The article describes the results of an experimental campaign carried out at ITC-CNR in outdoor test cells to evaluate the energy performance and the related comfort level achieved through a coupled system made up of a dynamic window and a heat recovery unit.
The test was carried out on two calibrated test cells with the same geometric, constructive and thermo-physical characteristics. They were appropriately monitored, throughout the year 2013. In the reference cell, called C2, a traditional window with double glazing, aluminium frame and indoor blind was installed, while the air circulation was provided by a centrifugal extractor. In the second one, called C3, a dynamic window with integrated blind was installed and the air circulation was provided by a heat exchanger. The air conditioning systems consist of electric heaters in winter and heat pumps in summer.
The different operating configurations allowed the trends of the dynamic system to be assessed in two different phases: analysis of seasonal energy behaviour and analysis of the thermal comfort conditions.
The first phase consisted in the assessment of the energy consumption of the two test cells using the co-heating methodology. The results showed an overall lower consumption of C3 compared to C2, both in winter and in summer, with 20% and 15% peak energy savings, respectively. The results were also confirmed by the analysis of Energy Signature.
During the second phase, the psychrometric analysis was introduced to better understand the complex heat fluxes management actions carried out by the dynamic window-heat recovery integrated system: action of heat recovery unit; dual action to reduce heat transfer in the dynamic window; air pre-heating action by the dynamic window, before entering in the exchanger.
The transformed patterns confirmed the positive synergy during the winter season (maximum yield equal to 1.9), while, for the summer season, they provided a clear interpretation of the better operation of the system only with the heat recovery unit turned on (average yield minimum of 0.7).
The analysis of the PMV and PPD indices showed that, when the maximum solar radiation is less than 600 W/m2, the C3 recorded a slightly higher PPD. With average external temperatures equal to about 20 °C and maximum solar radiation of approximately 900 W/m2, the values of PPD and PMV of the two cells were equivalent. When the dynamic glass was turned off and only the recovery unit worked, the C3 provided the best comfort conditions.
Finally, the Fusion Tables, a web service provided by Google, were used to extend the results to the Italian provinces taking into account the standard monthly climate data. It was showed that with decreasing latitude, the energy savings of the combined system increased and reached the maximum value calculated for cities located in the south.