1. Can COVID-19 be transmitted through HVAC (ventilation) systems?
The risk of spreading SARS-CoV-2, the virus that causes COVID-19, through ventilation systems is not clear at this time. Viral RNA has reportedly b...
2. How long will it take to dilute the concentration of infectious particles in a room once they are...
While large droplets (100 micrometers [µm] and larger) will settle to surrounding surfaces within seconds, smaller particles can stay suspended in...
3. Can ventilation filters effectively capture SARS-CoV-2 viral particles?
Filters for use in heating, ventilation, and air conditioning (HVAC) systems are generally tested under procedures outlined in ANSI/ASHRAE Standard...
4. What is meant by “directional airflow?” How and where should it be used?
Directional airflow is a protective ventilation concept where air movement flows in a clean-to-less-clean direction. This ventilation concept is ap...
5. What is a HEPA filter and why use a portable HEPA air cleaner?
Research shows that the particle size of SARS-CoV-2 is around 0.1 micrometer (µm). However, the virus generally does not travel through the air by...
6. Does ultraviolet germicidal irradiation (UVGI) kill SARS-CoV-2?
Yes. Ultraviolet germicidal irradiation (UVGI), otherwise known as germicidal ultraviolet (GUV), is a disinfection tool used in many different sett...
7. What types of ultraviolet germicidal irradiation (UVGI) devices are available for cleaning and di...
Upper-room UVGI Upper-room (or upper-air) UVGI uses specially designed UVGI fixtures mounted on walls or ceilings to create a disinfection zone of...
8. Many new air disinfection devices are marketed for their ability to inactivate SARS-CoV-2. How ca...
CDC does not provide recommendations for, or against, any manufacturer or product. There are numerous technologies being heavily marketed to provid...
9. Can carbon dioxide (CO2) monitors be used to indicate when there is good ventilation?
Carbon dioxide (CO2) monitoring can provide information on ventilation in a given space, which can be used to enhance protection against COVID-19 t...
10. Should indoor temperature and humidity be used to help reduce the risk of COVID-19 transmission?
For COVID-19, the first steps in reducing the indoor concentrations of the virus are wearing face masks, physical distancing, and reducing occupanc...
Why do hospitals need ventilation?
Healthcare facilities have ventilation requirements in place to help prevent and control infectious diseases that are associated with healthcare environments. For more information, see the CDC Guidelines for Environmental Infection Control in Health-Care Facilities.
What are some areas where ventilation improvements can be applied to reduce the spread of the virus?
In addition to buildings, vehicles – including public transportation such as buses, subways, trains, school buses, carpools, and rideshares – are also areas where ventilation improvements can be applied to reduce the spread of the virus and lower the risk of exposure.
What is rebalancing HVAC?
Rebalance or adjust HVAC systems to increase total airflow to occupied spaces when possible.
How to create directional airflow?
This can be done passively, through intentional placement of supply and exhaust heating, ventilation, and air conditioning (HVAC) grilles, or by the intentional creation of pressure differentials between adjacent spaces through specification of offset exhaust and supply air flow rates. Creation of the directional airflow can also be done actively, through the use of fans exhausting through open windows, strategic placement of ductwork attached to portable HEPA filtration units, or dedicated exhaust systems (installed or portable) that generate a desired airflow by exhausting air out of windows, doorways, or through temporary ducts . In specific settings, specialized local control ventilation interventions that establish the desired airflow directions can also be used (see the NIOSH Ventilated Headboard ).
What is the ANSI standard for air filtering?
Filters for use in heating, ventilation, and air conditioning (HVAC) systems are generally tested under procedures outlined in ANSI/ASHRAE Standard 52.2-2017- Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. This standard was developed by ASHRAE, a global society focused on building systems, indoor air quality, and sustainability in the built environment, and is available for free online viewing external icon during the ongoing pandemic. Based on the filtration efficiency determined by the testing procedures, filters are assigned a Minimum Efficiency Reporting Value (MERV). The MERV provides a measure of the “filter efficiency” over the range of particle sizes prescribed in the test procedure. MERV values range from 1 to 16 and higher MERV values correspond to more efficient filters.
How long does it take for particles to settle in the air?
It can take several minutes for particles 10 µm in size to sett le, while particles 5 µm and smaller may not settle for hours or even days. Dilution ventilation and particle filtration are commonly used to remove these smaller particles from the air. Larger particles can also be removed using these strategies, but since they fall out of the air quickly, they might not have a chance to get captured by filtration systems.
How to exhaust air from a window?
One helpful strategy is to use a window fan, placed safely and securely in a window , to exhaust room air to the outdoors. This will help draw outdoor air into the room via other open windows and doors without generating strong room air currents. Similar results can be established in larger facilities using other fan systems, such as gable fans and roof ventilators.
What is supply only ventilation?
Supply-only ventilation systems usually deliver ventilation air through the same ducts used for heating and cooling. To prevent overventilation, the fresh air duct should include a motorized damper, and the damper should be controlled by an AirCycler control. Many installers forget to commission the ventilation system — that is, to measure and adjust the ventilation rate to confirm that ventilation airflow complies with ASHRAE 62.2.
Why should ERV be installed with dedicated duct systems?
After several discussions with ERV manufacturers’ support staff, I have come to the conclusion that they should be installed with dedicated duct systems to avoid the complexity of control systems and the energy use involved with running the blower motor.
What is a supply only HVAC system?
Supply-only systems normally have an outside air intake into the HVAC return plenum with a controller that turns on the HVAC blower motor and opens a damper when air is needed.
Can an ERV motor move air through a duct?
In doing some research on ERVs, I learned that if they are connected to whole-house duct systems, the air handler blower must run to move the outside air throughout the house – the ERV motor can’t move enough air through a duct system.
Can you use a continuous vent fan in a bathroom?
In the humid Southeast, we tend to discourage exhaust-only systems, but some developers and contractors meet the requirement by using a continuous bath vent fan – not the most efficient method, but it is simple.
Do you need a high ventilation rate for frying turkeys?
I kind of like this last idea, because the designed rate seems to me to be somewhat arbitrary. It has to be either too high or too low for most people. If you have a bunch of dogs, smoke tobacco, fry turkeys indoors, and don’t vacuum your carpet, then you probably need a high rate of ventilation – maybe even more than the ASHRAE 62.2 rate. If you don’t wear shoes in the house, don’t smoke, don’t have pets, and keep your turkey frying outdoors, then you need less.
What is required for ventilation and space conditioning?
All mechanical ventilation and space-conditioning systems shall be designed with and have installed ductwork, dampers and controls to allow outside air rates to be operated at the larger of (1) the minimum levels specified in Section 120.1 (b)1; or (2) the rate required for make-up of exhaust systems that are required for an exempt or covered process, for control of odors, or for the removal of contaminants within the space.
How far from the roof of a hotel must a ventilated room be?
Exception to Section 120.1 (b)1A: Naturally ventilated spaces in high-rise residential dwelling units and hotel/motel guest rooms shall be open to and within 25 feet of operable wall or roof openings to the outdoors.
What is Exception 1 to Section 120.1 C)1?
Exception 1 to Section 120.1 (c)1: Demand control ventilation . In intermittently occupied spaces that do not have processes or operations that generate dusts, fumes, mists, vapors or gasses and are not provided with local exhaust ventilation (such as indoor operation of internal combustion engines or areas designated for unvented food service preparation), the rate of outdoor air may be reduced if the ventilation system serving the space is controlled by a demand control ventilation device complying with Section 120.1 (c)4 or by an occupant sensor ventilation control device complying with Section 120.1 (c)5.
How many feet of roof openings are allowed for natural ventilation?
Natural ventilation. Naturally ventilated spaces shall be permanently open to and within 20 feet of operable wall or roof openings to the outdoors, the openable area of which is not less than 5 percent of the conditioned floor area of the naturally ventilated space.
When does an occupancy sensor allow pre occupancy purge?
One hour prior to normal scheduled occupancy, the occupancy sensor ventilation control shall allow pre-occupancy purge as described in Section 120.1 (c)2.
What is a 120.1 exception?
Exception to Section 120.1 (a)1: Refrigerated warehouses and other spaces or buildings that are not normally used for human occupancy and work.
How many CFM per person?
15 cfm per person times the expected number of occupants. For meeting the requirement in Section 120.1 (b)2B for spaces without fixed seating, the expected number of occupants shall be either the expected number specified by the building designer or one half of the maximum occupant load assumed for egress purposes in the California Building Code, whichever is greater. For spaces with fixed seating, the expected number of occupants shall be determined in accordance with the California Building Code.
What is the purpose of ventilation?
It’s your ventilation system’s job to rid the indoor air of these pollutants.
What happens if your ventilation isn't working properly?
If your ventilation isn’t working properly, these harmful components make their way into your airways. Damage and irritation of the lung tissue can lead to activation of inflammatory reactions. This is believed to be the biggest driver of diseases and health problems related to air pollutio n. If you are exposed to this over time, the ailments can become chronic.
How do you know if the indoor climate and air quality are good enough?
Then you should check how good the air quality is to determine if you need to take further action .
Why is my indoor air quality so poor?
Ventilation and indoor climate go hand in hand. The most common cause of poor air quality is that the building has an old or poorly maintained ventilation system.
What are the requirements for a workroom?
Workrooms and staff rooms must be designed and furnished to have a satisfactory climate, in terms of temperature, humidity, drafts, air quality and annoying odours. They must be protected against substances that are hazardous to health.
Can polluting activities be encapsulated?
Polluting activities and processes shall, where possible, be encapsulated or equipped with point extraction.
Do ventilation systems need to be equipped with error notification?
Ventilation systems must be equipped with an error notification, if necessary, for the health of the employees
Why do HRVs need ventilation?
Such needs could occur as a result of larger gatherings of people; smoking; a hobby or activity using paint, glues or other air-quality contaminants; or for any other reason that requires additional ventilation to improve the quality of indoor air.
Where do ventilators need to be in the attic?
For proper cooling and efficient operation, any whole-house comfort ventilator requires adequate, unobstructed outlets in the attic through soffit vents, grilles or louvers.
How to determine the NFA of a static ventilator?
To determine the static ventilator net free area (NFA) needed for your attic space, determine the area of the attic in square feet. Divide that area by 150 to determine the square feet of attic ventilation needed. Since manufacturers of static ventilation products rate their products in square inches of NFA, it will be necessary to multiply that value by 144 to determine the square inches required.
How to calculate minimum soffit vent intake area?
To calculate the total minimum soffit vent intake area in square inches, divide the CFM of the PAV by 300 and multiply the result by 144 .
How many CFM inlet area for a fan?
A minimum of one square foot of inlet area for every 300 CFM of HVI-Certified fan capacity is required for proper fan operation.
What is an inflated performance rating?
Inflated performance ratings are common for range hoods that are not HVI-Certified. Selecting range hoods with HVI-Certified Performance Ratings will ensure that ventilation expectations and building code requirements are met.
How to calculate flow rate for whole house ventilator?
The required flow rate can be calculated by multiplying the gross square footage of the entire house (including unoccupied areas like closets) by 3. Be sure to include the "upstairs" area of multilevel homes. This formula assumes an eight-foot ceiling and takes into account typical unoccupied areas.
How long does an outdoor air ventilation system operate?
Exception: The outdoor air ventilation system is not required to operate continuously where the system has controls that enable operation for not less than 1 hour of each 4-hour period. The average outdoor air flow rate over the 4-hour period shall be not less than that prescribed by Equation 4-9.
Where are local exhaust systems required?
Local exhaust systems shall be provided in kitchens, bathrooms and toilet rooms and shall have the capacity to exhaust the minimum airflow rate determined in accordance with Table 403.3.2.3.
What is primary airflow?
Primary airflow: The airflow rate supplied to the zone from the air-handling unit at which the outdoor air intake is located. It includes outdoor intake air and recirculated air from that air-handling unit but does not include air transferred or air recirculated to the zone by other means. For design purposes, Vpz shall be the zone design primary airflow rate, except for zones with variable air volume supply and Vpz shall be the lowest expected primary airflow rate to the zone when it is fully occupied.
What is the minimum openable area to the outdoors?
The minimum openable area to the outdoors shall be 4 percent of the floor area being ventilated.
How far from lot lines should intake openings be?
401.4 Intake opening location. Air intake openings shall comply with all of the following: 1. Intake openings shall be located not less than 10 feet (3048 mm) from lot lines or buildings on the same lot. 2.
Is recirculation of air prohibited?
Recirculation of air that is contained completely within such spaces shall not be prohibited. Where recirculation of air is prohibited, all air supplied to such spaces shall be exhausted, including any air in excess of that required by Table 403.3.1.1. 4.
Can outdoor air be recirculated?
The outdoor air required by Section 403.3 shall not be recirculated. Air in excess of that required by Section 403.3 shall not be prohibited from being recirculated as a component of supply air to building spaces, except that:
What is a supply ventilation system?
Like exhaust ventilation systems, supply ventilation systems are relatively simple and inexpensive to install. A typical supply ventilation system has a fan and duct system that introduces fresh air into usually one -- but preferably several -- rooms that residents occupy most (e.g., bedrooms, living room). This system may include adjustable window or wall vents in other rooms.
How many fans does a balanced ventilation system have?
A balanced ventilation system usually has two fans and two duct systems. Fresh air supply and exhaust vents can be installed in every room, but a typical balanced ventilation system is designed to supply fresh air to bedrooms and living rooms where occupants spend the most time. It also exhausts air from rooms where moisture and pollutants are most often generated (kitchen, bathrooms, and perhaps the laundry room).
Why do exhaust systems have higher heating and cooling costs?
Exhaust ventilation systems can also contribute to higher heating and cooling costs compared with energy recovery ventilation systems because exhaust systems do not temper or remove moisture from the make-up air before it enters the house.
What are the concerns with exhaust ventilation systems?
One concern with exhaust ventilation systems is that -- along with fresh air -- they may draw in pollutants, including:
Why mix indoor and outdoor air?
May require mixing of outdoor and indoor air to avoid drafts in cold weather
Is a balanced ventilation system more expensive to install than a supply or exhaust system?
Because they require two duct and fan systems, however, balanced ventilation systems are usually more expensive to install and operate than supply or exhaust systems.
Can exhaust vents be used in cold climates?
Exhaust ventilation systems are most appropriate for cold climates. In climates with warm humid summers, depressurization can draw moist air into building wall cavities, where it may condense and cause moisture damage.
Supply-Only System Problems
ERVs: Are They as Good as We Think They Are?
- In doing some research on ERVs, I learned that if they are connected to whole-house duct systems, the air handler blower must run to move the outside air throughout the house – the ERV motor can’t move enough air through a duct system. After several discussions with ERV manufacturers’ support staff, I have come to the conclusion that they should be installed with de…
So How Much Ventilation Do We Really Need?
- I’ve heard Terry Brennan suggest that ASHRAE 62.2 is too low a ventilation rate. I’ve heard Armin Rudd say it may be too much. Joe Lstiburek recommends installing systems that provide 1.5 times the required rate, but setting them to run initially at ½ the rate, letting the occupants adjust it themselves. I kind of like this last idea, because the d...