Indoor environment and air quality (T3) Flashcards
Externally pollutants
- Vehicle exhaust emissions
- CO, CO2, NOx, SO2
- Particulates PM10 and PM2.5 (particle diameters less than or equal to 10 μm and 2.5 μm, respectively)
- VOCs (eg from petrol and oil)
- Ozone (from action of sunlight on nitrous oxides from vehicles)
- Discharges from combustion appliances
- Industrial processes and power station emissions
- Fungal spores, pollen
monitoring of outdoor air quality
- Control/containment of industrial pollutants covered by the Environmental Protection Act
- Local Authorities must collect pollutant concentration data
- Areas of poor air quality are designated Air Quality Management Areas…remedial plans established
- Met Office provide daily forecasts
Implications for architectural design
location of outdoor areas for people
ventilation arrangement for buildings
definition of ‘good’ indoor air quality
‘Good IAQ may be defined as air with no known
contaminants at harmful concentrations’
sources of pollutants in buildings
- Building materials (eg sealants, adhesives, paints) • Cleaning materials, solvents, consumer products
- Furnishings, fabrics (eg carpets)
- Furniture
- Gas cookers, heaters, other fuel-burning appliances (unflued) • Equipment (eg photocopiers, printers)
- Glues
- House dust mites
- Moulds, bacteria
- Pesticide products
- Pets
- Tobacco smoking
- Emissions from the ground
pollutants that are released by sources
asbestos and man-made mineral fibres bacteria, mould spores carbon monoxide chlorintaed organic compounds dust mite formaldeyde nitrogen dioxide particles polyclinic aromatic hydrogencarbon volatile organic compounds ozone radon
why is ventilation required?
- Providing fresh air for people to breathe
- Dilution and removal of contaminants in the space
- Extracting contaminants at source (e.g.extract systems)
- Satisfying combustion needs for appliances
- Distributing conditioned air (for heating / cooling)
- Space pressurisation (inhibit ingress of pollutants)
- Pre-cooling building fabric (e.g. night ventilation)
infiltration
- Uncontrolled leakage through building gaps and cracks
* Driven by wind and indoor/outdoor temperature difference
natural ventilation
- Deliberately-sized openings
* Also driven by wind and temperature differences, so only partially controllable
mechanical ventilation
- Uses fans, ducting
- Requires energy
- Fully controllable
prescribed outdoor air supply rates
- When main pollutants are odours from humans
- Based on number of occupants in a given space
- Basis for guidance in UK Building Regulations
- For office environments (no tobacco smoke)….
- 10 litres per second per person (unless otherwise stated)
- Other flowrates recommended for specific areas – see guidance
- Minimum should not be less than 0.3 litres / sec per m2 internal floor area
specific pollutants comtrol
- For a specific pollutant emitted at a constant rate
- Calculate ventilation rate needed to maintain a pollutant concentration below its ‘threshold limit value’ (TLV)
- A formula to do this calculation can be found in: CIBSE Guide A, ‘Environmental Design’
- Ventilation rate depends on room air distribution pattern
- (Slide at end of lecture gives the formula)
indoor pollution concentration
CE = ( qv Co + qe ) / ( qv + qe )
CE is the steady state concentration in ppm
qv is the ventilation rate in litres per second
Co is the volumetric concentration outside in ppm
qe is the pollutant emission rate in litres per second
equation to estimate the room fresh air ventilation rate
qv =qe (1–CE )/(CE –Co )
CE is the steady state concentration in ppm qv is the ventilation rate in litres per second
C0 is the volumetric concentration outside in ppm qe is the pollutant emission rate in litres per second
air quality monitoring
- Can monitor CO2 to estimate IAQ and room ventilation
- Only suitable when main source of pollutant is the occupants themselves
- Not suitable if more toxic pollutants are present
definition of thermal comfort
‘That condition of mind that expresses satisfaction with the thermal environment’
heat transfer mechanisms
convection = affected by room air temp and room air speeds
evaporation (diffusion and sweating) = affected by room humidity
radiation = affectedly room surface temperature
respiration ( sensible and latent) = affected by air temperature and humility
thermal balance with your surroundings
Heat generation rate = heat loss rate (+ heat storage rate)
out of balance = thermal discomfort
estimate heat balance between a person and a room
- Room air temperature
- Room surface temperatures…‘mean radiant temperature’
- Room humidity
- Room airspeeds near a person
- Insulation of clothing, and
- The body’s rate of heat generation (the metabolic rate)
linking heat loss to thermal sensation
Of room: Air temp., mean radiant temp, humidity, air speed
Of person: clothing insulation, metabolic rate
then linked to the scale
cold–cool–sl.cool–neutral–sl.warm–warm-hot
predicted mean vote (PMV)
The vote you would expect from a large group of people experiencing a particular thermal environment
application of Fanger’s PMV approach
basis of thermal comfort
signing spaces from comfort - roomfactors
post-occupancy
predicted percentage of dissatisfied (PPD)
estimate likely % of complainers in an enivorment
acceptable for general comfort 10%
adaptive thermal comfort approach
- PMV not the whole story…not just a heat transfer matter
- Psychological, behavioural and cultural factors are involved
- Adaptive approach can be used for environments with operable windows that open to outdoors, and are controllable by the occupants…’free-running’ buildings (PMV not best predictor for these)
- And no usage of mechanical systems
- Developed from large field study dataset
