HOBO Datenlogger Versteckte Energieverschwendung aufspüren

The key to energy performance is a reliable source of accurate data and analysis. Complex metering systems are often expensive to install, operate and maintain. Data loggers are simple, robust measurement and recording devices that can save companies significant energy costs. The first step to reducing costs is to identify energy waste. Data from monthly utility bills and appliance ratings are useful, but not enough.

Compressed air is a convenient way to power industrial equipment, and it's useful in many other ways as well. Unfortunately, it is also inefficient and wasteful. Less than 10% of the energy supplied is ever converted into useful work, and 70% of the energy supplied is converted into heat in the compressor.
An important aspect of the compressed air system is compressor control. If you have more than one compressor, it is very important to know how the machines share the load. The air demand in the system changes and rarely matches the rated capacity of all machines, so one or more machines may need to run at less than 100% capacity. Partially loaded compressors are not as efficient as fully loaded machines.
The best way to distribute the load is to run all but one machine, known as the "swing machine", at base load. The swing machine maintains the system pressure by changing the output of the compressor as required. All other machines are operated at constant capacity at maximum efficiency or are idle when not required to meet the load.

Data loggers are used to verify the proper loading of the machine as follows:
1. install a data logger and a current transformer on one phase of each compressor and record the load current for one week with a sampling interval of 30 seconds.
2. calculate the input power of the compressor at each interval assuming a nominal voltage and a power factor of 86% using the formula Input power [kW] = 1.732 x nominal voltage x line current x 0.86 / 1000
3. plot the input power for all machines in a diagram and check that only one machine is operating in the partial load range at any one time. Other important observations - examine the performance profiles of your compressors and take them into account:
1. what does it cost you to run your air compressors in a year?
2. does the compressed air consumption follow the production activity?
3. how much energy (and money) is wasted on compressed air when the system is not in operation?
4. how much of the compressor output do you think is due to leaks in the distribution pipes?
5. what is the value of waste heat and how can it be utilized?

If you are operating a chilled water system with evaporative cooling, you should analyze the entering condenser water temperature and how it changes with the weather. Portable data loggers can be used to monitor the water temperature along with the ambient temperature and relative humidity. If the entering condenser water temperature remains constant as the weather changes, you are wasting energy because you are operating at a fixed pressure. The condenser temperature has a significant impact on the efficiency of the chiller as it determines the head pressure and compressor capacity. If evaporative cooling is used, the operator should set the condenser inlet temperature to 5 °F above the ambient wet bulb temperature. This will save 2 to 8% of electrical energy if set manually and 4 to 20% if set automatically by an electronic controller. In practice, this means that the water temperature must be lowered as much as possible if the outside air temperature and humidity are given. Lowering the condenser water temperature does require more energy for pumps and fans. However, this additional energy is more than compensated for by the lower pressure and the resulting lower power consumption of the compressor.

Bonus: The suction pressure of the compressor is also an important determinant of energy consumption and efficiency. It is related to the chilled water supply temperature set point. An increase of just 1 °F can significantly reduce energy consumption. A higher chilled water supply temperature may require a higher water flow, but the savings on compressors often make this a good move. Use data loggers to track chilled water supply temperature trends and run the system at the highest level required for cooling.
Note: Be careful when using electrical load current [amps] to estimate actual power [kW].
Electricity is sold in units of real energy [kWh] and power [kW]. You will not find any reference to electrical current or amperes (current flow rate) on your electricity bill. Accurate measurement of AC electrical energy requires measurement of the load current and grid voltage. This must be done in such a way that the phase angle between these two quantities can also be determined. The electricity meters used for billing have this capability.
For energy management studies, we often use a simple current transformer (CT) to measure the load current and assume a nominal voltage and phase angle to estimate the actual power and energy. While these assumptions are valid in many situations, they are not valid in all situations.
The phase angle between current and voltage (power factor) can vary over a wide range for large inductive loads (motors) and capacitive loads (not so common). In these cases, a simple measurement of the load current does not provide accurate information about the actual power and energy consumption.
An example is an induction motor, which may have a power factor of 0.85 at full load and 0.10 or less at start-up. In this case, we cannot assume a constant phase angle (power factor) and a direct measurement of the actual power and energy is required.
A constant power factor is not always a valid assumption - in some cases, such as when starting induction motors, it can be completely wrong.

Imagine driving a car from New York to Seattle without a working speedometer. Three weeks after arriving in Seattle, you receive several speeding tickets and a $1,000 fine for speeding in Iowa, South Dakota and Wyoming. The value of a real-time speed display is obvious: you might have been able to avoid the violations, or at least know when and where they were committed. The same is true for commercial and industrial electricity consumers.
Most commercial and industrial electricity tariffs include energy costs
[¢/kWh] and peak demand charges [$/kW]. Many users do not know when the consumption peaks occurred or which electrical loads contributed to the peaks. The average electrical load [kW] recorded every 15 minutes is very useful in reducing peak demand charges.

The data loggers are used to create load profiles as follows:
1. install a data logger and a current transformer on one phase of the facility's power system and set the measurement interval to 1 minute. If the power exceeds 600 amps (maximum size of current transformer available) and there are multiple conductors per phase, place the transformer around one of the conductors and assume that the current is the same in all conductors.
2. calculate the average power over a 15-minute interval assuming nominal voltage and 90% power factor using the expression (power [kW] = 1.732 x nominal grid voltage x grid current x 0.90 / 1000). A spreadsheet program is helpful.
3. examine the profile and look for clear peaks in energy consumption,
as in this example:

A small grocery store had a peak load of 359 kW every morning at 8:00 am caused by defrosting all freezers at the same time (red line). The green line shows the resulting load profile one week later, after the timers were set to avoid the peak load. The billing demand was reduced from 359 kW to 302 kW, resulting in annual savings of nearly $10,000.