Mechanical Ventilation and Air Conditioning, what is the difference

As we experience warmer summers and cold winters, we turn to regulate the temperature of the air by installing an air conditioning unit or a heat pump that can both heat and cool. While this is great for thermal comfort, this is a separate issue to ventilation.

Thermal comfort is the temperature range (typically between 18 and 24 degrees Celsius) that our human bodies feel comfortable within and therefore operate well. This means we need to either heat or cool our interior spaces relative to the exterior conditions to achieve thermal comfort. Ventilation is the replenishment of air, also a fundamental process needed for a healthy interior environment.

Ventilation can remove heated or cooled air, conditioning the air doesn’t replace air. Both principals need to operate together despite seemingly working in opposition to each other. It is possible to have both work in one unit, called in the industry a heat recovery ventilation system

An everyday example of the difference between Mechanical Ventilation and Air Conditioning?

To make this very tangible, let us talk about cars.

When we get into a car, we know that we need to open up some vents to get some fresh air inside. Either those are the vents that are connected to the cars ventilation system (which only goes when our car is running) or we need to open the windows.

Our open windows are natural ventilation, fine on a warm day, but in the middle of winter a little uncomfortable. We close the windows to reduce the heat loss and turn on the air conditioning to warm up the car. But with that air conditioning, we also need fresh air to be supplied into our car space, that is the mechanical ventilation which can operate with or without air conditioning. You do not need to touch the air conditioning for ventilation to happen.

It is the same for your home. We need to supply fresh air to our interior spaces, but that can happen with or without conditioning the air. Simply conditioning the air does not mean that by circulating air and constantly heating or cooling it, we are refreshing it. When installing an air conditioning system, check if its supplies fresh air, ask about the air change rate, and make sure it is ventilating too.

Both are important and yet they seem to work in opposition to each other. Fresh colder air removes the warmed air and only recirculating warm air means we reduce the oxygen level in our internal air.

This is where a heat recovery system is pretty smart. It brings in fresh cooler air and then exchanges the heat, but not air in an exchanger so that the heat can be transferred to the fresh air coming in.

While there is so much more on this topic, particularly moisture control and air tightness, I hope this touches on the need to ask your Architect or Architectural Designer about ventilation systems and how best to accommodate its installation and operation into the design of your home.

Architectural Design with people and planet in mind. Hamilton, Raglan, Te Awamutu, Cambridge, and Waikato Surrounds. ⁠New Zealand.