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

Transcription

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

2 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

3 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.

4 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) higher than the tested surf. Hot wall (vf = 0.2) , controlled to maintain same MRT as cool wall conditions Cool ceiling (vf = 0.12) Hot ceiling (vf = 0.12)

5 % comfortable votes for slightly cool to slightly warm sensations Sensation scales: 1. Cold 2. Cool 3. Slightly cool 4. Neutral 5. Slightly warm 6. Warm 7. Hot Comfort scales: A. Comfortable B. Slightly uncomfortable C. Uncomfortable D. Very uncomfortable E. Intolerable control hot wall Data including only comfortable votes and sensation between slightly cool to slightly warm

6 KSU results: percentage of comfortable votes for occupants experiencing neutral sensation The hot wall (130F) was found to be the most uncomfortable Comfortable (%) Control 79.5 Cool wall 87.1 Hot wall 59.5 Cool ceiling 88.0 Hot ceiling 78.8

7 Summary of DTU studies of radiant ceilings and walls on comfort Fanger et al Conditions maintained at subjects preferred temperatures Radiant test Tested surface temperatures (F) Operative temperature (F) Cool wall (vf. 0.2) Warm wall (vf. 0.2) Cool ceiling (vf. 0.11) Warm ceiling (vf. 0.12)

8 DTU found warm ceilings more uncomfortable than warm wall

9 Asymmetry limits in standards

10 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 Young men (seated, standing) and women (standing) Comfortable temperature Young women (seated) Older men (seated) Older women (seated) 75-95

11 DTU studies of floor temperature Olesen (1975, 1977). Test condition Floor conductivity Results Bare feet 10 min (16 subjects) With shoes 3 hours (85 subjects) Wood and concrete Material judged to be unimportant optimal floor surface temperature: 79 84F Optimal floor surface temperature: 77F for seated and 73F for standing; below F, the percentage of people experiencing cold feet increases rapidly

12 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.

13 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)

14 Radiation Model

15 Comfort temperatures with radiant systems using the CBE advanced comfort model Radiant floor; standing Radiant ceiling Radiant floor, seated

16 Acceptable temperatures for radiant ceiling (met = 1.2) Comfort band for T ceiling = T air

17 Acceptable temperatures for radiant floors (met = 1.2) (ºF)

18 Technology transfer

19 Method of calculating short wave solar radiation on comfort Direct solar radiation

20 Shortwave radiation webtool demo

21 Comparison with CBE advanced comfort model Azimuth 30 Azimuth 90

22 Comparison results: Solar load on the whole body (W) Azimuth Simplified method result Advanced model result Simplified method result Advanced model result Standing Seated

23 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

24 Radiant Ceiling + Acoustic Panels Velocity [m/s] If 70% of ceiling is shaded by suspended acoustic panels, cooling capacity reduced by 10-15% compared with the case without suspended ceiling Temperature [K]

25 Integrating a ceiling fan into a suspended acoustical ceiling Radiant slab Radiant slab Acoustical panels Fan blowing downwards Acoustical panels Fan blowing upwards

26 Radiant Ceiling + Acoustic Panels + Fan 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%

27 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 s study in 1979 on 16 college students