We often hear the term “redundant UPS”, or N + 1, but can we know how many UPS’s we need to design our data center?
The first thing we must consider is the amount of equipment that our UPS must support, in addition, we must determine which are mission critical equipment and which are not.
The UPS is also an equipment that serves as a harmonic filter that supplies clean energy to your data center.
Now, if you want to certify the data center, you must consider the level of availability that we want to obtain.
Here are the levels that you can obtain depending on the infrastructure you have according to ICREA:
LEVEL I: Computer room in Certified environment • QADC (Quality Assurance Data Center). For 95% availability
LEVEL II: Computer room in a World Class Certified Environment • WCQA (World Class Quality Assurance). For 99% availability
LEVEL III: Reliable computer room with World-class Certified Environment • S-WCQA (Safety World Class Quality Assurance). For 99.9% availability
LEVEL IV: High Security Computer Room with Certification. HS-WCQA (High Security World Class Quality Assurance), for an availability of 99.99%
LEVEL V: High Security and Availability Computer Room with World-Class HSHA-WCQA (High Security High Available World Class Quality Assurance) certification, for an availability of 99.999%
LEVEL VI: High security and availability computer room with world class RHA-WCQA (Redundant High Available World Class Quality Assurance Data Center Net) Certification, for an availability of 99.9999%
We must consider that to relate the watts of our source to the VA of the UPS, a concept called "Power Factor" or "CFP" must be used.
The power factor (CFP) of a computer equipment ranges from 0.7 to 0.6; we are going to use the most conservative value 0.6; therefore the relationship between Watts and VA that matters to us is: (VA) x (CFP) = Watts
This means that a UPS that is marked 1000VA can power a 1000x0.6 source, that is, a maximum of 600Watts. Similarly, if you want to know the VA that your source needs; divide the power by 0.6; so if your source is 1000W, then the UPS you need is at least 1000W / 0.6 or 1666 VA at least.
How to calculate the effective backup time of a UPS?
As an example we are going to use a 1750 VA UPS. You will have to practice a formula. It's not difficult, but it will give you exceptionally useful information. You will use the following data:
- B = number of batteries in the UPS
- V = battery voltage
- Ah = Ampere-hours of the batteries
- Ef = UPS efficiency (as a rule, it usually ranges between 90% and 98% depending on the brand)
- VA = Volt-Amps of the UPS
All UPS's must have at least one battery ... be careful because many times we buy voltage regulators instead of UPS.
In this article, we are practical and we get you the information you need:
B: We will assume that your UPS has 1 battery. Of course there are units with more than one battery. Pay attention to this information, in case a UPS with more than one battery comes into your hands.
V: You will use 12 volts (generally all UPS batteries are 12V, but there are different types of battery. You must validate this information with the manufacturer of your UPS).
Ah: We will take 9 Ampere Hours (you can validate it in the manufacturer's manual). For small UPS it can be 7, 9 or 12
Ef: UPS have an average efficiency of 95%. You will use 0.95 (NOTE: IT DEPENDS ON THE BRAND AND THE TECHNICAL DATA OF EACH UPS. I RECOMMEND YOU TO REVIEW THIS DATA IN YOUR EQUIPMENT MANUAL). The higher the efficiency, the better the equipment you select.
VA: Remember that it is Volt-Amps from the UPS.
In other words…
The blackout service time formula is: ((B x V x Ah x Ef) / VA) x 60 = Service minutes. In order to determine the amount of UPS for a data center it will depend on the availability that we want our data center to have, now in order to determine the capacity of the UPS it is necessary to add all the consumption in watts or in VA of all the equipment to back up, and then multiply it by 30% as a growth factor, you should consider a minimum of 5 min to back up at full load to give time for your emergency money to be able to take over all the load when the power supply.
Remember that a UPS is a transition equipment, this means that it will only give you a limited time of energy so that you can take other actions that help you to continue operating your data center.
Tip: the more full load backup time you need, the more batteries you will use, so your UPS solution may be more expensive than expected, so I recommend that you consider at the same time as your UPS, a power plant backup.