T 0576/95 15-04-1997

Reasons for the Decision

1. The appeal is admissible.

2. Novelty

2.1. (D6) cited for the first time in the Statement of Grounds of Appeal discloses a method for regulating a central or district heating plant provided with a differential pressure valve for circulating a heat carrying fluid, such as water, said plant comprising several radiators each provided with a thermostat valve (RAV) and with a differential pressure valve, the latter valve being placed after the radiators in the direction of flow and having an inlet and an outlet and a closing device (6) therebetween controlled by a membrane (9) for regulating the flow of the heat carrying fluid through a passage between the inlet and the outlet (see page 2, figure under the heading "Konstruktion and Beschreibung" and Figure 2).

The further feature according to the preamble of Claim 1 that every room of the building to be heated has at least one radiator has not been described expressis verbis in (D6). The disclosure on page 2 under the heading "Allgemeines" in (D6) that in large heating systems often load variations occur due to the necessary local adjustments, makes it clear to the skilled person that in (D6) a heating system is disclosed which is intended to be used with the radiotors spaced apart in a building. Such a configuration of a heating plant corresponds to the typical situation prevailing in heated buildings, which normally have a number of rooms having each at least one radiator.

Hence, (D6) discloses all features according to the preamble of Claim 1. Furthermore, (D6) specifies that for the purpose of limiting the mass flow the pressure difference across a fixed resistance (restrictor or valve) is maintained constant (see "Beispiel 2" on page 3). The differential pressure valve of the type AVD safeguards that a selected value of the mass flow is not exceeded (see the first page, central column, paragraph 4) which means that the mass flow is limited to a maximum value regardless of the state of distribution of pressure in the plant, in accordance with the interpretation of Claim 1 given by the Respondent on page 4, paragraph 2 of his letter dated 20. December 1995.

The above considerations apply basically also to Claim 5 which in its first portion incorporates the features according to the preamble of Claim 1 in the form of "product"-features.

Hence, (D6) is more relevant to the claimed subject-matter than (D1) considered in the contested decision to describe the nearest prior art, and is, therefore admitted to the proceedings.

2.2. Both Claim 1 and Claim 5 differ from the disclosure of (D6) by the features that the throttle of the differential pressure valve is provided between the inlet and the closing device of the valve and that the throttle is adjustable.

2.3. It follows from the foregoing that the subject-matter of Claim 1 and of Claim 5, respectively, is novel. Since novelty was no longer disputed in the oral proceedings before the Board, this issue needs no further argument.

3. Inventive step

3.1. The technical problem underlying the patent in suit as indicated in the description and maintained in the Respondent's letter dated 7 April 1997, page 7, paragraph 2, is to reduce unwanted heat losses due to excessive circulation of the heating fluid in case of thermostatic valves in the circuit during heating conditions, for instance during the time in which the room is cooled by opening the windows and the valves are not closed. As explained on page 2, lines 47 to 52 of the patent in suit, the total amount of heat carrying liquid through the plant can be limited by providing the differential pressure valve with an adjustable throttle even if all the thermostat valves are opened at a maximum which means that the throttling which normally takes place in the plant by the combined effect of a plurality of thermostat valves, is transferred down to the differential pressure valve. In this way a constant loss of pressure is provided across the thermostat valves and/or the throttle in the differential pressure valve, regardless of whether the thermostat valves are more or less open.

It is clear that also with a differential pressure valve comprising a throttle of a fixed size a constant loss of pressure is provided although with such a throttle the pressure loss cannot be varied by adjusting the throttle.

According to (D6) which describes a system comprising a heating plant with thermostat valves and a differential pressure valve with a fixed-size throttle the above-cited problem has already been solved. It must therefore be investigated which problem remains effectively to be solved by the features of Claim 1.

3.2. In the present case, the problem-solution approach as advocated in a number of decisions of the Boards of Appeal (see e.g. T 248/85 (OJ EPO 1986, 261) and T 162/86 (OJ EPO 1988, 452)) has been applied for examination of the claimed subject-matter. In accordance with this method, the technical problem has to be identified on the basis of objective criteria, i.e the problem which can be seen to have been actually solved in the light of the closest prior art which may be different from the prior art which was at the disposal of the inventor.

Having regard to the above-cited features distinguishing Claim 1 from the arrangement disclosed by (D6), according to the latter, the throttle is provided outside of the differential pressure valve and is of a fixed size (see Figure 2 "Mengenbegreuzer", the figure below the heading "Konstruktion und Beschreibung" and "Beispiel 2"). Due to these differences the system according to (D6) suffers from the detriments that the valve requires a large space and cannot be easily adapted to different values of the maximum amount of fluid mass flow.

The inherent objective problem solved by Claim 1 when starting out from (D6) as the relevant prior art resides therefore in providing a compact differential pressure valve which is easily adaptable to different values of the maximum amount of fluid mass flow, e.g. in the case of changes in the number or size of radiators.

3.3. It has to be investigated now whether the posing of this problem requires from the skilled person already more than customary considerations.

It comes within the normal experience of the skilled person that the time and expense required for mounting or dismounting a valve depends on the number of components to be handled for the replacement of the valve. It is moreover self-evident for the skilled person that the complete replacement of a valve in a duct system is more laborious than an adjustment of a valve of the type the characteristics of which can be changed. Thus, the objective problem becomes evident from the drawbacks revealed during operation of the heating system described in (D6) when the skilled person has to adjust this known system to accomadate a different number and/or size of radiator.

It has therefore to be concluded that the recognition of the underlying problem as such cannot contribute to an inventive step of the subject-matter of Claim 1.

3.4. (D2) relates to a system comprising a differential pressure valve installed in the return pipe of a heating plant (see Figure 3 "Typ 46-6 (DN 15...25) and Figure 4 on page 3 with the corresponding description). Thus, the citation concerns the same technical field as according to the patent in suit.

This known differential pressure valve comprises an adjustable throttle (1.2) provided between the inlet and the closing device (2, 3) of the valve, the valve serving the purpose of allowing an amount of fluid to pass which is adjustably limited to a maximum value (see page 1, section "1. Aufbau und Wirkungsweise", paragraph 2 and last paragraph).

The skilled person studying the disclosure of (D2) would immediately recognise that the particular construction of the valve described therein overcomes the disadvantages connected with a valve throttle which is of a fixed size and is arranged outside of the differential pressure valve.

Contrary to the opinion of the Respondent, the skilled person would be motivated to substitute the differential pressure valve described in (D2) for the valve illustrated in (D6) and would thus arrive readily at the subject-matter of Claim 1 and Claim 5, respectively. He would see that by such a substitution advantages as to an easy adaptation of the valve to different values of the maximum permissible amount of the fluid flow and, respectively, as to a compact construction of the valve are to be expected.

3.5. The Respondent argues further that the system described in (D2) does not dispose of thermostat valves and cannot, therefore, be combined with the system known from (D6).

It is true that in (D2) there is no express reference to the use of thermostat valves. There can be, however, no doubt that at the date of publication of (D2), that is January 1988, the provision of the radiators with thermostat valves was the normal situation and was even prescribed in one of the member states of the EPC (see (D5), §7(2)). The use of thermostat valves in the heating system disclosed in (D2) would, therefore, be regarded by the skilled person as at least not excluded, even if not implicitly included.

Furthermore, it must be emphasized that (D6) which expressly refers to radiators comprising thermostat valves provides already the solution to the problem of avoiding unwanted heat losses in connection with thermostat valves, for example in the case of opened windows in the compartment to be heated. The skilled person having studied (D6) is therefore only confronted with the objectively underlying problem as indicated above to which (D2) - even in the case that it would not implicitly disclose a heating plant having on the user side thermostat valves - offers the solution as claimed.

3.6. The subject-matter of Claim 1 and of Claim 5, respectively, is not therefore based on an inventive step (Article 56 EPC) so that Claims 1 and 5 cannot be maintained.

4. Since the Board is bound by the single request of the Respondent, it is not necessary to comment on the Claims 2 to 4 and 6 to 8 dependent on Claims 1 and 5, respectively. These claims must therefore fall with Claims 1 and 5.