BUILDING MAGAZINE 30.09.2011

Building CPD Module 5

INTRODUCTION

The purpose of ventilation is to provide goodindoor air quality throughout a building in bothsummer and winter and to prevent odours fromseeping throughout internal spaces. It is suggestedby the Chartered Institute of Building ServicesEngineers (CIBSE) that in all occupied areas, eightlitres of fresh air per second per person (l/s/p)should be provided to prevent pockets of stagnantair and address air temperature gains produced byhumans, solar radiation and machines. In all otherareas, such as corridors and halls, 3l/s/p should beprovided. In summer, it may be necessary toprovide more than the recommended level toremove unwanted heat gains, and additionalventilation is required where fumes or dustaccumulate, such as in kitchens. Poor ventilationleads to damp conditions, a build-up of dust and dirt and the possibility of an unhealthyenvironment.

HOW TO USE THIS MODULEBuilding’s free continuing professionaldevelopment distance learning programme is opento everyone who wants to develop and improvetheir professional knowledge and skills. Thesemodules can contribute to your annual programmeof CPD activity to help you maintain membershipof professional institutions and bodies.

All you have to do is read this module and thenanswer the multiple choice questions on the finalpage; complete your personal details and fax thepage to 020-7560 4014 or scan it and email tobuilding.cpd@ubm.com. Alternatively, for aquicker, greener way of completing this module, goto www.building.co.uk/cpdReturn your answers by 18 November 2011

PRIVACY POLICYInformation you supply to UBM Information Ltdmay be used for publication (where you providedetails for inclusion in our directories orcatalogues and on our websites) and also toprovide you with information about our products or services in the form of direct marketing activityby email, telephone, fax or post. Information may also be made available to third parties on alist lease or list rental basis for the purpose ofdirect marketing.

If at any time you no longer wish to receiveanything from UBM Information Ltd or to haveyour data made available to third parties, pleasewrite to the Data Protection Coordinator, UBMInformation Ltd, FREEPOST LON 15637,Tonbridge, TN9 1BR, Freephone 0800-2790357 or email ubmidpa@ubm.com. View our fullprivacy policy online at www.building.co.uk/cpd

IN THE FIFTH OF OUR REGULAR SERIES OF CPD MODULES, WE LOOK AT THEBENEFITS OF NATURAL VENTILATION AND WHAT YOU NEED TO KNOW TO SPECIFY IT.THIS MODULE IS SPONSORED BY GDL AIR SYSTEMS

BUILDING CPDNATURAL VENTILATION

Carbon dioxide is often measured to ascertainindoor air quality. It indicates the number ofoccupants and if levels of C02 are high, adequateventilation is not being provided. Exposure to highlevels of CO2 is not dangerous, but may affectperformance – some studies have shown it can leadto a lack of concentration and symptoms of sickbuilding syndrome. A build-up of CO2 may indicate abuild-up of other contaminants. CIBSE recommendsa CO2 concentration of no more than 900 parts permillion (ppm) in occupied spaces to control odoursand create a comfortable environment. Byincorporating CO2 monitoring within a ventilationsystem, ventilation rates in each area can bedesigned to be dependent on occupancy. CO2

sensors in a natural ventilation system preventwastage of energy in buildings where occupancyvaries during the day. In summer, ventilation rateswill be controlled by temperature sensors, but lowerwinter ventilation rates will be controlled by CO2

sensors. This limits the fresh air entering thebuilding in order to maintain internal temperature.

THE IMPORTANCE OF CARBONDIOXIDE MONITORING

For the £5m refurbishment of the University of

Sheffield’s Student Union building, GDL supplied a

natural ventilation solution where roof-mounted

penthouse louvres are used in place of mechanical

ventilation in the assembly area

30.09.2011 BUILDING MAGAZINE

Building CPD Module 5Building CPD Module 5

Solar power is commonly used to assist in theeffective operation of a natural ventilationsystem, powering the penthouse turret fan. Thismethod is an energy efficient and cost-effectiveway to increase the ventilation rate throughoutthe building, rather than incorporating a costly

mechanical arrangement. A solar photovoltaiccell is located on the roof of the turret itself. Thispowers a DC battery that runs a reversible fan,allowing 24-hour supply or extract ventilation.This can work in harmony with the wall unit or asa standalone product using the downflow effect,

whereby fresh air circulates and stale air isextracted via the roof-mounted penthouseturrets. GDL’s Solarstore solution allowsincreased ventilation in summer and at times ofhigh occupancy, and also improves theeffectiveness of night-time cooling.

Most natural ventilation wall-mounted units are generally made up of thefollowing components: weather louvre, insulated damper, acoustic panel,heating coil, fascia grille. In a GDL system, the characteristics of eachcomponent is as follows.nWeather louvre – a quality, high-performance weather louvre is required toprevent rain from entering the buildingn Insulated damper – the insulated damper must be a tight shut-off damper,with a leakage rate of less than 2.5m3/hr/m2 at 50pa. It should have insulationquality equal to the window it replaces (approximately 1.6W/m2K. The damper

should be controlled by a modulating controller, which will give a better energysaving than positional or open/close models.n L-shaped heating coil – an L-shaped coil eliminates the “cold drop” effect,where incoming air in winter falls to the floor creating a blanket of cold air. Thisalso allows better convection, so the coil can be used as a front-line heatingsystem in winter when air is recirculating around the room.

Units are controlled by wireless CO2 sensors and temperature sensors, andhave a manual override. A single control system can control up to five units.Wireless controls are optional, but do offer cost savings over hardwiring.

REGULATIONS

COMPONENTS OF AN EFFICIENT NATURAL VENTILATION SYSTEM

SOLAR-POWERED NATURAL VENTILATION

It is fundamental that all buildings, new orrefurbished, comply with the relevantregulations. Building Regulations Part F(Means of Ventilation) and Part L(Conservation of Fuel and Power) ensure the

adequate provision of ventilation inbuildings, good air quality and the avoidanceof overheating. The Building ResearchEstablishment’s BREEAM scheme is anenvironmental assessment that ensures the

optimum environmental performance ofbuildings, and produces an overall ratingaccording to the efficiency and effectivenessof all aspects of a building’s design,including its services.

CONSIDERATIONS WHEN SPECIFYINGNATURAL VENTILATION SYSTEMS

BUILDING MAGAZINE 30.09.2011

The fundamental difference between natural andmechanical ventilation is that natural ventilationuses encapsulated wind and solar power to fullyventilate a building. Natural ventilation is driven bywind and stack effects based on outdoor windspeed and indoor and outdoor temperature andpressure differences. In order to maintain acomfortable environment, with the correct air

temperature and velocity, a combination of windowvents, extract grilles and ventilation turrets orstacks is required. Both temperature and CO2

sensors are also necessary to control ventilationrates. Ventilation demand will change dependingon the season and occupancy levels. In a school,for example, occupancy in each room variesthroughout the day, so a controlled ventilation rate

using natural ventilation would be both cost-effective and energy efficient. Natural ventilation isa popular method of ventilating offices, restaurantsand educational facilities, and is particularlyeffective in open spaces that have a highoccupancy, such as warehouses, distributioncentres, gymnasiums, sports halls, assembly areasand supermarkets.

INTRODUCTION TO NATURAL VENTILATION

BENEFITS OF NATURAL VENTILATION

n Cost-effectiveNatural cooling eliminates the need formechanical air conditioning, which leads tolow energy consumption, low operating costsand low maintenance costs. Night purgingreduces day-time cooling needs by refreshingthe room with cooler night-time air, loweringthe temperature of the building structure, toprovide a comfortable environment for

occupants the following morning.n SustainabilityHarnessing natural wind power andtemperature buoyancy (as air is warmed inan occupied space it rises upwards) toventilate a building means that no fossilfuels are needed to run mechanical fans,which contributes significantly to energyconservation.

n Health benefitsA constant supply of cool fresh aireliminates “sick building syndrome”, wherein a mechanically ventilated buildingrecirculated air can cause occupants tobecome ill. A continuous supply of fresh airreplacing stale air increases concentrationlevels. By replacing open windows, securityrisks are also reduced.

When designing a suitablenatural ventilation system, itis crucial to understand bothwind and buoyancy. Warm airis less dense than cold air.When the two meet, thedense, cold air will fall,displacing warmer airupwards. As warmer air risesand cold air falls within aroom, this promotes a flow ofair to produce the requiredventilation rate. The heightand layout of a building willaffect its ventilationrequirements. There arenumerous options to allowfor the most effective airflowthroughout the building.Natural ventilation systems

are not suitable in areas witha high level of pollutants,fumes and odours – egkitchens, laboratories,toilets and areas with highfunctional heat gains.Operating theatres alsoneed to be mechanicallyventilated so that outside aircannot bring potentialpollutants. Mixed modesystems can be used tominimise the cost of amechanical arrangement byusing natural ventilationwhere possible, and solar-powered systems can reduceenergy demand wherepower-assisted fans arerequired.

TYPES OF AIRFLOW

Natural ventilation systems can use different types of airflow.

n CrossflowAir enters at low level and leavesthrough the opposite wall at a highlevel, usually driven by wind power.This can be as simple as opening twowindows on opposite sides of theroom, or by installing two wall-mounted units to allow controlledcrossflow ventilation. It is suitable forany room, though as the air movesacross the room there is an increasein temperature and concentration ofpollutants, and so there is a limit tothe width of room that can be cross-ventilated. CIBSE’s guidance statesthat the maximum distance overwhich crossflow is effective is fivetimes the floor-to-ceiling height. Thecross-ventilation method is normallycombined with a penthouse turretapplication to dispose of the stale aironce it has left the room, using thestack effect.

n DownflowIn this scenario, air enters via a roof-mounted penthouse turret at a highlevel, and the stale air leaves thebuilding via the same penthouseturret. This method is particularlyeffective in large, open spaces withhigh ceilings, such as warehouses,distribution centres, gymnasiums,sports halls, assembly areas andsupermarkets. Within GDL naturalventilation split turrets, there is aninternal split within the turret unit andduct extension sleeve, so the supplyand extract air are kept separate,avoiding cross-contamination andshort-circuiting.

n Stack effectIn this scenario, air is drawn in byeither a window or wall unit andacross the space, as described in thecrossflow ventilation method. Staleair is then exhausted via a roof-mounted penthouse turret at a high level. The air flows across thewidth of the building. The systemuses the buoyancy effect, wherewarmer, lighter air is displacedupwards when it meets cold, denseair. The design of the system willdepend on the layout of the building.

n Single-sided This can be as simple as opening awindow on one side of the room,which means the air enters andleaves via the same window. Thisworks more effectively if internaldoors are closed. As a general guide,airflow within a room will only workeffectively where the width of thespace is no more than approximatelytwice the floor-to-ceiling height. Windturbulence is the main driving factor.

GDL’s Intellivent Wall Mounted units were used in place of mechanical ventilation to

supply fresh air throughout the new building for Holte, Mayfield & Lozells School, built to

achieve CO2 emissions of just 27kg/m2 under Birmingham’s Building Schools for the

Future programme.

30.09.2011 BUILDING MAGAZINE

Building CPD Module 5Building CPD Module 5

Solar power is commonly used to assist in theeffective operation of a natural ventilationsystem, powering the penthouse turret fan. Thismethod is an energy efficient and cost-effectiveway to increase the ventilation rate throughoutthe building, rather than incorporating a costly

mechanical arrangement. A solar photovoltaiccell is located on the roof of the turret itself. Thispowers a DC battery that runs a reversible fan,allowing 24-hour supply or extract ventilation.This can work in harmony with the wall unit or asa standalone product using the downflow effect,

whereby fresh air circulates and stale air isextracted via the roof-mounted penthouseturrets. GDL’s Solarstore solution allowsincreased ventilation in summer and at times ofhigh occupancy, and also improves theeffectiveness of night-time cooling.

Most natural ventilation wall-mounted units are generally made up of thefollowing components: weather louvre, insulated damper, acoustic panel,heating coil, fascia grille. In a GDL system, the characteristics of eachcomponent is as follows.nWeather louvre – a quality, high-performance weather louvre is required toprevent rain from entering the buildingn Insulated damper – the insulated damper must be a tight shut-off damper,with a leakage rate of less than 2.5m3/hr/m2 at 50pa. It should have insulationquality equal to the window it replaces (approximately 1.6W/m2K. The damper

should be controlled by a modulating controller, which will give a better energysaving than positional or open/close models.n L-shaped heating coil – an L-shaped coil eliminates the “cold drop” effect,where incoming air in winter falls to the floor creating a blanket of cold air. Thisalso allows better convection, so the coil can be used as a front-line heatingsystem in winter when air is recirculating around the room.

Units are controlled by wireless CO2 sensors and temperature sensors, andhave a manual override. A single control system can control up to five units.Wireless controls are optional, but do offer cost savings over hardwiring.

REGULATIONS

COMPONENTS OF AN EFFICIENT NATURAL VENTILATION SYSTEM

SOLAR-POWERED NATURAL VENTILATION

It is fundamental that all buildings, new orrefurbished, comply with the relevantregulations. Building Regulations Part F(Means of Ventilation) and Part L(Conservation of Fuel and Power) ensure the

adequate provision of ventilation inbuildings, good air quality and the avoidanceof overheating. The Building ResearchEstablishment’s BREEAM scheme is anenvironmental assessment that ensures the

optimum environmental performance ofbuildings, and produces an overall ratingaccording to the efficiency and effectivenessof all aspects of a building’s design,including its services.

CONSIDERATIONS WHEN SPECIFYINGNATURAL VENTILATION SYSTEMS

BUILDING MAGAZINE 30.09.2011

The fundamental difference between natural andmechanical ventilation is that natural ventilationuses encapsulated wind and solar power to fullyventilate a building. Natural ventilation is driven bywind and stack effects based on outdoor windspeed and indoor and outdoor temperature andpressure differences. In order to maintain acomfortable environment, with the correct air

temperature and velocity, a combination of windowvents, extract grilles and ventilation turrets orstacks is required. Both temperature and CO2

sensors are also necessary to control ventilationrates. Ventilation demand will change dependingon the season and occupancy levels. In a school,for example, occupancy in each room variesthroughout the day, so a controlled ventilation rate

using natural ventilation would be both cost-effective and energy efficient. Natural ventilation isa popular method of ventilating offices, restaurantsand educational facilities, and is particularlyeffective in open spaces that have a highoccupancy, such as warehouses, distributioncentres, gymnasiums, sports halls, assembly areasand supermarkets.

INTRODUCTION TO NATURAL VENTILATION

BENEFITS OF NATURAL VENTILATION

n Cost-effectiveNatural cooling eliminates the need formechanical air conditioning, which leads tolow energy consumption, low operating costsand low maintenance costs. Night purgingreduces day-time cooling needs by refreshingthe room with cooler night-time air, loweringthe temperature of the building structure, toprovide a comfortable environment for

occupants the following morning.n SustainabilityHarnessing natural wind power andtemperature buoyancy (as air is warmed inan occupied space it rises upwards) toventilate a building means that no fossilfuels are needed to run mechanical fans,which contributes significantly to energyconservation.

n Health benefitsA constant supply of cool fresh aireliminates “sick building syndrome”, wherein a mechanically ventilated buildingrecirculated air can cause occupants tobecome ill. A continuous supply of fresh airreplacing stale air increases concentrationlevels. By replacing open windows, securityrisks are also reduced.

When designing a suitablenatural ventilation system, itis crucial to understand bothwind and buoyancy. Warm airis less dense than cold air.When the two meet, thedense, cold air will fall,displacing warmer airupwards. As warmer air risesand cold air falls within aroom, this promotes a flow ofair to produce the requiredventilation rate. The heightand layout of a building willaffect its ventilationrequirements. There arenumerous options to allowfor the most effective airflowthroughout the building.Natural ventilation systems

are not suitable in areas witha high level of pollutants,fumes and odours – egkitchens, laboratories,toilets and areas with highfunctional heat gains.Operating theatres alsoneed to be mechanicallyventilated so that outside aircannot bring potentialpollutants. Mixed modesystems can be used tominimise the cost of amechanical arrangement byusing natural ventilationwhere possible, and solar-powered systems can reduceenergy demand wherepower-assisted fans arerequired.

TYPES OF AIRFLOW

Natural ventilation systems can use different types of airflow.

n CrossflowAir enters at low level and leavesthrough the opposite wall at a highlevel, usually driven by wind power.This can be as simple as opening twowindows on opposite sides of theroom, or by installing two wall-mounted units to allow controlledcrossflow ventilation. It is suitable forany room, though as the air movesacross the room there is an increasein temperature and concentration ofpollutants, and so there is a limit tothe width of room that can be cross-ventilated. CIBSE’s guidance statesthat the maximum distance overwhich crossflow is effective is fivetimes the floor-to-ceiling height. Thecross-ventilation method is normallycombined with a penthouse turretapplication to dispose of the stale aironce it has left the room, using thestack effect.

n DownflowIn this scenario, air enters via a roof-mounted penthouse turret at a highlevel, and the stale air leaves thebuilding via the same penthouseturret. This method is particularlyeffective in large, open spaces withhigh ceilings, such as warehouses,distribution centres, gymnasiums,sports halls, assembly areas andsupermarkets. Within GDL naturalventilation split turrets, there is aninternal split within the turret unit andduct extension sleeve, so the supplyand extract air are kept separate,avoiding cross-contamination andshort-circuiting.

n Stack effectIn this scenario, air is drawn in byeither a window or wall unit andacross the space, as described in thecrossflow ventilation method. Staleair is then exhausted via a roof-mounted penthouse turret at a high level. The air flows across thewidth of the building. The systemuses the buoyancy effect, wherewarmer, lighter air is displacedupwards when it meets cold, denseair. The design of the system willdepend on the layout of the building.

n Single-sided This can be as simple as opening awindow on one side of the room,which means the air enters andleaves via the same window. Thisworks more effectively if internaldoors are closed. As a general guide,airflow within a room will only workeffectively where the width of thespace is no more than approximatelytwice the floor-to-ceiling height. Windturbulence is the main driving factor.

GDL’s Intellivent Wall Mounted units were used in place of mechanical ventilation to

supply fresh air throughout the new building for Holte, Mayfield & Lozells School, built to

achieve CO2 emissions of just 27kg/m2 under Birmingham’s Building Schools for the

Future programme.

30.09.2011 BUILDING MAGAZINE

Building CPD Module 5

Having read the CPD module, you should now beready to answer the questions below. Please tickonly one box per question.

1. According to CIBSE, what is the recommendedlevel of ventilation in occupied areas?

a. 8l/s/p

b. 6l/s/p

c. 4l/s/p

d. 3l/s/p

2. In which of the following environments wouldnatural ventilation NOT be suitable?

a. Supermarkets

b. Classrooms

c. Operating theatres

d. Sports halls

3. Which of the following correctly describes whathappens when warm air meets cold air in anenclosed space?

a. Cold air is less dense than warm air, so the

lighter cool air rises and the warm air falls.

b. Cold air is less dense than warm air, so the

lighter warm air rises and the cool air falls.

c. Warm air is less dense than cold air, so the

lighter warm air rises and the cold air falls.

d. The cold air remains at a high level.

4. In which of the following types of airflow doesair enter and leave a space through a roof-mounted penthouse turret?

a. Crossflow

b. Downflow

c. Stack effect

d. Single-sided

5. What is the maximum ratio of room width tofloor-to-ceiling height for effective single-sidedventilation?

a. 5:1

b. 4:1

c. 3:1

d. 2:1

QUESTIONS

BUILDING MODULE 5 DEADLINE: Return your answers by 18 November 2011To take this module, you can return the answers one of following ways:n Complete the form online at www.building.co.uk/cpdn Fax the form to 020-7560 4014n Scan the form and email to building.cpd@ubm.comIf successfully completed, certificates will be distributed two weeks after the module closes.

PRIVACY POLICYInformation you supply to UBM Information Ltd may be used for publication (where you provide details for inclusion in our directories orcatalogues and on our websites) and also to provide you with information about our products or services in the form of direct marketing activityby email, telephone, fax or post. Information may also be made available to third parties on a list lease or list rental basis for the purpose ofdirect marketing. If at any time you no longer wish to receive anything from UBM Information Ltd or to have your data made available to thirdparties, please write to the Data Protection Coordinator, UBM Information Ltd, FREEPOST LON 15637, Tonbridge, TN9 1BR, Freephone0800-279 0357 or email ubmidpa@ubm.com. View our full privacy policy online at www.building.co.uk/cpd

FORM“UBM Information Ltd” may from time totime send updates about Building CPDand other relevant UBM Informationproducts and services. By providing youremail address you consent to beingcontacted by email for direct marketingpurposes by “UBM Information Ltd” orother third parties as outlined in ourPrivacy Policy.

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