Freeze Frame

One of the great underrated bands of a bygone era…

Despite the embarrassing music video, the J. Geils Band had their only #1 album in 1982 with Freeze Frame.  Thank you MTV!

And speaking of  freezing, what impact does glycol have on flow and, by extension, head loss?

Last time we showed that glycol kinda messes with the Universal Hydronics Formula.  For 100% water, the formula reads:

GPM = BTUH ÷ (ΔT × 500)

That 500 comes from multiplying the weight of 1 gallon of water (8.33 lbs) by the number of minutes in an hour (60) and by the both the specific heat and specific gravity of water (both are 1).

But glycol is heavier, thicker and a less effective heat transfer fluid than water, so that 500 will change.  As we showed last time, if we used full-power Cryo-tek -100 (which will provide burst protection to -100 degrees, F), the 500 changes to 468.  What does that do to our design?

Well, let’s say we have a 75,000 BTUH system and we’re designing to a 20 degree ΔT.  We want to determine the flow rate for the job so we can size the boiler piping and the system circulator.

If we were using 100% water, here’s what we’d come up with:

GPM = 75,000 ÷ (20 × 500)

GPM = 75,000 ÷ 10,000

GPM = 7.5

So our circulator would need to provide 7.5 GPM worth of flow, and using standard hydronic pipe sizing guidelines, our boiler piping would need to be 1 inch.

With full strength Cryo-tek -100, we’d come up with this:

GPM = 75,000 ÷ (20 × 468)

GPM = 75,000 ÷ 9,360

GPM ≈ 8

With glycol in the system, we’d need to pump about a half a gallon more per minute to deliver the same amount of heat.

In this example, the pipe sizing wouldn’t change, and it’s doubtful the circulator sizing will change, but it’s always good to double-check because changes in flow will result in changes in system head loss.

Let’s presume the system we’re looking at calculated out to 7 feet of head at 7.5 GPM.   That operating point puts this system right in the Taco 007’s wheelhouse.

 

But with glycol, we’re talking about a flow rate of 8 GPM.  What would the head loss be at that flow rate?

Fortunately, there’s a math formula to help figure it out!

(Head 1 ÷ Head 2) = (Flow 1 ÷ Flow 2)2

Head 1 is the original head; Head 2 is what you’re trying to find out.
Flow 1 is the original flow; Flow 2 is what you’re plugging in.

So let’s plug in what we know:

Head 1 = 7’

Head 2 = ✗

Flow 1 = 7.5 GPM

Flow 2 = 8 GPM

So here goes…
(Head 1 ÷ Head 2) = (Flow 1 ÷ Flow 2)2

(7 ÷ ✗) = (7.5 ÷ 8 )2

(7 ÷ ✗) = .942

(7 ÷ ✗) = .88

Now for some of that 7th grade Algebra we swore we’d never use in the real world:

First, multiply both sides by x (we need to isolate the x!)

7 = .88✗

Now divide both sides by .88 to isolate the x.

7 ÷ .88 = ✗

And now we finish it off:

✗ = approximately 8’ of head.

Not a lot of difference, is there?

While there was nothing in the Cyro-tek spec sheets, the Noburst -100 spec sheet did have this nice little tidbit:

-The pump head should be increased by 10% over the minimum requirements for those with plain water.

Adding 10% to 7’ of head would give us 7.7’ of head.

Close enough!

And how about one more from the Wolfa Goofa with the green teeth

The J. Geils Band was a finalist for the Rock ‘n Roll Hall of Fame in 2011, but didn’t make it.

But ABBA did.  Go figure…

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