Design Considerations For

Human Comfort and Health Design considerations for: thermal, lighting and acoustic comfort indoor 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 Handbook Standards: 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 25000µg/m3.

Example – Acoustics

health – Noise at work regulations (SPL(Leq)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:

θ res

. θa v θ mrt + 317 = 1 + 317 . v ≈ 1 2 θ mrt + 1 2 θ a for v ≤ 01 . m/s

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%

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. The draught 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 40% and >1

skating rinks, offices, homes, cars, shops homes, offices, cars, public facilities, bars, restaurants homes, restaurants, public facilities, offices, hospitals homes, skating rinks

20 µg/m3

>1

homes, buildings

asbestos

fireproofing

>1

homes, schools, offices

viable organisms

humans, pets, rodents, insects, plants, fungi, humidifiers, air conditioners electric arcing UV light sources

n/a

>1

20 µg/kg 200 µg/kg

1

homes, hospitals schools, offices, public aeroplanes offices

respirable particles organic vapours nitrogen dioxide sulphur dioxide

ozone

IAQ – control (AIVC Technical Note 26) Indoor pollutant

Effects

Indoor concentration limit

Control measures source control

Minimum ventilation rate

Preferred strategy

Tobacco smoke

annoyance, irritation, health risks

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

restriction of smoking, separation of smokers and non-smokers

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

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

Particles

see above

75 µg/m3

see above

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

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

Body odour

annoyance

0.10% CO2 (0.15% CO2)

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

ventilation variable with occupancy, if occupancy predictable

Humidity

damage to building fabric

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

extract ventilation in kitchen and bathroom

approx. 0.5-1.0 ac/h

extract ventilation at main sources and minimum whole house ventilation rate

Indoor ionising radiation (radon)

health risks

200-400 Bq/m3 as action level

sealing to the soil, avoiding negative pressure gradient

no generally valid ventilation rates

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

Combustion products


e.g.WHO guidelines

replacement of unvented combustion appliances, local extract ventilation


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

Selected organic substances


for some substances, limits have been established

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


product control; restriction/interdiction, limitation of emission rates

Lighting Design aims: To enable the occupant to work and move about in safety To enable tasks to be performed correctly and at an appropriate pace To 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 100

Interiors used occasionally e.g. corridors

200

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

300

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

500

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

1000

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

2000

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

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