The weatherization of existing homes or airtight con= struction of new energy-efficient homes can produce high indoor moisture levels during the winter. These undesirable moisture levels can potentially lead to a number of moisture-related problems. While ventilation is traditionally used for moisture control, # may be ineffective during certain climatic conditions. The occurrence of these conditions is not uncommon during periods of mild and wet weather in the fall, winter, and spring in the western portions of the Pacific Northwest. One potentially effective and relatively inexpensive means of satisfactorily controlling high indoor moisture levels is by use of a portable electric dehumidifier. However, because most dehumidifiers lack automatic defrost control, they do not work effectively at winter indoor air temperatures, which typically fall between 60°F (15.9°C) and 70°F (21.4°C). fortunately, prior to this study, the effectiveness, water removal capacities, and performance characteristics of portable electric dehurnidifiers, with or without defrost control capabilities, operating at typical winter indoor air temperatures were largely unknown. Thus, a preliminary field study of the winter perforrnance of a portable electric dehumidifier was undertaken. This paper describes the study and its findings.

During the winter and spring of 1987 a dehumidifier with automatic defrost control was installed in an occupied home and monitored to evaluate its effectiveness in controlling indoor moisture levels. A microcomputerbased data acquisition system was used to gather and record the inputs from various probes and equipment used in the study. The dehumidifier was found to reduce indoor relative humidity levels within the residence and provided satisfactory moisture control Moreover, it did not increase the total energy use of the home, as would a ventilation system used for moisture control. In fact, the use of the dehumidifier slightly reduced the total heating cost of the electrically heated test home. Further detailed results and conclusions are presented, along with recommendations for further testing in order to answer remaining questions regarding the winter effectiveness of portable electric dehumidifier.