Up Around The Bend

1970 was very kind to Credence Clearwater Revival.  And if you want a song to kick off a new decade, here ya go…

“Up Around the Bend” hit #4 on the Billboard charts in the spring of ’70 and opened Side 2 (remember album sides?) of their classic Cosmo’s Factory LP.  The album was loaded with top 10 hits and ranks 265th of Rolling Stone’s 500 Greatest Albums of All Time list.

Now that we’re around that bend, let’s reminisce.  We’ve been calculating electrical consumption and operating costs for circulators in recent blog posts (here and here), and we’ve established two truths:

  1. Residential ECM circulators (i.e. Taco Bumblebee) don’t use very much electricity.
  2. Standard split-capacitor motor circulators (i.e. Taco 007) use more, but not much more.

Here’s the beef:

A Taco 007 at 81 Watts, running 2,500 hours over a heating season at 10 cents/KWh, costs roughly $20.25 to run.  A similar sized ECM circulator averaging approximately 25 Watts would cost $6.25 to run.

That’s a 70% savings. It’s also only 14 bucks.

At 3,000 hours and 20 cents per KWh?  The annual difference is about $33.00. Over 10 years, factoring in rate hikes, the “savings” may total $415.00 – or just under $6.00/month.

Why is the dollar difference so small?  The amount of electricity used is small.

So why use a high efficiency circulator?

Efficient components are nice, but we want an efficient system.  A variable speed circulator may help make your system more efficient, depending on how it varies speed, either Delta-P or Delta-T.

A Delta-P circulator tries to maintain a consistent pressure differential.  As zones open and close, the circulator goes faster or slower to keep that pressure differential relatively fixed, which is nice (more on Delta-P vs. Delta-T here).

Delta-T varies speed to maintain a consistent fluid temperature differential (sensors are strapped to the supply and return piping).  Delta-T, a core fundamental of hydronics, is a key element in the Universal Hydronics Formula:

GPM = BTUH ÷ (ΔT × 500)

GPM = gallons per minute flow rate required at any given point in time.
BTUH = heat required at that given point in time.
Delta-T = designed-for fluid temperature drop.
500= constant for 100% water.

For a baseboard system needing 53,000 BTUH under design conditions with a 200 Delta-T, you’d plug in the following numbers:

GPM = 53,000 ÷ (20 × 500)

GPM = 53,000 ÷ 10,000

GPM = 5.3

To deliver 53,000 BTUH at a 200 Delta-T, you’d need 5.3 GPM.

A Delta-T circulator will always provide the right flow rate for the system. When the load is 53,000 BTUH and the Delta-T is fixed at 200, the flow rate will have to be 5.3 GPM. If a zone satisfies and the zone valve closes, that means the system needs fewer BTU’s.  When that happens, the system return water temperature starts going up, making the system Delta-T smaller.  The return sensor sees that and the pump immediately slows down to keep the Delta-T constant.

The opposite happens with zone valves open.

In addition, a Delta-T circulator varies speed based on how cold it is outside.  In the above example, the circulator delivers 5.3 GPM under design conditions.  At 350, the BTUH load would only be 26,500. The circulator would only provide 2.65 GPM.

How does it know?  As fewer BTU’s are taken out of the system, the Delta-T will try to get smaller.  The circulator sees this and will slow down until it finds its happy place while maintaining the designed-for Delta-T.

For the types of systems we install in the US, the Delta-T approach makes a ton of sense because it will basically always run at the right speed.  This impacts boiler operation as well, as we’ll see in the next installment.

The curtain came down on some major musical acts in 1970.  That’s the year The Beatles broke up, as did Simon & Garfunkel. Heck, even Davy Jones left The Monkees.

But for sheer musical impact, it’s hard to underestimate the breakup of the original Bonzo Dog Doo-Dah Band

The Bonzo’s went their separate ways in 1970.  The world hasn’t been the same since.


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