Assessing Thermal Comfort in Deep Underground Mines By Maurice N. Sunkpal MSc. Candidate (Mining Engineering) Advisor: Dr. Charles Kocsis Department of Mining and Metallurgical Engineering Fall-2015

Prelude Fundamentally, comfort involves a heat balance (a thermal equilibrium) … where: heat in ≈ heat out where “heat in” is provided by metabolism, radiation, conduction, convection where “heat out” is via radiation, conduction, convection, evaporation

Individual Differences  Age effects  Nationality  Sex effects  Time-of-day Non-Significant Thermal Comfort ≈ Heat balance Physiological Inputs  Metabolic rate  Clothing Yes No In Thermal Comfort Zone Out of Thermal Comfort Zone Air Temperature Air Humidity Air Velocity Radiant Temperature Climatic Parameters Prelude

1.Scope 2.Objective 3.Introduction 4.Assessing thermal climates: Related research 5.Assessing mine climates Required sweat rate Required Skin wettedness Worker safe exposure time 6.Results 6.Conclusion 7.Acknowledgements Outline

Prediction of thermal stress in conditions likely to lead to excessive dehydration in the human body Prediction of exposure times with which physiological strain is acceptable Investigation in the effects of changing the comfort parameters on required sweat rate (SWreq), skin wettedness (w) duration limit of exposure (DLE) Investigation will be used by a graduate student to assess and determine a heat stress index that will protect U/G workers in hot mines Objectives

An analytical evaluation and interpretation of thermal stress in a hot environment A method to predict required sweat rate that the human body will respond to in underground working conditions thermal stress The effects of physical and environmental parameters influence on thermal stress experienced by a mine worker Scope

Thermal Comfort: “Thermal comfort” describes a person’s psychological state of mind and is usually referred to in terms of whether someone is feeling too hot or too cold The best that you can realistically hope to achieve is a thermal environment that satisfies the majority of people in the workplace, or put more simply, “reasonable comfort”. ASHRAE considers ~80 % persons satisfied as reasonable Introduction

The most commonly used indicator of thermal comfort is air temperature not a valid or accurate indicator of thermal comfort or thermal stress Thermal comfort should always be considered in relation to other environmental and personal factors Air temperature Radiant temperature Air velocity Humidity Air temperature Radiant temperature Air velocity Humidity Clothing Insulation Metabolic heat Introduction Environmental factors Personal factors

Why is thermal comfort important? Introduction

Thermal comfort is defined as being an opinion (essentially an individual perception) A perception (condition of mind) is best assessed by asking workers (occupants) how they feel Subjective Evaluation (Asking) The traditional 7-point “status” scale: cold | cool | slightly cool | neutral | slightly warm | warm | hot An alternative “action” scale: Would you prefer: to be warmer | no change | to be cooler A post-occupancy evaluation (POE) tool If workers are in the environment being evaluated Not directly usable as a design tool There is no occupied space during design Assessing Hot Environments

Comfort = S = 0 Heat In Heat Out Assessing Hot Environments

Comfort Indices One way to evaluate thermal environment is to use thermal comfort indices, which combines two or more parameters of thermal climate into one variable. Empirical Index Direct Index Rational Index Sophisticated indices, which integrate environmental and physiological variables; they are difficult to calculate and are not feasible for daily use Assessing Hot Environments

Fangers’ PMV and PPD Models A commonly used method for assessing thermal comfort is the Fangers’ –Predicted Mean Vote (PMV) and –Predicted Percentage of Dissatisfied (PPD) Assessing Hot Environments ValueThermal Scale +3Hot +2Warm +1Slightly Warm 0Neutral Slightly Cool -2Cool -3Cold (ASHRAE, 2005) The recommended acceptable PMV range for thermal comfort from between -0.5 and +0.5 for an interior space.

Limitations of Fangers’ model The PMV equation only applies to humans exposed for a long period to constant conditions at a constant metabolic rate. PMV predicted actual thermal sensation most accurately for clothing insulation in the range 0.3 to 1.2 clo, for activity levels below 1.4 met (80 W/m 2 ). Assessing Hot Environments Range of validity for ISO 7933, 2004Fangers‘ Model ParameterMinMaxMinMax Relative humidity, RH (%) Air Temperature (tr=ta), (° C) Air Velocity, va (m/s) Clothing Insulation (clo) Metabolic rate, M (W/m 2 )

Sweat rate, Skin wettedness and Maximum exposure time Assessing Hot Environments

The method assesses comfort based on: –Required Sweat Rate, –Required Skin Wettedness, and –Maximum Worker Exposure Time These indices are predicted and compared to the allowable maximum under the prevailing thermal conditions A criteria is used for acclimatized and unacclimatized workers If required sweat rate is achieved with acceptable dehydration, no limit is put on heat exposure for the 8 hr. shift Assessing Comfort Using Sweat rate, Skin wettedness and Maximum exposure time

Assessment Methodology Climate conditions (ta,tr, va, RH) Physical parameters (clo, M) Comfort Engine Evaluate using the human balance equation Predict stress/strain (SW, TLV, w)

Limit Criteria Maximum skin wettedness, w max –0.85 for unacclimatized –1 for acclimatized Maximum sweat rate, Sw max –SWmax =2.6 X (M-58) g/h –SWmax unacclimatized = 650 – 1000 g/h Maximum dehydration, D max (which is strain criteria) –D max = lies between 3.5 % and 7 % of and average body mass of 75 kg –Admissible working time = Acclimatized workers sweat more, sweat early, able to endure greater water loss D max SWreq D max = 3900 g (5.2 %)

Climatic conditions with air temperatures in the range of 10 °C to 50 °C and one other parameter varying as indicated ParameterRangeConstant value Relative Humidity, RH (%) ,60,..100 Mean Radiant Temperature (tr=ta), (° C) Air Velocity, va (m/s) 0-40,1,1.5….4 Clothing Insulation (clo) Metabolic rate, M (W/m^2) Data Measurement

Estimating Personal Factors Affecting Comfort Physical –Clothing (specifically its insulation value in “clo”) –Activity level (specifically metabolic heat production in “met”) Type of Clothing Rcl, clo, (m^2)/W fcl hcl=1/R, W/(m^2K) No clothing ∞ Shorts Shorts and a thin short sleeved shirt Thin trousers, long-sleeved shirt Thick trousers, long sleeved shirt Overalls, long shirt (Waclawik & Branny, 2004) (1 Clo = m 2 /W insulation value).RatingActivity Metabolic Rate 0RestingM≤117 W 1Low metabolic rate117 < M ≤ 234 W 2Moderate metabolic rate234 < M ≤ 360 W 3High metabolic rate360 < M ≤ 468 W 4Very high metabolic rateM > 468 W (ISO 7243, 1989)

Varying M, RH ab Analysis of Required Sweat Rate

a b Varying M, RH Analysis of Skin Wettedness

Analysis of worker tolerable time Varying M, RH ab

Analysis of required sweat rate Varying Va, M ab V=1.5 m/s

Analysis of required skin wettedness Varying Va, M M=320 ab

Analysis of worker tolerable time Varying Va, M ab

Analysis of required sweat rate Varying Va, M a b

0.85 ab Analysis of required skin wettedness Varying Va, M

M=300 W/m 2 Analysis of worker tolerable time Varying M, RH ̊C ̊C

Sensitivity Analysis on Comfort Varying M and RH Metabolic Activity (W/m 2 ) Humidity (%) Air Temperature (°C) Decreasing Ambient Temperature Requirements at the Face (%)

RH = 70 % Air Velocity (Va), m/s Metabolic Rate W/m Increasing Ambient Temperature Requirements at the Face (%) Sensitivity Analysis on Comfort Varying M and Va

M=200 W/m 2 Air Velocity (Va), m/s Relative Humidity (RH), % T a (°C) Increasing Ambient Temperature Requirements at the Face (%) Sensitivity Analysis on Comfort Varying Va and RH

M=200 W/m 2 Air Velocity (Va), m/s Relative Humidity (RH), % Decreasing Ambient Temperature (°C) Requirements at the Face (%) Sensitivity Analysis on Comfort Varying Va and RH

Conclusion Maximum thermal satisfaction is attainable with higher air velocities than those that can be obtained at the lower airflow velocity The method developed makes it possible to determine changes in environmental parameters (e.g. T a, RH, Va) to obtain desirable maximum exposure times in the working area This study analyses and summarizes the thermal stress evaluation indices of ISO 7933 from simulations performed on the mathematical model From the simulated results based on the thermal parameters of the environment, upper working limits of air temperature, activity, humidity, and air velocity can be determined and recommended The limits can be verified by simulation results of subjective evaluation indicators, including sweat rate, skin wettedness and the upper limit of working time

Conclusion Optimum air temperatures are achieved at air velocities of 1.5 m/s. When the air motion across the skin increases, thermal comfort will increase and that the optimum air velocity for comfort is 1.5 m/s The analysis also observed that humidity contributes a lot more to deviations from comfort. It is followed by activity level and then airflow velocity. Note that in this study values for clothing (clo) are kept constant, and T a is equated to T r Results form this research work was used by a graduate student to assess and determine a heat stress index that will protect U/G workers in hot mines

Thank You! ? ACKNOWLEDGEMENT: Dr. Robert Watters Dr. Javad Sattarvand CDC/NIOSH