DEFROSTING SYSTEM FOR REFRIGERATOR DOORS

• US 3,859,502 A
• Filed: 02/11/1974
• Issued: 01/07/1975
• Est. Priority Date: 02/11/1974
• Status: Expired due to Term

• Current Assignee: James J. Heaney
• Original Assignee: James J. Heaney
• Inventors: Heaney, James J.
• Primary Examiner(s): Albritton, C. L.
• Application Number:
  US05/440,988
• Time in Patent Office: 330 Days
• Field of Search: 219/218 62/150,176,248,275 165/21,30 52/173 73/336.5
• US Class Current: 219/218
• CPC Class Codes: G01N 27/121 for determining moisture content, e.g. humidity, of the fluid moisture content of the tested material G01N27/048
• CPC Class Codes: H05B 1/0236 for vehicles
• CPC Class Codes: H05B 2203/035 Electrical circuits used in resistive heating apparatus
• CPC Class Codes: H05B 3/84 Heating arrangements specially adapted for transparent or reflecting areas, e.g. for demisting or de-icing windows, mirrors or vehicle windshields

Abstract

A system for defrosting large commercial refrigerator doors in which electrical heating means for heating the metal frames and/or the surface of the glass is turned off or on, depending upon whether the relative humidity is below or above a selected level.

Claims

1. Defrosting apparatus for display type refrigerator and freezer equipment having a door with a glass viewing area, comprising:

electrical heating means associated with the door for heating portions of the door, a relative humidity-sensing element mounted outside the door for sensing ambient relative humidity, and control means responsive to the humidity-sensing means for connecting the heating means to an electrical power source only when the relative humidity exceeds a predetermined level.

2. Apparatus of claim 1 wherein the electrical heating means includes an electrically resistive coating on the glass viewing area, the control means connecting the coating to the power source.

3. Apparatus of claim 1 wherein the door includes a metal frame mounted in a metal jamb, and the electrical heating means includes a resistance element embedded in the frame, the control means connecting the resistance elements to the power source.

4. Apparatus of claim 1 wherein the door includes a metal frame mounted in a metal jamb, and the electrical heating means includes a resistance element embedded in the jamb, the control means connecting the resistance elements to the power source.

5. Apparatus of claim 1 wherein the door includes a metal frame mounted in a metal jamb, and the electrical heating means includes a resistance element embedded in the frame and jamb, the control means connecting the resistance elements to the power source.

6. Apparatus of claim 5 wherein the electrical heating means includes an electrically resistive coating on the glass viewing area, the control means connecting the coating to the power source.

7. Apparatus of claim 1 wherein the relative humidity-sensing element includes resistance means that varies in resistance in response to changes in relative humidity.

8. Apparatus of claim 7 wherein the control means includes a resistance bridge circuit with the sensing element resistance means connected as one leg of the bridge, and means for adjusting the resistance of a second leg of the bridge to vary the humidity level at which the bridge is balanced.

9. Apparatus of claim 8 wherein the control means further includes switching means responsive to the bridge circuit for making and breaking an electrical path to the heating means with unbalancing of the bridge by changes in resistance of the sensing element.

10. Apparatus of claim 9 wherein the control means further includes a power supply having a lower voltage isolating transformer connecting the power supply to the power source.