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Remember the ventilation is only working all the time when in fan mode because the system turns ON and OFF in heat and cooling mode. This is called an on demand system.
Start by gathering the data for fan mode because when guests visit the system fan should be turned ON.
Most but not all Commercial systems are always ON regardless of heat or cooling because the air must be recirculated in public spaces. Staff must be directed to turn ON the fan in a commercial setting before the public arrives. For example many clubhouses use on demand systems and the fans must be turned ON when there are events.
Data can be gathered for heat, cooling, and fan mode. The fan speed varies with the mode in homes. The best case will be fan and cooling modes. Typically when in heat mode the fans run at a lower speed.
Observations Based Approach
The following is a procedure used to gather data and calculate the ACH in a facility using mechanical ventilation without using room size and anemometer measurements. This is called seat of the pants analysis but it is amazing how close the results will match results using tape measures for room sizes and an anemometer.
Estimate the facility size. A good gauge to use is to look at the outside windows. Count the number of windows along the wall. Approximate the width of each window using 3 feet, 4 feet, or 6 feet. For walls where there are no windows visualize how many windows might be along the wall. For the height of a facility visualize how many people can be stacked until the ceiling is reached. Use 6 feet for each person. Alternatively think in terms of 10 foot sections stacked up.
Count the number of ventilation vents. Look around the facility and find the ventilation vents. There may be different sized vents. Count the vents for each size vent. Label then Vent A, B, C etc. Next estimate the size of each vent. They are standard sizes. For homes they tend to be 6 X 12 inches but the openings are 3 X 9 inches. Think in terms of 3, 4, 6, and 12 inches wide and 12, 24, 36, and 48 inches long. Vents in ceiling tile tracks may be 4 X 48 inches.
When you get home or to the office enter the data in the ACH Calculations table.
How can I do this: Ventilation Site Survey
Where to find data: Finding Facility Data
Before you start it is suggested that this entire HELP section be reviewed, starting from the top.
Capture the Room size, Vent Sizes, and Vent Air using the following steps. When an HVAC company prepares balance reports they will provide data marked with an Asterisk *. Many times the height data is not provided. In that case you must estimate the height data.
When a Room Name is provided and Calculate ACH is pressed a new row is added for a new room entry. Start by adding the facility name and press Calculate ACH. Add a room name and press Calculate ACH. Repeat until all the rooms are added. You could use multiple entries for a single room and treat each vent separately.
Add the room sizes as feet-inches (e.g. 10-5 for 10 feet 5 inches). Add the total Vent Air in ft/min for all the vents in a room or for each vent of the same type as v1v2vn (e.g 450+325). If you decided to use multiple entries for a room for each vent enter the vent data.
Each time Calculate ACH is pressed the data is saved when a facility name and location is entered. However, we will periodically remove the saved data. For your records, save the webpage as html on your computer. You can open the saved webpage in your browser and continue from where you may have stopped. Press Calculate ACH often to get the latest updates. Save the html page often on your computer just to be safe, just in case we do maintenance and remove saved surveys. After loading a saved HTML page, press the Calculate ACH button before making new entries, to make sure it is working. Once done close the browser tab.
The multiple vents analysis is used if only the size of the facility is known but not the room sizes. The multiple vents analysis can be used as a sanity check for the room analysis, there are areas like closets with no ventilation. A quick ACH assessment would be to get all the vent data, then just enter the facility size. A more detailed ACH assessment would be to get all the room sizes.
Checking this box will insert a new row between existing rows.
This is a required entry for the data to be accepted. When a room name is added a new row is added at the bottom so that a new room can be added
All entries are in feet and inches. They are entered as ft-in (e.g. 10-3) Enerting the L W H will calculate the Room sq-ft and cu-ft.
If sq-ft and H are entered then L and W is marked as NA and the cu-ft is calculated.
If cu-ft is entered further in the table then L W H and sq-ft are marked as NA.
The room cu-ft is needed to calculate the room ACH.
These are some general rules to estimate the rooms size.
Occupancy based Estimate
Ceiling Height Estimate
Room Length and Width Estimate
All entries are in inches.
The following tables list differnt vent, diffuser, and return grill sizes that can be used to estimate the size of the vents in a facility.
There are basically 3 types of vents:
Look at the ceiling and look for the most common vent. Usually it is always the same type of vent but there may be a mix near fringe spaces in the room. The following tables list differnt vent, diffuser, and return grill sizes that can be used to estimate the size of the vents in a facility.
Vent, Diffuser, and Return Grill Sizes
When looking at a vent, diffuser, or return grill the outside size is larger than the actual vent opening. The following tables identify the vent, diffuser, and return grill openings. The vent, diffuser, and return grill size exceeds the opening on each side by 1 inch. So a vent that looks like and measures from the outside as a 4 x 12 inch vent is really a 2 x 10 inch vent because that is the size of the opening. Also, the opening might be partially blocked around the perimeter and with reinforced strips down the middle. So a 4 x 10 vent might scale down to a 3 x 8 vent opening.
Vents
If applicable pick a vent size (Length and Width). Keep in mind the FPM level for when the Vent Air FPM is requested.
Vent Sizes
Note: Most likely near 350 FPM |
Diffusers
The FPM numbers in the table are the upper limit and the airflow will Most likely be near 350 FPM.
If applicable pick a Diffuser size and enter the neck diameter. Keep in mind the FPM level for when the Vent Air FPM is requested.
4-Way Diffuser Sizes
Note: Most likely near 350 FPM Round Diffusers
Neck Sizes are: 8, 10, 12, 14 inches Note: Most likely near 350 FPM |
Linear Diffuser Sizes
Note 1: 50mm/slot or 1.95 inches/slot |
The following table can be used to deal will mixed sized vents in a room.
Neck Size (in) |
Area sq-in |
6 |
28 |
8 |
50 |
10 |
79 |
12 |
113 |
Return Grills
You can measure the ventilation level using the vents / diffusers or return grills. The return grills suck in the air, send it through the system, and then expels the air out the vents / diffusers. Measuring the return grills will provide an indication of the percent of outside air being introduced into the space. It is also a good sanity check of the vent diffuser measurements.
percent outside air = grills total FPM / vents total FPM
The following are return air grills. The return air grills are similar in size to vents. The data in the following tables are based on 350 linear feet per minute (FPM) as measured at the grill.
If applicable pick a vent size (Length and Width).
Horizontal Return Air Grilles
Note: Most likely near 350 FPM |
Square Return Air Grilles
Note: Most likely near 350 FPM |
Verticle Return Air Grilles
Note: Most likely near 350 FPM |
All entries are in FPM (ft/min). The entry can be a single value or multiple values using a plus sign (+) and or a multiplication sign (*). (ventA + ventB + ventC + ventD*2 + ventE*4...)
The Vent Air can come from observations of the grill size and the general air observations, measured using instruments like an Anemometer, or come from balance reports performed by a vendor.
Vent Air General Observations Appoach
If you feel air across your face the facility ventilation is not bad. In the calculations you can assume 100, 200, 300, 400 linear feet per minute per vent. If you don't feel air across your face but you hear the system you can assume 100, 150, 200 linear feet per minute. If the air is stale and you can't hear or feel air movement assume 0, 50. In general assume 350 FPM unless you detect something to suggest a lower or higher level.
See section Vent Length Width Diameter for more insight.
Vent Air Measurement Approach
Measurements can be performed using an anemometer. Set the anemometer to read the maximum value and move it across the vent. This will provide the maximum FPM from the vent. Enter the value in the ACH Calculations table. For hard to reach vents or high ceiling vents use a selfie stick or a broom handle to attach the anemometer. Example anemometer:
https://www.amazon.com/Anemometer-Handheld-Detector-Temperature-Windsurfing/dp/B07ZJ38ZMX
Balance Reports Approach
HVAC vendors produce balance reports for large facilities. They will have the room ventilation rate as either FPM or liters/sec or liters/sec per person. If it is a per person reading then multiple the maximum occupancy number by liters per second. However this suggests that design data was used instead of actual site survey data. Do not trust the design data. Do the survey and capture the current state of the room, even if it is observation based. You will detect problems if they exist.
The Room sq-ft is calculated from the room measurements of Length, Width, and Height or it is entered from another source like balance reports. If is is entered then the room Length and Width, are marked as NA and the user needs to enter Height data.
The Room cu-ft is calculated from the room measurements of Length, Width, and Height or it is entered from another source like balance reports. If is is entered then the room Length, Width, and Height are marked as NA.
The Vent CFM (cuft/min) is calculated or entered as a number from another source like balance reports. If it is entered then the Vent Size and Vent Air FPM are marked as NA.
Is there a permanently installed Unit Ventilator in the room, not to be confused with portable sanitizers. Look at the image.
These units come in 750, 1000, 1250, 1500 CFM in physical sizes of 69, 81, 93, 105 inches or 5.75, 6.75, 7.75, 8.75 feet.
Is there an Inverter 360 Cassette installed in the room. Look at the image.
The Inverter 360 Cassette is a ceiling mounted ventilator that uses circular ventilation to evenly spread the ventilation across the ceiling while taking in the air from the bottom of circular structure. The air flow rate is selectable and comes in High, Mid, Low or 874, 729, 621 CFM.
The vent CFH (cuft/hr) is calculated.
This calculated using the entries made in the Vent Air FPM area. For example 350 is 1 vent, 350+350 is 2 vents, 350+350+350*2 is 4 vents.
This is calculated using the room cu-ft and vent CFH.
Some facilities have multiple HVAC zones. This is used to document the zone associated with a room. A zone is typically a standalone HVAC unit but not always. If it is a standalone HVAC unit the air is isolated from other zones.
This documents if the vents are blocked by room obstructions. The values are yes / no.
This documents if the system is on, off, or in a failed condition. For example in a clubhouse the fan may be turned off and only runs to maintain temperature. If a user turns on the fan switch, the fan may not activate and this is a fail condition. The values are yes / no / fail
This is entered by the user. The value is determined by the UV-C installer. These systems can offer up to 24 eACH. In the absence of design data and test results to backup the facility installation assume 12 eACH. This is a tried and true system with over 80 years of operational experience.
These systems can offer up to 24 eACH. In the absence of design data and test results to backup the facility installation assume 12 eACH. This is a new system but it is based on the Ceiling Level UV-C technology with a long history of understanding and performance. The figure and table shows how the eACH level drops off as a function of distance.
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Use this to enter other ACH or eACH data. Provide comments in the comments area to indicate the type of ACH. For example there may be a previous site survey that was certified by a City, State, or Federal Government but there may be no other data.
Use this also for other entries like Ionizer eACH Calculations. These systems can have an ACH component and an eACH component. The ACH level is calculated using the CFM output published in the product literature. The CFM typically ranges from 300 to 500 CFM per device. Use the ACH Calculations tool above to determine what values will yeild 300 - 500 CFM. For example: vent length 10, vent width 10, no of vents 1, Vent Air ft/min 450 will equal 312.5 CFM. The eACH level is more problematic and there is no way to determine the eACH levels of these devices in a typical room setting. If design and test data for the installed facility are provided then use that data to enter the eACH level.
Use this entry to add the risk reduction because of the dilution that occurs in large spaces. The risk reduction factors that can be applied are as follows:
Space cu-ft |
Volume Ratios |
Square Footage Ratios |
Wells Riley LS Factors |
400,000 |
40 |
12 |
7.75 |
300,000 |
30 |
9 |
5.94 |
200,000 |
20 |
6 |
4.14 |
100,000 |
10 |
5 |
2.35 |
50,000 |
5 |
3 |
1.49 |
20,000 |
2 |
2 |
1.06 |
<10,000 |
1 |
1 |
1 |
For example, assume that there is a 400,000 cu-ft facility with 2 ACH. The equivalent Large Room Factor ACH (lrfACH) from a risk perspective is 2*7.75 = 15.5 lrfACH. You can do the mechanical ventilation observations or measurements that would result in 2 ACH and then add the difference of 13.5 in the ACH Other field and the total ACH is then 15.5 that includes the ACH and lrfACH components.
The is the total ACH level in a room. ACH Total = ACH + eACH
Enter the Length Width and Height of the building. This is used to compare the size of the rooms in the building to determine if spaces have been missed. There will be differences because of closets, stairs, and other spaces.
Enter the facility name. If there is more than one facility such as in the case of a company with multiple buildings or a franchise enter the address. The address must be separated from the facility name with a dash (-). This is used to disambiguate between the ACH and CAB database. For example, the CAB database may have 1 entry for 50 locations, but there may be 50 ACH site surveys, one for each location.
Use the comments field as a scratchpad area when making facility observations if you are visiting the facility and you are only making visual observations. Once you have the room size and a handle on the vents then use this data to populate the ACH Calculations table.
In the comments use words and phrases like:
The calculate ACH button is used to calculate the data and display the results.
The data is not stored in the database until there is a facility name.
