In this study, using construction activities as an example, a proposal is made for the time-dependent prediction of the thermal sensation and the performance loss using a cooling vest, under transient conditions. The approach presented here can, mutatis mutandis, be used for any work activity and the use of a cooling vest, whether or not in a building.

This paper has the objective to initiate a discussion on potential improvements or extension of the validity of the original equation of the Predicted Percentage of Dissatisfied (PPD), according to (NEN-)EN-ISO 7730. This paper is to be regarded as a supplement to a paper on a re-derivation of the PMV equation in the Fanger model (Roelofsen, Jansen, and Vink 2021). In practice, in scientific research it regularly appears that the PMV (Predicted Mean Vote), and by extension the PPD, are applied outside the range based on which the PMV and the PPD equation are derived. In practice, this can occur, for example, in the evaluation of the measurement or calculation of temperature exceedances in a room, for sedentary activities. As it turns out, a PMV equation with an application of −3 to 3, for at least sedentary activities, would be useful in the different fields of study. For that reason, Roelofsen has adapted the PMV equation in the (NEN-)EN-ISO model. But to what extent should the PPD equation also be adjusted? After all, the PPD is also derived from and limited to a PMV of −2 to 2, according to (NEN-)EN-ISO 7730.

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 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. A calculation study was carried out on the basis of four validated mathematical models, namely a cooling vest model, a thermophysiological human model, a dynamic thermal sensation model and a performance loss model for construction workers. Findings: The use of a cooling vest has a significant beneficial effect on the thermal sensation and 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/m²), the cooling capacity (Auc; in Wh/m2) and the time (tc; in minutes) after which the cooling power is negligible. In order to objectively compare cooling vests, a (preferably International and/or European) standard/guideline must be compiled to determine the cooling power and the cooling capacity of cooling vests. Practical implications: It is recommended to implement the use of cooling vests in the construction process so that employees can use them if necessary or desired. Social implications: Climate change, resulting in global warming, is one of the biggest problems of present times. Rising outdoor temperatures will continue in the 21st century, with a greater frequency and 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. Originality/value: The value of the study lies in the link between four validated mathematical models, namely a cooling vest model, a thermophysiological human model, a dynamic thermal sensation model and a performance loss model for construction workers.

For sedentary activities, the PMV equation, derived by Fanger, is mainly based on the research of Nevins et al. (720 test subjects). Nevins' experiments were later on repeated by Fanger, but with 128 college-age Danish subjects and 128 elderly Danish subjects, instead of American subjects. Rohles did the research from Nevins et al. again, but over a more extensive temperature range and more, namely 1600, test subjects. Rohles' research results have been partly included in the derivation of the PPD equation, but not in the derivation for the PMV equation. Rohles' experimental results are published at a later time than the publication of the thesis of Fanger. The question arises: ‘If Rohles' experimental results were included in the derivation of the PMV equation, instead of Nevins' experimental results, to what extent does that change the PMV equation and the application area of the PMV equation, with regard of validity, for sedentary activities?'. In the same way, as Fanger described in his thesis, and using the results of Rohles’ experiment, this study is limited to the derivation of a PMV equation with a wider PMV range than −2 to 2, for sedentary activities.

There are different thermal perception models linked to a mathematical thermophysiological human model, with which the thermal sensation under stationary and/or dynamic conditions can be evaluated. Each of these perception and thermophysiological models have their own field of application. Stolwijk developed a thermophysiological human model without an associated thermal perception model, which today is still the basis for other mathematical thermophysiological models. Fiala developed the FPC model, also based on the Stolwijk model, and is one of the latest developments in the field of thermophysiological human models. In the FPC model, an equation is included with which the thermal sensation under stationary and dynamic conditions can be assessed; the so-called Dynamic Thermal Sensation (DTS). The DTS equation is, however, specifically developed for use in combination with the FPC model. In contrast to the Stolwijk model, the source code of the computer programs of the later developed thermophysiological human models is not freely available, which limits the use and applicability of the models in practice. It is precise because of the availability of the source code that the Stolwijk model is still used in industry and the research world. The question, therefore, arises: ‘To what extent can a human transient thermal sensation equation be derived, combined with the Stolwijk model, in a similar way to that used for the DTS equation in the FPC model?’.

Stolwijk developed a thermophysiological human model which, to day, is still the basis and inspiration for many other thermophysiological human models. The Stolwijk model used in this study is improved with regard of the calculation of the skin temperature and equipped with clothing as well as thermal sensation. Fiala also developed a thermophysiological model, based on the Stolwijk model, and is currently considered to be the latest development in thermophysiological human models. The current version of the Fiala model is known in practice as the Fiala thermal Physiology and Comfort (FPC) model. In the FPC model an equation is included to predict the thermal sensation under dynamic conditions, the so called Dynamic Thermal Sensation (DTS), based on the simulated core temperature and the mean skin temperature. This DTS-model was developed based on the subjects’ votes in early studies, which did not involve physiological measurements; instead, Fiala used his physiology model to predict the skin and the core temperatures from environmental variables measured in the tests. The correlations are therefore specific to the Fiala physiology model. In order to find out to what extent the DTS calculation results of the modified Stolwijk model deviate from the FPC model (version 5.3), in this study a number of variant calculations were carried out. Three well described and known scientific experiments from the professional literature are used for this, for a homogenous step-change transient thermal environment and for sedentary activity.

Different researchers found an influence of the air temperature, the air humidity and the air velocity on the perceived air quality, which within the olf-decipol method of Fanger is not taken into account. It is possible, with the aid of the freshness of the air and the olf-decipol method of Fanger, to distract a methodology for the evaluation of the perceived air quality depending on the air temperature, the air humidity and the air pollution, caused by human bioeffluents. The aim of this study is to incorporate air velocity at neck height, as an extra parameter in this methodology, as well.

The key question in this study is: ‘To which extent is the difference in thermal comfort mathematically to describe by temperature sensation and the percentage of dissatisfied, between the elderly and non-elderly, related to the Fanger model?’. This study proves that it is possible to mathematically describe the difference in thermal comfort between elderly and non-elderly by means of a comparison between the calculation results of a thermophysiological two-node model, adjusted for individual characteristics, and different experimental studies. Since the various subgroups of elderly are increasing in number disproportionately to other age groups, adapting the existing thermophysiological human models, for predicting the thermal response of people depending on age and sex, is important. In this way, useful insights can be realized from modelling the thermal behaviour and response patterns of the elderly for the future design of buildings and climate installations.

BACKGROUND: The original Stolwijk model is not equipped with clothing, thermal sensation, comfort indices, individual characteristics and performance loss models. OBJECTIVE: This study attempts to modify the model to include clothing, thermal sensation as well as the calculation of the percentage of dissatisfied as a result of general discomfort. The model is useful for the evaluation of thermal comfort in the built environment by professionals. METHODS: Methods described in literature with regard of clothing, the research of Fiala as well as some in the literature recommended and validated adjustments, to improve the simulation of the skin temperature per body segment, are implemented in the here assembled Stolwijk computer model. Finally, for verification of the above adjustments, the model was compared with experiments conducted in the field of thermal sensation at various levels of temperature change. RESULTS: By improving the simulation of the skin temperature per body segment and by adding clothing and thermal sensation, suitable for the assessment of steady state and transient thermal conditions, and fixed with this the percentage of dissatisfied, the scope of the Stolwijk model has become larger than it was before. CONCLUSION: On the basis of the calculations and the experimental results, it was concluded that the adjusted Stolwijk model was suitable for the simulation of the thermal sensation under steady state and transient thermal conditions.