While the design and construction of envelopes for Passive House certified homes in central European climates is well developed and has achieved widespread acceptance and reliability, the same cannot be said in colder climate regions such as the United States’ upper Midwest (DOE climate zones 6 and 7) and Scandinavia. The objective of this research was to study some of the typical building performance issues relating to Passive House envelope construction for single family homes in cold climates by testing and developing a group of 8 envelope options. Typical issues include unfamiliarity with performance of thermal bridge details, added embodied energy and carbon due to increased insulation and structure, and increased risk of moisture damage due to thicker, multi-layered assemblies and smaller drying potentials. The basic envelope types were selected from case studies, then tested and developed to meet set levels of moisture safety, life cycle energy and carbon impacts, and Passive House thermal bridging and energy performance requirements. The envelope options were compared using a number of software tools. Athena life cycle analysis software was used to determine embodied energy, carbon, and environmental impacts of the envelope types. WUFI hygrothermal modeling was used to determine moisture performance and risk relating to mold growth. The EN ISO 6946 2-D U-value calculation protocol was used to investigate the loss of insulation value due to repetitive thermal bridges within a wall or roof assembly, while THERM software was used to determine the performance of a selection of thermal bridge details. Although significant variation was found in the performance of these eight envelope types, all of them were found capable of meeting the energy efficiency and thermal bridging requirements of the Passive House certification in a very cold climate, while maintaining moisture safety, durability, and significant life-cycle energy and carbon savings. These findings demonstrate that even in cold climates, a variety of envelope types can be used successfully for certified Passive Houses.

Abstract

Efficient energy recovery from used air with the goal of reducing energy use is important for realizing low energy houses. Rotary heat exchangers are very energy efficient, but have the drawback of transferring odours from exhaust air to fresh supply air. To avoid this, flat plate heat exchangers are commonly used where odour transfer might cause problems. Nevertheless, these may not properly handle water condensation and frost formation at low outdoor temperatures. The so-called membrane-based energy exchangers are an alternative to the flat plate heat exchanger. In a membrane-based exchanger, moisture is transferred from the humid exhaust air to the dry supply air avoiding condensation at the exhaust airside. In this work, a membrane energy exchanger was compared to a thin non-vapour permeable plastic foil heat exchanger. The study focused on verifying condensation and freezing problems and evaluating the performance of the membrane energy exchanger. The experiments showed that non-permeable heat exchangers have problems with condensation and freezing under test conditions. Under the same conditions, the membrane-based exchanger did not experience the same problems. However, additional problems with swelling of the membrane in high humidity conditions showed that the tested membrane type had drawbacks and needs further development to become commercially applicable.

Abstract

Efficient energy recovery from used air with the goal of reducing energy use is important for realizing low energy houses. Rotary heat exchangers are very energy efficient, but have the drawback of transferring odours from exhaust air to fresh supply air. To avoid this, flat plate heat exchangers are commonly used where odour transfer might cause problems. Nevertheless, these may not properly handle water condensation and frost formation at low outdoor temperatures. The so-called membrane-based energy exchangers are an alternative to the flat plate heat exchanger. In a membrane-based exchanger, moisture is transferred from the humid exhaust air to the dry supply air avoiding condensation at the exhaust airside. In this work, a membrane energy exchanger was compared to a thin non-vapour permeable plastic foil heat exchanger. The study focused on verifying condensation and freezing problems and evaluating the performance of the membrane energy exchanger. The experiments showed that non-permeable heat exchangers have problems with condensation and freezing under test conditions. Under the same conditions, the membrane-based exchanger did not experience the same problems. However, additional problems with swelling of the membrane in high humidity conditions showed that the tested membrane type had drawbacks and needs further development to become commercially applicable.

Abstract

The application perspective of aerogel glazings in energy efficient buildings has been discussed by evaluating their energy efficiency, process economics, and environmental impact. For such a purpose, prototype aerogel glazing units have been assembled by incorporating aerogel granules into the air cavity of corresponding double glazing units, which enables an experimental investigation on their physical properties and a subsequent numerical simulation on their energy performance. The results show that, compared to the double glazing counterparts, aerogel glazings can contribute to about 21% reduction in energy consumptions related to heating, cooling, and lighting; payback time calculations indicate that the return on investment of aerogel glazing is about 4.4 years in a cold climate (Oslo, Norway); moreover, the physical properties and energy performance of aerogel glazings can be controlled by modifying the employed aerogel granules, thus highlighting their potential over other glazing technologies for window retrofitting towards energy efficient buildings. The results also show that aerogel glazings may have a large environmental impact related to the use of silica aerogels with high embodied energies and potential health, safety and environment hazards, indicating the importance of developing guidelines to regulate the use of aerogel glazings.

Abstract

Phase change materials (PCM) have received considerable attention over the last decade for use in latent heat thermal storage (LHTS) systems. PCMs give the ability to store passive solar and other heat gains as latent heat within a specific temperature range, leading to a reduction of energy usage, an increase in thermal comfort by smoothing out temperature fluctuations throughout the day and a reduction and/or shift in peak loads. The interest around PCMs has been growing significantly over the last decade. Hence, several commercial products have arrived on the market with various areas of use in building applications. This study reviews commercial state-of-the-art products found on the market and show some of the potential areas of use for PCMs in building applications. Examples of how PCMs can be integrated into buildings, and furthermore building materials and projects using PCMs that have already been realized, have also been reviewed. There seems to be a scarcity of data published on actual performance in real life applications so far. However, many laboratory and full scale experiments have shown positive results on energy savings. Furthermore, future research opportunities have been explored and challenges with the technology as of today have been discussed.