As we move towards sustainable building practices, understanding and implementing effective ventilation systems is crucial. This blog post will delve into the specifics of natural ventilation systems with mechanical extract, based on the standards defined in TGD Part F, 2019. We'll also walk through a detailed calculation example for a typical house unit to illustrate how these principles are applied in real-world scenarios.
What is Natural Ventilation with Mechanical Extract?
Natural ventilation utilizes natural forces such as wind and thermal buoyancy to move fresh air through a building. When combined with mechanical extract systems, it ensures adequate indoor air quality and comfort by removing stale air and pollutants. This hybrid approach optimizes energy efficiency while maintaining a healthy indoor environment.
Key Principles of TGD Part F, 2019
Air Permeability: For our calculations, air permeability is assumed to be less than 5m³/(h.m²).
Background Ventilators: Minimum required areas are calculated as per TGD Part F, ensuring sufficient airflow into the building.
Extract Flow Rates: Defined minimum extract rates ensure effective removal of indoor pollutants.
Wet Rooms: For rooms like kitchens and bathrooms, mechanical extract ventilation with an automatic 15-minute overrun is essential if there's no other ventilation provision.
Internal Rooms: Must have a permanently open-air inlet with at least 7,000 mm² clear equivalent area.
Placement of Ventilators: Background ventilators should be located to avoid draughts, typically above 1.75m from the floor.
Additional Notes on Ventilation Requirements
Natural Ventilation - Ventilation Rates (1.2.4.1 Part F): Where the air permeability is greater than 3m³/(h.m²) and lower than 5m³/(h.m²), the minimum total equivalent area of background ventilators providing general ventilation should be 42,000 mm², with an additional 7,000 mm² for each additional 10 m² floor area above the first 70 m² of floor area measured. For single-storey dwellings situated at ground level or on any storey up to four storeys, an additional 7,000 mm² per dwelling should be provided. The areas specified should be increased by 25% where the free area of ventilators is used instead of the equivalent area.
Purge Ventilation - Windows (Habitable Rooms) (1.2.4.6 Part F): For a hinged or pivot window that opens 30° or more, or a sliding sash window, the height multiplied by the width of the opening part should be at least 1/20th of the floor area of the room. For a hinged or pivot window that opens between 15° and 30°, the height multiplied by the width of the opening part should be at least 1/10th of the floor area of the room.
Mechanical Extract Fans (1.2.4.8 Part F): The appropriateness of a particular fan for a particular use should be verified by reference to the manufacturer's data. The aerodynamic performance of the extract fans should be established using the test methods specified in I.S. EN 13141-4:2011. For cooker hoods, the test methods are specified in I.S. EN 13141-5:2004.
Case Study: House Type Unit D
Let's look at a practical example to understand these principles better. Here's a detailed breakdown of the minimum ventilation requirements for a typical house unit.
Ground Floor
Hall
Area: 8.60 m²
Ceiling Height: 2.50 m
Volume: 21.50 m³
Equivalent Area: 3500 mm²
Extract Ventilation: N/A
Free Area: 4375 mm²
Purge Ventilation: Window/Door Openings Kitchen
Area: 10.90 m²
Ceiling Height: 2.50 m
Volume: 27.25 m³
Equivalent Area: 10000 mm²
Extract Ventilation: 30 l/s
Free Area: 12500 mm²
Purge Ventilation: Window/Door Openings
Store/Utility
Area: 3.04 m²
Ceiling Height: 2.50 m
Volume: 7.60 m³
Extract Ventilation: 30 l/s (Make-up from Kitchen)
Purge Ventilation: 1/20th of room floor area
WC
Area: 1.60 m²
Ceiling Height: 2.50 m
Volume: 4.00 m³
Extract Ventilation: 6 l/s (Make-up from Hall)
Living/Dining
Area: 23.80 m²
Ceiling Height: 2.50 m
Volume: 59.50 m³
Equivalent Area: 11000 mm²
Free Area: 13750 mm²
Purge Ventilation: Window Opening Section
First Floor
Landing
Area: 5.90 m²
Ceiling Height: 2.70 m
Volume: 15.93 m³
Hot Press (HP)
Area: 0.50 m²
Ceiling Height: 2.70 m
Volume: 1.35 m³
Bathroom
Area: 4.30 m²
Ceiling Height: 2.70 m
Volume: 11.61 m³
Equivalent Area: 8000 mm²
Extract Ventilation: 15 l/s
Free Area: 10000 mm²
Purge Ventilation: Window Opening Section
Bedroom 1
Area: 12.10 m²
Ceiling Height: 2.70 m
Volume: 32.67 m³
Equivalent Area: 14500 mm²
Free Area: 18125 mm²
Ensuite
Area: 2.40 m²
Ceiling Height: 2.70 m
Volume: 6.48 m³
Extract Ventilation: 15 l/s (Make-up from Bedroom 1)
Bedroom 2
Area: 13.10 m²
Ceiling Height: 2.70 m
Volume: 35.37 m³
Equivalent Area: 10000 mm²
Free Area: 12500 mm²
Bedroom 3
Area: 7.80 m²
Ceiling Height: 2.70 m
Volume: 21.06 m³
Equivalent Area: 10000 mm²
Free Area: 12500 mm²
Total Ventilation Requirements
Whole House Ventilation Rate: 42,000mm2+7,000mm2 per 10m2>70m2+(7,000mm2)
Equivalent Area: 66,500 mm²
Free Area (+25%): 83,125 mm²
Conclusion
Natural ventilation with mechanical extract is an effective strategy for maintaining indoor air quality and comfort. By following the guidelines set out in TGD Part F, 2019, and understanding the specific requirements for different rooms and spaces, you can ensure that your building is both energy-efficient and comfortable.
Discover more about sustainable building practices and design strategies on our HVAC Design Blog.
For further inquiries or assistance, feel free to contact us.
Disclaimer:
The information provided in these posts is for informational purposes only and should not be considered design advice, specifications, or a calculation template. We assume no responsibility or liability for the use of the information presented. For professional advice or design services, please contact us via our contact form.
Comments