thermal comfort in the edward arens, phd center for the ...thermal comfort in the context of radiant...
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Thermal Comfort in the Context of Radiant Systems
Edward Arens, PhDCenter for the Built Environment
University of California Berkeley
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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
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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.
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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
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% “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
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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
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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
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DTU found warm ceilings more uncomfortable than warm wall
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Asymmetry limits in standards
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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
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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
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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.
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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)
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Radiation Model
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Comfort temperatures with radiant systems using the CBE advanced comfort model
Radiant ceiling
Radiant floor, seated
Radiant floor; standing
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Acceptable temperatures for radiant ceiling (met = 1.2)
Comfort band for Tceiling = Tair
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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)
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Technology transfer
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Method of calculating short wave solar radiation on comfort
Direct solar radiation
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Shortwave radiation webtool demo
http://smap.cbe.berkeley.edu/comforttool/
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Comparison with CBE advanced comfort model
°
Azimuth 30° Azimuth 90°
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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)
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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
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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]
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Radiant slab
Acoustical panels
Fan blowing downwards
Radiant slab
Acoustical panels
Fan blowing upwards
Integrating a ceiling fan into a suspended acoustical ceiling
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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
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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