During an investigation responding to a temperature complaint for Toronto General Hospital’s (TGH) 5MB Medicinal Chemistry Lab, we found the lab was running full air flow 24/7, so we identified it as a potential energy saving opportunity.
This lab has (3) supply air valves, (2) exhaust air valves and (8) fume hoods. A fume hood is standard equipment used in biology and science labs. It exhausts any fumes or gases that might be generated during experiments, protecting people while they use potentially dangerous materials in the quest to further science and health. As Ed mentioned, “fume hoods do a very good job of keeping strong chemicals out of sensitive things like eyes and ears and lungs.”.
Fume hoods act much like the vent hood over your stove, but much stronger, and self-contained in a cabinet with a sash that opens and closes for access. While fume hoods need to move 100% fresh air while in use, they don’t when not in use, and the surrounding lab does not need that much either.
After investigating, we found out the whole lab was supplied 4000 CFM (cubit feet/minute) or 1888 L/S (liters/second) 100% fresh air, and exhausted 4750 CFM (2241 L/S) air 24/7. This 10.4 air change rate (ACH – air changes per hour) was designed for full lab operation. The original design had occupancy control built in, but it was never implemented. After consulting with an engineer to make sure we are doing the right thing, we found industry regulations allow labs to run at a reduced air flow when not occupied.
After referring to regulations and the technical specifications of the air control devices, we formed the proposal below. During the unoccupied period, supply air is set at 2160 CFM (1019 L/S), and exhaust air is set at 2910 CFM (1373 L/S). This is well above the required regulations and maintains sufficient air flow and offset (the amount of difference between exhaust and supply) to make sure any chemical fumes released during that time can be ventilated out of the building. Below are illustrations of the concept.
On how to determine when the space should go into unoccupied mode, we got very lucky here. There are 4 movement-sensing occupancy sensors in this lab, which are part of lighting control system. The lighting control system is very reliable at responding to occupancy, according to scientists working there. We simply needed to take that signal and use it to control the air flow system in addition to the lights it already turned on and off. Nothing could be easier!
The Energy Team held multiple meetings to discuss this issue with the UHN Research team and the UHN Health and Safety team. All team members were very supportive but also very cautious about safety. Many questions and suggestions were put on the table, such as:
- How to deal with personnel’s short time leave like lunch?
- What if the sash/sashes are not closed at the end of the day?
- What if one or more sensors fail?
- How can it send an alarm if something is wrong?
We worked together to find and agreed upon solutions to implement into the control logic. We have a green light to test run this way for a three-month probation period. During this period, a team with representatives from Energy & Environment, Research and Health and Safety will monitor the situation and collect feedback for this change. Below are BAS graphics of occupied mode and unoccupied mode.
With this in practice, we estimate a total saving is $3750 per year based on working hours of Monday to Friday, 8am-8pm. Breaking down the estimate, we should save $2,250 in electricity; $1,400 in steam; and $100 in chilled water.
Beyond the financial savings, there’s climate-friendly savings too. This project estimates greenhouse gas (GHG) emissions reduction of 15 tonnes per year, which is like taking over 3 cars off the road, or not burning 35 barrels of oil each year, or the environmental benefit you get from 7.4 hectares (18.4 acres) of forest sequestering carbon with all its trees. Not bad for a project that started with a simple temperature complaint!