Delta (T) Dawn

Okay, I admit it.  I’m a rocker from way back, but I do like me some country music…

That’s a 13-year-old Tanya Tucker singing “Delta Dawn,” a top-10 country hit in 1972.  A year later Helen Reddy made it a #1 Pop hit, but it says here the original is still the best.

And speaking of Delta Dawns, here’s another variable speed Delta-T story for you, courtesy of Richard McGrath – one of New Jersey’s finest hydronics pro’s:

Two winters ago, Richard was servicing a small apartment building on the Jersey Shore (sorry, no Snookie here!).  There was an old-ish Weil McLain oil-fired boiler with four old-ish B&G circulators serving 4 zones.  According to Richard, the most recent fuel bills were averaging around $900.00 per month.  On top of that, the tenants complained the comfort was, at best, spotty.

“We decided to make some changes,” says Richard.  Out went the four old B&G circulators, and in went 4 Taco 570 Series Zone valves.

Along with a Taco 0013-VDT variable speed circulator, set to operate at a 20o Delta T.

Everything else in the system remained the same.

A little over a month later, Richard was back at the apartment house on a plumbing service call.

“The building owner came up to me with her latest oil bill.  She wanted to know what the heck I had done to her boiler.”


“She showed me the bill for the past month.  The very same boiler had used only $600.00 worth of oil even though the month was, on average, about 8 degrees colder than the month before.

“And she told me the tenants were telling her how much more comfortable they were. Talk about a win-win!”

What this shows is the benefit of a circulator that always provides the right flow rate.  A 00-VDT will speed up and slow down in order to maintain a fixed Delta-T in the system.  And since GPM equals the BTUH load at any given point in time (which is based on how cold it is) divided by the product of the system Delta-T times 500, a 00-VDT will vary its speed based on how many zones are calling, on what combination of zones are calling and on how cold it is outside.

What does that mean to the boiler?  You’re taking out only the BTU’s you need while making sure the water coming back to the boiler is always around 20 lower than the water going out.  As a result, a large mass boiler such as the big old Weil in question will wind up firing less often but for longer intervals.  The system takes advantage of residual heat in the boiler, and short-cycling is sharply reduced.

The end result? A 33% reduction in oil consumption during a colder month.

And that’s an attention-getter!

Was the electric consumption lower?  Yep, but the savings paled by comparison.

Want to know more about variable speed Delta T circulators?  Click here, here and here!

And if classic country isn’t your cup of tea, try a little classic Cocker


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