TGD Part F Ventilation 2019 | Check Out The New Article !

Ventilation Validation Scheme

One of the main changes in TGD F 2019 is the introduction of the Ventilation Validation Scheme.

As part of this scheme all residential buildings with mechanical ventilation systems are to be tested to ensure compliance with the regulations set out in Part F have been achieved.

The role of the Ventilation Validator is as follows.

To ensure that airflow rates have been calculated correctly, in line with TGD F 2019
Test the actual airflow rates in all properties to ensure they match with the designed airflow rates.

What is Compliance?

TGD Part F – Main Points & 2019 Updates

Mechanical Ventilation must be installed in buildings with an airtightness level <3m3/h.m2
Ventilation units must have a minimum capacity 25% above the general ventilation rate
General ventilation rates of 0.3 l/s/m2 or 5 l/s + 4 l/s/person
All mechanical ventilation systems must have a status indicator to show that the system is running/faults have occurred
Systems to be designed & installed by a ‘competent person’
All systems to be verified by a ‘Ventilation Validator’ to show TGD Part F compliance

Competent Persons

Any person designing or installing mechanical ventilation systems should be able to demonstrate that they can be considered a ‘competent person’.

The only certified way to demonstrate competence is by obtaining a City and Guilds Ventilation Certification. This can be obtained from several ETB centres nationwide.

There are other alternative methods to show competence but the above is the most straight forward method.

Any designer or installer should be able to provide proof of competence to ensure compliance is achieved. Airflow measurements should be performed using a calibrated airflow device with an appropriate hood attachment.

Methods of Achieving Compliance – Mechanical Ventilation

After the introduction of the NZEB standards and the upgrades to both Part F and Part L of the building regulations there has been a move to discourage the use of Natural Ventilation. Unless buildings have an airtightness of between 3 m3/h.m2 and 5m3/h.m2 Natural Ventilation cannot be used.

The size & number of openings required in the buildings fabric to achieve compliance has led to Natural Ventilation not being an attractive solution.

There are 2 Mechanical Ventilation Methods detailed in TGD Part T that are recommended to achieve compliance: Continuous Mechanical Extract Ventilation (cMEV) and Mechanical Ventilation & Heat Recovery (MVHR).

Compliance can be achieved using other Mechanical Ventilation Methods, but they must be accompanied by an Agrement Cert to show that it is an appropriate solution.

Continuous Mechanical Extract Ventilation (cMEV)

This is the most cost-effective, basic method of achieving compliance in buildings with airtightness levels <3m3/h.m2 using Mechanical Ventilation Systems.

cMEV Systems must consist of the following to ensure compliance with these regulations.

A Centralised Extract Fan (cMEV Unit)

The unit must be sized appropriately to the building with a minimum of 25% capacity above the General Ventilation Rate.
The unit must be listed on the PCDB Database for use with DEAP to avoid having to use default values which may impact your BER Rating.

Ducting to all Wet Rooms (Kitchen, Utility, Bathroom, Sanitary Rooms)

Ducting to be sized appropriately to designed airflow and distances
Ducting to be Rigid/Semi Rigid – Flexible Duct is not compliant

Exhaust ducting to the outside to remove stale air from the building

Insulated as appropriate

Boost Switch (where applicable based on calculations)

External Openings in habitable rooms of min. 2500mm2 equivalent area for provision of fresh air into the building

Typically, in form of a 100/125mm standard wall vent (hit/miss type)

Control indicators must show occupier the unit is running or if a fault has occurred

Control indicators must be in a visible location and not above the ceiling

Extract rates to be designed as per the formulae in TGD Part F and the unit to be commissioned to these rates, both by a competent person

O&M Manuals must be available to the occupant so that the system can be operated and maintained correctly

Benefit – Fully Part F Complaint, Cost Effective, Fast Installation, Commissioning with Standard Airflow Device

Mechanical Ventilation & Heat Recovery (MVHR)

Easily the most Energy Efficient Method of achieving compliance in buildings with an airtightness of <3m3/h.m2 using Mechanical Ventilation. This system extracts stale air from the wet rooms and uses the energy in this air to warm up the incoming fresh air which is being supplied to habitable rooms, but the extract and supply airs never mix.

MVHR Systems provide a constant supply of fresh, filtered & warmed up air to a property. This can be more applicable in buildings looking to achieve top quality energy ratings as well as locations where air quality and/or external noise may be an issue, e.g., adjacent to a busy road.

A MVHR/HRV System must consist of the following to ensure compliance with regulations

A Centralised MVHR unit with both an extract & supply fan and a heat exchanger

The unit must be sized appropriately to the building with a minimum of 25% capacity above the General ventilation rate
The unit must be listed on the PCDB database for use with DEAP to avoid having to use default values which may impact the BER rating
The unit should be located within the thermal envelope where possible to allow for easy access for the occupant for maintenance
Where there is a risk of overheating, it is recommended that the system allows for a bypass of the heat recovery function

Ducting to all Wet Rooms (Kitchen, Bathroom, etc.) & Habitable Rooms (Bedrooms, Living Room, etc.)

Ducting to be sized appropriately to designed airflow and distances
Ducting can be rigid/semi rigid – flexible duct is not compliant
Ducting to terminate at an adjustable supply/extract valve which enables balancing at commissioning stage

Ducting to outside to exhaust stale air from the building & supply fresh air to the MVHR unit

Insulated as appropriate

Boost Switch (where applicable based on calculations)

Control Indicators must show the occupier that the unit is running or if a fault has occurred

Control indicators must be in a visible location and not above the ceiling

Extract/Supply Rates are to be designed as per the formulae in TGD Part F and the unit to be commissioned to these rates, both by a competent person

O&M Manuals must be available to the occupant so that the system can be operated & maintained correctly

Benefit – Fully Part F Complaint, Improved Indoor Air Quality, Reduced Heat Loss compared to other solutions, Increased Occupant Comfort, Less Noise Ingress from Outside, Fewer openings in the building’s envelope, no additional Agrement Certs necessary, commissioned using Standard Airflow Devices

Other Methods of Compliance – Mechanical Ventilation

It is possible to use alternative methods of mechanical ventilation to achieve compliance with TGD Part F. To achieve compliance these alternative systems will have to prove they can fulfil the regulation as set out below

Adequate and effective means of ventilation shall be provided for people in buildings. This shall be achieved by:

limiting the moisture content of the air within the building so that it does not contribute to condensation and mould growth, and
limiting the concentration of harmful pollutants in the air within the building.

There is an onus on the manufacturers/suppliers of other methods of mechanical ventilation such as DCV or Decentralised MVHR to provide the adequate documentation that demonstrates compliance with the regulation above. This can be achieved by providing and Agrement cert.

Certain elements such as providing a control indicator and O&M manuals will still need to be undertaken using alternative methods.

Specialist commissioning equipment may be necessary for the correct balancing of these systems. It should be noted that ventilation validators may not have the necessary specialist testing equipment. Applicable alternative methods include:

Demand Controlled Ventilation (DCV)

This is essentially an MEV system with additional sensors and air volume control devices that react to certain pollutants such as humidity and CO2.

They often include external wall grilles that open/close based on the humidity level in a room in place of standard hit/miss wall grilles. This is to reduce heat loss at times when humidity levels are at an acceptable level.

Specialist pressure-based tools may be necessary to commission the system. DCV systems do not achieve any additional compliance benefits over MEV systems. Many standard MEV systems will include humidity, presence, and CO2 sensors in addition to the standard, compliant, operation features.

Decentralised Mechanical Ventilation with Heat Recovery (dMVHR)

This is a ductless heat recovery system that includes small, oscillating, heat recovery units in each room. It is necessary to link units together to ensure the supply/extract is always in balance.

While popular in buildings where ducting is not possible it can be costly to supply and install these systems compared to traditional MVHR systems. Due to the number of units, there can be an increased maintenance and replacement cost incurred by building owners.

It must also provide control indicators for each unit to ensure compliance with TGD Part F.

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