**3.2. Calculating the electricity use from logged data**

Logged data can be used for calculating:

**•** Uptime.

**Unit process Power data source Time data source Comments**

clamp 4.

clamp 1 and 2.

clamp 3.

clamp 1.

**Table 3.** Example of plan for energy measurements to allocate electricity use to unit processes.

Logged data from current

Oral info on working hours. Verify with data from current

Air handling unit control system. Verify with data from current clamp 1 and 2.

Logged data from current

Logged data from current

In this case we will have a measurement from a switchgear cabinet that covers several unit processes, for example lighting and forklift charging for a garage and picking stock, as shown in Figure 8. The data from clamp no. 1 in the switchgear must be complemented by simulta‐ neous measurements from clamps 2 and 3 in the distribution board, where clamp 2 measures the total incoming current to the Central Garage board and clamp 3 measures the outgoing

Later, the data from clamp 2 in the Central Garage distribution board can be subtracted from clamp 1 in the switchgear to get a picture of the energy use in Central Picking Stock and Central

At the same time you have parallel measurements of the air compressor from clamp no 4. The clamp meter is placed in the switchgear, where the compressor has directly connected con‐

ductors, or in the compressor, depending on where you have the best access.

Clamp 4 settings:

to 60 s.

interval 60 s.

interval 60 s.

interval 60 s.

Packing.

range 200 or 500 A, sampling interval 5

Clamp 1 settings: range 200 A, sampling

Clamp 2 settings: range 200 A, sampling

Clamp 3 settings: range 20 A, sampling

The residual energy is logged data from current clamp 1, minus clamp 2 and the energy for lighting and ventilation. The residual is equal to the energy for

Compressed air Instantaneous

134 Sustainable Energy - Recent Studies

Ventilation Instantaneous

Packing Rated power,

current to the forklift chargers.

Large Hall.

measurements.

measurements.

chargers combined with logged data from current

Internal transport Rated power for forklift

clamp 3.

instantaneous measurements.

Lighting Rated power, verified by instantaneous measurements.


In the example below the case is an hydraulic press, but the same procedure can be used for other equipment, for example to calculate the energy used to cover leakage in compressed air systems. With some more measurements and analysis, it can also be used for a complete building or workshop.

The idling energy, uptime and average power can be calculated in a few steps:


How to do this will be shown with measurements from a hydraulic machine for sheet metal processing.

*3.2.3. Analyse the graph*

to the machine and after it was disconnected.

energy use for the different modes.

ous measurements of the power factor.

**Table 5.** Power and energy use for a hydraulic press during one week.

*3.2.4. Convert the current to power*

**Mode Power**

**factor, λ**

From the graph (Figure 9), it is clear that the machine is not used Friday to Sunday and for some hours during the nights. The machine is turned off during non-production hours. None‐ theless it has some idling power during the weekend and nights. The conclusion is that there are in fact three different modes to consider: active, idling and standby. The periods with zero current in the beginning and the end of the graph is the time before the logger was connected

Industrial Energy Auditing for Increased Sustainability − Methodology and Measurements

http://dx.doi.org/10.5772/51717

137

**Figure 10.** Duration diagram of the current used by a hydraulic press during almost one week (6,8 days). The active

One way to analyse the graph is to create a duration diagram with the logged data, as in Figure 10. The duration diagram can be used to distinguish between the modes and to estimate the

The power can roughly be estimated with the duration diagram together with the instantane‐

Active 0,82 270 230 150 20 3000 Idling 0,38 180 230 47 36 1700 Standby ? 5 230 3,5 108 400 SUM 5100

**Current (A) Voltage (V) Power (kW) Duration (h) Energy**

**(kWh/week)**

mode lasts for about 20 hours, the idling mode for about 1,5 day and the standby mode for about 4,5 days.
