Envelope Leakage Research Articles

Impacts of airtightening retrofits on ventilation rates and energy consumption in a manufactured home

A retrofit study was conducted in an unoccupied manufactured house to investigate the impacts of airtightening on ventilation rates and energy consumption. This paper describes the retrofits and the results of the pre- and post-retrofit assessment of building airtightness, ventilation, and energy use. Building envelope and air distribution systems airtightness were measured using fan pressurization. Air change rates were measured continuously using the tracer gas decay technique. Energy consumption associated with heating and cooling was monitored through measurement of gas consumption by the forced-air furnace for heating and electricity use by the air-conditioning system for cooling. The results of the study show that the retrofits reduced building envelope leakage by about 18% and duct leakage by about 80%. The reduction in the house infiltration rates depended on weather conditions and the manner in which the heating and cooling system was controlled, but in general these rates were reduced by about one third. The energy consumption of the house for heating and cooling was reduced by only about 10%, which is relatively small but not totally unexpected given that infiltration only accounts for a portion of the heating and cooling load.

Monitoring of Internal Moisture Loads in Residential Buildings

An insufficient amount of measured data is available on actual indoor humidity levels in U.S. households, making it difficult to design durable homes. This research project has collected 1 full year of indoor temperature and humidity data for a sample of 60 homes across three different climate regions - the hot and humid Southeast (Zone 2), the cold Northeast (Zone 5), and the marine Northwest (Zone 4).This research was in direct support of the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), Inc. Standard 160, Criteria for Moisture-Control Design Analysis in Buildings. A research methodology was developed with assistance from Oak Ridge National Laboratory (ORNL), a subcontractor and member of Standing Standards Project Committee 160 that acted in an advisory role. The monitoring protocol involved three site visits to each home to perform tasks such as collecting basic house and equipment characteristics, installing data loggers, performing testing to quantify envelope leakage and duct leakage, and collecting data recorded by the loggers. Data compiled in the field tests were analyzed to identify the potential relationships between certain household characteristics and the measured internal humidity levels.This report presents significant findings from the study. Correlations between indoor moisture levels and climate, occupant density, and house characteristics are the focus of the results. Conclusions and recommendations for indoor moisture management or future research needs are also discussed.

Ventilation Research on Australian Residential Construction

This paper applies established and new testing methods to discover the ventilation performance of various residential building envelope constructions in Australia. Under the definition of ‘ventilation performance’ we imply the building envelope leakage (or infiltration) of the living space air change rates, the volumetric flow rates and the pathways of air flow between subfloor, living and roof spaces. All of the methods applied and discussed here are on-site, evidence-based performance of actual structures as tested by the Mobile Architecture and Built Environment Laboratory and Air Barrier Technologies. The testing processes primarily involve the Tracer Gas Decay Method (TGDM) and the fan pressurisation method (FPM a.k.a ‘blower door’). All the measurements are performed with respect to the external wind speed and direction as well as the typical weather parameters. This paper discusses the differences and similarities of both testing methods as well as several other testing procedures that can inform the researcher on air leakage pathways. Findings of a simultaneous TGDM and FPM air leakage rate comparison are also encountered in this paper. One of the most informative testing methods, is the application of three different tracer gasses introduced into different spaces (subfloor, living and roof) to discover pathways of air flow within residential construction.

A New Statistical Methodology for Delta_Q Method Collected Data Manipulation

The Delta_Q duct leakage test method was created to improve upon existing duct pressurization tests. The method focuses on measuring the building envelope and HVAC duct air leakage under operating conditions and provides data needed for energy loss calculations or for infiltration impact. Laboratory measurement data used for Delta_Q estimations are introduced into the balance equations in a dimensional mode, which involves uncertainty and error distribution in the calculation process. The aim of this study is to use a dimensionless data approach for online data calculations as part of an automated experimental method and for statistical data modeling. Using deterministic statistical models for the envelope and duct system leakage behavior prediction allows for the creation of a new technology for data manipulation. The modified balance equations derived for a Delta_Q test application can be used in development of the statistical model.

Case studies of building envelope leakage measurement using an air-handler fan pressurisation approach

The air-handler fan pressurisation method can be a practical way to estimate envelope leakage in large scale or tall buildings where a conventional blower door test is not practical. Standards such as CGSB 149.15 describe desirable test conditions and protocols for such tests. However, because of the variety of building air handling system constructions and site conditions, and limited time and budget available for testing, one may not be able to perform the test under the recommended standard conditions, especially when the system configuration and operation at the site are unfavourable. This study describes air-handler fan pressurisation tests performed for two existing buildings having problematic site conditions affected the ability to perform standard test protocols. Envelope leakage was measured with and without sealing of elevator shafts. Both buildings were found to have standard leakage flow rates that exceed typical levels, with or without elevator shaft leakage. This paper provides some insight into what should be done to ensure a successful air-handler fan pressurisation test by describing what was done to deal with undesirable site conditions which could occur in many buildings. Practical applications: This study shows that air-handler fan pressurisation tests can be performed even in problematic buildings by improving test conditions at the site by adjusting the system operation and by utilising site specific measurement techniques and instrumentation. The applicability of recently developed fan airflow and outdoor intake flow measuring sensors to the air-handler fan pressurisation test is also discussed. However, it also shows that perfect implementation of standard air-handler fan pressurisation test procedure may be difficult in real buildings for a reasonable cost. Published case studies providing methods for solving various practical problems at the test site are very rare. This paper is useful for engineers who are seeking practical information about the air-handler fan pressurisation.

Impact of surface roughness on particle penetration through building envelope leakage

Infiltration is the main ventilation style during heating and cooling seasons in residential building of China. Human inhalation exposure to particles of outdoor origin depends substantially on the degree to which particles can penetrate through building envelope. In the paper, we analysed the impact factors of particle penetration into indoor environment, and developed a mathematical model to simulate particle penetration through cracks with rough inner surfaces. Results indicate that roughness elements play a greater role in enhancing deposition for d > 0.04 µm particles than for ultrafine particles. For cracks H > 1 mm, building envelop is not effective at removing infiltration particles.

Architectural Engineering Approach to Building Façade Design, Construction, and Evaluation

Whether you are looking at high performance facade components as part of building “green” or more traditionally from a weather barrier perspective, facade systems remain one of the most important aspects of a building design, and often one of the most problematic. Building facades involve a unique combination and integration of manufacturing, design, construction, and maintenance to perform as expected. Advances in technology and materials have made available an expanded number of system options that provide the owner and designer with additional cost and performance choices. While new choices are welcomed by the industry, the importance of proper design and execution remains as important as ever. This is true for all building types from single family residential construction with siding or brick cavity walls, to commercial and institutional construction with traditional masonry facades and punch through windows, to modern high performance curtain walls. While new buildings are important because they set the tone for the future, existing structures and their facades are subjected to a multitude of factors including aging, weathering, structural damage from severe environmental impacts, and, unfortunately, in some cases, mistakes of the past such as inadequate design and construction. Those who believe in an integrated architectural engineering AE approach to building design and construction will likely agree that AE as a profession is well situated to advance the art and science of design and construction of facades for new buildings, as well as investigation and repair of existing building facades. Unfortunately, as a profession, we do not always take full advantage of that potential. In addition to meeting the general requirements of model codes such as the International Building Code IBC and the required structural loads from ASCE-7 and similar standards, proper facade design for new or retrofit/repair situations necessitates a review of a number of important issues including, but not limited to, the following: 1. Overall energy issues including heat gain and loss and how they impact the design and control of the building’s mechanical systems. 2. Acoustics and sound control, especially in urban environments. 3. Natural ventilation as appropriate to the climate and location of the building. 4. Indoor air quality and the relationship to items such as ventilation quantities, vapor drive, and tightness of the envelope leakage rates . 5. Incorporation of a properly designed and constructed envelope including roof system that integrates best practice

An attic-interior infiltration and interzone transport model of a house

A detailed model is developed for predicting the ventilation rates of the indoor, conditioned zone of a house and the attic zone. The complete set of algorithms is presented in a form for direct incorporation in a two zone ventilation model. One of the important predictions from this model is the leakage flow rate between the indoor and attic zones. Ventilation rates are predicted from a steady state mass flow rate balance for each zone where all individual flow rates through leakage sites are based on a power law expression for flow rate versus pressure difference. The envelope leakage includes distributed leakage associated with background leakage, localized leakage associated with vents and flues, and active fan ventilation. The predicted ventilation rates agree quite well with field measurements of ventilation rates in houses and attics with different leakage configurations, without the use of any empirically adjusted parameters or constants.

Air and Pollutant Transport from Attached Garages to Residential Living Spaces – Literature Review and Field Tests

The National Institute of Standards and Technology (NIST) is conducting a study on the indoor air quality (IAQ) impacts and engineering solutions related to the transport of pollutants from attached garages to residential living spaces. Natural or fan-induced pressure differences across air leakage paths in house-garage (HG) interfaces can result in the transport of the contaminants generated in garages into adjacent living spaces. This paper summarises a literature review on the transport of pollutants from garages to residential living spaces and describes a field study to estimate the range of airtightness of attached garages and of HG interfaces in the United States.Although the body of literature on pollutant transport from attached garages to residential buildings is limited, the studies reviewed provide substantial evidence that transport of contaminants from garages has the potential to negatively impact residential IAQ in either an acute (e.g., carbon monoxide from automobiles) or chronic manner (e.g., storage of chemical products). However, the literature contains few answers on issues such as the airtightness and geometry of the HG interface, the impact of heating and cooling equipment in the garage, and the effectiveness of potential engineering solutions.To address one gap in understanding these issues, the airtightness of garages and HG interfaces was measured in five residences using fan pressurisation. While the small sample of houses limits generalisation of the results, a range of house ages, styles, and sizes was included. For all homes tested, the garage was found to be at least twice as leaky as the house, based on air change per hour at 50 Pa. The leakiness of the garage envelope, based on surface area normalised effective leakage area at 4 Pa (ELA4/SA), ranges from a high of nearly eleven times to a low of two and a half times that of the house exterior envelope leakage. On average, the HG interface was almost two and a half times as leaky as the rest of the house envelope, when based on ELA4/SA. However, this average is somewhat skewed due to one HG interface measured in this study that is almost eleven times as leaky as the rest of the house envelope. Conversely, a larger Canadian study found HG interfaces to be comparable to house envelopes but found the average garage to be about ten times as leaky as houses – possibly because Canadian houses are consistently tighter than U.S. houses (Fugler et al. 2002).The knowledge gained from this review and the field study will be used in a simulation study of the potential occupant exposure to pollutants from attached garages and to explore potential engineering solutions to this IAQ problem.

A comparison of the power law to quadratic formulations for air infiltration calculations

Although the power law has been broadly accepted in measurement and air infiltration standards, and in many air infiltration calculation methods, the assumption that the power law is true over the range of pressures that a building envelope experiences has not been well documented. In this paper, we examine the validity of the power law through theoretical analysis, laboratory measurements of crack flow and detailed field tests of building envelopes. The results of the theoretical considerations and field and laboratory measurements indicate that the power law is valid for low pressure building envelope leakage.

Controlled background ventilation for large commercial buildings†

A preliminary study was carried out on a naturally ventilated office built as a low-energy building. The study uses a multi-zoned prediction program to determine a ventilation strategy to provide controlled background ventilation. Full-scale, whole-building pressurisation measurements are used to provide envelope leakage characteristics. The surface wind pressure coefficient data are provided through measurements carried out in the Building Research Establishment's Environmental Wind Tunnel. This study assessed the effectiveness of permanent but controllable background ventilators in naturally ventilated office-type buildings with various envelope tightnesses. Preliminary results show that, during the heating season, it is possible to provide adequate background ventilation for occupant comfort by incorporating commercially viable, manually controllable trickle ventilators within each room. Recommendations for possible consideration may be that 4000 mm2 open-area ventilators could be used in rooms with floor areas less than 10 m2, and 400 mm2 per m 2 (of floor areas) for those which are larger.

Single-Zone Stack-Dominated Infiltration Modeling

Simplified, physical models for calculating infiltration in a single zone, usually calculate the air flows from the natural driving forces separately and then combine them. For most purposes -- especially minimum ventilation or energy considerations -- the stack effect dominates and total ventilation can be calculated by treating other effects (i.e., wind and small fans) as perturbations, using superposition techniques. The stack effect is caused by differences in density between indoor and outdoor air, normally attributable to the indoor-outdoor temperature difference. This report derives an exact, but practical, expression for calculating the stack effect from the air densities and leakage distribution using the power law formulation of envelope leakage. The neutral height -- the height at which there is no stack-related indoor-outdoor pressure difference -- is a key intermediate in stack modeling. This report defines a computable parameter called stack height, which contains all of the leakage distribution information necessary for estimating stack flows, thus freeing the model from specific assumptions (e.g., that the leakage is separable into evenly distributed floor, wall, and ceiling components). Example calculations including comparisons with other models, as well as validations using measured data from dwellings, are also presented. The dimensionless neutral level, which ismore » related to the neutral height, is often used as an indicator of leakage distribution and in superposition. Its definition and role in these regards are discussed in detail. The more exact formulation is then used to analyze the simple box cases normally assumed in infiltration modeling and other approximations. Measured ventilation data will be used to infer leakage distributions and neutral levels as well as for example calculations.« less