Fundamentals of Data Center Power: Power Calculations

[00:00:00] Speaker 1: Hi, this is Dave Cole. I'll be instructor for Power Calculations module as we continue talking about power in the data center. We're going to look at some power calculations. If you have any questions as we're going through this module, please be sure to use the question comment box and happy to get right back with you with answers to your questions. So, let's get started. Let's look at the topics that we're going to cover in this module. We're going to look at calculating power requirements. So, in the data center, if I'm building a new data center or if I'm adding onto a data center, how much power do I need to be able to power all the equipment that I'm going to put into that data center? And we're going to look at power consumption in the data center. Where's my power going in the data center? I know I'm consuming it, but what is it that's using up the power? So, let's look at calculating the power requirements. It's pretty straightforward, but it is complicated a little bit by how much redundancy am I going to have and calculation of future load. It's important that we're as accurate as possible when we're calculating power requirements. If we underestimate power requirements, we may have some future power disruptions. We never want to get caught without enough power or cooling or space. On the other hand, if we overestimate power requirements, we're going to run into excessive initial costs and we're going to have higher ongoing maintenance costs because our energy efficiency is not going to be very good. So, the more accurate we can be, the better chance we're going to have of being reliable and available in our data center and also operating energy efficiently. Where's our power going in the data center? As much as half of it can go to cooling. So, we talked a little bit about cooling and we're going to talk quite a bit more about cooling and ways we can be more efficient, but cooling is often half of the power in the data center. Then we have our critical loads, which can be a third or maybe closer to a half on that. And we also have UPS in efficiency when we're charging our UPS batteries. That can be quite a bit of our overall power usage. And then lighting in the data center. We don't think too much about lighting, but it's out there, right? So, we would like to be as efficient as we can in all of these areas. So, let's go through an example of what a typical data center design company would use to calculate what your power is going to be in the data center. So, we have to start with some assumptions. Let's assume we're going to have a 5,000 square foot data center. Put 150 racks in there and half of our cooling is going to be direct expansion and half of it's going to be chilled water. We don't need to worry too much right now if we're not sure what direct expansion cooling is or chilled water, but it's important to know that there is a difference in cost for different types of cooling strategies. So, first thing we're going to do, we're going to start by determining the size of our critical load. What's in our critical load? Things like servers and routers, storage devices, telecommunications equipment, security, fire monitoring, right? All of these things are our critical load. These are all the things that we want to make sure are going to be up all the time, right? We're going to make a list of all of these devices. We're going to look at what their power rating is. We can look at nameplate values, but ideally we're going to use the manufacturer calculators and figure out how much power we think these devices are really going to draw. So, we're going to look at the power rating, voltage requirements. Do we need single or three phase, right? We need to know all of this stuff ahead of time because we're really trying to design a power system to match the equipment that we have. So, let's put this together in a little grid and ideally we want to do this at a rack by rack basis because if we've got kind of a standard rack and we can spend a little bit of time with that rack figuring out how much power it's going to draw and if we then say most of our racks are going to be the same, it now makes our calculations much easier. So, just for purposes of example, let's say we're going to have a couple of servers and there's our power ratings and a couple of storage arrays. So, we're going to say total at this rack we think it's going to be one and a half kilowatts of power. Now, knowing that we're going to put 150 racks in here, I can take one and a half kilowatts of rack, multiply that times 150 racks and we're at 225 kilowatts. Well, that was pretty easy, except we're not there yet, right? Because this is only our critical load. We've got to worry about our infrastructure and cooling and lighting and everything else. But it's a good start. We've gotten somewhere. So, let's take our critical load and now we need to figure out how big are we going to get. Our data center is undoubtedly going to grow over time. So, what do we think our future load is going to be? Again, we don't want to get caught without power. So, let's try to give ourselves a little bit of leeway here. So, let's figure about 20% growth. So, that's another 45 kilowatts, right? 20% of our 225s, another 45 kilowatts. So, now we're up to 270 kilowatts. Sometimes in the year, we're going to max out our data center. Let's imagine an amazon.com the day after Thanksgiving. As we get into holiday season, people start buying gifts. Maybe all their servers are really cranky. Or maybe it's an accounting firm, you know, on right before taxes are due. Or whatever your business model happens to be, there's going to be some times when you're drawing a lot of additional power. We're going to call that a peak power multiplier. And what we're going to do is give ourselves a 5% overhead for when everything's cranking at the same time. So, now we take our 270 kilowatts, we can multiply that by 1.05, our peak power multiplier. And that's going to give us an extra 13.5 kilowatts of power that we need to account for. Okay? So, now we've got our critical load. Now we want to figure out what's our UPS load. This is where we start looking at things like UPS efficiency. Okay? Let's assume our UPS efficiency is 88%, which means if I put 100 kilowatts in, 88 kilowatts come back out, right? So, I'm going to lose some of my power inside the UPS. I need to account for that because that's going to be a big number for us. I also need to remember that my UPS is going to try to take care of itself. So, if its batteries aren't charged, as much as 20% of the power going into the UPS is going to be used to charge the battery. So, I have 12% inefficiency. I have 20% battery charging that I need to worry about. That's 32%. 32% of my critical load is 86.5 kilowatts. I need to account for that when I'm looking at my total power. And in normal conditions, with a charged battery, my charging load is negligible. But if it's completely discharged or partially discharged, again, 20% of that could go to charging the battery. Now, let's look at lighting. For lighting purposes, we're going to estimate about 2 watts per square foot. We have 5,000 square foot, 2 watts per square foot. That's 10 kilowatts for our lighting load. Now, we start adding all of these up. So, we started with our critical load. Our server and IT equipment, routers and things like that. That was 225 kilowatts. We put in 20% for our future load. We added a peak power adjustment. We added our UPS and battery overhead. We added lighting. And now, we're up to 380 kilowatts. Our load is starting to grow. We need to account for all of that. Now, I need to add in cooling. And I said, for purposes of this example, half of my cooling is going to be done with chilled water. So, I'm going to cool 190 kilowatts with chilled water. Chilled water is pretty efficient. So, it's going to take me about 0.7 of that is how much power it's going to draw. So, I take 0.7 times that 190 and I get 133 kilowatts. Direct expansion, not quite as efficient. So, I'm going to take for me to cool 190 kilowatts, it's going to take me another 190 kilowatts to cool that. So, now, my cooling load, I add those two together and I get 323 kilowatts. Now, our numbers are starting to get pretty big. Remember, we started way back when with just 225 kilowatts for our critical load. But we've added future load, peak power draw, UPS and battery inefficiency, lighting, and now we're going to add in this big chunk for cooling. And all of a sudden, we're looking at this at 703 kilowatts. These are pretty conservative numbers that we use. But again, I don't want to get caught without space power and cooling. Those are big important things for me. Now, how much do I need to tell the utility company? How much power do they need to give me? Well, I can't tell them 703 kilowatts, even though I think that's what my total power is. I don't ever want to use more than 80% of what they give me. I want to have that 20% overhead according to the National Electric Code. So, I need to take my total power, my 703 kilowatts, multiply that by another 25%. So, I need to tell the utility company, "Hey, Mr. Utility Company, I need 879 kilowatts." So, way back with our 225 kilowatts, all of a sudden, a number almost three or four times that is what I have to tell the utility company. Again, pretty conservative numbers, but this is the process that we would go through to calculate power in a data center. So, here it is all kind of laid out for you. Now, I want to look at how big a generator do I need. I look at my generator in two different stages, one for my critical load and one for my cooling load because I may or may not want to run my cooling off my generator. I have pretty low density data center in this case. I may not need my cooling to be run off generator. So, we split these out. Plus, the calculations are a little bit different for cooling versus my critical loads. So, I take my total power load, 380 kilowatts. I multiply that by 1.3 to get how big a generator, how much generator I need to supply power for that much load. For cooling, I have to multiply that number by 1.55. Because we've got mechanical gear, we've got pumps and motors and things like that on cooling, it's harder for a generator to supply that power. So, if I add those up, I get 995 kilowatts is the size of the generator that would be required if I want to support both my IT equipment plus my cooling. So, again, these numbers add up very, very quickly. People forget about things like UPS charging and they forget about things like lighting and future loads and things like that. But these numbers can grow very, very quickly. Where's my power going in the data center? Ideally, all my power to the data center would go to my IT load. Right? That's the important stuff. My servers, my storage, my telecommunications equipment. Unfortunately, all the power going in the data center doesn't go to my IT load. Some of it gets sidetracked. Some of it's going to go to my support infrastructure, my cooling and lights and security and things like that. Right? And part of it's going to go to my UPS, my PDU cabling and switches, and I'm going to have power losses. Anytime I run power over a cable, I lose some of that power. Every time I run power through a UPS, I lose some of that power. Every time I go through a PDU transformer, I lose some of that power. So, I have these losses in the power system. The remaining power now is what goes to my IT load. Right? So, certainly not all the power. Maybe only half the power. Maybe only a third of my power is now going to my IT load. So, we have a metric, an energy efficiency metric in the data center called PUE. Power usage effectiveness. And what this value is, is the total power to my data center. Right? Everything going to my data center divided by how much of that power actually gets to the IT load. We would like that number to be one. That's as low as it could get. That would mean that every bit of power going to the data center is going to my IT load. Right? Typical data center is about two. That means about half of the power going to the data center actually makes it to my IT load. Because of the support infrastructure and these losses in the power system. So, let's look at this power consumption data center. We looked at this before, but now we're going to break it into a little bit more detail. So, we've got power going to IT equipment. You know, maybe 30%. Maybe my computer and air conditioner, my crack unit, maybe that's taking 9%. My humidifier may take some. My chiller may take some. My UPF, my PDU, my lighting. Right? So, a lot of different entities want to grab some of my power. And the reason I break this up, and your mileage is certainly going to vary in your data center, but the reason I bring this up is if I want to improve my energy efficiency in the data center, I'm probably not going to start with lighting because that's only 1% of my total load. I want to look at the big areas. I want to look at IT equipment and my crack unit and my chiller and my UPS because those are taking bigger chunks of my power consumption in the data center. So, it's kind of a recap. We talked about where was the power going in the data center and certainly a lot of that power is going to be wasted. We're going to talk in future modules about some other modules about how we can reduce some of that wasted power in the data center. We talked about how we can calculate in a new data center or an expansion of a data center how much power we're going to need. If you have any questions about that, please feel free to use the question comment box. We'll be happy to get back to you as soon as we can with any questions on that. In the meantime, thank you very much for joining us in this module and look forward to having you in other modules as we move forward.