Improvement of the Methodology of Efficiency Measurement for Domestic Boilers

Jean Schweitzer; Christian Christiansen,  May 1999, R9912

Abstract

The objective of the present project is to solve some of the existing measurement problems in order to allow a satisfactory application of the directive 92/42/EEC for fuel oil and gas boilers. The project was organised in 3 separate but complementary parts:

  1. Identification of the remaining measurement errors and proposal for solutions (inter-comparison of reference material).
  2. Organisation of a network of laboratories which will agree upon new test procedures in order to keep the measurement quality at the highest level and amend the relavant CEN standards.
  3. Development of a simple, but accurate part load model as an alternative to the 30%

    part load efficiency measurement.

The main results obtained are the following:

1) Concerning the intercomparison, the action carried out has proved to be efficient as a large number of errors has been detected. The laboratories tested have got valuable information on their own system.

The problems identified can be classified in two categories:

  • Problems for which immediate action is possible (e.g. correction of systematic error on temperature probes, replacement of a meter).
  • Problems for which further action is necessary (e.g. recalibration of gas meter).

But an even more important result is that a number of important conclusions of general interest has been reached. Among the most important points we discovered that

1. Only few laboratories have a precise idea of their uncertainty

2. A lot of progress can still be achieved in the optimisation of the quality control procedures. Working on those points will not only help in having better measurement quality, but it sill also reduce the testing costs.

Therefore the following action is suggested:

- Extend the test carried out to other laboratories (about 20 type testing laboratories + manufacturer laboratories).

- Develop an uncertainty diagnosis method including the procedures/protocols to measure e.g. the drift of meters and other individual error sources. The method of uncertainty developed under a previous project [1] is not sufficient. Moreover, the laboratories tend to underestimate or neglect some important factors of uncertainty owing to a general lack of knowledge on the real performances of the instruments.

- Share the knowledge on meters.

At the time the laboratories having the best knowledge of their uncertainties are somehow penalised because they can have larger figures than laboratories that know only little about some of the error sources. Therefore a harmonised procedure including the determination of the individual error methods shall be developed for a fair information to the manufacturers, but also to allow the laboratories detect their own weak points so they can continue improving their own system themselves.

2) Concerning the creation of a network, 21 laboratories have agreed on a letter of intent. The activities have already started and the next meeting is planned in June 1999 where the financing of network activities shall be discussed and decided.

The large commitment of laboratories is a sign that they are taking care of the problem seriously and that they intend to improve the situation even if this will have a cost for each of them.

The activities of the network should include the organisation of intercomparison tests and the updating of the GLP document. The support of the Commission (V framework programme) will be requested to run the network.

3) The development of a simple model for 30% part load efficiency (based on BOILSIM) has been achieved. The results of validation are quite good.

As a result it is now possible to propose the replacement of the 30% test by a standardised method of calculation for most of the boiler types. (There are some boiler types not included in BOILSIM which are not treated in the simple model).

As a result of the whole project, the improvement of the interlaboratory reproducibility is now achievable through the following tools:

- The control of the laboratories with the new reference test rig (and action in case there are discrepancies).

- The respect of the GLP document which development and maintenance is done by the network of laboratories.

- The use of part load model instead of part load test.