EP3879200A1

EP3879200A1 - Radiator with temperature limitation

Info

Publication number: EP3879200A1
Application number: EP21159013.8A
Authority: EP
Inventors: Tomasz Trzesowski
Original assignee: Zehnder Group International AG
Current assignee: Zehnder Group International AG
Priority date: 2020-03-12
Filing date: 2021-02-24
Publication date: 2021-09-15
Anticipated expiration: 2041-02-24
Also published as: EP3879200C0; PL3879200T3; EP3879200B1

Abstract

The invention relates to an electric radiator (1) for heating a room. The radiator (1) comprises a first electric heating element (H1) and a second electric heating element (H2) both electrically connected in parallel to the electric power source 3. A temperature limiter (TL1) is provided for temporarily switching off the second electric heating element (H2) while maintaining the electric power flow to the first electric heating element (H1).

Description

The invention relates to a radiator for heating a room and to a method of operating such a radiator for heating a room.
It is well-known to provide a radiator with a temperature-limiter. Such a radiator comprises an electric heating element electrically connected to an electric power source and thermally connected to the radiator. In addition, such a radiator comprises a temperature limiter for limiting a surface temperature of the radiator during radiator operation by temporarily switching off said electric heating element. In other words, the electric heating element can be switched off and on again (one switching cycle) by the temperature-limiter as a function of radiator surface temperature.
A temperature-limiter, also referred to as "limiter", is especially important for radiators that are used for drying and/or warming towels hung onto them, thus covering a portion of the radiator surface which may lead to dangerous overheating of the radiator. Such radiators may be referred to as "towel rads" or "towel warmers".
Such temperature-limiters have a given lifetime. Their lifetime is primarily determined by the number of switching cycles, i.e. the number of "switching-off-and-switching-on-again" cycles carried out by the temperature-limiter. A typical temperature-limiter has a lifetime of about 10'000 cycles.
If a radiator is regularly used for drying and/or warming towels, the temperature-limiter will undergo many cycles for each period of drying and/or warming a towel. As a result, the lifetime of the temperature-limiter and of the entire radiator may be quite short.
It is an object of the present invention to increase the lifetime of a temperature-limiter and of a radiator equipped with such a limiter.
According to a first aspect of the invention, the object of the invention has been achieved by providing a radiator for heating air in a room, typically by radiation and/or convection, said radiator comprising an electric heating element electrically connected to an electric power source and thermally connected to said radiator, a temperature limiter being provided for limiting a surface temperature of said radiator during operation of said radiator by temporarily switching off said electric heating element, wherein said radiator comprises a first electric heating element and a second electric heating element, each electrically connected to said electric power source, said temperature limiter being provided for, i.e. being configured for, temporarily switching off said second electric heating element, while maintaining the electric power flow to said first electric heating element.
As a result, if a surface temperature of the radiator increases to a critical value, for instance if a towel is hung onto it, and the temperature-limiter turns off the second heating element, the first heating element still keeps generating heat within the radiator with only a portion of the nominal power rating of the radiator after the temperature-limiter has turned off the second heating element. This causes the surface temperature of the radiator to decrease more slowly than in the case of a conventional radiator with only one heating element where the entire generation of heat is turned off by the temperature-limiter. Thus, it takes more time for the temperature-limiter to again turn on the second heating element and the duration of a switching-off-and-switching-on-again cycle is increased. Therefore, each towel hung onto the radiator according to the invention causes fewer cycles in the temperature-limiter than in a conventional radiator. As a result, the lifetime of the temperature-limiter and of the radiator according to the invention are significantly increased.
Preferably, the temperature limiter is provided for, i.e. is configured for, temporarily switching off the second electric heating element only. As a result, the first heating element will not be affected by the switching operations of the temperature-limiter.
In a preferred embodiment, the first electric heating element and the second electric heating element are connected in parallel. This electrical configuration lends itself to many geometrical configurations of a radiator with these two heating elements integrated in it.
Preferably, at least one of said first and second electric heating elements is a resistive heating element having a resistive load.
Preferably, the first and second resistive heating elements have a first resistive load R1 and a second resistive load R2, respectively.
Preferably, a ratio R1/R2 between the first resistive load R1 and the second resistive load R2 is between 5/1 and 1/5. More preferably, this ration is between 2/1 and 1/2, and most preferably, this ratio is equal to 1 (R1 = R2).
As an alternative, instead of a pure resistive electrical heating element, the at least one of said first and second electric heating elements may be a magnetron (of the type as used in microwave ovens). In operation, the magnetron provides both electromagnetic radiation and heat from its casing. On the one hand, the magnetron radiation, when radiated into a water-filled radiator with metal walls, causes rapid heating of the water. On the other hand, the heat from the magnetron casing causes somewhat slower heating of the water.
Preferably, the first electric heating element is a resistive heating element and the second electric heating element is a magnetron.
Preferably, at least one overcurrent protection device is connected in series with the electric power source and with at least one of said first and second electric heating elements.
Preferably, only one overcurrent protection device is connected in series with the electric power source and the parallel connection including the first electric heating element and the second electric heating element.
Preferably, the at least one overcurrent protection device is a circuit breaker, preferably with self-holding function, and/or a fuse.
The radiator may have a towel hanging function.
The radiator may have a flat, plate-like shape.
The radiator may be provided with a towel bar and/or a towel opening and/or a towel hook.
In a further preferred embodiment, the first electric heating element and the second electric heating element are arranged adjacent to each other at or within the radiator. As a result, the two adjacent heating elements can be regarded and treated as one single resultant heating element (one effective heating element) which is practical.
In a hydronic radiator version primarily using internal liquid convection, the first electric heating element and the second electric heating element may be encapsulated in a heating cartridge (i.e. immersion heater) extending into a liquid-filled chamber of the radiator. Preferably, the liquid is water or oil.
In a solid radiator version primarily using internal heat flow, the first electric heating element and the second electric heating element may be embedded in the radiator material of the radiator. Preferably, the radiator material in which the heating elements are embedded, is aluminum and/or steel and/or graphite.
In a heat-pipe radiator version primarily using enhanced/super internal heat flow, the first electric heating element and the second electric heating element constitute a heat source in or at a radiator filled with a fluid forming a condensate/vapor system within the radiator.
According to a second aspect of the invention, the object of the invention has been achieved by providing a method of operating a radiator, preferably as defined in any one of the preceding paragraphs, for heating a room, which method comprises the following steps:

a) providing heat to the radiator via a first electric heating element and a second electric heating element by electric power from an electric power source for operating the radiator at a temperature T between a lower threshold temperature T1 and an upper threshold temperature T2;
b) if a surface temperature of the radiator reaches a value above the upper threshold temperature T2, turning off the electric power flow to the second electric heating element by the temperature limiter and maintaining the electric power flow to the first electric heating element; and
c) if a surface temperature of the radiator reaches a value below the lower threshold temperature T1, again turning on the electric power flow to the second electric heating element by the temperature limiter and maintaining the electric power flow to the first electric heating element.

Preferably, the method comprises the following step:
d) if a surface temperature of said radiator reaches a value above said upper threshold temperature T2 and if said temperature-limiter (TL1) does not turn off the electric power flow to said second electric heating element (H2), turning off the electric power flow to both of said second electric heating element (H2) and said first electric heating element (H1) by a circuit breaker.
The foregoing features and other features of the invention will now be briefly described with reference to the drawings of a preferred embodiment. The illustrated embodiment is intended to illustrate, but not to limit the scope of the invention.

Fig. 1: shows an electrical configuration of an electric radiator of the prior art;
Fig. 2: shows an electrical configuration of an electric radiator according to the invention;
Fig. 3: shows a typical profile of temperature as a function of time for the radiator of Fig. 1;
Fig. 4: shows a typical profile of temperature as a function of time for the radiator of Fig. 2.

Referring to Fig. 1, an electrical configuration of an electric radiator 1' of the prior art is shown. The radiator comprises an electric heating element H electrically connected to an electric power source 3' and thermally connected to the radiator 1'. A temperature limiter TL is provided for limiting a surface temperature of the radiator 1' during radiator operation by temporarily switching off electric heating element H.
Referring to Fig. 2, an electrical configuration of an electric radiator 1 according to the invention is shown. Radiator 1 comprises a first electric heating element H1 and a second electric heating element H2, both connected in parallel to an electric power source 3. A temperature limiter TL1 is connected in series with the second heating element H2 in the second branch of the parallel connection for temporarily switching off the second electric heating element H2 while maintaining the electric power flow to the first electric heating element H1. As a result, temperature limiter TL1 will temporarily switch off the second electric heating element H2 only. Each of the first and second electric heating elements H1, H2 are a resistive heating element having a resistive load R1 and R2, respectively.
A ratio R1/R2 between the first resistive load R1 and the second resistive load R2 may be selected to be between 5/1 and 1/5. In the configuration of Fig. 2, this ratio is 1, i.e. the resistive loads are equal (R1 = R2). As a result, if both electric heating elements H1 and H2 are turned on, each heating element H1, H2 will generate the same thermal power P/2, i.e. half the entire thermal power P.
An overcurrent protection device 4 is connected in series with the electric power source 3 and the parallel connection including the first electric heating element H1 with resistance R1 and the second electric heating element H2 with resistance R2. The overcurrent protection device 4 is a temperature limiter TL2 with self-holding function and optionally a fuse F.
Referring to Fig. 3, a typical profile of temperature T as a function of time t for the radiator 1' of Fig. 1 is shown. Heat is provided to radiator 1' via an electric heating element H by electric power from an electric power source 3' for operating the radiator 1' at a temperature T between a lower threshold temperature T1 and an upper threshold temperature T2 of a temperature limiter TL.
If a surface temperature of radiator 1' reaches a value above the upper threshold temperature T2, temperature-limiter TL will turn off electric power to electric heating element H. If a surface temperature of radiator 1' reaches a value below the lower threshold temperature T1, temperature-limiter TL will again turn on electric power to electric heating element H.
As a result, if radiator 1' is partially covered by a towel, a surface temperature of radiator 1' will increase until it passes the upper threshold temperature T2. Now, power to heating element H, i.e. the entire power to radiator 1', is turned off and the surface temperature will decrease until it passes the lower threshold temperature T1. Now, power to heating element H is again turned on and the surface temperature will again increase until it again passes the upper threshold temperature T2. The cycle starts over again.
As can be seen from Fig. 3, about 12 cycles occur within about 12 hours. In other words, temperature-limiter TL switches off about 12 times and switches on about 11 times within 12 hours.
Referring to Fig. 4, a typical profile of temperature T as a function of time t for the radiator 1 of Fig. 2 is shown. Heat is provided to radiator 1 via a first electric heating element H1 and via a second electric heating element H2 by electric power from an electric power source 3 for operating the radiator 1 at a temperature T between a lower threshold temperature T1 and an upper threshold temperature T2 of a temperature limiter TL.
If a surface temperature of radiator 1 reaches a value above the upper threshold temperature T2, temperature-limiter TL1 will turn off electric power to electric heating element H2 only, while maintaining electric power flow to first electric heating element H1. If a surface temperature of radiator 1 reaches a value below the lower threshold temperature T1, temperature-limiter TL1 will again turn on electric power to electric heating element H2.
As a result, if radiator 1 is partially covered by a towel, a surface temperature of radiator 1 will increase until it passes the upper threshold temperature T2. Now, power to second heating element H2, i.e. a portion of the power to radiator 1, is turned off and the surface temperature will decrease until it passes the lower threshold temperature T1. Now, power to heating element H2 is again turned on and the surface temperature will again increase until it again passes the upper threshold temperature T2. The cycle starts over again.
As can be seen from Fig. 4, less than 1 cycle occurs within about 12 hours. In other words, temperature-limiter TL1 switches off less than once and switches on less than once within 12 hours.
Due to the continued power supply from the first electric heating element H1 which is never switched off during the cycling of the second electric heating element H2 by the temperature-limiter TL1, the temperature decreases more slowly within each temperature cycle than in the configuration shown in Fig. 3.

Claims

Radiator (1) for heating a room, said radiator comprising an electric heating element (2) electrically connected to an electric power source (3) and thermally connected to said radiator (1), a temperature limiter (TL) being provided for limiting a surface temperature of said radiator (1) during radiator operation by temporarily switching off said electric heating element (2), wherein said radiator (1) comprises a first electric heating element (H1) and a second electric heating element (H2), each electrically connected to said electric power source (3), said temperature limiter (TL1) being provided for temporarily switching off said second electric heating element (H2) while maintaining the electric power flow to said first electric heating element (H1).
Radiator (1) as defined in claim 1, wherein said temperature limiter (TL) is provided for temporarily switching off said second electric heating element (H2) only.
Radiator (1) as defined in claims 1 or 2, wherein said first electric heating element (H1) and said second electric heating element (H2) are connected in parallel.
Radiator (1) as defined in any one of claims 1 to 3, wherein at least one of said first and second electric heating elements is a resistive heating element having a resistive load, wherein preferably said first and second resistive heating elements (H1, H2) have a first resistive load R1 and a second resistive load R2, respectively.
Radiator (1) as defined in claim 4, wherein a ratio R1/R2 between said first resistive load R1 and said second resistive load R2 is between 5/1 and 1/5, preferably between 2/1 and 1/2, and most preferably equal to 1.
Radiator (1) as defined in any one of claims 1 to 5, wherein at least one overcurrent protection device (4) is connected in series with said electric power source (3) and with at least one of said first and second electric heating elements (H1, H2).
Radiator (1) as defined in claim 6, wherein only one overcurrent protection device (4) is connected in series with said electric power source (3) and said parallel connection including said first electric heating element (H1) and said second electric heating element (H2).
Radiator (1) as defined in claims 6 or 7, wherein said at least one overcurrent protection device (4) is a circuit breaker, preferably with self-holding function, and/or a fuse, wherein preferably said circuit breaker is a temperature limiter (TL2) with self-holding function.
Radiator (1) as defined in any one of the preceding claims, wherein said radiator has a towel hanging function, wherein preferably said radiator has a flat, plate-like shape.
Radiator (1) as defined in claim 9, wherein said radiator is provided with at least one of a towel bar, a towel opening and a towel hook.
Radiator (1) as defined in any one of the preceding claims, wherein said first electric heating element (H1) and said second electric heating element (H2) are arranged adjacent to each other at or within said radiator.
Radiator (1) as defined in claim 11, wherein said first electric heating element (H1) and said second electric heating element (H2) are encapsulated in a heating cartridge extending into a liquid-filled, particularly water or oil filled, chamber of said radiator; or wherein said first electric heating element (H1) and said second electric heating element (H2) are embedded in the radiator material, such as aluminum, steel and/or graphite, of said radiator; or wherein said first electric heating element (H1) and said second electric heating element (H2) constitute a heat source of a radiator filled with a fluid forming a condensate/vapor system within said radiator.
Method of operating a radiator (1), preferably as defined in any one of the preceding claims, for heating a room, said method comprising the following steps:
a) providing heat to said radiator via a first electric heating element (H1) and a second electric heating element (H2) by electric power from an electric power source (3) for operating said radiator at a temperature T between a lower threshold temperature T1 and an upper threshold temperature T2;

b) if a surface temperature of said radiator reaches a value above said upper threshold temperature T2, turning off the electric power flow to said second electric heating element (H2) by said temperature limiter (TL1) and maintaining the electric power flow to said first electric heating element (H1); and

c) if a surface temperature of said radiator reaches a value below said lower threshold temperature T1, again turning on the electric power flow to said second electric heating element (H2) by said temperature limiter (TL1) and maintaining the electric power flow to said first electric heating element (H1).
Method of operating a radiator (1) as defined in claim 13, said method comprising the following step:
d) if a surface temperature of said radiator reaches a value above said upper threshold temperature T2 and if said temperature-limiter (TL1) does not turn off the electric power flow to said second electric heating element (H2), turning off the electric power flow to both of said second electric heating element (H2) and said first electric heating element (H1) by said circuit breaker.