Wisconsin Residential Moisture Monitoring Project Life-Cycle Energy Costs and Greenhouse Gas Emissions for Gas Turbine Power

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1 report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report report energy center Report Summary Wisconsin Residential Moisture Monitoring Project Life-Cycle Energy Costs and Greenhouse Gas Emissions for Gas Turbine Power A Field Study December April, ENERGY CENTER OF WISCONSIN

2 Research Report Wisconsin Residential Moisture Monitoring Project A Field Study December 2002 Prepared by Cautley Engineering and Energy Center of Wisconsin Prepared for 595 Science Drive Madison, WI Phone: Fax: ecw@ecw.org

3 Copyright 2002 Energy Center of Wisconsin All rights reserved This document was prepared as an account of work sponsored by the Energy Center of Wisconsin (ECW). Neither ECW, participants in ECW, the organization(s) listed herein, nor any person on behalf of any of the organizations mentioned herein: (a) makes any warranty, expressed or implied, with respect to the use of any information, apparatus, method, or process disclosed in this document or that such use may not infringe privately owned rights; or (b) assumes any liability with respect to the use of, or damages resulting from the use of, any information, apparatus, method, or process disclosed in this document. Project Manager Craig Schepp Energy Center of Wisconsin Acknowledgements Dave Borski (Madison Gas & Electric) Ed Carroll (Wisconsin Energy Conservation Corporation) Andres Dejarlais (Oak Ridge National Laboratory) Achilles Karagiozis (Oak Ridge National Laboratory) Len Linzmeier (Windsor Homes) Mary Meunier (Wisconsin Department of Administration) Don Olson (Madison Area Technical College) Dave Osborne (Conserv Products) Kevin Pitts (Wisconsin Public Service Corporation) Leroy Stublaski (Wisconsin Department of Commerce) Anton TenWolde (U.S. Forest Products Laboratory)

4 Contents Introduction...1 Method...3 Results...7 Data Overview...7 Effect of Temperature on Measured Moisture Content...7 Moisture Content Trends in 12 Test Bays...8 Moisture Content Comparisons by Wall Type...12 Comparative Drying Times by Wall Type...16 Comments on Cold Weather Wall Performance...17 Warm Weather Wetting Episodes...17 Discussion...19 Measurement Methods...19 Moisture Performance...19

5 Figures Figure 1. Moisture probe locations...3 Figure 2. Apparent moisture content vs. temperature - Bay 5 middle outer, 3/11/ Figure 3. Test home bay 4: No VB, ½" XPS, airtight daily average moisture content (outer locations)...8 Figure 4. Test home bay 3: Poly VB, ½" OSB, airtight. Daily average moisture content (outer locations) - 11/26/00 8/12/ Figure 5. Test home Bay 6: No VB, ½" OSB, airtight. Daily average moisture content (OSB locations)...10 Figure 6. Winter average moisture content by measurement position in 12 test bays (north and west walls)...11 Figure 7. Estimated upper and lower limits of winter period average moisture content at wall framing locations...12 Figure 8. Comparative winter average moisture content by measurement position...13 Figure 9. Comparative winter average moisture content by measurement position OSB vs. XPS sheathing...14 Figure 10. Comparative winter average moisture content by measurement position. Not airtight vs. airtight...15 Figure 11. Drying times for outer bottom (wettest) measurement locations...16 Figure 12. Test home Bay 25: South wall, below window daily average moisture content (uncorrected)...17 Figure 13. Moisture content, precipitation, and south wind during wetting episode. Bay 25 hourly average values..18

6 Abstract This study examines the effects of moisture in a variety of residential wall systems in one test home in Madison, Wisconsin from November 2000 to August The wall systems consisted of 12 test bays with various combinations of oriented strand board or extruded polystyrene sheathing, with and without a vapor barrier, and made airtight or not airtight. Moisture was measured in both framing and sheathing. Results are given by date, sheathing type and location within the wall cavity. The results show the critical important of a vapor barrier to reducing wintertime moisture accumulation. i

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8 Introduction As a result of reported problems and an interest in new materials and technologies, the buildings community has become increasingly interested in the moisture performance of building envelopes. This interest has increased the need for improvements in quantitative performance prediction and measurement methods. This project addressed this need through developing and applying a system for measuring moisture content in wood frame structures under field conditions. Project objectives included developing a system for long-term multi-point moisture monitoring in structures, generating detailed data for use in modeling, and evaluating actual in-service performance of several wall sections. 1

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10 Method A Wisconsin monitoring system was installed and data were gathered for nine months in an unoccupied Madison, Wisconsin test home. The home is conventionally constructed, with 2 x 6 wall framing 16 in. on center, drywall, a polyethylene vapor barrier, fiberglass insulation, OSB or extruded polystyrene sheathing, an exterior air barrier, and vinyl siding. Figure 1 shows the locations where moisture content was measured. Locations 1 12 represent the 12 test bays that were monitored intensely. Figure 1. Moisture probe locations Various combinations of vapor barrier and sheathing type were used in 12 wall cavities selected for detailed data collection (Table 1). Nine of the 12 bays were made as airtight as possible, allowing comparison of the data to results of modeling that does not consider airflow. 3

11 Residential Moisture Monitoring Table 1. Test bay construction and probe configuration Test Bay Designation (Orientation) Sheathing Type Vapor Barrier Intentionally Airtight? Moisture Probe Locations (Total Number) Note 1 Thermocouple Locations (Total Number) Note 2 1 (W) ½" OSB No Tight F (6) F (6) 2 (W) ½" XPS Poly Tight F (6) F (6) 3 (W) ½" OSB Poly Tight F, S (9) F, S, D (12) 4 (W) ½" XPS No Tight F (6) F, S, D (12) 5 (W) ½" XPS No Tight F (6) F (6) 6 (W) ½" OSB No Tight F, S (9) F,S,D (12) 7 (N) 1" XPS No Not Airtight F (6) F (6) 8 (N) 1" XPS No Tight F (6) F,S,D (12) 9 (N) 1" XPS No Not Airtight F (6) F (6) 10 (N) 1" XPS Poly Tight F (6) F (6) 11 (N) 1" XPS Poly Not Airtight F (7) F (7) 12 (N) ½" OSB ½" XPS No Tight F, S (9) F,S,D (12) Note 1 Moisture probe locations: F - 6 probes in framing (top, middle, and bottom) S - 3 probes in sheathing (top, middle, and bottom) Note 2 Thermocouple locations: F - 6 thermocouples on framing, adjacent to moisture probes S - 3 thermocouples on sheathing, adjacent to moisture probes D - 3 thermocouples on back side of drywall, near moisture probes Moisture measurements were based on the established relationship between moisture content and electrical resistance of wood. Moisture probes consisting of pairs of metal pins were inserted into wood framing and sheathing, either ½" from the drywall ("inner" locations) or ½" from the sheathing ("outer" locations). To monitor wood moisture content below the surface, the pins used in the 12 test bays were insulated to ¼" depth. A total of 153 moisture probes were successfully monitored. Resistance, temperature and other data was collected every 15 minutes through an automated system onsite and downloaded remotely. 4

12 Method We performed linear regressions for each available daily data set of moisture content and temperature and used 4,428 regression results with a coefficient of determination (R 2 ) greater than 0.85 to establish a temperature correction factor. This factor was applied to all moisture content data where temperature was also measured. 5

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14 Results Data Overview Data collection was nearly continuous from November 25, 2000 to August 12, Calibration data indicated good accuracy above a moisture content of about 8%, while lower moisture content values must be viewed as approximate. Two patterns of anomalies appeared in the moisture content data. The first, consisting of consistently low and sometimes negative values, appears to result from small errors in the measurement of very dry wood. The observations in this group are assigned a moisture content value of 6.4%. The second pattern involves much larger negative values, fast changing values, and in some cases, a reversal of the effect of temperature on measured values. This pattern usually appeared at locations where condensation was judged likely, and is thought to be associated with surface wetness. Observations in this category are not interpreted as quantitative moisture content values. Indoor relative humidity was held at 40 to 50 percent early in the measurement period, resulting in significant amounts of condensation on windows and in the perimeter of the floor system. Our intention was to drive the indoor humidity levels to limits that are higher than most occupied homes. After observing considerable frost and condensation on windows in the sill boxes, the humidity control point was reduced several times during the winter. Effect of Temperature on Measured Moisture Content The recognized trend of decreasing electrical resistance of wood with increasing temperature appears clearly in our data. The relationship between apparent moisture content (i.e. moisture content uncorrected for temperature) and temperature is most often positive, and often quite linear for observations over one day or so, when the actual moisture content changes very little (see Figure 2). Figure 2. Apparent moisture content vs. temperature - Bay 5 middle outer, 3/11/01 12 Apparent Moisture Content (%) Tem perature (F) 7

15 Residential Moisture Monitoring Moisture Content Trends in 12 Test Bays Moisture content trends in the outer locations of Bay 4 demonstrate trends that are common to many measurement locations (see Fig. 3). The elevated moisture levels at the bottom outer location is probably due to condensation on the sheathing, which may then drip or wick through the fiberglass insulation to the bottom plate. Elevated relative humidity at the outer locations keeps moisture content higher during the winter. Figure 3. Test home bay 4: No VB, ½" XPS, airtight daily average moisture content (outer locations) 30 Moisture Content (%) Bottom Outer 4 Middle Outer 4 Top Outer /15/00 12/15/00 1/14/01 2/13/01 3/15/01 4/14/01 5/14/01 6/13/01 7/13/01 8/12/01 Date 8

16 Results Bay 3 includes a poly vapor barrier, and shows moderate moisture content values throughout the winter (Fig 4). Elevated moisture content indicating some condensation does appear in some bays with vapor barriers, however. Figure 4. Test home bay 3: Poly VB, ½" OSB, airtight. Daily average moisture content (outer locations) - 11/26/00 8/12/01 Moisture Content (%) Bottom Outer 3 Middle Outer 3 Top Outer /15/00 12/15/00 1/14/01 2/13/01 3/15/01 4/14/01 5/14/01 6/13/01 7/13/01 8/12/01 Date Measured moisture content often appears to change more quickly than is expected in solid wood, suggesting that in spite of using insulated pins, the measurements reflect conditions at the surface of the wood rather than at a depth of ¼". Moisture content at inner locations, ½ from the drywall, generally remains below 10 percent, with some elevated levels measured on the bottom plate, probably due to wicking of condensed moisture from the outer side of the wall. 9

17 Residential Moisture Monitoring Moisture content measured in the OSB sheathing generally follows trends similar to the moisture content in the outside framing locations. Bay 6 OSB (see Fig 5) shows persistent high values throughout the winter, resulting from the absorption of surface condensate combined with high local relative humidity. Figure 5. Test home Bay 6: No VB, ½" OSB, airtight. Daily average moisture content (OSB locations) 30 Moisture Content (%) Bottom OSB 6 Middle OSB 6 Top OSB /15/00 12/15/00 1/14/01 2/13/01 3/15/01 4/14/01 5/14/01 6/13/01 7/13/01 8/12/01 Date 10

18 Results Figure 6 presents average winter period moisture content by measurement position across the 12 test bays. These values show the effects of higher local relative humidity at the outer locations and the effects of condensation on the bottom outer locations. Figure 6. Winter average moisture content by measurement position in 12 test bays (north and west walls) 20 Average Moisture Content (%) Bottom Inner Middle Inner Top Inner Bottom Outer Middle Outer Top Outer Measurement Position Equilibrium moisture content (EMC), the stable moisture content reached by wood after prolonged exposure to specific environmental conditions, provides a basis for estimating the expected moisture content in the test home walls. The conditions within the wall cavity are bounded by indoor and outdoor absolute humidity and temperature. We have estimated these bounds, and the corresponding EMC, for the three sheathing types used (1 inch XPS, ½ inch XPS, and ½ inch OSB). 11

19 Residential Moisture Monitoring Figure 7 shows that in every case, the average measured values are between the upper and lower limit established by environmental conditions. This demonstrates that winter moisture behavior in the 12 test bays is driven primarily by water vapor transmission, rather than condensation and absorption of liquid water. Figure 7. Estimated upper and lower limits of winter period average moisture content at wall framing locations Low EMC Estimate Measured Average MC High EMC Estimate Moisture Content (%) Inner Outer 1" XPS Outer 1/2" XPS Outer OSB Locations, Sheathing Type Moisture Content Comparisons by Wall Type We can also explore the effect of the use of a vapor barrier, sheathing type, and airtight construction on wintertime moisture performance by comparing average moisture content values between locations that are identical except for the parameter being investigated. 12

20 Results Figure 8 shows comparative average winter moisture content by measurement position for locations with and without a vapor barrier. The effect of a vapor barrier in reducing average moisture content is clear, with average moisture content always the same or higher in locations without a vapor barrier compared to those with a vapor barrier. Figure 8. Comparative winter average moisture content by measurement position Paired Difference in Percent Moisture Content Bottom Inner Middle Inner Top Inner Bottom Outer Bays 1&6 vs 3 Bays 4&5 vs 2 Bay 8 vs 10 Bays 7&9 vs 11 Middle Outer Top Outer 3.7 Measurement Position Note: Positive values indicate higher moisture content in locations with no vapor barrier. Outer measurement locations clearly experienced higher levels of moisture. Top outer locations also showed higher moisture content, though not as significant. The highest levels of moisture were observed at bottom, outer locations, especially in the test bays sheathed by ½ OSB and ½ XPS. Measurement locations in test bays with a vapor barrier showed the lowest levels of moisture. 13

21 Residential Moisture Monitoring Figure 9 compares moisture content for locations with ½ OSB sheathing to those with XPS (either ½ or 1 ) sheathing. The effect of sheathing type on moisture content varies among locations and pairs, with no clear overall trend. There are several competing factors, including permeance, absorbance, and insulating value, that may contribute to the mixed moisture performance results for these sheathing types. Where a vapor barrier is present, the ½ XPS had greater moisture in the middle locations. Where a vapor barrier is absent, the ½ XPS showed higher moisture content than the ½ OSB only at bottom, outer locations. Figure 9. Comparative winter average moisture content by measurement position OSB vs. XPS sheathing Paired Difference in Percent Moisture Content Bottom Inner Bay 3 vs Bay 2 Bays 1&6 vs Bays 4&5 Bay 12 vs Bay Middle Inner Top Inner Bottom Outer Middle Outer Top Outer Measurement Position Note: Positive values indicate higher moisture content in bay with OSB 14

22 Results Figure 10 compares airtight construction to construction that has not been made exceptionally airtight. Once again, the results are mixed, with average moisture content lower in airtight locations in some cases, and higher in airtight locations in other cases. The ambiguous results may be related to competing effects of airflow at different times and locations. In general, airflow through a bay is expected to accelerate both heat transfer and moisture transfer from the direction of the airflow. The result may be a relative increase or decrease in moisture content at any given location and time. Figure 10. Comparative winter average moisture content by measurement position. Not airtight vs. airtight. Paired Difference in Percent Moisture Content Bottom Inner Bay 8 vs Bays 7&9 Bay 10 vs Bay 11 Middle Inner Top Inner Bottom Outer 0.1 Middle Outer -1.1 Top Outer 0.4 Measurement Position Note: Positive differences indicate higher moisture content in locations that are airtight. 15

23 Residential Moisture Monitoring Comparative Drying Times by Wall Type Relative drying rates within the test bays can also be used to compare the performance of various wall sections. The dates on which the bottom outer locations in Bays 1 through 12 dried to below 12% and 10% moisture are shown in Figure 11. Figure 11. Drying times for outer bottom (wettest) measurement locations Test Bays /3/01 3/5/01 4/4/01 5/4/01 6/3/01 7/3/01 8/2/01 Date Note: Each bar starts when location dried to below 12% moisture and ends when location dried to below 10% moisture. Locations in Bays 2 and 3 never exceeded 12% moisture. Early drying of Bays 2 and 3 shows the effect of a vapor barrier in limiting winter moisture accumulation. Bays 7, 9, 10, and 11 (all with 1 XPS), all either include a vapor barrier, were not made airtight, or both. While vapor barriers limited winter moisture accumulation, air leakage allowed faster drying when outdoor temperatures increased. Bays 4, 5, and 8, which lack a vapor barrier and have XPS sheathing, experienced intermediate drying times. The last locations to dry fully were Bays 1, 6, and 12, where moisture storage in OSB sheathing delayed drying. 16

24 Results Comments on Cold Weather Wall Performance Fungal decay and paint peeling are associated with moisture content levels greater than the fiber saturation point, typically between 25 and 30 percent. Since only a few moisture content observations in the test home exceeded 25 percent, it does not appear that fungal decay or paint peeling would be potential issues in the test wall system. The conditions required to support mold growth may occur where surface relative humidity is 70 to 80 percent or higher and the temperature is about 40 F to 100 F. These conditions appear to have existed in the walls of the test home at times during the winter. Thus, mold growth could have occurred in some wall cavities under the operating conditions used during the study. Warm Weather Wetting Episodes Probe placement in wall locations beyond the 12 test bays focused on identifying envelope leakage, with all probes in "outer" positions, ½ inch from the sheathing, and most below windows or other envelope penetrations. Wall construction in these locations included an exterior air barrier lapped under window mounting flanges, 1" XPS sheathing, a polyethylene vapor barrier, and no special air sealing. Winter moisture content trends at these locations are similar to those in the 12 test bays. During spring and summer weather, however, five episodes of sudden wetting occurred, followed by drying over a period of days. Three episodes occurred in Bay 25 (see Fig. 12). Figure 12. Test home Bay 25: South wall, below window daily average moisture content (uncorrected) Moisture Content (%) A 25E 25F 25J /15/00 12/15/00 1/14/01 2/13/01 3/15/01 4/14/01 5/14/01 6/13/01 7/13/01 8/12/01 Date 17

25 Residential Moisture Monitoring All of the episodes occurred under windows and each was preceded by measurable rainfall and wind toward the wall in question (see Fig. 13). Thus, these wetness episodes appear to be cases of rainwater leakage, probably at the perimeter of the windows. The small number of such episodes is consistent with the generally high construction quality of the test home, although additional attention to lapping and sealing of the air barrier around windows might have reduced leakage even further. However, wherever possible, these situations should be controlled to prevent bulk water from ever entering in the first place. Figure 13. Moisture content, precipitation, and south wind during wetting episode. Bay 25 hourly average values 40 25A E Moisture Content (%), South Wind Speed (mph) South Wind Speed Precipitation 0.5 Hourly Precipitation (In) /20/01 4/21/01 4/22/01 4/23/01 Date 18

26 Discussion The results show that envelope leakage can be identified using multi-point monitoring. Identifying leaks appears to be very sensitive to moisture probe location, however, and this monitoring method may be more useful in testing for leakage at specific critical locations, rather than screening of whole buildings. Measurement Methods This project demonstrates a method for implementing multi-point moisture content monitoring for the evaluation of moisture performance in wood-frame structures. Anomalies appearing in the data require explanation, and the cost of the system must be reduced to allow practical future use. Multi-point monitoring of moisture content in a wood frame structure is an effective tool for evaluating the seasonal moisture performance of walls. The system can identify episodes of envelope rainwater leakage, but is sensitive to the precise location of probes. Moisture Performance The effectiveness of a poly vapor barrier in reducing average moisture levels in the test home during the winter was clearly established. The use of a vapor barrier did not, however, completely eliminate intermittent condensation on sheathing surfaces. The effect of sheathing type and air leakage on winter moisture content in the test home is unclear. There are competing factors that may explain these mixed results. Moisture conditions in the walls of the test home were not conducive to fungal decay or paint failure, since moisture content did not stay above the fiber saturation point for significant periods. The conditions observed, especially in those situations with high moisture accumulation and retention, could result in mold growth in wall cavities. These situations tended to be in bays with no vapor barrier and in lower wall cavity locations. Worst-case locations for winter condensation and high average moisture content are at the bottom plate near the exterior sheathing, and in wood-based exterior sheathing material. The earliest post-winter drying times were in locations with 1 XPS sheathing, with and without a vapor barrier. However, wall cavities with ½ OSB or ½ XPS and with a vapor barrier experienced the lowest winter accumulation in the first place. The test home experienced just a few cases of rainwater leakage that could be identified. While the envelope of the test home was well-constructed, and not very susceptible to rainwater leakage, window and door joints could have been sealed better. 19

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29 ENERGY CENTER OF WISCONSIN 595 Science Drive Madison, WI Phone: Fax: Printed on Plainfield Plus, a recycled chlorine-free stock containing 20% post-consumer waste.