[Greenbuilding] NYC 90% emissions cut with windows

[Michael Iversen]

I reviewed the '90 by 50' report, and its conclusions are based on 
invalid assumptions, extrapolations and projections placed outside the 
context of reality in terms of economic and social behavior. Basically, 
the report concludes that IF ALL buildings in NYC were retrofitted or 
designed with rigorous energy measures, and IF ALL buildings were 
equipped with rooftop photovoltaic systems, and IF ALL source energy was 
carbon-free electricity, then a 90 percent reduction in building 
sector-related GHG emissions is possible by 2050.

*Report Assumption 1*: All building stock is assumed to be retrofitted / 
designed with existing and near-term efficiency technologies, 
specifically; air sealing, heat recovery ventilation, and additional 
insulation, to a point where all heating, cooling, and hot water can be 
provided by electric heat pumps. Capital outlays are estimated at a 
discounted net present value $94 billion.

- /Comment/: While energy retrofitting of existing building stock is a 
valid strategy to reduce GHG, the projection of findings based on 
perfect model simulations for each building type to the entire building 
stock is extremely unrealistic, in terms of financial costs and building 
ownership / management behavior. The $94 billion costs need to be placed 
in the context of local, state, and federal economic deficits. The 
report needs to project the extent of retrofitting based on historic 
data, not unrealistic goals.

*Report Assumption 2*: All remaining building loads to be carbon-free 
electricity. After reducing total building energy use by 50 to 60 
percent, all remaining building energy in 2050 (50.6 TWh) is to be 
supplied by carbon-free electricity, in order to meet the 90 percent 
reduction target.

Photovoltaic arrays may be added to every single building in NYC 
(covering up to 60 percent of the available rooftop area), so as to 
provide 10.7 TWh.

The report enumerates potential sources of adequate carbon-free 
electricity, but states that a detailed analysis is beyond the scope of 
this study. Besides the previously mentioned electricity from 
photovoltaics (10.7 TWh), the remaining 39.9 TWh are to be provided a) 
2,600 4.0MW wind turbines, occupying 35 to 40 square miles, b) an 
additional 86 million square meters of photovoltaic panels with a 
footprint of 66 square miles, c) 3 or 4 new 1000 MW nuclear power 
plants, d) increased hydropower from Quebec, and e) electricity 
generation from biogas derived from waste and sewage treatment.

- /Comment:/ To assume 100% of buildings will be retrofitted with pv 
arrays covering 60% of roof area is an unsubstantiated overestimate, and 
does not factor building structural capacity, financial capacity, and 
social behavior of private building ownership / management.

- /Comment:/ To simply assume that 39.9 -- 50.6 (TWh) of source energy 
is to carbon free is equivalent to saying it will be provided by magic 
beans. Any proposed strategy would be valid of all remaining source 
energy would be carbon free.

*Summary*: if anything, this report points to how difficult it is to 
achieve a 90 percent reduction of GHG emissions related to the building 
sector by 2050. While some of the data findings were of value and 
interest, any interpretation of findings, unless grounded in the 
relatity of economic and social behavior, will provide only false 
conclusions.

I welcome other viewpoints on this study.

Michael Iversen
Architect, LEED AP, PhD Candidate
Department of Urban Planning and Policy
University of Illinois at Chicago

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