learning psychrometrics and sensors measuring t and rh

Learning Psychrometrics and Sensors measuring T and RH 方煒

台大生機系教授

Wei Fang, Ph.D., ProfessorDept. of Bio-Industrial Mechatronics Engineering, National Taiwan University

Analog Dry Bulb Temperature sensor

Analog Dry and Wet Bulb Temperature

Digital Dry Bulb Temperature reader

Infra-red Dry Bulb Temperature

Thermal Imager

http://us.fluke.com/usen/products/CategoryTI/

http://www.landinst.com/infrared/products/thermal_imaging/tp8_portable_imager.htm

http://www.landinst.com/infrared/products/thermal_imaging/guide_M4_thermal_imager.htm

Sensing element

Dry and wet Bulb Temperature sensors in Weather station and greenhouse

RH = f(Tdb, Twb)

Patm = 101.325 kPa

Tdb and RH Sensors

Tdb and RH data logger

Day/Night trends of T and RH

High T coexist with Low Hum.

午夜 中午 午夜

溫度

濕度

High humid Env.

Low T, High RH High T, Low RH

Forced ventilation

Evaporative cooling

Fogging

Evaporative cooling

Pad and Fan system

Approach to release thermal stress

Approach to release thermal stress

Beware of the side effect.

Psychrometric Chart

Process: from one state to another

Human comfort zone

Animal comfort zone – T only

Dry bulb temperature

Pro

duct

ivity

Impact of T and RH on milk production of cows

THI>85, no recovery

Adapted from ASHRAE Fundamentals, 1999

75.73 79.96 63.765.0572.3268.4763.39 76.68

90.0987.09

88.06

64.31

64.6582.49

86.0182.09

82.3684.21

Reduction of milk vs. Temperature-Humidity Index (THI)

Adapted from ASHRAE Fundamentals, 1999

Milk Production=f(HD74, HA80S)

MP = 21.48 – 0.051 * HD74 – 0.0099 * HA80S

Where,– MP: Milk production (in kg/day/cow)– 21.48: daily production (in kg) per cow in normal wea

ther condition– HD74: total hrs of THI > 74 for previous 4 days– HA80S: square of total hrs of THI > 80 for previous d

ay Linvill and Pardue (1992)

THI lines on Psychrometric chart

More about Psychrometric chart

Following contents, created by the author, are available from DSpace at UVM.

• Tutorial for digital psy chart

• Digital psychrometric chart software

The End