Tom Székely, P.E., LEED AP



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April 18, 2007

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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.

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