Main focus:
Optimal system size, investment costs and Total Cost of Ownership

In an interview with POWER news (PN), Ronald Metzig analyses the economic aspects.

Power supply systems for IT applications usually have a service life of 10 – 20 years. Choosing the right system size at the time of installation is therefore of great relevance. If at some point the installed system proves to be too small, it will have to be upgraded or replaced. This measure can involve very high investment costs.
If, on the other hand, the newly installed system were too large – i.e. overdimensioned – investment capital would have been wasted in a system with lower energy efficiency and higher operating and maintenance costs. Both have a significant impact on the total cost of ownership / TCO.

In an interview with POWER news (PN), Ronald Metzig analyses the economic aspects.

Ronald Metzig,
Head of Office East, Germany
BENNING

Mr Metzig supervised the planning and implementation of the UPS system for the Leipzig 2 data centre.

PN: Mr. Metzig, we sometimes hear the statement: “Our UPS systems are scalable and can grow with the requirements.” What is behind this statement?

Metzig: Dynamically changing requirements and the necessary change in system and server technology make it almost impossible to reliably predict the required performance and the optimal system size over a period of 10 to 20 years. For this reason, almost all systems are overdimensioned at the time of installation.
What turns out to be profitable for the system manufacturer, on the other hand, means that there is a high probability of overinvestment for the operator, and that higher maintenance and service costs will arise during the operating phase.

UPS room of the company data centre Taucha — The UPS system is scalable and can grow in parallel with the expansion of the data centre

PN: So the only way to minimize TCO would be to install a UPS system that has the right power at all times?

Metzig: Yes, that would be the ideal goal, but let’s break it down further. In a power supply system, three main factors influence the TCO:

Initial investment costs
Power losses, a function of system efficiency
Maintenance and repair costs

The problem is that these factors influence each other. They must therefore be considered together and optimised holistically in order to minimize the TCO.

PN: You mentioned the initial investment costs. We know that this market is highly competitive. But the main task of the UPS is to protect the critical load, isn’t quality and price like two boxers in a ring?

Metzig: A nice metaphor, but yes, that’s unfortunately the case. We therefore always advise, when comparing systems, to question whether the system with the lowest initial investment costs also uses the highest quality components and works just as energy-efficiently. If this is not the case, the operating costs incurred afterwards could be higher than necessary. It would also be likely that high maintenance and repair costs are associated with it.

PN: You brought up the topic of energy efficiency and probably also mean the performance losses mentioned before. Can you give us an example of that?

Metzig: Let’s assume a critical load of 1 000 kW for the sake of simplicity. Reducing the system efficiency by 1% already causes a power loss of 10 kW. If you extrapolate this for a whole year, there is a loss of 87 600 kWh with operation 24 hours a day, 365 days a year. With a term of 20 years, this corresponds to 1 752 000 kWh. As you can see, the energy efficiency of the system has a greater impact on the TCO than the initial investment costs.

PN: If you look at this loss, it certainly makes sense for an operator to take a detailed look at the efficiency curves of the various UPS systems, doesn’t it?

Metzig: It’s nice that you’re talking about curves, because unfortunately, excuse me for saying that, the maximum efficiency point is often put forward for marketing reasons. However, what really matters is the degree of efficiency. Or even better, the assessment of the different efficiency curves that result from the different operating modes between which the UPS system can switch.
Basically, it should be ensured that the power supply system always works in the optimum range of its efficiency curve. With almost all modern “transformerless” UPS systems, the efficiency curve increases to approx. 30% of the output performance rises steeply and then runs relatively flat. In normal operation, an efficiency of > 95% is reached early on, but the optimal system efficiency (> 96%) is in a power range of 40% to 60%. If you were to overdimension a system right from the start and therefore only operate it at about 30% of its possible output at the beginning, the loss of 1% mentioned in our equation above would already result.

PN: So you are counting on the so-called normal operation here. In your project with envia TEL you describe the SEOO mode of ENERTRONIC modular SE. In addition to the automatic shutdown of modules that are not required, is there also a difference in the efficiency curve?

Metzig: Yes, two things intertwine here. The system efficiency in SEOO mode, for example, is already 95.8% with an output power of 25%. If the UPS system manages to operate the entire system continuously in the optimal efficiency window by automatically switching modules on and off, the efficiency can be increased by about 3% compared to an initially overdimensioned system.

PN: But doesn’t this advantage of 3% disappear when the data centre later reaches its maximum capacity?

Metzig: That’s not entirely true, the advantage is only reduced. On the one hand, such an expansion process usually takes place over many years, on the other hand you have to consider that the loads in a data centre fluctuate very dynamically over the course of the day and week. With the SEOO operating mode, we ensure that, depending on the performance requirement, only the number of modules actually required is operated. In this way, we always stay within the ideal efficiency window. This accounts for a general efficiency advantage of about 2%.

PN: So basically simple maths, it seems to us. But let’s now talk briefly about the maintenance and repair costs you mentioned at the beginning. What should an operator pay particular attention to here?

Metzig: All UPS systems consist of electrical and mechanical components that are subject to a limited useful life. In order for the power supply system to be able to ensure the required availability over an operating period of 10 – 20 years, regular maintenance and, if necessary, replacement of components is required.

If, as indicated before, a system that was inexpensive at the time of the initial investment may have lower quality components, the maintenance costs incurred during the planned service life will probably also be higher as the components have to be serviced or replaced more frequently.
Therefore, it makes sense to talk to your UPS supplier about the various maintenance options and the expected maintenance costs before you make your purchase. In addition, the operator should find out exactly what the proximity to the manufacturer’s nearest service location looks like. The same applies when stocking spare parts, as the current situation is teaching us.

PN: Mr. Metzig, thank you very much for your clear explanations. Our takeaway from the conversation is that a system that is sized perfectly for the critical load from day one and can increase or decrease its performance according to the critical load guarantees the lowest TCO.
The initial investment cost of a system is not the only determining factor when it comes to TCO. Instead, energy efficiency and ongoing maintenance costs greatly affect the total cost of ownership of the system. Our conclusion: All three factors are equally important and must therefore be taken into consideration equally.