Monoblock vs Modular UPS

A brief educational program for beginners on why modular UPSs are cooler and how it happened.

Uninterruptible power supplies for data centers according to the architecture of construction are divided into two large groups: monoblock and modular. The former belong to the traditional type of UPS, the latter are relatively new and more advanced.

What is the difference between monoblock and modular UPS

In monoblock uninterruptible power supplies, the output power is provided by one power unit. In modular UPSs, the main components are made in the form of separate modules, which are placed in standardized cabinets and work together. Each of these modules is equipped with a control processor, charger, inverter, rectifier and represents a full power part of the UPS.

Let us explain this with a simple example. If we take two uninterruptible power supplies - monoblock and modular - with a capacity of 40 kVA, then the first will have one power module with a capacity of 40 kVA, and the second will consist, for example, of four power modules with a capacity of 10 kVA each.

Scaling options

When using monoblock UPSs with an increase in the need for power supply, it is necessary to connect another full-fledged unit of the same capacity to the existing one in parallel. This is a rather complicated process.

Modular solutions are more structurally flexible. In this case, one or more modules can be connected to an already functioning unit. This is a fairly simple procedure that can be performed in a short time.

Smooth Power Capabilities

Smooth capacity building is important at the initial stage of the data center. It is logical that in the first months it will be loaded at 30-40%. It is more practical and economical to use uninterruptible power supplies designed specifically for this power. As the customer base replenishes, the data center load will increase, and with it the need for additional power supply will increase.

It is convenient to increase the power of the UPS in stages along with the technical infrastructure. When using monoblock uninterruptible power supplies, a smooth increase in power is impossible in principle. With modular UPSs, it is easy to implement.

UPS Reliability

Speaking of reliability, we will operate with two concepts: mean time between failures (MTBF) and mean system recovery time (MTTR).

MTBF is a probabilistic value. The mean time between failures is based on the following postulate: the reliability of the system decreases with an increase in the number of its components.

In this parameter, the advantage of monoblock UPSs. The reason is simple: in modular uninterruptible power supplies there are more structural elements and detachable connections, each of which is considered as a potential point of failure. Accordingly, theoretically, the possibility of failure is higher.

However, for the uninterruptible power supplies used in the data center, it is not the failure itself that matters, but how long the UPS will remain inoperative. This setting is determined by the average system recovery time (MTTR).

Here the advantage is already on the side of modular units. They are characterized by a low MTTR because any module can be quickly replaced without interruption in power supply. This requires that this module be in stock, and its dismantling and installation can be performed by one specialist. In fact, this takes no more than 30 minutes.

With monoblock uninterruptible power supplies, the situation is much more complicated. They cannot be repaired so quickly. This can take from several hours to several days.

To determine the fault tolerance of the system, you can use one more parameter - availability or in some other way performance. This indicator is the higher, the longer the mean time between failures (MTBF) and the shorter the average system recovery time (MTTR). The corresponding formula is as follows:

average availability (availability) =

With regard to modular UPSs, the situation is as follows: their MTBF is less than that of monoblock ones, but at the same time they have a significantly lower MTTR. As a result, the performance of modular uninterruptible power supplies is higher.

power usage

A monoblock system requires significantly greater energy consumption, because it is redundant. Let us illustrate this with an example for the N + 1 redundancy scheme. N is the amount of load required to operate the data center equipment. In our case, we take it equal to 90 kVA. The N + 1 scheme means that in the system 1 spare element remains unused until the failure.

When using a monoblock uninterruptible power supply with a power of 90 kVA, to implement the N + 1 circuit, you will need to use another same block. As a result, the total system redundancy will be 90 kVA.

When using 30 kVA modular UPSs, the situation is different. At the same load, to implement the N + 1 circuit, one more module is needed. As a result, the total redundancy of the system will no longer be 90 kVA, but only 30 kVA.

Hence the conclusion: the use of modular power supplies can reduce the power consumption of the data center as a whole.

Economy

If you take two uninterruptible power supplies of the same power, then monoblock is cheaper than modular. For this reason, monoblock UPSs remain popular. However, an increase in the output power will double the cost of the system, because one will have to add one more unit to the existing one. In addition, there will be a need to install patch panels and distribution boards, as well as laying new cable lines.

When using modular uninterruptible power supplies, the system power can be increased smoothly. This means that you will have to spend money on the purchase of so many modules that are enough to satisfy the existing need for power supply. Without unnecessary stock.

Conclusion

Monoblock uninterruptible power supplies are not expensive, easy to set up and operate. At the same time, they increase the energy consumption of the data center and are difficult to scale. Such systems are convenient and efficient where small capacities are required and their expansion is not expected.

Modular UPSs are characterized by easy scalability, minimum recovery time, high reliability and availability. Such systems are optimal for building data center capacity to any limits with minimal cost.