By Tom Prevish & Caton Mande
COVID-19 has permanently or temporarily altered numerous aspects of our lives. As a testing, adjusting and balancing provider, NorthWest Engineering Service, Inc. was one of many entities to immediately recognize the importance of ventilation and ASHRAE recommended air changes per hour in mitigating the effects of coronavirus . In fact, ventilation is arguably one of the more important recommendations being discussed in the first months of the crisis.
Unfortunately, the answer was not as simple as maximizing outside air and walking away – that is a temporary solution at best. It is important to recognize the energy and equipment lifetime impacts that can happen when HVAC systems are called upon to operate beyond design intent.
The ideal solution, technically, would be to undertake a full room-by-room TAB project to make sure all building occupants are breathing properly diluted air in every part of every room.
But this is certainly not the ideal solution from the standpoint of budget. In particular, clients with many, multi-story buildings, like hospitals, colleges and large school districts, don’t typically plan for a campus-wide TAB project in a single year. And even if money can be found, more time cannot.
In the latter months of this past summer, when it became apparent that schools were going to bring students back to classrooms, numerous colleges and schools contacted TAB providers, and they all wanted their entire campus ready for students in September. There weren’t enough TAB professionals, balometers and manhours in the country to rigorously balance every room in every building.
To serve as many clients as possible, we worked with the facilities teams to prioritize buildings based on analyses of the HVAC equipment, sub-divided areas into zones focused on outside air intake and exhaust measurements to screen buildings. Recommendations were made for those requiring further attention.
Situations like this make it intriguing to learn more about the low-cost screening tool being prototyped at the UC Davis Western Cooling Efficiency Center with funding from the Office of Naval Research (Contract: N000142012216). The tool directly measures the air change rate for each zone by assessing the rate that carbon dioxide is removed.
This tracer gas dilution method measures the zone air change rate because the air displaced by introducing outside air into the zone reduces the total tracer concentration. This method has been extensively studied in scientific literature and there are measurement standards published by ASHRAE, as well as International Organization of Standards. The WCEC tool aims to provide the industry with the ability to perform accurate and low-cost screening measurements to enable more data-based decision making for how to best use available budget and resources.
WCEC has developed the prototype using commercial-grade nondispersive infrared CO2 sensors, with off-the-shelf microcontrollers, that communicate to a central hub through a wireless mesh network with long-range (~1000ft) capability. The screening tool has advantages over existing products because using CO2 as a tracer does not raise any health concerns, it does not require direct access to every grille and it does not assume the ventilation air has been well mixed in the HVAC system.
A measurement is performed by:
- Distributing wireless sensors in the zone and one outside to monitor the outside air concentration
- Running the HVAC system in desired mode
- Artificially increasing the zone concentration to at least twice the outside air concentration
- Monitoring the decay over a period of 15-60 minutes
At the end of the test, the prototype returns the air changes per hour, the ventilation rate if the zone volume is provided and the test data for quality control. WCEC has tested the prototype in the laboratory, on the UC Davis Campus and at Naval Base Kitsap (Table 1). Compared to baseline balometer measurements and recent TAB reports (if available), the screening tool measurements were within ± 5%.
Additionally, the prototype successfully identified zones with inadequate ventilation or provided quantitative data when data was not available in the building management system.
Table 1: Summary of UC Davis WCEC Prototype Results
|Location||HVAC Type||# of Zones||Ventilation Type||Baseline||Result||Outcome|
|Lab||Split system||1||Ducted||28 cfm||28 cfm||Benchmark Test|
|UC Davis Campus||VRF||10||Ducted||0.15 cfm/sqft||0 cfm||Result helped discover the ventilation system was never connected|
|UC Davis Campus||VRF||4||DOAS||0.15 cfm/sqft||0 – 0.2 cfm/sqft||Found one office with no ventilation|
|Naval Base||Split system||1||Ducted to AHU||Unknown||179 cfm||No original design documents and tenant improvements made it impossible to get access grilles|
|Naval Base||Split system||2||Ducted to AHU||300 cfm||288 cfm||Quicker than balometer|
|Government Building||VAV||2||Ducted to central AHU||Unknown||0.9 – 1.2 cfm/sqft||Older meeting rooms with no ventilation rate measurement. Allowed room occupancy to increase during COVID|
Pandemic, epidemic, endemic or outbreak – regardless of how COVID-19 settles in coming years, there will always be a need for a low-cost, fast-screening tool that TAB professionals can use to plan complex balancing projects.
It will be interesting to see how the WCEC CO2 tracer gas tool progresses to meet this challenge.
Tom Prevish, Ph.D., P.E., CEM, is president of NorthWest Engineering Service, Inc. Caton Mande is a research and development engineer at UC Davis Western Cooling Efficiency Center.
Editor’s Note: NorthWest Engineering Services, Inc. is an Associated Air Balance Council and AABC Commissioning Group member company. This article is an extension of a July 2021 AABC TAB Talk Webinar presented by Caton Mande, UC Davis Western Cooling Efficiency Center.