Abstract
A common envelope performance problem in buildings is thermal bridging through balcony slab connections, which can be improved with the use of commercially available thermal break products. Several prior studies have used simulation-based and/or hot box test apparatus approaches to quantify the likely effect of balcony thermal breaks on effective thermal resistance of building enclosures. However, in-situ measurements of thermal performance in real buildings remain limited to date. This study uses a combination of field measurements and models to investigate the effects of installing balcony thermal breaks on the interior surface temperatures, effective thermal resistance, and annual building energy consumption. For the field experiment, yearlong measurements were conducted on the 13th floor of a 14-story multi-family building in Chicago, IL, in which thermocouple sensors were embedded into eight balconies and their adjacent interior floor slabs just before concrete was poured to complete the construction. The eight balconies included four control balconies without thermal breaks and four thermally-broken balconies with a commercially available thermal break product installed. The experimental data were then combined with 2-D heat transfer modeling and whole building energy simulations to investigate the impacts of the thermal break product installation on the envelope thermal resistance and overall energy use in the case study building as well as in several more generic building designs with simpler geometries. The results demonstrate that although the balcony thermal breaks helped regulate interior slab temperatures and improved the effective thermal resistance of the curtain wall enclosure assembly by an estimated ~14% in the case study building, the predicted effect on annual energy consumption in all modeled building types was small (i.e., less than 2%). The results also highlight the importance of paying careful attention to envelope design details when using thermal break products and considering the use of thermal break products in combination with other energy efficiency strategies to achieve high performance enclosures.
Highlights
IntroductionA very common thermal bridge in the building envelope of mid- and high-rise residential buildings occurs at the balcony slab connection [1,2]
One of the most prevalent envelope performance problems in buildings is thermal bridging.A very common thermal bridge in the building envelope of mid- and high-rise residential buildings occurs at the balcony slab connection [1,2]
The effective resistance of the thermal break product in this installation can be calculated as the difference between the resistances of the control and thermally broken slabs, which results in an average value of 0.12
Summary
A very common thermal bridge in the building envelope of mid- and high-rise residential buildings occurs at the balcony slab connection [1,2] These balcony slab connections are commonly not thermally broken, which can lead to poor building thermal performance and increased energy consumption due to increased heat loss in winter and heat gain in summer [3,4,5,6]. Another problem with balcony slab connections is that cold indoor floor slab surfaces at the building perimeter can contribute to occupant thermal discomfort in winter. The insulation materials typically include extruded polystyrene, expanded polystyrene, or mineral wool, all of which have similar levels of thermal conductivity (i.e., 0.025–0.040 W/m·K) [8]
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