In 2009, California Institute of Technology hired an engineering firm to perform a careful analysis of lab energy use in a lab there in the interest of reducing plug loads. Their conclusion was that vacuum pumps represented 15% of plug loads in the labs analyzed. This is a number that will vary from lab to lab, but the math indicates that a substantial reduction in energy use by vacuum pumps could reduce total lab plug loads by 10 percent. Further, a recent laboratory survey found that 17 percent of respondents reported using “water-jet aspirators” in their labs to create vacuum. These devices are inexpensive to buy, but each device (serving one user) can waste and pollute 50,000 gallons of water a year, amounting to hundreds of thousands of gallons for a university in which use is widespread.
It’s clear, then, that there is an opportunity to reduce resource waste associated with vacuum production for science labs. If we can improve sustainability and support the science by making changes in approaches to vacuum supply that lower lifetime operating costs, it’s a home run. But before we consider vacuum options, let’s review how vacuum is used in labs.
When we refer to “vacuum,” what we are really talking about is air pressure less than atmospheric pressure. Scientists use vacuum to lower air pressure and create a pressure differential. A small differential is enough vacuum to produce suction (like sucking on a straw). With more vacuum, you can induce evaporations (for example, getting water to boil at room temperature). Once we know how the scientists plan to use the vacuum (suction or evaporation), and how many people will need vacuum in the lab, we can begin to define the vacuum options.
Traditional Approaches to Providing Vacuum to Science Labs
There are three traditional approaches to providing vacuum to science labs: central systems, hybrid systems, and individual mechanical pumps in the lab. With central vacuum, two or three large pumps bring down the pressure in the building-wide network of pipes that deliver vacuum to every lab. The vacuum is generally deep enough to support the suction operations (filtration and aspiration) but not to efficiently support the evaporative work. (Supplemental pumps are needed for those operations.) Depending on the pump technology, the pumps may have to operate 24/7 so there is always vacuum if needed anywhere in the building. This uses a lot of electricity to provide vacuum, and in some pumps also uses and contaminates millions of gallons of water per year as a lubricant and seal. Finally, central systems exhaust a lot of vapors to the atmosphere through roof fans.
One alternative to the central vacuum system historically has been water jet aspirators, often seen as an inexpensive, in-lab way to generate vacuum. In fact, these “hybrid” systems produce vacuum locally, but rely on building-wide water supply infrastructure. At modest usage levels (10 hours a week), each unit can use 50,000 gallons of water a year to produce vacuum, leading to very high operating costs. (By contrast, a gallon per flush urinal would need to flush once every two minutes, 8 hours a day for an entire school year to use as much water.) Beyond that, the vapors from the vacuum applications get sucked into the water used to produce vacuum, polluting it and imposing water treatment costs. So what looks like inexpensive vacuum in the lab turns out to be very costly – so costly that water savings will often recover the cost of a pump in one to three years, depending on local water rates. For all of these reasons, once-through water aspirators are not allowed in buildings seeking LEED certification.
Individual pumps have also been widely used in labs for decades, in some cases because there is no central vacuum, or because the vacuum provided by the central system is inadequate, either in depth of vacuum or stability. Individual pumps can be matched exactly to the scientific need, making them very adaptable over time.
They also operate only when vacuum is needed, which saves energy. Further, individual oil-free pumps can be equipped with vapor capture accessories, reducing the total load of waste chemical discharged to the atmosphere. On the other hand, vacuum is typically used intermittently in labs, so one pump per scientist can be an inefficient use of space and capital for routine applications.
A Modern Alternative to Improve Lab Sustainability
With that as a quick review of traditional technologies, what are the modern alternatives that can improve sustainability? We’ll consider four here: Special purpose pumps, variable speed pumps, multi-user vacuum networks in the lab, and local vacuum networks with variable speed pumps.
Special purpose pumps: Especially in multidisciplinary science buildings, you may only need vacuum in a small or isolated space for a few users, or for a specialized need. For example, cell culture labs often need aspiration vacuum for biosafety cabinets, and an integrated unit that provides vacuum, a sterile filter to prevent escape of bio-aerosols, and a bleach-resistant receiving flask can serve this purpose. Further, by pumping only when needed, such a pump can save energy and serve sustainability goals, without the infrastructure of a building piping system. While the aspiration system serves the cell culture lab, pumps with deeper vacuum capacity and electronic controls may be a better fit for chemistry labs.
Variable speed pumps: A second option is to use variable speed pumps for the more demanding applications. Variable speed motors in fume hoods have been shown to make major contributions to energy savings in lab buildings. The same principles apply to vacuum pumps. Besides the very significant energy savings, these dry (oil- and water-free) pumps can also be equipped with on-board vapor capture systems that can capture 90 percent or more of the residual vapors coming off vacuum applications. This allows you to reduce building emissions and collect waste solvents for reuse or proper disposal.
The variable speed pump gets much of its advantage from the fact that it takes a lot more power to pump a vessel down to create vacuum than to sustain the vacuum once established. The variable speed unit pumps quickly to establish the vacuum, then ramps back to pump only as much as needed to maintain the desired vacuum level. The result is that energy consumption with the variable speed motor is about 10 percent of that with a fixed speed pump.
Multi-user local vacuum networks: With this technology, a dry vacuum pump is installed under the lab bench or fume hood, and plumbed to specialized vacuum turrets that enable the small, quiet vacuum pump to provide stable vacuum for numerous users. The vacuum quality is sufficient to obviate the need for many of the dedicated pumps that chemists use to supplement the central vacuum supply.
The network pump can also condense and collect waste vapors from vacuum applications on the network, so much less is vented to the atmosphere. The pump produces vacuum on demand, so you only use enough energy to run a small pump when someone in the lab needs vacuum, rather than having a large central pump producing vacuum 24/7 in a building that is usually empty nights and weekends – that is, 70 percent of the time.
These local networks are plumbed with tubing made of a material – PTFE – that is much more chemical resistant than the copper typically used in vacuum systems, ensuring long, leak-free life. The PTFE tubing is quick and easy to install, in contrast to large diameter copper tubing building-wide, so local networks can even be installed by facility personnel in operating buildings, and adapted as needs change. The pumps are oil-free with long service intervals, which saves on waste oil disposal and maintenance costs. The net benefit of the local vacuum networks is that you can save upfront on the capital costs, but also save on installation, energy, service, and supplemental pumps, while producing deeper, more stable vacuum than that which a central vacuum can produce.
Local vacuum networks with variable speed pumps: The ultimate in sustainable vacuum supply arises when you produce vacuum for multiple users on local networks using variable speed vacuum pumps. With this set-up, the variable speed pumping system pumps as much as needed to support as many users as are on the network at one time, and goes on stand-by automatically when the network is not in use. Even when pumping, the unit typically draws only a fraction of the rated power; on stand-by, the pump draws 2 watts to monitor demand. Combining the multi-user supply with the variable speed vacuum, energy savings can exceed 90 percent compared with conventional vacuum supply, and maintenance costs are similarly reduced, while the network pump permits convenient collection of waste vapors from vacuum processes.
Sustainability and Cost Savings
In short, by adopting innovative vacuum approaches, the possibility exists to reduce energy consumption for vacuum supply by as much as 90 percent, lower total in-lab plug loads by as much as 10 percent by reducing vacuum needs, save hundreds of thousands of gallons of water, and eliminate resource intensive, building-wide vacuum systems.
In addition to offering lower lifetime operating costs, these approaches also allow us to use technologies that can adapt as the scientific needs of the building change, reduce building emissions from vacuum applications, and support research with superior vacuum performance while conserving lab and bench space, and researcher time. It’s a pretty appealing combination of science, sustainability, and sustainable cost savings.