Before a room can receive the correct amount of airflow, the blower in the air-handling equipment must move it through the duct system. Many installations are doomed from the start due to restrictive filters, coils, and weak blowers. Poorly selected equipment and components are frequent offenders when fan airflow is low.

The next stop in airflow distribution is the duct system itself. Let’s face it, most ducts are severely undersized and poorly installed. If you began testing today, you would find more messed-up systems than you could ever correct. We used to call this inventory. Improper sizing techniques, poor installation practices, and inadequate access negatively impact room comfort.

To rule out airflow as a contributing factor, you’ll need to measure and diagnose the air side of the system. This begins with static pressure testing and evolves into airflow testing at the equipment and individual rooms. Once you have these values, compare them to equipment specifications and industry standards. You can’t eliminate airflow as a potential suspect until it has been measured.

DUCT TEMPERATURE LOSS

The second factor influencing individual room comfort is temperature loss through the duct system. Temperature is the second ingredient added to airflow that determines if the right amount of Btu are delivered to a room. Proper temperature and airflow are necessary to properly heat and cool a room. You can have the right amount of airflow and still have comfort issues if temperature is absent.

Factors frequently contributing to duct temperature loss include:

• No insulation;
• Poor duct location, like a 140° attic;
• Inflated R-value ratings of the insulation type you use;
• Improper installation of duct insulation; and
• Return duct leakage pulling in unconditioned air.

The easiest way to determine if you have a duct temperature loss issue is to compare equipment temperature change to the room temperature change. There shouldn’t be any more than a 10 percent difference between them. If your values exceed this, you’re likely losing too much temperature through the ducts.

AIRFLOW IMBALANCES

Imbalances created by out-of-proportion airflow also contribute to individual room comfort problems. When these conditions exist, airflow is pulled or pushed out of a building through sources that add extra load to the building. In many cases, this can overwhelm the capacity of the HVAC system and reduce its capacity. If you find yourself addressing a room complaint where humidity is the issue, an airflow imbalance might be the source.

Some of the most common sources of airflow imbalances include:

• • Duct leakage;
• • Central return installations;
• • Closing interior doors;
• • Absence of air balancing; and
• • Exhaust fans.

To uncover the impact of airflow imbalances, testing becomes a bit more specialized since you’re looking at airflow interactions within a building. You’ll need to eliminate each of the potential sources above as suspects. Airflow and room pressure testing are important tests to track down and provide solutions to this elusive source.

BUILDING DEFECTS

If the HVAC system checks out fine, it’s time to expand your search to the building. Remember, the building is an extension of the HVAC system and the connection point between airflow from supply registers to return grilles. When there are flaws in the building, even the perfect HVAC system won’t be able to overcome these issues.

Some of the most common sources of building defects include:

• Inadequate insulation;
• Improperly installed insulation, such as bonus room kneewalls and floors; and
• Holes in the building, commonly known as thermal bypasses.

You might be wondering why this conversation switched from HVAC to insulation and holes in a building. These flaws affect what is known as the mean radiant temperature (MRT). A standard thermometer won’t pick up this comfort influencer, as it’s a calculated value based on air temperature and surface temperatures.

The ideal conditions for comfort to exist occur when the surfaces of a building are very close to the temperature on the thermostat. If these temperatures are close, your customers will likely be comfortable. As these temperatures begin to drift farther apart, it becomes harder to maintain comfort.

Thermal imaging cameras are a valuable test instrument to use if you suspect a surface temperature issue.

INTERNAL LOADS

The last source of an uncomfortable room can be the easiest to solve — internal loads that haven’t been accounted for can wreak havoc on room temperatures. Be aware of additional loads adding excessive heat to a room. Comfort issues in bedrooms can often be solved by making changes in lighting, television type, or removing a mini-fridge from the teenager’s room.

In the end, it’s all about Btu. If you can’t control and counteract the amount of heat being added to or removed from a room, there will be comfort complaints. Unless you measure Btu and understand these influencers, your solutions to these problems will always be a guess. You can quantify the sources that lead to the biggest issues your customers have and solve them with time proven methods.  

Publication date: 8/28/2017

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