Heat balance and performance testing are final steps of boiler implementation. The final act of performance testing is followed by taking over of the plant by the owner and final finan­cial settlements. The warranty period of the boiler commences thereafter. Therefore, it is very important that the testing procedures are conducted impartially to avoid expensive legal battles. American Society of Mechanical Engineers (ASME) performance test code (PTC) 4 is very widely followed. BS 2885 and DIN 1942 are the equivalent British and German codes.

Performance testing is best done on a new boiler before the natural wear and tear sets in. But this is usually not possible for various reasons. At the time of sale it is usual to decide the time limit before which the testing is to be carried out and the way it is to be performed. In small and medium plants it is possible to vent the steam for the duration of testing and complete the formality of testing.

Is it necessary to conduct the performance test? If it is not mandatory as per contrac­tual terms, the test is often waived. This is because the preparatory work for testing is demanding in terms of manpower and other resources. Besides, it is necessary that the plant be handed over to the supplier to allow for tuning of the boiler for about a week. This leads to a certain loss of boiler availability, which the plant may not be able to afford. Also, the plant operators can easily determine whether a boiler is meeting performance standards. A boiler test is usually required only when there is a fear of reduced or mar­ginal performance.

Gross efficiency = net output % (1.8)

Total input

It is a direct measurement of efficiency if steam output can be measured. Rewriting the formula by substituting output = input — loss, we arrive at

Gross efficiency = 100 — heat loss % (1.9)

Fuel input

The loss is measured instead of the output. Boiler efficiency as derived this way is the gross efficiency. When the heat equivalent of auxiliaries is subtracted from the output, the efficiency calculated is the net efficiency. The input comprises the fuel input plus the heat

Credits to the system if any, such as the air temperature rise in the fans. Thus,

Gross efficiency = 100 —————— heat losses——————— % (^

Fuel heat input + heat credits

Performance evaluation serves two purposes:

1. A routine measurement in a running plant to assess whether course correction is needed

2. Acceptance of a new or refurbished boiler to check whether the promised perfor­mance has been delivered