Transcript BEM class 3 Building Thermodynamics

BEM class 3
Climate & 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 humidity
From 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 allglass buildings. Why?
Function of distance and
angle from warm or cold
surface
Calculating MRT
(Mean Radiant Temperature)
Thermal Lags
Low- and High-Mass
Constructions
• Building dynamics,
non-steady-state
effects of “thermal
mass”
• Most important as
weather conditions
swing daily
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)
So now, for NYC you have heating design delta-T of 74 – 17 = 57 dF.
AC SIZING ALSO REQUIRES CONSIDERATION OF HUMIDITY, SOLAR GAIN AND
INTERNAL GAINS
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
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 80
CDD = 15
Weather “Tapes” for use in models
• Typical Meteorological Year (TMY) (see Hensen ch 3)
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”
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Comparison issues. Normalize by DD?
“Design-for-climate” approaches.
Resilience and climate adaptation.