The Aldo Leopold Foundation (ALF) located nearBaraboo, WI, employs several passive approachesincluding using a Horizontal Earth Tube System(HETS). The simulation during the design levelindicated that HETS would perform better than anenthalpy-heat-recovery system precooling anddehumidifying the air, but not quite as well preheatingthe air in winter. The earth tube model which was usedin the design simulation had not been validated. Thispaper focuses on setting up a data collection system tomeasure the amount of precooling. A bulk flow modeland a CFD1 model are further developed based on thecollected data.