The benefits of conditioning air in your indoor space are numerous, but what factors should you consider when choosing your air handling unit? (AHU). One of them is L/s. Don’t worry if you haven’t heard of it before, we answer some questions to help you have a better understanding before you make a decision.

What is the purpose of an air handling unit?

An air handling unit is designed to regulate and circulate air throughout a space. Usually it’s the air handlers that condition the air and move it into the space through a connected ductwork system. The indoor air and the outdoor air mixture are cleaned and improved by components inside the air handling unit. The air is then circulated through the building by ducts and is distributed into the space via outlet grilles that are usually positioned in the ceiling. Improvements include filtration cleaning, controlling humidity, heating and cooling.

What is l/s?

L/s (litres per second ) is the volumetric unit used to calculate the amount of air that an air handler can condition and distribute. Therefore you use the l/s to gauge the capacity of the air handler.

For example, if you have a 1000 l/s (1m3s) air handler and if the space you want to air condition is (5mx5mx5m = 125m3, , the old air in the space would take just over 2 minutes to be replaced by the conditioned air.

How do I choose an air handling unit?

When you choose your air handling unit you will have to calculate the thermal load of the space that you want to be air conditioned. After you have calculated this you will get the desired l/s). Based on that, you can then choose a suitable AHU. Any part of the AHU can be changed depending on what you need it to do within your specifications and your budget. There will be decisions to make and these can vary depending on the l/s you need, but you will be guided by an expert advisor.

How do I calculate l/s for an air handling unit?

First you must calculate the volume of the space to which the AHU is providing ventilation. When you have the volume of the space then you can decide the number of air changes required depending on the application for which the space is being used. There are guidelines on the correct selection of the number of air changes from organisations like CIBSE. Once you have the volume of the space and number of times you wish to change the air you can arrive at a l/s rate to deliver this requirement.

How many l/s do I need to cool a room?

As a broad guide, based on the average air quantity needed for a room or entire building, roughly 5.5 l/s is needed per square meter of floor area (1m2). The result is also based on an assumption that the insulation is average, there are no window areas which are out of the ordinary and the ceiling height is 2.4m2. This number is based upon an average heat load calculation for comfort cooling.

Interested to find out more?

There is a huge range of air handling equipment available to choose from, and we can help you to calculate the l/s and go from there. If you want to know what would be best for your building, just give us a call on 01494 525342 or 07557 747 400 and speak to Tim who can give you all the information you need to make an informed decision.