Economizers- An Introduction

Energy costs are becoming more and more expensive by the day. The need for an intelligent, economic design and planning is not only necessary from an environmental point of view; it is also beneficial from the business point of view. It not only helps in reducing the energy costs of the data center, it also extends the life of data center equipments and gives you enough time to plan ahead and adjust the budgets to invest in new equipments when it’s time for an upgrade.

Since ASHRAE has made it mandatory for data centers to use economizers in their cooling systems, there is an increased need to know more about the functioning and the types of economizers and which is more feasible to implement to suit your requirements. Through this article, we would like to address some of the basic questions about economizers.

Economizers provide what is referred to as “free cooling”. That means that they utilise the air from the surrounding when the conditions are favourable. This reduces or sometimes, even eliminates the need for air compression within the air conditioning units. This by itself can cut down cooling costs of a data center by a substantial amount. It is to be noted that the economizers can be used only when the weather is suitable. In areas with high levels of humidity and high temperature, it serves no purpose at all. Not just that, it is also seasonal. Economizers come in handy only during winters, spring and fall.

There are two types of economizers: fluid economizers and air economizers.

Fluid Economizers

Fluid economizers work side by side with an evaporative cooling tower and absorb heat from the room. It is generally used in a chilled water based cooling system. The chilled water is passed through a separate coil and is made to absorb the room heat so that the compressor’s load is reduced. This water then rejects the heat to outside cold air through heat exchange.

Air Economizers

This uses sensors to sense the temperature of the outside air. If it matches the required criteria, then a certain predetermined volume of air is blasted into the CRAC systems that reduces or eliminates the use of condensers. Since the temperature of the outside air is already low, the load to the condenser is drastically reduced. Suitable dampers have to be provided to maintain the pressure within the room. The outside air also needs an outlet; else the pressure is bound to rise.

The disadvantage with air economizers is that directly introducing outside air into the data center can be quite fatal. It might contain dust and humidity level also matters; air must be conditioned before it is passed into data centers. Of course, one can always use humidifiers or dehumidifiers as per the requirement but it reduces the saving achieved by the economizers. With fluid economizers, there is no need for conditioning air since there is no direct contact between data center equipments and the air from outside.

Depending on the location of the data center, one can save almost up to fifty percent of the cooling energy costs with fluid economizers. With an air economizer, one can achieve almost up to sixty percent cost cutting but with the implementation of a humidifier/ dehumidifier, the actual saving is slightly lower.

If one is planning to implement a fluid economizer in their data center, it is important to note that optimal efficiency can be achieved when the temperature is below 48° F and that for air economizer is between 41.9° to 59° F. In case the temperature is below 41.9° F, one will have to make use of humidifiers and if it is above 59° F, dehumidifiers are mandatory.

While installing air economizers, some alterations have to be made to the CRAC systems. The system will need two dampers: one for return air from the room and another for conditioned outside air to enter into the data center. Filters will have to be installed and has to be regularly maintained or replaced. A fan is installed in the system that will direct the airflow to and from the room. The fan also draws some energy as it is subject to pressure for filtering and routing airflow. This also adds to reduction in the cost saving. A stringent control system must be incorporated to check for air contamination, temperature etc. If the conditions are not favourable, the access should be either rectified or totally cut off.

Fluid economizers can be used in any climate where there is scope for heat transfer from the water to outside air, especially if the surrounding is slightly polluted. But the initial costs are slightly higher. If the company is able to afford to be slightly extravagant with the economizer plans, it’s best to adopt this system as the chances of risks is minimised.

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