storage is numerically simulated in order to figure out its actual behaviour and the relevance of geometrical parameters on its effectiveness. A Schumann two-phase model is used to simulate a free-cooling ventilation system with rock-bed heat storage for a new building, to be built in Pesaro, Italy. Results show that for time shifting of temperature peak, heat storage volume is relevant rather than its length. This makes it possible to realize low energy demand ventilation systems by reducing pressure drop through the heat storage. Besides, when optimizing system use, its length becomes relevant again.