This is the third in a three part series on strategies to close the operational performance gap; the 10-30% savings that can be achieved in low- and high-performing buildings by enhancing the synergies of existing building systems.
In our first post, we discussed the strong correlation between collaborative property teams and high performing properties. Our second post focused on operational and property team engagement strategies to enhance value and marketing efforts when positioning properties for purchase. The final post in this series highlights an often misunderstood and low-cost operational strategy to quickly reduce energy waste; mitigating the building stack effect.
Follow your senses
When you arrive at work in the morning and enter your building, does outside air follow you in from the street? During the winter, do you feel cold air drafts in the lobby? Do you hear the unmistakable low frequency roar of air flowing through the elevator and stairwell shafts? These may be the symptoms of a negatively pressurized building with stack effect; the vertical movement of air through a building caused by differences in indoor and outdoor temperatures and pressures.
When outside air leaks into a building, an equal volume of indoor conditioned air escapes from the building, along with the energy used to heat or cool the air. Properly sealing openings where air is escaping and entering the building will help mitigate the stack effect, reduce energy costs, and improve occupant comfort.
Identify the pathways
The path of least resistance for air movement in a building is through unobstructed vertical shafts, such as elevator and stairwell shafts. You can quickly identify obvious pathways for air movement in a building by sensing temperature changes. If a stairwell is colder in the winter than other building spaces, cold outside air is leaking into the building, moving vertically through the stairwell shaft, and escaping through openings at the top of the stairwell. This same concept applies to elevator shafts and electrical, mechanical, and plumbing chase ways, which are also positioned along vertical risers.
NYC Case Study
A de-energized stairwell pressurization fan (turned off) on the roof of a high-rise office building in NYC. The duct does not contain an isolation damper and the fan is rotating from 15,000 cubic feet per minute (cfm) of uncontrolled air leakage. Installing a $5,000 isolation damper reduced property energy costs by over $100,000 annually.
Find openings where air is escaping
Once you have identified potential air pathways, walk the penthouse and roof levels to find openings where air is escaping from the building.
- Stairwell shafts: Check relief openings, pressurization fan ducts, and poorly sealed or unsecured doors or hatches.
- Elevator shafts: Check relief air openings at the top of elevator shafts and in elevator machine rooms.
Look for the presence or absence of isolation dampers on all relief openings and ducts, including the toilet exhaust fans, and confirm that existing dampers are well sealed, operate properly, and close tightly. Installing isolation dampers in relief air openings and ducts, and properly sealing doors and hatches will typically provide a payback period of 1-9 months, depending on the building design and location. Enhancing the control of building pressurization by properly controlling supply and exhaust air fans through the building automation system (BAS) will further mitigate the stack effect, reduce energy costs, and improve occupant comfort.
Before taking corrective action, review the building mechanical design drawings to verify the existence and location of isolation dampers. Review the mechanical system Sequence of Operations to determine the intended operations of the fans and dampers in both occupied and unoccupied modes. Additionally, confirm that the proposed modifications comply with local code requirements. This will ensure your stack effect mitigation strategy complements indoor air quality control strategies and HVAC system operations, and is in compliance with local code requirements.