Center for the Built Environment October 2013

Transcription

1 Thermal Comfort in the Context of Radiant Systems Center for the Built Environment University of California Berkeley Center for the Built Environment October 2013 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 Radiant Energy Seminar 10/16/2013 1

2 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). Neutral overall temperatures were not always preserved. 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) Radiant Energy Seminar 10/16/2013 2

3 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 Summary of DTU studies of radiant ceilings and walls on comfort Fanger et al Conditions maintained at subjects neutral temperatures Radiant test Tested surface Operative temperature (F) temperatures (F) Cool wall (vf. 0.2) Warm wall (vf. 0.2) Cool ceiling (vf. 0.11) Warm ceiling (vf. 0.12) Radiant Energy Seminar 10/16/2013 3

4 DTU found warm ceilings more uncomfortable than warm wall Asymmetry limits in standards Radiant Energy Seminar 10/16/2013 4

5 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) 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 Radiant Energy Seminar 10/16/2013 5

6 Limits to 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) Radiant Energy Seminar 10/16/2013 6

7 Radiation Model Comfort temperatures with radiant systems using the CBE advanced comfort model Radiant floor; standing Radiant ceiling Radiant floor, seated Radiant Energy Seminar 10/16/2013 7

8 Acceptable temperatures for radiant ceiling (met = 1.2) Comfort band for T ceiling = T air Acceptable temperatures for radiant floors (met = 1.2) (ºF) Radiant Energy Seminar 10/16/2013 8

9 Technology transfer CBE Comfort Web Tool Added a feature to evaluate short wave solar radiation on comfort indoors Method of calculating short wave solar radiation on comfort Direct solar radiation Radiant Energy Seminar 10/16/2013 9

10 Shortwave radiation webtool demo Comparison with CBE advanced comfort model CBE advanced comfort model calculates solar load on a person by dividing the human model into 5000 polygons Comparison were done for standing, seated, azimuth 0, 30, 60, 90, 120, 180 Azimuth 30 Azimuth 90 Radiant Energy Seminar 10/16/

11 Comparison results: Solar load on the whole body (W) Azimuth Standing Simplified method result Advanced model result Seated Simplified method result Advanced model result 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 Energy Seminar 10/16/

12 Radiant Ceiling + Acoustic Panels Velocity [m/s] If 70% of ceiling is obstructed by suspended acoustic panels, cooling capacity reduced by 10 15% compared with the case without suspended ceiling Temperature [K] Integrating a ceiling fan into a suspended acoustical ceiling Radiant slab Radiant slab Acoustical panels Fan blowing downwards Acoustical panels Fan blowing upwards Radiant Energy Seminar 10/16/

13 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% 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 seated occupants; or ~3 C/m The limit was based on Olesen s study in 1979 on 16 college students Other researchers have found the stratification limit to be within 3 5 C/m or greater. Radiant Energy Seminar 10/16/

14 Summary of suggest limits from literature Study Limit Observations McNair 1973 & F 6-11 F Wyon and Sandberg F Ilmarinen and Palonen to 9 F Wyon and Sandberg 1993 & 1996 Kawahara F Yu, 2006, F ±6 F for male and 11 for female ±11 F No discomfort; gradient was insignificant discomfort not due to stratification, but tolerance for raised temperature in the breathing zone it is surprising to note how small effect the temperature gradient has on acceptance thermal gradient had no significant effect local discomfort due to cold feet, not due to the asymmetry winter tests summer tests Olesen F gradient effect was insignificant Tanaka F (25 20C) Eriksson F (reverse stratification) Discomfort does happened at 25 30C environments (overall warm) Heavy outdoor clothing (1.5 2 clo) Questions Radiant Energy Seminar 10/16/

15 Model results Operative temperature (ºF) Acceptable Stratification (ºC) ASHRAE 55 and ISO Class B limit Operative temperature (ºC) Stratification is defined as: T air,head T air,feet Radiant Energy Seminar 10/16/