2.1.3. HVAC System and Operational Strategy

The output of a radiant system should vary with climatic change, and the hydronic system has variable water flow rate but constant supply temperature. For considering the effect of thermal mass surrounding a hydronic system (the concrete slab acts significantly as a regenerator in TABS [35]), the embedded surface cooling system (ESCS) is only selected to determine the significant effect of thermal mass in the external walls on the heat transfer and transmission load in the zone with a radiant system.

The auxiliary CAS in the combined system (ESCS+CAS) is only responsible for fresh air cooling load and indoor latent load. It supplies conditioned air with a constant flow rate (1 ac/h) at a constant dry-bulb temperature (15 ◦C). Thus, the CAS is simulated with priority.

System operation strategy is a main factor which affects the thermal mass performance [13]. The conventional operation scheduling technique (OPCT), wherein the cooling system is available 24 h/day and the room temperature set point is adjusted to achieve energy savings, has been widely applied [45–48]. Thus, the auxiliary CAS runs continuously during the occupied period, and the hydronic system in ESCS operates according to the setting of the room thermostat.

An equivalent CAS is also considered in the identical perimeter zones and operates according to the strategy OPCT.
