The following information is intended as a guide only and should be read in conjunction with the government regulations and guidance documents listed at the end of this document. For Design Guidance on Smoke Control – Click Here For Design Guidance on Ventilation – Click Here
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BB101 has one aim – to produce a comfortable and healthy teaching environment utilising natural ventilation, solar control, natural daylighting and passive heating & cooling systems with the desire to be in control of this environment at all times. Of fundamental importance is:
BB 101 recommends purpose-designed and fully automatic control of natural ventilations systems as opposed to simple window-opening strategies, which will provide the following advantages:
However BB 101 does recognise that mechanical methods or even hybrid systems containing both natural ventilation and mechanical heating/cooling systems (such as Colt WRF Caloris water source heat pumps) may provide the best solution.
Ventilation Requirements:
Heating Requirements:
Lighting Requirements:
Carbon Dioxide Requirements:
Noise Abatement:
Design Options
Firstly, before we go into the detail we need to understand the principles of human comfort.
There are six main factors governing comfort:
As everyone will know, the main parameters for human comfort are air temperature (convective), radiation from our bodies as well as clothing, surrounding structures and surfaces, the humidity of the air, air movement, noise and odours. Get these parameters right and you have a comfortable environment.
Let’s review each of these in detail:
Air Temperature
The optimum air temperature, where the majority of people will be comfortable is between 18°C and 22°C. In the UK (London and South England) summer temperatures are frequently high twenties and even exceed 30 degrees on occasion. North England, Scotland, Wales and Ireland tend to be a bit cooler.
With current climate change and global warming these temperatures are only going to increase in the future. Add to this the internal heat gains of people, lighting, computers, etc and you can have an uncomfortable working environment.
Radiation
When the air temperature is 25°C and the surroundings 35°C, the body ceases to radiate heat. The body compensates by increased evaporation levels (in other words sweating).
If the body suffers a net radiation gain from hot processes or sun shining through glazing, evaporation losses can result in the body losing one pint of fluid per hour.
Humidity
If the surrounding moisture content of the air (humidity) is excessive then evaporation cannot occur, creating a feeling of clammy and uncomfortable conditions. A temperature between 18-22°C (optimum temperature) can feel uncomfortable if the humidity is high. If the humidity is too low, as created through air conditioning systems if humidifiers are not incorporated, then the skin and eyes can dry as well as causing static.
Air Movement
Air movement is a valuable aid to cooling the human body. However, excessive movement needs to be avoided.
Insufficient air movement will give rise to a feeling of stuffiness and, subsequently lethargy.
Increasing air movement can be more effective than lowering air temperature as it provides cooling by removing heat convected from the body as well as evaporating moisture from the skin. Correctly designed air movement using fresh air ensures fresh, odour free conditions. Excessive air movement can have a negative cooling effect and cause drafts.
Noise
A proper sound level study should be carried out for the external and internal condition of every project which Colt can assist with. While the legal maximum is 85 dBA for an exposure of 8 hours/day, much lower noise levels are required in many situations. Table 1.15 in CIBSE Guides A provides recommended noise levels for all building types and applications. For schools please refer to BB 99 and information provided below.
Odour
Possibly the most subjective but can significantly affect work performance as well as health. Odours can vary in source, content and effect.
People can become sensitised to certain odours which can lead to a severe reaction, such as chest complaints and skin rashes.
As previously discussed, lack of air movement and fresh air supply will cause the build up of odours which will aggravate and distract pupils, hence reduce performance. Severe odours may also result in affect on health.
What are all the effects of these?
Failure to provide suitable comfortable environmental conditions will have a negative affect on the performance of pupils and staff. It will increase the quantity and duration of intervals between studying and will increase absenteeism.
What can be done to avoid these problems?
There are a number of solutions:
For this exercise we will concentrate on Natural Ventilation.
The basic principle of natural ventilation is to remove hot air at high level, while replacing it with fresh cooler air at low level – SIMPLE!
There are two types of natural ventilation solutions.
Wind Driven and Stack Effect.
Stack effect is temperature induced. When there is a temperature difference between two adjoining volumes of air the warmer air will have lower density and be more buoyant; thus it will rise above the cold air creating an upward air stream.
Wind driven effect, as the name suggests this is where air movement is created by the external environment. Turret ventilation is a common example of this. Generally more suited to low rise buildings, ventilators can provide both supply and extract functions by axially splitting the trunk of the ventilator into segments to separate the supply and extract airflows. The flow direction in each segment (supply or extract) extract varies according to the wind direction.
Natural Ventilation at its most basic form
Low level window allows fresh air at outside ambient to enter the classroom and then be exhausted as warm air through high level window.
Single Sided Ventilation
For small areas such as classrooms single sided ventilation, relying on wind turbulence can be sufficient. The inlet and exhaust can be via one window or ventilator, where in theory the bottom half will inlet and the top half will exhaust. In reality the split may not be even. Alternatively two separate windows can be used with one at high level and one at low level.
This type of system’s effectiveness is restricted to the room depth being no greater than 2.5 times the height.
Wind – induced natural “cross flow” ventilation
For larger classrooms cross flow ventilation can be used where again wind driven air movement is used, with hot air exhaust from one side of the building while fresh inlet air enters from the other.
The restriction for this particular method that the room depth is no greater than five times the room height.
Stack effect methods, such as the one illustrated above, operate by cooler inlet air at low level heating up and naturally rising and being exhausted at high level. It is important to compensate for wind effects on the exhaust, if vertically installed, to ensure that the exhaust does not become inlet due to wind pressure. This can be achieved by providing extract on all four elevations.
For multi-level buildings, as found in colleges and universities, care should be taken to ensure that inlets act as inlets and do not become exhaust.
The system should be correctly designed to ensure that the neutral layer is above the inlets but lower than the exhaust. Openings below the neutral layer will have a negative pressure and therefore inlet and openings above the neutral layer will have a positive pressure and therefore exhaust.
Incorrectly designed systems can have noticeable results!
The Benefits of a correctly designed Natural Ventilation System are clear
Design Considerations
The following items should be taken into consideration when designing a natural ventilation solution.
Design Considerations for Noise
Air quality studies by UCL (2008) have shown that by increasing the ventilation rate from 8 to 10 l/s/person improved performance in school by 14.5%.
Reducing temperature by 1°C improved performance by 3.5%.
You can reduce internal heat gains by simply using low energy lighting (try to utilise natural lighting at all times) and equipment. Turn off computers, lights, board projectors etc. when not is use.
Another major item that is sometimes disregarded to reduce internal heat gains is solar shading. External solar shading louvres are an excellent and cost effective way to reduce the solar gain and radiated heat from entering the building in the first place.
Solar gain is a considerable element to internal heat gains, especially in glazed atriums and structures.
Natural Ventilation Conclusions
Correct Design + Common Sense =
Effective Natural Ventilation
For help and guidance on naturally ventilating education facilities, please contact Colt International limited.
HOWEVER!
Sometimes a single Natural Ventilation solution is not enough, but a full mechanical system can be expensive to operate and requires greater maintenance.
A potentially more environmentally and financially sound solution than adopting a full mechanical ventilation system is to adopt a ‘hybrid’ or mixed mode ventilation strategy.
The underlying principle of a hybrid system is that the building is designed as a naturally ventilated building – without ductwork for air transport – but provision is made to assist the airflow through the space when natural driving forces are inadequate.
Heat Pump technology linked to air source or ground source systems can be utilised to ‘top up’ the cooling requirement in the summer and used as heating in the winter.
Colt design, manufacture and install water source heat pump systems, ideal for colleges and universities. Our Colt WRF Caloris is one such system installed in many universities across the UK. Please click on the ‘projects’ link and ‘Universities’ tab for some recent examples.
For further information on Natural Ventilation, Solar Shading, Smoke Control and/or WRF heat pump air conditioning please contact Colt International Limited.
Building Bulletin 100, Design for Fire Safety in Schools, applies to nursery schools, primary and secondary schools, academies and city technology colleges, special schools and pupil referral units. It is the normal means of compliance with Building Regulations for fire safety design in new school buildings and sets out the DCSF policy on fires within schools.
School fires put lives at stake and disrupt the education of tens of thousands of pupils across the UK each year. They are also expensive - school fires in 2006 cost £74 million. This figure is rising every year.
Fires are the most destructive, disruptive and costly cause of damage to school property. A fire represents probably the most single catastrophic event a school is likely to experience and carries with it risks to the safety and lives of the occupants. School fires are often caused by momentary acts of carelessness, ignorance or failure to take account of fairly obvious hazards, but a disturbing trend since 1970 has been the increasing number of destructive fires which have been started deliberately.
School fires cause consequential losses, which can be expensive and are often not insured against. These costs can include the provision of temporary buildings. They can also involve the loss of irreplaceable records of continual assessment, pupil's course-work and practical projects.
The prevention of fires in schools requires awareness and the adoption of good fire prevention practice. There are many ways of reducing the probable consequences of fire, such as using automatic fire and smoke detection systems, automatic fire extinguishing systems and substantial physical separation and smoke compartmentation. However, unless these are built in at the start, the cost of such measures are seen as excessive in existing premises. This places a heavy reliance on good management practices to reduce risks.
BB 100 provides guidance on four main fire detection systems, namely
For this exercise we will look at smoke control and sprinklers systems and the interaction between the two.
Firstly, smoke is by far the biggest killer – not fire.
Source: Fire Statistics UK, 2006 DCLG.
Sprinkler Systems
Sprinkler systems, by controlling or extinguishing fires while they are still small, have obvious benefits for reducing fire damage. The sprinkler systems can be designed to sound an alarm via an Alarm Receiving Centre (ARC) to initiate a response by the Fire and Rescue Service which is a further benefit for property protection. If the fire is kept small or put out, this will also significantly reduce the amount of smoke produced, which buys more time for evacuation before escape routes become untenable due to smoke logging.
Smoke Control Systems
The detailed design guidance mainly relies on containment by walls and doors to prevent smoke from entering escape routes. Automatic smoke control systems (triggered by an automatic detection system) can achieve the same ends, by extracting smoke from the building. This provides benefits for means of escape and also facilitates access by the Fire and Rescue Service.
It is important to note that most Natural Ventilation solutions can be utilised for due purpose smoke control with little design change.
So, why provide smoke control?
What’s the difference between Smoke Clearance and Smoke Control?
Smoke Clearance Ventilation
Uses a notional amount of ventilation to assist fire fighting operations, allowing fire fighters to clear smoke from the relevant building or part of building often after the fire has been extinguished.
This can be achieved by two simple methods:
By definition, smoke clearance offers very little benefit during evacuation and has a much simplified design basis.
Smoke Control Ventilation
Smoke Control Systems are designed to control or restrict the movement of smoke within the building.
In order to do this it is usually necessary to estimate the amount of smoke produced by a fire and in some cases the amount of energy present. Then measures such as ventilation can be used to remove smoke to provide vertical control and smoke barriers (curtains) can be used to control horizontal smoke movement.
Again, these can be natural or mechanical systems, but the design is much more complex and usually requires an estimate of the fire size.
How does Smoke Control interact with Sprinklers?
Sprinklers are designed to reduce damage, but offer limited benefit to occupants. Smoke ventilation alone will not save the building but is primarily designed to assist escape.
Sprinklers
Smoke Control
Travel Distances
The maximum travel distance from any point within the education building to a final exit or a storey exit is shown below.
Some typical examples of travel distances are illustrated below:
Travel distances in dead end condition.
Angle A, B and D should be at least 45°. C, B & A or C, B & D (whichever is less) should be no more than maximum distance given for alternative routes and C, B should be no more than the maximum distance for travel where there are no alternative routes.
Alternative escape routes.
Alternative routes are available from C because angle A, C & B is 45° or more and therefore C, A or C, B (whichever is the less) should be no more than the maximum distance for travel given for alternative routes.
Alternative routes are not available from D because angle A, D, B is less than 45° (therefore see figure 12). There is also no alternative route from E.
Dead end corridors should be avoided in new construction.
Inner rooms and access rooms.
Buildings with more than one exit in a central core should be planned so that storey exits are remote from one another and so that no two exits are approached from the same lift hall, common lobby or undivided corridor, or linked by any of these
Exits in a central core
Note: The doors at both ends of the area marked ‘S’ should be self-closing fire doors unless the area is sub-divided such that any fire in that area will not be able to prejudice both sections of corridor at the same time. If that area is a lift lobby, doors should be provided as shown in Figure 8 in BS 5588: Part 11: 1997.
Key:
L |
Lift |
S |
Services, toilets, etc |
Fd |
Self-closing FD20S fire doors |
Fda |
Possible alternative position for fire door |
C |
Corridor off which accommodation opens |
PS |
Protected stairway |
A |
Accommodation (eg, teaching space) |
Mechanical ventilation systems
Any system of mechanical ventilation should be designed to ensure that, in a fire, the ductwork does not assist in transferring fire and smoke through the building and put at risk the protected means of escape from the accommodation areas. Any exhaust points should be sited so as not to further jeopardize the building, ie, away from final exits, combustible building cladding or roofing materials and openings into the building. Ventilation ducts supplying or extracting air directly to or from a protected escape route, should not also serve other areas.
A separate ventilation system should be provided for each protected stairway.
Where the ductwork system serves more than one part of a sub-divided escape route, a fire damper should be provided where ductwork enters each section of the escape route operated by a smoke detector or suitable fire detection system. The fire dampers should close when smoke is detected. Ducts passing through the enclosure of a protected escape route should be fire-resisting.
Fire dampers activated only by fusible links are not suitable for protecting escape routes. However an ES classified fire and smoke damper which is activated by a suitable fire detection system
For further information on the design of Smoke Control Ventilation systems within Schools, please contact Colt International Limited.
Design Guidance Documents
The information provided is intended as guidance only and should be read in conjunction with the government regulations and guidance documents listed below.
BB 87 – Environmental Design This document can be freely downloaded from: http://www.teachernet.gov.uk/docbank/index.cfm?id=4753
BB 90 – Lighting Design for Schools This document can be freely downloaded from: http://www.teachernet.gov.uk/docbank/index.cfm?id=8413
BB 93 – Acoustics This document can be freely downloaded from: http://www.teachernet.gov.uk/docbank/index.cfm?id=5649
BB 95 – Schools for the Future This document can be freely downloaded from: http://www.teachernet.gov.uk/docbank/index.cfm?id=5543
BB 100 – Designing & Managing Against the Risk of Fire in Schools This document can be freely downloaded from: http://www.teachernet.gov.uk/_doc/12199/BuildingBulletin100_OnlineVersion.pdf
BB 101 – Ventilation of School Buildings This document can be freely downloaded from: http://www.teachernet.gov.uk/docbank/index.cfm?id=9953
These documents form part of The Education (School Premises) Regulations 1999.
This document can be freely downloaded from: http://www.teachernet.gov.uk/docbank/index.cfm?id=3928
Further guidance documents should also be considered:
Building Regulations – Part F Ventilation Building Regulations – Part L2 Conservation of Fuel and Power Building Regulations – Part E Resistance to the passage of Sound
Building Regulations – B1 – B5
B1 – Provisions of Means of Escape B2 – Control of Fire Growth B3 – Fire Containment B4 – Controlling External Fire Spread B5 – Facilities for the Fire & Rescue Service