BEM class 3 Climate & Human Comfort. Class (lecture) objectives Appreciation of the indoor and outdoor environments and how they relate to our energy.

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.