Heat recovery in ventilation systems in different climates: energy and economic comparison in old and new schools in COVID-19 pandemic conditions

Ensuring adequate ventilation and increasing total airflow supply to occupied spaces is one of the recommendations of the World Health Organization to contain the airborne diffusion of COVID-19 virus in schools. In this article, different technical solutions are compared combining thermal recovery by a sensible or a total heat exchanger and thermodynamic recovery by a heat pump (HP). An energy analysis is carried out in two different climates and for different values of the ventilation load to the heating + cooling load ratio, to evaluate the relative advantages of the systems in old schools (mostly diffused and poorly thermal insulated) and new ones (highly thermal insulated). Results indicate that the combined HP - total heat recovery system is the most efficient solution both in colder and milder climates, giving a nonrenewable primary energy (PE) ratio of 3.9 and 3.0, respectively. PE saving compared to PE consumption varies between 6 and 20% for the different systems in old poorly thermal insulated schools, increasing remarkably in new high energy performance buildings. An economic analysis reveals that the preferable solution is the HP only. A sensitivity analysis allows to evaluate how energy and economic results vary with the parameters considered.