Thermal Performance Implications of a Housing Warrant of Fitness

<p>A housing Warrant of Fitness (WoF) has been independently proposed by three organisations as a way of improving the quality of rental housing in New Zealand and reducing housing related injuries and health problems. The New Zealand Green Building Council and the Housing and Health Research Programme (University of Otago, Wellington) have jointly developed a WoF based on Homestar and the Healthy Housing Index (labelled the GH WoF in this document). Housing New Zealand is in the process of developing a WoF for their properties (HNZ WoF) , it has been tested on a number of state houses but the results have not yet been fully released. Both the GH WoF and the HNZ WoF target thermal and moisture performance amongst other minimum requirements for rental housing. The WoFs specify slightly different housing features as minimum acceptable standards. Both of the WoFs are structured as a checklist, with all items considered mandatory to pass the assessment. This research investigated the impact of meeting the WoF criteria which impact thermal performance. A thermal model of a villa style house suitable for a family of 4 was modelled in the thermal simulation programme EnergyPlus with a minimum practicable level of thermal performance. A range of New Zealand input values were sought and a number of sensitivity analyses were carried out to validate the model’s performance. Combinations of features each meeting the different criteria of the WoFs (such as insulation, ventilation and curtains) were then added to this house. The results of these models demonstrated that while adding these features will improve thermal performance, a simple pass/fail may be misleading because a house which fails may have equivalent thermal performance to a house which passes. The pass/fail result does not acknowledge trade-offs between temperature, energy consumption and running cost. Neither WoF accounts for the impact of climate on the ability to achieve comfortable indoor conditions, which has a greater impact than passing or failing a WoF. The criteria targeted at moisture performance were unable to be analysed as the moisture loads put into EnergyPlus could not be adequately verified. The research showed that while both WoF could lead to improved thermal comfort in rental housing, meeting the GH WoF requirements would bring about greater thermal performance benefits, the HNZ WoF enables the affordability of heat to be considered when insulating is not feasible.</p>

Thermal Performance Implications of a Housing Warrant of Fitness

<p>A housing Warrant of Fitness (WoF) has been independently proposed by three organisations as a way of improving the quality of rental housing in New Zealand and reducing housing related injuries and health problems. The New Zealand Green Building Council and the Housing and Health Research Programme (University of Otago, Wellington) have jointly developed a WoF based on Homestar and the Healthy Housing Index (labelled the GH WoF in this document). Housing New Zealand is in the process of developing a WoF for their properties (HNZ WoF) , it has been tested on a number of state houses but the results have not yet been fully released. Both the GH WoF and the HNZ WoF target thermal and moisture performance amongst other minimum requirements for rental housing. The WoFs specify slightly different housing features as minimum acceptable standards. Both of the WoFs are structured as a checklist, with all items considered mandatory to pass the assessment. This research investigated the impact of meeting the WoF criteria which impact thermal performance. A thermal model of a villa style house suitable for a family of 4 was modelled in the thermal simulation programme EnergyPlus with a minimum practicable level of thermal performance. A range of New Zealand input values were sought and a number of sensitivity analyses were carried out to validate the model’s performance. Combinations of features each meeting the different criteria of the WoFs (such as insulation, ventilation and curtains) were then added to this house. The results of these models demonstrated that while adding these features will improve thermal performance, a simple pass/fail may be misleading because a house which fails may have equivalent thermal performance to a house which passes. The pass/fail result does not acknowledge trade-offs between temperature, energy consumption and running cost. Neither WoF accounts for the impact of climate on the ability to achieve comfortable indoor conditions, which has a greater impact than passing or failing a WoF. The criteria targeted at moisture performance were unable to be analysed as the moisture loads put into EnergyPlus could not be adequately verified. The research showed that while both WoF could lead to improved thermal comfort in rental housing, meeting the GH WoF requirements would bring about greater thermal performance benefits, the HNZ WoF enables the affordability of heat to be considered when insulating is not feasible.</p>

Sensitivity analysis of hygrothermal performance of wood framed wall assembly under different climatic conditions: the impact of cladding properties

One of the parameters that influences the moisture performance of the wood framed wall assembly is the material properties of exterior cladding. The uncertainties of its properties, would result in a range of wall performance. The objective of this study was to investigate the impact of uncertainties in cladding material properties on moisture performance of wood framed wall assembly under different climatic conditions. A wood framed (2×6 wood stud) wall with exterior brick cladding was simulated assuming 1% rain leakage deposited on the exterior side of sheathing membrane. A parametric study was carried out to analyze the impact of the cladding properties on the moisture response of OSB. The simulations were conducted in five different cities located in different climate zones across Canada. The aim was to identify the most influential cladding property on the moisture response of OSB, i.e., mould growth index and moisture content, to the varying cladding properties under different climatic conditions i.e., different cities under historical and future conditions. In general, it was found that liquid diffusivity is the parameter that has the most influence on moisture response of OSB in all the five cities. Also, the significance of this influence varies depending on the climatic conditions.

Hygrothermal simulations of timber-framed walls with air leakages

Air leakages can create substantial excess moisture loads into envelope structures and degrade their hygrothermal performance. Multiple previous research projects have studied the behaviour and modelling of air leakages in building physics applications, but it is still quite rare to see air leakages being considered in practical building design simulations. The purpose of this paper is to present the selection of input parameters for air leakage simulations, utilisation of a factorial design to manage simulation cases and the results for a timber-frame wall with and without air leakages. According to the results, the air permeability of mineral wool and the air pressure difference over the envelope were the two most important factors for the dry air mass flow through the structure, as opposed to gap width and leakage route. An ideally airtight structure had a better hygrothermal performance compared to leaky structure. However, when leakages were present, the exact yearly average air flow rate in the range 70…420 dm3/(m2h) did not have a strong correlation to the performance indicators. For the other studied variables, the existence of a 50 mm thick mineral wool insulation on the exterior side of the gypsum board wind barrier and the impacts from climate change had the biggest effect on the moisture performance of the structure.

Identifying the critical orientation of wood-frame walls in assessing moisture risks using hygrothermal simulation

Hygrothermal simulations can be used as a reliable tool in analysing moisture performance. For an efficient analysis, it is important to appropriately select the wall orientation in the simulations. ASHRAE 160 recommends to using orientation with highest amount of annual wind-driven rain (WDR) and the orientation with the least annual solar radiation. The objective of this work was to identify the orientation which leads to the worst moisture performance of different wall assemblies under historical climate in different Canadian cities. Four cardinal orientations (North, East, South, and West) and orientation receiving the highest amount of annual WDR (Default) were tested in this study. The simulations were carried out assuming three scenarios of moisture loads for four different wood-frame (2×6 wood stud) wall systems that differ by their claddings: brick, fibreboard, stucco, and vinyl. With an assumption of no WDR, north facing wall always leads to the worst moisture performance. In the presence of WDR, with and without water source, default orientation leads to the worst moisture performance with few exceptions. As default orientation was based on total sum of WDR, it sometimes may not lead to worst performance and hence hourly distribution of WDR should be taken into consideration.

Effects of climate change on the moisture performance and durability of brick veneer walls of wood frame construction in Canada

The objective of this study was to assess the potential effects of climate change on the moisture performance and durability of red matt clay brick veneer walls of wood frame construction on the basis of results derived from hygrothermal simulations. One-dimensional simulations were run using DELPHIN 5.9 for selected moisture reference years of the 15 realizations of modelled historical (H: 1986-2016) and future (F: 2062-2092) climate data of 12 Canadian cities. The mold growth index at the outer layer of the OSB sheathing panel was used to compare the moisture performance under H and F periods. Results for the base design that meet the minimum requirements of the National Building Code of Canada showed that cities within the interior of the country, characterized by a low annual rainfall, are less likely to develop significant mold growth under H and F periods, whereas cities in coastal areas, characterized by high annual rainfall, present a heightened risk to mold growth under both H and F periods. For cities located on the west coast, a possible solution could be to use a 38-mm ventilated drainage cavity as this measure would help dissipate moisture from within the cavity. On the east coast, apart from using a 38-mm ventilated drainage cavity, other measures aiming at reducing the wind-driven rain deposition (i.e., increasing overhang ratio or the height of the roof) could be introduced. However, the feasibility of such measures needs to be considered in respect to whether these are to be implemented as part of a new building or retrofit of an existing one.

Assessing the Energy, Indoor Air Quality, and Moisture Performance for a Three-Story Building Using an Integrated Model, Part Three: Development of Integrated Model and Applications

The overall building performance depends mainly on the energy performance, indoor air quality, and moisture performance. In order to accurately calculate the building performance, the development of a model with the ability to integrate all three performances is required. In this research, a combination of three models namely EnergyPlus for energy, CONTAM for indoor air quality, and WUFI for moisture transport are used to develop an integrated model. The mechanism of this combination is based on the exchange of temperatures, airflows, and heating-cooling flows control variables between all three sub-models. By using the paired sample t-test, an integrated model is verified and its accuracy is validated. The accuracy of the integrated model is verified by the paired sample t-test. In order to analyze the accuracy of the integrated model in comparison with single models, four scenarios of airtight fan off, airtight fan on, leaky fan off, and leaky fan on are defined for a three-story-house subjected to three different climate cities of Montreal, Vancouver, and Miami. Percentage differences of simulated measures with the ASHRAE Standard are considered as the performance criteria. The simulated results by single and integrated models are compared and analyzed. Finally, the scenarios with the high performances are evaluated in terms of energy efficiency, indoor air quality, and moisture for Montreal, Vancouver, and Miami. Overall, it can be concluded that an integrated model should be developed.

Assessing the Energy, Indoor Air Quality, and Moisture Performance for a Three-Story Building Using an Integrated Model, Part Two: Integrating the Indoor Air Quality, Moisture, and Thermal Comfort

In this paper, an integrated model that coupled CONTAM and WUFI was developed to assess the indoor air quality (IAQ), moisture, and thermal comfort performance. The coupling method of CONTAM and WUFI is described based on the exchange of airflow rate control variables as infiltration, natural and mechanical ventilation parameters between heat and moisture flow balance equations in WUFI and contaminant flow balances equations in CONTAM. To evaluate the predictions of the integrated model compared to single models of CONTAM and WUFI, four scenarios were used. These scenarios are airtight-fan off, airtight-fan on, leaky-fan off, and leaky-fan on, and were defined for a three-story house subjected to three different climate conditions of Montreal, Vancouver, and Miami. The measures of the simulated indoor CO2, PM2.5, and VOCs obtained by CONTAM; the simulated indoor relative humidity (RH), predicted percentage of dissatisfied (PPD), and predicted mean vote (PMV) obtained by WUFI; and those obtained by the integrated model are compared separately for all scenarios in Montreal, Vancouver, and Miami. Finally, the optimal scenarios are selected. The simulated results of the optimal scenarios with the integrated model method (−28.88% to 46.39%) are different from those obtained with the single models. This is due to the inability of the single models to correct the airflow variables.

A method for determining the relationship between increasing insulation and potential freeze thaw damage in brick masonry walls.

When considering insulation retrofits, property limit distances and setbacks make interior insulation of residential homes the only viable option. When pursuing an interior insulation retrofit the potential for brick masonry freeze thaw damage needs to be considered. Studying the impacts of an interior insulation retrofit Pre-World War 2 residential building in Toronto, Ontario, a comparison of the retrofitted building using WUFI against 8 other insulation types was completed to determine if the change of insulation affects the potential for freeze thaw damage. Based on the results of the WUFI analysis the answer would be yes. The insulation type and R value does have an impact brick masonry freeze thaw resistance. However this relationship is general and not linear. The method provided shows that if critical saturation (SCRIT) is known predictive modeling on the impacts of interior insulation on the moisture performance of the brick masonry wall can be used.