Using chilled beams for lab ventilation to maximize energy efficiency

Chilled beam insights

• The Loyola Marymount University Life Sciences Building showcases the successful integration of chilled beam systems to meet stringent laboratory ventilation requirements.
• Effective chilled beam design in laboratories hinges on meticulous planning, including detailed equipment heat release information and room air balance checks.

There has been an all-time high demand for life sciences laboratory space post-pandemic, compared to a low demand for office space as people shift to work-from-home schedules. Office to lab conversion have, therefore, become a popular choice, but this is not easy to accomplish. Office spaces require substantial upgrades to accommodate lab-specific needs for safety, space, environmental controls and system infrastructure.

The main challenge when using existing systems when converting offices to labs is the increased ventilation requirements in laboratory buildings. The Loyola Marymount University (LMU) life sciences building demonstrates how chilled beams can reduce the overall-air system capacity and help convert an office space to a laboratory.

LMU life sciences building

The building, completed in 2015, has three underground basement parking levels with 272 vehicle spaces, and a three-story aboveground building of 110,000 square feet. The life sciences building, which is for biology, chemistry and natural sciences, contains teaching laboratories, lab support space, faculty offices, classrooms, shared public spaces and a 280-seat auditorium for the entire campus. There are also holding rooms and a vivarium in the basement.

Figure 1: This diagram demonstrates the mechanisms of an active chilled beam. Courtesy: Stantec

Sustainability was an important factor in the design and construction of this building, and it was awarded a U.S. Green Building Council LEED Gold Certificate in November 2015.

This life sciences building, with 114 variable air volume fume hoods, has been served by six air handling units (AHUs), four laboratory exhaust fans manifold in a laboratory exhaust plenum on the roof, 226 chilled beams and 45 radiance panels. The mechanical system design uses active chilled beams in the lab rooms, radiance panels in the office areas and a displacement system in the auditorium to meet sustainability considerations.

Codes and standards regulating lab design

Laboratories normally use far more energy than office buildings because of the intensive ventilation requirement that addresses the unique environmental, health and safety concerns.

Ventilation-related energy use for laboratory buildings accounts for almost half of their total energy use. Reducing ventilation requirements in laboratories offers opportunities for energy conservation.

Ventilation design of laboratories should generally be based on performance data to address the specific requirements of a given lab space. Minimum ventilation rates should be established on a room-by-room basis and should consider the hazard level of materials expected to be used in the room depending on the intended operations and procedures. As the operation, materials and hazard level of a room change, an increase or decrease in the minimum ventilation rate should be evaluated.

In the United States, the only prescriptive requirements for ventilation rates in a chemistry laboratory are the educational laboratory ventilation requirements specified in ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality and laboratories in healthcare facility in ASHRAE Standard 170: Ventilation in Health Care Facilities . Beyond the prescriptive air change per hour (ACH) rate, codes and standards provide some guidance on air change rates for labs. Table 1 is a summary of codes and standards recommendations for laboratory ventilation.

Table 1: Laboratory ventilation rate in codes and standards Air Change Rate in Laboratory, courtesy: Stantec

All-air versus hybrid systems

Air cooling and heating systems can be classified in 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. All-air systems use air to satisfy both the ventilation requirement and the building cooling and heating loads.

In general, this system has a central AHU that delivers enough cool or warm air to meet the building loads. Diffusers mounted in the space or room deliver this air in a way that promotes comfort and evenly distributes the air.

On the other hand, hybrid systems combine an air-side ventilation system and hydronic water-side system. The air-side system (typically a 100% outside air system) is designed to meet the ventilation requirements for the building as well as satisfy the latent load. The water-side system is designed to meet the sensible cooling and heating loads. 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.

An active chilled beam is a hybrid system that is fundamentally different from the conventional all-air system. The hydronic system is integrated with primary ventilation and uses air pretreated from the AHU to satisfy the ventilation requirement. It then uses water to handle the space’s sensible load, such as sensible heat from the building envelope, lighting or equipment loads.

Chilled beams, however, are not necessarily appropriate for all type of spaces, including ones with many fume hoods or with high occupancy density/high latent load.

Example of chilled beam use

The scenario: A single interior office, 150 square feet with one person occupying it. An AHU will deliver 53.1°F dry bulb and 53.0°F wet bulb air to the space to maintain 74°F and 55% relative humidity.

The above example demonstrates that by using a chilled beam system, the air delivered to the space can be reduced from 67.8 cubic feet per minute (cfm) to 22 cfm to satisfy the latent load and the ventilation requirement. This reduction of ventilation airflow will significantly decrease the fan power and improve efficiency of the heating, ventilation and air conditioning (HVAC) system.

With the sensible load increase — the building envelope load and the room equipment load increase — the use of a chilled beam system will further increase the energy efficiency.

The first step to using a chilled beam in a laboratory is to identify the driving force of a lab ventilation system. There are two types of laboratory spaces for mechanical design: air- or cooling-driven spaces.

Air-driven spaces are normally rooms with a lot of fume hoods. As the result, a significant amount of makeup air is required to satisfy the exhaust requirements and to maintain the room at a correct negative pressure.

Cooling-driven spaces are normally the rooms with a lot of sensible loads, like equipment load, lighting load and people load, but with few to no fume hoods. Table 2 is an example of how to identify spaces as air- or cooling-driven. As seen in the table, air-driven room chilled beams cannot provide any energy saving.

Table 2: Identifying a room as air-driven or cooling-driven Identify driving force of a room. Courtesy: Stantec

Chilled beam system design in laboratories

The first and most fundamental step of a lab design is to obtain a scrutinized list of the equipment used in the laboratory with a detailed heat release information. Identify the equipment that runs continuously or that generates a substantial amount of heat at intermittent times.

If the cooling system isn’t adequately sized, not only will the space be uncomfortable, but there will also be a negative impact on the life and maintenance of the lab equipment. Working with the lab users and understanding the equipment used in the lab space is necessary to mechanical system design in labs.

If the heat gain information cannot be provided by the equipment manufacturer, ASHRAE provides guidance on heat load calculations for some common lab equipment. The mechanical engineer should carefully estimate the equipment load to ensure proper cooling is provided. Table 3 is part of the equipment load table for the LMU life sciences building.

Table 3: An example of a lab equipment heat release for Loyola Marymount University’s Life Sciences Building Lab Heat Release Example. Courtesy: Stantec

On the other hand, equipment used in laboratories normally generates a significant amount of heat, which the HVAC system needs to get rid of to maintain the comfort level. Improper design can have detrimental impact on lab function and safety, as well as energy use of the building.

HVAC considerations

Chilled beam systems are prevalent in commercial office buildings, but not widely used in laboratories. The main concerns are that chilled beams systems may not be able to satisfy the intensive ventilation requirement of laboratories.

In addition, the mechanisms of chilled beam air distribution may have a risk of inducing contaminant air and recirculating it back into the space. The engineer needs to be careful when designing chilled beam layout so that air flow is away from fume hood and will be perpendicular to the fume hood opening.

Critical considerations in chilled beam design in laboratory are:

• Obtaining a scrutinized equipment list of the lab rooms so the cooling load can be accurately estimated.

• Chilled water temperature to the chilled beam is generally higher than conventional chilled water temperature at around 60°F.

• Dewpoint temperature needs to be monitored to prevent condensate.

• Chilled beams need to be kept away from the fume hood.

• Layout of a chilled beam should be perpendicular to the fume hood to minimize the risk of inducing room air near the fume hood back to the room.

Once mechanical system layout has been completed, all laboratory room air balancing should be checked to ensure the space pressure relationship is correct (see Table 4).

Table 4: A laboratory room air balance and pressure relationship Lab Room Air Balance Table Example. Courtesy: Stantec

The LMU life sciences building mechanical system design has demonstrated that use of a chilled beam in laboratories is possible and can achieve energy conservation as long as it’s designed carefully.

The steps of design chilled beam system in laboratory can be:

• Obtain the equipment list and heat release information. This can be done with a performance trace calculation.

• Check lab exhaust requirements. A chilled beam is not feasible when the offset of the supply air to maintain negative pressure is greater than the supply air, as calculated by simulation software.

• Select chilled beams. Chilled beams will have constant air flow and obtain the cooling capacity of the chilled beams. There are two portions of chilled beam cooling capacity, air system and water systems.

• Use variable supply air to maintain the room at 6 ACH during occupied time and 4 ACH during unoccupied time.

• Check the space latent load. If the airflow from the chilled beams plus supply air cannot satisfy the space latent load, either reduce the moisture of supply air from the AHU, or increase the supply air until the latent load is satisfied. Be careful when reducing the moisture of supply air from the AHU. Reduction of the moisture in the supply air will reduce the dewpoint temperature. Select a chilled water temperature above the dewpoint temperature.

• Produce a room air balance table to ensure that either during the occupied time or unoccupied time, the space will always maintain a negative pressure with the adjacent clean space. The offset between supply and exhaust will be minimum 150 cfm per single swing door. At the same time, be careful not to over pressurize the room to avoid door open issue.

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