Heating Systems
2nd law of thermodynamics—heat
always flows from a hotter to a
colder substance
Explain why the heat flow for a
home is different in the winter vs.
the summer.
Summer– outdoor air temperature
is greater than indoor air
temperature (flow is from outside
in)
Winter—indoor temperature is
greater than outdoor temperature
(flow is from inside out)
Commom Fuel Sources for Heating
•
•
•
•
Wood
Coal
Oil
Natural Gas (methane)
Methane
CH4
Pre-Mid 1700’s
• Open fire
• Fireplace with brick
• Fuel Source: wood
Mid-1700’s to 1800’s
• Fireplace with brick
• Franklin iron wood stove
• Fuel Source: wood
1885-1900
• Coal Boiler
• Natural convection (no electricity for pumps)
• Fuel Source: coal
1900-1930’s
• Coal Boiler
• Circulated water or steam to radiators
• Fuel Source: coal
1930’s • Radiant Heat and Forced Air Heating Systems
• Circulated “heated” water or steam to
radiators and “heated” air through ducts to
registers
• Fuel Source: natural gas and oil
1950’s -• Trend towards forced air heating systems to
accommodate central air conditioning
• Fuel Source: forced air heating(natural gas)
• Air conditioning (electricity from coal)
Radiant Heating System
radiator
Radiant
energy
Water-filled
pipes
90 F
150 F
Heat a
fluid
Circulate a
heated fluid
Burn a fuel
Forced-air Heating System (can be adapted to central whole-house air conditioning)
convection
Heat a
fluid
Circulate a
heated fluid
Burn a fuel
Convection, Conduction or Radiation?
1. Stick in campfire
2. Hot air balloon rising
3. Hot concrete surface
at pool
4. Lizard sunning itself on
a rock
5. Pan of soup warming
on the stove
6. Foot on cold tile floor
• Conduction
• Convection
• Radiation
• Radiation
• Convection
• Conduction