The Kitchen Fridge: A Microcosm of Building Energy, Environment, and Efficiency

1. Infer Model Adjust Control Law The Kitchen Fridge: A Microcosm of Building Energy, Environment, and Efficiency Jay Taneja, Prabal Dutta, Jorge Ortiz Building Refrigerator Information Technology Overlay 7°C Cooling Tower Temp Humidity $ Air Measurement Points 3°C Return Air Vent Condenser Pump Temp? Water Condenser Chiller $ Temp? Compressor Expansion Valve Refrigerant Evaporator Air Vent Zone Temp? Chilled Water Pump Temp? Control Points (on/off/variable) Warm Gas Air Handling Unit Incorporate - System Model - D/R Signals - Market Data - User Prefs Warm Dense Gas Cool Gas Exhaust Air Fan Supply Air Fan Cool Liquid A Real-World Example Fit to Exp2 model - Asymptotic temperature curve suggests 0.1° C increase if one cycle of compressor is skipped Vertical/Horizontal Temperature Variations Compressor Dinner Door Openings - Large humidity spike • - Modest temp delta • - Higher cycle frequency • - Higher cycle duration Breakfast Door Openings - Large humidity spike - Small temp delta Mini-Fridge without Compressor 6 Cycles 7 Cycles 6 Cycles 9 (Long) Cycles Average Power = 35 W Average Power = 188 W Light Power Draw Focusing on the Refrigerator Study Applications to the Building Ecosystem • System coverage achieved through model in combination with an AC meter and suite of climate sensors • Refrigerator model allows exploration of 'slack' (e.g. increase set points, defer compressor/defrost cycles, etc.) • Energy-saving tips: (1) keep fridge stocked instead of empty (Cair < Cfood); (2) a stocked fridge can withstand higher set points; (3) let food cool before inserting in fridge (smaller ΔT) • Solid state is much less efficient than compressor refrigerator • Building HVAC uses similar components to refrigerators – think “Building ≈ Large Refrigerator” • Coverage of HVAC system is a superposition of subsystems, monitored by well-placed electricity, gas, and climate sensors • Building subsystems are easier to decompose than fridge (larger scale, more sense points, less perturbation by human activity) • Refrigerator efficiency, driven by policy, still has room to improve. Building HVAC, with less strict policy, is less refined.