Green Notes

SearchDatacenter.com recently had a great article by Bob McFarlane with several handy tips on sizing computer room air conditioners and save on energy. Here are some excerpts:

Sizing a data center air conditioner is not like choosing a refrigerator. Bigger is not necessarily better! Correct sizing is even more critical to effective operation and energy efficiency than right-sizing the uninterruptible power supply (UPS). But with so many factors that determine capacity, it can be a bit tricky.

 

When someone plays with the thermostat at home (not you of course!), the temperature is never right. It gets too hot, then too cold. It’s worse with computer room air conditioners (CRACs). The unit that’s the wrong size can mess up cooling. Wrong settings or improper location will make it even worse.

 

Under-sizing can’t cool effectively — that’s obvious. But over-sizing won’t either. Thankfully, many CRACs will adjust to a range of loads, but there are many that won’t. They all need to be sized realistically, but over-sizing will always result in cooling going on and off too often. It’s called “short cycling,” which is hard on the machine and does a lousy job of maintaining room temperature and humidity. Yes, temperature swings do hurt computing hardware!

Air conditioners have to deal with two kinds of heat. Sensible heat — the kind we can feel — is what our computers give off. Latent heat is what evaporates moisture. Simplistically, dealing with moisture or humidity requires more latent capacity from our air conditioners, which steals from sensible capacity. There’s not much reason to keep a data center above 45% relative humidity (RH), but if you over-cool you’ll pull moisture out of the air (latent cooling) and have to use more energy to re-humidify. The problem is that relative humidity is “relative” to temperature. Warmer air has a lower relative humidity for the same moisture content because it can hold more vapor than cool air. Temperatures in a data center vary widely, so RH depends on where it’s measured, which is why we’re trying to get away from using it. However, RH is still the most common way to determine humidity.

Thankfully, today we can use variable frequency drives (VFDs) to automatically adjust fan speeds for appropriate air flow, controlled by sensors in the room. These can be retro-fit to most existing CRACs, and can save a lot of energy. (A professional computational fluid dynamics, or CFD, analysis is a good idea before buying any expensive air conditioner.)

So Step 1 is to know your real loads. Step 2 is to see if you can get higher temperature return air back to the CRACs. Step 3 is to decide cold air temperature. The American Society of Heating, Refrigeration & Air Conditioning Engineers (ASHRAE) Technical Committee 9.9 has recently increased the temperature envelope, so there’s no need to over-cool the equipment. Step 3 is to set your humidity standard. ASHRAE TC 9.9 now recommends dew point monitoring and control, but existing CRACs may not be able to do that, so you’ll still need to control relative humidity. Then, if possible, pick an air conditioner that can adjust to load and choose a sensible capacity that will operate Day 1 in its midrange. That will give the best stability and control.

Let’s look at three other important issues before we finish: reheat, humidification, and water temperature. If you have more than three or four CRACs, it should not be necessary to put humidifiers on every unit. Moisture diffuses and stabilizes in the room pretty quickly (another reason for dew point sensing). Putting humidifiers on every air conditioner can be counterproductive if one unit humidifies while another de-humidifies. That’s wasted energy for no better result.

Reheat was the norm for years, and it’s the biggest energy waster of all. The CRAC over-cools the air and a heater warms it back up to discharge temperature. In many situations it’s possible to design without reheat, or to use minimal reheat. But it takes a knowledgeable engineer to make that determination and to provide a proper design.

If you’re using chilled-water computer room air handlers, you’ll need to have a knowledgeable engineer involved. Published capacity ratings are based on specific entering water temperature and water temperature rise. Chiller plants today may be designed on higher numbers to improve energy efficiency, but that reduces the effective cooling capacity of the CRAHs.

For the full version of the original article, visit  http://searchdatacenter.techtarget.com/tip/0,289483,sid80_gci1371079,00.html?track=sy185# . Free Registration might be required on the site to view content . To know more about Green Rack Systems and the suite of services we offer in addition to sustainable cooling practices for Data centers, contact us at sales@GreenRackSystems.com .

IBM, Syracuse University (SU), and New York State have built a computer data center on the university’s campus that  incorporates advanced infrastructure and smarter computing technologies to make it one of the most energy-efficient data centers in the world. The data center is expected to use 50% less energy than a typical data center today making it one of the greenest computer centers in operation.

A key element of the design is an on-site electrical co-generation system that uses natural gas-fueled microturbine engines to generate all the electricity for the center and provide cooling for the computer servers. SU will manage and analyze the performance of the center, as well as research and develop new data center energy efficiency analysis and modeling tools. The data center operates completely off-grid.

In addition, a liquid cooling system has been created that will use double-effect absorption chillers to convert the exhaust heat from the microturbines into chilled water to cool the data center’s servers, with sufficient excess cooling to handle the needs of an adjacent building. Server racks  incorporate IBM’s Rear Door Heat eXchanger “cooling doors” that use chilled water to remove heat from each rack far more efficiently than conventional room-chilling methods. Sensors  monitor server temperatures and usage to tailor the amount of cooling delivered by each Rear Door Heat eXchanger–further improving efficiency.

The project includes the creation of a direct current (DC) power distribution system. In a typical data center, alternating current (AC) electricity is delivered by a central power plant through the local utility’s electric grid and then converted to DC to power the servers. This conversion process results in power loss. By directly generating DC power on-site, transmission and conversion losses are eliminated.

What makes the IBM-Syracuse University project different from many other similar ventures is the fact that special attention has been paid to greening the actual infrastructure of the data center itself, not just the computer hardware and software. Other design solutions that we recommend at Green Rack Solutions to update your data center’s basic design are:

• Managed airflow system to avoid hot spots, to assess cooling capacity required for IT equipment and to separate cool intake air from warm server exhaust air.
• Using energy saving cooling methods such as airside economizers and direct evaporative cooling.
• Larger but fewer variable speed motors to power air handlers for energy saving.
• Data center designs that eliminate need for raised floor which creates additional losses and leakages in the air handling system, thereby reducing the efficiency of the overall cooling systems.
• Designing by density zones. High-density applications represent 10 percent to 15 percent of a total data center usage. Medium-density apps account for another 20 percent. The rest is low-density. If you mix and match densities you save money on the build-out.

Did you know that only about half of the energy used in a data centre goes to the IT loads? All the rest is lapped up by your hungry network-critical physical infrastructure (NCPI) equipments. It makes sense therefore to reassess and reprioritize the NCPI devices to maximize energy efficiency. Some of the common NCPI that you will find in Data Centers are transformers, UPS (uninterruptible Power supplies), wiring, fans, pumps, humidifiers, lighting, air conditioners and all other non-IT equipment that are required for the proper functioning of the IT components. You can increase efficiency of your NCPI by improving your basic design of the NCPI, picking the right size devices to match correctly with the IT equipment and using the right equipments. Sounds simple enough. But the reality is that the information provided by most manufacturers is not enough to put together an interconnecting infrastructure that works in total cohesion with the IT components to reduce power consumption.
One handy data center wisdom is that it is not always about the individual devices but how they all work in relation to each other that is the key. Here’s another one for you- the right sizing of the devices and not just the brand could help reduce as much as half of your energy bills. In fact most data centers have many “no load losses” based on the NCPI size be it your lighting, generators etc irrespective of the data center load. So size becomes extremely critical to prevent useless expenses so that you do not end up paying for something that was never in use. Also ill fitted infrastructure design could relentlessly deplete your power supply. Cooling systems for example are a classic victim of ill fitted design.There is a lot of talk about new and improved cooling equipments and methods. But a lot of wastage of power actually is due to poor design that inherently fails to separate the hot air from the cold, than the devices themselves. In such a scenario, alternative design solutions like correct positioning ,direction and containment of devices to segregate the hot segments from the cold can be applied. Then there are problems that sometimes arise because of multiple air conditioners that undermine each other’s performance. It is always beneficial to enlist the help of Power and cooling experts like the ones at Green Rack and leverage their technical expertise to weather the complications that arise from design nitty gritties which may escape the novice eye.