This article is the third in a series of Data Centre Best Practice articles provided by Future-tech Ltd.
In this article we seek to highlight the starting points for any data centre project in relation to Environmental Control and lay down the basics for success in both the Build and Use phases.
Environmental Control directly relates to Cooling and Humidity management in data centres and represents one of the areas where Best practice can have a major impact on both Energy Efficiency and Cost Reduction during operation. When planning or designing a data centre there is an onus on all of the disciplines involved to make sure that the site involved is able to be as energy efficient and therefore also as cost efficient as possible for the particular level of availability / resilience required.
Environmental Control Best Practices
The following section details general practices should be considered relating to environmental control in particular.
As a minimum arrange cabinets in rows to establish Hot and Cold Aisles. Cabinets should be aligned front-to-front along cold aisles, and back-to-back along hot aisles.
Within each row, cabinets should be connected side to side with no gaps. This is the most basic first step to achieving cooling efficiency and for this strategy to work, cold air must be delivered to cold aisles and hot air extracted from hot aisles.
Hot exhaust air and cold supply air should not be allowed to mix as this causes short cycling of the cooling system. Use empty cabinets or partitioning to fill gaps between cabinets to reinforce hot aisle / cold aisle layout or containment if installed.
Build rigid enclosures / containment to fully separate the heat rejected from the rear of IT equipment from the cool air intakes on the front. Hot aisle containment is the most effective for a variety of reasons. Alternatively use flexible strip curtains in legacy sites to improve the separation by blocking any open spaces above the cabinets.
Standardise on cabinets designed for High-Density Environments. Standardising on an appropriate cabinet design makes it much easier to establish and enforce effective power and thermal policies. Avoid shallow cabinets to make sure in-cabinet cabling does not obstruct airflow. Select equipment cabinets that do not have an internal configuration that would obstruct smooth cooling airflow through the installed IT equipment.
Overhead return plenums need to be sized to allow for the large quantities of air flow that is required. Common obstructions such as piping, cabling trays, or electrical conduits need to be accounted for when calculating the plenum space required. Blockages can cause high pressure drops and uneven flow.
In non-contained aisles there should be at least 1 metre clearance between the top of the equipment cabinets and the ceiling. Insufficient ceiling height will obstruct the delivery of efficient air cooling technologies such as raised floor, suspended ceiling or ducts within the data centre. If a raised floor is present and intended to be used as a supply plenum remember that is essential to maintain a constant and even Static Pressure under the raised floor to achieve effective cooling through the vented floor tiles.
The equipment cabinets should be laid out perpendicular to the Air Handling Units to minimise the recirculation of hot air returning over the top of the cabinets.
Air Handling Units within the room should be located in opposing pairs at each end of cabinet rows / contained aisles with a maximum distance between the pair of units being in the order of 20m.
The cold aisle should be a minimum of 2 floor tiles wide (using a gap of 3 tiles may be more effective at high densities).
If deployed, humidification should be centralised and not included in individual CRAC or AHUs.
Reference ASHRAE TC9.9 for details on environmental parameters and how these should be employed and measured. A very condensed version provided by ASHRAE as an errata to the current published documents is available here and free to download Thermal Guidelines for Data Processing Environments
Remember that temperature and humidity measurements should be at the front (supply side) of the equipment cabinets (the Cold Aisle), and that measurements in the Hot Aisle are relatively unimportant providing the heat is being removed effectively. The days of “Ambient Temperatures’ or “Room Temperature’ have long been superseded and are likely to result in problems.
CRAC units or AHUs should have temperature monitoring and control on the supply side. Return temperature monitoring (which was standard 20 years ago when data centre airflow management was poorly understood), is only useful for more sophisticated monitoring of cooling efficiency rather than to maintain environmental conditions or support SLAs.
SLAs or environmental monitoring / control based on a very limited number of sensors placed randomly in a room will almost inevitably be contradictory and very likely to be extremely misleading. Nonetheless this still in place in many smaller legacy sites.
Reference The EU Code of Conduct on Data Centre Energy Efficiency for further information on Energy Efficiency Best Practices (This document is free to download) Data Centres Code of Conduct. Future-tech have been designing, building and managing business critical data centres since 1982. The experience gained in being involved in the data centre sector from the outset has resulted in Future-tech sites achieved 99.999% uptime during 35+ years of operation. Future-tech has a team of experienced, skilled and highly trained in-house Data Centre Engineers capable of properly maintaining and operating business critical data centre sites of all sizes. For more details please contact Richard Stacey on 0845 900 0127 or at rstacey@future-tech.co.uk