Ventilation In Classrooms An overview of the requirements and the methods available for achieving and maintaining acceptable Indoor Air Quality (IAQ)

Transcription

1 Ventilation In Classrooms An overview of the requirements and the methods available for achieving and maintaining acceptable Indoor Air Quality (IAQ)

2 Agenda The need for good Indoor Air Quality (IAQ), effects of poor IAQ, Legislative & Design requirements Solutions Natural ventilation Powered systems

3 Reasons For Ventilation Maintaining acceptable Indoor Air Quality (IAQ) Removing odours Controlling summertime temperatures Pre-cooling of building structure with night-time cooling

4 Effects Of Poor IAQ - General Stuffiness Build-up of contaminants Sick building syndrome Facilitates transmission of infectious agents

5 Effects Of Poor IAQ - Classrooms Air quality has a greater impact on cognitive performance than elevated temperature, in the temperature range 20-25degC (ASHRAE/International Centre for Indoor Environment and Energy) Potential lawsuits relating to IAQ are being considered in many sectors so there is the possibility of litigation by parents

6 Other Considerations Variable occupancy Seasonal variation in ambient temperatures Wind speed/direction fluctuation Energy conservation BREEAM

7 General Relevant Regulations Building Regulations Part F (Ventilation) Building Regulations Part L (Conservation of fuel and power) Educational buildings Building Bulletin 87 (BB87) Guide for Environmental Design in Schools Building Bulletin 93 (BB93) Acoustic design of schools Building Bulletin 101 (BB101) - Ventilation of school buildings Other local planning requirements

8 Regulatory Requirements Fresh air rates No less than 3 litres/second/person (l/s/p) Minimum daily average 5 l/s/p Capability to achieve 8 l/s/p CO 2 levels Not to exceed 5,000ppm during teaching day Average during normal school hours not to exceed 1,500 ppm Ability to lower levels to 1,000ppm

9 Temperature Regulatory Requirements Temperature not to exceed 28 C for more than 120 hours during school year (BB101). But BREEAM recommends no more than 60 hours. Temperatures in normal classrooms should not be lower than 18 C. In areas of greater activity (e.g. drama workshop), 15 C is considered acceptable (Education (School Premises) Regulations 1999) ΔT between indoor and outdoor should not be more than 5 C in summer conditions Internal air temperatures not to exceed 32 C when rooms occupied

10 Energy Regulatory Requirements Mechanical ventilation weighted average fan power not to exceed 0.8W/l/s Demand controlled ventilation aligns energy consumption to ventilation requirements (Part L and BREEAM) Sound Upper limit for the indoor ambient noise level for classrooms and general teaching areas is 35 L Aeq,30min (db)

11 The Importance Of CO 2 CO 2 is a good indicator of general IAQ (BB87) CO 2 is a useful measure of occupancy levels CO 2 is a good indicator of ventilation effectiveness (Health Council of the Netherlands) Elevated CO 2 levels (>1500ppm) result in 5% decline in Power of Attention measures (University of Exeter) Occupants do not notice as air quality slowly deteriorates, so a measurable parameter is required CO 2 can be monitored with reliable sensors and used as the control parameter for Demand Controlled Ventilation

12 Maintaining CO 2 levels For all of these reasons CO 2 is a sensible measurement parameter for the control of IAQ. The Health Council of the Netherlands recommends that consideration is given to improving filtration and the control of ventilation rates, while taking account of noise levels and energy consumption An additional benefit is that if the CO 2 levels are below the threshold (<1500ppm) fresh air ventilation is unnecessary, as shown on the graph.

13 7:00 7:20 7:45 8:10 8:35 9:00 9:20 9:45 10:10 10:35 11:00 11:20 11:45 12:10 12:35 13:00 13:20 13:45 14:10 14:35 15:00 15:20 15:45 16:10 16:35 17:00 17:20 17:45 Daily CO 2 Levels & Fresh Air Volumes C o 2 P P M Co2 Air Volume With a modern, correctly designed ventilation system, the CO 2 levels can be maintained in accordance with the regulations. This graph shows how a 30 pupil primary school classroom performs during a typical school day. The average fresh air volume is 32 l/s (1.0 l/s/person). However, regulations & guidance require the ventilation system to be designed to provide 3, 5 or 8l/sec per occupant

14 Maintaining CO 2 levels CONDITION AVERAGE VENT RATE l/s PER PERSON MAX INSTANTANEOUS VENT RATE l/s PER PERSON MAX INSTANTANEOUS CO 2 ppm Primary School Autumn Term Primary School Spring Term Primary School Summer Term Secondary School Autumn Term Secondary School Spring Term Secondary School Summer Term The above table shows that regardless of what the outside conditions may be, good indoor air quality of 1200ppm can be achieved with an average of 1.6 l/s/person of fresh air

15 Other Design Considerations Match heating and ventilation requirements Need to compensate for cooling by external air Ventilation system should respond to CO 2 levels and temperature Cooling requirements in summer, potentially >8 l/s/p Potential for night-time cooling of building s thermal mass BREEAM/LEED DfES design tools: ClassVent ClassCool

16 ClassVent Spreadsheet

17 ClassCool Spreadsheet

18 Natural ventilation Opening windows Louvres Ventilation stacks Ventilation tubes/catchers Powered Ventilation Ventilation Options Fan convectors with fresh air dampers Underfloor heating with high level supply & extract Constant volume high level supply & extract Displacement with low level supply and high level extract

19 Natural Ventilation System 1 Standard radiator heating no ventilation

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21 Natural Ventilation System 2 Underfloor heating or radiator providing heating and manually opening windows providing fresh air ventilation.

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23 Natural Ventilation System 3 Integrated radiator providing heating and ventilation. Fresh air supply by natural, unpowered ventilation with high level extract.

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25 Advantages: Natural Ventilation Inexpensive when delivered by manually opening windows Simple & easy to understand (opening windows only) Quiet (in operation but may be external influences) Local control (where applicable) Potential BREEAM points

26 Disadvantages Natural Ventilation Building compromised with large multiple grille/damper assemblies Power supply required if dampers/louvres used Expensive when using motorised windows or louvres Limited control Performance affected by wind speed and direction (pressure variation) Limited opening may limit level of summer cooling available Limited scope for night time cooling

27 Disadvantages (cont) Natural Ventilation Potential loss of heated air, wastes energy The CO 2 levels in naturally ventilated classrooms are often above 1,000ppm and frequently exceed 2,000ppm (Technical University of Denmark) Natural ventilation does not provide effective control of IAQ, even with cross-flow heat exchangers Limited cooling effect in summer due to poor mixing

28 Natural Ventilation Additional Disadvantages Relating To Manually Opening Windows Control subjective rather than determined by measured parameters Windows tend to be opened in response to higher temperatures but not elevated CO 2 levels (Technical University of Denmark) Where IAQ does trigger window opening, IAQ is already poor i.e. Reactive rather than preventative BREEAM recommends that opening windows should NOT be used where any part of the school building is within 5m of a car park or roadway

29 Natural Ventilation Additional Disadvantages Relating To Manually Opening Windows (contd) Limited penetration at low wind speeds Tendency for cold air to fall to floor and open TRVs, wasting heat Risk of cold draughts at high wind speeds Noise Security

30 Powered Ventilation System 4 Standard fan convector, no ventilation.

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32 Powered Ventilation System 5 Fan Convectors With Fresh Air Dampers. Fresh air drawn in through air inlet with damper system, using fans in convector unit.

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34 Powered Ventilation Fan Convectors With Fresh Air Dampers Advantages Simple Familiar Localised control at room level (BREEAM points may be available)

35 Powered Ventilation Fan Convectors With Fresh Air Dampers Disadvantages Basic control options, no graphical interface Effective mixing with room air requires higher fan speeds, using more energy High potential for draughts Potentially noisy Require large air intakes through building fabric

36 Powered Ventilation System 6 Underfloor heating high level fan assisted supply and extract with heat recovery

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38 Powered Ventilation System 7 Radiator heating, central system constant volume, high level supply & extract.

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40 Powered Ventilation Constant Volume, High Level Supply And Extract Advantages Central extract plant easier for maintenance in new build projects Potential for heat recovery at extract

41 Powered Ventilation Constant Volume, High Level Supply And Extract Disadvantages Potential for coanda effect on ceiling, poor mixing with room air Potentially noisy Typically not demand controlled Central plant requires additional dampers for local control Decentralised plant results in increased maintenance costs

42 Powered Ventilation System 8 Low Level displacement fresh air supply with high level extract.

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44 Powered Ventilation Displacement With Low Level Supply & High Level Extract Advantages Low fan speeds, no draughts, low energy consumption, low noise Supply and extract rates synchronised to ensure balanced air flows Effective mixing of fresh air and room air with no draughts Potential for modulating fresh air control in relation to CO 2 levels Localised control at room level possible (potential BREEAM advantage)

45 Powered Ventilation Displacement With Low Level Supply & High Level Extract Advantages (cont) Potential links to other control systems, including BMS Ventilation operates independently of heating Potential low energy solution (inverter fans/ec motors) Graphical display of energy consumption possible

46 Powered Ventilation Displacement With Low Level Supply & High Level Extract Disadvantages Poor extract design can result in short-circuiting of air flow Requires multiple units to achieve sufficient flow rates with low volume and low velocity, thus increasing maintenance requirements. More expensive than simple fan convectors

47 Summary Of Key Points IAQ is a key factor in children s academic performance Systems must Respond to variation in occupancy and ambient temperature Be immune to the effects of wind speed and direction Be energy efficient Comply with regulations CO 2 is the most practical measure of IAQ to use as a control parameter All systems have advantages and disadvantages

48 Summary Of Key Points (cont) On balance, displacement ventilation systems would appear to offer the best combination of IAQ control, energy efficiency and effective fresh air distribution.

49 Q & A Thanks For Listening!