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Abstract
Radiant chilled ceilings with displacement ventilation represent a promising system that combines the energy efficiency of both subsystems with the opportunity for improved ventilation performance. Laboratory experiments were conducted for an interior zone office with a very high cooling load (91.0 W/m2) and with two different heat source heights to investigate their influence on thermal stratification and air change effectiveness. The results showed that displacement ventilation with a chilled ceiling is able to provide a stable thermal stratification and improved ventilation effectiveness compared to mixing ventilation for a wide range of configurations. Stratification and air change effectiveness decreases when a larger portion of the cooling load is removed by the chilled ceiling. For every degree decrement of the surface temperature of the radiant ceiling, the stratification decreases by 0.13 K and the air change effectiveness by 0.13. Moving the computer processing units (representing 51% of the total room heat gain) from the floor level to 1.5 m height markedly increased the room median stratification and the median air change effectiveness (from 1.15 to 2.90). Therefore, increasing the height of heat sources has the potential to reduce energy use and improve indoor air quality.
Acknowledgment
The authors would like to thank Tom Epp of Price Industries for his help in the laboratory testing.
Nomenclature
| ACEX | = | air change effectiveness measured at X = 0.6, 1.1, and 1.7 m |
| CC | = | chilled ceiling |
| CL | = | total cooling load (W) |
| CLCC | = | cooling load removed by chilled ceiling (W) |
| CLDV | = | cooling load removed by displacement ventilation system (W) |
| cp,w | = | specific heat capacity of water (J/(kg K)) |
| DV | = | displacement ventilation |
| mw | = | water mass flow rate (kg/s) |
| p | = | number of radiant ceiling panels |
| s | = | air temperature stratification between 0.1 and 1.1 m (°C or K) |
| tair,0.1 | = | air temperature measured at 0.1 m (°C) |
| tair,r | = | return air temperature from displacement ventilation system (°C) |
| tair,s | = | supply air temperature to displacement ventilation system (°C) |
| top | = | operative temperature (°C) |
| tp | = | surface temperature of panel, here supposed equal to tw,m (°C) |
| tw,m | = | mean water temperature; average of tw,s and tw,r (°C) |
| tw,r | = | water temperature returned from chilled ceiling (°C) |
| tw,s | = | water temperature supplied to chilled ceiling (°C) |
| Vair | = | airflow rate of displacement ventilation system (L/s) |
| η | = | ratio of cooling load removed by chilled ceiling CLCC over total cooling load CL |
| φ0.1 | = | dimensionless air temperature measured at 0.1 m |