FAQ's - Passivent Commercial

Q. How does Natural Ventilation work?
A. The principle natural ventilation strategies are outlined in the natural ventilation for non-domestic buildings brochure. Passive stack ventilation is the most effective strategy – it is driven by naturally occurring forces in two ways – warm air rising results in air being drawn upwards through the building by the chimney stack effect. The venturi effect results from wind passing over high level terminals causing additional ventilation through suction.

Q. What are the design requirements?
A. Within the design of a natural ventilation system, we have to reduce peak internal temperatures, draughts and CO2 to acceptable levels. Our products are designed to achieve these requirements whilst maintaining weather integrity and the insulation of the building envelope. The new Part L encourages the use of solar shading and night cooling to assist any natural ventilation scheme.

For all types of buildings we design to Building Regulations and CIBSE Guidelines. An example is school ventilation where DfES guidelines state 3 l/s and 8 l/s per person for background and summertime ventilation, respectively.

Q. When is the best time to design a natural ventilation system into a new building?
A. Preferably when the project is in the early stages of the design with the architect and the building services engineers. Building plan, orientation and other factors will enable the most effective use to be made of natural ventilation and we can advise them on sizing of equipment.

Q. Do Passivent provide an Installation Service?
A. Passivent have trained and accredited Mastercare Installers. Their installations are regularly reviewed to make sure the installations are completed to Passivent’s fixing instructions and are operating correctly.

We can provide fixing instructions, technical details and wiring diagrams for supply only projects. Passivent can issue final drawings of our products on your building for approval by the client once ordered.

Q. What research have we undertaken?
A. Since 1983 Passivent has been at the forefront in developing energy-efficient natural ventilation solutions for many kinds of buildings including student accommodation, nursing homes, flats, offices and schools.

We were one of the nine NatventTM Project partners in seven countries involved with research into the use of natural ventilation in commercial buildings and the development of products and software to calculate natural ventilation flow rates. (http://projects.bre.co.uk/natvent/index.html)

The Airscoop displacement ventilation terminal has been independently tested at the Silsoe Research Institute in Bedfordshire. This involved three phases of field monitoring to ensure optimum internal design layout and flow performance. This has enabled us to develop calculation software to determine the size and quantity of Airscoops required for specific projects.

Other specific projects include;
Sheffield Hallam University EPSRC funded project to determine the airflow performance of ventilators for natural ventilation.
University of Nottingham ETSU funded project involving a number of partners including the BRE to develop a novel ventilation cooling system for reducing air conditioning in buildings.
DTI part funded PII project with BSRIA as the main project leader – Development of Design and Application Guide for roof mounted natural ventilation devices. Two year project with BBSRC and Silsoe Research Institute to investigate the performance of natural ventilation devices in low wind speed conditions. Installation and monitoring of a mixed mode ventilation system with Passive stack and Airscoop devices, with the research undertaken with Brunel University.

Q. What tests are performed on our products?
A. All of our products are tested to the relevant standards appropriate to their purpose. These include water resistance, fire retardant, leakage rate and acoustics. Further information is available on request.

Q. Do we have any case studies?
A. Passivent is actively involved in case studies. We believe this helps us to gain more information to help with future projects and customer feedback. Please visit the downloads section on our website.

Q. What is your standard delivery time?
A. Standard delivery is 8 weeks from receipt of full and final information. This is because each product is made to order due to specific manufacturing requirements.

Q. Why naturally ventilate a school?
A. Ventilation in schools is governed by building regulations Part F and refers to DfES Building Bulletins 87, 93 and 101. This states ‘Wherever possible school buildings should be naturally ventilated’. The rates of ventilation stated in these guidelines leads to a fresher healthier environment and increased learning.

Q. Why naturally ventilate an office?
A. Natural ventilation reduces the amount of harmful CO2 emissions. Naturally ventilated buildings typically consume less than half the energy used in air conditioned buildings. 90% of building occupants prefer naturally ventilated buildings.

Q. Why use Mixed Mode Ventilation in an office?
A. Mixed mode ventilation is used in an office environment when a natural ventilation system can be used for most of the year, but during the peak summer months the internal gains can not quite be removed by a natural ventilation system alone. Here the assistance of comfort cooling is required to maintain a comfortable environment. Ventilation is still important when the comfort cooling is running to ensure good indoor air quality in maintained hence a Mixed Mode system.

Q. What are the benefits of Mixed Mode Ventilation?
A. The natural ventilation aspect of this type of ventilation provides good indoor air quality and removes heat gains for most of the year, as well as offering free night time cooling. This in turn reduces the amount of time that the comfort cooling in operation, therefore reducing running costs of the system and also the amount to CO2 given off by the building. These are benefits that can help with BREEAM assessments and SBEM calculations.

Q. Do your products require an electrical connection?
A. All Aircool units, Airscoops, Insulated Louvres and Litevents require an electrical connection, wiring diagrams are available on request. 24V or 240V actuators are included in our prices.

Q. Do you supply control panels for your products?
A. We have a range of standard controls packages for our equipment which include single zone and multi zones environmental controllers. The single zone controllers are available in 24V or 240V supply and most ranges have a manual override facility, where as the multi zone controller operates on 24V. Should it be required BMS controllers can be supplied for specialist projects.

Q. Can you offer flexibility with your products?
A. With our in house design team, we have the facility to provide flexibility outside our standard range with product solutions to suit your building.

Q. How do the terminals fix to the roof?
A. All High Capacity Terminals and Airscoops are supplied with an integral sub-base and the terminal is fixed to the sub base. The sub base is made to suit the roof pitch, rafter clearance and specific fixing method.

Q. How long can a Sunscoop Tubular Rooflight be?
A. Leading independent research by Nottingham and Napier Universities in collaboration with tubular rooflight manufacturers indicates that the maximum practical length for rooflights using specular reflective tubes is around 10 times the tube diameter. This will provide sufficient daylight for task lighting assuming bright external conditions. Whilst daylight would be visible at greater lengths, it would not be considered usable for task lighting; it may nonetheless be desirable to complement artificial lighting.

Q. How do Airscoops work when there is a low external wind speed?
A. Airscoops are wind driven ventilators that operate at all wind speeds, but at low wind speeds it is feasible that they do not achieve the desired performance. This manly happens on a calm warm summers day, but should there be concerns over local wind speeds, we can design around this. Introducing low level motorised Aircool louvres to the building can assist and revert the displacement ventilation system (Airscoops) to passive stack system where buoyancy is a key factor in the ventilation system.

Q. How do I carry out an Air Tightness Test on my building with Passivent products installed?
A. In line with the Air tightness testing of the building envelope, we have discovered further clarification guidance in the British Standard BS EN 13829:2001 that the ATTMA Air tightness Testing Document is based on.

The ATTMA document states (Section 3.4) that it “is generally compliant with BS EN 13829:2001 Method B – Test of the Building Envelope”.

Referring to this British Standard, which is to be satisfied, it states (Section 5.2.3) the following
“Air terminal devices of mechanical ventilation or air conditioning systems shall be sealed. Other ventilation openings (for example openings for natural ventilation) shall be closed for purposes of method A and sealed for method B.”

Therefore, with reference to the appropriate British Standard referenced in the ATTMA document we can confirm that natural ventilation devices for the purposes of air tightness testing of a building are to be sealed.

Links to:
BSRIA - www.bsria.co.uk
Chartered Institute of Building Services Engineers (CIBSE) - www.cibse.org
Building Research Establishment (BRE) - www.bre.co.uk
Ventilation, energy & environmental technology - www.veetech.co.uk
Building Product Design (BPD) - www.buildingproductdesign.com

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