GB2122460A - Electric heater - Google Patents

Abstract

An electrical heater comprises a metal-sheathed mineral-packed electrical heater element 25 within a housing incorporating four longitudinal members 13, 14, 15 and 16 supported in bulkheads. Air inlets 17 and 18 and outlets 19 and 20 are provided to induce natural convection. Members 13, 14, 15 and 16 have sheet steel inner and outer surfaces packed with insulation material to restrict conduction through the housing and prevent excessively high temperatures at the outer face of the heater. The heater may be used in conjunction with a clothes drying rack. <IMAGE>

Description

SPECIFICATION Electrical heater The invention relates to electrical heaters. Heaters to which the invention relates may be used as a source of hot airfor drying clothes or may be used as domestic space heaters.

One objective ofthe invention isto provide a heater which can be small, simple, reliable and safe. Electrical heaters which heat a supply of air passing through the heater are often preferred to radiant electric heaters because the air heater can provide a much more satisfactory distribution of heat within a room and because a risk offire or personal injury by burning is; morse significantwith a radiant heater.

There are two established kinds of air heater. One of these, know as a convector heater, normally employs a heaterelementwithin a large metal housing. The housing has an airflow passage for natu ral convection from an inletoverthe heaterelementto an outlet.

Substantial height is useful in such a heater to provide effective natural convection and thus assist to keep down the temperature of the heater. A large surface area forthe heater also help to dissipate heat and contributes to the maintenance of a low exterior temperature. In this way the exterior surface temperature is kept sufficiently lowto minimise fire risk or personal injury by burning. A disadvantage of such convector heaters is their large size.

The otherwell established kind of air heater is know as afan heater. An electrically driven fan is provided in the airflow passage to blow air overthe heater element. The large volume flow ofairbythis forced convection can keep the exterior surface of the heater acceptably low even when the heater is small and compact. However, as the electric motor and fan ofthe fan heater are moving partstheheaterislessreliable than a natural convection heater. Operation of the fan also generates some noise, which isanotherdis- advantage.

In accordance with the present invention there is provided an electrical heater comprising a heater element within a housing, a natural convection air flow passage within the housing leading from an air inlet overthe heater element and to an outlet and insulaton to restrict heattransferfrom the element to theexteriorsurface ofthe housing to preventexces- lively high temperatures at the outer surface of the housing.

Preferablythe housing has an inner metal surface which is insulated from the exterior of the housing by the insulation and which achieves a high temperature to facilitate heat transfer to the air being convected through the heater. Preferably the heater also has an exterior metal surfaceto provide the heaterwith strucutral strength and to protectthe insulaton against damage.

In this way a compact, reliable and small electrical heater can be obtained.

In accordance with a second aspect of the invention there is provided a clothes drying installation comprising a heater in accordance with the invention as defined above in conjuncton with a clothes rack arranged above the heater and a coverforthe clothes drying rack which allows airflowfrom the heater over the clothes and out through an opening at the top of the cover.

An embodiment ofthe invention will now be described by way of example only with reference to the accompanying drawings in which: Figure lisa side elevation ofthe heaterwith part removed to show its interior; Figure 2 is a plan view ofthe heater of figure 1; and Figure 3 is a cross section on section line Ill-Ill of figure 1.

The structure ofthe heater is based primarily on two bulkheads 11 and 12 formed of sheet steel and joined together byfour longitudinal members 13,14, 15 and 16. Upper and lower longitudinal members 13 and 14 extend across the whole width ofthe rectangular cross section of the heater as shown in figure 3. Longitudinal side members 15 and 16 do not cover the whole depth ofthe heater and leave air inlets 17 and 18 nearthe bottom of the heater and air outlets 19 and 20 nearthe top ofthe heater. The inlets and outlets are slits extending the whole length between bulkheads 11 and 12.

Bulkheads 11 and 12 may be flanged steel pressings or may have four separate flanges bent up individually. Each longitudinal member is made from sheet steel bentto form an inner surface such as 21 and an outer surface such as 22 joined for structural purposes by edges 23 and 24. The interior of each longitudinal member is packed with a high density glass-fibre insulation material suitable for use at high temperatures.

A metal-sheathed mineral-packed electrical heating element 25 is mounted as a cantilever in bulkhead 11 and extends for most ofthe length of the heater towards bulkhead 12. As best seen in figure 2, inner ends of the two legs of the heater element are clamped between angle brackets 26 and 27 by a clamp bolt 26, the angle brackets being spotwelded to the bulkhead 11. Awire strut 29 carrying a silica sleeve 30 extends across between the two longitudinal side members 15 and 16 between the upper and lower sections of the heaterelementto provide additional stabilityforthe element.

Awiring bayforthe heater is provided on the end of the heater adjacent to bulkhead 11 and is consituted by a further bulkhead 31 which is spaced from and joined to bulkhead 11 by a bent steel sheet member 32 forming upper and side wallsforthe wiring bay. A lower access cover completes the wiring bay. Electrical leads 33 extend from the terminals 34 ofthe heater elementthrough a grommetin a sidewall ofthewiring bay. If a switch is required on the heater itself this may be incorporated in the wiring bay.

Bulkhead 31 carries a handle 35 to facilitatetrans- port of the heater. Fourfeet 36 are provided to support the heater just above the ground and prevent it scratching a surface on which it is placed.

In use, when electrical current is applied to the heater, some heatistransferred directlyto airinthe localityofthe element and the innersurfaces ofthe longitudinal members are heated by radiation from the element. These inner surfaces also heat air in their locality.Theexistenceoftwo Iowinletsand high outlets results in a natural convection currentthrough the heater, this air being heated both directly from the elementandfrom the inner surfaces. Because the outersurfaces ofthe longitudinal elements are insulated from their inner surfaces, they do not become excessively hot even when the heater ele mentdissipatesmorepowerthanwould be normal for a natural convector of the size of this heater.The substantial airflowthrough the inlets and outlets tends to keepthe metal edges such as 23 and 24ofthe panels cool so that heat conduction from the innerto theoutersurfacesofthe longitudinal members through this continuous metal route is limited.

The heater may be used in any situation where domestic air heating is required. One particularly useful application ofthe heater is in the drying of clothes arranged on a drying rack. The heater may be placed on the ground immediately below a clothes drying rackwhilethe rack (and clothes on it) are enclosed by a coverwhich is just clear ofthe ground to provide a lower inlet and has an upper outlet Hot air generated by the heater produces upward convection currents of heated air mixed with unheated air. This flow of air up through the clothes has proved to be a particularly effective way of drying clothes at low cost using a limited quantity of electricity. For example, a 0.5 kilowatt heater will dry a typical load of wet clothes in about six hours.Such a heater is very safe forth is kind of application because the insulaton prevents unduly high exteriortemperatures. The large slots extending the length of the heater reduce the risk of completely closing offthe inlets and outlets and even ifthese inlets and outlets are closed off by loose clothing it has been found that sufficient air passes through the heater and the clothing to prevent excessive temperature build up and any likely hood of fire.

CLAIMS (Filed on 23-5-83) 1. An electrical heater comprising a heaterele mentwithin a housing, a natural convection airflow passage within the housing leading from an air inlet, overthe heater element and to an outlet and insulaton to restrict heattransferfrom the elementto the exterior surface ofthe housing to prevent excessively high temperatures atthe outer surface of the housing.

2. An electrical heater as claimed in claim 1 wherein the housing has an inner metal surface which is insulated from the exterior ofthe housing by the insulation and which achieves a high temperature to facilitate heattransferto the air being convected through the heater.

3. An electrical heater as claimed in claim 2 wherein the heater also has an exterior metal surface to provide the heater with structural strength and to protectthe insulaton against damage.

4. An electrical heater substantially as described with reference to and as illustrated in the accompany ing drawings.

5. Aclothesdrying installation comprising a hea teras claimed in any preceding claim in conjunction with a clothes rack arranged above the heater and a coverforthe clothes drying rack which allows airflow from the heater over the clothes and out th rough an opening atthe top ofthe cover.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. heater, some heatistransferred directlyto airinthe localityofthe element and the innersurfaces ofthe longitudinal members are heated by radiation from the element. These inner surfaces also heat air in their locality.Theexistenceoftwo Iowinletsand high outlets results in a natural convection currentthrough the heater, this air being heated both directly from the elementandfrom the inner surfaces.Because the outersurfaces ofthe longitudinal elements are insulated from their inner surfaces, they do not become excessively hot even when the heater ele mentdissipatesmorepowerthanwould be normal for a natural convector of the size of this heater. The substantial airflowthrough the inlets and outlets tends to keepthe metal edges such as 23 and 24ofthe panels cool so that heat conduction from the innerto theoutersurfacesofthe longitudinal members through this continuous metal route is limited. The heater may be used in any situation where domestic air heating is required. One particularly useful application ofthe heater is in the drying of clothes arranged on a drying rack. The heater may be placed on the ground immediately below a clothes drying rackwhilethe rack (and clothes on it) are enclosed by a coverwhich is just clear ofthe ground to provide a lower inlet and has an upper outlet Hot air generated by the heater produces upward convection currents of heated air mixed with unheated air. This flow of air up through the clothes has proved to be a particularly effective way of drying clothes at low cost using a limited quantity of electricity. For example, a 0.5 kilowatt heater will dry a typical load of wet clothes in about six hours.Such a heater is very safe forth is kind of application because the insulaton prevents unduly high exteriortemperatures. The large slots extending the length of the heater reduce the risk of completely closing offthe inlets and outlets and even ifthese inlets and outlets are closed off by loose clothing it has been found that sufficient air passes through the heater and the clothing to prevent excessive temperature build up and any likely hood of fire. CLAIMS (Filed on 23-5-83)

1. An electrical heater comprising a heaterele mentwithin a housing, a natural convection airflow passage within the housing leading from an air inlet, overthe heater element and to an outlet and insulaton to restrict heattransferfrom the elementto the exterior surface ofthe housing to prevent excessively high temperatures atthe outer surface of the housing.

2. An electrical heater as claimed in claim 1 wherein the housing has an inner metal surface which is insulated from the exterior ofthe housing by the insulation and which achieves a high temperature to facilitate heattransferto the air being convected through the heater.

3. An electrical heater as claimed in claim 2 wherein the heater also has an exterior metal surface to provide the heater with structural strength and to protectthe insulaton against damage.

4. An electrical heater substantially as described with reference to and as illustrated in the accompany ing drawings.

5. Aclothesdrying installation comprising a hea teras claimed in any preceding claim in conjunction with a clothes rack arranged above the heater and a coverforthe clothes drying rack which allows airflow from the heater over the clothes and out th rough an opening atthe top ofthe cover.