TRACE 700 incorporates two chilled beam strategies: passive and active. Passive chilled beams consist of a fin-and-tube cooling coil, contained in a housing (or casing), suspended from the ceiling. Chilled water passes through the tubes. Warm air from the space rises toward the ceiling, and the air around the chilled beam is cooled, causing it to descend back toward the floor. It essentially cools the space through convection. Passive chilled beams are used for sensible cooling only (no latent cooling, no dehumidification). A building with passive chilled beams requires a separate mechanical ventilation system to deliver the required amount of ventilation air to each space and deliver that air dry enough (at a low dew point) to offset the space latent loads and maintain the indoor dew point low enough to avoid condensation on the chilled beams. Figure 4 18 Passive chilled beam Active chilled beams also consist of a fin-and-tube cooling coil, contained in a housing, suspended from or recessed into the ceiling. Active chilled beams are also used for sensible cooling only (no latent cooling, no dehumidification). Active chilled beams 4 79
differ from passive chilled beams because they have an integral air supply. This primary air passes through nozzles at a high velocity. As a result, air is induced from the space through the cooling coil. Because of the induction process, active chilled beams provide more cooling capacity than a same-sized passive chilled beam. By definition, active chilled beams are combined with a separate primary air system that 1) delivers the required amount of ventilation air to each space, 2) delivers the air dry enough (at a low dew point) to offset the space latent loads and maintain the indoor dew point low enough to avoid condensation on the chilled beams, and 3) delivers enough primary air to induce sufficient room airflow to offset the space sensible cooling loads. Although active chilled beam systems include the ability to provide some heat ing, cooler climates may necessitate additional heating systems (e.g., baseboard heating). Figure 4 19 Active chilled beam primary air ceiling coil induced air Application considerations Chilled beam systems require smaller ductwork, air handlers, and fans than a comparable VAV system. However, energy use depends on climate, operating hours, and building use. Chiller plant arrangement may also play a role in energy use. To avoid condensation, chilled beams must be supplied with warmer-than-normal chilled water temperatures. When coupling chilled beams with a traditional air handler for the primary air 4 80 TRACE 700 User s Manual CDS-PRM001-EN
system, designers may choose a dedicated chiller arrangement (one plant delivering very cold water to the primary air handlers and a separate plant delivering warmer chilled water to the chilled beams) or a shared plant serving both chilled beams and air handlers. Consider the advantages and disadvantages of both options when determining your plant configuration. Due to the potential for condensation, special consideration should be given to the geographic region where chilled beams are employed. Sample scenario An active chilled beam system satisfies the ventilation and cooling requirements for an office building. Supplemental heating in the form of radiant floor heating will be included to satisfy any heating requirement the primary air system is unable to handle. To model each active chilled beam: 1 Create an airside system and define it as Active Chilled Beam. Active chilled beams are zone level coils. 4 81
2 Click the Options tab and click Advanced Options. 3 Select the control method. Also, ensure the Type reads Active Chilled Beams. 4 Select the Auxiliary heating coil type. Note: Unlike other systems, Cooling supply and Leaving cooling coil temperatures (found under the Temp/Humidity tab) entered by the user will be ignored for both passive and active chilled beam systems. TRACE 700 calculates the supply temperature based on the upper limit of the room dew point plus a safety margin. 5 On the Fans tab, choose a fan type for the primary air handler fan. 6 Enter a static pressure for the primary air handler. 4 82 TRACE 700 User s Manual CDS-PRM001-EN
7 Use water-cooled chiller and boiler to begin defining the cooling and heating plants for the air handler. Rename the cooling plant to Air Handler and heating plant to Air Handler Heat. 8 Use the water-cooled chiller and boiler to begin defining the cooling and heating plants for the air handler. Rename the cooling plant to Chilled Beam and heating plant to Radiant Floor. Note: Two chiller plants and two heating plants were created. This models a dedicated chiller arrangement. One chiller provides chilled water to the chilled beams, while the other chiller provides chilled water to the main cooling coil in the primary air handler. One boiler provides water to the main and preheat coils found in the primary air handler. The other boiler provides water for the radiant floor. 4 83