Method for threading a string through HVAC ducts

Abstract

The invention is a method for threading a thin string through an HVAC duct system from a vent to the HVAC equipment supply plenum where the vent is connected to a small supply duct which in turn is connected to a large supply trunk connected to the plenum. The method uses a high speed blower at the vent to propel a small resistance object connected to the string through the small duct until it reaches the trunk. Then a capture mechanism is used from the HVAC plenum to capture the object and pull the string to the plenum. In an example of the method, the resistant object includes a packed parachute that is released after it travels a predetermined distance.

Description

BACKGROUND OF THE INVENTION[0001]1. Technical Field of the Invention[0002]This invention relates generally to HVAC zone control systems for retrofit, and specifically to methods for threading air tubing and wires through concealed HVAC duct systems.[0003]2. Background Art[0004]Most zone control systems for HVAC systems use electromechanical dampers to selectively control the airflow through portions of the trunk and duct system. Installation of these zone systems requires access to the ducts at multiple locations so that the dampers can be installed. However, in many building the ducts are not easily accessible because they are embedded in walls, ceilings, and floors. Even when a duct is accessible for damper installation, there may no be a clear path to run control wires outside the duct from the damper to the control system. In nearly all cases, the interior of the duct system provides a path from each vent to the central HVAC equipment. The existing ductwork can be used as a cond...

AI Technical Summary

Benefits of technology

[0015]The invention is a process for threading a thin string through an HVAC duct system from a vent to the HVAC supply plenum where the vent is connected to a small supply duct which in turn is connected to a large supply trunk connected to the plenum. The method uses a high speed blower at the vent to propel a small resistance object connected to the string through the small duct until it reaches the trunk. Then a mechanism is used from an access in the plenum to capture the resistance object and pull the string to the plenum. The capture mechanism can be a hose, rod, tube, o

Problems solved by technology

However, in many building the ducts are not easily accessible because they are embedded in walls, ceilings, and floors.

Even when a duct is accessible for damper installation, there may no be a clear path to run control wires outside the duct from the damper to the control system.

However, this method does not work well for certain duct systems and paths.

However, leaks in the duct system can also supply some of the airflow.

If the leakage is excessive, there is insufficient airflow at the vent to inflate and pull the parachute.

In a small vent, a large portion of the parachute is in contact with the walls of the duct creating significant friction, and making it more likely screws or sharp edges will snag the parachute.

Increasing the air flow to increase the pulling force also increases the friction since the parachute is pushed harder against the duct walls.

The combination of significant friction and a small force makes it difficult for the parachute to pass through the duct.

As the duct cross-section increases, the air velocity decrease and the small parachute can not product enough force to pull the string to the HVAC equipment.

In some duct networks with long duct runs with many turns, the resistance between the string and the duct walls become excessive as the length of the string being pulled increases.

The force generated by the parachute is not sufficient to overcome the string pulling friction.

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