So how do you effectively and efficiently reduce the large amounts of energy that is used for ventilation while at the same time maximize safety in the lab? In balancing these two factors more exhaust air is not always the answer – after all, more air out requires more air in. As a result, excessive ventilation can actually diminish safety conditions in the labs. Currently Labs 21 is supporting optimization rather than maximization.
Just as a reference point, a typical lab building consumes 3 to 5 times more energy than a typical office building. Per Labs 21 If you break down consumption annually it would look like the chart below.
It is obvious that ventilation is by far the largest consumption of energy. The primary factor creating /contributing to the high energy output for ventilation is the minimum air changes per hour (ACH) controlled by codes, standards and guidelines (I have listed these below). In looking at the tables below you will notice that most of the recommendations around ACH fall in the Standards/Guidelines categories for labs built today. The building code only dictates the CFM for “H Classifications” (i.e. hazardous laboratory usage). These classifications come into play when certain chemical quantities are exceeded, therefore in most labs these guidelines could result in excessive ventilation which means higher energy cost and possibly reduced safety for the occupants.
Air Changes per Hour (ACH) is one of the guidelines that is most discussed during the design process of a lab but typically ACH does not measure the ventilation effectiveness and the protection of the lab personnel. The factors that should influence the ventilation rate are:
- Toxicity and properties of a wide range of hazardous materials present
- Availability and use of local ventilation capture – control contaminates at the source
- Use of gases, volatile liquids and fine powders or aerosols requiring specialized exhaust
- Flexibility and adaptability of the lab space
- The SOP’s for training & compliance in the facility
These are some strategies you should consider in order to optimize energy consumption and maintain or increase safety:
- Right size all new hoods. By this I mean ask yourself the question what do I need this hood for and could this process be done with a localized exhaust. This might be a conversation between the designer, Safety Officer and the design team.
- Sash management: Per NFPA 45 recommends closing the sash manually whenever possible, however, that takes some enforcement. There are automatic sash positioning systems (ASPSTM ) that can automate this process for you. This system reduces energy and thus saves money by ensuring that the sash is closed in a unoccupied mode. This system allows the VAV system to reduce airflow consumption by as much as 80% and protects the user by automatically closing the sash when occupants are away. Conversly, the ASPS™ detects the technician approaching the fume hood and automatically opens the sash. This allows for a hands and barrier-free work environment.
- In the design phase, understand the difference between heat loads and exhaust requirements. If you can effectively isolate heat loads from exhaust demand you can employ supplemental cooling methods that will greatly reduce the demand for air.
- Use a Zone Presence Sensor (ZPS). This will reduce air flow but in a different way by reducing the open sashes face velocity when unoccupied and could achieve a 40% flow reduction.
- Use Variable Air Volume (VAV) hood in conjunction with a VAV control system which controls thermal loads.
- Occupancy control: Providing occupancy sensors that are tried to the VAV system that can setback the ACH to the NFPA 45 recommended 4 ACH minimum while the space is unoccupied.
- Centralized Demand Control Ventilation (CDCV) is a design refinement of the laboratory’s supply and exhaust system. It provides increased airflow and negative pressurization in emergency situations. Utilizing a CDCV in a lab would allow for variable air changes per hour based on indoor air pollutants not simply based on the guidelines listed above. Typically these ACH would be between 4 to 16 ACH vs. a fixed 9 ACH in a typical lab. If you already apply VAV technology to the fume hoods and thermal loads why not apply it to the ACH/dilution. Keep in mind that this system must rely on sensors. These sensors tend to be expensive and they have to be calibrated frequently. Also note that the long-term reliability of these sensors is unknown. To help overcome these issues OptiNet collects air samples in the room and routes them to a central sensor suite for evaluation every 30 to 40 seconds. These sensors can pick up air cleanliness, lab specific chemicals, and contort and ventilation. By using a central sensing suite you can provide better sensing and reduce calibration cost.
All of these methods are based on reducing the demand air and will save your lab and the facility money. With energy rates increasing it is important to utilize as many of these as possible. But, before you start down this road of deciding your laboratories ventilation rate you should:
- Ensure that the authority having jurisdiction is identified and involved from the start.
- Define energy savings goals for this project. Are you going for LEED or is there a mandate form the state or company to be more energy efficient?
- Have a design/LEED charrette which brings together all ventilation stakeholders to discuss the goals of the project, budget, and possible concepts. Discussions around each concept should include safety implications, start-up costs of the system, and life cycle costing.
- After all has been decided implement the strategies.