Doing the Right Thing, Part the Third
In
the last issue, I said there’d be more, and soon. Is this soon enough?
You
may recall that I began to discuss LEED Sustainable Sites, the first of
six rating areas in each type of construction category for which the
USGBC has developed rating criteria, and that I explained the intent
behind the Stormwater and Light Pollution “credits”. I also mentioned the Heat Island
Reduction credit, which has a rather less obvious intent behind it.
As
a start, some reflection upon the last issue’s explanations of
stormwater and light pollution shows that only a little bit of thought is
necessary to see that storm water is a concern because development puts
the waterproof “skin” over the
undeveloped landscape which forces the existence of sewers to prevent
flooding. The natural equivalent
of a river which sometimes
overflows its banks and causes local flooding seems no different from a
sewer backing up under extreme storm conditions, but to get back to the predicate, and what is
the difference, is that this “skin” of urban development prevents rainfall from
recharging aquifers.
Similarly,
the Light Pollution issue is, even more instinctively, immediately
understood as a waste of energy via the spilling of light where it’s not needed.
But the
reduction of “heat islands”? Why couldn’t they just have said hot
spots?
The
answer to that, my friends, is contained in one of the things I continue
to harp upon – heat and hot aren’t the same
thing. In fact, I last harped upon
this last May, in Vol.6,
No.5 , which you’ll find via the embedded link in the
website version of this document.
In
passive solar design, a heat island is a good thing, a place to suck up
and store the sun’s energy in the winter for use within the
structure. The sun, baking a stone
outcrop all day, raising the temperature of the rock face by tens of
degrees, doesn’t make it
very hot, but it does pump several thousands or tens of thousands of BTU’s of heat into it.
Put
such an outcrop in a dwelling, behind thermal glazing, and it becomes a
Trombe wall which can discharge 90 degree air into a house on a winter’s day.
Heat
islands in the summer,
however, are another matter, forcing us to provide more air conditioning
than we’d otherwise need,
to overcome the changes they cause in local, especially
urban, microclimate.
The
“tar beach” of a
tenement rooftop and the change in temperature when walking from a blacktop
parking lot to a picnic table in an adjacent park are immediately sensed
examples of the phenomenon, and the LEED criteria address exactly these
two points, offering separate credits for mitigation of heat absorption
by paved areas and by roof construction.
In
the next rating area, Water Efficiency, the Existing Building category
has a pair of prerequisites having to do with waste water pollutant
removal and system modifications and calculations proving waste water
usage with extant or replacement fixtures is comparable to that which
would have existed were low-flush
fixtures conforming to 1992 Energy Policy Act performance requirements
installed. After these prerequisites have been satisfied, the Existing
Buildingcategory’s
concerns with regard to additional reductions in potable water use,
conservation of irrigation water, and getting what would have been
wastewater back into the aquifer, are very similar to like requirements
for the New Construction category.
A
prerequisite, such as those mentioned in the beginning of the last
paragraph, is a recurring theme in the LEED criteria. This is like
anteing up to get into a poker game, and is a measure of the realities
which led to the creation of the LEED criteria in the first place. While it may come as a surprise to some
of those who speak most loudly on the issue, this has nothing to do with the politics of
Global Warming (read Michael Crichton’s Next) and everything to do with an understanding of what is meant by “stewardship” and “husbandry”.
This
completes the Water Efficiency rating area, and brings us to Energy and
Atmosphere, the meat of the HVAC engineer.
The
focus on what I consider to be the overlooked or otherwise ignored
obvious, will be at the forefront of my explications of this area, in
keeping with one of the reasons behind this publication, that which my
younger brother calls my belief that, “everyone’s entitled to my opinion.”
So,
to get right on into it, and in keeping with what I just finished
discussing, both LEED-NC and LEED-EB have as pre-requisites 1 and 2,
Commissioning (Vol.5,
No.3 ), and Minimum Energy Performance. The reasoning behind the former is
explained in the parenthetical reference.
The latter, however, is applied so as to reflect the differences
between new construction and existing buildings.
This
is accentuated by the fact that the LEED-EB Energy and Atmosphere
category has a third prerequisite, Ozone Depletion, having to do with
moving away from the CFC refrigerants extant only in existing
buildings. Furthermore, the
LEED-EB Minimum Energy Performance metric restates a crucial difference
between EB and NC criteria which resurfaces in every LEED-EB category;
the notion of LEED re-certification in
recognition of the fact that existing buildings and their systems must be
maintained.
Recertification
must be accomplished at least once every five years in order to maintain
a building’s LEED-EB rating,
and is encouraged every year as an operations and maintenance
tool. New buildings which have not
already obtained a LEED-NC rating become available for LEED-EB
certification only after they are at least two years old.
Getting
back to the Minimum Energy Performance metric, LEED-NC is concerned with
the design of the building’s system complying with ASHRAE/IESNA
Standard 90.1-2004, the 2001 version of which, by the way, is
enshrined in the current NYS
Energy Conservation Construction Code as a
legal requirement. LEED-EB, on the other hand, is
concerned with the evaluation of the performance
of existing systems, to be validated by a Professional Engineer via,
where applicable, the EPA’s Energy
Star Label for Buildings. For
such buildings, the EPA provides an online interactive
benchmarking tool, Portfolio
Manager, to aid the PE in the preparation of Statement of Energy Performance,
with a minimum score of 75 for EPA acceptance, but only 60 for the LEED
prerequisite.
More
to come.
