Thermal

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Qualitative

Intelligent envelope

Sunshade devices

Active systems

The hydronic system

Quantitative

HVAC system

A thermal environment is a term defined as those aspects of a workplace that include the local temperature, humidity, and air velocity as well as the presence of radiating surfaces.

As we can see from the figure, this is the bioclimatic design system of Federal Center South Building 1202. And we can find some aspects of the building of the thermal comfortable design.

Orientation and massing optimize daylight while reducing solar heat gain. The U-shaped form of the office bar creates daylight access on both sides of the floor plate, providing natural light to over 90% of the building to enhance energy performance and human comfort.

Exterior orientation-specific sun-shading elements, clerestory glazing, and internal adjustable window coverings control heat gain and glare while providing uninterrupted views to the outdoors, as well as time of day and weather condition awareness. The ribbon system is design with vertical blades across the entire perimeter.

The system is augmented with horizontal sunshades tuned to the orientation starting with zero on the north and transitioning to one, two and three as the facade transitions around the oxbow from east to south. Peak cooling loads are targeted for a 30% reduction in the perimeter zone, resulting in a 10% reduction in the central plant cooling capacity.

High-efficiency boilers, cooling towers and heat pumps generate the required heating and cooling. The equipment efficiencies are high per current best practice, with the difference being that design integration has resulted in systems substantially smaller than would conventionally be required.

The hydronic system allowed for the efficient integration of ground source heat and the inclusion of a phase change material (PCM) tank for thermal storage. Polyethelene tubing was run into 135 hollow structural steel piles that were driven an average of 160 ft deep through the sandy riverbank soil to find bedrock.

The PCM tank, a large cylindrical tank filled with stacked containers of eutectic salts that change phase at 55°F, acts as a direct source of chilled water for the chilled beams and as a source of heat for the heat recovery chillers to deliver 120°F heating hot water. The PCM tank, in theory, operates similarly to a ground source system, but with a daily, rather than a seasonal, cycle. The PCM system was designed to address typical Seattle days where morning warm-up and afternoon cooling are required. It also helps store cooling generated from economizer cycles that run during the cool summer nights. During the commissioning process, it was discovered that the capacity of the PCM tank was less than promised by the manufacturer.

This was mitigated by changes in controls and greater reliance on the energy piles, which were recharging more rapidly than expected, most likely due to the adjacency to the Duwamish Waterway. The systems are meeting 90% of the building’s heating load with heat recovery chillers sourcing heat from the ground loop, the PCM tank or simultaneous 24/7 cooling loads. The remainder of loads are met with a traditional boiler and the heat recovery chiller acting as a traditional chiller.

The facility is heated and cooled via reversible heat pumps that exchange thermal energy with foundation integrated energy piles. The HVAC delivery system includes a 100% outdoor air ventilation supply, passive chilled ‘sails’, buoyancy-driven return airflow through the atrium and ventilation heat recovery.

During the first quarter of operation the HVAC systems and control strategies were tuned to improve thermal comfort and acoustics in select spaces. Glare concerns were identified and resolved. Opportunities to reduce plug loads, which were significantly higher than design assumptions (50 percent higher during occupied hours, 300 percent higher overnight), were suggested but couldn't be acted upon. After one year of operation the building was tuned from 10 percent over the target in the first quarter to 12 percent below in the fourth quarter.

Hydronic system

Distribution of EUI in Whole year

EUI of final predicted performance