Transcript DESIGNING FOR COMFORT - Home | College of Engineering
DESIGNING FOR COMFORT
Richard B. Hayter, Ph.D., P.E.
Kansas State University Manhattan, KS, USA
Annual Operating Costs in U.S.
Energy: $2.00 to $4.00/ft 2
Annual Operating Costs in U.S.
Energy: $2.00 to $4.00/ft 2
Maintenance: $2.00 to $4.00/ft 2
Annual Operating Costs in U.S.
Energy: $2.00 to $4.00/ft 2
Maintenance: $2.00 to $4.00/ft 2
Owning or Leasing: $10.00 to $40.00/ft 2
Annual Operating Costs in U.S.
Energy: $2.00 to $4.00/ft 2
Maintenance: $2.00 to $4.00/ft 2
Owning or Leasing: $10.00 to $40.00/ft 2
Personnel: $200.00 to $400.00/ft 2
Optimizing Environmental Control May
Minimize operating cost including energy
Optimizing Environmental Control May
Minimize operating cost including energy
Improve productivity
Evolution of Controllers
On/Off
Proportional Control
Dead Band
Comfort Controllers
Fuzzy Logic
Indoor Design Conditions 2003 ASHRAE Applications Handbook - Office Buildings, Summer 74 o F (23 o C) - 78 o F (26 o C) 50 - 60% rh
Indoor Design Conditions
2003 ASHRAE Applications Handbook Office Buildings, Summer 74 o F (23 o C) - 78 o F (26 o C) 50 - 60% rh
Footnote: “This table ... should not be used as the sole source for design criteria.”
Indoor Design Conditions ASHRAE/IES 90.1-2001: “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
Humans transfer sensible heat by conduction, convection and radiation.
Humans transfer latent heat by evaporation from the skin (evaporation of perspiration) and through respiration.
Metabolism
Ranges from approximately 340 Btu/Hr (sedentary) to 3400 Btu/Hr (strenuous).
Metabolic capacity of trained athlete can reach 20 times their sedentary rate.
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
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.
Shivering = Increases Metabolism.
Thermal Neutrality 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.
Individual Differences
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.
Elderly are more susceptible to extremes.
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.
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(?)
Motivation more dominant than comfort.
Comfort = Productivity(?)
Motivation more dominant than comfort.
Productivity = f (1/discomfort)
Variables Affecting Comfort
Typical Controlled Variables
Dry Bulb Temperature
Relative Humidity (Water Vapor Pressure)
Air Velocity
Possible Controlled Variables
Mean Radiant Temperature
Radiant Asymmetry
Drafts
Vertical Temperature Stratification
Floor/Ceiling Temperature
Non Steady State Conditions
–
Rate of Change
–
Amplitude and Basal Temperature
Possible Non Thermal Controlled Variables
Noise
Air Quality
Lighting
Typical Uncontrolled Variables
Activity Level of Occupants
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 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.
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.
Assumes sedentary activity. (Includes provisions for adjustment.)
Assumes similarity in clothing for season. (Includes provisions for adjustment.)
For 80% occupant acceptability
Other Criteria-Air Velocity
No minimum specified. Temperature may exceed upper limit of zone if compensated with elevated air velocities.
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).
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
No restrictions on rate of change of cyclic temperatures if peak-to-peak difference is less than 1.1
o C (2 o F).
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
Limits on vertical temperature gradients within the occupied zone are specified.
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.
Floor surface temperatures shall be between 19 o C (66 o F) and 29 o C (84 o F).
Evaluation of Thermal Environment 1.
2.
3.
4.
5.
6.
Measuring Device Criteria Measurement Positions Measurement Periods Measuring Conditions Mechanical Equipment Operating Conditions Validating the Thermal Environment
International Standards
ISO Standards
“This standard (55-2004) is in close agreement with ISO Standards 77261 and 7730.2”
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
Greater application of multivariate controllers including fuzzy logic will provide comfort at minimum energy use.
The Future
Greater application of multivariate controllers including fuzzy logic will provide comfort at minimum energy use.
Introduction of convenient design tools.
The Future
Greater application of multivariate controllers including fuzzy logic will provide comfort at minimum energy use.
Introduction of convenient design tools.
Revisions to comfort standards.