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“Watch what you say, or they’ll be calling you a radical…”
In hydronics, there’s no radical, cynical, liberal, animal, vegetable or mineral.
But there is logical. In fact, it pays to be downright Spockian when thinking about your systems and how all the parts and pieces work – both on their own but in particular how they work together within the dynamics of the system.
Because after all, it is a system.
Let’s consider the logic behind variable speed circulators, both Delta-T and Delta-P. The prevailing attitude is that they always give you the right flow, no matter what.
But that’s not logical. As we’ve said before (here and here), they’re not that smart.
For either circulator to “always” give you the right flow, each would have to have some way of knowing what the BTUH load of the system is at any given point in time. They’d also have to have an idea of what the outdoor temperature is at any given point in time, as well as how much radiation is installed.
As we’ve said many times in this space before (here, and here), Delta-P circulators are best suited for panel radiator/thermostatic radiator valve jobs. The trigger that tells a Delta-P circulator to speed up or slow down is resistance against the impeller. More resistance (head pressure from the system), it slows down. Less resistance, it speeds up.
So, When TRV’s close, that means the heating load is either satisfied or at least going down. Closing TRV’s increase resistance against the impeller, ergo the pump slows down. When TRV’s open, the opposite happens.
Pretty slick, right?
But Delta-P circulators, even with the vaunted “auto-adapt” function, still work on a fixed pump curve. It’s a funny-looking, inverted V shaped curve, but it’s still fixed. And because it’s a fixed curve, the system will always work where the pump curves and system curves intersect, due to that pesky law of thermodynamics that states energy in = energy out.
In a zone valve application, a Delta-P pump only knows when zone valves are open or closed, and in what combination. It has no way of knowing what the actual load of the system is at any given point in time, so it will have to work on a fixed, inverted V-shaped pump curve. It has no way of knowing the actual heating load, and therefore has now way of knowing how much flow is required. It only reacts to whether a zone is open or closed.
Therefore, in a zone valve application, a Delta-P pump will run the same speed in October as it does in January as it does in March.
Delta-T, on the other hand, measures the temperature drop of the fluid as it goes through the system. What makes the fluid temperature drop as it goes through the system?
Logically speaking, the fluid gives off energy to the heat emitters, which in turn deliver heat to the rooms.
And the colder it is outside, the more heat is needed.
Delta-T is designed with that logic in mind. By monitoring the supply-return water temperature differential (Delta-T), the circulator’s logic can tell when more or less flow is needed. When it gets colder out, or when more zones are calling, more energy is being taken out of the fluid. The Delta-T will naturally want to get wider. The circulator senses that, and speeds up to deliver the required flow and BTU’s.
When it gets warmer out, or when zone valves close, the Delta-T will want to get narrower since the system needs fewer BTU’s. The Delta-T control tells the circulator to slow down.
Therefore, we can reason that a Delta-T circulator will not only vary its speed as zones open and close (just as a Delta-P circulator will), but that it will also vary its speed as the heating load changes with the outdoor temperature.
That’s a darn sight closer to providing the right flow most of the time.
Last time out (click here) we discussed the importance of thinking for today’s hydronics professional, and the dangerous and downright insulting advice that any product – even so-called “smart” pumps – can “do the thinking for you,” “take the thinking out of it,” or even worse: “take the guesswork out of it.”
Gang, we all know there’s only one way to take the guesswork out of hydronics…
Do the math!
“Smart” pumps? Please – they’re not that smart. Here are two examples of how “smart” pumps behave in a thermostatic radiator valve (TRV) system:
Delta-T: The external info a Delta-T residential circulator uses to vary its speed is the systemwide Delta-T, meaning the temperature difference between the water leaving the boiler and the water coming back from the system. The pump is set for a default 20* Delta-T (adjustable from 5 to 50), and will go faster or slow depending on how many BTU’s are being taken out of the system at any given point in time.
In a panel radiator system, when a TRV closes (meaning there’s enough heat in the room), the Delta-T across that radiator will actually increase. This would be a message for the circulator to speed up, even though the radiator is fine.
Kinda goofy, right?
But common sense tells us there’s more than one radiator in a system, and more than one TRV. While one is closing, another may beopening, and another may be holding steady. There’s no way for a Delta-T pump to know what each radiator needs. So what does it do?
It varies its speed based on the boiler supply temperature and the common return temperature. That’s all it knows.
Delta-P: Delta-P varies its speed based on changing pressure differentials in a system, and was designed for TRV applications. But even here Delta-P isn’t that smart.
The “trigger” that tells a Delta-P circulator to speed up or slow down (even with so-called “AutoAdapt) is resistance against the impeller. When there’s enough heat in a room a TRV will start to close, placing more resistance against the impeller. The circulator senses that, and slows down.
So far, so good, right?
But again, common sense tells us there’s more than one radiator in a system, and more than one TRV. While one is closing, another may be opening, and other may be holding steady. What’s a Delta-P circulator to do?
Same thing as Delta-T: react to the overall system-wide changes in pressure differential.
It varies its speed based on overall system pressure differential. That’s all it knows.
Heating Man Smart, but “smart” pumps definitely not smarter!
And try keeping this Belafonte classic from banging around your head the rest of the day…
If the Queen of Soul says “think,” we should probably listen.
Which is why I drop my Popsicles whenever I hear hydronics salespeople say things like the following:
“It’s a ‘Smart’ pump. It does the thinking for you!”
It does the thinking for you?
“It takes the thinking out of it – and takes the guesswork out of it”
Takes the “thinking” out of it?
Is this what we, as an industry, want? To not have to think?
Sorry, but it’s the ability to think about systems – to understand them, to know what they do and, most importantly, why they do them, and to have the ability to think about why we’re using the specific products we’re using and making sure we apply them properly – is what separates the competent from the incompetent.
It’s what separates the “hack” from the “jack.”
It is, friends, what separates the pro from the amateur.
Takes the guesswork out? Really?
Sorry again, but there are NO products out there made by any hydronics manufacturer in Europe or the US that “do the thinking for you.”
And there’s really only one sure-fire way to take the “guesswork” out hydronics.
It’s called “doing the math.”
Variable speed pumps are very nice and useful things, and can do some pretty cool stuff. But “thinking for you” ain’t one of ‘em. As a professional, you have to know what you’re holding in your hands, what it does and and what it doesn’t do, and – most importantly – why you’re using it.
There’s no such thing as a “smart” pump, regardless of whether it’s Delta-T or Delta-P. Of the two, Delta-T variable speed circs (such as the Taco BumbleBee), will at the very least automatically adapt to the changing needs of the system and get you close to the right flow. That’s because by watching the system Delta-T, it has a pretty good idea of how many BTU’s are being taken out of the system at any given point in time, and can speed up or slow down accordingly.
Delta-P, however, “adapts” only to predetermined algorithms and will still work on a fixed pump curve, which means the system is going to do what the pump says (For a Delta-T/Delta-P comparisons, click here, here, here and here).
Both are very good pumps, and work great in the right applications. But neither is what you’d call “smart.”
The real smarts come from you.
I get that guys working in the trenches are busy. You wear lots of hats — lead mechanic and installer, troubleshooter, dispatcher, scheduler, bookkeeper, payroll officer and human resources manager. Oh, and you probably want to have a life in there somewhere, too.
Anything that saves time is a good thing.
And sometimes doing the math sounds like it takes too much time. It’s sure sounds easier to just “push a button and let the pump do the thinking for you.”
But two things…
#1: Thinking is what separates you from the DIY’er, handyman or moonlighter. Your value isn’t in just “pressing a button.” Your value is in knowing what you’re doing, why you’re doing it and being able to select the right product for the right job. Your value is in knowing the difference between a “system” and a “bunch of parts.”
It doesn’t take a particularly impressive skill set to slap together a bunch of parts – no matter how fancy – that’ll keep someone from freezing to death and call it good. It does, however, require a professional to put together a system that provides comfort, efficiency and long-term performance.
And that requires thought.
And then there’s #2: Pardon me if this is repetitive but (ahem)…
Smart pumps can’t do the thinking for you. They’re NOT THAT SMART!!! And they’re certainly not smarter than you are!
And if you really want to take the guesswork out of it all, well, there’s only one way to really do that.
And speaking letters, I received a very happy one in my inbox this week, courtesy of one of my favorite industry writers, Bob Mader of CONTRACTOR magazine, regarding…wait for it… a new study.
Studies can tell us many things. And for every study that says “yes,” there’s another study that says “no.” Personally, I’m still looking for the study that proves slightly overweight, balding, middle-aged hydronics trainers are irresistible to women.
But I’m not holding my breath.
Anyway, Bob wrote this week of a new study in Canada, commissioned by Canada’s “Beautiful Heat” campaign (check ‘em out here) , that backs up something many of us in the business have long maintained:
Radiant heating is more efficient than forced air.
Here’s the skinny (and you can click here for the details): Canadian consulting firm ICF Marbek conducted energy simulations on a variety of homes in six different parts of Canada and concluded that radiant heat can save up to 17% when compared to forced hot air.
As with any study, the Devil is in the details.
In existing older homes, built pre-1980, the study says single story homes could reduce heating costs by around 5%, while two-story homes could reduce costs around 12%. In newer homes those numbers ranged between 5 and 10%. Overall, that turns out be a dollar savings (US currency) of anywhere from $36 annually on the low end to over $210 on the high end.
It’s in multi-zone systems with setback in basements and living rooms at night and in bedrooms during the day, that savings mounted even more. A 2-degree setback resulted in heating cost reductions of over 10.5% in new 2-story homes and nearly 12.5% in older 2-story homes.
Now here’s the part that surprises me: with a more aggressive setback of around 7-degrees, the savings in new homes grew to over 15%, and 17% in existing homes.
Color me orange on this one – I maintained for years that aggressive setbacks with radiant weren’t – from an energy savings standpoint – a very good idea. The theory was that it would take more energy to recover from that deep of a setback than it would take to simply maintain the set point.
It’s also often been said that since radiant heat is just plain different (it’s not air-based), you can be more comfortable at a lower thermostat setting than with forced air. Again, this study bears that out.
The study says that to maintain ideal comfort, thermostats could be set an average of 4-degrees lower in single story homes with radiant, and nearly 6-degrees lower in two-story homes (both new andexisting).
Some more details: all homes were modeled with your standard single zone forced air system, with the thermostat most likely placed in the main floor hallway (which is dumb, because no one hangs out in the hallway, but that’s another blog!). The radiant systems were modeled as a 3-zone system (basement, living area, bedrooms).
So what conclusions can we draw from this study?
1. Radiant heat certainly can save money in heating costs compared to forced air. We’ve always known that, but here’s a study that can bear it out.
2. Saving a couple hundred bucks a year on heating costs is nice. Really, really nice – but it won’t make anyone rich or change anyone’s life. Does it add up over time? Absolutely, but be careful not to fall into the “payback” trap (click here and here to review).
3. There is no substitute for comfort, and when it comes to comfort, there’s no substitute for radiant.
4. Zoning is good. Don’t skimp on the zoning.
So, what are your thoughts on the study? How do you plan to make use of the data?
Inquisitive sorts like me want to know!!
And if you’re going to come in through the bathroom window…
Nothing like a little late 60′s soul to help you get your groove on…
Mel & Tim from ’69 with a cautionary tale of rule breaking and flying penalty flags.
See if that doesn’t stick in your head the rest of the day…
A couple weeks back (click here) we talked about what would happen if you used a European-style steep curve 3-speed pump on a zone valve job. A low-flow, high-head, steep curve pump will create greater and greater pressure differentials as zone valves close, and the end result – more often than not – are noisy, banging zone valves.
Zone valves don’t like closing against the kinds of pressure differentials created by your typical Grundfos 15-58 or Taco 0015 3-speed. You can’t argue with physics.
Mel and Tim would call that “offsides and holding…”
Assuming neither you nor your customer wants to live with banging zone valves, how do you quiet them down?
Hmmm mmmm hmmm…..
Yes, you in the back…
You must add a pressure differential bypass valve, you say?
Well, that’s one way of dealing with the problem.
Unfortunately, it’s also the most expensive, most difficult and least effective way of dealing with the problem.
“But all the really smart guys in the industry say you need to have them…”
No, you don’t.
Let’s call a pressure differential bypass valve (PDBV) what it really is – it’s a band-aid for a self-inflicted wound – the wound of using the wrong pump for the zone valve job in the first place. As we’ve stated many times here, flat curve pumps and zone valves go together like football and cheerleaders – it’s what flat curve pumps were made for.
A PDBV is a spring-loaded, pressure activated valve that allows excess pressure differential created by a circulator to bypass the system, thus quieting down banging circulators.
Essentially, all a PDBV does is turn a steep curve European-style pump into a flat curve American-style pump.
All you need to do to is purchase and install the valve itself, plus all the associated piping, and then figure out how to set the valve so it does what you want, while trying to decipher instructions badly translated from German or Danish.
All for a freaking band-aid.
Seems like a lot of work, doesn’t it?
Or, you could simply use a flat curve American-style circulator in the first place.
As chronicled here, here, here and here, flat curve circulators such as the Taco 007 are designed for the types of zone valve jobs (and zone pumping jobs) fairly common here in the US. Steep curve pumps, such as the Grundfos 15-58, the Taco 0015 and other 3-speed circulators, are designed for traditional European-style systems: small PEX pipe, large designed-for system Delta-T’s (30* or more) and panel radiators with thermostatic radiator valves.
I tend to cringe (or worse) when PDBV’s are touted as “necessary, standard equipment” on zone valve jobs, because “with those high head pumps, the zone valves will bang. This is what you have to do to keep ‘em from banging.”
That’s like saying “here – buy this extra sharp knife set from me and use them to learn how to juggle. Oh, and you’re gonna need to buy these band-aids from me, too. You might bleed a little…”
Hydronics really is quite simple when you look at it through the proper lens. When you use the wrong (low-flow, high-head, steep curve) pump with zone valves, the zone valves are most likely going to bang. When you use the right (high-flow, low-head, flat curve) pump with zone valves, they won’t.
You can leave the band-aids to the knife jugglers.
Want some more early 70′s soul? Get yer funk on with the Chairmen of The Board…
If you like baseball history, you’ll love this tune…
That’s “Pastime” by The Baseball Project, a tune chockfull of baseball trivia (stand and be counted if you know what “two round-trippers and a no-hitter, that’s Rick Wise” means!).
And it’s a perfect song with which to celebrate Opening Day, 2014.
Taco’s “spring training” season has been on-going since late January. So far this year we’ve put on nearly a dozen full-day training programs across the country, with more than 400 participants in areas such as Massachusetts, Northern Virginia, Maryland, Wisconsin, Seattle and Colorado.
But today is Opening Day for more than just baseball.
Regular season training for Taco gets underway in earnest this week, with a full-day program in beautiful Thunder Bay, Ontario. After that you’ll have a slew of training opportunities both in the field and at the Taco factory in Cranston, RI.
Starting next week and running through June will be full-day “American Hydronics Revolution” classes at the factory, hosted by the one-and-only Dave Holdorf. These classes are region specific, so if you’re in New England, New Jersey, upstate New York, Long Island, Pennsylvania or Canada, contact your local wholesaler or Taco manufacturer’s representative to get signed up.
Also starting next week is our flagship factory training program, “Residential Hydronics; Advanced Soup to Variable Speed Nuts.” This two-day program is the most complete factory training program in the industry, covering everything from heat loss and boiler selection to pump selection, zoning options and controls wiring. The first program – April 10-11 – is already sold out, as are the June 12-13 and July 31-Aug 1 classes.
We still have openings for our May 8-9 class, as well as our Fall dates (Sept 18-19 and Oct 23-24). These programs include 2 days of training, hands-on controls wiring opportunities, meals, ground transportation, two nights hotel and a fun night out on the town for $299. All you have to do is get yourself to Rhode Island – we’ll take care of the rest! Click here for more details and to register online.
In addition, we have lots of field training opportunities coming up this spring. If you’re in Ontario (Toronto or Thunder Bay), Alaska (Fairbanks or Anchorage), Saskatchewan (Regina or Saskatoon), Spokane, Colorado (Denver or Montrose) or elsewhere, we most likely will have something in your vicinity. Check with your local Taco rep to see what’s going on, or just comment here and we’ll see if we can hook you up.
I understand there’s no such thing as a “good time” to go to training. We’re all busy and a day spent at a training class is a day not spent generating income. But as on old boss once told me, “don’t be so busy chopping wood that you forget to sharpen your axe.”
But since you have lots of wood to chop, whatever training classes you choose to attend better be more than worthwhile. As a simple rule, you should:
- Avoid product-specific training classes. These are usually thinly-disguised sales pitches and tend to be a waste of your time.
- Look for “application-based” classes that stress hydronics fundamentals and info you can use regardless of which product you choose.
- Make a “learning plan,” meaning don’t just show up hoping to “learn something.” Plan ahead and take control of your learning – have 2 or 3 specific things you’d like to learn when attending a class.
- Show up early, sit up front, turn the cell phone off, ask questions, take lots of notes and then study your notes when you get home. This guarantees you’ll be able to use the stuff you learn, and make the information part of your skill set.
And with that, it’s now time to….
And just a little reminder of how last year ended…
Could Elvis have possibly been writing about pump curves?
“Turn it down a little bit or turn it down flat. Pump it up when you don’t really need it. Pump it up until you can feel it.”
I’d say it’s pretty clear that he was.
In light of our last few blog posts, I’d like to pose a question:
Which is the “stronger” circulator – a high-head, steep curve pump, or a low-head, flat-curve pump?
Answer: It depends on how you keep score.
European style steep-curve pumps provide higher head pressure, but lower flow rates. American style flat-curve circulators prover higher flow rates, but lower head pressure.
Is higher head pressure “better?” Not if you don’t really need it.
Is a higher flow rate better? Not if you can’t feel it.
The “promise” of the 3-speed circulator is that it’s the one circulator that can do everything. It’s supposed to make circulator selection easy and it’s supposed to replace 7 or 8 different models with just one.
And you know what? On paper, it does just that.
On paper, the performance curves of the most common 3-speed circulators out there, the Grundfos 15-58 or the Taco 0015 (both steep-curve pumps), do cover nearly all the flow-and-head performance requirements you’re likely to encounter in residential hydronics.
Problem is, we don’t install circulators on paper.
We install them on actual heating systems, in people’s basements.
As we’ve shown in recent blogs (click here, here, here and here to review), installing a European style steep-curve pump on a typical zone valve job would “work,” but not without noise issues – banging zone valves and possible velocity noise. And if programmed in “no call-back” mode (AKA – Speed 3), you also have tiny system Delta-T’s, which promotes boiler short-cycling, which reduces system-wide economy of operation.
But no one will be cold.
But they will have system that’s noisy and nowhere near as efficient as promised.
By the same token, installing a flat curve pump, such as a Taco 007, in a panel radiator/TRV job may present other issues. If there’s more head loss in the piping system than the pump head can overcome, the house may not be able to heat when it’s really cold outside.
But the system will be quiet.
Install either pump as a zone pump and it’ll work. You may very likely have noise problems with the 3-speed pump in “no call-back” mode, but no one will freeze to death.
Armed with this info, you have a couple of fixed speed options.
#1. Always use a 3-speed high-head, low-flow, steep-curve pump – even on zone valve jobs – and figure out how to deal with the noise issues (more on this later this week). You can’t do anything about the shrinking Delta-T.
#2. Use a 3-speed, high-head, steep-curve pump where it makes sense (panel radiator jobs, zone pumping), and use a flat-curve pump where it makes sense (zone valve jobs, zone pumping).
And if you are in an emergency situation (Friday afternoon, middle of winter, dead pump), you’ll most likely wind up using whatever pump you have on the truck. That’s fair enough, but what kind of pump should you keep on the truck?
I would think it would depend on what kinds of systems you normally service.
More to come, so in the meantime, you better listen to the radio…
So we’ve discussed why European-designed circulators have steep pump curves (click here), and why American-desiged circulators have flat curves (click here). The performance curves for both circulators are specifically engineered for, and fit perfectly, the types of systems traditionally installed on each continent.
In Europe, that would be a parallel-piped panel radiator system with thermostatic radiator valves. This type of system requires a low-flow, high-head, steep curve pump.
In North America, it started with the old venturi-tee or two-pipe systems, which morphed into series loop systems with fin-tube baseboard. These systems require high-flow, low-head, flat curve pumps.
But what would happen if we pulled the old switcharoo?
First, let’s look at what would happen with a flat curve circulator, like a Taco 007, installed in a typical European system:
Under design conditions, the system requires 10 GPM at 12′ of head. Pretty clear the 007′s performance curve won’t be able to deliver.
As you know, systems always operate where the system curve intersects the pump curve. For much of the heating season, this setup should work just fine. However, as it gets colder out, the 007 would not be able to overcome the head loss of the piping system in order to deliver the required flow.
Two things would happen.
First – the measured supply and return Delta-T would be far greater than design – a sure sign of underpumping.
And second – some rooms will be warm, while most others will be cold. And you’ll have an unhappy customer.
Now, what would happen if you installed a steep curve pump in a typical American system? We’ve touched on this before (click here, here and here for the full story), but here’s the Reader’s Digest version:
Systems always run where the system curve intersects the pump curve. When using a “European” style pump, the system curve “backs up” the pump curve as zone valves close. Each time another zone valve closes, the zone valve has to close against a higher and higher pressure differential, while the circulator delivers more flow than is required.
Is this a problem? Depends on how you define “problem.”
If you define “problem” only as someone calling you on the phone screaming they don’t have heat, then you probably won’t have a problem.
You’ve met the bare minimum requirement for a passing grade.
You’ve earned a D-.
If you have a broader definition of “problem” – one that includes banging zone valves, incessant boiler short cycling, premature component failure and systems that aren’t nearly as economic to operate as promised or expected, then you have some things to think about.
A European style low-flow, high-head, steep curve circulator installed in a typical zone valve application can cause all of these problems. An American-style high-flow, low-head, flat curve circulator won’t.
Because this is the type of application it was designed for.
Makes sense, doesn’t it?
We’ll examine this dynamic in greater detail, as well as how each circulator performs when used as a zone pump.
Gotta say Steve Miller’s tunes pre-Joker were, by and large, awesome!
Some people call him the Space Cowboy, some call him the Gangster of Love. But Steve Miller’s always lived in the USA…
Great rocker from – are you ready – 1968!
So far this month, we’ve learned why Europeans primarily install panel radiator systems with TRV’s (click here to review) and, as a result, why European-designed circulators typically have low-flow, high-head, steep performance curves (click here to review).
Quite simply, the most practical installation method bred a circulator designed to match the system requirements.
Why, then, is the classic “American” style pump curve a high flow, low head, flat curve?
In older cities, the “next-to” communities started growing in the mid-to-late 1800′s due to new transportation technology – electric street cars and that new-fangled “horseless carriage” made it easy to live out there and travel into the city to earn your daily bread. If you’ve ever worked in any of those older homes you’ve seen amazing old heating systems, mostly steam or converted gravity systems.
These home had lots of heat loss (therefore lots of flow) and big pipe (therefore very little head loss). Fast forward into the 30′s and what homes that were being built during the depression (with enticements from the newly formed FHA) had either 2-pipe hydronic systems or venturi-tee systems.
Reading through the B&G Hydronics Design Handbook published in 1940 is fascinating – a design example shows a venturi-tee system requiring 12.5 GPM (120,000 BTUH, using their math) with an estimated 4′ of head.
High flow, low head.
Look and compare:
After WWII, VA loans made buying a home in the suburbs less expensive than renting an apartment in the city. And new tax laws allowed homeowners to, for the first time, deduct mortgage interest from their taxes. It was a perfect storm for suburbia to explode.
And explode it did.
You all know the story of Levittown, but similar communities were sprouting all over the country. And many of those homes had hot water heat with venturi-tee systems or two-pipe systems with cast iron baseboard, radiant floor heat or another new-fangled development: fin-tube baseboard zoned by circulator or zone valve.
These homes shared relatively speaking high heat loads, and since the design standard of the day was a 200 Delta-T, the required flow rates were high. But since the pipe was large (¾ or 1″ copper or black iron), the head losses were fairly low. Here’s an example:
100,000 BTUH = 10 GPM
Biggest zone = 40,000 BTUH or 4 GPM
Length of biggest zone: 120 feet
The head loss of ¾” L tubing (most common back then) at 4 GPM is .04′ of head per foot of pipe. If the adjusted length (taking into account fittings, valves, etc) of that longest loop is 160 feet, then the overall head loss would be:
160 feet × .04′ of head per foot of pipe = 6.4′ of head.
So if this were a zone valve job, we’d need a circulator capable of 10 GPM at 6.4′ of head.
Again, ideal for a high flow, low head, flat curve circulator, no?
Bottom line: both in North American and in Europe, circulators were developed to work in the systems most commonly installed in those markets. There’s nothing inherently better about a high head circulator or a low head circulator.
The best circulator is the one that fits the job you’re working on.
As we continue this series, we’ll discuss what can happen when you stick the proverbial square peg into a round hole.
Gotta hand it to ole Stevie — he’s an American Original…
And just to make you feel old, Steve just turned 70 last fall.
And you don’t mess around with Jim. Croce, that is. Miss this dude…
Ever wonder why pump curves look the way they do? I mean, why is a 007 curve “flat” while the curves of a 0015 3-speed, or a Grunfos 15-58 3-speed are “steep?”
Well, it’s not “just because.”
In the pump world, a high-flow, low-head flat curve is often called an “American” pump curve, while a low-flow, high head steep curve is referred to as a “European” curve.
It has to do with the types of systems those circulators were designed for.
Last time we discussed how the typical European hydronic system – panel radiators, TRV’s and home-run piping – became the typical European system: it was the easiest, most convenient and least expensive system to retrofit into millions of old, existing homes that had no central heating.
And these old, pre-1960 structures weren’t very well insulated and leaked heat like a sieve.
When you design this kind of system, specific pumping requirements take shape.
Consider an old, leaky cottage somewhere in Belgium or Germany. It gets quite cold, so let’s assume a heat loss of 100,000 BTUH. When picking a circulator for a parallel piping system, you size for the total flow rate of the system, but only the head loss of the worst case piping loop. What you select as a designed-for Delta-T makes a huge difference.
Let’s presume the longest piping run of ⅜” (≈ 14mm) PEX is 100′ total – 50′ there, 50′ back – and the radiator needs to deliver 16,000 BTUH at design conditions. Here’s the required flow rate at a 200 Delta-T:
So that one radiator needs 1.6 GPM. What would the pressure drop be?
Let’s look it up.
At 1.6 GPM you’d get .45′ of head per foot of ⅜” PEX. Multiply that by 100′ and you’d have 45′ of head
As a result, European panel rad systems are designed around Delta-T’s of 30 or 40 degrees, not because it’s “better” or “optimal,” but because that’s what’s needed to keep circulators for those types of systems reasonable to install and reasonably priced.
At a 300 Delta-T, the flow rate for that radiator would be around 1 GPM, but the S&R piping head loss would be around 20′.
At 400, the flow rate drops to 0.8 GPM, making the head loss only 11′ of head per foot of pipe. At a total run of 100′, that’s 11′ of head. Add for the TRV and other components and you’re looking at around 12′ for the worst case loop.
The total load was 100,000 BTUH, so at a 400 Delta-T the required flow rate would be 5 GPM. Your pump requirement would be 5 GPM at 12′ of head.
See where it fits? Right in the “wheelhouse” of the low-flow, high-head, steep “European” pump curve.
So, that’s why European pump curves are steep – because the steep curve fits the most common application in Europe. Traditional flat “American” curve pumps – made famous by Taco and B&G – are flat for the exact same reason, as we’ll discuss next time.
In the meantime, stay away from those Car Wash Blues…