In our February 2016 edition we published an article, “Results may vary: Reducing energy usage with cool roofs,” by Craig Tyler. Kurt Shickman of Global Cool Cities Alliance wrote in to comment on what he calls an “inaccurate down-portrayal of roof reflectivity and peak energy demand reductions.”
We shared his comments with the author and now present them here:
The article, “Results may vary: Reducing energy usage with cool roofs,” by Craig Tyler, published in the February 2016 issue of The Construction Specifier, included a section in which the author inaccurately downplays new research linking roof reflectivity and peak energy demand reductions. Most commercial consumers pay a peak demand charge, which is often a substantial (30 to 50 percent or more) portion of their bill. The good news is that research—including the paper cited by the article’s author—shows these charges can be significantly reduced with reflective roofing. Further, there are trusted online tools that factor in peak demand charge savings to help commercial energy consumers determine how much they can save with reflective roofing.
The author dismisses peak demand charges as an obscure utility rate practice most businesses would not need to pay. In fact, a simple Google search reveals that utilities in all 50 states have a demand charge for commercial/industrial users. You can see if you are being charged differently for peak usage on your own bill. The charge will appear in kilowatts, rather than kilowatt-hours. Medium to large commercial companies are almost certainly paying a peak demand charge every month.
The author states that cool roofs may only have “some effect on certain building owners with peak energy demand charges.” This phrasing downplays the potential to reduce demand charges by installing cool, reflective roofing. The savings on demand charges is large, and up until very recently, a largely hidden benefit to the commercial energy consumer. The paper the author cites shows significant demand charge savings accruing when cool commercial roofs are installed. That paper evaluated new buildings in every climate zone using a conservative demand charge and base rate. The demand charge savings outpace the base rate savings in every zone and, in the coldest climates, make cool roofs a net economic benefit to buildings. In short, understanding and capturing the demand charge impact of cool roofs is critical to an accurate cost/benefit analysis.
With the peak demand savings version of the Department of Energy (DOE) Roof Savings calculator mentioned in the paper, it is possible to easily calculate the effects of cool roofs on peak demand charges. It is free and it comes with links to additional energy information that can help a building designer make the best design decisions for any situation. This tool could actually increase the value that the building professional brings to the table in establishing the ultimate roof design.
Mr. Shickman is correct when he stated that in my article I “downplayed” the role of peak demand as the topic is more complicated than the article length would allow. Conversely it is not as simple as a simple “Google search” either. The energy generation and distribution in the United States is not uniform from State to State and “results may vary”. Peak Demand is not obscure but it is also not cut and dry. A large manufacturing facility in Pennsylvania, such as the company I work for, does not see a peak demand charge on their bill because there isn’t one. This means the local energy supplier has chosen to either include a peak demand in the actual cost of the electricity per kW without labeling it as such or has determined the electricity use on some other calculation and is billing at a fixed rate due to the large consumption of energy, a kind of “discounted rate”. My residential electric bill, when I lived in Saint Louis, MO, did not have a peak energy rate on the bill either, but my residential bill in Pennsylvania does.
The phrasing in my article is correct. Check your bill, at home or office, and if you are a commercial building owner, especially, find out for yourself. Not all electricity providers have a peak demand charge. Also keep in mind that electricity distributed to a building by a supplier is only one energy source that a building may use. Natural gas (for HVAC or Hot Water), on-site solar (PV/solar hot water), and/or wind turbines will also off-set electrical energy use of a building and will not be subject to a Peak Demand Charge. A building using Natural Gas as the main heating source in a heating dominated climate such as Chicago or Boston will not reap the same benefits from cool roofing in the summer due to the “heating penalty” as if it were used in Dallas or Miami. The heating penalty is the difference in cooling energy summer savings and the winter heating energy losses. If the cool roof stays cooler in the summer, it is also true that it is cooler in the winter, which means the roof is losing more heat (from the building) through the roof than if the roof were warmer , when using a darker material like tan, gray or black.
I suggest looking at your own bill, discuss it with your building owner and maybe run a calculation with the DOE Roof Savings Calculator, you will be better informed to make a decision about energy savings, Peak or not, using a cool roof.
The author may wish to review work published by Princeton University (The influence of albedo and insulation on roof performance : An Observational Study Energy and Buildings, 23 February, 2015), as it relates to the benefits of cool roofs in northern climates, in which they concluded:
“… summarizing our findings leads us to conclude that white/reflective membranes with high R-value should be recommended for the Northeastern US region where our study took place. The insignificant differences observed between the heating loads of white/cool and black roofs during winter months, which we linked to the negligible impact of albedo during peak heating periods (as opposed to its crucial role during peak cooling), support a broader conclusion that cool roofs can help reduce building energy consumption in many cold climate areas that have much higher heating degree days than cooling degree days, which is the case for our study area (heating degree days are almost 5 times the cooling degree days in Princeton, NJ)….”