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Re: [Strawbale] Embodied/embedded energy figures
On Mon, 17 Oct 2011 20:41:18 -0400, wrote:
On Mon, 17 Oct 2011 in GSBN Digest, Vol 7, Issue 24
David Eisenberg wrote:
To: Global Straw Building Network
[<snipped> & <pasted>]
energy efficiency folks... dismissed the importance of embodied energy
argument was that if you compared operating and embodied energy,
embodied energy was insignificant
They often used percentages to compare the two and I would say,
okay using that method, what is the percentage of embodied energy
when operating energy is zero?And how much have you increased the
embodied energy in order to get to net-zero?
we're typically using much higher embodied energy materials and systems
in most of these buildings to get to low operating energy performance-
which amplifies the problem. And the global warming potential also
typically goes way up.
( The above message in its entirety and the thread to which it belongs can
be viewed at
http://sustainablesources.com/pipermail/gsbn/2011q4/001616.html
)
In the much of the non-First World, people have been living in zero energy
(ZE) or near ZE homes for centuries, many of those houses being made of
low embodied-energy, natural materials.
In the First World, the lowest per-capita energy consumption figures are
associated with those households whose annual income is under $20k ...
while the energy consumption of households whose income is in the six
figures can be as much as double or more that of the under-$20k households.
Not too long ago in the US news media, there was a piece trumpeting a new,
5000 sq ft, Net-Zero Energy home, no doubt costing a $bazillion or
$gazillion.
And if you Google "Net-Zero Energy Homes" no doubt you will find some
quotes about how NZE will add about $100 -$120k to the cost of a new home.
We know from experience here in Canada (ie in a 7500 - >11,000 heating
degree-days/yr climate) over the past three decades or so that one can
build very energy efficient homes where about 75% of the building's
heating load can be provided via passive means and the cooling load is
practically nil, and the house would not look much different than a
conventional home, the incremental cost for energy-efficiency improvements
(read: higher levels of insulation, better air-sealing strategies) costing
about 10% over conventional "built-to-Code" construction ... which is to
say that it is possible to minimise the energy consumption for space
heating/cooling to near-zero, even in Cold Climates ... simply via
siting, orientation, massing, appropriate levels of insulation and
effective air-sealing. (Note that the preceding can all be accomplished
utilising "natural" and low embodied-energy materials if one so desires.)
(And "yes" air-tight construction is an absolute necessity when the
building envelope utilises higher levels of insulation
re: Graham North's comment:
> I also question (and here I risk swearing in church) the whole
philosophy
> of tightly sealed "passiv haus" which are then mechanically ventilated.
An ineffective air-sealing strategy will result in moisture problems
for the envelope materials, higher-than-necessary energy consumption
for space heating/cooling, poor interior air quality and poor occupant
health.
Air-tight construction does not necessarily imply mechanical ventilation.
Exhaust-only, passive-inlet ventilation strategies (EOPIVS) are entirely
possible, but only in relatively mild climates (ie <6500 HDD/yr),
smaller houses (ie under 1200 sf) and single-storey dwellings.
However, without mechanical ventilation (ie a device with energy recovery
on the exhaust air stream) there will be about 20% higher-than-necessary
energy consumption for space heating/cooling, assuming that the house
occupants are being provided with the minimum ventilation recommended by
ASHRAE (ie the worst ventilation rate below which the house occupants
are subjected to health risks due to poor interior air quality (IAQ).)
But returning to the topic of NZE ...
If the building's energy requirements for space heating/cooling are
already minimised to near-zero (ie 75% of total provided by passive means)
at a minimal incremental cost (ie the 10% mentioned, as is typical for
homes built in Canada that meet or exceed the almost three decades-old
R2000 performance standard) ... then the balance of the energy consumption
of that household is attributed to lifestyle.
Lifestyle determines the amount of energy a household consumes for hot
water heating, lighting, appliances, electronics.
(If one Googles "Domestic Energy Consumption" or such-like one will come
up
with figures that are in the following neighbourhood,
(chosen from Wiki for ease of copying since most "real" data
will likely be available as PDF documents) :
======Copied material with no assertions as to accuracy
but in rough, general agreement with other sources ==============
Average domestic energy consumption per household in temperate climates
Heating................ 12,000 kWh/yr
Hot Water.............. 3,000 kWh/yr
Cooling/Refrigeration... 1,200 kWh/yr
Lighting................ 1,200 kWh/yr
Washing & Drying........ 1,000 kWh/yr
Cooking ................ 1,000 kWh/yr
Misc Electric Load...... 600 kWh/yr
======== End of copied material ====================
It is the energy consumption for the latter (ie lifestyle vs building
envelope) that determines the amount of active solar gizmology that would
be required to bring that household to Net-Zero Energy. If a house
requires $100k-or-more-worth of solar panels to bring that house to NZ,
that's got nothing to do with "the energy-efficient folks".
While the idea of having NZE house is laudable, the reality is that for
people who are living in locales that are grid-connected and electricity
is being supplied to the consumer typically at rates of $0.12/kWh (or
less), installing photo-voltaics at $2-$8 per watt of supply capacity to
bring that household to net-zero would be feasible only for upper-level
income households.
Point being, the rants that have appeared on this List so far against
"energy-efficient buildings" are, I would argue, misdirected. I would
venture that the rants should be directed at consumptive lifestyles-- a
matter of personal choices.
I would further venture that the "embodied-energy signifcant or
insignificant" debate is unnecessary.
Any competent evaluation of environmental impacts for a design that
aspires to be truly "Green" would include energy breakdowns for
embodied-energy AND total operating energy (ie life-cycle energy),
consideration for (if not breakdowns for) air emissions, water
consumption, habitat destruction, occupant health (ie breakdowns of indoor
air pollutants) , maintenance/replacement material costs etc.
--
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c at Y a h o o dot CA >
(manually winnow the chaff from my edress if you hit REPLY)