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Taking your measure: a do-it-yourself calculation benchmarks your building's ene
Habitat’s column dedicated to helping you reduce operating costs using green initiatives examines your building’s energy performance and how you can calculate it.
Your building’s heating bills are going through the roof. You’ve heard about energy audits but you’ve also heard about the hefty price tag that comes with them – as much as $15,000. If you are going to spend that kind of money, it would be helpful if you had an idea about whether it would actually be worth it. Will you be able to find real energy savings – or will you spend all that money just to find out there’s nothing you can do?
The good news is there is a do-it-yourself method to calculate energy performance. The bad news is that wading into the world of energy efficiency can be confusing and complicated. If your building is going to begin to take green steps, however, wade you must.
“Buildings fall into one of three categories,” says Cecily Channell, an architect at Steven Winter Associates, a building systems consultant firm specializing in energy-efficient properties. “They are either a good, average, or poor energy performer.” The mark of your building’s performance lies in the number that equals your British Thermal Units (BTU) per square foot per heating-degree-day (HDD). This number can then be compared to a universal scale, which will tell you in what category your building falls.
Ironically, the hard part is not the calculation – that is within the capabilities of any middle-school student – but the gathering of the data. “You need two years’ worth of fuel bills with the exact date of delivery, the volume, and the price,” explains Andrew Padian, director of multi-family services at Steven Winter Associates, which has performed audits in multi-family buildings for the Department of Housing and Urban Development, the Environmental Protection Agency, and others.
For buildings that have access to their fuel bills, the raw information needed to do the math can be found there. But this means retrieving all the bills for the past two years – a time-consuming task. For oil users, another method is to request a detailed usage report from your oil supplier. (Be careful: you don’t want a summary report that merely gives you monthly usage, because you need actual delivery dates and gallons delivered if you’re to calculate correctly.) If your building is heated with gas or steam, however, you need your account numbers; then you need to go to the Con Edison website and pull up your usage figures. (Gas customers go to www.coned.com; steam customers go to www.coned.com/steam. Once there, click on “Customer Central.”) If Con Ed isn’t your supplier, go to the web site of your utility company and follow similar steps.
Figuring square footage can also be simple. For box-shaped buildings, it is width times depth times the number of floors. Padian suggests measuring two adjacent sides of the roof, if necessary. He emphasizes that you need to make calculations for the whole building, not just the residential-unit area. Hallways, lobbies, and utility rooms have to be heated, too.
For irregularly shaped buildings, the total square footage should be noted on the building plans and may also be recorded on official documents. There are also on-line resources available. Total area is not one of the data points given in the Department of Buildings’ Building Information System, but it is included on the free part of Property Shark, www.propertyshark.com. (You’ll have to register with Property Shark to access the free portion, but you’ll find lots of wonderful information about your building, including square footage.)
“You find the lowest heating use for midsummer and find the average daily use. Multiply that use by 365 days in the year, and you have your base load for hot water and other operations,” Padian notes. “Anything above that you consider to be heating.” (See calculation guide and worksheets, p. 7).
But don’t rush to calculate winter heating load just yet. “Most buildings do not address their hot water use very closely,” says Padian. “Minimum code temperature in New York City is 120 degrees Fahrenheit, which is perfect. But 140 degrees is very common, and I have often seen higher.” That starts to become not just wasteful but dangerous: at 137 degrees, water will burn.
Padian says that controlling hot-water temperature can be done easily by adjusting the boiler, and installing 2.5 gallons-per-minute showerheads. He adds that many boilers, even in relatively upscale buildings, may not have proper temperature-control devices. But the nominal cost of having one installed will pay for itself very quickly.
Once you have the base summer heat use and average annual daily use, it is simple to calculate the differential from winter peak heating. To follow the steps for the final calculation, the only other figure you need is “heating degree days,” which is available on-line from many sources, including the National Weather Service.
Then comes the fun part. Once you have a BTU per square feet per HDD number – be it 5, 15, or 40 – you can decide whether you need a full-blown audit or not. Says Padian: “We have seen lots of buildings at 5 or 6 BTU per square feet/HDD. That is about as good as you can get. If you are in single digits, you probably don’t even need to have an energy audit.”
On the far other end of the scale are the buildings in the 30s and 40s. “If your building is a 40, it’s [an energy-wasting] pig,” Padian notes. “You ought to fire your super and your management company.”
To put the problem in another light, in buildings with usage numbers in the 30s and 40s, the residents – not the board, super, or manager – are making the heating decisions for the building. “People in the upper floors are opening their windows in the middle of winter to control the heat in their apartments,” says Padian. “But that only creates a chimney effect, making their units warmer and the lower floors colder. So who is running your building?”
For worst-case scenarios, he suggests starting at the ends and working your way to the middle. Adjust the heat in the upper floors to a reasonable level, and be sure all the windows are shut. Then go to the basement and first floor. Foam all the cracks and close all the windows. The temperature should stabilize within the entire building relatively quickly.
Padian is also a strong advocate of turning the heat down at night. “Most of this stuff is really so simple. Just a 10 percent setback for eight hours cuts heat use 12 percent. Most clanky 12-year-old heat timers can do that. And they are just slightly more expensive than a plain mixing valve.”
Padian points out that similar buildings can have vastly different energy usage levels. All across the country he says his company has found remarkably uniform differences from building to building within a complex. They vary by a ratio of seven to one, which is borne out on scale of BTU per square feet per HDD – the best buildings are 5 or 6, the worst are 40.
“If you own several different buildings you need to find the sevens and ones in your collection,” says Padian. “In most cases the sevens will not be properly served by renewable energy strategies until the [energy use] load is cost-effectively reduced. In our experience, most buildings waste 40 percent of their energy through a combination of construction defects and management or maintenance choices. You need to start there.”
Last year, the New York State Energy Research Development Authority tracked 175 buildings across the state in areas ranging from 4,800 HDD to 9,000 HDD. The worst buildings had heating usage of 35 BTU per square feet/HDD while the best were at 5.
One important factor that Steven Winter Associates has also found is that insulation is often misunderstood and misused. “If insulation is already sufficient, adding more will not make a significant difference,” says Padian. “And if existing insulation is not air-sealed, then, air in the building can circumvent the insulation, making it less effective.” In short, it doesn’t matter what you put under your roof if the residents in the apartments below have their windows open.
Looking further down the road, Padian has a grand idea: management companies should compete with each other on the basis of their buildings’ heating efficiency. “Management companies don’t look at these numbers because co-op and condo boards don’t ask them about those numbers. But I believe the really good operators could use their BTU/square feet/HDD numbers as a marketing tool. They should publish them as a competitive advantage.”
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