Thermal Physiology and Comfort

Thermal physiology and comfort

Hui Zhang Center for the Built Environment University of California at Berkeley Presentation outline

. 1) Distributions and characteristics of thermoreceptors of human body . 2) “Alliesthesia” . 3) The CBE advanced thermal comfort model

November 12 2013, ARPA-E Workshop 1) Distributions and characteristics of thermoreceptors of human body

November 12 2013, ARPA-E Workshop Thermoreceptors – source of thermal sensation

(°F) 32 41 50 59 68 77 86 95 104 113 122 131 140

Impulse frequency (firing rate, imp./sec) Skin temperature

November 12 2013, ARPA-E Workshop Depth of cold and warm thermoreceptors

epidermis Cold thermal receptors: 0.15 – 0.17 mm, immediately beneath the epidermis

Warm receptors: 0.3 – 0.6 mm, upper layer of the dermis

dermis

Schematic representation of a cold receptor (Hensel, 1974)

November 12 2013, ARPA-E Workshop Thermoreceptors distributions

Cold receptors Warm receptors (from Strughold Cold receptors (from Rein 1925) 1931) Number of cold and warm spots per cm2 in human skin

cold receptors warm receptors

Warm receptors

Cold (dots) and warm (triangles) spots mapping over 100 cm2 of the dorsal side of the forearm (Strughold, 1931)

from Strughold from Rein

November 12 2013, ARPA-E Workshop Dynamic response of thermoreceptors

November 12 2013, ARPA-E Workshop 2) “Alliesthesia”

November 12 2013, ARPA-E Workshop Word created by Cabanac in 1970s

Neutral whole-body Hyperthermic Hypothermic

Cabanac (1969)

Mower (1976) Alliesthesia: esthesia (sensation) and allios (changed) Animal behavior is triggered by internal Hensel signals “milieu interieur” (1982)

November 12 2013, ARPA-E Workshop What is alliesthesia

. Sensory pleasure with variation. In transient or non-uniform environments, an environmental stimulus that has the prospect of restoring body to thermal comfort, that is perceived as very pleasant (positive alliesthesia)

November 12 2013, ARPA-E Workshop Testing sensitivities of cooling/heating on each of 16 body parts

November 12 2013, ARPA-E Workshop What we saw in our lab studies

Neutral condition

warm body applying foot cooling cold body applying foot heating cold body applying foot cooling

4 very comfortable

2 comfortable

just comfortable 0 -6 -4 -2 0 2 4 Foot Comfort -2

-4 Foot Sensation

November 12 2013, ARPA-E Workshop Comfort in transient conditions

comfort overshoot - alliesthesia

November 12 2013, ARPA-E Workshop A paradigm shift in the notion of comfort

A word that might fundamentally change the approach to providing thermal comfort

•Static and isothermal neutral environments are energy intensive and incapable of satisfying more than 80% of an occupancy •A more thermally dynamic and non-uniform environment would satisfy more, even to the point of delight, and focus energy use where it is needed

November 12 2013, ARPA-E Workshop Two types of alliesthesia

• Temporal (transients); deDear at Sydney • Spatial (non-uniformities across the body); CBE at Berkeley

• Personal comfort systems address: o Local body segments o Spot heating/cooling within those segments o Dynamic stimuli; rates of change at neural sensor sites

November 12 2013, ARPA-E Workshop Temporal alliesthesia

November 12 2013, ARPA-E Workshop Pleasure under thermal transients

Turkish bath

Japanese hot spa

Image courtesy of Kuno

November 12 2013, ARPA-E Workshop Preference for natural over constant wind

Airspeed turbulence testing at Tsinghua University 2000-2012

constant simulated since curve stochastic nature wind

November 12 2013, ARPA-E Workshop Spatial alliesthesia

November 12 2013, ARPA-E Workshop Pleasure from non-uniform thermal stimuli

November 12 2013, ARPA-E Workshop CBE spot heating chair

control panel and occupancy sensor

• Heating: 5% of the seat area •Can maintain comfort conditions at 60.5F

Max heating power 14 W

November 12 2013, ARPA-E Workshop A planned lab study: to apply spot heating/cooling alliesthesia

• Effective regions • Effective spot heating/cooling sizes • Effective thermal stimulus temperatures

November 12 2013, ARPA-E Workshop 3) The UCB multi-segment thermal comfort model

November 12 2013, ARPA-E Workshop UCB 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)

November 12 2013, ARPA-E Workshop Radiation calculation

November 12 2013, ARPA-E Workshop Solar load on the body

November 12 2013, ARPA-E Workshop Extremity blood flow model

skin skin skin fat

fat

muscle

core

core core core fat skin fat skin fat skin

muscle

Upper Arm Lower Arm Hand

November 12 2013, ARPA-E Workshop Body builder

The UCB “Body Builder” will translate simple parameters (height, weight, gender, age, body fat) into physiological parameters for the thermal comfort model (blood volume, surface area, thermal conductivity, basal metabolic rate, etc.).

Differences in Physiology

November 12 2013, ARPA-E Workshop Model output

My leg is Overall, uncomfortable I’m warm

My leg Overall, I’m is cold uncomfortable

The UCB Comfort Model predicts local sensation and comfort as well as overall sensation and comfort.

November 12 2013, ARPA-E Workshop Local comfort model for each body part

Warmer overall Cooler overall thermal state thermal state Warmer overall thermal state

November 12 2013, ARPA-E Workshop Impact of local body part cooling/heating on whole-body sensation – an alliesthesia model

Swhole-body = Swhole,bigger-group + [delta Soverall,max + 10% delta Soverall,second max ]

November 12 2013, ARPA-E Workshop Local body parts cooling/heating

• Independent heating and cooling of 16 body parts using air sleeves

• 109 tests performed

Validation test in Delphi Wind Tunnel

November 12 2013, ARPA-E Workshop Subjective voting scales

Please rate your overall thermal sensation: Please rate your overall thermal comfort: very cold -4 very comfortable 4 cold -3 comfortable 2 cool -2 slightly cool -1 just comfortable 0 neutral 0 just uncomfortable -0 slightly warm 1 warm 2 uncomfortable -2 hot 3 very hot 4 very uncomfortable -4

Sensation and comfort votes were collected for each body part as well as for the whole body (‘overall’)

November 12 2013, ARPA-E Workshop Skin temperature measurements

November 12 2013, ARPA-E Workshop Core temperature measurement

CorTemp wireless system provides continuous core temperature measurement

November 12 2013, ARPA-E Workshop Conclusions

. Local body part (or even spot) cooling/heating could provide comfort (thermal pleasure, alliesthesia) . Research needed to examine effective spot cooling/heating areas for different body parts; the results can be directly applied to local alliesthesia-based personal comfort devices.

November 12 2013, ARPA-E Workshop Questions?

November 12 2013, ARPA-E Workshop