Furnaces are the most commonly used heating
system in the United States. More efficient
furnaces are called “condensing” furnaces.
While conventional natural gas furnaces have
efficiencies (AFUE, the “Annual Fuel
Utilization Efficiency”) that top out at
about 80 percent, condensing furnaces start
at 90 percent and go up to 96 percent or
better. The difference is simple: burning
natural gas (or propane) forms water vapor,
CO2, and minor amounts of contaminants.
Conventional furnaces waste energy to keep
the water vapor formed in combustion as
steam, and prevent contaminants from
corroding the furnace (or boiler).
Condensing furnaces are designed to capture
the latent heat that is released when the
steam condenses. The small amount that
condenses drains to a sanitary sewer.
A boilers heat works by burning fuel to heat
water or steam that circulates through
radiators, baseboards, or radiant floor
systems. Several recent features have
improved boiler efficiency: electronic
ignition, which eliminates the need to have
the pilot light burning all the time, and
technologies that extract more heat from the
same amount of fuel.
Heat pumps provide both heating and cooling
in one integrated system.
With the advent of zoning, combination
humidity systems and dynamic air handling,
HVAC has joined the march toward greater
returns with a smaller carbon footprint.
air conditioning effects
savings of up to 15-20%
Air-Source Heat Pumps (ASHPs).
ASHPs, often used in moderate climates, use
the difference between outdoor and indoor
air temperatures to cool and heat. They also
provide a higher Heating and Seasonal
Performance Factor (HSPF), which measures
the heating efficiency of the heat pump
GHPs are similar to air source heat pumps,
but use the ground instead of outside air to
provide heating, cooling, and often water
heating. By using the earth's natural heat,
they are among the most efficient and
comfortable heating and cooling technologies
currently available. The heat extracted
through a geothermal heat pump can come from
any source, despite the temperature.
Ventilation energy recovery
Energy recovery systems sometimes utilize
heat recovery ventilation or energy recovery
ventilation systems that employ heat
exchangers or enthalpy wheels to recover
sensible or latent heat from exhausted air.
This is done by transfer of energy to the
incoming outside fresh air.
Central Air Conditioners
Most central air conditioners are called
“split-systems” because they have an outdoor
component with a condenser and compressor
and an indoor component with an evaporator
coil. ENERGY STAR qualified central air
conditioners have higher SEER (Seasonal
Energy Efficiency Ratio) and EER (Energy
Efficiency Ratio) ratings than today’s
standard models. SEER is the most commonly
used measurement of efficiency for air
conditioners. It measures how efficiently a
cooling system will operate over an entire
season. EER measures how efficiently a
cooling system will operate when the outdoor
temperature is at a specific level (95