Energy codes have all kinds of requirements. You have to have certain R-values in walls, floors, and ceilings. Your windows have to have the right U-values and solar heat gain coefficients. The infiltration rate and duct leakage have to be measured and come in below a threshold for your climate zone. And then there are the different pathways for compliance: prescriptive, UA tradeoffs, performance, or HERS Index. But what if all you needed to do was to hit two numbers?
The Perfect Energy Code
Henry Gifford and Chris Benedict put on a little 10 minute, one-act play last year called The Perfect Energy Code (watch below), and they propose a dramatic simplification of the energy code in New York City. No more energy modeling. No more reference designs. No more prescriptive or performance paths. Just hit their two numbers with your design and you get your permit. Install the equipment you designed into the building and you get your certificate of occupancy (CO).
Simple enough for you? Watch the video to see what they say about it.
The only two numbers you need
The two numbers they put in their perfect energy code are described in this screenshot from the video:
You design your building and specify the heating and cooling equipment you’re going to use. Then divide the total input capacity of those systems by the square footage of the building. They give 15 BTU per hour per square foot for heating and 5 Watts per square foot as the thresholds for New York City.
For the nitpickers, yeah, those equations above shouldn’t both have an x on the right. If the heating has to be less than x, the cooling would need to be less than y, but you get the point.
Each location would then have its own numbers for x and y. The colder the climate, the bigger the x would be. The hotter the climate, the bigger the y would be. It’s a lot like the new climate-specific passive house standard from PHIUS in that way. Those numbers would also have to depend on what type of building it is. Supermarkets, hotels, schools, and homes have different needs and consumption patterns.
Their numbers are a kind of energy use intensity (EUI), which is the energy consumed by a building per square foot. Normally it’s calculated for all energy used over the course of a year. Their numbers are based only on heating and cooling rather than all energy, and they use rated input energy rather than actual measured energy use.
Could it work?
It would definitely be simple. It also, as they say in the video, would eliminate a lot of the ways people game the system with energy modeling. Verifying compliance would be a breeze, too. So what are the downsides?
The designers of new buildings would still have to do some modeling to make sure they size their systems properly. They’d still have to make sure the building enclosure is well-insulated and airtight, as long as the x and y are low enough for the climate and building type. If the equipment specified turned out to be inadequate because of poor building design or installation problems, someone would have to pay to fix the problems.
Will people try to cheat? Probably. But with a simpler energy code, it would be harder to cheat, I think. What could they do? Install one system for the final inspection and then replace it with a bigger one after they get the CO? Try to have extra capacity hidden in the building somewhere and hope the inspector doesn’t find it? Come in afterward and install mini-split heat pumps if there are problems? Certainly possible but not smart.
I think something like this really could work.
What’s Your Energy Efficiency Number? — my article on EUI, with a spreadsheet calculator
I Use an Air Conditioner Sizing Rule of Thumb! — similar idea to Chris’s and Henry’s
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