Automatic estimation of clothing insulation rate and metabolic rate for dynamic thermal comfort assessment

Abstract

Existing heating, ventilation, and air-conditioning systems have difficulties in considering occupants’ dynamic thermal needs, thus resulting in overheating or overcooling with huge energy waste. This situation emphasizes the importance of occupant-oriented microclimate control where dynamic individual thermal comfort assessment is the key. Therefore, in this paper, a vision-based approach to estimate individual clothing insulation rate ($I_{\rm{cl}}$) and metabolic rate (M), the two critical factors to assess personal thermal comfort level, is proposed. Specifically, with a thermal camera as the input source, a convolutional neural network (CNN) is implemented to recognize an occupant’s clothes type and activity type simultaneously. The clothes type then helps to differentiate the skin region from the clothing-covered region, allowing to calculate the skin temperature and the clothes temperature. With the two recognized types and the two computed temperatures, $I_{\rm{cl}}$ and M can be estimated effectively. In the experimental phase, a novel thermal dataset is introduced, which allows evaluations of the CNN-based recognizer module, the skin and clothes temperatures acquisition module, as well as the $I_{\rm{cl}}$ and M estimation module, proving the effectiveness and automation of the proposed approach.

Appendix

According to Annex H of ISO 9920 [18], $I_{\rm{cl}}$ can be calculated from the mass of the clothes and the body surface area covered by clothing, that is

$$\begin{aligned} \begin{aligned} I_{\rm{cl}}\,=&0.919+0.255 \times 10^{-3}\cdot m-0.00874\cdot A_{\rm{cov}, 0}\\&-0.00510\cdot A_{\rm{cov}, 1} \end{aligned} \end{aligned}$$

(9)

where m is the mass of the clothes, without shoes, in grams; $A_{cov,0}$ is the body surface area not covered by clothing; $A_{cov,1}$ is the body surface area covered by a single clothing layer; both $A_{cov,0}$ and $A_{\rm{cov},1}$ are expressed as percentages of the total body surface area shown in Table 13.

Table 13 Body surface area percentage [18]

When a person rolls up the sleeves or unzips the zipper, the mass of the clothes remains the same, while the $A_{cov,0}$ or the $A_{cov,1}$ is changed, leading to a correction in $I_{\rm{cl}}$ by Eqs. (4, 5 or 6) in Sect. 3.3.

According to Section 9 of ISO 9920, when a person is sitting, the compressed air between the body and the clothes leads to a decrease in $I_{\rm{cl}}$ by 6–18%. Office chairs introduce an increase in $I_{\rm{cl}}$ of 0.04–0.17 clo. We use the median values of these fluctuations as 12% and 0.105 clo, respectively, and get Eq. (7) in Sect. 3.3.

According to Section 8.2 of ISO 9920, the dynamic clothing insulation rate $I_{cl,d}$ under a condition having air and body movement can be calculated from

$$\begin{aligned}I_{cl,d}=\frac{(0.6-I_{cl,s})\cdot I_{a,d}+I_{cl,s}\cdot I_{t,d}}{0.6}-I_{a,d}\,\,(0< I_{cl,s} \le 0.6) \end{aligned}$$

(10)

$$\begin{aligned}I_{cl,d}=I_{t,d}-I_{a,d}\,(0.6< I_{cl,s} < 1.4) \end{aligned}$$

(11)

$$\begin{aligned}&I_{t,d}=I_{t,s}\cdot C_{t} \end{aligned}$$

(12)

$$\begin{aligned}&I_{a,d}=I_{a,s}\cdot C_{a} \end{aligned}$$

(13)

$$\begin{aligned}&I_{t,s}=I_{cl,s}+I_{a,s} \end{aligned}$$

(14)

$$\begin{aligned}&C_{t}=e^{\left[ -0.281\cdot \left( v_{\rm{{a}}}-0.15\right) +0.044\cdot \left( v_{\rm{{a}}}-0.15\right) ^{2}-0.492\cdot v_{\rm {w}}+0.176\cdot v_{\rm{{w}}}^{2}\right] } \end{aligned}$$

(15)

$$\begin{aligned}&C_{a}=e^{\left[ -0.533\cdot \left( v_{\rm{{a}}}-0.15\right) +0.069\cdot \left( v_{\rm{{a}}}-0.15\right) ^{2}-0.462\cdot v_{\rm{{w}}}+0.201\cdot v_{\rm{{w}}}^{2}\right] } \end{aligned}$$

(16)

where $I_{t,d}$, $I_{a,d}$, $I_{cl,s}$, $I_{t,s}$, $I_{a,s}$, $v_{a}$, and $v_{w}$ are the dynamic total thermal insulation, the dynamic air insulation, the static clothes insulation, the static total insulation, the static air insulation, the relative air velocity in relation to human motion, and the human motion velocity, respectively.

As Section 6 of ISO 9920 mentions, the static air insulation $I_{a,s}$ in most studies is around 0.7 clo. When the human motion velocity is $\hbox {1}\rm{m/s}$, for a wind-free environment (air velocity is smaller than $\hbox {0.2}\rm{m/s}$), the relative air velocity in relation to human motion is about $\hbox {1}{m/s}$, and then from Eqs. (10)–(16), Eq. (8) in Sect. 3.3 is derived.