HVAC mitigation guidelines

UW Bothell / Cascadia College
Heating, Ventilation, and Air Conditioning (HVAC) System
Mitigation Guidelines as of September 10, 2020

We are maximizing the amount of fresh air introduced into our buildings to the maximum extent possible without negatively affecting our indoor temperature and humidity.

The vast majority of campus HVAC systems are configured such that our maintenance technicians can control the amount of outdoor air. At this time, the minimum outside air damper set points have been raised from 10% to 30%.

About 3 years ago, we increased the filtration level to MERV 15 in our central HVAC systems. Currently, campus laboratory, research, office, classroom, and administration spaces in the common core of buildings are served by these filters. With the Discovery Hall lab building being 100% outside air, with the wildfires causing smoke in the air, we installed our pleated carbon filters in that building.

Because of COVID, our campus HVAC systems have continued to operate as they would at full occupancy. Our HVAC systems have retained their existing temperature and humidity set-points.

The set points are 74 degrees cooling and 70 degrees heating. At this time, our air handling units come ON at 5:30 am and most turn OFF at 5:00 pm. The warmer/cooler adjust varies + or – 2 degrees. We are monitoring our few occupants in the buildings to allow extra run time if they are in the building other than those hours. Naturally, we will adjust the times on and off when the Fall quarter begins.

Pressurization: The HVAC equipment serving our laboratory and research spaces will continue to operate per design and provide the necessary differential pressure to maintain laboratory isolation to surrounding spaces. All labs are running at with proper supply and meeting the differential settings for exhaust to establish proper negative pressure. Fume Hoods are being calibrated in UW3, UW2 and CC1 at this time.

Increasing airflow/air changes per hour: Increasing the amount of outside air provided to classrooms and other learning spaces will decrease the amount of CO2 in these spaces and increase the frequency that air is changed and filtered. We will continue to strive increase 2- 3 times the ASHRAE’s recommended minimums for air changes per hour in each space.

The AHUs are mostly 100% outside air when OA is below 63 degrees. This is when systems are in economizer (our free cooling) mode. When the air handling unit mode changes to mechanical cooling, the OA damper will stay at 30% until the return air level requires more outside air.

Glossary

air change rate: volume of air supplied to and removed from a space, via mechanical systems or through the building enclosure, per unit of time divided by the volume of the space, using the same units for volume such that the unit is inverse time.

air changes: expression of the amount of air movement or air leakage into or out of a building in terms of the number of building volumes or room volumes exchanged.

air changes per hour (ACH): ventilation airflow divided by room volume. It indicates how many times, during one hour, the air volume from a space is replaced with outdoor air.

constant air volume (CAV): HVAC system where the supply air flow rate is constant, but the supply air temperature is varied to meet the thermal loads of a space.

fresh air makeup: volume of outdoor air introduced into a space.

HVAC: heating, ventilating, and air-conditioning system.

HVAC system: the equipment, distribution systems, and terminals that provide, either collectively or individually, the processes of heating, ventilating, or air conditioning to a building or portion of a building.

indoor air volume: the entire air volume of a space or building in which the ventilation air is distributed, including ductwork and plenums. The volume of indoor furnishings, equipment, and occupants must be subtracted from the gross indoor volume that is based on interior dimensions of the space or building.

makeup air: (1) dedicated replacement air. (2) air brought into a building from the outdoors to replace air that is exhausted. Makeup air may or may not be conditioned. (3) any combination of outdoor and transfer air intended to replace exhaust air and exfiltration. (4) in a cleanroom, air introduced to the secondary air system for ventilation, pressurization, and replacement of exhaust air. (5) in a laboratory or kitchen, outdoor air deliberately brought into the building from the outside and supplied to the vicinity of an exhaust hood to replace air, vapor, and contaminants being exhausted. Makeup air is generally filtered and fan forced, and it may be heated or cooled depending on the requirements of the application. Makeup air may be delivered through outlets integral to the exhaust hood or through outlets in the same room.

outside air: air external to a defined zone (e.g., corridors).

outdoor air: (1) air outside a building or taken from the external atmosphere and, therefore, not previously circulated through the system. (2) ambient air that enters a building through a mechanical ventilation system, through intentional openings for natural ventilation, or by infiltration. (3) compare to outside air.

variable air volume (VAV): HVAC system that controls the dry-bulb temperature within a space by varying the volumetric flow of heated or cooled supply air to the space.

ventilation rate: rate of airflow to or from a space, expressed in terms of volume per unit of time, either through the ventilation system or infiltration through building envelope. These are commonly expressed as cubic feet per minute (CFM).