Lab spaces in K-12 schools and especially on university campuses are notorious for consuming a large proportion of the overall energy expenditure in their building portfolios. This is largely because of the necessary safety measures that are taken to maintain a high indoor air quality, combatting hazardous fumes and chemicals. Because of the potential health risks involved, there is a limit to the level of energy efficiency that a lab space can attain. There are a few simple measures, however, that Facility Managers and Commissioning Agents can take to limit their consumption while maintaining comfort and safety standards for their occupants.
Ventilation serves multiple purposes in a lab space. As always, occupant comfort is incredibly important, and proper ventilation is a key component of adequately heated and cooled spaces. In a lab space, optimum temperature (ventilation) not only keeps occupants comfortable, but also keeps lab equipment and chemicals and other sensitive materials in top shape. This may require different ventilation equipment (requirements) depending on the intended use of the lab.
Keeping a space properly ventilated requires a negative pressure between laboratories and other spaces. The US National Resource Council noted that “a differential should exist between the amount of air exhausted from the laboratory and the amount supplied to the laboratory to maintain a negative pressure between the laboratory and adjacent non laboratory spaces. This pressure differential prevents uncontrolled chemical vapors from leaving the laboratory.”
LABORATORY CHEMICAL HOODS
Of all of the requirements in laboratory spaces, chemical hoods are “the most important components used to protect … personnel from exposure to hazardous chemicals and agents.” Because these pieces of equipment are so vital to creating a safe environment, they must be well maintained and consistently tested for functionality.
Chemical hoods’ performance can be affected by their proximity to windows and doors, traffic within the space, and supply air diffusers in the space. To monitor hood performance, do an initial check on new hoods and follow up at least once a year to retest their functionality. The hoods’ face velocity should meet your lab’s standards. Additionally, check that there isn’t excessive turbulence and ensure that a continuous performance monitoring device is in place to more closely monitor hoods on a day-to-day basis.
Though sprinkler systems are not required in all buildings, it is highly recommended to employ sprinklers in lab spaces regardless of building codes. This helps drastically mitigate potential fire hazards and damage done to the lab as well as adjacent spaces. To avoid damaging water-sensitive equipment that is frequently used in laboratories, one option is to use precaution systems.
OPEN LABORATORY DESIGN
There are advantages and drawbacks to an open layout. In an open design, there can be increased cost savings for ongoing operations “compared with smaller, enclosed laboratories.” The drawback is that balancing the ventilation system can prove as a challenge for Facility Managers. Choosing the right setpoints can help alleviate this issue, and may be well worth the effort in exchange for lower energy consumption.
SMALL CHANGES FOR ENERGY IMPACT
To lower energy expenditure in your lab space with your occupant’s safety and comfort in mind, there are several factors to consider. The main energy wasters in this environment are an overabundance of laboratory chemical hoods, laboratory chemical hoods with large bypass openings, dampers which are in fixed positions, over ventilated laboratory spaces, excessive duct pressure, fans set to override position, fans that are no longer operating efficiently, constant volume systems with no setback for temperature or airflow when unoccupied, and high face velocities. Employing occupancy sensors and educating occupants about small changes they can make to limit energy use are powerful tools that will help cut down on (energy) consumption.
LEVERAGING DATA TO LIMIT ENERGY CONSUMPTION IN LAB SPACES
The Building Automation System (BAS) can be used to verify laboratory air change rates even with limited data. If we look at a typical example of a lab with a fume hood, we want to make sure that that the lab space is negatively pressurized to the common area (hallway) and that the hood is negatively pressurized to the lab space. The simplest way to accomplish this is with a supply air offset.
Consider the following diagram:
- The Supply VAV
- Exhaust VAV
- Fume Hood Exhaust (Constant volume or Variable)
- Door to the lab
The primary data points are the Fume Hood Exhaust CFM, Room Supply CFM, and Room Exhaust CFM. Your Engineering Consultant will specify a constant offset to maintain proper room pressurization. This provides our governing equation for the space.
(Offset) = (Room Supply CFM) — (Fume Hood Exhaust CFM) — (Room Exhaust CFM)
For the Sake of this example, let’s assume that the offset is -100 CFM and the Room Supply has a Heating CFM setpoint of 300 CFM and a Cooling CFM setpoint of 1000 CFM; and the Fume hood is a constant volume fume hood of 200 CFM.
When the lab is in ventilation or heating mode (300 CFM) then the Room Exhaust VAV would need to maintain 200 CFM to maintain proper pressurization.
-100 = 300–200–200
As the Supply CFM increases to handle cooling load within the lab the Room Exhaust VAV will follow to maintain the -100 CFM offset.
These four data points can be linked together on the BAS and an alarm can be used to alert you if the lab pressurization is not being maintained. Make sure to add a timer (5 min) to the alarm, especially in teaching labs, students entering and leaving the space will cause dramatic and short fluctuations in the space pressure which can be observed at the VAV air flow sensors. If you have differential pressure sensors between the lab space and common area, these fluctuations can create over alarming as well if not properly timed and allowed to level out.
Since the actual offset can be measured, it can be trended, reviewing these trends on a regular basis is a great way to identify the positive and negative trends. A positive trend would be maintaining proper pressurization all of the time. A negative trend would be not maintaining pressurization for extended periods of time, say during a lead \ lag exhaust or supply system swap over.
Also note that too much negative pressure in a lab can be bad as well, with fume hood sashes fully open under extreme negative pressure the air flow dynamics across the hood can create a reverse flow turbulent zone at the lower half of the hood. Also depending on how the doors to the space open in or out, the negative pressure can prevent the door from opening. Ie 0.1 PSI of negative pressure on a 6’x3’ door is 250lbs of force working against you. This has been observed first-hand on systems where the Fire Alarm shut down the Supply AHU’s but left the Fume Hood Exhaust fans running, where the doors to the space open out to the hallway. (This is why we commission buildings).
A COMMUNITY EFFORT FOR SMART ENERGY USAGE
The ultimate goal of optimizing laboratory spaces in K-12 schools and on university campuses is, of course, ensuring students and staff are in their safest and most productive states. Involving them in the conversation about energy use and sustainability can make a big impact on their comfort as well as their consumption. As Peter Turek, a Commissioning Agent at DLR Group aptly commented, “lab spaces consume a high percentage of a facility’s total energy usage, but steps can be implemented to have the occupants aware and conscience of their actions. Energy dashboards can be installed in facility entry ways educating the individuals how the facilities are functioning, and compare to similar facilities locally. Building automation systems can be programmed to send out alerts not only to the facility engineer but also to the responsible professor fume hoods are open requiring excessive energy usage while the classroom is empty. One suggestion is to tax the professor if they are not conscious and waste energy continuously and refuse to operate efficiently. The intent is to provide an atmosphere that will encourage the students to participate and the staff to create a classroom that inspires them to be more engaging with the student. The more welcoming an environment the staff creates, the better the reviews they receive on “Grade Your Teacher” for example. Last, whatever the profession if you are a teacher with a classroom or you are responsible for a team of engineers, the feeling you receive when one of the members “gets it” is why you do it.”