Sunspace thermal dynamics in the pacific northwest: A field and modeling study

Four residential sunspaces in Eugene, Oregon were instrumented January-June 2011, measuring indoor air, globe, and surface temperatures, mass surface heat fluxes, relative humidity, and incident solar radiation. Concrete and soil thermal properties were estimated by fitting finite difference heat flow models to field data. EnergyPlus models using these parameters, site characteristics, and 2011 weather data were then used to quantify heat flow pathways. In March and April (i8±4 daily HDDo, mean sky cover 80%), months most promising for passive solar heating, two of the sunspaces captured an average of 25kWh/d, comparable to RECS-reported regional space heating use of i-2kWh/HDD6. per dwelling (27); 01150 days, captured energy exceeded 15kWh. Over 60% of this energy entered as diffuse radiation, challenging the notion that cloudy sides foil solar heating. Only 7-15% was stored in mass and later returned, however: 20-30% escaped through uninsulated floors and walls, 15-25% was lost from windows, and infiltration claimed 18-28%, reflecting sizable passageways for frogs, cats, and garden hoses. Greatest losses occurred when outside conditions cooled rapidly, as at dusk and during rain; accordingly, modeled addition of glazing and slab insulation, and sealing of large openings, allowed an impressive io-2okWli/d to be retained during these months.