CPD Presentation: Key considerations when specifying weather louvres
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The purpose of our presentation is to highlight areas of consideration for both Architects and Service Engineers to ensure that specifications adequately reflect design requirements and performance expectations.
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CPD Presentation: Key considerations when specifying weather louvres
- 1. Colt Louvre CPD Colt Technical Seminar
- 2. A brief history of Colt British Private Company founded in 1931 I J O’Hea OBE (1897 - 1984) 2011 Group Turnover £160 million Manufactures in the UK, Holland, Saudi Arabia, China and Singapore I J O’Hea Colt founder
- 3. Current UK Business markets Smoke Control Louvre Natural Ventilation Environmental Comfort Control Solar Shading
- 5. Louvre • • • Allow air in or out Exclude wind driven rain Provide cosmetic screening
- 6. Louvre CPD Seminar Outline A. What is a louvre? B. Function & form C. Testing & classification D. Specification
- 7. A: What is a Louvre? • Definition: “One of a set of boards or slats set parallel & slanted to admit air, but not rain” • All louvres are not the same • What do you want to achieve, and under what conditions? • What is important to the success of your design ?
- 8. London Wall
- 11. NATS, Prestwick
- 14. B: Function & Form • Purpose / application • Airflow / sizing • Rain defence • Louvre appearance • Other considerations
- 15. Purpose / Application of the louvre? Performance – Air flow performance – Rain defence – Relationship between air flow and rain defence – Wind load resistance Aesthetics – Dimensions – Decorative finishes – Continuous appearance Durability – Fixing method – Manufacturer guarantee
- 16. Aerodynamics & Rain Defence Ideal design solution: 100% rain defence and 100% air flow. • 100% airflow is never possible • Maximum Air Flow • Even a fully opened • But rain gets in! door is only 60% efficient (Cv=0.6) • 100% rain defence. • But no airflow.
- 17. Aerodynamic performance Air Flow • Volume flow rate (m3/s) – Depends on the ventilation and plant design requirements – Normally decided by the Mechanical Services Design Consultant Resistance to Air Flow • Maximum acceptable pressure drop – Resistance to airflow the fan needs to overcome – There is no direct correlation between percentage free area and pressure drop!
- 18. Louvre sizing • Design Criteria: – Air flow rate through the louvre (m3/s) – Limiting air velocity (m/s) or Pressure loss (Pa) • Air flow performance: – Characterised by the Coefficient (Cv) which is determined by testing – Percentage free area is not a good guide to performance
- 19. Louvre sizing - Example Size a louvre with a Cv of 0.308 to give a maximum pressure drop of 25Pa (Ps) at a flow rate of 2.5m3/s V = Cv Ps 25 = 0.308 × = 1.99m / s 0.5 ρ 0 .5 × 1 .2 110 p = Density of dry air @ 20°C = 1.2kg/m3 100 90 Pressure Drop (Pa) 80 70 60 Core area = 2.5 / 1.99 50 = 1.26m2 40 30 20 10 0 0.0 0.5 1.0 1.5 2.0 Face Velocity (m /s) 2.5 3.0 3.5 4.0
- 20. Rain Defence • Common Terms – Rain Defence – Weatherproof – Storm Proof • What do they mean? • What performance is actually required? • What is the maximum acceptable water penetration? TKO hospital, Hong Kong
- 23. Internal view
- 24. Rain defence options Single bank louvre
- 25. Rain defence options Double bank louvre Triple bank louvre
- 26. Rain defence - drainage How a multi bank louvre works ♦ Air and Rain enter between louvre blades ♦ Air passes efficiently through, but water is collected into second louvre blade (and third if fitted) by “tangential separation” ♦ Water is drained into hollow section mullions where it can be drained directly to outside over the cill
- 27. Wind load resistance • Under local maximum design wind loads the louvre panel should: – Retain its structural integrity – Not deflect excessively – Not suffer visible permanent deflection
- 28. Louvre Appearance • Many materials and finishes available • Consider: – Louvre material – Operating environment – Durability
- 30. Ancillaries • • • • • Bird guard and/or insect mesh Doors & access panels Mitred / facetted / curved corners Thermal insulation / blanking panels Acoustic louvre
- 31. C: Testing & Classification • Louvre performance can be specified by reference to BS EN 13030:2001 – Technically equivalent to the HEVAC test method on which it was based – Now also incorporated as an option within AMCA 500 • Quantifies both air flow and rain defence performance
- 33. Air flow testing
- 34. Louvre classification RAIN DEFENCE AIR FLOW CLASS EFFECTIVENESS CLASS COEFFICIENT A B C D 1.0 to 0.99 0.989 to 0.95 0.949 to 0.8 below 0.8 1 2 3 4 0.4 and above 0.3 to 0.399 0.2 to 0.299 below 0.2 Rain defence classifications should always be linked to a suction velocity – it’s much easier to achieve class A at 0m/s than at 3.5m/s
- 35. What the classifications mean 16 14 12 10 8 WATER ENTRY UNDER TEST (litres per hour per square metre) 6 4 2 0 1 0.95 0.9 0.85 Effectivness 0.8
- 36. Classification of Colt louvre systems Louvre Coefficient type 1UL/SH 0.0 0.44 Class 1 2UL/SH 0.31 Class 3 ERD Class 2 1.5 2.0 2.5 3.0 3.5 D1 D1 D1 D1 D1 D1 D1 A2 A2 B2 B2 C2 C2 D2 1.00 0.999 0.998 0.998 0.997 0.996 0.996 0.995 A3 0.3 1.0 0.997 0.996 0.992 0.986 0.96 0.90 0.81 0.74 A2 0.28 0.5 0.73 0.66 0.60 0.62 0.60 0.59 0.51 0.50 D1 Class 2 3UL/SH Rain Defence Effectiveness at core velocity (m/s) A3 A3 0.993 0.985 0.968 0.95 0.89 A2 A3 B2 A3 B2 B2 C2 A3 A3 A3 0.69 0.42 0.35 D2 D2 D2
- 37. In house performance testing Airflow test Rain penetration Deflection under load
- 38. D Specification National Building Specification (NBS) • Manufacturer • Product Reference • Material • Decorative / Protective Finish • Performance (Airflow and Rain Defence) • Ancillary Items –Bird guard / Insect Mesh / Blanking Panels etc.
- 39. The performance specification The louvre shall have an aerodynamic coefficient of at least [insert value or class here] when tested in accordance with BS EN 13030. The louvre shall have a rain defence effectiveness of at least [insert value or class here] at the design air velocity for the installed louvre when tested in accordance with BS EN 13030. NOT The louvre shall have a free area of at least 50%. The louvre shall be storm proof.
- 40. Decision making So, to summarise: Decide what you (or your client) will want the system to look like and expect the system to do Decide who is responsible within the design team to actually specify this Ensure that all relevant information is obtained Ensure that the performance specification is very specific and that the final product verifiably meets the specification
- 41. Before and after Dun & Bradstreet, High Wycombe Perforated single bank louvre
Editor's Notes
- Welcome to our CPD seminar on louvre systems and how to specify them. And yes, the picture does show louvre; the entire pyramid at the top of the Canary Wharf tower is made of stainless steel louvre with a surface finish carefully chosen by the architect to give a softer look than would be achieved by normal polished sheet.
- Founded in 1931 the Colt Group are represented around the world through a network of subsidiaries, licensees and distributors. Colt is a privately owned British company with its corporate and UK headquarters based at Havant in Hampshire. All Colt manufactured products sold in the UK are made either in the UK at Havant or in Holland. Our other factories are there to serve their local markets.
- By investing in innovation, products, services and people, Colt International has established itself as an international leader in the fields of: Smoke Control Solar Shading Natural Ventilation Louvre Environmental Comfort Control (HVAC)
- Louvres are commonly used on most types of building and have three basic uses, individually or in combination – permit air flow, keep out rain, look good. Many designers still give insufficient consideration to exactly what they want the system to achieve, this is particularly true when it comes to “Performance Louvre” and the need to exclude wind driven rain. The purpose of our presentation is to highlight areas of consideration for both Architects and Services Engineers to ensure that specifications adequately reflect design requirements and performance expectations.
- The purpose of this presentation is to take you through the basic steps of Louvre selection and to give a clear understanding of the important issues.
- What is a Louvre? A question which many people seem to interpret differently. A dictionary definition of “Louvre” recognises the two basic functional requirements “to admit air, but not rain”. Designers can assume that all louvres are the same - Wrong! Levels of admission of air and protection from rain vary tremendously between louvre systems. Even louvre systems with the same “free area”. In order to ensure that design requirements are met, some basic questions need to be considered and answered.
- The simplest use of louvre is as a “vision screen / cosmetic screening” usually to hide plant or equipment. This image shows inverted louvre acting as Rooftop Plant Screen at 1 London Wall. The louvre has been inverted to avoid “vision through” from lower levels. There is no requirement here for the louvre to significantly reduce rain entry.
- Here at the new BMW Plant (Hams Hall) a large panel of louvre is used for air intake and exhaust from a plant room. The louvres are continuous in line with concealed supporting mullions. Single, double and triple bank louvres can be incorporated into a common elevation to provide location specific performance while looking visually identical from outside.
- Louvre turrets are commonly used for natural ventilation. Rain penetration is usually an important issue, therefore double or triple bank louvre may be needed.
- Louvres for rain screening a ventilation openings at the National Air Traffic Services, Prestwick.
- Louvre screens are not always functional. This system has very limited rain defence but gives the building the aesthetic required by the architect. If the rain needs to be kept out, this type of system needs a wall behind it!
- Louvre screens are an effective method for controlling solar heat gain in buildings. Here a brise soleil is installed to reduce summer heat gain while allowing useful winter solar gain from low angle sunlight. Louvre systems designed for solar shading have a different set of performance requirements and therefore different designs. We will not be discussing these today.
- In this section we will discuss “Function & Form” – what are the design criteria and how do we meet them?
- Function – What is the purpose / application of the louvre? Who will be responsible for establishing and specifying functional requirements? “Decide what you require the louvre to do”. It is not uncommon for this to slip unnoticed between Architect and Engineer! Specification is generally based on a mix of essential and desirable characteristics: performance, aesthetics and durability. The importance of each will vary from contract to contract. We will now run through the main parameters.
- There is no such thing as the perfect louvre. All designs are a compromise between competing performance parameters. We want the best compromise for the project between an open hole and a brick wall. The best compromise is project specific – hence the range of louvres on offer from manufacturers.
- Air Flow The air flow rate required will be a determining factor for the minimum louvre panel size. The air flow may be required as supply or exhaust to a fan, condenser cooling flow, general plant room ventilation, or any other purpose. Resistance to Air Flow This usually combines with the air flow requirement to provide the minimum louvre size. The maximum acceptable pressure drop is usually set by the fan performance. However, where good rain defence is also required, this may become the limiting factor. Designing for an unnecessarily high pressure drop in order to reduce louvre size is usually a mistake since a high pressure drop increases fan power requirements and running costs and may also require larger plant.
- The air flow rate and maximum pressure drop (or limiting core velocity, or both) are used to size louvre. A limiting velocity is generally used either where an excess velocity could cause unacceptable rain entry or noise or to avoid draughts. This data should usually be provided by the Building Services Engineer. Once this data is available the louvre can be quickly sized. To carry out air flow calculations, the performance of the louvre needs to be characterised. Sizing is done using the louvre coefficient (Cv), which is found by test. The Cv is related to the k factor (or zeta factor) used in ductwork calculations by k = one over Cv squared. There is no direct conversion between measured free area and Cv, therefore specifying a design measured free area is meaningless in terms of achieving a desired performance.
- The formula shown (Bernoulli) allows us to calculate the core velocity required through the louvre from a known air flow rate and maximum pressure drop. This velocity can then be used with the air flow rate to provide a minimum core area for the louvre. Core area is the area inside the framing with all louvres removed, so this area then has to be adjusted for the support framing to give a final face area for the complete louvre panel. Colt use core area as this gives the most accurate results for a wide range of louvre configurations. Face area, as used by others, is simpler but can be very inaccurate. Often manufacturers produce graphs or nomograms for their products to ease selection and eliminate the use of calculations.
- It is not uncommon for specifications to contain very loose ‘terminology’ like these that do not adequately define exactly what degree of rain defence performance is required - or what is expected to be delivered. Such loose terminology is bad enough in the UK, but in places like Hong Kong, with regular typhoon conditions, inadequate rain defence specification is soon shown up. Experience has shown that this can lead to contractual conflict, site problems and longer term rectification costs. It is often difficult and expensive to rectify a problem once installed. A specific, quantifiable performance measure is needed.
- The St.David’s Hotel in Cardiff (for Rocco Forte) was an architecturally acclaimed design.
- Louvre was used extensively on the building, including air intake to a first floor plant room, located directly over the main restaurant. The plant room faces directly onto Cardiff Bay, and is subjected to wind driven rain.
- The louvre system was purchased as a single bank “Weather Louvre” (not from Colt) but a significant quantity of rain water passes straight through and into the plant room. No provision was made within the plant room for protection or drainage, and the plant room regularly flooded. Water then drained down into the restaurant below. A retrofit double bank louvre draining to outside, mounted behind the original louvre has now solved the problem. The original louvre was retained to keep a coherent appearance for all louvre on the building.
- How can you ensure adequate air intake, and yet prevent water entry. As we’ve seen, In engineering terms these are two opposing requirements, so any design will be a compromise. The trick for louvre designers is to maximise air flow performance for a selected rain defence performance. The trick for specifiers is to select the louvre system that best matches your own project requirements. On the left you can see a traditional “Z” section louvre. Air flow performance is pretty good but the sharp edges create turbulence, limiting the performance. On the right is the smoother design of Colt 1/UL, which reduces turbulence and thus provides better air flow performance. Neither design provides great rain defence as the designs prioritise air flow. They are suitable for use when the location is very sheltered or where rain entry is not important. One problem with Z section louvres is that water leaves the rear edge of the louvre with an upward trajectory, resulting in deeper penetration. This could be critical where electrical plant or switchgear is to be located behind the louvre panel. It is tempting to think that if a louvre is used in an exhaust application the outward air flow will limit rain entry so a low specification louvre may be used. It is true that an exhaust air flow will improve rain defence, but can you guarantee that the exhaust will run 24/7? It is possible to add extra lips or mouldings to z section louvre designs. This improves the rain defence, but results in increased resistance to airflow. It is the approach generally taken for single bank rain defence louvres.
- Double bank louvres are designed to achieve both a good rain defence performance and a good air flow performance. Triple bank louvres are designed to achieve an excellent rain defence performance, particularly at higher air flow velocities where the performance of a double bank louvre tends to drop off. The designs shown use separate louvre blades so that water is separated out of the air stream utilising the principle of “tangential separation”. Where the airflow is forced to turn through 90 degrees, the water droplets impinge on the underside of the second louvre and are collected by the return edge of the louvre where they can be safely drained away into hollow section mullions that act as “drainpipes”. On any rain defence louvre system drainage becomes critically important when dealing with large panels. There is no point in collecting large quantities of water in the louvre blades if this cannot be quickly and effectively drained to the outside of the building.
- This diagram shows the drainage process with some of the front louvres removed. Water can be drained directly onto the cill, or collected in a gutter and piped away. Guttering is usually considered where very large louvre panels could lead to water discharge causing “streaking” to the face of building.
- Louvres are often located in exposed locations and need to be robust enough to withstand the resulting wind pressures. In particular they should not deflect excessively or, worse, shed louvres. In general terms, the higher the wind load, the narrower the spacing between louvre mullions needs to be and the closer any horizontal secondary steelwork centres need to be. Any reputable supplier should be able to configure their louvre to meet wind conditions anywhere in the UK. However, closing mullion and steelwork gaps reduces the working area of the louvre, so to retain the performance of the louvre a larger face area will be needed.
- Most current louvre systems are manufactured from extruded aluminium, which limits the decorative finish, usually to a post manufacture paint or anodised finish. Other systems utilise roll forming techniques, allowing them to be manufactured from a variety of base materials such as: Aluminium Galvanised Steel Stainless Steel Copper In some cases the material may also be available pre-coated, perforated or with embossed or textured finishes as well as polished sheet. The default material is usually aluminium and, in terms of durability, there is usually no need for any protective finish. But the surface of aluminium tarnishes over time, leaving a dull silver/grey appearance. Thus most installations have some kind of protective surface finish. Where louvre is provided for decorative purposes only or for solar shading, totally special louvres may be manufactured using for example wood, terracotta, plastic, or a fabric wrapping.
- Here a leisure complex in Milton Keynes (Xscape) where a variety of different louvre materials and finishes were incorporated. High level louvre was silver Stucco Embossed aluminium, with the band at low level being pre-coated Corus “Celestia” to match adjoining flat panel cladding. Louvres in other locations were treated with stoved polyester powder paint.
- In addition to the basic requirement, there are often other considerations: Bird guard and Insect Mesh Bird guard is a common requirement which has little effect on louvre performance. Insect Mesh, on the other hand, will have a significant impact on airflow and louvre efficiency, adding considerable resistance. This will increase the required louvre panel size (and cost) for a given airflow performance Doors and access panels Consider the frequency of use, and ease of access required. Where doors are likely to receive heavy use (and possible abuse) special consideration may be required - crash bars etc If thermally insulated blanking panels are required, what “U” value performance should be achieved, and how will the panels be integrated ? Where attenuation is required, special acoustic modules may be required to meet the noise reduction performance criteria (300mm minimum depth) Attenuation When attenuation is required, this can be provided using an acoustic louvre or a conventional attenuator. Acoustic louvre is generally used for modest noise reduction and minimum depth. Attenuators are usually specified when an insertion loss of more than 10 -15 dBA is required, at the expense of greater depth. Attenuators are always mounted behind a louvre system. Acoustic louvres may be exposed or hidden behind conventional louvres if additional rain defence is required or for aesthetic reasons.
- This European standard provides test methods and classification for both air flow performance and rain defence of louvre systems. It is based on, and technically identical to, the original HEVAC test method. AMCA (Air Movement and Control Association) in the USA have incorporated the basic test method into their AMCA 500 louvre standard. The test method is thus recognised in most parts of the world. The test rig required is large, so there are only 2 laboratories offering the testing. In the UK most test data will have come from testing at BSRIA. The tests provide “comparative” performance data for both air flow and rain defence and thus offer protection to the specifier and clear guidance to contractors on project requirements and performance expectations. It is worth noting however, that all tests are carried out on louvre panel sizes of 1m x 1m and scaling of performance to other shapes and sizes of louvre panel is heavily dependent upon issues not addressed in the standard such as aspect ratio, mullion centres and drainage. The test method has been in use now for more than 25 years and test data is freely available. One therefore wonders why the inferior terms “percentage free area” and “storm proof” are still widely used in specifications. ----------------------------------
- The principle of the testing is simple. An opening is prepared in the test wall of the test rig the same size as the louvre panel, nominally 1m x 1m. The fans and rain spray are switched on and set up to give a wind speed of 13 m/s in front of the louvre and water entry through the opening at a rate of 75 litres per m2 opening area per hour. The opening is replaced by the test louvre and the wind and rain switched back on. Measurement of the water entry through the louvre is made under a range of suction velocities between 0 and 3.5m/s through the louvre. The performance of the louvre at each suction velocity is given by the proportion of the water kept out, which equals 75 minus rain entry rate, all divided by 75. This should always be between 0 and 1, with high numbers indicating the best performance.
- With the louvre in position in the test wall and the wind and rain switched off, the pressure difference across the louvre is measured at a range of suction velocities between 0 and 3.5m/s. The information is correlated to allow calculation of the aerodynamic coefficient (Cv) of the louvre panel. The result is again a value between 0 and 1, with higher numbers indicating the best performance. Most louvres achieve a coefficient between 0.2 and 0.45. If you’re more used to using CIBSE pressure loss (zeta) factors, there is a direct correlation. Zeta equals one over Cv squared.
- The standard provides 2 separate classifications for air flow coefficient and rain defence effectiveness. Ideally all louvres would be class A1. In practice the best rain defence louvres fall into class A2 or A3. When specifying louvre it is important to link the required rain defence to the suction velocity expected through the louvre on site. This is taken as zero if the louvre is used for exhaust as the worst case will be when the ventilation system isn’t running.
- The rain defence classification, while numerically precise, is intended to be used as a comparative tool between louvres, not as an accurate predictor of rain entry on site. The variability of sizes and locations of louvres and site exposure mean that louvres of the same design may perform differently on different sites. Experience is needed to make an informed selection. Note also that a seemingly small change in effectiveness can make a great deal of difference. Under test conditions a louvre with a coefficient of 0.97 will let in 2.25 litres per hour per m2, 3 times as much as a 0.99 louvre and 30 times as much as a 0.999 louvre. Even within class A, where the range is only 0.99 to 1.00, there can be a significant difference in performance, ranging from zero water entry up to three quarters of a litre per hour per metre squared of louvre. Even in a class with such a restricted range not all louvres equal. If performance is critical it is better to specify an effectiveness directly and not rely simply on a class.
- You can see from the chart just how much variation there can be in performance between different louvres and how the intake air velocity has a major effect on rain defence performance. The chart only provides data for intake velocities up to 3.5m/s. Velocities above this are outside the range of EN 13030 and are rarely specified since, even with the most aerodynamic louvre, the pressure drop at this velocity is about 40 Pa and most rain defence louvres will have a pressure drop of 90 Pa or more. The two video clips show the rain ingress through 1UL and 3UL under the same external conditions – the difference between an A rated louvre and a D rated louvre is plain to see.
- Of course manufacturers do not always want to have to go to BSRIA for development testing, so in house test facilities are very useful for development, testing larger panels, comparison testing and client demonstration. And of course for tests outside the scope of BS EN 13030 such as load testing. The video clip shows the Colt rain test rig and explains its benefits.
- A good specification should include these items. All are equally important. The NBS Specification format is convenient and suppliers can often supply prepared specifications for their products in this format.
- It’s not difficult to write a good performance specification for a louvre as shown. In fact it’s almost as easy as writing a bad one!
- Finally a a pair of images showing how louvre can significantly improve the appearance of a building. Dun & Bradstreet Headquarters. Offices were built on top of the employees cark park. After completion a decision was made to hide the car park from the outside as it looked unsightly compared to the rest of the modern building. Naturally the car park needed to retain sufficient ventilation area, and in some places it needed protection from rain entry as large puddles would form, discouraging parking of cars in those areas. Perforated single bank Universal Louvre was selected. This gave excellent ventilations levels with the added benefit of the perforations letting in additional natural daylight. In this application (with no suction velocity) single bank louvre provided sufficient protection from rain, allowing all parking spaces to be used, regardless of weather conditions.