In today’s lab world, most people are aware of the amount of air they use in their labs. Along with this well-known fact, lab owners and users both know the use of air in a lab environment is the single biggest issue with energy consumption, and that labs are energy hogs. With these realizations, lab owners and users must find one or more strategies to fix this issue, and do so fast.
One common trend observed in lab ventilation strategies for energy-efficient labs is taking advantage of the after use of energy within air—strategies like heat recovery have been prominent. However, people are now looking at reducing the amount of air before they even get started recovering energy from over-ventilated spaces.
With this, labs are beginning to look at more program-based approaches to save energy in their labs, using ventilation as a whole.
In terms of reducing air change rates, there are a number of strategies labs can deploy. With a large focus on minimizing plug loads, implementing higher-efficiency freezers can reduce plug loads, the thermal characteristics of a building and, in some case, the need for air to cool lab spaces based on the heat generated by the equipment. On the fume hood side, there’s talk about the ANZI 9.5 standard that can now permit the reduction of the minimum airflow through a fume hood when the sash is closed and the ability to implement higher-efficiency fume hoods, which use less air.
“In addition to lowering thermal demand and increasing the efficiency of fume hood flows, the amount of dilution air used in a lab can also be optimized to balance both safety and energy savings,” says Chuck McKinney, VP of Strategic Sales and Marketing, Aircuity. “VAV systems are prevalent in labs, and these systems can be better utilized to deliver the right amount of air on a zone-by-zone basis by utilizing active monitoring systems that can raise or lower air change rates based on lab activity.”
The great air change debate
The obvious answer to the commonly asked question of what’s the correct air change rate is, in fact, there’s no one right answer. Even in a lab where you know exactly what’s going on at any given time, one air change rate won’t be perfect for another period of time in that exact lab setting.
“The reason is simple,” says McKinney. “When there is a lot of benchtop activity happening in a lab, higher air change rates can quickly cleanse the lab areas and remove airborne contaminants, but if there is no lab activity, lower air change rates will save a significant amount of energy. The difficulty is knowing when there is activity that might need higher air change rates.”
However, it’s difficult to understand the hours researchers work, and even if there is no one in the lab, chemical vapors and particulates can build up due to fugitive emissions or ongoing research activities. “According to ASHRAE guidelines, a lab operating on a night setback schedule should run at higher ACH rates for an hour prior to anyone returning to that lab; enforcing this safety precaution can be difficult at best,” says McKinney.
Additionally, even occupancy sensors, which are mandated by law in certain regions, can be defeated or inaccurate. “So, you actually need something that can accurately detect what’s going on in a lab from a contaminant basis since that is the real issue not whether there are necessarily people in the lab.” says McKinney.
However, when there is activity, regardless of the time of day or night, lab owners want air changes high enough so the lab is maintaining a safe, productive environment. This is the real key. And when the lab indoor environmental quality is accurately monitored, air change rates can go as low as between 2 and 4 ACH during the day; and 2 ACH can be achieved at night when there isn’t activity in the lab.
“Monitoring gives you the ability to dynamically change air change rates even in the middle of night when there’s nobody there, in case there’s a procedure setup that might be off gassing,” says McKinney.
Yet, air change rates in labs are typically in the range of 6 to 12 ACH, depending on the type of lab work done.
“There has been research at Yale Univ. that has shown there’s a significant impact, for example, on a cleaning and purging standpoint to get up to at least 8 ACH and diminishing returns above 12 ACH,” says Gordon Sharp, Chairman, Aircuity. “Therefore from an airflow purging standpoint, using at least 8 to perhaps as high as 15 ACH provides the best or optimum performance for cleaning of the lab air.”
However, to get lower than the recommended 8 to 12 ACH, technologies like demand-controlled ventilation is important.
The term demand-controlled ventilation has been around for a long time, and it’s close to what Aircuity does. Aircuity uses the similar term Demand-Based Control to describe how it simply monitors the indoor environmental quality of the lab air and then varies the lab’s minimum airflow rate to keep the air clean and free of contaminants. When the air is already clean, which it is typically 98 to 99% of the time, this approach can be used to reduce airflow minimum down to 4 or even 2 ACH.
However, when the system senses something in the air, either a particulate or chemical, or for some labs maybe CO2, it increases the airflow and rapidly purges the lab. By doing this, the system brings a higher airflow such as 8 to 15 ACH to provide a more effective purge than running continuously at say 6 ACH, according to Sharp.
Since VAV has become the standard for most labs, demand-controlled ventilation is becoming more standard. “This allows for the ability to vary air volume,” says McKinney. And once users have good control of the air volume in their lab spaces, the information to properly control the spaces is right at the hand of the researchers.
While demand-controlled ventilation is important for reducing a lab’s energy consumption by alleviating air volume issues, it’s also important for safety. “You want to know you are bringing down the air change rates safely,” says McKinney. “And to date the arguments related to air change rates seem to pit energy managers against EH&S and occupants. It feels like a tug-of-war between trying to push for lower air change rates to give energy savings relative to the perception of higher air change rates for safety.”
With actual data provided to a lab’s BMS, owners and users can now make an informed, automatic decision about what air change rate is appropriate. “Adding data into this argument really stops the war and allows both sides to get what they want,” says McKinney.
Along with demand-based ventilation, chilled beams also provide for an energy-efficient lab ventilation strategy. “One advantage of chilled beams is that they decouple the thermal load from the airflow,” says Sharp. “If used in conjunction with a demand-based control approach and labs with lower hood densities, chilled beams can save energy by reducing the use of outside air when room cooling is needed. Even more important is that this combination can also significantly reduce project capital costs by allowing the HVAC capacity to be safely reduced with maximum room airflows set in the very low range of 2 to 4 ACH.”
“With chilled beams you don’t need to pull as much air from the outside for cooling purposes,” says Sharp. “You don’t need to take air that might be much hotter or colder outside and condition it for cooling use in the lab.”
“The key is by just implementing a chilled beam system with demand-controlled ventilation, the total outside airflow requirements of the lab are reduced since air in the lab is now cooled locally with chilled water allowing the primary HVAC system equipment costs to be reduced,” says Sharp.
Giving users ownership
There is much discussion in the lab design world about what the right level of energy monitoring (metering energy use) is to help modify occupant behaviors. In the same way, monitoring indoor environmental quality (IEQ) on a dynamic basis gives the BMS the ability to optimize ventilation rates for both energy conservation and safety.
Essentially, monitoring is an important piece of the puzzle for lab users. “What happens in many situations is people install energy-efficient technologies into labs that do yield initial savings,” says Sharp, “However, over time, most systems will degrade, have programming changes or have issues that will increase energy usage.”
The problem then becomes, that if you aren’t monitoring for energy purposes, you won’t see these gradual increases in energy usage. Feedback is needed, and this monitoring, as well as some form of automated analysis or diagnostics of this data, can point out issues that can then be resolved to maintain a high level of energy savings over time.
“In order to maintain savings for the long haul it is important to gather data on energy, airflow and lab air cleanliness as well as provide a means to analysis this data,” says Sharp.
The future of lab ventilation
What is in the future for lab ventilation? Sharp believes it’s the continued use of the combination of demand-based control and chilled beams.
Along with the combination approach, energy and airflow monitoring will also become more important in lab settings. Analytics is becoming an increasingly important area of labs because people don’t have the time to analyze the data coming out of the lab looking at energy, airflow, or IEQ. “So, I think one of the trends going forward is the increasing use of expert systems and automated analytics,” says Sharp. The idea is to have automated approaches to look for issues in the lab, define them and hopefully solve them.
Overall, the idea is to bring attention to the causes of potential increased energy use so people don’t need to spend dollars combing through data trying to understand why a lab’s energy bill went up.
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