Thermal mixing loss increases energy consumption for HVAC systems caused by the air movement due to the simultaneous heating in the perimeter zones(PZ) and cooling in the interior zones(IZ) in an office space in winter. We conducted real scale experiments of a HVAC system composed of fan coil units for the PZ and an AHU system for the IZ, choosing some operating parameters to analyze the thermal characteristics of its losses. As a result, the following results were obtained:
1. When the control setting values of room temperature for each of the two zones were selected to be different, the control performance got worse due to the stronger air movement between the two zones.
2. The PMV (predicted mean vote) values for each zone were satisfactorily +0.5 to -0.5 under the conditions of the control setting values of room temperature; 24 °C for the IZ and 22 °C to 24 °C for the PZ. But the PMV values were below -0.5 under the conditions of those; 22 °C for the IZ and 24 °C for the PZ. The air temperature difference between ceiling and floor grew with the increase of mixing losses as the outdoor air temperature fell.
3. The PZ heating loads grew as the losses increased and the outdoor temperature decreased, while the IZ cooling loads grew only as the losses increased.
4. The losses were evaluated for energy saving using the newly defined “possible minimum loss” that shows the estimation of minimum loss if the most optimum operation could be achieved.
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