Thermal Comfort

CLOTHING INSULATION VALUES units - Clothing attire: Light summer clothes ? Winter Outdoor working ?

.05 clo 2.5 clo

What are the two basic mechanisms that the body uses to involuntarily adjust body temperature ?

1. change of metabolism and 2. change in the rate of blood circulation near the surface of the skin.

ASHRAE Standard 55-2017, Thermal Environmental Conditions for Human Occupancy, specifies combinations of indoor space environmental and personal factors that will produce thermal environmental conditions where __________ of the occupants do not express dissatisfaction with the room conditions; that is, the given condition is not acceptable to __________of the occupants

80 % 20 %

Effects of the heat index (shade values) Yellow ; Caution Yellow-orange ; Extreme Caution Orange ; Danger red ; Extreme Danger What are the heat index temp and meaning?

80-90 °F Caution: fatigue is possible with prolonged exposure and activity. Continuing activity could result in heat cramps. 32-41 °C 90-105 °F Extreme caution: heat cramps and heat exhaustion are possible. Continuing activity could result in heat stroke. 41-54 °C 105-130 °F Danger: heat cramps and heat exhaustion are likely; heat stroke is probable with continued activity. over 54 °C over 130 °F Extreme danger: heat stroke is imminent

What is the average core temperature of the human body?

98.6°F It can range from 97.5° to 99°F

ATC​

Adaptive Thermal Comfort. It is a comfort model that is used to measure thermal comfort in naturally ventilated spaces. In naturally ventilated spaces occupants open and close windows, their thermal response depends on the outdoor conditions, and may have a wider comfort range than buildings with a centralized HVAC system. The model assumes that occupants adapt their clothing to changes in thermal conditions, and that are sedentary (1.0 to 1.3 met). In the presence of mechanical systems, this method can not be applied. For naturally ventilated buildings, the adaptive thermal comfort model calculates an indoor design temperature, around which a range is defined as comfortable for 80% (or 90%) of people.

Environmental factors affecting occupant comfort are typically grouped into four classifications (4)

Air Temperature Relative Humidity Air Movement Mean Radiant Temperature

The body passes heat in 4 ways:

Convection: air passing over the surface of the skin absorbs/adds heat to/from the skin. Conduction: by touching surfaces. Radiation: electromagnetic, infrared heat. Evaporation: from perspiration or wetting of the skin

Activity level Units - Sleeping? Climbing Stairs? Walking 3mph?

Met .07 10.0+ 2.3

The human thermal response, perceived as thermal comfort or discomfort, is shaped by six primary factors: What are they?

Metabolic rate (met), Clothing insulation (clo), Air temperature, Radiant temperature, Air speed, and Relative humidity.

The comfort of a building occupant depends on: (3)

Personal factors: clothing, cultural background (i.e. Eskimo vs Hawaiian) Environmental factors: measurable things such as temp., humidity. Air velocity. Psychological: color, sound, light.

What is PMV​?

Predicted Mean Vote Index. It is a model that is recognized as thermal comfort mode. It uses the principles of heat balance and experimental data that was collected in a climate chamber under steady conditions. This model is used to calculate which zone people are most comfortable in. This tool offers designers a way to evaluate comfort in conventional building systems. The model is used to input different parameters such as metabolic rate, insulation, temperature, airspeed, mean radiant temperature, and relative humidity. Various combinations of the parameters factor into the PMV value. +3 translates as too hot, while -3 translates as too cold. In order to comply with ASHRAE 55, the recommended thermal limit on the 7-point scale of PMV is between -0.5 and 0.5, but can be different for various factoring conditions.

PPD​

Predicted percent dissatisfied. This index measures thermal comfort of a group of people in a specific thermal environment. It is estimated that five percent of people in the group will be dissatisfied with the thermal conditions of the room. We use PVM to predict comfort in a room, but using PPD helps us consider the level of satisfaction between the occupant and a space. This PPD can be found after calculating the PPD. Factors that contribute to discomfort and the PPD are unwanted cooling or heating from an occupant. A PPD less than 20 percent can be considered a good percentage.

The comfort zone

The range of combinations of dry bulb temperature, relative humidity, mean radiant temperature, air speed, clothing insulation, and activity that are deemed comfortable for most people. These conditions may be outlined on a psychometric chart or embodied in computer software. is the combination of temperature and humidity where people report comfort.

Mean Radiant Temperature

Weighted avg of the various surface temps in a room, angle of occupants exposure to those surfaces and any sunlight

What are the condition of thermal comfort?

activity level level of clothing temperature and relative humidity of the room air air velocity types of heating and cooling systems types and materials of construction

operative temperature

average of Air Temperature and Mean Radiant Temperature being based on an arbitrary set of indexes that combine into a single number the effects of dry bulb temperature, radiant temperature, and air motion on the sensation of warmth or cold felt by the human body.

effective temperature (ET)

combines the effects of air temperature, humidity, & air movement as an arbitrary, experimentally determined index used to rate the various combinations of dry bulb temperature, relative humidity, radiant conditions, and air movement that create the same thermal sensation.

Thermal Comfort

is a condition of mind that expresses satisfaction with the thermal environment; it requires subjective evaluation. the condition of mind that expresses satisfaction with the thermal environment

Heat index (HI) / ambient temperature? Dry Bulb Temp Relative Humidity

is a measure of the contribution that high ambient air temperature and high humidity (expressed either as relative humidity or dew point temperature) make in reducing the body's ability to cool itself. a chart that combines air temp with relative humidity to determine the apparent temperature Explains the heat index: https://youtu.be/dTGt3ylVA-4

Wind Chill - Dry Bulb Temp and Wind speed

is the lowering of body temperature due to the passing-flow of lower temperature air. Frost Bite Increment for from: 30 10 5 Min https://youtu.be/6Azu4tZeo7M

If conditions are to the ______ of the comfort zone, then there is a need to increase heating (e.g., by increasing dry bulb temperature or shading devices).

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Besides the environmental factors mentioned previously and the body's ability to make slight physiological adjustments, body heat generation and heat transfer is influenced by two additional factors that are not related to the environment but rather to the ___________. What are those two factors?

occupant Activity Level Clothing Level

Besides the physiological adjustments made by the body, heat transfer from the body is influenced by several environmental factors. These factors affect an ___________________________ in a space. They can be reasonably controlled by the designer of the space and usually play a larger role in body comfort than the physiological adjustments made by the body

occupant's temperature sensation

If conditions are to the _______ of the comfort zone, then there is a need to increase cooling (e.g., by decreasing dry bulb temperature or increasing airflow).

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