AU727664B2 - A Heated Air Duct - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT

APPLICANT:

GORDON JOHN BUICK

NUMBER:

FILING DATE: Invention Title: A HEATED AIR DUCT The following statement is a full description of this invention including the best method of performing it known to us: -1- A HEATED AIR DUCT BACKGROUND OF THE INVENTION This invention relates to a heated air duct.

0 There are situations where it is desirable or necessary to heat air flowing in a duct or conduit or other flow passage.

For example with domestic air drying systems intended to provide ventilation for say curing condensation ambient outside air is drawn into a dwelling. In winter or during 1 5 periods of cold weather the drawing in of cold air can impact on the inside air temperature. This can result in discomfort to those living in the dwelling and the need for higher heat input from heating installations located within the dwelling to maintain a comfortable or desirable temperature inside the dwelling.

The installation of electric heating elements within the airflow to impart heat to the incoming colder air is not effective nor efficient. Not only is insufficient heat exchange with the air able to take place due to the flow of air through the duct but also the positioning of heating elements within the airflow can adversely impact on the required airflow.

SUMMARY OF THE INVENTION It is thus an object of the present invention to provide a heated air duct whereby efficient and effective heating of airflow through the duct can be achieved without disturbing airflow through the duct.

Broadly in one aspect of the invention there is provided a heated air duct comprising a tubular body defining an internal airflow passage, a carbon-resistance heating element engaged about the exterior of the tubular body an insulating encasement about the heating element, the heating element being adapted for connection to a power source.

In a preferred form of the invention a thermal-cutout device is incorporated with the heating element.

Preferably the insulating encasement is formed by insulating material engaged about the heating element on the tubular body and a protective skin or covering located over the 20 insulating material.

Broadly in a second aspect of the invention there is provided eea heated air duct including a duct body having an internal wall surface defining an internal air flow passage and a carbon-resistance heating element embedded within the body adjacent said internal wall surface, said heating element being adapted for connection to a power source.

ego• being adapted for connection to a power source.

BRIEF DESCRIPTION OF THE DRAWINGS .10 o o• •2 1 o°°oee oooo o Figure 1 is a perspective view of the heated air duct according to one form of the present invention, Figure 2 is an end elevation view, Figure 3 is a cross-sectional elevation, Figure 4 is an illustration of the heated air duct in an in-use situation with an anti-condensation and central house ventilation unit, and Figure 5 is a cross-sectional illustration of a further form of the heated air duct according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrated, the heated air duct D according to one form of the invention comprises a tubular (preferably circular cross-section) body 10 the internal bore 11 of which provides or defines an airflow passage. Wrapped about the external wall surface 12 of the tubular body 10 is a flat, hi-tech carbon/graphite resistance based radiant heating element which as illustrated covers only part of the length of the tubular body Engaged about the heating element 13 is a suitable thermal insulation material 14. This is encased with an outer cover forming a protective skin which in the preferred form extends over the peripheral surface and ends of the insulation material 14.

According to one form of the invention the central or primary tubular body 10 is formed of aluminium ducting while the cover or external encasement 15 can also be of aluminium construction.

0 According to a preferred form of the invention, the tubular body 10 is powder coated black or at least the internal wall surface 14 is painted with a black or dark colour.

.°oooi For the heated air duct D to be used in an anti-condensation and cental house ventilation system as shown, for example, in Figure 4, the heating element 13 can be of type having a power rating of 800 watts. This is adapted for connection (preferably via a thermal-cutout device) to a mains power supply. The thermal-cutout can be adjusted to cut power to S• 20 the heating element upon the temperature of the tubular body increasing to a pre-determined maximum. This may occur, for example, if the fan or air flow generating means ceases to operate or for some reason does not provide sufficient airflow.

Heating of air takes place as the air passes along the flow passage due to radiant heat. The heat density is due to the longer wave length of radiant heat than convective heat and its ability to target and bounce off all surfaces within the tube.

The heated air duct according to the present invention can be used in many different applications where an airflow through the ducting is to be heated. One such arrangement is an anti-condensation and central house ventilation unit as shown in Figure 4 where the heated air duct D is located between 0 the fan and control unit 16 and a flexible ducting 17 connected to a diffuser 18. In use the control unit 15 draws ambient outside air and passes it through bore or flow passage 11 of the duct D whereupon heat is applied to the air as it passes therethrough.

Tests have been carried out to determine the effectiveness of the heated air duct according to the present invention. The tests were performed in a cooling chamber having a natural temperature variation of around 0.5 0 C with no external influences (ie. door kept closed) but variations could occur around 0.5-1 0 C in the event that the chamber door was opened to check on or change the test device. Therefore small rises in temperature could occur between each test though attempts were made to minimise any external influences. In any event once temperatures had stabilised each test was monitored over a period of time before an average temperature was establish.

Temperature measurements were performed with two "Fluke 51" digital thermometers.

An initial test was carried out without the flexible ducting 17 attached to duct D. The voltage of the heating element 13 was varied between 120 volts and 200 volts. The test results are noted below.

1. Initial Test Results: Without flexible ducting Air temperature input 3-5 0 C (Cooling temperature) Chamber Volts Power In (ac) (watts) Wall Temp

(C)

Air Temp (close to wall) Air Temp (middle of tube) 100v 120v 140v 160v 180v 200v 143w 202w 280w 366w 463 571w Following this initial test further tests were carried out with different variations associated with painting of the central tube 10 and with and without insulation on the flexible ducting 17. The test results are indicated below: 2. Tests performed at 200 Volts (571 Watts) input to heater only TEST 1:*No Painted Tube *No Insulation on 90 degree bend Average Input Temperature 3.2 degrees Celsius Average Output Temperature 13.2 degrees Celsius Temperature Increase (Input to Output) 10 degrees Celsius TEST 2:*No Painted Tube *WITH Insulation on 90 degree bend Average Input Temperature 3.5 degrees Celsius Average Output Temperature 14.2 degrees Celsius Temperature Increase (Input to Output) 10.7 degrees Celsius TEST 3:*WITH Painted Tube *NO Insulation on 90 degree bend Average Input Temperature 3.4 degrees Celsius Average Output Temperature 14.5 degrees Celsius 20 Temperature Increase (Input to Output) 11.1 degrees Celsius TEST 4:*WITH Painted Tube *WITH Insulation on 90 degree bend Average Input Temperature 3.3 degrees Celsius Average Output Temperature 15.3 degrees Celsius Temperature Increase (Input to Output) 11.9 degrees Celsius The test results show that air passing through the heated air duct according to the present invention results in increases in air temperature sufficient to remove the adverse effects of incoming cool air. The heated air duct by having no heating elements in the air flow passage thus provides for unimpeded airflow yet enables air in the airflow to increase in temperature in an energy efficient manner.

The invention is open to modification as will be appreciated 10 by those skilled in the art. According to one modified form of the invention as shown in Figure 4 the tubular body with internal bore or airflow passage 11 is moulded from a fibre (glass) reinforced plastics material with the carbon graphite element 13 embedded therein during the construction of the body 10 so that the element 13 is located adjacent the internal wall surface defining the bore 11. According to one form of the invention the element 13 can be located approximately 2mm in from the internal wall surface and in from the external wall surface. According to this particular arrangement the carbon graphite can be applied to an open weave fibreglass cloth rather than be sandwiched according to normal elements of this type between mylar sheets. The use of an open weave cloth or similar enables the element to be anchored into the reinforced plastics construction.

r The heated air duct can be used to provide efficient background home heating and accelerate the drying out process of many dwellings suffering from condensation, mould, mildew and dampness. In addition the heated air duct can function in other applications where air in an airflow is required to be taken to an increased temperature.

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Claims (4)

1. 2. A heated air duct comprising a tubular body defining an internal air flow passage, a carbon-resistance heating element engaged about the exterior of the tubular body, an insulating encasement about the heating element, the heating element being adapted for connection to a power source.
2. 3. A heated air duct as claimed in claim 2 further including a thermal-cutout device incorporated with the heating element.
3. 4. A heated air duct as claimed in claim 2 or 3 wherein the insulating encasement is formed by insulating material engaging about the heating element on the tubular body. 0000 0
4. 49.. 0.00. 0 0* 000 25 5. A heated air duct as claimed in claim 4 wherein a protective skin or covering is located over the insulating material. 6. A heated air duct as claimed in any one of preceding claims 2 to 5 wherein the tubular body is formed by aluminium ducting. 7. A heated air duct as claimed in any one of the preceding claims wherein the internal wall surface defining the airflow passage is provided with a coating of a dark colour. 8. A heated air duct as claimed in claim 6 wherein the internal and external surfaces of the tubular body are powder coated in black or a dark colour. 9. A heated air duct as claimed in claim 1 wherein the duct body is formed from reinforced plastics material and the heating element is embedded therein. a: 10. A heated air duct as claimed in claim 9 further 5* 20 including a thermal-cutout device coupled to the heating element. o 11. A heated air duct as claimed in any one of the preceding Sea& claims wherein the heating element extends substantially O completely about the airflow passage but does not extend for the full length of the body. 12 12. A heated air duct substantially as herein described with reference to the accompanying drawings. DATED this aZday of March 1997. JAMES MURRAY CO P O Box 1521 Black Rock Victoria 3193 Australia 0 g* 0