Architects and M & E consultants are increasingly considering mixed mode hybrid ventilation systems to help deliver sustainability and lower user costs. This blog looks at the types of products for each system and how they can work together.
What is mixed mode ventilation?
Mixed mode ventilation combines mechanical and natural ventilation. Natural ventilation is used during mild weather and can be supplemented by mechanical systems in winter or where poor air quality is a particular problem.
What products are used in a hybrid ventilation system? Natural Ventilation
Natural Ventilation facilitate passive airflow based on wind pressure and thermal buoyancy. Here are some examples of natural ventilation products:
Passive Stack
Stack Effect (Buoyancy-driven)
- Warm air inside a building is lighter than cooler outdoor air.
- As it rises, it creates a low-pressure zone at the base of the building.
- Cooler, denser outside air enters through lower level openings like vents or windows.
- The warm, stale air escapes upwards through vertical ducts or chimneys – the passive stacks.
Wind Assistance
This helps pull air up and out of the building more efficiently. Win blowing across the top of a building can create a suction effect at the stack outlet.
We’ve written a blog about the ways in which roof stacks can be used in schools and other buildings with atrium spaces that are particularly good for passive stack systems.
Benefits
- Zero fan energy and low running cost
- Quiet operation
- Simple and durable
- Works well in schools, residential and stairwells
Limitations
- May not provide enough airflow during still weather conditions
- Requires careful design of openings to balance intake and exhaust, consult the experts!
- Less controllable than mechanical systems but can be used effectively in hybrid setups with fan assist.
Wall vents
Allow controlled airflow through facades. They provide natural ventilation to classrooms, laboratories, music rooms, gymnasiums, hospitals and commercial buildings. They can be installed into glazing, brick or blockwork. Tek also manufacture an insulated one piece frames which provides weather seals and prevents cold bridging.
Benefits
- Improved air quality – vents allow fresh air in and stale air out
- Energy efficiency – passive or trickle vents don’t use electricity
- Moisture control – Proper ventilation helps prevent condensation, mould and damp
- Thermal comfort – internal temperatures are regulated by enabing air movement
- Low maintenance – no moving parts and occasional cleaning
- Quiet operation – unike fans, vents are silent
- Cost effective – cheaper than mechanical systems and quick and easy to install
Limitations
- Limited control unless automated or manually adjustable
- Weather dependent – relies on outdoor conditions and may underperform when air is still. A well designed building and clever placement of vents can help to overcome this.
- Heat loss of gain – open vents can lead to heat loss or gain but this is easily mitigated for by adding the ability to open and close.
- Noise – Tek offer acoustic vents which are designed to reduce noise when open
Dampers
Ventilation dampers are devices installed within ductwork, vents, or openings that regulate, block or direct airflow in ventilation systems. They are like valves for air: they open, close, or adjust to control how much air moves through a system.
Where Are Dampers Used?
- In hybrid and mechanical ventilaiton systems to move between natural and forced ventilation
- Inside passive stacks to regulate flow or close them in cold weather
- In rooftop units, ductwork, facades and window systems
- In zoned buildings to enable smart control of air delivery
Benefits
- Improve energy efficiency by avoiding over-ventilation
- Enhance occupant comfort
- Allow automated demand control
- Provide fire safety and pressure balancing
Limitations
- Require maintenance, especially motorised types
- Incorrect sizing or poor placement can reduce system performance
- Must be compatible with control systems for automation
What products are used in a hybrid ventilation system? Mechanical Ventilation
A mechanical ventilation system uses powered equipment (usually fans) to move air in and out of a building, regardless of wind or temperature differences. These systems are precise, controllable, and can be integrated with filtration and heating/cooling. Here’s a breakdown of the key products used:
- Fans – push fresh air into the building often with filters and heat exchangers
- Extract fans – pull stale air out of the building
- Ducting – air pathways that distribute and extract the air as part of the mechanical system
Benefits
- Improved indoor air quality
- Consistent airflow – regardless of weather or building orientation
- Heat recovery systems recover heat from outgoing air
- Humidity control
- Good for airtight buildings
- Demand controlled systems based on levels of CO2 or occupancy
- Flexibility
Limitations
- Energy consumption – fans and controls use electricity, costs can be high especially at the moment
- Maintenance – filters, fans and ducts require inspection, cleaning and replacing
- Installation cost – more expensive upfront that natural ventilation especially in retrofits
- Noise – can be an issue in poorly designed or maintained systems
- Space requirements – ducting and equipment
- Over use – without controls, there is the potential to waste energy
Why is hybrid ventilation a good idea?
Hybrid ventilation provides the best of both systems balancing energy efficiency, comfort and control. Natural ventilation is used when conditions are favourable (mild weather, good outdoor air quality), saving energy. Mechanical ventilation kicks in when natural forces aren’t enough, for example, cold, hot or still days. Natural ventilation works very well in Spring and Autumn and mechanical ventilation can be used to give a boost in extremely hot or cold weather, offering the best of both worlds.
Cost savings are made because fans are only used when they are really needed, making it ideal for public sector buildings on tight budgets like schools, hospitals and local government offices. It is also a more sustainable system than pure mechanical ventilation.
If you would like to discuss a hybrid ventilation project with us, get in touch.
