Like radiant heating and cooling system, active and passive beam system use water as well as air to transport energy throughout the building. Like radiant and cooling systems, they offer saving in energy, space and maintenance costs. Unlike radiant heating and cooling systems, however, these technology deliver the majority of their cooling and heating through convection, often leading to a fully mixed environment. This chapter introduces active and passive beam system and their design considerations, and addresses the unique requirements of some of the most common application.

Management of heat load can generally be classified into two different types: all air systems or hybrid systems. All air systems have been the most prominent and have been in use since the advent of air-conditioning. These system use air to service both ventilation requirement as well as the building cooling loads. In general, these systems have a central air handling unit that delivers enough cool and warm air to satisfy building load. Diffusers mounted in the zone deliver this air in such a way as to promote comfort and evenly distribute the air. In many cases, the amount of air required to cool or warm space or the fluctuations of load make designing in accordance to these principles difficult.

Hybrid systems combine an air-side ventilation system and a hydronic (or water-side) system. The air- side system is designed to meet all of the ventilation requirements for the building as well as satisfy the latent loads. It is typically a 100% outside air system and because the primary function of the supply air system is ventilation and dehumidification as opposed to sensible cooling it can be supplied at higher supply air temperature than is typical of traditional mixing air distribution system. The water side system is designed to meet the balance of the sensible cooling and heating loads. These loads are handled by water-based products, such as active and passive beams, which transfer heat to the zone by induction.

Active and passive beam systems provide an effective method for providing heating or cooling to a space while promoting a high level of occupant comfort and energy efficiency. There are two distinct system design philosophies that are considered when applying hydronic heating and /or cooling:-

• Hydronic heating or cooling where the hydronic systems are integrated with the primary ventilation system. These are active beam    systems (figure 1)
• Hybrid heating or cooling system where water- based devices is used in conjunction with a scaled-down ventilation system, and    manages the bulk of the sensible cooling load. These systems generally use passive beams (figure 2)

There are many benefits to heating and cooling using active or passive beams. Advantages of water-based heating and cooling systems over other mechanical systems include:

The heat transfer capacity of water allows for a reduction in the energy used to transport an equivalent amount of heat as an all-air system. These reductions can be found primarily through reduced fan energy.
The higher chilled water supply temperature used with active and passive beam system, typically around 58o F (14o C), provide many opportunities for a reduction in energy use, including increased water side economizer use. This increased CHWS temperature also allows for more wet-side economizer hours than would be possible with other systems where CHWS temperature is typically ~ 45o F [7oC].

Depending upon application, under maximum load, only~ 15 to 40 % of the cooling air flow in a typical space is outdoor air required by code to satisfy the ventilation requirements. The balance of the supply air flow is recirculated air which, when not treated, can transport pollutants through the building. Active and passive beam system transfer heat directly to / from the zone are often used with a 100% outdoor air system that exhaust polluted air directly to the outside, reducing the opportunity for VOCs and illness to travel between air distribution zones.

The induction of room air, rather than the supply of recirculated air results in more consistent room air temperature and lower room air velocity, thereby increasing occupant comfort.

The reduced supply air volume of a hydronic system reduces ductwork requirements, resulting in the ability to reduce plenum heights. This allows beam systems to be installed in tight spaces, and creates the potential for lower construction costs, higher ceilings, and more usable floor space. In addition, the air handling equipment may be able to be downsized – saving cost and potentially allowing it to be moved indoors.

Due to the reduction in moving parts and mechanical equipment associated with beams, these systems typically have lower maintenance costs than all-air systems.

With the elimination of the majority of filters and drain pans, there is a reduction risk of mold or bacteria growth in the mechanical system.