Common Questions Around Air Conditioning and Ventilation Systems

Building owners and users regularly confuse Air Conditioning and Ventilation systems, discussing them as though they perform the same role.  While they both contribute to an optimum indoor environment, their roles are quite different – sometimes you need both, sometimes just one or the other!  We have listed out some questions that we get asked, and an explanation around these.

What Is The Difference Between Air Conditioning And Ventilation?

This is answered in more detail in a previous blog, but in short:

  • Air Conditioning cools or heats the air, within the area that it serves. It does not introduce any fresh air.
  • Ventilation involves fresh air being introduced to space, with the stale air being extracted

Why Does It Feel Stuffy In Our Office, Even Though The Air Conditioning Is On?

This is likely because there is no fresh air being introduced to the space.  Air Conditioning circulates the air, heating or cooling it depending on what mode it is set to.  If there is no means of ventilation, even in the form of opening windows, the space will certainly start to feel stuffy and airless after a while.

A series of air conditioning condenser units.

There Are Pipes That Run In Between The Indoor And Outdoor Air Conditioning Units, Do These Carry Fresh Air?

No, they don’t.  They carry refrigerant – which is either in gas or liquid form, depending on what part of the refrigeration cycle they are in.  These pipes form part of a closed refrigeration cycle, which is effectively an ongoing energy transfer cycle, absorbing heat from the indoors and rejecting it via the outdoor condenser (in cooling mode).

A busy plant deck with both ventilation and air conditioning systems installed.

Does My Ventilation System Offer Heating Or Cooling As Well As Fresh Air?

This depends, and there are many different types of mechanical ventilation:

  • In the case of a basic supply/extract fan, there is no heating or cooling – air will be brought into the space at the outdoor temperature, and will rely on other climate control systems to adjust its temperature. e. in winter, cold air will be brought into space, relying on the radiator heating system to bring this air up to the desired temperature.
  • Image 2. The next level of the ventilation system would be an MVHR unit (Mechanical Ventilation with Heat Recovery).  While this doesn’t strictly cool or heat (it doesn’t have a coil in it), it does utilise heat recovery, which works as follows:
    • (In the instance of a cold day) As the stale, warm air is extracted out of the room, it passes across a heat exchanger plate – this then pre-heats the incoming cold air from outside. These systems can offer efficiency of up to 80% (i.e. the incoming air will be pre-heated to 80% of the indoor room temperature).
  • Standalone Air Handling units take many forms but often include heating and/or cooling coils. In this instance, they will provide fresh, heated/cooled air to each area.
    • Heating coils can be either via a hot water coil, or a DX coil
    • Sometimes AHUs are fitted with a pre-heat coil – this is used to temper the cold air up to a certain level, with the main heating coil bringing it right up to temperature. A pre-heat coil or heater battery is used to reduce the load on the main heating coil.
    • Cooling coils can also be via chilled water, or a DX refrigerant coil with an externally linked condenser

An air handling unit with heating coils.

Do I Need Both Air Conditioning And Ventilation?

This depends on a few factors including the type of building concerned and the activities performed within a space.   It is certainly beneficial to have both air conditioning and ventilation installed, and in some cases it is essential.

Many smaller commercial buildings do not have mechanical ventilation installed, relying on opening windows to provide the required fresh air, and utilising air conditioning to control the temperature.   However in practice, the windows remain closed most of the time (not least to save putting the air conditioning system under additional strain), and the internal air quality deteriorates.

An environment like a server room will have completely different requirements to an occupied space – this environment needs to be kept within a set temperature, but as there is no one working in the space, there is no requirement for ventilation.

Some environments like sports Gyms are required to meet a certain level of ventilation, so will nearly always need mechanical ventilation systems.  For the comfort of the users they will also almost certainly have air conditioning systems installed as well.

Ventilation is critical in a gym environment.

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Rob Tuffin