Have you ever noticed dirt streaking out of the sides of any of the supply vents on the HVAC systems you service? Dirt streaking on supply vents is a common problem HVAC professionals encounter on a daily basis. The underlying cause is often blamed on the HVAC system’s air filtration and is never considered again. In this scenario, no solutions are truly offered, and the streaking often continues. Is it possible there is more to dirt streaking around supply vents than just the quality of the air filter being used?
To keep it simple, I am using “vent” as a generic term to cover all the varieties of terminal devices that could cover a supply branch outlet. Vents are really broken down into the three categories of diffusers, grilles, and registers. Each of these has its own characteristics and definitions that I won’t get into in this article.
A Call for Help — We Have Streaks
My first run-in with dirt streaks occurred about 10 years ago. We received a call to examine dirt streaking on an expensive ceiling. The building was approximately two years old, and the original HVAC company could not determine what was causing the issue. The contractor’s technicians added 1-inch pleated filters in an attempt to better filter the air and solve the problem with no luck.
The HVAC system was equipped with four-way diffusers, which left a nice multi-directional pattern of dirt streaks coming out of the edges. Due to the style of the ceiling and the purposes the building was used for, this issue had to be solved. It wasn’t acceptable for these dirt streaks to be running across the ceiling, as they were pretty noticeable looking up from the ground.
The original company recommended extending ducted sleeves from each diffuser to move them away from the ceiling. This would prevent the dirt streaking and allow the ceiling to be cleaned up. This must have been a good idea, as a couple of other companies made the same suggestion. The only problem with this was it would be more of an eyesore than the dirt streaking. The building owners weren’t buying this solution.
After some digging around, my suggestion for correcting the dirt streaking was a bit more simplistic. When advised they could correct this issue with a case of caulk and a caulk gun, I got a lot of odd looks. It was too simple of a repair. Once I explained what was occurring, and how the caulk could cure it, they were delighted. It was also a solution a member of their staff could easily correct, once shown how.
So, what was the source of this dirt streaking, and why would caulk fix it?
The Source of Dirt Streaking
One of the main contributors to dirt streaking is the turbulence of the conditioned air coming out of a supply vent. When air leaves a supply vent, it is coming out at a high velocity due to being squeezed through the louvers of the vent. This action is similar to placing your thumb over the end of a water hose to increase the distance water can spray.
These particles of dirt often come from two different sources. One common source is from within the room itself. Depending on what is occurring in the room, the duct streaking can have various contributors, such as carpeting, candles, pets, and people. These dirt contributions become entrained in the conditioned air coming out of the supply vent and stick to the surfaces the conditioned air is moving across.
The second common source is unsealed openings where supply boot penetrations are made, such as through drywall or a subfloor. When this occurs, insulation particles or other particulate from the unconditioned space is pulled into the airstream. As these particles from the unconditioned space become entrained in the conditioned air, they are also distributed across the surfaces the conditioned air is blowing on and leave a trail of streaking.
Depending on the conditions of the living space, dirt streaking may be amplified when certain factors exist. For instance, excessive moisture in the room air can allow particles to develop stickiness, while a lack of moisture can cause the dirt particles to be attracted to the building surfaces. The Coanda Effect is another variable that needs to be considered here, as it has a direct influence on how well air is projected across a surface.
Dirt Streaking Solutions
The first step is to determine the source of the dirt. This begins with a visual inspection of the system and the environment it is operating in. One of the first things you should do is examine the equipment and the ducts feeding the vents that have streaking issues.
If the equipment, coil, and ducts feeding the vents that have streaking issues are clean, you can eliminate filter bypass issues or duct leakage as a contributing factor to the dirt streaking. This leaves you with determining if the source of dirt is from particulate within the room itself, or if it is being brought into the room through unsealed boot penetrations.
A common cure in commercial buildings, where the dirt sources are internal, is anti-smudge rings around the vent penetration. You will see these rings on many restaurant vents as sheet metal collars that protrude down from the vent approximately 1.5 inches. These rings break up the action of the air as it exits the register and forces it downward instead of across the ceiling.
When the dirt sources are external, such as from an unconditioned space, sealing the boot penetration to prevent any gaps between the conditioned space and unconditioned space usually does the trick. This was the recommended correction for the issue of dirt streaking I mentioned previously. There were massive gaps around the boot penetrations in the ceiling of this building that were allowing attic air containing cellulose dust to be entrained and spread across the ceiling. Once the boots were sealed, the dirt streaking stopped.
Understanding air properties can make you a real rock star when it comes to solving issues associated with the buildings you service. These issues might not have anything to do with your system, but they appear to. Take a look at the building side of the duct system, and understand the cause-and-effect relationships that influence your systems and the environments they condition.
With the increase of storms in Canada and major floods representing almost 40 per cent of all natural disasters recorded, we need to take the proper preventive measures to combat extreme weather at the cottage.
Recent evidence suggests that the severity and frequency of severe weather, such as storms, floods, droughts and landslides, as well as extreme heat and smog, will continue to rise. According to Environment Canada, data show that the average summer temperatures have climbed one degree since 1970 and precipitation has increased about five per cent.
Seasonal properties are especially vulnerable because they're isolated and occupied less frequently. A rural location can also often mean more expense to repair any damage.
With increasingly severe and changing weather patterns, it's crucial that cottage owners are well informed about their insurance needs. It's important for all cottage and homeowners to speak with their insurance providers to ensure they have adequate coverage.
Aviva Canada, one of Canada's leading lifestyle and leisure insurers shared these simple tips for cottage owners to consider.
Backup power. A backup system will keep your cottage safe during a power failure.
Roof repair. Cottage country is often windy, but with regular maintenance such as cleaning the eaves troughs and drains, you can prolong the lifespan of your roof.
Rot-not strategy. Heavy rain and flooding can result in rotting decks and foundations. Ensure proper preservation from rot by spraying your deck with a zinc-based wood preservative.
To hunt down airflow restrictions, you’ll need the following test instruments and accessories to get started:
• A digital camera;
• An analog or digital manometer;
• One length of tubing (3/16-inch inside diameter [ID] neoprene works well);
• One Dwyer Model A-303 Static Pressure Tip;
• A 3/8-inch bullet-tip drill bit with a sheath to prevent drilling in too far;
• A 3/8-inch plastic test port plugs; and a
• Carrying Case.
If you’re going to hunt, you have to have the right stuff. Otherwise, you’re only posing as a real airflow hunter.
SCOUTING FOR AIRFLOW RESTRICTIONS
Good hunters scout their locations before starting any hunt. They look for visual clues that identify deer have been traveling in the area, signs of deer tracks, scrapes on trees, and frequently used trails. These are all visual indications that deer are present.
Airflow restrictions can have visual clues indicating they are present, too.
Your first step should be a visual inspection. What type of visual clues are you looking for? Check for the following when you suspect an airflow problem:
• Pinch points in flexible duct systems;
• Restrictive duct fittings;
• Improper flexible duct suspension;
• Branch ducts that are too long;
• Too many elbows;
• Dirty air filters; and
• Dirty blower wheels.
Your solution to an airflow restriction might be as simple as correcting one of the defects mentioned above. If you uncover one of these issues, take a digital photo and share your find. Customers like to see what was causing their pain. If the problem is a bit more complicated, and it often is, the hunt is going to get a lot more interesting and fun.
TIME TO HUNT
Some airflow restrictions will be harder to find and won’t provide any visual clues. You’ll need to go one step further to track them down. In this case, you have to identify the location of the airflow problem. Is it isolated to a particular room or area, or is the problem spread across the entire system?
If the problem affects the entire system, begin by measuring total external static pressure (TESP). Excessive TESP is a sign that a hidden airflow problem exists. It won’t identify the restriction as additional pressure tests will be needed to track it down. If the issue is isolated to a particular room or area, you can jump straight to measuring duct pressures to track down the problem.
START AT THE AIR-HANDLING EQUIPMENT
To pinpoint an overall airflow restriction, first measure TESP and then add air filter pressure drop and indoor coil pressure drop to this reading. This provides an overall picture of what’s happening with the system. To do this, you’ll need to install 3/8-inch test ports (drill holes) where air enters and leaves the equipment.
You’ll need to drill into areas that could cause refrigerant or water leaks so be careful. Use a drill bit sheath, so the drill bit only penetrates the metal 1/8th of an inch or so and doesn’t get pulled into the equipment.
Once test ports are installed, measure pressure entering and leaving the equipment and add these pressures together to determine TESP. The side of the system with the highest pressure reading is often where the airflow restriction is located. If measured TESP exceeds the air-handling equipment’s maximum rated TESP, an airflow problem likely exists.
AIR FILTER PRESSURE DROP
If the air filter is located at the air-handling equipment, start by measuring its pressure drop. Many times a clean filter made of a restrictive media type or one that is undersized in surface area will choke down airflow across the entire system.
Measure filter pressure drop by measuring pressure before and after the filter. Once these readings are obtained, subtract them from one another to determine filter pressure drop.
A properly sized air filter should typically have a filter pressure drop no more than 20 percent of the air-handling equipment’s maximum rated TESP. This rating is usually found on the equipment nameplate of the air-handling equipment. For a system rated at a maximum total external static pressure of 0.50 inch of water column, the pressure drop across the filter should not exceed 0.10 inch water column (20 percent x 0.50 - 0.10).
If the system you’re testing has a return air filter grille away from the equipment, you still measure filter pressure drop, just in a different location. Measure pressure drop across the filter by piercing the static pressure tip through the return air grille and filter.
Pressure drop will be read directly on the display of the manometer. If filter pressure drop is acceptable, continue hunting, you haven’t located the restriction yet. It’s time to move to the indoor coil.
INDOOR COIL PRESSURE DROP
Measuring indoor coil pressure drop is usually a roadblock for many hunters as they worry about piercing the coil and causing a refrigerant leak. If you carefully inspect behind coil access panels before drilling and use a drill bit stop or sheath, your chances of piercing a coil are greatly reduced.
To measure coil pressure drop, measure pressures before and after the coil. Once these readings are obtained, subtract them from one another to determine the pressure drop across the coil. Also, a wet coil will often have a significantly higher pressure drop than a dry coil.
A properly sized, clean coil should typically have a pressure drop no higher than 0.20 to 0.30 inch of water column. If the pressure drop exceeds this, it could be an indicator the coil is too restrictive for the proper amount of airflow.
ADD DUCT SYSTEM PRESSURES
When filter and coil pressure drop are acceptable, or your airflow problem is isolated to a particular room or area, look at supply and return duct pressures to continue hunting the airflow restriction. The pressure on either side of the duct system should not be higher than 0.10-inch water column.
First, measure the return duct pressure. If you measured filter pressure drop at the equipment, this will be the same pressure reading as the pressure entering the filter. Next, measure the supply duct pressure. If you measured indoor coil pressure drop, this will be the pressure reading taken in the supply plenum.
The side of the duct system with the highest pressure is the one that is the most restrictive and should be tested first. From the test location, start working down the duct system by installing test ports every 4 feet or so downstream. Be sure to measure the pressure drop across suspect duct fittings like sharp transitions and turns.
Once you identify a drastic pressure change, note what is inside the duct that could be causing it. Common causes include loose duct liner, closed fire dampers, and collapsed ducts.
Simply, when you find the resistance, you find the restriction — fix the resistance and you fix the airflow restriction.
Warning — just because you correct a duct pressure issue, it doesn’t mean the overall airflow issue has been fixed. You could still have issues with high static pressure or undersized ducts. It’s a good idea to measure total external static pressure just to ensure a hidden airflow problem doesn’t exist.
Hopefully, the next time you discover an airflow restriction, you’re better equipped to hunt it down. In some hunts, you’ll have to bring out specialized equipment, such as air-balancing hoods or anemometers, to continue tracking bigger game and larger trophies.
As part of their ongoing commitment to safety and customer satisfaction, Enbridge Gas Distribution has changed the number of days given to make repairs or corrections to a B tag from 35 days to 42 days. They are making this change to harmonize processes with other natural gas utilities in Ontario and provide a consistent experience for contractors, appliance installers, certificate holders and builders.
Enbridge will begin to use the new 42 day warning tag and process on Monday, August 13th, 2018.
As communicated previously, faxes are no longer accepted. Technicians can simply take a picture with their phone or tablet and email it directly to Enbridge. This is more reliable, trackable and avoids delays in processing.