Introduction to Passive Design

THREE QUESTIONS TEST

  1. What is the merit of cooling a place using AIR, a good insulating medium, with low thermal capacity?
  2. If you want to empty a tank, do you pump it out or would you rather drain it?
  3. Which heat transfer process would you choose: A or B?
    1. linearly proportional to temperature difference (i.e. doubling ∆ T = 2 x heat transfer rate)
    2. proportional to 4th power of temperature difference (i.e. doubling ∆ T = 16 x heat transfer rate)

LETS EXPLORE WHY

Thermal ConductivitySpecific Heat CapacityDensity
(W/mK)(W/kg.k)(kg/m3)
Air0.031.0041.225
Water0.64.181000

Water presents a significantly higher heat transfer capacity:

  • The multiplier of specific heat capacity and density for water vs. air is ~ 3400 (heat absorption per unit volume)
  • The thermal conductivity multiplier for water vs. air is ~ 20 (heat transfer per unit area per unit thickness)
MediumCooling CapacityFlowrate RequiredPower Required
Air100 TR~ 40,000 cfm22 kW
Water100 TR~32 cfm3.7 kW

SAMPLE IMAGE

Test