1 SUNSPACE THERMAL DYNAMICS IN THE PACIFIC NORTHWEST: A FIELD AND MODELING STUDY Alexandra R. Rempel Environmental Studies Program 5223 University of Oregon Eugene, OR 97403 arempel@uoregon.edu Ken Gates Ken Gates Construction 3045 Bailey Hill Road Eugene, OR 97405 kenngates@comcast.net Alan W. Rempel Katharine V. Cashman Department of Geological Sciences 1272 University of Oregon Eugene, OR 97403 rempel@uoregon.edu cashman@uoregon.edu Catherine J. Page Department of Chemistry 1253 University of Oregon Eugene, OR 97403 cpage@uoregon.edu Barbara Shaw Barbara Shaw Management 61 West 34th Avenue Eugene, OR 97405 2barbshaw@comcast.net ABSTRACT Four residential sunspaces in Eugene, Oregon were instrumented January-June 2011, measuring indoor air, globe, and surface temperatures, mass surface heat luxes, relative humidity, and incident solar radiation. Concrete and soil thermal properties were estimated by itting inite difference heat low models to ield data. En- ergyPlus models using these parameters, site character- istics, and 2011 weather data were then used to quantify heat low pathways. In March and April (18±4 daily HDD 65 , 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 1-2kWh/HDD 65 per dwelling (27); on 50 days, cap- tured energy exceeded 15kWh. Over 60% of this energy entered as diffuse radiation, challenging the notion that cloudy skies foil solar heating. Only 7-15% was stored in mass and later returned, however: 20-30% escaped through uninsulated loors and walls, 15-25% was lost from windows, and iniltration claimed 18-28%, relect- ing 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 10-20kWh/d to be retained during these months. 1. INTRODUCTION Passive solar heating is promising in northern climates because heating needs typically increase with latitude more rapidly than solar resources decline, particularly when radiation on tilted or vertical surfaces is consid- ered: MacGregor’s 1981 work showed a total solar con- tribution four times greater in Lerwick, Shetland Islands (60°N) than in Messina, Italy (38°N), for example (1). This result relects both a greater total heating need and the duration of the northerly coastal heating season well past the spring equinox. These characteristics are shared by Eugene, OR (44°N) and other cities of the Paciic Northwest: Portland, OR (45°N), Seattle, WA (47°N), and Vancouver, BC (49°N) (Fig. 1., (2,3)). A comparison of Eugene’s heating season with those of other cities of comparable annual heating need, in addition, illustrates the coastal inluence in both moderating the depth of