New York City has been studying ways to decrease carbon emissions that other regions of the country have found useful their own climate mitigation efforts. New York City developed OneNYC, a blueprint for New York City to decrease carbon emissions by 30% by 2030. Now the New York State branch of the U.S. Green Building Council, known as the Urban Green Council, has put out a report, called “90 by 50: A path to deep co2 reductions in NYC”, which concentrates on building efficiency in an effort to cut NYC’s carbon emissions by 90% by 2050.
The report concentrates on buildings because in New York City 75% of carbon emissions are caused by buildings (and the U.S. Green Building Council is, naturally, focused on buildings). In most of the rest of the country half of emissions generally come from buildings, a quarter from transportation, and a quarter from industry and commercial activities. But New York City is transit-centered, leading to less emissions from transportation, and has deindustrialized to a great extent.
The “90 by 50” report uses an inventory of the entire building stock of New York City, using city housing data, which they matched up with a study by Con Edison of the electric use of various kinds of buildings. The aggregate floor space by building is different for New York City than for much of the country, with single and double family plus row house buildings accounting for 23% of floor space in NYC, low rise residential 27%, low rise commercial 20%, and high-rise residential and commercial the remaining 30%. But the techniques that the report highlights to minimize carbon emissions therefore clearly analyzes all kinds of buildings, including the predominantly low-rise buildings that characterize the rest of the country.
According to the report, it should be possible to actually make buildings completely greenhouse gas free, mainly by increasing heating and cooling efficiency, and by heating and cooling with carbon-free sources of electricity, both from the building and from the electric grid. They estimate that single and two family homes could be the most self-sufficient by using solar energy to provide about 80% of electricity needs.
How do you minimize building energy use? You can minimize air exchange losses, increase insulation, use triple-glazed windows, add sunshades to south-facing windows, add heat recovery ventilation, and the use of various kinds of heat pumps. They emphasize that combining these techniques is much more effective than just using a few alone. For instance, better insulation in the walls is not nearly as efficient if the windows are very leaky, and vice versa.
Insulation also affects another variable, ventilation. All houses need some kind of input of clean outside air and expulsion of stale air. In most buildings, this air exchange takes place because there are leaks in the walls, and the windows let in air. Obviously, this is not an optimum situation if you are trying to conserve energy and minimize heating and cooling bills. The solution used in what is called a “Passivehaus” design, in which there is virtually no outside energy needed for heating or cooling, is to have mechanical ventilators do the air exchanges instead of the leaks.
So while the Green Council calls for much greater use of insulation and better windows, it also calls for mechanical ventilation, which uses very little energy to pre-heat outside air in the winter and pre-cool outside air in the summer, while transporting stale air to the outside.
They also call for a fair amount of insulation. Insulation is rated using the “R” scale, where a lower number indicates a lower capability to stop heat from being transferred, that is, losing heat or coolness. Uninsulated brick or wood buildings have ratings of R-2 to R-4, whereas code compliant buildings are closer to R-8 or R-10. The Council calls for R-20 for one or two family homes, and R-30 for commercial buildings (p.18-19). This would mean either applying insulation within walls, if that is possible, or if not, covering the building with insulation or applying insulation to interiors. Obviously, this could be expensive, particularly if the insulation detracted from the aesthetics of the building.
In addition, windows can be quite a severe source of energy loss as well. A single-pane, or glaze, window has an R value of 1; even double-glazed windows, which have been installed since the 1980s, only have R values of 2 or 3 (windows are usually listed with a U value, which is the inverse of the R value). High-quality triple glaze windows have an R value of 5, and there is research going on now for windows that are R-20, as good as an insulated wall. In addition, putting 3-foot sunshades on south-facing windows blocks the sun in the summer, but lets the sun through in the winter because the sun is lower in the sky in the winter months.
The other major technique for decreasing the need for energy for heating or cooling is to use the technology of heat pumps. Heat pumps use the heat difference between the temperature of the outside air, water, and/or ground and the temperature of air in the building. For instance, for a ground-source heat pump, plastic pipes are installed to a depth of at least five feet, where the temperature stays constant all year round (generally around 55 degrees in the United States). When the building is hot, heat is transported out by the liquid that fills the pipes, and when the building is too cool, heat is transported in. Generally, ground-source heat pumps use only about one-third of the electricity of an all-electric heating system (I once calculated that you could shut down all of the coal plants in the U.S. if you installed ground-source heat pumps under all residential and commercial buildings).
In the case of a well-insulated building, these heat pumps would not need to be as powerful as for a noninsulated building, another example of the advantages of using all energy efficiency techniques at the same time (sometimes referred to as positive feedback loops, or self-reinforcing feedback loops). Air heat pumps can also be used to heat water, although since this takes heat out of the air, this would require more heating for the building in the winter. In addition, the report calls for spreading the technique used by most single family homes now, to place the condenser for the air conditioner outside, thus eliminating the leaks of window-mounted air conditioners, (called “mini-split heat pumps”).
Still, some electricity would be needed, even in an energy-efficient building, to power the ventilators and heat pumps, as well as the appliances. For a single family home, only 1/7th the energy would be needed in a well-insulated building (This is assuming gas stoves would be replaced with electric ones) As the report points out, “Solar energy is perhaps the most abundant, yet underutilized, of all potential renewable energy sources.” (p.24).
The amount of solar energy falling on the ground is called “insolation”, and for New York City about 4.34 kilo-watt hours of energy fall on a square meter of surface per day, if you average over the entire year. For comparison, that is about the same as Germany, which has had a boom in solar energy installation and can occasionally provide up to 20% of its electricity from solar. Even low-rise residential buildings could get about 40% of their electricity from solar panels on their roofs, and as previously stated, for single family buildings, the figure goes up to 81%(p.24). All extra electricity could be provided by a fairly small amount of electricity generated by wind farms.
We’ve been exploring the wonderful world of buildings, the focus of the report focuses. But for areas outside NYC, transportation looms large as an energy consumer. In NYC, it would be relatively easy to cut down on carbon emissions from transportation because you can increase transit, since buildings are densely packed. You could also mandate that cars and trucks be hybrid or all-electric, since the distances travelled are small enough for actually-existing electric vehicle technology.
However, outside NYC, these techniques become more difficult to transfer. The great problem outside NYC is the lower density (sometimes called sprawl, if we want to be undiplomatic), which makes transit much more difficult to implement, or at least, to make cost-effective. The long-term solution is to create walkable communities and create higher density, but that is a subject that is far beyond the scope of this essay, as prudent authors say when they encounter an interesting but monumental additional topic.
What would a program such as this cost? The Council’s report argues that, when you consider the energy saved, the building program would just about pay for itself. The cost for a single family home would be about $26,000; since the report is considering the world of 2050, then we have 37 years to repay the cost of the retrofits, as well as replacement of things like boilers that usually are swapped out over that long of a time span in any case. For New York City, including transportation costs and also some costs associated with cutting down on waste emissions, the 37 year total would be $167 billion out-of-pocket, or about $5 billion per year (p.28).
The big question is, how can this be financed? Energy efficiency has become a classic problem of “market failure”, that is, there is an obvious, predictable return-on-investment, yet the market is not providing the required services. The Federal government had to step in, starting in the 1930s, in order to build a mass market for home mortgages; might the Federal government, or perhaps the State government, be able to do the same for the very practical and urgently needed program of making all buildings energy efficient?