BEM class 3 Climate & Human Comfort. Class (lecture) objectives Appreciation of the indoor and...
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Transcript of BEM class 3 Climate & Human Comfort. Class (lecture) objectives Appreciation of the indoor and...
BEM class 3Climate & Human
Comfort
Class (lecture) objectives
Appreciation of the indoor and outdoor environments and how they relate to our energy models
Understand design decisions in selecting conditions
Know key terminology and manual methods for annual weather normalization and energy use
Human Comfort in the Indoor Environment
ASHRAE Std. 55 (-2013) “Thermal Environmental Conditions for Human Occupancy”
Heat Exchange at the Human Body boundary
Sensitivity to air temperature, surface (radiant) temperatures, humidity, air movement
Dependence on clothing, activity. Role of culture and expectations.
Comfort Conditions
Temperature range
70 – 78 dF
Humidity control – Psychrometrics
Zoning for gain, loss and use factors The Psychrometric Chart
Comfort Conditions – Psychrometric Chart
Dry bulb (db) temperature
Absolute humidity
Dew point
Wet bulb (wb) temperature
Relative humidityFrom Tao & Janis Mechanical and Electrical Systems in Buildings
Interior Air Movement
Evaporative effects of air movement
HVAC System Effectiveness
• ASHRAE 62 (2013) Ventilation for Acceptable Indoor Air Quality
• Different types of air distribution systems
• Air distribution under varying conditions• Short-circuits. Stratification. • "droop" at low flows in variable
volume systems. • Use of CFD.
Radiant Heat Effects
Comfort / Discomfort from building surfaces
Especially important in all-glass buildings. Why?
Function of distance and angle from warm or cold surface
Calculating MRT (Mean Radiant Temperature)
Thermal Lags
• Building dynamics, non-steady-state effects of “thermal mass”
• Most important as weather conditions swing daily
Low- and High-Mass
Constructions
Outdoor Conditions & Thermal Loads
Thermal loads driven most significantly by outside TEMPERATURE
2 aspects:
(1) Design - selection of mechanical equipment
(2) Annual Energy Use
Outdoor Design Conditions for Heating & Cooling
ASHRAE Handbook - Fundamentals (2013)
AC SIZING ALSO REQUIRES CONSIDERATION OF HUMIDITY, SOLAR GAIN AND INTERNAL GAINS
So now, for NYC you have heating design delta-T of 74 – 17 = 57 dF.
From Peak (design) to Annual – how hot/cold over time?
Hourly outdoor temperatures – recorded by US Weather Service
Manual Methods • Bin data – hourly occurrences in 5-degree “bins” (see next slide)
• Degree-days – reported in newspapers on running daily basis
Weather “Tapes” for use in models • Typical Meteorological Year (TMY) (see Hensen ch 3)
HDD: 65 – daily avg temp eg – high 25 low 15 avg 20 HDD= 45
CDD: daily avg temp – 65 eg – high 90 low 70 avg 80CDD = 15
Sample Bin Data
Weather & Climate
• Not the same - Weather is highly variable. Climate shows patterns over time.
What does climatic variation say to us about our design-conditions?
• Climate “regions” or “zones” • Comparison issues. Normalize by DD? • “Design-for-climate” approaches.• Resilience and climate adaptation.