Comfort and performance improvement through the use of cooling vests for construction workers

Purpose – The purpose of this study is to analyze the question “ In what order of magnitude does the comfort and performance improvement lie with the use of a cooling vest for construction workers? ” . Design/methodology/approach – The use of personal cooling systems, in the form of cooling vests, is not onlyintendedtoreducetheheatload,inordertopreventdisruptionofthethermoregulationsystemofthebody, butalsotoimproveworkperformance.Acalculationstudywascarriedoutonthebasisoffourvalidatedmathematicalmodels,namelyacoolingvestmodel,athermophysiologicalhumanmodel,adynamicthermal sensationmodelandaperformancelossmodelforconstructionworkers. Findings – Theuse of acoolingvest has a significant beneficialeffect onthe thermal sensationand the loss of performance, depending on the thermal load on the body. Research limitations/implications – Each cooling vest can be characterized on the basis of the maximum cooling power (Pmax; in W/m 2 ), the cooling capacity (Auc; in Wh/m2) and the time (tc; in minutes) after which thecoolingpowerisnegligible.Inordertoobjectivelycomparecoolingvests,a(preferablyInternationaland/or European)standard/guidelinemustbecompiledtodeterminethecoolingpowerandthecoolingcapacityofcoolingvests. Practicalimplications – Itisrecommendedtoimplementtheuseofcoolingvestsintheconstructionprocess so that employees can use them if necessary or desired. Social implications –


Introduction
Climate change, resulting in global warming, is one of the biggest problems of our time.Rising outdoor temperatures will continue in the 21st century, with a greater frequency and IJCST 35,1 duration of heat waves.Some regions of the world are more affected than others.Europe is one of the regions of the world where rising global temperatures will adversely affect public health; especially that of the labor force, resulting in a decline in labor productivity.It will be clear that in many situations air conditioning is not an option because it does not provide sufficient cooling or it is a very expensive investment; for example, in the situation of construction work.In such a situation, personal cooling systems, such as cooling vests, can be an efficient and financially attractive solution to the problem of discomfort and heat stress.The use of personal cooling systems, in the form of cooling vests, is not only intended to reduce the heat load, in order to prevent disruption of the thermoregulation system of the body, but also to improve work performance.The question is "In what order of magnitude does the comfort and performance improvement lie with the use of a cooling vest for construction workers?".To answer this question, a calculation study was carried out on the basis of four validated mathematical models, namely a cooling vest model linked to a thermophysiological human model, a dynamic thermal sensation model and a performance loss model for construction workers.The starting points, the calculation results as well as the findings are set out in this paper.

Cooling power and cooling capacity cooling vest
As yet there is no standard or guideline that states how the cooling power, the cooling capacity and the maximum cooling time of a cooling vest should be determined.In practice, it is therefore difficult to objectively compare cooling vests and to make an optimal choice for a specific type of work and working environment.
However, each cooling vest can be characterized on the basis of the maximum cooling power (Pmax; in W/m 2 ), the cooling capacity (Auc; in Wh/m2) and the time (tc; in minutes) after which the cooling power is negligible, namely 20 W/m 2 .The cooling capacity of a cooling vest is then approximately 10% of the amount of heat produced per m 2 -body surface, with a metabolism of 58.2 W/m 2 (a sitting activity; the surface of the trunk is approximately 30% of the total body surface).Ergo, below this value it can be assumed that a cooling vest provides the body insufficient cooling (Figure 1) (Ciuha et al., 2020).
(3) Hybrid cooling vests (P max 5 57-75 W/m 2 ,t C 5 194-226 min., Auc 5 127-146 Wh/m 2 ) (e.g.Inuteq International B.V.) Ad 1 a.Air cooling vests Air-cooled vests provide a constant flow of (cooled) ambient air or (cooled) compressed air into the micro space between the torso and vest, promoting heat dissipation through evaporation of sweat and convection around the torso of the body.As a result, the cooling Use of cooling vests for construction workers efficiency depends, among other things, on the moisture of the skin and the air that is drawn in.Actively cooled vests allow only limited freedom of movement when connected to a device that supplies air.There is no such limitation with fans in a cooling vest that are powered by a battery.

Ad 1 b. Liquid-perfused cooling vests
In a liquid-cooled vest, a cooled liquid, usually water, circulates through small tubes, close to the skin, through the fabric of the vest.The liquid is pumped from a container, which may or may not be contained in the vest.

Ad 2 a. Evaporative cooling vests
With this type of a cooling vest, the outside is moistened.The body is then cooled by natural evaporation.The cooling vests perform best in an environment with low humidity.The air flow around the body determines the degree of cooling.It is therefore important that no other clothing is worn over the cooling vest.

Ad 2 b. Vests with PCM and gel inserts
In this type of vest there is room for exchangeable cooling elements, consisting of a so-called PCM or a gel.The elements extract heat from the body through phase change (melting) and conduction.This type of vest is suitable in warm and humid environments and to be worn under protective clothing; for example, in melting, welding or extinguishing work.
Ad 3. Hybrid cooling vests Hybrid cooling vests combine two or more of the cooling concepts described above.

Thermophysiological human model of Stolwijk
For the calculation study, use was made of the mathematical thermophysiological human model of Stolwijk, developed on behalf of National Aeronautics and Space Administration (NASA).The Stolwijk model consists of six segments (namely the head, the trunk, the arms, the hands, the legs and the feet), each with four layers (namely the core, the muscles, the fat layer and the skin layer).The head is represented as a sphere.The other segments are represented as cylinders.Each cylinder consists of the aforementioned four layers.An extra element is the blood, which transfers the heat via convection from and to the layers and from and to the segments themselves.For the parts that are in contact with the environment, the mathematical relationships apply for heat loss via radiation, convection and evaporation as well as the influence of the clothing.For each component, dynamic energy balances are drawn up, the metabolism is calculated and the blood flow is determined.The cardiac output, heat production and heat losses through evaporation, etc. are obtained by summing them over the segments.The skin blood flow and average skin temperature are calculated by summing the skin blood flow and the skin temperature of each segment, weighted by skin area.Likewise, the average body temperature is obtained from the average of all segment temperatures with their specific heat capacity as a weighting factor.The total heat storage for the whole body is obtained by summing the individual storage per segment.The model can be used to simulate thermophysiology, thermal perception and performance loss under dynamic conditions.For detailed information about the model, please refer to the literature (Roelofsen, 2016).The cooling power of a cooling vest, as shown graphically in Figure 1, is built into the Stolwijk model.

ASHRAE 7-point scale
To quantify the thermal sensation, the 7-point psycho-physical ASHRAE scale is used: In general, a thermal sensation of À0.5 to 0.5 is used for the comfort zone, in accordance with category II in NEN-EN-15251 (NEN-EN-15251, 2007).See the green-shaded area in the figures.

Dynamic thermal sensation (DTS)
In the Stolwijk model, an equation is included to predict the thermal sensation under dynamic conditions, the so-called dynamic thermal sensation (DTS), originally developed by Fiala (1998), based on the simulated core temperature and the mean skin temperature.The equation for predicting the thermal sensation is based on a large number of independent experiments.Using a multivariate analysis, it was found that the mean skin temperature, the core temperature and the rate at which the mean skin temperature changes are the parameters affecting the thermal sensation under dynamic conditions.The thermal sensation was assessed on the basis of the ASHRAE 7-point scale.The DTS is calculated as follows:

Use of cooling vests for construction workers
Performance loss as a function of the thermal sensation Mohamed and Korb (2002) found relationships for the performance loss of light, mediumheavy and heavy construction work as a function of the thermal sensation, based on 200 datasets of research conducted by several other scientists.The relationships derived by them were later tested in practice and slightly modified (Mohamed and Korb, 2003) Experiments showed that the predicted DTS and the PMV were in agreement (Fiala, 1998), so in this study the DTS is used instead of the PMV.

Variant calculations
To get an impression of the comfort and performance improvement through the use of a cooling vest for construction workers, a few variant calculations were performed using the aforementioned human model.The following principles have been used for this: [À]; for ΔT sk,m < 0 ΔT sk,m 5 (T mean skin -34.4) [K] ø 5 b 1 *exp(b 2 /(ΔT hy þ0.4)þb 3 / (ΔT sk,m À4)) [À]; ø 5 0 when ΔT hy þ0.4 ≤ 0 or ΔT sk,m À4 ≥ 0 The scenario considered concerns an hour of sedentary activity, then an hour of light/ medium-heavy or heavy activity, half an hour of sedentary activity, one hour of light/ medium-heavy or heavy activity and finally another half hour of sedentary activity.The first situation concerns activities, varying from light, medium-heavy and heavy, without the use of a cooling vest (Figures 2, 4, and 6).In the second situation (Figures 3, 5, and 7), it is assumed that a cooling vest will be worn after 150 min at the start of the activity.It can clearly be seen to what extent the thermal sensation and the loss of performance, as a result of the thermal load, are influenced by the cooling with a cooling vest.
The calculation results are shown graphically in Figures 2-7.
The improvement of the thermal sensation (ΔTSV) as well as the reduction in performance loss (ΔPerf), after 210 min, due to the use of a cooling vest, depending on the activity, are shown in Table 1.
In order to gain an impression of the influence of the cooling power curve on the thermal sensation and the loss of performance, two additional variant calculations were performed for light activity.The cooling capacity of the cooling vests are the same (i.e. 90 Wh/m 2 ), but the cooling power per time unit differs from each other (see Figure 8).
The calculation results are shown graphically in Figures 9 and 10. (5) The performance improvement through the use of a cooling vest is relatively the greatest in medium-heavy activities (6) In situations where air conditioning is not an option, the use of cooling vests is an efficient and financially attractive solution to the heat stress of construction workers, as, the investment is small it increases the allowable exposure time under warm conditions it improves physical and cognitive performance it, after exertion and strain, promotes comfort and recovery and reduces fatigue (7) It is recommended to implement the use of cooling vests in the construction process so that employees can use them if necessary or desired.
Figure 2. Thermal sensation and performance loss.Without a cooling vest.Light activity