Let’s keep rolling the Rockpile, shall we?

“Heart,” with Billy Bremner on vocals. Rockpile’s Seconds of Pleasure may have been the most underrated album of the 80′s.

Tapping toes everywhere agree!

Last time we examined the very real functional differences between a “properly” programmed Delta-P variable speed circulator and the Taco BumbleBee Delta-T circulator in a typical zone valve application.  To get the most out of the Delta-P circulator that little red “Max Head” dial has to be set as close as possible to the correct head loss of the system.  In theory, that would get your funny-looking-inverted-vee-shaped pump curve as close as possible to the system’s operating requirements at design conditions.

Two challenges though.  The first one we discussed last time: that funny-looking-inverted-vee-shaped pump curve is fixed – so the circulator runs on that line all winter long.  Not a big deal during the roughly 2.5% of the heating season spent at or near design conditions.  The other 97.5% of the time, however, we’re badly over pumping.

The other challenge is less obvious, but potentially more dramatic:

How do you determine the head loss needed to set the dial in the first place, especially in a retrofit or boiler replacement job?

Calculating flow rate is easy:  once you know the heat loss, divide the BTUH total for each zone by (DT x 500).  That gives you each zone’s flow rate. Add ‘em up for the total flow rate for the job.

To estimate head loss, first find the length of the longest zone (sometimes an educated guess, at best) and multiply it by 1.5.  This accounts for valves, fittings and other stuff – all of which add pressure drop.

Multiplying by 1.5 gives you the “total developed length.”  Next, multiply that number by .04 (4′ of head for every 100′ of straight, properly sized pipe).

Here’s an example:

30,000 BTUH zone (3 GPM at design conditions)

Total run: 125′ (measured from the outlet side of the circulator all the way back to the inlet side)

125′ x 1.5 = 187.5′ total developed length

187.5 x .04 = 7.5′ of head.

Let’s presume that’s the highest head loss zone in the system.  Let’s also presume there are two other smaller zones in the house, 20,000 BTUH or 2 GPM – each, and the math tells us the head loss for each zone is 5′.   The job totals are 7 GPM at 7.5′ of head.

Let’s plot this on the Delta-P pump curve:

Uh -oh.

By adjusting the red programming dial to match the estimated head of the system (7.5′), it sure looks like we’re going to be in an under-pumping situation when we’re at or near design conditions.  Most of the heating season this would work just fine.

Just not when it’s really cold out.

Hmmmm….

Same application, this time with a BumbleBee…

As you can see, the operating points fall within the shaded variable speed operating range.  So at design conditions, the BumbleBee will give you the right flow, no matter what combination of zones is calling.  The BumbleBee will also vary its speed as it gets warmer out, ultimately spending most of the heating season running at or near its minimum speed (line 1).

But estimating head loss is hard, especially in a retrofit when measuring the run can be, at best, an educated guess.  This formula shown here estimates head on the high side, so it’s “safe.” What would all this look like if we were a bit more precise in our head calculations?  Check back later this week for that one!

And while lip-syncing was all the rage back in the early 80′s, Rockpile live is a treat on a whole new level…

“JuJu Man,” from their 1980 concert in Hamburg. That’s some good rock ‘n roll right there…

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Left you last time with Dave Edmunds’ “Queen Of Hearts.”  Don’t know why, but part of me prefers this version…

Okay, okay, I know why…

Huge hit for Juice Newton back in 1981.

Gotta love a girl named “Juice.”

Last time we shared what would happen with a Wilo Stratos-Eco Delta-P variable speed pump installed in a specific zone valve application, with  “out-of-the-box” default programming.  We learned the circulator would only vary its speed under certain conditions.   The circulator would still run at full speed with 3 or 4 zones calling.

But what would happen with “proper” programming?  Here’s a look…

The red programming dial would have to be set as close to 5′ of head as you can manage.  In this case, the circulator will, in fact, vary its speed virtually all the time.  And at first glance, the operating requirements line up fairly well with that funny looking inverted-V shaped pump curve.

Closer examination, however, shows Points A & B falling slightly above that curve. Under design conditions is it possible the circulator may actually “under-pump” the zones?  It would seem so, but only when you have reached your outdoor design conditions (<2.5% of the heating season) and only if the heat load is dead-on accurate, with no added “fudge.”

Point C appears to be right on the pump curve, while Point D is below the pump curve, but not by all that much.

Perfect, right?

Well, that’s at design conditions.

However, this Delta-P pump is going to run on that line all winter long, despite the ever-changing BTUH load.  It runs that speed in January. It runs that speed in October.

When you’re at or near design conditions, you’ll have close to the right flow, more or less.  The rest of the heating season the circulator still operates on that line.

So what happens under milder conditions, at 50% heating load?

You see the new requirement points. However, the pump is still running on its fixed pump curve.  So even though the requirement with all zones calling is 5 GPM, the Stratos-Eco will still give you around 10 GPM, and the resulting system Delta-T will be around 10*.

And keep in mind roughly 50% of the heating season is spent at 1/3 load or less.  So even when programmed “properly,” this circulator delivers the “right” flow rarely, and by coincidence.

Does this mean the system “doesn’t work?” Nope, not at all.  But we can do better.

How would the BumbleBee fly in this same application? Remember it comes out of the box programmed for a 20* Delta-T…

Those 4 lines are the BumbleBee’s capabilities in the Fixed Speed mode.  The shaded area between lines 1 and 4 is the Variable Speed Delta-T operating range.

Because GPM = BTUH ÷ (DT × 500), the BumbleBee will vary its speed accordingly to hit Points A (almost full speed), B and C, as well as the requirements of any combination of zones.

The line representing Speed 1 is the BumbleBee’s minimum speed.  When only Zone 1 is calling, the BumbleBee will “over pump,” and the actual operating point will be very close of the Stratos-Eco’s operating point.

But now look at what happens at 50% load…

Are we “over-pumping” in this example?  Pretty much, but we’re now operating at the BumbleBee’s lowest possible speed for the bulk of the heating season – with a power draw of roughly 9 watts. You can extrapolate the system curve lines to see where they intersect the Speed 1 line.  Not perfect, but considerably better than what we had with the Delta-P circulator. Note with all 4 zones calling we are delivering almost exactly 5 GPM, which is what is required.

How about that?

Now, it won’t be varying its speed at this point, but at a power draw of 9 watts and with flow rates a darn site closer than its “variable speed” brethren, we’re in very good shape.

Will the system Delta-T at this point always be the 20* you designed for?

Nope.  It’ll be a tad lower.  But as we stated in a previous blog, Delta-T is not the target. BTUH delivery is the target.  Delta-T is simply an aiming device to help you get there as efficiently, effectively and economically as possible.

So what’s the significance of all of this?  Is it the difference between one system “working” and the other “not working?”

No, far from it.

It’s the difference between an okay system and an exceptional system operating at its peak for comfort and overall efficiency. It’s about knowing how things work, what they do, and matching the right product for the right application.

There’s one  big elephant in the room, however.  When it comes to Delta-P  programming, how the heck do you determine the system head loss, especially in a retrofit?

Great question – one we’ll address next time.

Okay, okay, enough of that.  How about a tall glass of Juice from the MTV years?

Try getting THAT out of your head for the next few days.

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“…Mama, big things one day come.”

Another classic from our man Dave Edmunds.  Try getting that out of your head the rest of the day.

Last time we started looking at how a typical Delta-P “variable-speed” circulator would work in a zone valve system (click here to review).  So far in our example, there’s nothing “variable-speed” about it.

We left off with three zones calling and a design-condition (coldest day of the year) load of 60,000 BTUH, or 6 GPM.  We found that the Delta-P Wilo Stratos-Eco, under those conditions, would still be running at full speed.  In addition, it would be delivering 9 GPM, some 50% more flow than the 6 GPM required.

In addition, the Stratos-Eco would be doing this every day of the winter, regardless of outdoor temperature or BTUH load.

Now let’s take a look at what happens with only the two smaller zones calling.

Let’s presume now that only 2 zones are calling, with a total combined load of 30,000 BTUH.  That’s 3 GPM worth of required flow at a 20⁰ designed-for Delta-T. Further, the worst-case head loss of the remaining zones is just under 4’ of head.  That operating point is below as Point C.

Last time we said this type of Delta-P circulator operates on a fixed pump curve.  It’s funny looking, but it’s determined when you adjust the red programming dial.

So looking at reality, where will the system operate with only the two small zones operating?

Again, it’s where the two-zone system curve line intersects the down-slanting portion of the pump curve line – at approximately 4½ GPM at nearly 8’ of head.

This also represents the first time in our system the circulator has actually “varied” its speed.  Also note that once again we’re getting 50% more flow than we actually require.

Now let’s get down to just 1 zone calling, with requirements of 1 GPM (10,000 BTUH) and only 2½’ of head (it’s a little zone!).  The requirement shown below is Point D, but the actual operating point would be at nearly 2 GPM and 5’ of head – roughly double what is required.

And again, this circulator will run on that performance curve all the time.  It’ll run that speed in January.  It’ll run that speed in October.

The examples shown are “design conditions,” the so-called “coldest day of the year.”  When it’s warmer than that out – as it is nearly 98% of the time – the circulator is still going to run at those same speeds even though the heating loads (and required flow rates) will be drastically lower.

Tell me again how this is a “variable-speed” circulator?

It’s more of a “how-many-zones-are-open” speed circulator. In the example shown, with the combination of zones shown, the circulator will run at 3 distinct speeds.

With different combinations of zones calling the circulator will run at other speeds. It will always, however, run somewhere on that fixed, albeit funny-looking, pump curve.

Because of its electronics, the pump will slow down as zone valves close, but the speed at which it ultimately runs has nothing to do with the actual flow rate required by the system at that given point in time, nor does it have anything to do with the actual head loss of the system at that given point in time.

The system just runs on that line.

All the time.

Understand that no one is saying this circulator is a piece of junk.  It’s a high quality product made by a world-class manufacturer for a very common European application: panel radiators in a parallel piping system using thermostatic radiator valves.

In a series loop zone valve system the Stratos-Eco, with right-out-of-the-box programming, is functional, but we can do better.

Next time we’ll discuss what would happen if we actually set the programming dial to match the actual head loss of the system and change that funny looking pump curve.

And we’ll leave you with another one of Dave’s best…

“…knowing it ain’t really smart.”

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There are some things you can’t cover up with lipstick and powder…

Dave Edmunds, Nick Lowe and the boys with “Girls Talk, ” a top-20 hit from waaaay back in ’79.

Online discussion forums are both fun and infuriating because everyone’s an “expert.”  These “discussions” start with questions, but usually devolve into calling the other guy an idiot because he doesn’t agree the sound logic of your “fact-based” position.

Never mind the “facts” supporting those “fact-based” positions are only facts because the holder of that position constantly repeats them and proudly calls them “facts.” If someone asserts what they’ve just stated is a “fact,” it kinda closes off discussion, doesn’t it?

And you can always make a statement even more factual BY USING ALL CAPS, FOLLOWED BY MANY EXCLAMATION POINTS!!!

This online dynamic thrives in discussions comparing Delta-T and Delta-P variable speed circulators.

With that prelude, what follows is simply information – use it as you wish.

We’ve beaten the drum in this blog on Delta-T circulator operation (click here, here, here and here to review).  But we’ve never focused on what makes Delta-P tick.

Well, here goes.  You may be surprised.

Here’s a pump performance curve for a Wilo Stratos Eco.  It’s a very nice pump curve.  At full speed it very much mirrors a Taco 008.

See that diagonal line going down and to the left, starting at about 10′ of head and ending at 5′ of head?  That line’s pretty important.

Delta-P circulators basically chop off the upper portion of the pump curve. How much is chopped depends on where you set the red programming dial.  The 10-5 line is default.

This line is the Delta-P circulator’s new, fixed pump curve.  No matter what happens, the circulator will operate on this line.

Those curvy lines starting in the lower left corner of the chart and flowing up to the right are sample system curves.   No matter what the system actually requires in terms of flow or head, this circulator is going to force the system to operate at a point where the system curve intersects the pump curve.

For example, let’s say we have a 4-zone system that requires a total flow of 10 GPM (100,000 BTUH), with a maximum head loss of 5 feet under design conditions – not an unusual system. That’s Point A below.

Now the $64,000 dollar question: when all 4 zones call for heat, where will the system actually operate?

If you said roughly 11½ GPM at roughly 6½’ of head, you win! (Not sure why? Follow the system curve line)

And 1 bonus point if you also said the circulator will be running at full speed.

Why? Because this type of circulator – even though it’s called “variable speed,” still operates on a fixed pump curve.  It’s a funny looking sorta upside-down V-shaped curve, but it’s still fixed.  The heating system has to work on that curve, because energy in equals energy out.

Now let’s say our biggest zone, worth about 40,000 BTUH (or 4 GPM) satisfies and the zone valve closes.  The total flow requirement of the 3 remaining zones is 6 GPM. Let’s presume we still have the highest head loss zone (5’) calling (this isn’t to prove a point, it’s just to make use of the existing lines for clarity).

So the flow/head requirement is Point B.  For another $64,000, where will the system actually operate?

Did you say 9 GPM at 10’ of head?  Ding-ding-ding! We have a winner!!!

And another bonus point if you said the circulator is still running at full speed.

And an automatic entry into our “Lightning Round” if you said the “variable speed” circulator has yet to vary its speed, and is delivering 50% more flow and 100% more pressure differential than the system requires.

And if you said that this circulator will deliver this same fixed flow rate and head pressure in October – when the heating load may only be 25% of the total, in December – when the heating load may only be 75% of the total, and in that 2-day stretch in January when the heating load is around 98% of the total (provided the heat loss calculations have no added “fudge-factor”), then you receive an automatic entry into our “Tournament of Champions.”

Will this system “work?”  Of course!  Shove 15-to-50% more flow than you need through a system, it’s gonna deliver BTU’s.  If that’s you’re only requirement though, it’s doubtful you’re even considering a variable speed pump. My guess is you’re expecting more.

You’re expecting a variable speed pump to, you know, vary its speed.

Which hasn’t happened yet.

Yeah, it works. but what does it all mean? Why does it matter?  We’ll look at these and a bunch more questions in the coming weeks.

And next time we’ll take a look at what happens when the pump does vary its speed.

Till then, take it away Dave…

Edmunds and Lowe in Rockpile – one great band!

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Leave it to Marvin…

No plumbing, heating or BumbleBee’s today.  Just this piece from comedian Patton Oswalt, which he posted on Facebook yesterday…

“I remember, when 9/11 went down, my reaction was, ‘Well, I’ve had it with humanity.’

But I was wrong. I don’t know what’s going to be revealed to be behind all of this mayhem. One human insect or a poisonous mass of broken sociopaths. 

But here’s what I DO know. If it’s one person or a HUNDRED people, that number is not even a fraction of a fraction of a fraction of a percent of the population on this planet. You watch the videos of the carnage and there are people running TOWARDS the destruction to help out.  This is a giant planet and we’re lucky to live on it but there are prices and penalties incurred for the daily miracle of existence. One of them is, every once in awhile, the wiring of a tiny sliver of the species gets snarled and they’re pointed towards darkness. 

But the vast majority stands against that darkness and, like white blood cells attacking a virus, they dilute and weaken and eventually wash away the evil doers and, more importantly, the damage they wreak. This is beyond religion or creed or nation. We would not be here if humanity were inherently evil. We’d have eaten ourselves alive long ago. 

So when you spot violence, or bigotry, or intolerance or fear or just garden-variety misogyny, hatred or ignorance, just look it in the eye and think, “The good outnumber you, and we always will.”

Then there was this piece of goodwill from George Takei, the former Mr. Sulu from Star Trek turned internet philosopher:

“When tragedies strike, heroes rise to meet the challenge: the first responders seen sprinting toward the blast site, the runners who changed course to run to local hospitals to donate blood, and the fine citizens of Boston who at once opened their homes to marathoners in need of a place to stay. When we come together, we cannot be brought down.”

And lastly, this one has been posted repeatedly online, an appropriate final word…

Here’s to the helpers.  When we come together, we cannot be brought down.

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I got a fever, and the only cure is…more Nick Lowe!

Okay, so there’s some music from the 80′s that isn’t awful.

Interesting discussion from a training class not too long ago.  Since GPM = BTUH ÷ (ΔT × 500), couldn’t you just increase the output of a zone by increasing the flow?

Let’s look at fin-tube baseboard for a minute.  We shared this Slant/Fin chart with you a couple of blog posts ago: 

Note the two output rows – one row for output at 1 GPM, the other for output at 4 GPM.

And a change from 1 GPM to 4 GPM is an increase in flow of 400%.

Yep, 400%

If we look at the BTUH/ft output ratings at a 170* average water temperature, you see at 1 GPM you’ll get 510 BTUH/ft.

At 4 GPM you’ll get 540 BTUH/ft.

Which would be more.

Only about 6% more, but it is more.

So if a room has, say, 12 feet of baseboard in it, goosing the flow rate would ad 360 BTUH to the output. Your mere presence in that room (400 BTUH) would add more heat than boosting the flow 400% would.

And also note from the chart that as the average water temperature decreases at the 4 GPM flow rate, so does the rate of increase in output.

So yeah, you can increase output by increasing the flow rate, but not enough to matter.

Facts are interesting things, aren’t they?

One concern occasionally raised in training classes is if you have a 20 degree Delta-T in a system, the water won’t be hot enough in the last piece of baseboard in series loop to get enough output.

Sure, the water temperature entering the last piece of baseboard is going to be lower than the water temperature that entered the first piece of baseboard.  But that’s true no matter what your designed-for Delta-T is, what kind of variable speed circulator you have on the system and no matter what the actual Delta-T is once the system is up and running.

If you try to follow the logic of that particular argument,  then series loops shouldn’t work at all, regardless of circulator.  And any type circulator, fixed speed or variable speed circulator, Delta-P type or Delta-T type, would have to have some sort of a temperature drop across the loop to give off BTU’s.

So how come a 15- or 16-degree temperature drop with a Delta-P circulator is acceptable and will “work” when a 20 degree temperature drop with a Delta-T circulator won’t work?

Doesn’t make much sense, does it?

Series loop baseboard systems have been designed for a 20 degree Delta-T for ages.  The reason may be arbitrary (easier math), but the bottom line is that it works.

As mentioned in a previous blog post, a specific Delta-T isn’t the target in your system, it’s merely an aiming device designed to help you hit your target – which is BTUH delivery.

Lots more to talk about when it comes to system design, Delta-T’s and variable speed circulators.  Stay tuned!

Till next, time, some more Nick to keep you rocking!

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-16 wind chill in Minnesota this morning,  and Nick Lowe captures my mood perfectly…

First day of Spring my you-know-what.  “I don’t think it’s funny no more…”

Okay, now that the venting is over, let’s get back to business! Last time we discussed how variable flow rates and water temperatures affect fin-tube baseboard output.

The verdict?  Some, but not enough to matter, for one simple reason.

While the per-foot output may change, the amount of feet installed does not!  We’re gonna have enough output.

Okay, Captain FloPro, but what about panel radiators? Surely your Delta-T circulator will send one of those systems into litigation land!

Hold your horses, Perry Mason.  Read on.

For reference, let’s use the Runtal VLX 56 Panel Radiator.  This radiator has a rated output of 1,840 BTUH/FT at a 180* AWT  (Average Water Temperature – 190* Supply, 170* Return).  However, in our setup we’re using a Supply Water Temperature (SWT) of 180*.  At a 20* Delta-T, the return water temp would be 160*, for an AWT of 170*.

That changes the output of the radiator slightly.  Runtal supplies the following factors to figure the output at lower AWT’s:

180* = 1
170* = .89
160* = .78
150* = .67
140* = .57
130* = .48
120* = .38

Using the .89 multiplier for 170* AWT, we find the VLX 56 will have an actual output of 1,638 BTUH/FT.  To offset the overall heat load, we’d need to install 25 feet of VLX 56, for a total potential output of 40,950 BTUH.

So when it’s 0* out with 170* AWT (average water temp), we’re good to go as long as we deliver 4 GPM at a 20* Delta-T, as designed.

When it’s 35* outside, the system only needs 20,000 BTUH and only 2 GPM.

A variable speed Delta-T pump would slow down to deliver just that.

Perfect!

But what in the name of LA Law would happen with outdoor reset?

Same thing only different, friend.

We know from the factors above that the lower the AWT, the lower the output of the radiator.  Will we be able to keep up?

Let’s take a gander at an outdoor reset curve, courtesy of Heat-Timer, and see what’s what:

The SWT at Design Conditions (0* outside) is 180*.  At a 20* Delta-T, that’s an AWT of 170*.  Using this particular reset curve (shown in red), when it’s 35* outside the SWT would be 140*, the AWT 130*.

And at 130* the potential VLX 56 radiator output would be 22,080 BTUH.

At 35*, we’re at exactly half load, so we only need 20,000 BTUH.

I’d say we’re good.

Some simple fundamentals to remember: with outdoor reset, water temperature goes down as outdoor temperature goes up.

But when outdoor temperature goes up, the BTUH heating load goes down.

When the BTUH heating load goes down, the required GPM flow rate to satisfy that heating load also goes down, regardless of the supply water temperature.

With ANY circulator (fixed speed or variable speed) the water temperature has to be high enough for the radiation to deliver the required BTU’s.

But in every case – the amount of radiation installed REMAINS THE SAME. Can’t get around that one.

Nowhere does it say that the higher the water temperature, the lower the required flow rate. Nor does it say anywhere that the lower the water temperature, the higher the required flow rate.

Lots more to kick around on this topic, which we’ll do next time!

Until then, dream of the beach!

If you can’t get up and dance to that one, then you’re definitely frozen!

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It’s true that sometimes “was” or “used to be” is confused with “ought to be,” but it’s very hard to argue with The Kinks’ efforts to save the Village Green…

“Village Green Preservation Society,” from the similarly titled masterpiece of an album - an ode to simpler time.  Village Green kinda got lost in the shuffle though, due to bad timing – it was released the same day as The Beatles White Album.

So far we’ve looked at two “simple” solutions to this particularly vexing radiant design problem:

The single biggest goal of a simple solution is to actually solve something.  With that in mind, let’s review our options.

Option 1 (click here to review):  145-degree water with one zone – uses the simplest control strategy and the fewest parts (read: least expensive), but just doesn’t cut it.  Some rooms will be too hot, some rooms will be too cold and the one area that has the thermostat will be just right.

Fine for Goldilocks, but no matter how much you try to manage customer expectations, my gut feeling is your customer won’t be singing the praises of radiant comfort.

And “tweaking” the flow through each loop in hopes of “balancing” it all out?  Good luck with that.  It’s simple to say, but impossible to do, for several reasons:

• Any flow adjustment will take hours to show any impact
• Any flow adjustment to one loop affects flow to all the others
• How much time are you planning to invest in “tweaking?”
• “Tweaking” is another word for “guessing”
• “Guessing” is another word for “hoping”
• “Hope” is not a viable control strategy

Option 2 (click here to review): three separate water temperatures – works.  It provides the right water temperature to each area, and each area is its own zone.  However, now you’re dealing with three tempering valves, three manifolds, three relays, three circulators…

It’s like cutting butter with a chain saw – it works, but it’s a bit much.  You have more parts, more materials, more wiring, more labor.  We’re trying to make this simple.

Which brings us to the third, best and simplest solution:

Zone the sucker!

This is about as easy as it gets – run 145-degree water to a single manifold, with three or four zones using thermostats and manifold actuators.

Now you have 1 water temperature, 1 manifold, 1 circulator, 1 electronic control, 1 thing to pipe up and 1 control to wire up.

Oh, and it solves the problem.  Each area is just right all winter long.

It’s pretty simple – when the thermostat is satisfied, the manifold actuators close.  When the manifold actuators close, flow to the zone stops.  When flow to the zone stops, the floor surface doesn’t get any warmer.

And when the floor surface doesn’t get any warmer, the room doesn’t get any warmer.

To simplify that equation:  When the thermostat’s satisfied, the room doesn’t get any warmer.

This is the simplest and most effective way to solve the problem.  You don’t have to “tweak” flow.  You don’t need three water temperatures.

You don’t have “manage expectations.”

You don’t have to guess or hope that something will “work” or be “good enough.”

You install the job, you collect your money, you go home.

And other than ignoring the problem, it’s the least expensive way to solve it.

Beautiful simplicity.

And speaking of beautiful simplicity…

“Waterloo Sunset,” #3 on my all-time hit parade.

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Any faithful reader of this blog knows it’s a Nick Lowe world and we’re just watching…

Oh change of mind, sound of breaking glass…

Last blog we discussed Delta-T, moving targets and aiming devices.

But we also mentioned that when flow to a heat emitter is reduced, its output is reduced as well.

If a variable speed pump (any of ‘em, not just the BumbleBee) reduces flow to a heat emitter, wouldn’t you run the risk of not having enough heat output in milder conditions, especially if the water temperature is lower with outdoor reset?

Another dandy question!

Let’s examine one scenario, using a simple zone of fin-tube baseboard. We’ll use Slant/Fin #30 as our reference product.

Looking at the manufacturer’s specs, we find the following:

Output with 170* AWT (average water temperature) at 4 GPM flow rate: 540 BTUH/ft

Output with 170* AWT at 1 GPM flow rate: 510 BTUH

170* AWT is 180* out, 160* back at a 20* Delta-T.

The zone is question is a big one – 40,000 BTUH at design conditions (let’s presume 0*outdoors at 70* indoors). The Universal Hydronics Formula tells us the required flow rate for this zone under design conditions would be 4 GPM.

Note the Slant/Fin specs show the output at both 4 GPM and 1 GPM.  The specs also say that if you don’t know for sure you’ll have a 4 GPM flow rate, you should size the zone based on the 1 GPM output. If we do that, we’ll need 79 feet of baseboard in the zone.  Let’s call it an even 80.

One thing we know for sure is that if we installed a BumbleBee (or it’s older brother, the 00-VDT), we would definitely have a 4 GPM flow rate under design conditions, because GPM = BTUH divided by (Delta-T x 500).

That’s the law.

Simple math says:  540 BTUH/ft x 80 feet (at 170* AWT and 4 GPM) = 43,200 BTUH worth of output.

So far, so good.

Now let’s say it’s 35*outside, and we’re at 50% load.  The zone now requires only 20,000 BTUH worth of output.  The boiler has outdoor reset, and is now supplying 150* AWT (160* out, 140* back). At that temp,  Slant/Fin #30 will put out 380 BTUH/ft at  1 GPM flow rate.

The output of the entire 80 foot zone at that point would be 30,400 BTUH.

In other words, enough.

And we also know the Delta-T pumps will be delivering 2 GPM (that pesky Universal Hydronics Formula thing again), not 1.

What if it were a mod-con boiler, and the AWT was lower at 35 degrees outdoors?

At 140* AWT = output is 320 BTUH/FT
320 x 80 = 25,600

At 130*AWT: output is 260 BTUH/FT
260 x 80 = 20,800

At 120* AWT: 210 BTUH/FT
210 x 80 = 16,800 BTUH

These outputs are based on 1 GPM, but a Delta-T pump would still be giving us 2 GPM.

We’re good.

Why are we good?  Bottom line is 80 feet of baseboard is 80 feet of baseboard.  Average water temperature changes the per foot output, but it doesn’t change how many feet are installed.

And flow rate changes output, too.  But how significant is it?

At 1 GPM and a 170* AWT, Slant/Fin #30 has an output of 510 BTUH.  At 4 GPM it has an output of 540 BTUH.

So math tells us that a 75% drop in flow rate slashes the per foot output of the baseboard less than 6%.

I think we can handle that.

How would panel radiators fare in this same scenario?  Next time, dear reader.  Next time…

And so it goes…

Nick with Rockpile from 1978.

Little known fact – Nick and I had the same hairstyle that year.

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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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