The same machine run for twelve hours in one day and run four times for three hours each will not give the same electricity bill. The difference is not in the machine itself but in the share of ineffective running time in the two ways of using it. In continuous running the loads — heating, vacuum and the pumps — stay in a stable condition for a long time, and the machine is doing useful work throughout. In intermittent running every start has to bring the oil up from a cold state to the set temperature again, and the heat stored up from the previous run is wasted on each repeat of the warm-up.
Where continuous running saves
The total power of the ZYD-100 is 72 + 5 kW and the supply is three-phase 380V / 50Hz. The power consumption of this machine is made up mainly of three parts: the heating section, the vacuum pump and roots blower section, and the oil pump section. In continuous running the heating is continuously on, but the vacuum system and the pumps only reach their highest efficiency in a stable operating condition: the pumping speed no longer has to be established again and again at every start and stop, and the condition inside the pump chambers does not have to be run through from the beginning each time.
Temperature matters more. The temperature control range is 45–80 °C, with the upper limit pulled down to 70 °C when the water content is high. When the oil temperature is stable within the range, the degassing result is stable with it; every restart has to go through the whole rise from ambient temperature to the set value again, and during that time the machine is not treating oil, but the electricity has already been spent. The ambient temperature range marked for the machine is -20–45 °C, and in winter this warm-up period is longer and the difference is more obvious.
Where intermittent running saves
Intermittent running is not necessarily more expensive in electricity, it has its own reason. If this batch of oil is only a dozen cubic metres or so and the machine is stopped once it has been processed, then letting the machine idle until the end of the shift, holding the vacuum and holding the heating, costs several hours of electricity during a time in which it processes nothing. Intermittent running suits the periods with little work.
So the conclusion is not that one way is better than the other, but that it depends on two points: the ratio between the total volume of this batch of oil and the flow rate of the machine, and the longest continuous running time allowed on site. When the volume is large enough to keep the machine working to capacity, continuous running is more sensible; when the volume comes in small amounts and the waiting time between runs is longer than the running time, intermittent running is more sensible.
| Operating mode | Where the main power consumption falls | What to record |
|---|---|---|
| Continuous running | The steady heating power and the vacuum system | The length of the continuous run, whether the oil temperature is stable within the set range |
| Intermittent running | The warm-up period after every start | The length of each run and the time needed to reach the set temperature |
| Stopped and on standby after the batch is finished | Keeping the temperature up after shutdown or starting again | The interval between shutdown and the next start of work |
| Continuous unattended running | The parts that run continuously, such as the heating and the automatic defoaming | The number of actions of the infrared level and foam detection |
What has to be recorded to work out the figures
- Record the start and end time and the volume treated in each run, and keep the record format the same for continuous and intermittent running, so that the two can be put together for comparison.
- Mark the period from start-up to the oil temperature reaching the set value separately; this is the period in which the two ways of running differ most.
- Record whether the machine was stopped part-way through the treatment; one stop in the middle means the cost of one start-up has been paid twice.
- Use the same type of oil when comparing different ways of running, otherwise the differences in the oil itself will mask the differences brought about by the running mode.
- Calculate the electricity consumption with the same meter and the same supply line, so that the consumption of the other equipment in the workshop is separated out.
- Also record what is done with the oil during shutdown: keeping the oil in the tank for the next run or draining it away directly affects the time needed for the next start-up.
The saving does not depend on how long the machine runs, but on how much of that time the machine spends with the temperature already reached, doing useful work.
