Thermal Comfort in the Edward Arens, PhD Center for the ...Thermal Comfort in the Context of Radiant Systems Edward Arens, PhD Center for the Built Environment University of California

Thermal Comfort in the Context of Radiant Systems

Edward Arens, PhDCenter for the Built Environment

University of California Berkeley

Overview of talk

• A brief summary of research up to now– Radiant walls, ceilings, and floors

• Kansas State University (KSU) • Danish Technical University (DTU)

• Radiation and surface temperature limits in standards• Modeling radiant effects

– Comfort with radiant ceilings and floors– Shortwave (solar) radiation and comfort

• Radiation and comfort in systems– Radiant cooling when accompanied by fans– Displacement ventilation and stratification limits

KSU radiant wall study

Under non-extreme conditions (overall sensation between ‘cool’ and ‘warm’), Schlegel and McNall (1968) found that a wall 6.7C (12F) warmer or cooler than the rest of the surfaces was not noticeably different from uniform surfaces throughout.

KSU tests of radiant walls and ceilings under wider temperature ranges

The authors then examined the impact of hot and cool walls and ceilings, with a wider range of radiation asymmetries (McNall and Biddison 1970).

The room air temperatures were maintained at various levels. A control test was also conducted with a neutral uniform environment (78F).

Test configuration(vf = view factor)

Test surface temperature (F)

Remaining room surface temperatures (F)

Cool wall (vf = 0.2) 48-76 20 higher than the tested surf.

Hot wall (vf = 0.2) 130 55 – 85, controlled to maintain same MRT as cool wall conditions

Cool ceiling (vf = 0.12) 51 80

Hot ceiling (vf = 0.12) 130 61

% “comfortable” votes for “slightly cool” to “slightly warm” sensations

Sensation scales:1. Cold2. Cool3. Slightly cool4. Neutral5. Slightly warm6. Warm7. Hot

Comfort scales:A. ComfortableB. Slightly uncomfortableC. UncomfortableD. Very uncomfortableE. Intolerable

Data including only “comfortable” votes and sensation between “slightly cool” to “slightly warm”

hot wall

control

KSU results: percentage of “comfortable” votes for occupants experiencing “neutral” sensation

Comfortable (%)

Control 79.5

Cool wall 87.1

Hot wall 59.5

Cool ceiling 88.0

Hot ceiling 78.8

The hot wall (130F) was found to be the most uncomfortable

Summary of DTU studies of radiant ceilings and walls on comfort

Fanger et al. 1985 Conditions maintained at subjects’ preferred temperatures

Radiant test Tested surface temperatures (F)

Operative temperature (F)

Cool wall (vf. 0.2) 33 - 64 76

Warm wall (vf. 0.2) 91 - 158 74.3

Cool ceiling (vf. 0.11) 33 - 61 73

Warm ceiling (vf. 0.12) 93 - 156 75.7

DTU found warm ceilings more uncomfortable than warm wall

Asymmetry limits in standards

KSU studies of floor temperatures

(Nevins et al. 1958, 1964, 1967, Michaels et al. 1964) Activities: three hours of simulated light office work:

seated (reading) and standing (writing and sorting bibliography cards)Clothing: summer clothing, with shoes

Subjects and test conditions Comfortable temperature

Young men (seated, standing) and women (standing)

56 – 90

Young women (seated) 56 – 85

Older men (seated) 75 – 100

Older women (seated) 75 - 95

DTU studies of floor temperature

Olesen (1975, 1977).

Test condition Floor conductivity Results

Bare feet 10 min (16 subjects)

Wood and concrete optimal floor surface temperature: 79 – 84F

With shoes 3 hours (85 subjects)

Material judged to be unimportant

Optimal floor surface temperature:77F for seated and 73F for standing; below 68 – 71.4F, the percentage of people experiencing cold feet increases rapidly

Comfortable floor temperatures

Olesen (1997) recommended:• Shoes: 20 – 28C (68 - 82F)• Bare feet: 23 – 30C (73 – 86F)

ASHRAE and ISO standards:• 19 – 29C (66 – 84F) for 10% dissatisfaction, based on Olesen’s studies.

CBE Comfort Model

• 16 body segments

• Transient

• Blood flow model

• Heat loss by evaporation(sweat), convection, radiation, and conduction

• Clothing model (including heat and moisture transfer)

Radiation Model

Comfort temperatures with radiant systems using the CBE advanced comfort model

Radiant ceiling

Radiant floor, seated

Radiant floor; standing

Acceptable temperatures for radiant ceiling (met = 1.2)

Comfort band for Tceiling = Tair

60.8 62.6 64.4 66.2 66.2 68 69.8 71.6 73.4 75.2 77 78.8 80.6 82.4 (ºF)

140

122

104

86

68

50

Acceptable temperatures for radiant floors (met = 1.2)

Technology transfer

Method of calculating short wave solar radiation on comfort

Direct solar radiation

Shortwave radiation webtool demo

http://smap.cbe.berkeley.edu/comforttool/

Comparison with CBE advanced comfort model

°

Azimuth 30° Azimuth 90°

Azimuth° 0 30 90 120 180

Standing

Simplified method result

170 165 140 148 165

Advanced model result

157 169 125 144 160

Seated

Simplified method result

178 173 159 145 126

Advanced model result

150 162 145 144 120

Comparison results: Solar load on the whole body (W)

Radiant slabs and suspended acoustic ceilings

Background

Bare concrete slabs are highly sound-reflective

Vertical-wall acoustic panels are ten times more expensive then ceiling panels

Suspended panels reduce cooling capacity of thermally activated concrete slabs

Suspended panels covering 60% of slab are acoustically equal to 100% coverage

Source: Crocker Higgins, 2012

Radiant Ceiling + Acoustic Panels

If 70% of ceiling is shaded by suspended acoustic panels, cooling capacity reduced by 10-15% compared with the case without suspended ceiling

Velocity[m/s]

Temperature[K]

Radiant slab

Acoustical panels

Fan blowing downwards

Radiant slab

Acoustical panels

Fan blowing upwards

Integrating a ceiling fan into a suspended acoustical ceiling

Panels coverage

No fan

Fan down

Fan up

0% (baseline) 100% ND ND

26% 96% 144% 144%

35% 91% 139% 153%

43% 88% 139% 154%

56% 88% 139% 151%

68% 89% 132% 152%

Radiant Ceiling + Acoustic Panels + Fan

Impact of stratification on thermal comfort

ASHRAE 55 and ISO 7730 define a 5°F (3°C) limit on vertical air stratification between head and foot heights for standing occupants; or ~2°C/m

The limit was based on Olesen’sstudy in 1979 on 16 college students