DataCenter CRAC Unit Pressure Drop

Engineering Brain Workout

     Eileen N. Walls is the Mechanical PM in charge of Data Center HVAC. She's been asked to estimate the pressure drop across an open floor tile 8 feet away from a new CRAC unit. Given that the CRAC unit puts out about 40,000 CFM, the raised floor system is about 1.5 feet deep, the initial air velocity from the CRAC is about 25 feet per second, and the static pressure at the CRAC outlet is measured to be 0.75 inches of H2O (gage), how could she approach this problem and what should her result be? (Hint: she only has a pencil and paper - no CFD)

Engineering Brain Workout

     Chuck U. Farley lives on the East Coast and is in the middle of changing SUV tires in his auto shop when it starts to snow. They just delivered the customer's wheel mounted tires so he starts rolling up one of his 70 pound tires straight up the driveway which has an incline of about 1/4 inch per foot. The snow starts to pack around the back of the tire at about 3 inches deep.

     Given that the static coefficient of friction between the tire rubber and the snow is estimated to be about 0.08 and his tire has a 19 inch diameter, do you think the tire will slip out from under him? You can assume that the tire doesn't deform and is rigid.

Possible Answers:

(A) The tire will slip out from under him -  he has no business out in the snow anyway because he grew up in Southern California.

(B) He's lucky because the tire will not slip and, even if it did, the snow will keep it from moving down the incline.

(C) The tire will slip, start to spin, and fall down the incline plowing into an unsuspecting dear.

(D) None of the above because I don't believe in physics.

Data Center Energy Efficiency

     So, what is a "Data Center"? And, how can Mechanical Engineering help increase the efficiency of data centers?

     I recall being introduced to the concept of a data center while working in the Telecommunications industry. When I started, I was given a tour of a local phone company's "Central Office". At the time, the "clickidy-clack" sounds of actual switches (yes, mechanical switches used to exist) permeated the air - as opposed to the din of the "whhhrrrrrrrrrrrrrrrrrrrrrrr" from the small fans cooling the high-tech [and VERY high heat-density] rack equipment of today's buildings. Soon, the term "Server Farm" arose...and then...the data center!

     To a Mechanical Engineer, there is only the flow of heat regardless of building use. Whether you're trying to get rid of it, store it, or transfer it somewhere else. Your mind is constantly occupied with Temperatures & flows (and COP, EER, ASHRAE 90.1, etc.). 

     That's not to say that you're not mindful of the Systems Engineering coordination with IT, other A/E, the GC, subs, and especially the bottom-line '$' for the customer. Because I'm talking purely ME here, I'm also not talking about building use, permitting, and other municipality regulation - All of these factors come into play in the Project Management space.

     Back to efficiency. For the better part of the last two decades, I've seen industries transform from dinosaur-like relics following Standard Operating Procedure "by the book" (that was written centuries ago) to Dynamic Agile organizations that strive to continually reduce cost & increase efficiency. According to a recent ASHRAE Article written by M. Hastbacka, M. Rutberg, and A. Bouza; about 385 kWh per year can be shaved off of a 62 MWh per year office building. This is done by using laptops & desktops that are "ENERGY STAR" certified. Of course, this example seems tiny but imagine "tweeking" ALL of the energy-consuming equipment.

     While these concepts are not new (I saved an estimated $100k after the first few years of a multi-story lighting retrofit long ago), there is an exponential increase in the urgency to execute these types of projects. This drive comes from the impact on high-energy use buildings like data centers plus the multiplicative effect these savings have on the supporting power infrastructure. This multiplicative effect comes from the fact that the electrical load being saved no longer traverses down-stream from the house service, through the power-loss-inducing wires, transformers, through the batteries, and finally to the floor equipment etc.

     So how can Mechanical Engineering help increase Data Center Energy Efficiency? Well, newer HVAC technologies allow greater efficiencies though the use of "heat wheels" (aka "enthalpy wheels" aka "Sensible / Desiccant & Total Energy Wheels") that temper the outside air. Also, an ME can design a transfer of waste heat into areas where the heat can be consumed and where this waste meets certain quality criteria. The ME can analyze and redirect data center floor space heat flow with Computational Fluid Dynamics (CFD), and she/he can collect actionable metrics from the data center equipment along the entire Energy Value Chain.

     ["Value Chain" = corporate-speak for "System"]

     The well known ASHRAE Guideline 14-2002 was written to help determine how to measure energy and demand savings in pre- and post-retrofit applications.

     Not to mention the calibration of existing chiller/AHU/Cooling Tower equipment by the Building Technician whose job it is to live with whatever is designed. [Lesson #1, NEVER have design meetings without the Building Tech buy-in]. He/She may adjust the Chiller compressor guide vanes, ensure the chiller operation at optimal Temperatures/Pressures, and flows, and do a host of other maintenance adjustment tasks (VFDs, etc.) geared toward high efficiency.

     It's important to note that leveraging AutoCAD with BIM, CFD, SolidWorks, and even Mobile Apps [eg. Android - as The Disney Imagineering Team does] is a foregone conclusion in that the Professional Engineer should leverage the currently available tools to increase accuracy and Agility :)

Is Mechanical Engineering HARD?

Is Mechanical Engineering Hard?

[I am interpreting this typical question as: “is getting a BSME Hard to do?” as opposed to the question of integrating resources to design & build a new product.]

     Because it really depends on the kind of person you are (or want to be), this question is really subjective. However, if you ask a recent graduate with little real world experience, you might get a resounding "YES!". (Now…you might want to sit back and put a few things into perspective before approaching your guidance counselor on your academic goals.)

     Take the following anecdotal story for example:

     A few years ago while working for a small engineering design firm, I walked into the "Dilbert" cubicle of a relatively young engineer. At the time, my role was focused on Financial Management for the enterprise. As I was new to the organization, I wanted to introduce myself to him. So, I looked curiously at his white-board and started asking him questions regarding the type of Pressure Vessel he was trying to design. His eyes widened as he looked up at me and said "You're in the Finance department, right?". To which I replied "Yes, but I have a Mechanical Engineering background".

"Oh…So your not a complete idiot!", he replied.

     Now, if you haven't been to Engineering school yet or you haven't at least passed your first semester of Physics, his response might be off putting to say the least. However, if you're an Engineer with a few years of experience and at least one other non-engineering degree, you - like me - continue the conversation with an understanding smile on your face. You see, what I'm trying to get at with this story is 1) Yes, Mechanical Engineering is VERY HARD [Just like skiing a double black diamond slope is VERY HARD for someone that's never skied before.] and 2) You WILL be proud of yourself once you've completed your degree - and sometimes - Chip-On-Your-Shoulder proud.

BUT (and MOST IMPORTANTLY)

3) Negotiating the REAL WORLD with all of the challenging political, financial, social, familial, legal,…decisions you'll have to make put Mechanical Engineering classes into perspective. Remember, a class of students is typically a controlled environment where all the answers are in the back of the book - or at least in a separate solutions manual. So, if I assert that Mechanical Engineering is "HARD", you have to put it into a larger perspective like that of a rain droplet being absorbed into the Pacific Ocean.

     As I said, answering the question "Is Mechanical Engineering Hard?" is really subjective. I'm very sure that other endeavors are harder. So, here's a list of things that I've ranked from my own personal experience from 1) "HARDEST" to 10) "EASIEST". I'm sure that the relative rankings will be different for everyone [Although the first 4 are private, know this - they are ALL from just living life]:

1) XXXXXXXX

2) XXXXXXX

3) XXXXXXXX

4) XXXXXXXX

5) Bachelor of Science in Mechanical Engineering

6) Master of Business Administration

7) Project / Program Management

8) Professional Engineering License

9) Android Application Development

10) Professional Financial Management

So, what are your thoughts? Please chime in – especially if you’re an Engineer     Cheers!