Designing and testing an air-PCM heat exchanger for building ventilation application coupled to energy storage

This paper studies a PCM heat exchanger coupled to a building ventilation system. This PCM module can either store
heat during the day (e.g. by cooling solar PV panels) and restore it to the building during the night for space heating
purposes or store coolness during the night and give it back during the day and thus act as a free cooling system. This
project aims to develop a performing air-PCM heat exchanger providing latent energy storage of 0.5 kWh, this energy
is delivered between 15 and 30°C. This heat exchanger is based on corrugated cells that can be easily filled, lined up
and then locked in a box, letting the air pass between the cells. The PCM used for the prototype is c omposed of fatty
acids. In order to develop an efficient PCM ventilation module, two different ways of investigation were followed and
used in parallel. The first one used CFD simulations and the second one, a semi-empirical model based on correlations.
The CFD simulations were able to predict the convection coefficient on the air side and also show the flow repartition
between the different channels whereas the semi-empirical model allowed a parametrical study in order to identify the
best geometry possible. Once the heat exchanger geometry was optimized, a test bench was built and a prototype of
air-PCM heat exchanger was manufactured in order to measure its thermal and hydraulic performances. The tests
consist in either a complete solidification or liquefaction of the PCM starting from respectively liquid PCM at 30°C
or solid PCM at 15°C. The airflow rate was set to 45m³/h, which corresponds barely to the ventilation rate of a
traditional room in a residential building. A comparison between the models and the measurements was carried out in
order to calibrate the semi-empirical model. It will be shown that a simple semi-empirical model satisfactorily predicts
the evolution of heat transfer rate for different operating conditions.