Hydronics, Circulators & Hot Wheels

Any of you old enough to remember playing with Hot Wheels cars?  I had a boatload of ‘em with about six miles of track, and would spend rainy Saturdays having a full-field drag race to determine my fastest Hot Wheel ever.  It was usually the Classic Chevy Nomad, the Silhouette or the Deora (lost the damn surf boards within a week!).  I always wanted the Jackrabbit Special to win, but it never did.

Sometime around 1970 Hot Wheels came out with something called the Super Charger. It was a little garage-looking building with some fast spinning rubber wheels inside.  When the car entered the Super Charger, it would hit the rubber wheels and come shooting out the other side wicked fast.  You didn’t need gravity anymore…the car would zip around the track all by itself.

Problem was you couldn’t make the track too long or too elaborate.  The car would slow down in the curves, as well as on the straight-aways.  Too long of a run, too many turns and the car wouldn’t make it all the way around, so you learned pretty quickly what kind of track would work best and what wouldn’t.


Too long of a track, too many turns and the car won’t make it all the around the track and back into the Super Charger?  If you substitute a circulator for the Super Charger, pipe for the orange Hot Wheels track, fittings for purple track connectors and plastic curves and water for the Splittin’ Image and you have….

A hydronic system!

The circulator is the Super Charger of the system. Instead of spitting a car out of one end and around the track until it comes back into the other side, the circulator moves water from the inlet to the outlet at a higher pressure, sending that water through the pipes back to the inlet side.  It has to move enough water (Gallons per minute) while overcoming the friction of the pipe and fittings, or the head loss.

Last time we figured out the flow rate needed for an 88,000 BTUH panel radiator system.  We calculated the required flow rate at a 30-degree Delta T to be roughly 6 gallons per minute.  That 6 GPM is the car.  Let’s call it the Red Baron (It would have been funnier if Hot Wheels had an Olds 88, but nothing’s ever perfect…)

Next we have to figure out how long the track, err…the piping run is for the worst-case zone (we’re doing a zone valve job, by the way).  We need this number to calculate the head loss that the circulator will need to overcome. For giggle and grins, let’s say all three zones are equal in terms of BTU’s, but the longest one runs about 140 feet from the outlet side of the circulator all the way around back to the inlet side.  (In zone valve applications, the circulator has to move the total GPM, but only has to overcome the worst-case head loss zone. If it can overcome that head loss, it can certainly overcome the others.  You don’t have to add the head loss from all three zones together).

Fittings also create pressure loss and we need to account for them.  The easiest way is tosimply multiply the length of the run by 1.5 – this adds an extra 50% to the overall run for fittings.  You could count the fittings and look up the equivalent pipe length for each fitting (a ¾” copper elbow, for instance, has the same pressure drop as 2½ feet of straight copper pipe), but in most cases, estimating is okay here.

Multiplying the length of the longest run by 1.5 gives you something called the “total developed length,” or “total equivalent length,” which is how long the pipe would be if you straightened out the fittings:

140 × 1.5 = 210’

You’d then multiply the total developed length by .04 to estimate the head loss.

The .04 represents 4 feet of head per 100 feet of straight, properly sized pipe (see sidebar for pipe sizing guidelines).

210’ × .04 = 8.4’ of head loss.

So when selecting our circulator, we’d choose one that could deliver 6 GPM while overcoming 8.4 feet of head loss.  Let’s look at a Taco pump curve chart and see which one makes the most sense…

From the looks of things, a Taco 007 would be a solid choice.  One could also select the 008 or, looking at the next chart, a 00R 3-speed (but both of those choices might prove to be problematic, which we’ll discuss next time) or even a 0010 3-speed.

Now remember, this is a head loss estimate.  There is a way to calculate head loss more accurately.  It’s a little more work, but the results will be interesting.  We’ll do that next time, as well.

Couple of questions for you first…

  1. Do you go through this level of analysis when you do a job?
  2. How do you select the right circulator for your jobs?
  3. Did you have any Hot Wheels?  What happened to them? (My nephew inherited mine – I expect to see them on eBay any day now…)

And THIS was one sweet car…

The Jackrabbit Special

6 Responses to “Hydronics, Circulators & Hot Wheels”

  1. And THIS was one sweet car…

    has a dead link in it….

  2. What I remember most about the hot wheels track was that my mom used to paddle my *ss with it whenever I misbehaved. In this instance, it was my mom’s arm, not the circ pump that was the damned supercharger. The only thing spinning around was me, with her ahold of my ear, slapping my *ss with the track, and me running in circles around her trying to get away!
    Lordy, thanks for the memories!

  3. Why is it that I can visualize this quite clearly? My mom never resorted to hitting — she was a Hall Of Fame “guilt-er” I think Italian mothers are born with this ability…

  4. You should have kept your Hot Wheels set, and introduce it into the apprentice training course.
    Since all the new apprentices played with video games and arent able to understand so quickly.
    I’m tired of the deer in the headlights look.

  5. Maybe when Super Mario gets new energy and can run faster?

    Nahh….that’s a stretch.

  6. How do you know when you have a particular gpm (1gpm,2gpm,etc) in the open tank with the control valve in the blog about pump performance curve?

    also, Ihad two super chargers and loved to put two cars on the track at the same time ,180 degrees apart to see who caught up to who. I later got a “straght scoop” Sizzler car that came with a re-charger in the shape of a gas pump called the juice machine. It didn’t need the super charger and was fast as hell!

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