Good design for clean room and laboratory HVAC is more than just totaling up numbers from a chart. Precision air flow controls systems have to take many variables into account if they’re going to work as well in practice as they do on the drawing board. Not all of the variables are due to the tolerances used during installation and the slow degradation of performance of systems when they get older. Probably the largest sources of variability in clean room environments are the habits of the people that work in them. Designing for machinery is very easy when compared to working around the likes and dislikes of personnel in a clean room environment.
The variation in the behavior of one worker to the next presents more than just HVAC design load problems. In clean room environments and laboratories where contaminants from the work can be dangerous or deadly, it is the duty of all the designers involved to take as many different scenarios as possible into account when introducing margins of safety into calculations.
While a desire for absolute safety can seem like a directive to overdesign any system in a laboratory environment, energy use is always a primary consideration as well. If a laboratory can be operated economically, more research can be performed on the same budget. In a production clean room environment, lower energy costs mean higher margins. Design and fabrication firms for precision air flow controls systems like PhoenixControls.com always advise their clients that intelligent design methods can always be brought to bear in order to improve energy savings without sacrificing productivity, worker comfort, or safety.
Meeting Energy Goals in Precision Air Flow Controls Systems
Precision air flow controls systems need to look out for variables in everyday laboratory use that can throw off their calculations during the design stages. Here are a few common obstacles to meeting energy targets in laboratory HVAC design.
Bad Fume Hood Habits
Workers in clean rooms that rely on precision air flow controls systems can get into bad habits that designers can have trouble foreseeing. Unusual fume hood habits are a common way that workers can throw off the best makeup air calculations. Workers often leave fume hood sashes open when they’re not actively working at the stations. This is not just when they step away for a moment to retrieve a tool or other item. Some workers get in the habit of leaving the fume hood open at all times. Others get in the habit of not only leaving the hood open, but entirely open. If this behavior is not modified at an early stage, it can quickly change to everyone leaving all the hoods open at all times. The final stage of this process is when the hoods are left open even when the room is not occupied.
It’s human nature for people who under time pressure to remove small annoyances that slow them down. It might seem like a trivial inconvenience to a precision air flow controls systems engineer to lift and lower a fume hood sash only while you’re actively working on a hooded desktop. However, during the course of a day, a worker in a lab might be forced to open and close a fume hood sash hundreds of times. The temptation will always be there to leave it open to save time.
That’s where good education is crucial if the engineering firm for the precision air flow controls systems is going to have their system work to plan. In many cases, workers many not know exactly how the fume hood exhaust works, or how makeup air is supplied to replace the air exhausted from their work areas. They also may not be aware how much safer they will be if they don’t open their fume hoods any higher than absolutely necessary. A good designer takes into account the natural variability in the actions of a group of people that use a facility, but them avoids the chances of large outliers blowing a hole in their calculations. Engineers shouldn’t expect the fume hood sashes to be opened and closed like clockwork, but they should work with the managers of the laboratory to implement smart protocols.
High Heat Loads
When clean rooms and laboratories are in the design stage, the engineer in charge of the precision air flow controls systems might not have all the information he or she needs to make all their calculations. When trying to meet energy savings goals, the airflow that brings cooled air in order to keep the occupants of the room comfortable has to take into account the amount of heat generated by all the equipment that will be running inside the room. Nailing down that information can be very difficult for the engineer early in the design process.
HVAC for clean rooms is usually brought on board very early in the design process, and it’s common to find out that the equipment that will be used in the laboratory hasn’t been specified yet. If it has been specified, it might only be in general terms like the number of workstations necessary. This leads to calculations based on rules of thumb, usually per-person or per-square-foot numbers. It’s important to follow up later to find out the precise amount of heat generated from the machines as soon as possible to make good projections of cooling loads.
Don’t Lose Your Savings Somewhere Else
Savings on one type of HVAC load can be dissipated by losses in another area if you’re not careful. For instance, if a machine that exhausts a substantial volume of air from the room is added late in the process, or even after the entire room is occupied, no one will make an allowance for where the makeup air will come from. That can lead to the room becoming de-pressurized and drawing in untreated air through infiltration. It’s important to educate the end user of the need to alter or adjust precision air flow controls systems as the nature of the infrastructure or the number of workers changes dramatically.