DESIGNING FOR COMFORT Richard B. Hayter, Ph.D., P.E. Kansas State University Manhattan, KS, USA

Annual Operating Costs in U.S. n n Energy: $2.00 to $4.00/ft 2

Annual Operating Costs in U.S. n Energy: $2.00 to $4.00/ft 2 n Maintenance: $2.00 to $4.00/ft 2

Annual Operating Costs in U.S. n Energy: $2.00 to $4.00/ft 2 n Maintenance: $2.00 to $4.00/ft 2 n Owning or Leasing: $10.00 to $40.00/ft 2

Annual Operating Costs in U.S. n n Energy: $2.00 to $4.00/ft 2 n n Maintenance: $2.00 to $4.00/ft 2 n n Owning or Leasing: $10.00 to $40.00/ft 2 n n Personnel: $ to $400.00/ft 2

Optimizing Environmental Control May n Minimize operating cost including energy

Optimizing Environmental Control May n n Minimize operating cost including energy n n Improve productivity

Evolution of Controllers n n On/Off n n Proportional Control n n Dead Band n n Comfort Controllers n n Fuzzy Logic

Indoor Design Conditions 2003 ASHRAE Applications Handbook - Office Buildings, Summer 74 o F (23 o C) - 78 o F (26 o C) % rh

Indoor Design Conditions 2003 ASHRAE Applications Handbook - Office Buildings, Summer 74 o F (23 o C) - 78 o F (26 o C) % rh Footnote: “This table... should not be used as the sole source for design criteria.”

Indoor Design Conditions ASHRAE/IES : “6.2.2 Load Calculations. Heating and cooling system design loads for the purpose of sizing systems and equipment shall be determined in accordance with generally accepted engineering standards and handbooks acceptable to the adopting authority (for example, ASHRAE Handbook – Fundamentals).”

Fundamentals of Thermal Comfort

“Thermal Comfort: That condition of mind which expresses satisfaction with the thermal environment and is assessed by subjective evaluation.”

Principles of Heat Transfer n Humans transfer sensible heat by conduction, convection and radiation. n Humans transfer latent heat by evaporation from the skin (evaporation of perspiration) and through respiration.

Metabolism n Ranges from approximately 340 Btu/Hr (sedentary) to 3400 Btu/Hr (strenuous). n Metabolic capacity of trained athlete can reach 20 times their sedentary rate. n More typical maximum is 12 times sedentary for age 20 and 7 times sedentary for age 70.

Thermal Equilibrium Is achieved when the metabolic rate equals rate of heat loss less work.

Physiological Responses n Sweating = Increased Evaporation (little benefit from dripping sweat) Note: If heat production is greater than heat loss, first mechanism is vasodilatation which can double or triple heat loss. Conditioned athletes sweat a higher proportion of water to oil. Note: If heat production is greater than heat loss, first mechanism is vasodilatation which can double or triple heat loss. Conditioned athletes sweat a higher proportion of water to oil. n Shivering = Increases Metabolism.

Thermal Neutrality That condition where no physiological response is needed other than vasomotion to maintain a normal body temperature. That condition where no physiological response is needed other than vasomotion to maintain a normal body temperature. Normally achieved between T o = 73 o F to 81 o F for clothed sedentary and 84 o F to 88 o F unclothed. Normally achieved between T o = 73 o F to 81 o F for clothed sedentary and 84 o F to 88 o F unclothed.

Individual Differences n n Elderly prefer same condition as young. Lower metabolic rate of elderly is compensated by lower latent loss from body. Preference for warmer thermostats is because of lower activity levels. n n Elderly are more susceptible to extremes. n n No difference between sexes in the unclothed condition. Clothed females may prefer warmer temperature because of lighter clothing.

Discomfort Localized discomfort will overshadow comfort even under conditions of thermal neutrality. Localized discomfort will overshadow comfort even under conditions of thermal neutrality. Causes of localized discomfort include asymmetric radiation, drafts, contact with cold or hot floors, vertical temperature differences. Causes of localized discomfort include asymmetric radiation, drafts, contact with cold or hot floors, vertical temperature differences.

Discomfort Continued Drafts have a disproportionate effect on comfort based on heat transfer. Dissatisfaction with the environment grows exponentially as air turbulence increases.

Comfort = Productivity(?) n Motivation more dominant than comfort.

Comfort = Productivity(?) n n Motivation more dominant than comfort. n n Productivity = f (1/discomfort)

Variables Affecting Comfort

Typical Controlled Variables n n Dry Bulb Temperature n n Relative Humidity (Water Vapor Pressure) n n Air Velocity

Possible Controlled Variables n n Mean Radiant Temperature n n Radiant Asymmetry n n Drafts n n Vertical Temperature Stratification n n Floor/Ceiling Temperature n n Non Steady State Conditions – – Rate of Change – – Amplitude and Basal Temperature

Possible Non Thermal Controlled Variables n Noise n Air Quality n Lighting

Typical Uncontrolled Variables n n Activity Level of Occupants n n Clothing

Operative Temperature (t o ) “The uniform temperature of an imaginary black enclosure in which an occupant would exchange the same amount of heat by radiation plus convection as in the actual nonuniform environment.”

Operative Temperature Cont. “Operative temperature is numerically the average of the air temperature and mean radiant temperature weighted by their respective heat transfer coefficients.” “Operative temperature is numerically the average of the air temperature and mean radiant temperature weighted by their respective heat transfer coefficients.”

Operative Temperature Cont. The operative temperature equals the dry bulb temperature in spaces where the temperatures of the surfaces surrounding the occupant and the dry bulb temperature are approximately the same.

Operative Temperature Cont. Environmental control systems must have some way to compensate when the surface temperatures are considerably different than the dry bulb temperature. Environmental control systems must have some way to compensate when the surface temperatures are considerably different than the dry bulb temperature.

Thermal Comfort Standards

Forward The standard is intended for use in design, commissioning, and testing of buildings and other occupied spaces and their HVAC systems and for the evaluation of thermal environments.

Purpose: “....” “... to specify the combinations of indoor thermal environmental factors and personal factors that will produce thermal environmental conditions acceptable to a majority of the occupants within the space.”

Six Factors for Comfort 1. Metabolic rate 2. Clothing insulation 3. Air temperature 4. Radiant temperature 5. Air speed 6. Humidity

Conditions for Acceptable Thermal Environment Cont. n n Assumes sedentary activity. (Includes provisions for adjustment.) n n Assumes similarity in clothing for season. (Includes provisions for adjustment.)

For 80% occupant acceptability

Other Criteria-Air Velocity n No minimum specified. Temperature may exceed upper limit of zone if compensated with elevated air velocities. n For sendentary occupants, temperature cannot exceed comfort zone by more than 3 o C(5.4 o F) nor compensating air velocity greater than 0.8m/s(160fpm). n Elevated air velocities must be under the control of the occupant.

Discomfort The local thermal discomfort caused by a vertical air temperature difference between the feet and the head by an asymmetric radiant field, by local convective cooling (draft), or by contact with a hot or cold floor must be considered in determining conditions for acceptable thermal comfort.

Other Criteria-Non Steady State n No restrictions on rate of change of cyclic temperatures if peak-to-peak difference is less than 1.1 o C (2 o F). n Temperature drifts and controlled ramp changes are acceptable under specified conditions and can exceed comfort zone within limits. (Such as night setback.)

Other Criteria-Nonuniformity n Limits on vertical temperature gradients within the occupied zone are specified. n Radiant asymmetry in the vertical direction shall be less than 5 o C (9 o F) under a warm ceiling and less than 10 o C (18 o F) in the horizontal direction from a cool wall. n Floor surface temperatures shall be between 19 o C (66 o F) and 29 o C (84 o F).

Evaluation of Thermal Environment Measuring Device Criteria Measurement Positions Measurement Periods Measuring Conditions Mechanical Equipment Operating Conditions Validating the Thermal Environment

International Standards

ISO Standards “This standard ( ) is in close agreement with ISO Standards and ”

CEN 156 Proposed Prestandard (never adopted) “Ventilation for Buildings Design Criteria for the Indoor Environment”

Proposed CEN Standard Scope: “...The indoor environment comprises the thermal environment, the air quality and the acoustic environment.”

The Future n n Greater application of multivariate controllers including fuzzy logic will provide comfort at minimum energy use.

The Future n Greater application of multivariate controllers including fuzzy logic will provide comfort at minimum energy use. n Introduction of convenient design tools.

The Future n Greater application of multivariate controllers including fuzzy logic will provide comfort at minimum energy use. n Introduction of convenient design tools. n Revisions to comfort standards.

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