It is often mistakenly
thought that "efficiency" is the synonomous with the efficiency
factor. That is only true, if both quantities on the right hand
side of the definition
= benefit / effort
have the dimension of
"energy" or "power". But very often the benefit
has nothing to do with energy. For example, the benefit can be a
mileage (unit "miles"). The effort e.g. is the fuel needed
(unit "gallons") and the efficiency of this service will
be given by
with the unit "miles/gallon".
In Europe the inverse value
is established: the specific
fuel requirement in (liter fuel)/(100 km). Such values characterising
the efficiency are not "efficiency factors" - they are
values with a dimension. It is not possible to introduce an efficiency
factor instead of these quantities. Looking at most services produced
by the use of energy you will find, that they do not have the dimension
of energy. And, there is no "minimum energy demanded"
for those services on physical reasons. The belief in the contrary
is widely spread, too - but not valid. The "minimum energy"
in most cases is zero (or, in same cases, an extremely small value
near to zero).
That sound like an academic
question? No, not at all. This is a key insight.
Let us look at an example:
The efficiency factors of heating
boilers can not be increased to more than 100% (law of energy conservation)
and contemporary values already are in the range of 90%. But: the
efficiency of the total service "heating" (to be measured
by the area heated with a given amount of fuel) can be increased
almost without any limit - by better insulation and heat recovery.
If you only look at the efficiency factor, there will not be a noteworthy
potential for energy saving for heating. But if we have a broader
look at the service and realise, that the so called "heating
demand" can be reduced to values near to zero (by insulation
and heat recovery), we will understand that there is a huge potential
for better efficiency. This has been demonstrated by the multitude
of Passive Houses which have already
been built and are occupied.
But it is not only true
for heating, it is quite similar with many other applications of
energy: At the end of the supply chain, the final use is made out
of the energy supplied. At this end there are the major potentials
for an increased efficiency: And it is not a few percents which
can be saved; it is the major part - in most cases.
storage can have an increased insulation; this will reduce the
energy needed to hold the temperature level (the principle of
- The same holds for
heat distribution pipes (especially domestic hot water and circulation
- Heat can be recovered
from hot waste water.
- Insulation, efficient
against heat losses, is efficient against "cold losses"
as well (see the example on left hand side).
- Even looking at industrial
processes energy can be used far more efficiently, e.g. by heat
regeneration. An example is a "counter direction production
line": finished baked goods (hot!) are transported on a production
line, while the cold, unbaked parts come along in counterflow
at another line.
- Increased efficiency
in the use of materials and recycling of energy intensive materials
will reduce the energy requirement, too.
A thorough analysis of
all services produced with the input of energy reveals: From a physical
point of view energy is used predominantly to maintain an unstable
situation. But these can be regularly transformed by smart measures
into near equilibrium conditions. To realise this, only a very small
amount of energy is required. Examples:
- Comfortable "heated"
unstable situation: "higher indoor temperature" compared
to "cold outdoor environment".
Smart measure: reduction of heat losses.
Practise: Passive House.
- Comfortable "air
conditioned" living space:
"cool indoor temperature / lower humidity" compared
to "hot environment / high humidity".
Smart measure: reduction of heat gains, heat recovery and humidity
Practise: Passive House with a compact ventilation system.
- Cooling chain:
"cool temperature in the cooling chamber" compared to
the "hot environment".
Smart measure: insulation.
Practise: vacuum insulated cooling chambers.
"not frictionless movement".
Smart measure: reduction of friction; recovery of braking energy.
to the page on efficiency.
article on energy efficiency (492 kB) (pdf, German).
Dr. Wolfgang Feist
2006-09-23 WF - thanks to Dylan Lamar for proof reading
Passive House Institute; unchanged copy is permitted, please give
reference to this page