Experimental Performance of Unglazed Transpired Solar Collector for Air Heating Hoy-Yen Chan Supervisors: Prof. Saffa Riffat and Dr. Jie Zhu Department of Architecture and Built Environment University of Nottingham, UK

Background Space heating: major energy consumption in cold countries. UK: 50% of the service sector energy consumption More heaters to satisfy thermal comfort Higher energy demand More power stations More CO 2 emissions Therefore, renewable energy has become vital energy sources for heating and cooling; e.g. solar energy

Introduction: the concept Solar radiation Ambient air Warm air Transpired metal plate Fan Insulated wall Fan Room Convection heat loss Forced into cavity by fan

Sandtile wall Tp Ti Tout Ta Fan Normal flow Vertical flow Research problems Transpired plate heat transfer correlation (Nu) since 1980s (Jet impingement cooling) Transpired plate heat transfer correlation (Nu) for solar collector (Experimentally and modelling) Effects: hole designs /geometry, porosity, thickness, wind Vertical flow heat transfer Height= m Effect of plenum depth Heat transfer from back-of-plate could take place Present study: Height= 2.0m No wind condition Vertical flow heat transfer & thermal performance Ratio of pitch/diameter: small Not suitable for solar collector Plate height <1.0m Vertical flow: NO heat transfer Acknowledge heat transfer might occur Simulation results based on CFD without experimental verification

Results: vertical flow Vertical flow contributes 40-50% of total temperature rise (3-10K) Modified Nusselt numbers: Normal flow: Nu=0.004Re 1.33, 260  Re  470 Vertical flow: Nu f,L = 0.182Re f 1.25, 1100< Re f < 2000 (laminar) Nu f,T = Re f 1.7, Re f  2300 (turbulent)

Thermal performance: Temperature rise Vs. Solar radiation Sandtile wall Tp Ti Tout Ta Fan

Thermal performance: Temperature rise Vs. Mass flow rate Sandtile wall Tp Ti Tout Ta Fan

Thermal performance: Efficiency & Heat exchange effectiveness Sandtile wall Tp Ti Tout Ta Fan Efficiency= mc p (Tout-Ta)/AI x 100% Heat exchange effectiveness= (Tout-Ta)/(Tp-Ta) x 100%

Conclusions Vertical flow heat transfer is inappropriate to be neglected Thermal performance increases with solar radiation but decreases with suction flow rate

Conclusions- cont. Benefits: Building integrated CO 2 emissions reduction not only helps to meet the international building emission targets but also creates more green energy construction jobs Suitable for building retrofit applications due to the system simplicity High efficiency of the system enable colours other than black can be used to better fit into the architectural plan of the buildings Low cost material. Metal material used in this design – i.e. aluminium sheet cost only about 15£/m 2 compare to the glazing material for most of the existing passive solar technologies which costs about 33£/m 2 It is a maintenance free solution – The transpired collector has porosity less than 1%. The actual air velocity in the holes is several meters per second which is high enough to keep dust from the building in the holes. – Due to the small hole size (1.2mm) and low porosity, only little rainwater can get through the holes. – The transpired metal plate is durable and can be easily to re-spray paint.

THANK YOU Department of Architecture & Built Environment, University of Nottingham