Natural convection energy recovery loop analysis, part I: energy and exergy studies by varying inlet air flow rate

Abstract

The natural convection energy recovery loop is analyzed experimentally in different airflow rates. The system was introduced previously as a prototype of the standalone air conditioning system and its transient and steady performance was verified. As a new generation of energy recovery tool between the building return and fresh air, the system is rated from the viewpoints of energy and exergy. Different forms of effectiveness and 2nd law efficiency are studied and their values extracted for inlet airflow rates of 2–6 m3/h. The results show that the prominent factor that controls the system behavior is the concentration ratio from which the solution free- motion originated. The maximum sensible, latent, and total effectiveness of the system are 0.23, 062, and 0.54 respectively and are for the airflow rate of 2m3/h. It is confirmed that the number of a transfer unit (NTU) and capacity ratio (Cr*) are not independent and are varied oppositely to each other. By increasing the airflow rate, the mass flow rate and heat capacity rate of desiccant solution increase more than that of air streams. For flow rates less than 3.5m3/h, external heat transfer is just enough to induce natural motion of desiccant and in this way the loop performance is similar to a forced convection energy transfer loop which exchanges heat and moisture only between the air streams.