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Choice Lochinvar WBN051 or Cadet CDN040?

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Choice Lochinvar WBN051 or Cadet CDN040? (61 Posts)

Choice Lochinvar WBN051 or Cadet CDN040?
It seems like my chose in boilers comes down to these 2 units. I have a heating load somewhat shy of 30,000 BTUs, and want to use a 20 gallon indirect for DHW. The Cadet has a net of 32, and the Lochinvar 39. The Cadet modulates down to 9 BTU input, and the Lochinvar 10. They are priced for me with the Cadet at about $500 less. Is the Lochinvar that much better? The Cadet seems to fit the load better. Any thoughts would be helpful. 
If the sizing worked
I'd prefer a WHN055 over either. It modulates down to 11k, but has a better HX design.
Given a choice between the two and the price difference, I'd likely give the Cadet a shot, though I'd want to take a good look at the controls before I committed. I believe both are based on a Giannoni HX.
Edit: Looks like the WBN051 is actually a discontinued product.This post was edited by an admin on February 12, 2013 11:37 AM. 
I Think All Three Are Sized
WHN055 
Sorry, I Think All Three Are Sized Okay
with them modulating down to 911. The WHN will help with DHW, and if they modulate based on demand, the larger boiler should just run at a small percentage of capacity, right? I can buy the WBN051 and the WHN055 for the same price. Is the HX on the 55 that much better? It looks to me like it's the WHN that is being discontinued. What's up with this? 
WHN
is based on the original Triangle Tube HX design. It has only been on the market for a couple of years.
http://www.lochinvar.com/products/search.aspx?mode=model&query=wbn051 tells its own story. 
No prim/sec?
Are you still going to ditch the prim/sec? I think the firetube will give you more fexiblility in this regard.
Water content:
cdn040  .3 gallons
wbn051  .6 gallons
whn055  2.5 gallons
I believe the cadet is using the same hx as the wbn051, just fewer loops. I wonder how the cadet can be rated at nearly the same btu input.
The 2.5 gallon firetube model may add a reletively significant amount of water to your system. (Keep in mind that 3/4 copper has about 2.5 gallons of fluid per 100 feet) This may help your low mass fin tube system a little, but it's a con for domestic hot water production during the summer, as a higher percentage of heat produced for the 20 gallon DHW tank gets left in the hx.
I looked through the install manuals. The knights have a "ramp delay" feature that does not *appear* to be available for the cadet. Check it out, because by my reading this feature will allow you a bit more control over how quickly and to what extant the burner will modulate. (for example you can force it to stay at min fire for awhile longer and ultimatly cap the output at say 30k for your system while keeping full fire available for DHW)
Look at the maintenance procedures. Are you going to be able to access the hx and whatever else is necessary if you install these units in a closet? 
Re boiler selection
Go with the WHN, much better heat x design. Same as Triangle as others have said. Good computer too. other item, with that small of a boiler, I would suggest a 45 gallon indirect, l think you wont be happy with 20 storage and only about a 1 gpm hw recovery at 55 degreee rise (guestimate).This post was edited by an admin on February 13, 2013 9:16 AM. 
Yes, I'm Going With the WHN055
Almost seems like a no brainerI think with a 1 gallon per minute recovery, and a 14 gallon initial drawdown, the 20 gallon tank will be fine for our 2 back to back showers, and the other light uses of DHW. Oh, yes, I am toying with the idea of no primary loopseems redundant for a single, split loop distribution system. Why not just run the whole thing at 3 GPM, on one circulator? Thanks for all of you input. 
Why not
Just make sure the pump can handle the combined load. Have you considered using a variable speed circulator? Both of the knights can directly control such devices via a 010 volt output. I think wilo makes a high efficiency ecm pump called the stratos that can be set to recieve this signal. I'm sure taco and grundfos have similar units. With this arrangement, the boiler/pump will maintain a user specified minimum delta under part load conditions by slowing down the pump speed.This post was edited by an admin on February 13, 2013 12:29 PM. 
Yes, I Like the Idea Of
a variable speed pump. In fact, when I was going to do the primary/secondary piping, I was going to use a Taco 008 variable delta t controlled pump for the heating loop. My concern here is maintaining the 3 GPM flow rate. How would I insure this minimum flow rate? 
vs pumps
"I was going to use a Taco 008 variable delta t controlled pump for
the heating loop. ...How do I insure this minimum (3) flow rate?"
By heating loop, are you referring to the baseboards? I believe taco variable delta t controls have a minimum speed setting. I'm not quite sure what you're getting at here you wanted to use this in conjugation with a fixed speed boiler pump?
I had something else in mind. The knight's computer has a setting to enable direct pump speed control via a 010 volt output. You would specify the minimum delta t, say ten degrees, and the boiler will manage the flow over the speed range of the pump. (Clearly you would need a variable speed unit capable of receiving such a signal.) Typically at some point the boiler will outpace the circulator's capabilities, raising the boiler delta as demand continues to increase this is where you need to specify a pump that can produce enough head at full speed to maintain an acceptable boiler delta at maximum btu output. 
Yes, the Baseboard Heat
I'm getting a little confused againI have about 12 pounds of pressure resistance in the loop, a little less than 200 feet, baseboard and piping. The boiler requires a 3 gallon gpm flowso 
doesn't sound right
You're saying you have a 12psi pressure drop in the existing system? Or you will have a 12psi drop at 3gpm? 
I'm Talking About Head Loss
which I thought was calculated at about 6 feet per 100 feet of 3/4'" pipethe boiler has almost no head loss 
at what flow rate?
A head loss of 12 feet is equal to a 5.2 psi drop. But this is not fixed, it varies with the velocity of the fluid. Your probably looking at a table that is assuming a flow of around 5 or 6 gallons a minute.
Incidentally, 12 feet of head at 6gpm is almost right on the pump curve for the taco 008.This post was edited by an admin on February 13, 2013 4:23 PM. 
At that System
Head loss your going to have to pipe pri/sec. Don't use the VDT us the Bumble Bee. Does the same thing except and ECM motor.."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price." 
Why Can't I Use One Circulator
to move water thru my heating zone as well as the boiler? I only need a flow rate of 3 GPM. 3 GPM puts me right in the middle of the 24 GPM advised flow rate for 3/4" fin tube baseboard, not to fast, not to slow. 
you can
By the way, at some point you said there are two loops. Is there 100 feet of 3/4 inch in each loop? Or is there 200 feet in each loop? Or another uneven combination?This post was edited by an admin on February 13, 2013 6:44 PM. 
You Said
You have 200' loop which is 12' of head using the method of longest run x 1.5 x .04. Now go pull the flow/head chart below from both boiler manuals add this head to the boiler head, can you do it? The cost of two closely spaced tees is considerable less then the cost of the circulator you would need. You could purchase a Taco 0015 (OOR) for the boiler pump and do a Taco Bumble Bee combined for a tad more then the cost of the Taco 009 which is what pump you would need.
Sized the pump off the 25 degree delta chart to get your boiler head loss down."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."This post was edited by an admin on February 13, 2013 7:10 PM. 
!
I didn't realize there was such a difference between the water tube and fire tube hx.
11 versus 0.27 @ 5gpm 
firetube
This is really a slam dunk for the firetube. There are a number of single pump solutions that you could employ. I thought Wilo had a small ecm circ that could except direct 010volt control from the boiler, but I don't see it in there product line up. You have the option of traditional variable speed pumps, fixed speed ecm pumps, and the ecm taco bumblebee pump. The firetube/bumblebee combo seems unbeatable. Just pin down your system flow requirements to confirm. 
Split loop
I have about 200 feet of total piping. It is split evenly down each side of the house, 90 feet of 3/4" piping and baseboard, with about 20 feet of 1" supply and return down the middle. Right now, a single Taco 007 handles all the pumping demand, works good. Am i misfiguring the resistance in the piping /heating system? 
By Eliminating Primary/Secondary
I would eliminate the warming of the return water, caused by the primary loop moving water with a flow rate greater than the secondary. To prevent this, the two circuits would have to flow at the same rate. I care because of condensation frequency being compromised. A single circulator eliminates any chance of this happening. 
huh?
The point of primary/secondary is to allow you to run different flow rates and/or ∆Ts for the boiler and distribution loops. They may increase or decrease condensation (and efficiency) depending on how they are pumped and controlled. 
Blended Water
is going to decrease the efficiency of the system because the returning water to the boiler will have a higher temperature than the water that is actually returning from the heating loop, if it is flowing slower than the water in the boiler loop. 
Is My Longest Run
200 feet, or 100 feet? Logic tells me that 2, 100 foot runs, running at the same time, will equal 1, 200 foot run, but am I wrong? This is a simple, split loop system. 
it's tricky
The delta p is the sum of one leg (one loop) of your baseboard and the 1 inch and the boiler. But notice the flow in the baseboard is half of the 1 inch and boiler. That needs to be accounted for.
delta P total = delta P baseboard @ 1/2 flow + delta P supply/return @ flow + delta P boiler @ flow
So to be clear, yes you are going about it wrong.This post was edited by an admin on February 14, 2013 4:15 PM. 
Two Circuit Series Loop System
So I have two circuits making up the single loop. Both circuits are always in operation. To figure pressure drop, or resistance, I would base my calculations on the longest of the two circuits? If so, it reminds me of trying to understand why a subpanel is wired with the neutral and the grounds isolated, but bonded in the main panel. Just can't quite get it, but I know it works. Maybe there is a simple explanation to what I'm missing It would explain why a 007 works fine on this type of system, because now we wold be dealing with less than 6 pounds, instead of 12. 
Where are you getting the 6 or 12 pounds from?
What formula are you using? Can you give me a link or type it up here? 
Simple Formula for Head
Longest Run x 1.5 x. 04 = Head Ft
100' Run x 1.5 x.04 = 6' Head
I'm still trying to figure in my mind how a Grundfoss UPS1558 on Speed 1 is only going to move 5gpm at the head they show. A pump operates on it's curve and at that head that little sucker is going to try and move about 9gpm. I did see in the manual where is states the supplied pumps are based on 20' of piping, 4 90's and 2 Full Port Ball Valves. That equates to around 1.2ft of head. Even at 2' of Head that pump is wanting to move 7gpm. Thoughts?"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."This post was edited by an admin on February 14, 2013 6:59 PM. 
I've never seen that before.
What is the significance of 1.5 and .04? What are they computed from? At what flow is this head loss for? 
Standard Formula
The 1.5 accounts for fittings, valves, etc. The .04 represents 4' of head in 100' of pipe based on the velocity of 4' per second.
You could always open the attached to page 25 and start racking your brain out.."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."This post was edited by an admin on February 14, 2013 7:30 PM. 
that's 6 gpm
For 3/4 inch copper that's about 6 gallons per minute. It sounds like you are implying there would be 6gpm in each loop. We only need around 2 or 3 or even less at max fire. 
It's a Basic Formula
Used industry wide! So, you do all that math from page 25 on and when your done, show me the fixed speed circulator that will give you exactly what you want. Now use the formula I provided they calculated the developed piping at 100.2 ft.
After all the math they came up with 4.93' head I come up with 6'  Is it going to change my circulator selection at 5gpm, 2gpm, 3gpm, 1gpm? How many Taco 003's, 005's or 006's have you seen installed in your lifetime? How many 007's? Every pump is a better choice over a 007."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price." 
You're talking about this example on page 28?
Example: Determine the head loss of the circuit shown in Figure 514, assuming it has water flowing through it at an average temperature of 140oF and a flow rate of 5 gpm.
Head loss at 5gpm:
H = (acL) x (f^1.75) = (0.0475 x 0.061957 x 100.2) x (5^1.75) = 4.93 feet
But what is it at 2gpm?
Head loss at 2gpm:
H = (acL) x (f^1.75) = (0.0475 x 0.061957 x 100.2) x (2^1.75) = 0.99 feet
That's about 5 feet of head versus 1 foot of head. I'm not sure what you are getting at with the pump selection.This post was edited by an admin on February 14, 2013 8:26 PM. 
No Speculation
What is the total connected load? Use the Universal Hydronic Formula to calculate the required flow. It's a split loop, so you have to balance the loops. 
30,000 btus
15k in each loop if I remember correctly.
That would be 3gpm at 10 degree delta, 1.5gpm at 20 degrees.This post was edited by an admin on February 14, 2013 8:43 PM. 
No
3gpm at 20* DeltaT. 30000 divided by 20 x 500 
Agree
3gpm through the boiler, 1.5 through each loop. This is why I'm questioning the use of a head loss estimate that assumes about 6gpm in each loop.
Where'd everyone go?This post was edited by an admin on February 14, 2013 10:35 PM. 
Busy
It's was Valentine's Day. Think reality. Do you know of a pump that is going to operate exactly based on your numbers? Pump is going to operate on it's curve. Your flow rate is going to be larger then your 3gpm unless you install circuit setters and a differential bypass. Your gpm is predicated on your deltat."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price." 
I'm Back
So, am I designing for pressure drop using 1 circuit in the loop, or 2? Sounds like only one. This is beginning to make sense to me, in that the flow resistance I will have, no matter how many circuits I have, 1,2 3, 5, ect. is the same, as long as they are the same length. If this is true, I only need a small circulator.
By the way, that is the formula I have been using to come up with my numbers.
I must say, I agree that the Taco Bumblebee might be ideal, it will give me speed control, as well as exact GPM readout. The VV taco circulators are awful expensive, but I like having the boiler's computer having the ability to control circulator speed.
Also, I notice that Triangle Tube does not use primary/secondary piping on a simple design like mine (same HX design), they just advise to maintain the minimum boiler flow. 
what formula?
?
Holy smokes, didn't realize that about the vv circs!This post was edited by an admin on February 15, 2013 12:53 PM. 
100' Run x 1.5 x.04 = 6' Head
This formula is for 3/4" pipe 
That's at roughly 6gpm
That's at about 6 gallons per minute. Head loss is an exponential function of fluid flow. It is not the hydraulic resistance.
www.tacohvac.com/uploads/FileLibrary/SelectingCirculators.pdf
Head loss = k * c * L * (f^1.75)
k and c are constants that depend on the diameter of the pipe and type of fluid. L is the length of pipe. f is the the flow rate and as you can see it varies exponentially with gpm. The product (k * c * L) is what is typically considered to be the hydraulic resistance and assumed to be constant. The head loss would vary for example if you installed a variable speed pump, it would go up and down in relation to changes in fluid flow. You are in the design phase here: pick a target flow rate, estimate the head loss at the target flow rate, and then go and try to find a pump that can meet or exceed your requirements. Look over the Taco tech pdf above to get an over view of this process.
The rule of thumb you are using gives one an idea of the head loss in X feet of 3/4 at the maximum recommended velocity of 4 feet per second for copper. (Copper suffers from a phenomenon called erosioncorrosion at high fluid velocities.) That's about 6 gallons per minute. What is the head loss estimate at your target flow?
Edit: Caught a typo ced!
Head loss = k * c * L * (f^1.75) that's f to the 1.75 powerThis post was edited by an admin on February 15, 2013 2:16 PM. 
Okay Eastman, I Think I Tried it Your Way?
I used this formula I got from Taco, and you, HL = k x c x L x (f1.75) and I come up with about .5 feet of head loss at the target flow, 1.5 GPM per circuit, 3 GPM, total. Sound right? I will probably design at 2 GPM per circuit, 4 GPM, total. When I add in things like a Flowchek valve, I will have to adjust. So having said all of that, how can I possibly need such a tiny circulator, still must be doing something wrong! 
Sounds about right, but...
did you see my typo? It's f to the 1.75 power. (f^1.75) Not f times 1.75.
Here's an example head loss calc for 100 feet of 3/4 @ 1.5gpm I rounded off some of the digits.
H loss = k x c x L x (f^1.75) = 0.003 x 1 x 100 x (1.5^1.75) = 0.3 x 2 = 0.6 feet of head loss
Now, without knowing all the elbows and tees etc used, most people would use 150 feet of equivalent straight copper as the starting point. That works out to a head loss of 0.9 feet.
The total head loss is the sum of this value with the head loss through the boiler and supply and return lines at 3gpm. (And whatever else you add to the system.) The pump performance would have to exceed total head loss at 3gpm.
But honestly, without knowing the particulars of your home, I would have to advise you to design with a smaller delta t across the baseboard. 15k btu of baseboard in series can heat unevenly if it spans multiple rooms, particularly if there's a big window or some other major heat loss in the room at the tale end of loop. With a 10 degree delta your target flow would be 3 gallons in each loop; 6 though the boiler. 3 gpm in the baseboard loop is around 2 to 3 feet, 6gpm though the firetube boiler is something under 1 foot. So you're looking at a total of 4 feet or less at 6gpm through the pump. If you look at the bumblebee's fixed power (fixed speed) pumping curves, you should see that it happens do 6gpm @ 3.75 feet on a speed setting of 2. And it will only use 22 watts. So we should expect a flow of around 6 gpm if you used this pump at speed 2. If our estimates are off a bit, you could set it to something else to achieve more or less flow, reduce system delta, or save a few watts. In summary, most systems are way over pumped and large delta t's may be uncomfortable in your home. 
For Those Following This Insanity
we have forgotten that the common piping is 1", not 3/4". To review, the two circuits are piped 3/4", but their common supply return is 1". So if the flow was 3GPM in the 1", flow in the 3/4" would be 80 percent , or 2.4 GPM. 
Double check
I understood the situation like this: You have a 1 inch supply from the boiler. This tees off to 3/4 on one side of the house and another to the other side. If there is a 3gpm supply in the 1 inch, logic dictates that the sum of the flows in the 3/4 must also add to 3gpm. If the flow is split evenly, that would be 1.5 + 1.5 = 3. 
I Think You are Right
in calculating required flow for btu's, you would divide the total by two, in a system with 2 equal circuits. But I think the physical flow would be calculated differently. If we were dividing a 1" pipe in half, the flows would be half, but if we split the 1" pipe into two, 3/4" pipes, i think the flow rate would drop by only a small percentage. 
It sounds like...
It sounds like you are trying to condense the problem down to a single head loss calculation. Something like: What is my HL at F gpm for X feet of 3/4 copper equivalent length. And then proceeded to try to come up with something for F and X so the Head loss could be computed.
Looking at the Taco pdf, I can see why someone would think that. The short discussion on parallel circuits really requires some more context.
You need to do 3 head loss calcs: 1 for one of the baseboard loops, 1 for the common supply and return, and 1 for the boiler. And then add them all together to get the total head loss. Now, the boiler manual already has the head loss for the boiler at a variety of flows. So we don't need to calc that one, just look it up in the table.
The head loss for the common supply and return needs to be calculated with the k value for 1 inch copper and a flow rate of 3 gpm. ***I forgot to add this step in the last example, I hope I didn't add to the confusion.*** 20 feet of 1 inch at 3gpm is about 0.1 feet of head.
The head loss for one of the base board loops needs to be calculated with the k value for 3/4 inch at flow rate of 1/2 of the 1 inch. (1.5 gallons).
The total head loss is the sum: H total = H baseboard + H common pipe + H boiler.
Drawing on some of our previous work for 1.5 / 3 gpm target flow:
H total = 0.6 + 0.1 + 0.15 ish (have to look at the boiler table)
for a grand total of under 1 foot. 1.5 feet if you add a 50% smudge factor. For a 3 / 6 gpm target flow it works out to be about 4 feet of head.
Why is it so low? Half of it is because you spec'd a firetube hx, the other reason is because you have a very small load that is piped in 3/4 and 1 inch. You're not dealing with 100's and 100's of feet of small diameter pex tubing. If you wanted to use a water tube hx, the heads are much higher. Still doable, but you might be forced to run at relatively high delta Ts that may heat the home unevenly.This post was edited by an admin on February 16, 2013 2:54 PM. 
Just Wondering Taco?
How can 2 different formulas for estimating head loss (both provided by Taco), wind up with answers that far apart? At FloPro U., they caution that you could oversize by as much as 50%, BUT 500%!!. It would seem...Hydronics Step by Step, becomes Misstep by Misstep. 
One is based on the other
The formula:
Head loss = equivalent pipe length * 0.04
is assuming a fluid velocity of 3 ft/sec. 3 ft/sec in 3/4 copper corresponds to about 4.8 gpm.
The 0.04 value is 0.04 feet of head per foot. It represents the head loss @ about 4.8 gpm for one foot of 3/4 copper tubing.
Does this seem reasonable? Let's do a head loss calculation for 1 foot of 3/4 @ 4.8 gpm. That would be:
Head loss = k * c * L * (f^1.75) with k= 0.003, c= 1, L= 1, and f= 4.8
Head loss = 0.003 * (4.8^1.75)
Head loss = 0.046 feet
So with a fluid velocity of 3 ft/sec corresponding to a flow rate of about 4.8 gpm, we do get about 0.04 feet of head per foot. 
yes
.046 x 150 = 6.9' You are solving for 1 ftThis post was edited by an admin on February 17, 2013 2:37 PM. 
100' Run x 1.5 x.04 = 6' Head
After trying lots of different formulas, this simple one seems to agree with most of the others, as long as I plugged in all of the right numbers. I am going to stick with it. All my confusion stemmed from not calculating the length of the longest circuit, and basing the loss on it. Instead, I was basing everything on the entire loop, all 2 circuits. This was wrong. 
HDS2
Have you guys taken a look at Siggy's Hydronic Design Studio2. It uses all your formula's and will give you an answer in 2 minutes.
John Pughe 
One Thing Not Taken
Into consideration is a fixed speed pump is going to operate on it's curve no matter how down to the science you get the head loss."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price." 
If
you've figured correctly, what is the down side to that? 
Paul
I was referring to this situation. The basic formula of Run x 1.5 x. 04 gets you the same pump in the end..I'm sure you like me haven't seen too many 003 or 005 Taco circs installed out there. In this case the 003 would be the right pump at twice the cost or more then a 007. This is where a Bumble Bee would fit rather nicely."The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price." 
Agreed
But then the Bumblebee is twice the price. It gives you way more bang for your buck. Which brings us back to P/S piping and the ability to run a 10* DeltaT on the system side(as suggested), while staying with at least a 20 through the HX.. 
rule(s) of thumb
Here is that general rule recalculated for a variety of different fluid velocities for 3/4 copper tubing:
Head loss @ 1.0 ft/sec = equivalent pipe length * 0.0069
Head loss @ 1.5 ft/sec = equivalent pipe length * 0.014
Head loss @ 2.0 ft/sec = equivalent pipe length * 0.023
Head loss @ 2.5 ft/sec = equivalent pipe length * 0.034
Head loss @ 3.0 ft/sec = equivalent pipe length * 0.047
Head loss @ 3.5 ft/sec = equivalent pipe length * 0.062
Head loss @ 4.0 ft/sec = equivalent pipe length * 0.078
So the head loss for 100 feet of 3/4 tubing would range from 0.69 feet @ 1.0 ft/sec through 7.8 feet @ 4.0 ft/sec 
Pipe Sizing
As long as you're within pipe sizing guidelines for flow, those calcs are not necessary.This post was edited by an admin on February 18, 2013 9:02 AM.