In-Situ Thermal Testing of Wall Sections in NWT
In 1989, research was carried out to evaluate the thermal performance of composite wall sections in Arctic housing. More specifically, the purpose was to determine if significant reductions in the insulating value of otherwise physically sound composite wall sections have occurred as a result of exposure to the harsh northern environment.
Heat loss from houses in the Canadian Arctic is a major concern. Fuel oil, which is used extensively for space heating in the remote northern communities, is costly. Energy efficient houses capable of sustaining the harsh conditions associated with extended winters and cold temperatures have been built.
Concerns were expressed that the severe climate in the Arctic may, over time, reduce the insulating value of the composite wall sections used in energy efficient houses. Contributing factors include shrinkage of wood members, shifting of structures and degradation of individual components within composite wall sections. These changes may create air spaces between the insulation and the studs, allowing air to penetrate or circulate within the building envelope. Actual degradation of individual building components may then be caused by moisture migration into the building envelope.
Over the past few years, houses were constructed which would be less susceptible to deterioration resulting from exposure to this uniquely severe environment. The degree of success of these efforts has been a concern of building officials from the Northwest Territories and Yukon Housing Corporations (NWTHC and YHC) and Canada Mortgage and Housing Corporation (CMHC). To address this concern, an evaluation of the aged, as-built thermal performance of various wall assemblies was performed.
The three main objectives of this project were:
Heat loss was determined by attaching a five-sided calorimeter box to the wall and measuring the energy required by a heating element to maintain the temperature inside the box at the same level as room temperature. This energy consumption corresponds to the heat loss through the area of wall covered by the box. The system is referred to as a guarded hot box calorimeter.
The performance testing included inspections using infrared thermography equipment as well as continuous monitoring using the guarded hot box calorimetry instrumentation. The infrared thermography scans were conducted first to ensure that the wall sections selected were properly insulated and of typical construction. Calorimeter placement was dictated by available wall area to fit the hot box size. Effective (measured) RSI values of the wall sections were determined from the data obtained from continuous monitoring of the calorimeter.
Four houses were selected in Rankin Inlet, NWT, each of different age and design. Older homes were compared to newer ones to determine if older sections showed greater deterioration. All houses were built after 1980, as pre-1980 houses are known to have deteriorated wall sections.
This nineplex was built in 1984 using traditional wood frame construction. The wall section is as shown in Figure 1. The unit tested was a three-bedroom dwelling, located at one end of the structure and the guarded hot box calorimeter was mounted on the northeast exterior wall. The overall calculated RSI value was 3.2 m2K/W.
This 1985 two-storey duplex is also of traditional wood frame construction. The wall section is shown in Figure 2. The tested section faced north on the first floor. The overall calculated RSI value was 4.5 m2K/W.
This 1976 single-detached unit had its walls upgraded in 1986. The retrofit wall section is shown in Figure 3. The tested section faced north. The overall calculated RSI value was 3.6 m2K/W.House 4
This 1986 two-storey duplex was constructed using traditional wood framing. The wall section is shown in Figure 4. The tested section faced southeast. The overall calculated RSI value was 4.8 m2K/W.
The effective RSI values measured in the four houses are presented in Table 1. Wall sections in the two duplex units were found to have the highest thermal resistance values. The measured values for houses 1, 2 and 4 (the nineplex and two duplex units) were about 13% higher than calculated. There are three possible reasons for this occurrence:
TABLE 1. Results Summary
Calculated (theoretical) RSI values were determined using individual component thermal resistance values, and adjustments made to account for thermal bridging of studs and strapping.
The results suggest that significant reductions in insulating value of composite wall sections in houses constructed after 1984 have not occurred.
To further substantiate concerns regarding gradual wall degradation from exposure to the northern environment, it is recommended that detailed infrared thermography inspections be conducted on many houses, encompassing a wide variety of wall construction types.
Identifying wall sections of sufficient surface area to accommodate the guarded box calorimeters was a difficult task. If further testing is to be carried out using guarded hot box calorimeters, it is recommended that smaller box sizes be used to allow for a greater choice in placement.
Research Report: In-Situ Testing of the Thermal Performance of Wall Sections in N.W.T., August 1989.
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