Bees Make Honey

Lost a great one yesterday.  Alvin Lee of 10 Years After...

The dude was in Clapton’s class for flying fingers. If you not convinced check out the “encore” video at the end of the blog!

As a trainer, you live by the notion that all questions are good questions.

Today, lots of those questions are “cyber-questions.”

You never know who’s asking, or why.  But sometimes you get a good one…

“Still don’t get why the BumbleBee varies its speed based on Delta-T.  Everyone knows Delta-T is a ‘moving target.’ Walk into any boiler room and the Delta-T will rarely, if ever, be what you designed it to be.”

Well, part of that statement is absolutely true.  With any fixed speed circulator, or a Delta-P variable speed circulator, for that matter,  the system Delta-T will be all over the map – wider when it’s colder out, much smaller when it’s warmer out.  We’ve touched on why that is in previous blog posts (here, here and here).

The first part of that statement is not only false, it’s irrelevant.

The Delta-T in a hydronic system is most definitely not a moving target.  In fact, it’s not a target at all.

Has a customer ever called to complain about his Delta-T?

Didn’t think so.

The real target in any heating system is BTUH.  That’s what delivers the wintertime comfort.  And as we all know, the BTUH load of a house or zone varies based on thermostat setting, time of day and, of course, the weather.

If you’re looking for a moving target, there it is.

And if you want to hit a target – moving or not – you need the right ammunition.  In hydronics, the right ammo comes in the form of flow rate (GPM or “gallons-per-minute”).  To hit the BTUH target, you need the right flow rate through the zone or system.

Hey hunters! If your target is fairly small and fairly close, small caliber ammo gets the job done, right?  If the target’s larger and farther away, small caliber ammo doesn’t work so well.  You need more firepower.

Flow rate is the same thing, only different.

If it’s mild out and the heating load is small, the required flow rate will be small.  When it gets colder, the load gets bigger and you’ll need more flow.

So BTUH load is the moving target, and flow rate is the ammo.  Where does Delta-T fit in?

Simple – Delta-T is your aiming device.  It’s the scope on your rifle that allows you to focus in on your moving target (BTUH) and nail it dead-center with the right caliber ammo (GPM) every time.

The Universal Hydronics Formula expresses this analogy mathematically:

GPM = BTUH ÷ (ΔT × 500)

BTUH is the heating load, which changes all winter long depending on a whole bunch of factors, including the weather.  GPM is the flow rate required to deliver the BTUH.  That flow rate changes in lock step with the BTUH heating load.  The greater the heating load, the more GPM is needed, and vice-versa.

Delta-T, of course, is the designed-for temperature drop across your piping circuitry.  Could be 20 degrees for fin-tube baseboard, panel radiators or fan-coils, or it could be 10 degrees for residential radiant floor heating.  Or it could be something else, depending on what you’re installing.

But the point is this: you deliver BTUH (the moving target) by providing the proper flow rate (which changes with the heating load).  To always deliver the right amount of flow based on the changing load, you’ll want to use a circulator that’ll do just that.

And if you vary the speed of a BumbleBee or 00-VDT to maintain that designed-for Delta-T, then you’ll always have the right flow.

One thing about changing flow, though.  It does affect radiator output.  We’ll look at that next time.

And safe home, Mr. Lee…

“Slow Blues In C.”  Talk about face-melting…

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