ENGINEERING BULLETIN

Overview of Chilled Beam Technology

Purpose

Chilled beam technology is new to the United States but has been used in Europe since the 1950’s. Chilled beams can reduce energy costs, improve indoor air quality, and provide an alternative for climate control in retrofit projects. The purpose of this engineering bulletin is to provide the fundamentals of design, installation, operation, and costs for chilled beams so that future projects can be evaluated for their potential use.

Summary

Chilled beams, also called induction diffusers, have been used mostly in office buildings but also have been used in academic, retail, laboratory, and healthcare buildings. Chilled beams can be configured to provide sensible cooling and heating.

Chilled beams are standalone components typically hung at the ceiling level from the building structure. Chilled beams are essentially coils, built of copper tubing and aluminum fins, and housed in decorative sheet metal enclosures. If desired, chilled beams can be equipped with lighting, occupancy sensors, daylight sensors, smoke detectors, public announcement speakers, sprinkler head openings, and connections for power, data, and voice. Piping specialties such as valves and hydronic controls can be also included as part of the chilled beam packages. They can be mounted exposed or as part of a suspended ceiling.

Theory

Chilled beams involve placing cooling coils at the ceiling level to cool the rising warm air. The cooled air then gently descends to occupant level, providing a pleasant cooling effect with minimal air movement. The sensible cooling is the result of conduction, convection, and radiation.

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System Types

Passive systems rely entirely on the natural convection process where warm air rises to the coils, is cooled, and then falls back down freely without use of fans.

Active systems connect to the room’s primary air supply ducts, mixing supply air with room air that is cooled by the coils. Primary airflow through the beam is typically constant and set at the minimum ventilation rate for the space. As the primary air is provided to the beam, room air is induced to the coil for higher cooling and heating capacities with air induction ratios of 1:1 to 5:1.

Advantages/ Disadvantages

Some advantages to the chilled beam technology include:

• Multi-purpose chilled beam units can include light fixtures, sprinklers, and other non-HVAC components. • High indoor air quality resulting from air recirculated within the zone versus mixed air from other zones. • Space savings resulting from reduced ductwork size. Floor- to- floor heights, shaft areas, and mechanical room spaces can be reduced. Reductions of 6 to 18 inches in floor heights are possible. • More uniform space temperatures and velocity distributions. • Lower maintenance costs and higher life expectancies resulting from no moving parts. • Integration of other economizer technologies such as geothermal. • Chilled beams can be used for retrofit projects where space is limited, the existing structure restricts equipment and ductwork, and risers are limited for fresh air. • Chilled beams can add 8 to 10 points to a LEED project score. • Chilled beams can provide more effective ventilation and possibly reduce outside air requirements by 20% per ASHRAE 62.

Some disadvantages to the chilled beam technology include:

• Chilled beams require more ceiling area than diffusers of a conventional system, thus leaving less room for lights and sprinklers. This can impact the aesthetics of the interior spaces and require a higher level of coordination for other systems such as lighting, ceiling grid, and fire protection. • Chilled beam technology is new to the United States and most mechanical contractors are not familiar with it. Therefore, they may charge more or not take on the project at all. • Chilled beams are currently manufactured outside the United States. Drawings, performance information, and documentation typically use metric units. • Recirculated air passing through an active beam is not filtered as it would be in a variable- air- volume system.

Limitations

Chilled beams should not be used in areas with high latent loads. A dry atmosphere is very important to prevent condensation from forming on the surfaces of the chilled beams. Areas such as conference rooms, meeting rooms, class rooms, restaurants, or theaters with dense populations are typically not conditioned with chilled beams. Portions of the building that are open to the outside are not conditioned with chilled beams. Also, the building envelope should be very tight construction for humid climates.

Buildings that can be naturally ventilated need to include sensors to measure dew point in the space and/or window position switches that automatically raise chilled water temperatures or shut down flows to the beams when high dew points are reached.

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Design Guides

Every application for chilled beams must be specifically engineered and include the manufacturer’s recommendations for design, installation, and operation. In general, the following guidelines apply to the design of chilled beams.

• Chilled beams provide sensible cooling only. Ventilation and dehumidification must be handled separately. Typically, a dedicated outdoor air system is used to provide the minimum ventilation and to handle latent loads.

• Room humidity should be controlled below 50° to 55° F wet bulb or 50 to 55% relative humidity at 72° F dry bulb.

• Chilled beams can be installed in areas with ceiling heights between 9 to 12 ft. Minimum spacing for beams is 6 ft for passive designs and 10 ft for active designs. Beams must be independently hung due to their size and weight. Main structural elements of the ceiling grid must run parallel with the chilled beams. Chilled beams require sufficient space above, to the sides, and below to ensure proper air flow. Typical clearances are based on percentage of coil width and are 50% coil width to the sides, 40% coil width above, and 3 inches below to ceiling for passive chilled beams.

• Maximum passive beam cooling capacities are 400 btu/h per ft of beam or 50 to 80 btu/h per sq.ft. of floor area. Maximum active beam cooling capacities are 600 btu/h per ft of beam or 80 to 110 btu/h per sq.ft. of floor area. Conservative cooling design capacities of 20 to 25 btu/h per sq.ft. of floor area (or 500 to 600 sq.ft. per ton) are typically used. Chilled beam capacities are based on air density at sea level and require capacity corrections (e.g.- 4% reduction at 1000 ft) at higher elevations. Chilled beam performance is also corrected for the difference between the water and the room air temperature. Ratings are based on 19° F difference with corrections made for higher differences (ie – 20° F / 1.05 correction) and lower differences (e.g.- 14° F / 0.74 correction). Corrections are manufacturer and model specific.

• Primary air to active chilled beams are typically 54° F db / 52° F wb (90% humidity). Typical room design temperature is 75° to 78° F. Capacities for chilled beams are therefore based on the temperature difference between the room and the primary air, with 21 F° as typical. Corrections for chilled beam capacities are made for higher differences (eg-24 F° / 1.14 correction) and lower differences (e.g. – 19 F° / 0.90 correction). Corrections are manufacturer and model specific.

• Chilled beam heating capacities are limited to 8 btu/h to 16 btu/h per sq. ft. of floor area. For heating applications, active beams provide more efficient heating than passive beams due to the ducted ventilation air.

• Passive chilled beams can be placed parallel to exterior perimeter walls to handle solar gains. These beams have high velocities just below the beams and therefore should not be placed directly above work areas. The capacity of passive beams can be reduced by high heat loads directly below the beams (ie- copy machines).

• Passive beams located in suspended ceilings require perforated ceilings with 50% minimum free area. This makes the building structure and services above the ceiling partially visible. Therefore, black paint is often used to mask these areas.

• Active beams induce warm room air at the center of the beams, then discharge conditioned air laterally across the top of the room. Therefore, active beams can be placed directly over work areas and high convective loads (e.g., copy machines).

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• High air flow rates to active chilled beams should be avoided to minimize the noise of the induction nozzles. High flows are avoided by using an adequate number of chilled beams to reduce the required flow per beam.

• The induction nozzles of chilled beams typically have a static pressure drop of 0.5 inch of water or less.

• To generate the warmer chilled water temperatures required by chilled beams, the typical 45 degrees F chilled water from a chiller can first be sent to a dedicated outside air unit then the return water from this unit can be supplied to the chilled beams.

• Water supply to the beams normally ranges from 59° to 65° F, or 3 to 4° F above the room dew point. Water temperature rise across the beams are typically 7° F. Therefore, return water from chilled beams can be as high as 70° F. Passive beams generally require higher temperatures (57° F entering water temperature / 63° F leaving water temperature) versus active beams (55°F entering water temperature / 61° F leaving water temperature). Typical water flow rates range from 0.5 to 1.5 gpm for each beam depending on type and capacity. Typical water pressure drops are 10 to 20 ft water for each beam.

• During cool weather, the ventilation system can be operated without the need for chilled water and primary air sent directly to the active chilled beams. Alternatively, chilled water can be routed to the outdoor air system unit to pre-heat the outdoor air during the winter and obtain free cooling for the chilled beams. As the outdoor air temperatures rise, free cooling can be obtained by coupling the chilled beam water loop with cooling tower water or ground water through a waterside economizer.

• Ductwork to the active chilled beams need to be sized only for the amount of fresh air required for the building. The fresh air can be controlled and delivered as the space requires. The ventilation can therefore be constant or variable volume, high or low pressure, and distributed to both active beams and diffusers. Typically, the primary airflows to the active chilled beams range from 25 to 200 cfm each.

• Radiant heating often accompanies chilled beam cooling since radiant heating requires lower water temperatures and high efficient condensing boilers can be used.

• Passive chilled beams can be combined with underfloor air distribution systems to provide a more even air distribution between floor to ceiling. Cooling and heating airflows can be reduced to 0.5 to 0.8 cfm per sq. ft.

• Air patterns from conventional diffusers should not interfere with the natural air patterns of the chilled beams.

System Components

Chilled beam installations include the beams, piping, pumps, ductwork, controls, and air handlers. The specifics for each of these components are briefly presented.

Chilled Beams

• Chilled beams can be configured as two- way with airflow discharge from both sides for beams located within a room or one-way with airflow discharge from one side for beams located at the perimeter of a room. Typical chilled beam dimensions are 24” wide by 120” long.

• Beam casings are generally constructed of galvanized steel or aluminum with trim kits available for drywall/plaster or T-bar lay-in ceilings. Aluminum is preferred over galvanized. Casings can be custom ordered by shape, size, and color.

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• Unless the chilled beams have integrated services or controls (e.g., lighting or communications), the beams require no electrical connections.

• Some chilled beam designs include drip pans for secondary containment of condensate.

• Passive chilled beams can be configured with flexible skirts along the outside lengths of the beams to increase stack effect and efficiency of the beam.

Piping and Pumps

• The typical water piping includes the primary chilled water loop coupled to a closed secondary chilled beam water loop through a heat exchanger. The secondary loop can be variable volume with a speed controller on the secondary loop pump, or a constant volume with three way or two way valves. Often, a buffer vessel is installed in the primary loop to minimize chiller cycling. Secondary loop pressures are similar to chilled water systems at 50 to 100 psi range. An alterative is to use separate chillers for the outside air unit and the beams since the operating temperatures are different.

• Chilled beams providing both heating and cooling can be configured for two pipe or four pipe systems and can be piped in a combination of series and parallel arrangements as needed.

• Metallic distribution piping to and from the chilled beams should be insulated but do not need a vapor barrier. An alternative is to use heavy walled plastic piping without insulation.

• Each beam is typically connected with flexible hoses and include isolating, balancing, and control valves. Typical pipe connections on the chilled beams are ½” in size with threaded or compression fittings.

• Chilled beam water mains are routed above the chilled beams with automatic vents on the mains only.

• Chilled beam water should be filtered, have a pH range of 6 to 9, and not contain any inhibitors.

Controls

• The controls associated with chilled beams depend on whether they provide heating and/or cooling, are passive or active, where they are located, how they are zoned, what level of safety is desired to protect against condensation, and what other energy saving technologies are to be implemented.

• Regardless of the control type, it is important to establish the relationship between the space temperature and humidity, and the chilled water supply temperature to the beam to prevent condensation on the chilled beams. Three- way valves are commonly used to blend the beam supply water temperature to its design temperature. If the space humidity in the area served by the chilled beams approaches the supply water temperature, the supply water temperature is reset higher. Multiple redundant sensors may be used. Components should be designed to a fail- safe (non-condensing) condition.

• Chilled beam capacity is controlled by regulating or isolating water flow through the beams. Control valves for each beam can be installed for individual control, or for a bank of several beams for larger areas. Controls can be integral to the chilled beams or remotely installed in the system piping. Controls can be self powered or electric with a variety of communications capabilities.

• Chilled beams can be part of a constant volume primary air system or a variable volume air system. In either case, chilled beams are often turned on after the dedicated outdoor air supply unit has been activated and has control over the space humidity. This may require both a cooling coil and reheat coil in the dedicated outdoor air supply unit.

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Ductwork • Primary air duct connections on active chilled beams typically range from four inch to eight inch round. Connections to building ductwork are usually made with straight duct or flexible duct.

Air Handlers

• The primary air supplied to the active chilled water beams needs to be controlled for temperature and humidity using cooling and heating coils. As previously mentioned, the volume of air is generally determined by the minimum fresh air required for the occupied spaces. The air provided to the active chilled water beams also needs to be filtered.

Manufacturers

Several companies manufacture chilled beams, including Trox Technik, Halton, Frenger, Flakt Woods, and Dadanco. Dadanaco appears to be the only company with manufacturing capabilities in the United States. These companies also manufacture other HVAC components and air devices.

Costs

The introduction of chilled beam technology to the United States has been driven mostly by the potential energy cost savings promised by this technology. As a result, each manufacturer provides their own case studies for installations demonstrating the cost benefits to this technology. Since every system is different, projections for savings vary widely. Therefore, when considering this technology for future applications, the total cost of ownership needs to be evaluated and include the costs of engineering, procurement, construction, operation, and maintenance.

• Engineering - Engineering costs might be slightly higher for designing chilled beam systems versus VAV systems until engineering is more familiar with the new technology.

• Procurement - Chilled beams require warmer chilled water which results in smaller chiller compressors. Lower purchase cost per ton and lower electrical support requirements are the result. Chilled beams are typically imported and custom ordered which results in longer deliveries and higher costs. In the next few years, chilled beams will be manufactured in North America resulting in improved deliveries and costs. Currently U.S. representatives do not use standard list pricing for chilled beams but quote every order separately due to exchange rates and availability. Passive beam budget pricing ranges 100 to 120 $/ft compared to 120 to 150 $/ft for active beams. An additional 100 to 200 $/ft covers the optional multi- services (ie- lighting, speakers, etc). Custom colors and shapes for aesthetics cost an additional 5% or more.

• Construction - Chilled beam systems may require up to 50% less ductwork than conventional systems. Reductions in air changes allow for reductions up to 40% for air handling units, exhaust fans, chillers, and boilers. Active chilled beam installations can cost less than standard VAV systems by as much as 15%. Budget costs on a sq.ft. basis for chilled beam installations have not been established.

• Operation - Potential energy reductions are estimated at 20 to 50% depending on the type of system, climate, and building. Climates with the highest outside air latent loads tend to have the highest savings potential but also the greatest risk of condensation. Once study showed a 35% reduction in energy for an active chilled beam system for a 93 db / 75 wb location versus a 25% reduction for a 80 db / 74 wb location in comparison with a VAV design. Savings depend also on the minimum ventilation rates, daily loads, and cooling system turndown efficiency. Since savings are primarily electric, areas with high electric rates or charge peak demand rates are good candidates for chilled beams. Savings result from reduced fan energy and minimization of reheat to achieve comfort. Estimated annual HVAC energy costs per sq. ft. for active beams run $ 0.90, and $ 0.74 for passive beams compared to $1.50 for VAV systems.

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• Maintenance - Chilled beams require vacuuming every one to three years. Chilled beams contain no motors, fans, filters, condensate pumps, condensate drawings, consumable parts, or moving parts that require additional maintenance.

• One study stated estimated life cycle costs (NPV) per sq. ft. for chilled beams are approximately $ 68 versus $ 118 for VAV systems.

Energy Modeling

In order to substantiate the energy savings cited by the reference publications as shown above, Hixson created two energy models made using Carrier’s Hourly Analysis Program Version 4.34. Both models were based on a single story free-standing office building of 10,000 sq ft on grade, located in Cincinnati, Ohio, and with average construction, lighting, occupancy, equipment, and infiltration loads. The building was divided into 1 interior zone of 3,600 square feet and 4 perimeter zones of 1,600 square feet each.

The first model representing a VAV system included a single air handler of 4,800 cfm supply and 1,400 cfm fresh air capacity with a hot water preheat coil and chilled water cooling coil. The air handler supplied (5) fan powered VAV boxes with hot water reheat. Chilled water was supplied by one 25 ton air cooled screw chiller supplying 44 F water at 1.2 kW/ton full load. Hot water was supplied by one 200 MBH output 80% efficient boiler.

The second model representing a chilled beam system was the same as the VAV model but with the following changes: Reduced air handler’s static from 6” to 4”, removal of fans from the VAV boxes to simulate the beam’s coils, chilled water temperature from 44 F to 55 F, chiller efficiency from 1.2 to 1.14 kW/ton full load, chilled water dT from 10 to 7 degrees F, hot water dT from 20 to 7 degrees F, and boiler efficiency from 80 to 90%. Electric costs of $ 0.10/kWh and gas costs of $1.20/Therm were used for both models.

The energy models resulted in an overall energy savings of 15% for the chilled beams versus a VAV system ( $ 0.79 / sq ft vs. $0.93). Electric costs were reduced by 17% compared with gas at 8%. The largest savings was fan energy at 39% followed by cooling, heating, and pumping (12%, 8%, and 4% respectively). The reduction in fan static pressures, increase in chilled water loop temperature, increase in chiller efficiency, and increase in boiler efficiency contributed to the energy savings as predicted.

Budget mechanical installation costs for the chilled beam system were 22% less than the VAV system ($19.50 versus $ 25.00 per square foot respectively). A life cycle cost analysis over 15 years at 8% discount rate favored the chilled beam system by 20% ($ 32.00 versus $40.00 per square foot respectively) when factoring in repairs, maintenance, and replacements in addition to the energy and installation costs.

Although the installation, energy, and maintenance costs estimates for the Hixson energy model were less than the references stated above, the savings are conservative, real, and indicative of the chilled beam technology. Further cost reductions for other areas such as electrical, structural, and architectural are highly possible and have not been included in the Hixson analysis.

Standards

Currently, chilled beams are currently designed, constructed, and tested to non-U.S. standards such as the V- method [ref National Swedish Institute for Materials Testing in Boras, Sweden (SP)] for heating and cooling capacities, internal environment to comply with the requirements of BE EN ISO 7730 (Moderate Thermal Environments), pressure requirements to comply with the Pressure Equipment Directive 97/23/EC, and noise levels to comply with ISO 7730.

Manufacturers currently rate performance based on a DIN 4715-1 test or Nordtest standard. Specifications should require the DIN test which is more stringent and more conservative.

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Commissioning

Commissioning usually involves adjustment of the primary airflow using the beam’s primary air balancing damper and a separate pitot tube to measure static pressure at the unit’s plenum. Manufacturers provide air flow ratings as a function of pressure for each unit. Water balancing valves for each chilled beam can be manually adjusted as needed.

Examples

The leading manufacturers provide generic descriptions of installations from around the world. In the United States, a few installations are noted as follows:

• Renovation of 17 lecture halls on the campus of a major Massachusetts university.

• 25,000 sq ft Sandhill Research and Education Center at Clemson University.

• 150,000 sq. ft. laboratory for pharmaceutical company in St. Louis.

References

Chill The Ceilings and Achieve Cool Energy Savings, Building Design and Construction, November 2005.

The Chilled-Beam Alternative, Laboratory Design Handbook, November 2006.

Next-Generation Cooling Is Looking Up, Engineered Systems, May 2007.

Chilled Beam Application Guidebook Number 5, REHVA, 2004.

Chilled Beams and Ceilings, Norman Disney & Young, 2004.

Chilled Beams in Labs, ASHRAE Journal, January 2007.

Chilled Beams Presentation, Clint Schwartz, P.E., Controlled Air, Inc.

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