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Hot aisle V’s Cold aisle containment for Data Centres

5 Considerations when Choosing a Solution

When comparing hot and cold aisle containment it should be noted that, based purely on the physics involved, both hot and cold aisle containment offer exactly the same level of energy efficiency. The reason aisle containment improves the energy efficiency of data centres is because it increases the temperature of the air returning to the air conditioning units and thus increasing their efficiency. This increase in return temperature can be achieved by either solution equally well however in practice hot aisle containment often reaches a higher level of operational energy efficiency. This is because “most” of the data centre e.g. all of the space barring the contained aisle at the back of the server cabinets is kept at the supply air temperature, often around 25°C. This means the return air leaving the servers (within the hot aisle) will rise to 34°C +. With a cold aisle containment system “most” of the data centre, e.g. all of the space barring the aisle at the front of the servers, would be kept at 34°C +, to gain maximum efficiency. Many data centre operators feel this is too hot for members of staff to work in and then don’t raise the temperature as high as they could. This in turn limits the efficiency gained from the containment system.

Putting this point to one side there are 5 other factors to consider before choosing which solution is right for your data centre.

1. Where are your UPS batteries stored?

it is generally accepted that for every degree above 25°C you store your UPS batteries they will loose one year of their useable life. For example keeping your 10 year life batteries at a temperature of 35°C could basically ruin them. It will take more and more electricity to charge the batteries. They will keep their charge for less and less time until they require replacing, potentially 7 or 8 years before they should. The cost of replacing the batteries is likely to counter all the energy savings made to that point. This potential problem can be designed out by keeping the UPS batteries in a separate area or within a cold aisle however it is important to be aware of this when choosing a solution.

2. Does your data centre have a return air plenum?

If your data centre uses a suspended ceiling with vented tiles to return the hot air back to the air handle units simply adding upstands (closing the gap between the top of the cabinets and the ceiling) will help increase energy efficiency. By installing doors and fully inclosing the hot aisle you will achieve maximum savings. If you have a return air plenum this is generally the best solution as you can achieve return air temperatures of 34°C + without impacting on the rest of the data centre space.

3. Does your data centre have an air supply plenum?

If your data centre delivers cold air to the servers via an under floor plenum but has no return air plenum (as above), containing the cold aisle is often the easiest solution and one that is suggested to many clients. The three main considerations when choosing this solution are;

Where are my UPS batteries stored?

Are my staff happy to work in 35°C?

How much height is available in the data centre? – if you have plenty of height available installing a suspended ceiling will give you the opportunity to contain the hot aisle negating the above considerations.

Providing these questions have been addressed cold aisle containment, when implemented with an under floor delivery plenum, is a simple and cost effective solution.


4. Where are the lights in your data centre?

Adequate lighting of 500 lux is required throughout a data centre. The layout of your light fittings will determine whether you should use a transparent system or not. Transparent panels allow adequate light to come through them. Non-transparent systems may require additional light fittings to be installed to achieve the minimum lighting levels. This will add additional cost to your aisle containment project.

5. Fire suppression?

it is important for the suppressing gas to quickly and evenly fill the data centre space. Some solutions have panels that either open or “pop” out when the gas is discharged and the panels put under pressure. Either system works very well however not all solution have this feature. Again this is important to factor in when choosing a solution as altering your fire suppression system could be costly and impact on the feasibility of your containment project.

Once the above factors have been addressed the most suitable system is often obvious. Most data centre operators are under financial pressure and most of the aisle containment projects Future-tech has worked on return their initial investment within three years. Many have paid for themselves within the first 12 months after installation.

Having had discussions with many data centre managers and operators a general consensus has arisen that for every one degree Celsius the air on or off temperatures are raised the efficiency of the cooling system will increase by approximately 2%. Many non-contained data centres have a return air temperature back to the air handling units of 24°C, by raising this to 30°C a data centre could easily see a 12% increase in the cooling systems efficiency.

If you would like to explore the feasibility of introducing aisle containment to your data centre and you would like some impartial advice contact or complete this form.