Human Comfort and Health

Design considerations for:thermal, lighting and acoustic comfortindoor air quality

Paul Strachan

Definitions

Comfort:“The condition of mind that expresses

satisfaction with the environment”

Health “A state of complete physical, mental and

social well-being, not merely the absence of disease and infirmity”

Sources of information

http://www.esru.strath.ac.uk (design class notes)CIBSE Guide A and ASHRAE HandbookStandards: PD CR 1752 (ventilation for buildings – design criteria), ISO EN 7730 (thermal comfort) and ANSI/ASHRAE 55-2004 (thermal environmental conditions for human occupancy)

Design for health and comfort

For some metrics, there are separate limits for health and comfort (and sometimes ecological impact)

Example - IAQ:Toxicological response to total VOC:comfort range <200µg/m3multifactorial exposure range 200-3000µg/m3discomfort range 3000-25000µg/m3toxic range >25000µg/m3.

Example – Acousticshealth – Noise at work regulations (SPL(Leq)<85dBA)comfort – NR<35 in offices

British Standards: PD CR 1752 criteria:

CIBSE comfort criteria: Sports Hall

Winter dry resultant temp: 13-16°C (for clothing level 0.4clo ; activity 3met)

Summer dry resultant temp: 14-16°C (for clothing level 0.35clo ; activity 3met)

Air supply rate: 8 litres/s/personMaintained illuminance: 300 luxNoise Rating: NR40-50

CIBSE comfort criteria: general office

Winter dry resultant temp: 21-23°C (for clothing level 0.85clo ; activity 1.2met)

Summer dry resultant temp: 22-24°C (for clothing level 0.7clo ; activity 1.2met)

Air supply rate: 8 litres/s/personMaintained illuminance: 500 luxNoise Rating: NR35

CIBSE comfort criteria: library reading rooms

Winter dry resultant temp: 22-23°C (for clothing level 1.0clo ; activity 1.1met)

Summer dry resultant temp: 24-25°C (for clothing level 0.65clo ; activity 1.1met)

Air supply rate: 8 litres/s/personMaintained illuminance: 300 luxNoise Rating: NR30-35

Aircraft

Aircraft operate in an external environment hostile to human life (ambient temperatures -43˚C to -65˚C, very dry air, too low a level of partial pressure of oxygen to sustain life, periodic episodes of high ozone and pockets of air turbulence, low atmospheric pressure).

Design conditions in aircraft must be healthy, safe and comfortable for passengers and crew.

Issues are recirculation of air (typically 50%; higher values may increase ozone levels), low humidity (10-25%, even 2% has been recorded!; difficult to increase because of the risk of condensation and corrosion), chemical contamination (from lubricating oils, hydraulic fluids, exhaust fumes, de-icing fluids), ozone levels occasionally above guidelines, low pressure (equivalent to an altitude of 2000-2500m), CO2 levels higher than normal.

HEPA (High Efficiency Particulate Air) filters should filter out all bacteria, viruses and endotoxins, if maintained to a high quality.

Aircraft

For summer, ASHRAE recommend mean ambient temperature between 23-26˚C with a minimum RH of 20%. In measurements, mean air temperature was found to be poorly regulated, with cooler temperatures than recommended and PPD’s typically >50%. Other studies have reported too high temperatures.

Recommended max. CO2 levels (for health) are 5000ppm (>30000ppm is hazardous for crew members). ASHRAE recommend a 1000ppm threshold level for acceptable indoor air quality. In measurements, the comfort limit was found to be sometimes exceeded but not the health limit.

Aircraft health concerns (Inst. For Environment and Health)

Thermal comfort metrics

Dry resultant temperature:

PMV represents the 'predicted mean vote' (on the thermal sensation scale) of a large population of people exposed to a certain environment. PMV is derived from the physics of heat transfer combined with an empirical fit to sensation. It varies from +3 (hot) to –3 (cold) with 0 as the neutral temperature.

PPD is the predicted percent of dissatisfied people at each PMV. As PMV changes away from zero in either the positive or negative direction, PPD increases. Often a PMV of ±0.5 is chosen as a design criterion, giving a PPD of 10%

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Thermal comfort metrics

Dry resultant temperature as a function of activity and clothing

Draught metrics

Draught: e.g. air speed > 0.15m/s at an air temperature of 20°C (or >0.1m/s if on the back of the neck)

PD or "predicted percent dissatisfied due to draught", is a fit to data of persons expressing thermal discomfort due to draughts. The inputs to PD are air temperature, air velocity , and turbulence intensity. A 'draught' is unwanted local cooling. Thedraught risk (or PD) equation is:

PD=(34-Ta) (v-0.05)0.62 (0.37 v Tu + 3.14)

Tu is the turbulence intensity expressed as a percent. 0 represents laminar flow and 100% means that the standard deviation of the air velocity over a certain period is of the same order of magnitude as the mean air velocity. v is the air velocity (in meters per second) and Ta is the air temperature in °C.

Draught metrics

A draught rating >15% is unacceptable.

Where air speeds are >0.15 m/s, resultant temperatures should be increased to compensate for cooling effect of the air

Graph shows air speed, temperature and turbulence intensity for DR=15%

Vertical air temperature gradients

General recommendation is that temperatures between head and feet should not differ by >3°C

Asymmetric radiation

3 cases:

1. Local cooling (e.g. near cold single glazing)

2. Local heating (e.g. near adjacent radiant heaters)

3. Short wave radiation (e.g solar radiation through windows)

Suggested limit is <5% dissatisfied

Humidity

Design conditions RH >40% and <70%

Buildings with long periods of high RH are likely to experience airborne fungi, housed dust mites. For air conditioning systems, a max of 60% is recommended for typical summer temperatures

Buildings with low RH can lead to dryness and throat irritations. Humidity below 40% is acceptable for short periods.

IAQ

Building occupants are exposed to large numbers of contaminants,usually at very low concentrations (e.g. 0.1% of occupational exposure limits)

Comfort levels are acceptable if:<=50% of occupants can detect odour<=20% experience discomfort<=10% experience mucosal irritation<=5% experience annoyance

For <2% of the time.

Note: some contaminants (e.g. radon gas) are not detected by humans so do not affect comfort, but can affect health.

IAQ – identify sources

laboratories, exercise rooms, food preparation areasSpecial use areas and mixed use buildings

fire damage, microbiological growth due to flooding or to leaks from roofs or piping

Accidental eventsOther sources

volatile organic compounds or inorganic compoundsChemicals released from building components or furnishings

microbiological growth in areas of surface condensation, dry traps that allow the passage of sewer gas

Unsanitary conditions and water damage

textured surfaces such as carpeting, curtains, or other textiles, materials containing damaged asbestos

Locations that produce or collect dust or fibresBuilding components and furnishings

airborne dust or dirt, volatile organic compounds from paintMaintenance activities

cleaning materials and procedures, airborne dust or dirt (e.g., circulated by sweeping and vacuuming)

Housekeeping activitiessmoking, cooking, body odour, cosmetic odoursPersonal activitiesHuman Activities

emissions from office equipment (volatile organic compounds, ozone)

Non-HVAC equipment

dust or dirt in ductwork or other components, improper venting of combustion products, refrigerant leakage

HVAC systemEquipment

crawlspace beneath buildingsMoisture or standing water promoting excess microbial growth

radon, leakage from underground fuel tanks, landfill gasSoil gas

exhaust from local vehicles, re-entrained exhaust from building

Emissions from nearby sources

pollen, industrial pollutants, general vehicle exhaustContaminated outside airOutside the Building

ExamplesSourceCategory

IAQ – limits (ASHRAE Fundamentals)

aeroplanesoffices

<1>1

20 µg/kg200 µg/kg

electric arcingUV light sources

ozone

homes, hospitals schools, offices, public

>1n/ahumans, pets, rodents, insects, plants, fungi, humidifiers, air conditioners

viable organisms

homes, schools, offices>>13000 mg/kgcombustion, humans, petscarbon dioxide

homes, schools, offices-n/aproducts, cloth, rugs, wallboardmineral and synthetic fibres

homes, schools, offices1<106 fibres/m3fireproofingasbestos

homes, buildings>>10.1 to 200 nCi/m3building materials, groundwater, soilradon and progeny

homes, offices>10.05 to 1.0 mg/kginsulation, product binders, particleboardformaldehyde

removal inside<15 µg/ m3matches, gas stovesulphate

homes, offices, transportation, restaurants

1100 µg/m3combustion, re-suspension, heating systemtotal suspended particles without smoking

removal inside<120 µg/m3heating systemsulphur dioxide

homes, skating rinks>>1200 to 1000 µg/m3combustion, gas stoves, water heaters, driers, cigarettes, engines

nitrogen dioxide

homes, restaurants, public facilities, offices, hospitals

>1n/acombustion, solvents resin products, pesticides, aerosol sprays

organic vapours

homes, offices, cars, public facilities, bars, restaurants

>>1100 to 500 µg/m3stoves, fireplaces, cigarettes, condensation of volatiles, aerosol sprays, re-suspension, cooking

respirable particles

skating rinks, offices, homes, cars, shops

>>1100 mg/kgcombustion equipment, engines, faulty heating systems

carbon monoxide

LocationIndoor-Outdoorconcentration ratio

Possible indoor concentration

Sources of indoor pollutionPollutant

IAQ – control (AIVC Technical Note 26)

product control; restriction/interdiction, limitation of emission rates

no generally valid ventilation rates

restriction/interdiction of use of carcinogens; limitation of emission rates

for some substances, limits have been established

annoyance, irritation, health risks

Selected organic substances

replacement, local extraction, corrective measures for chimney backdraughts (e.g. adequate outside air supply)

no generally valid ventilation rates

replacement of unventedcombustion appliances, local extract ventilation

e.g.WHO guidelinesannoyance, irritation, health risks

Combustion products

radon from soil: sealing, avoiding negative pressure gradientradon from building material: balanced mechanical ventilation

no generally valid ventilation rates

sealing to the soil, avoiding negative pressure gradient

200-400 Bq/m3 as action level

health risksIndoor ionising radiation (radon)

extract ventilation at main sources and minimum whole house ventilation rate

approx. 0.5-1.0 ac/hextract ventilation in kitchen and bathroom

relative humidity below 70% is a necessary but not sufficient condition

damage to building fabric

Humidity

ventilation variable with occupancy, if occupancy predictable

8.0 l/s per person (3-4 l/s per person)

0.10% CO2(0.15% CO2)

annoyanceBody odour

tobacco smoke is the main source of particles, therefore strategy as above

17.5l/s per person (based on average smoking habits)

see above75 µg/m3see aboveParticles

restriction or separation whenever possible, adequate ventilation in large public rooms or offices if smoking allowed

50-120 m3 per cigarette or 8-20 l/s per person (moderate smoking in large rooms/offices)

restriction of smoking, separation of smokers and non-smokers

annoyance/irritation for healthy person: 1-2 ppm CO

annoyance, irritation, health risks

Tobacco smoke

Preferred strategyMinimum ventilation rateControl measures -source control

Indoor concentration limit

EffectsIndoor pollutant

Lighting

Design aims:To enable the occupant to work and move about in safetyTo enable tasks to be performed correctly and at an appropriate paceTo create a pleasing appearance

People prefer daylight, and there is a requirement to provide daylight for all workers where reasonable practicable

Lighting – example recommended lux levels

Visual tasks very difficult – very small details; very low contrast; colour judgement may be required e.g. general inspection, electronic assembly, supermarkets

1000

Visual tasks exceptionally difficult – local lighting will be an advantage e.g. finished fabric inspection

2000

Visual tasks moderately difficult – details are of moderate size; maybe low contrast; colour judgement may be required e.g. general offices, kitchens

500

Continuously occupied interiors with visual tasks moderately easy e.g. lecture rooms, sports halls

300

Continuously occupied interiors with visual tasks not requiring perception of detail e.g. foyers, dining rooms

200

Interiors used occasionally e.g. corridors100

Lighting – daylight

Design criteria are in terms of daylight factor:

If it exceeds 5% on the horizontal plane, an interior will look cheerfully daylit

If it is <2% the interior will not be perceived as well daylit –artificial lighting may need to be in constant use.

0.61Concert halls

15Museums

0.62Hospital waiting rooms

3.55Sports halls

2.55Offices – computer use

DF minimum (%)

DF average (%)

Building type

Lighting - glare

Disability glare: veiling reflections affect visibility of task by reflection from the task area (e.g. when reading on a desk or looking at a computer screen). Can be eliminated by separating all area of high luminance from areas adjacent to the task.

Discomfort glare: occurs when the brightness of a surface or luminaire is higher than recommended (it does not directly affect the visual difficulty of tasks).

Avoidance of veiling reflections