Clap For The Wolfman

Back in the day, any guy who wanted to be a disc jockey had to try his Wolfman Jack impersonation.

The Guess Who on The Midnight Special with the one and only.  Another great hit from 1974.

You gotta clap for The Wolfman.

So last time we discussed how a Delta-T circulator would work in a panel radiator system with thermostatic radiator valves (click here to review).

How would a Delta-P pump work in that situation?

Well, since this is the job Delta-P pumps were designed for, you gotta assume they would work pretty well.

Panel rad/TRV systems are the most common hydronic installations in Europe. The radiators are piped home-run style – using small diameter pex – to a common manifold, so each radiator has its own dedicated supply and return and its own TRV for what amounts to room-by-room zoning.

As discussed last time, TRV’s are rarely, if ever, open or closed.  They modulate, which means they’re either opening or closing.  The mechanism that tells a Delta-P circulator speed up or slow down is resistance against the impeller.  As a TRV closes (meaning the radiator is getting closer to satisfying the TRV “thermostat”), there will be more resistance against the impeller.  This is a sign to the circulator that less flow is needed, so it slows down.

As a TRV opens (meaning the radiator needs to add more heat to the room), there’s less resistance against the impeller.  That’s a sign for the circulator to speed up.

The TRV regulates flow through the radiator.  The Delta-P circulator simply creates flow through the system.

As discussed last time, it’s virtually impossible for all TRV’s in a system to be doing exactly the same thing at exactly the same time.  Since TRV’s modulate, one TRV may be opening while another is closing. So one is telling the circulator to speed up while another is telling it to slow down.

What’s a circulator to do with all this conflicting information?

The same thing the Delta-T pump does – it, for lack of a better term, average it out.  The Delta-P looks at the resistance against the impeller created by the system as a whole.  If one radiator needs the circulator to speed up while another needs it to slow down, a Delta-P circulator is going to look at the overall resistance and then find its happy spot on its pump curve.  The TRV in the room that’s warm enough will continue to close, and the TRV in the room that isn’t warm enough will continue to open.

And this goes on with all the radiators on the job, with conflicting information causing the Delta-P circulator to bop up and down its fixed pump curve. The Delta-P pump doesn’t worry about what each individual TRV is doing – it can’t.  It can only react to changes in overall system-wide resistance against its impeller.  More overall resistance – the pump slows down.  Less overall resistance, the pump speeds up.

Delta-T does the same thing only different.  It reacts to the overall system-wide temperature difference – not the temperature difference across any individual radiator.

But remember, this is the job the Delta-P circulator was designed for.

Does it know exactly how much flow each radiator needs?


Does it know exactly how much flow the system needs?


Does it have any way of knowing, or even inferring, the BTUH load at any given point in time?


Delta-P works on its pump curve, and varies its flow based on the resistance against the impeller. It creates flow for the system, and the TRV’s regulate flow through each radiator.

Randy Bachman rocked lead guitar for the Guess Who long before the Bachman Turner Overdrive (who had a huge 1974) hit the airwaves.  The dude could play…

Does the drummer remind anyone else of John Goodman?

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