Duct leakage testing

Last updated
Duct leakage test in the US Duct Blaster.jpg
Duct leakage test in the US

A duct leakage tester is a diagnostic tool designed to measure the airtightness of forced air heating, ventilating and air-conditioning (HVAC) ductwork. A duct leakage tester consists of a calibrated fan for measuring an air flow rate and a pressure sensing device to measure the pressure created by the fan flow. The combination of pressure and fan flow measurements are used to determine the ductwork airtightness. The airtightness of ductwork is useful knowledge when trying to improve energy conservation.

Contents

Uses

Duct leakage testers are used in residential single family, residential multi-family, and commercial buildings that have a forced air delivery systems for heating and cooling.

Operation

A basic duct leakage testing system includes three components: a calibrated fan, a register sealing system, and a device to measure fan flow and building pressure. Supply registers or return air grills are sealed using adhesive tapes, cardboard, or non-adhesive reusable seals. One register or return is left unsealed, and the calibrated fan is connected to it. Pressure is monitored in one of the branches of the ductwork while the calibrated fan delivers air into the system. As air is delivered into the ductwork, pressure builds and forces air out of all of the openings in the various ductwork connections or through the seams and joints of the furnace or air-conditioner. The tighter the ductwork system (e.g. fewer holes), the less air is needed from the fan to create a change in the ductwork pressure.

A duct leakage test can be performed by either pressurizing or depressurizing the ductwork. Ductwork that is outside the building envelope, such as in an unconditioned attic or crawlspace, should be pressurized so as to not bring in unwanted contaminants such as dust.

Measurements

Duct tester airtightness measurements are presented in a number of different formats including but not limited to:

Air flow (CFM)

CFM25 is defined as the air flow (in cubic feet per minute) needed to create a 25 Pascal pressure change in the ductwork. CFM25 is one of the most basic measurements of ductwork airtightness. A pressure of 25 Pa is equal to 0.1 inches (0.25 cm) of water column.

Leakage area

Leakage area estimates are a useful way to visualize the equivalent cumulative size of all leaks or holes in the ductwork. There are a variety of standard calculation methods used to estimate leakage areas.

Ratings

Commercial and industrial ductwork is often tested to standards developed by the Sheet Metal and Air Conditioning Contractors' National Association (SMACNA). Ductwork is temporarily subjected to higher pressures, and then given a rating or classification rather than a leakage estimate.[ further explanation needed ]

Additional methods

Leakage to outside

The above test procedure describes how to determine total duct leakage, or how much leakage there is for all of the ductwork connected to the HVAC system. Another test is for duct leakage to the outside. Depending on the location of the house in the United States, some HVAC systems are completely inside the thermal envelope, some are completely outside the thermal envelope, and some are a combination of the two. Energy conservation is improved mostly by sealing ductwork that is outside the thermal envelope or connected to the outside. With mixed systems, it is possible to determine amount of leakage to the outside by simultaneously pressurizing the house while pressurizing the ductwork, and measuring the amount of flow that is required to equalize the pressure.

Blower door subtraction

Another form of duct leakage to outside uses a blower door to measure the total amount of leakage of the house, then seal off all registers and returns and to measure the leakage again. The next step requires measuring the pressure in the taped off duct system with respect to the building. The blower door manual will include a correction table to determine a correction factor based on the pressure in the duct work. To calculate the duct leakage to outside, subtract the leakage with the registers sealed from the total building leakage and multiply by the correction factor. [1]

Pressure pan test

Small pressure pan application Pressure Pan Application.JPG
Small pressure pan application

A third test method to determine if ductwork is leaking to the outside is to use a pressure pan, which is a register cover with a pressure tap for a hose connection. With the house pressurized (or depressurized) to 50 Pa (-50 Pa) using a blower door, a pressure gauge is attached to the pressure pan by means of a hose. If the pressure difference is near zero, this indicates that the ductwork associated with that particular register is not connected to the outside. A pressure 5 Pa or above indicates that the duct work is connected to or leaking to the outside. A smaller pressure difference indicates greater leakage. This method does not quantify duct leakage, but serves to identify locations of ductwork runs that are leaking to the outside. It is more of a qualitative measure, used for fault isolation.

Related Research Articles

Heating, ventilation, and air conditioning Technology of indoor and vehicular environmental comfort

Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to heat, cool, purify, replace, circulate, and control the humidity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR.

Blower door

A blower door is a machine used to measure the airtightness of buildings. It can also be used to measure airflow between building zones, to test ductwork airtightness and to help physically locate air leakage sites in the building envelope.

A sound attenuator, or duct silencer, sound trap, or muffler, is a noise control acoustical treatment of Heating Ventilating and Air-Conditioning (HVAC) ductwork designed to reduce transmission of noise through the ductwork, either from equipment into occupied spaces in a building, or between occupied spaces.

Damper (flow)

A damper is a valve or plate that stops or regulates the flow of air inside a duct, chimney, VAV box, air handler, or other air-handling equipment. A damper may be used to cut off central air conditioning to an unused room, or to regulate it for room-by-room temperature and climate control. Its operation can be manual or automatic. Manual dampers are turned by a handle on the outside of a duct. Automatic dampers are used to regulate airflow constantly and are operated by electric or pneumatic motors, in turn controlled by a thermostat or building automation system. Automatic or motorized dampers may also be controlled by a solenoid, and the degree of air-flow calibrated, perhaps according to signals from the thermostat going to the actuator of the damper in order to modulate the flow of air-conditioned air in order to effect climate control.

Air handler Device used to regulate and circulate air as part of an HVAC system

An air handler, or air handling unit, is a device used to regulate and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. An air handler is usually a large metal box containing a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers. Air handlers usually connect to a ductwork ventilation system that distributes the conditioned air through the building and returns it to the AHU. Sometimes AHUs discharge (supply) and admit (return) air directly to and from the space served without ductwork

Air door

An air door or air curtain is a device used to prevent air or contaminants from moving from one open space to another. The most common use is a downward-facing blower fan mounted over an entrance to a building, or an opening between two spaces conditioned at different temperatures.

Variable air volume (VAV) is a type of heating, ventilating, and/or air-conditioning (HVAC) system. Unlike constant air volume (CAV) systems, which supply a constant airflow at a variable temperature, VAV systems vary the airflow at a constant temperature. The advantages of VAV systems over constant-volume systems include more precise temperature control, reduced compressor wear, lower energy consumption by system fans, less fan noise, and additional passive dehumidification.

Duct (flow) Conduit used in heating, ventilation, and air conditioning

Ducts are conduits or passages used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air. The needed airflows include, for example, supply air, return air, and exhaust air. Ducts commonly also deliver ventilation air as part of the supply air. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal comfort.

Leak-down tester

A leak-down tester is a measuring instrument used to determine the condition of internal combustion engines by introducing compressed air into the cylinder and measuring the rate at which it leaks out.

Infiltration is the unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope and through use of doors for passage. Infiltration is sometimes called air leakage. The leakage of room air out of a building, intentionally or not, is called exfiltration. Infiltration is caused by wind, negative pressurization of the building, and by air buoyancy forces known commonly as the stack effect.

Centrifugal fan

A centrifugal fan is a mechanical device for moving air or other gases in a direction at an angle to the incoming fluid. Centrifugal fans often contain a ducted housing to direct outgoing air in a specific direction or across a heat sink; such a fan is also called a blower, blower fan, or squirrel-cage fan. Tiny ones used in computers are sometimes called biscuit blowers. These fans move air from the rotating inlet of the fan to an outlet. They are typically used in ducted applications to either draw air through ductwork/heat exchanger, or push air through similar. impellers. Compared to standard axial fans, they can provide similar air movement from a smaller fan package, and overcome higher resistance in air streams.

Industrial exhaust ducts are pipe systems that connect hoods to industrial chimneys through other components of exhaust systems like fans, collectors, etc. Ducts are low-pressure pneumatic conveyors to convey dust, particles, shavings, fumes, or chemical hazardous components from air in the vicinity to a shop floor or any other specific locations like tanks, sanding machines, or laboratory hoods. Ducts can be fabricated from a variety of materials including carbon steel, stainless steel, PVC, and fiberglass. They can be fabricated through rolling or extruded.

HVAC is a major sub discipline of mechanical engineering. The goal of HVAC design is to balance indoor environmental comfort with other factors such as installation cost, ease of maintenance, and energy efficiency. The discipline of HVAC includes a large number of specialized terms and acronyms, many of which are summarized in this glossary.

Biosafety cabinet

A biosafety cabinet (BSC)—also called a biological safety cabinet or microbiological safety cabinet—is an enclosed, ventilated laboratory workspace for safely working with materials contaminated with pathogens requiring a defined biosafety level. Several different types of BSC exist, differentiated by the degree of biocontainment they provide. BSCs first became commercially available in 1950.

Negative room pressure Health care isolation technique wherein some air is forced in to prevent disease spread

Negative room pressure is an isolation technique used in hospitals and medical centers to prevent cross-contamination from room to room. It includes a ventilation that generates negative pressure to allow air to flow into the isolation room but not escape from the room, as air will naturally flow from areas with higher pressure to areas with lower pressure, thereby preventing contaminated air from escaping the room. This technique is used to isolate patients with airborne contagious diseases such as: influenza (flu), measles, chickenpox, tuberculosis, Severe Acute Respiratory Syndrome (SARS-CoV), Middle East Respiratory Syndrome (MERS-CoV), and Coronavirus disease 2019 (COVID-19).

Dedicated outdoor air system

A dedicated outdoor air system (DOAS) is a type of heating, ventilation and air-conditioning (HVAC) system that consists of two parallel systems: a dedicated system for delivering outdoor air ventilation that handles both the latent and sensible loads of conditioning the ventilation air, and a parallel system to handle the loads generated by indoor/process sources and those that pass through the building enclosure.

Interstitial condensation is a type of condensation that may occur within an enclosed wall, roof or floor cavity structure, which can create damping.

Building airtightness can be defined as the resistance to inward or outward air leakage through unintentional leakage points or areas in the building envelope. This air leakage is driven by differential pressures across the building envelope due to the combined effects of stack, external wind and mechanical ventilation systems.

TightVent Europe

TightVent Europe is a platform, formed in 2011, with a focus on building and ductwork airtightness issues. The creation of the platform was triggered by the need for a strong and concerted initiative to meet the Directive on the energy performance of buildings ambitious targets for the year 2020 and overcome the challenges in relation to the envelope and ductwork leakage towards the generalization of nearly zero-energy buildings. The platform’s main activities, among others, include the production and dissemination of policy oriented publications, networking among local or national airtightness associations, as well as the organization of conferences, workshops and webinars.

Ductwork airtightness can be defined as the resistance to inward or outward air leakage through the ductwork envelope. This air leakage is driven by differential pressures across the ductwork envelope due to the combined effects of stack and fan operation.

References