The last five years have seen a steady increase in the rate of adoption of chilled beams in the United States, as designers and facility owners have become more aware of the many benefits this energy-efficient technology, popular in Europe, provides: improved indoor-air quality, low operating costs, thermal comfort, flexibility in unit design, ability to deliver multiple services with a single unit, low operating noise, adaptability where floor-to-slab height is minimal, reduced (by as much as 40 percent) outside-air-handler and ductwork size, and elimination of reheat, among others.

How Chilled Beams Work

Chilled beams, also known as induction diffusers, are fundamentally different than the all-air diffusers used in most U.S. buildings. There are two basic types: active and passive.

An active chilled beam receives outside air from an air-handling unit (AHU) and cold or hot water through a piping system with integral cooling coils. Primary airflow is introduced through small air jets built into the beam. These jets induce room airflow through the beam's coil (Figure 1). The induction process produces a forced-convection heat transfer with the coil.

A passive chilled beam relies on a room's natural convection and has no direct air supply. Warm room air rises to the beam's coil, which cools the air, causing it to fall into the occupied zone (Figure 2). Passive beams are best suited to cooling-only applications with low ventilation air requirements.

This article focuses on active chilled beams, referred to from this point simply as chilled beams.

In properly designed environments, chilled beams provide sensible cooling only, while a central air-handling system provides ventilation and latent cooling. In this way, cooling is “decoupled” from ventilation. The ventilation air handler is set up as a 100-percent-outside-air unit that does not recirculate air. This commonly is referred to as a dedicated outside-air system (DOAS). A DOAS provides better air quality than a variable-air-volume (VAV) system and requires significantly smaller ducting and air handlers.

Chilled-water temperature and humidity level are critical considerations when designing with chilled beams. Chilled beams do not condense water when designed with warmer (55°F to 60°F) chilled water. Higher chilled-water temperatures open the door to more efficient chiller operation and longer hours of water-side economizing.

Design Practices

Chilled beams available in the United States generally have a 3:1 induction (room air to ventilation, or primary, air) ratio, are capable of 100 to 200 cfm of primary air per 6 ft of beam, and provide from 4,000 btuh to 8,000 btuh of sensible cooling per 6 ft of beam. Airflow, cooling, and sound performance vary considerably by manufacturer.

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