When Duct Sealing Kills HVAC Equipment and Efficiency

When Duct Sealing Kills HVAC Equipment and Efficiency

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Session Overview Benefits of Duct Sealing Duct Sizing History The Dark Side of Duct Sealing When Equipment Life Expectancy and Efficiency are Reduced Ensure You Aren t Sealing the Death Sentence on an HVAC System Building a Bullet Proof Duct Sealing Program Overview

Benefits of Duct Sealing Duct Blowers operate on the concept of air leakage - there must be a hole and a pressure difference. The Duct Blower creates the pressure difference and a flow of air through leaks in the duct system will result. A test pressure of 25 pascals (.10 water column) is commonly used in residential duct leakage testing. You ll see this number again soon.

Benefits of Duct Sealing Duct leakage is a large contributor to wasted energy in homes across the country. It is estimated up to 30% of a systems efficiency is lost to duct leakage alone. Safety is another issue that duct leakage has an impact on. Return side duct leakage in an area that has combustion appliances can lead to backdrafting and spillage of flue gases. Pressure Imbalances are another byproduct of duct leakage. These imbalances can bring unconditioned outdoor air into a home and push conditioned air to the outside of the home.

Benefits of Duct Sealing Dominant Supply Duct Leakage

Benefits of Duct Sealing Dominant Return Duct Leakage

Benefits of Duct Sealing Equal or No Duct Leakage

Energy Code Requirements for Duct Leakage Post Construction Test: Less than 8 CFM 25 per 100ft 2 CFA duct leakage to the outside Less than 12 CFM 25 per 100ft 2 CFA total duct leakage Rough-In Test: Less than 6 CFM 25 per 100ft 2 CFA with the air handler installed Less than 4 CFM 25 per 100ft 2 CFA with no air handler installed *Duct tightness testing is not required if the air handler and all ducts are located inside conditioned space.

Energy Code Requirements for Duct Leakage Post Construction Test: Less than 4 CFM 25 per 100ft 2 CFA total duct leakage No duct leakage to outside provision in the 2012 IECC Rough-In Test: Less than 4 CFM 25 per 100ft 2 CFA with the air handler installed Less than 3 CFM 25 per 100ft 2 CFA with no air handler installed *Duct tightness testing is not required if the air handler and all ducts are located inside conditioned space.

Duct leakage is an important element when it comes HVAC system performance, but not the only element. Others include: Proper sizing Insulation Airflow delivery Benefits of Duct Sealing A duct system can only work properly when all 4 aspects fall into place.

Duct Sizing History Airflow has been assumed for decades based on various design methods and rules of thumb. The truth is very few duct systems perform as designed.

Duct Sizing Assumptions Design Static of.10 w.c. The existing duct system works correctly Equipment will fix a bad duct system A 6 duct magically delivers 100 cfm Where have these assumptions gotten us?

the system is needed for it to perform well. Think and speak of static pressure like blood pre ssure. High static pressure, like high blood pressure is not good and indicates an immediate improvement is needed. Tech Duct Tip: Comparing Sizing High Assumptions Static Pressure to High Blood Pressure National Typical Static Pressure Static pressure is the amount of pressure a fan pushes and pulls against to move air through an HVAC STATIC system. Each fan PRESSURE is rated with a maximum total / external BLOOD static pressure PRESSURE it can operate under. If static TABLE pressure exceeds the rated amount, the fan typically cannot move the required airflow. Here is a static pressure concept is that simple to understand and explain. The national typical residential total external static pressure is.82 w.c. One of the first tests taken to determine the performance of an HVAC system is to measure total external static pressure. This reading is compared to the equipment rated static pressure. If measured pressure is higher than rated pressure, this is not good for health of the system and a change in With many residential fans rated at.50,the typical residential system in the system is needed for it to perform well. Think and speak of static pressure like blood pre ssure. High static pressure, like high blood cooling mode is delivering less than 300 cfm per ton pressure is not good and indicates an immediate improvement is needed. STATIC PRESSURE / BLOOD PRESSURE TABLE Think and speak of static pressure like blood pressure. High static pressure, like high blood pressure is not good and needs immediate attention!

Duct Sizing Assumptions Static pressure is the amount of pressure a fan pushes and pulls against to move air through a duct system. This value is rarely considered. Duct leakage acts as static pressure relief. As duct leakage is sealed, static pressure increases. This is the dark side of duct sealing.

The Dark Side of Duct Sealing We assume the fan moves enough air Not all fans are equal Coil, filter, and duct restrictions Fan speed may be incorrect Fan data holds the truth

The Dark Side of Duct Sealing As static pressure increases, airflow decreases Engineering data courtesy of Goodman Manufacturing

The Dark Side of Duct Sealing All fans are not created equal. Engineering data courtesy of Goodman Manufacturing

The Dark Side of Duct Sealing Fan Data/Coil Resistance Engineering data courtesy of Goodman Manufacturing Total external static can t be over.30 for the fan to the move the proper amount of airflow! What about the filter?

The Dark Side of Duct Sealing Fan Data/Filter Resistance The filter added.25 worth of pressure drop to the coil. Engineering data courtesy of Honeywell International Inc.

The Dark Side of Duct Sealing Total Component Resistance Total external static pressure needed?.30 Coil pressure drop at 2000 cfm? Filter pressure drop at 2000 cfm? Total component pressure drops?.39.25.64 The fan is only strong enough to handle a filter! There is no additional capacity for a coil, ductwork, and grilles. Some fans are too weak to move the required airflow.

The Dark Side of Duct Sealing What about equipment with variable speed (ECM) fans? Engineering data courtesy of Ingersoll Rand

When Equipment Life and Efficiency are Reduced = Laboratory Conditions vs. Field Conditions

When Equipment Life and Efficiency are Reduced 2 ton system at 95º outdoor temperature, 67º entering wet bulb, and 800 cfm. Engineering data courtesy of Goodman Manufacturing

When Equipment Life and Efficiency are Reduced Three Forms of Heat (BTUs) 1. Sensible Heat 2. Latent Heat 3. Total Heat

When Equipment Life and Efficiency are Reduced Sensible Heat (Btu) Formula Sensible Btus = cfm x t x 1.08 CFM = Fan airflow t = The dry bulb temperature change 1.08 = Sensible Btu multiplier at sea level -.075 pounds of air per cfm x.24 (The specific heat of air) x 60 (minutes in an hour)

When Equipment Life and Efficiency are Reduced Sensible Heat (Btu) Example - Good Furnace rated at 60,000 Btu Output Based on measured total external static pressure and fan speed, the fan table shows the fan delivering 1040 cfm, and the temperature change through the heating equipment at 53.0. Calculate the equipment delivered BTUs 1040 cfm x 53.0 x 1.08 = 59,530 Sensible Btus The furnace is designed to deliver 60,000 Sensible Btus.

When Equipment Life and Efficiency are Reduced Sensible Heat (Btu) Example Not Good Furnace rated at 60,000 Btu Output Based on measured total external static pressure and fan speed, the fan table shows the fan delivering 720 cfm, and the temperature change through the heating equipment at 57.0. Calculate the equipment delivered BTUs 720 cfm x 57.0 x 1.08 = 44,323 Sensible Btus What happened? Which factor changed?

When Equipment Life and Efficiency are Reduced Total Heat To calculate total heat, measure wet bulb temperatures to measure the changes in heat and moisture in conditioned air. The total heat formula requires enthalpy as a factor in the formula. Find enthalpy by measuring wet bulb temperature and then converting it to enthalpy. An air conditioner removes two types of heat from the air that passes through it. It removes sensible heat and latent heat. Sensible heat (temperature change) is the same kind of heat, heating systems move. Cooling systems also remove latent heat (moisture) from the air.

When Equipment Life and Efficiency are Reduced Total Heat (Btu) Formula Total Btus = cfm x h x 4.5 CFM = Fan airflow h = The enthalpy change 4.5 = The total Btu multiplier at sea level. 4.5 equals.075 pounds of air per cfm x 60 (minutes in an hour)

When Equipment Life and Efficiency are Reduced Total Heat (Btu) Example - Good 3.5 Ton cooling system rated at 40,800 Total Btu Output Based on measured total external static pressure and fan speed, the fan table shows the fan delivering 1390 cfm, and the enthalpy change through the cooling equipment at 6.5 Btus per pound of air. Calculate the equipment delivered BTUs 1390 cfm x 6.5 Δh x 4.5 = 40,658 Total Btus The cooling system is designed to deliver 40,800 Total Btu.

When Equipment Life and Efficiency are Reduced Total Heat (Btu) Example Not Good 3.5 Ton cooling system rated at 40,800 Total Btu Output Based on measured total external static pressure and fan speed, the fan table shows the fan delivering 980 cfm, and the enthalpy change through the cooling equipment at 5.24 Btus per pound of air. Calculate the equipment delivered BTUs 990 cfm x 5.24 Δh x 4.5 = 23,108 Total Btus What tonnage is this system operating at?

When Equipment Life and Efficiency are Reduced The Results Furnace cycling on primary limit Premature heat exchanger failure Decreased heating capacity Laboratory rated efficiency isn t achieved

When Equipment Life and Efficiency are Reduced The Results Refrigerant floodback Intermittent coil freeze-ups Premature compressor failure Excessive runtime

Ensure You Aren t Sealing the Death Sentence on an HVAC System Account for Static Pressure Static Pressure is one of the foundations of airflow, it must be accounted for. When a duct system is sealed, static pressure will rise. Drastic reduction in airflow with constant speed fans. Increase in energy consumption with variable speed fans. This is in direct opposition to the good intentions of duct sealing. Unless you are measuring static pressure you will miss this every time.

Ensure You Aren t Sealing the Death Sentence on an HVAC System Measure Static Pressure 1. Measure Total External Static Pressure (TESP) and compare to nameplate rating 2. Use measured TESP and fan speed to plot fan airflow on manufacturer fan charts. Compare fan airflow to required airflow. 3. If static pressure ratings is high and/or fan airflow is low, additional diagnostics and duct repair is needed before duct sealing can begin.

Ensure You Aren t Sealing the Death Sentence on an HVAC System Measure Pressure Drops 1. Pressure Drop involves taking the static pressure on either side of a component in a duct system. 2. An alarming percentage of high efficiency filters and coils are too restrictive. 3. Pressure drop will help pinpoint many of these system performance issues.

Building a Bullet Proof Duct Sealing Program Duct Design Duct Sealing Performance Current Verification Methods are Missing Something

Building a Bullet Proof Duct Sealing Program To build a real duct sealing program, these system readings need to be measured and diagnosed to determine true performance of the HVAC systems. From these measurements, surgical repairs are then made. Static Pressure Temperature Delivered Airflow Delivered BTUs

Building a Bullet Proof Duct Sealing Program Measure Static Pressure 1. Measure Total External Static Pressure (TESP) and compare to nameplate rating 2. Use measured TESP and fan speed to plot fan airflow on manufacturer fan charts. Compare fan airflow to required airflow. 3. If static pressure ratings is high and/or fan airflow is low, additional diagnostics and duct repair is needed before duct sealing can begin.

Building a Bullet Proof Duct Sealing Program Measure Pressure Drops 1. Pressure Drop involves taking the static pressure on either side of a component in a duct system. 2. An alarming percentage of high efficiency filters and coils are too restrictive. 3. Pressure drop will help pinpoint many of these system performance issues.

Building a Bullet Proof Duct Sealing Program Temperature is a key indicator as to how well a piece of equipment and the installed system are operating. Equipment operating temperatures are indicators of how well the equipment is performing. System temperature measurements must be taken into account as they include duct system heat gain and heat loss.

Building a Bullet Proof Duct Sealing Program Delivered Airflow is measured with the use of an air balancing hood. In order for true comfort to be achieved, the proper quantities of airflow have to be delivered to the proper areas of a home. You will find on many test that the delivered airflow numbers rarely match design airflow numbers. When this occurs the duct system must be air balanced if capable.

Building a Bullet Proof Duct Sealing Program Delivered Btus are the end result when everything else comes into place. The only way that delivered Btus can be accomplished, is if the proper quantities of air with the proper air temperature is getting to the rooms you are trying to condition. As important as duct leakage testing is, there are no means for a duct leakage test to determine these important operating parameters of an HVAC system. All of the listed parameters above need to be in place before a properly operating system can be ensured. Any duct sealing program missing these aspects will fall short of intentions.

Conclusion Duct sealing has many benefits on a properly sized and installed duct system. These benefits cannot be denied. Due to duct sizing traditions and rules of thumb, the majority of existing duct systems are undersized and running high external static pressure. Sealing undersized duct systems reduces performance. o Airflow decreases due to an increase in static pressure. o Some fans are weak and cannot move needed airflow. o Variable speed fans consume more energy to move needed airflow.

Conclusion Airflow is one of the key factors in Btu delivery. When airflow is low, equipment and system performance degrade. The good intentions of duct sealing are being missed by overlooking and failing to allow for the true operation of the HVAC system. For duct sealing programs to work as intended, real performance measurements must be taken to gauge a systems current operating state. From these measurements, additional repairs may be discovered to upgrade a system to the point it can be sealed.

David Richardson National Comfort Institute 2016 NCI, Inc.