The appearance of an energy consumption clause in a technical agreement says something about what the buyer cares about: it has moved from whether the machine works to what the machine costs to run every day. The direction of the clause is sound. Whether it can be accepted depends on whether the text defines the boundary, and that is more worth discussing than the number itself.
The same machine gives different results under different clauses
The three models of the ZYD series have throughputs of 6000 L/h, 12000 L/h and 18000 L/h, and the total power of the ZYD-100 is 72 + 5 kW. Put these figures into a clause of the form no more than a given number of units of electricity per tonne of oil, and the questions begin: is the figure calculated on the rated throughput or on the throughput the site actually achieves; is the heating section included; is the reading taken from the meter of the machine itself or from the whole section from oil in to oil out; is it the average of one batch or a total over a day, a week or a month.
If one of these readings of the measure is left unwritten, the same machine and the same operating record can produce different conclusions. On the day of acceptance the argument is usually not about whether the machine is good or bad, but about something the original text never settled.
A clause also has to face the question of whether one machine can satisfy several requirements at once. With the ZYD series, 6000 L/h, 12000 L/h and 18000 L/h belong to different models, each with its own total power. If a technical agreement asks for a throughput range, a fixed specific energy and a specific model at the same time, the three do not necessarily hold together. Someone writing the clause who follows only one of them will often find at acceptance that the other two have no answer.
Four things the clause should state
| What has to be stated | What happens if it is not |
|---|---|
| Whether the rated throughput or the actual throughput is the basis | The same machine produces two different specific energy figures |
| Whether the measurement boundary includes the heating and the vacuum system | Different people read the meters over different boundaries |
| The statistical period and the operating condition | The first batches and the steady batches are averaged together |
| Which instrument is the basis for the measurement | A meter fitted locally on site has readings that cannot be compared |
There is a fifth point that is often left out: the oil. Different oils at the same throughput have different viscosities and different water contents, they need different temperatures and different times for degassing, and the power draw differs accordingly. A clause that says nothing about the oil leaves one variable outside.
The figure only means something once the clause is clear
- Write the definition of the specific energy into the clause: how many litres or tonnes of oil correspond to how many units of electricity.
- State the statistical period, and base it on continuous steady running, with the warm-up phase excluded.
- State the position of the measuring point, so that it corresponds to the meter actually fitted on site.
- State how abnormal conditions are treated: whether shutdown, element change and heat holding are counted in.
- State how the acceptance record is kept, whether by batch log or by a total over a period.
An energy clause can rule out the proposals that clearly do not match the site duty, and that is useful. Its value, though, rests on the clause itself being executable: a clause with no measurement method and no way for anyone to produce the matching records only turns into a dispute at acceptance.
The other way round, the more specific the clause is, the higher the cost of executing it, and that has to be counted as well. Every additional condition on the measurement boundary, the statistical period and the record keeping means one more registration step at site. What the energy figure is really worth depends on whether that cost stays inside what the site can carry.
Putting an energy figure into a clause is a good thing, provided the clause also says under which conditions it is measured.
