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ced48
Posts: **383**

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.

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## Comments

7,356I'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.

383WHN055

383with them modulating down to 9-11. 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?

7,356is 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.

782Are 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?

2,226Go 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).

383Almost seems like a no brainer-I 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 loop-seems 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.

782Just 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 0-10 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.

383a 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?

782"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 0-10 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.

383I'm getting a little confused again-I 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 flow-so-

782You're saying you have a 12psi pressure drop in the existing system? Or you will have a 12psi drop at 3gpm?

383which I thought was calculated at about 6 feet per 100 feet of 3/4'" pipe-the boiler has almost no head loss-

3,056Head 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..

782A 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.

383to 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 2-4 GPM advised flow rate for 3/4" fin tube baseboard, not to fast, not to slow.

782By 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?

3,056You 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.

782I didn't realize there was such a difference between the water tube and fire tube hx.

11 versus 0.27 @ 5gpm

782This 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 0-10volt 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.

383I 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 mis-figuring the resistance in the piping /heating system?

383I 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.

7,356The 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.

383is 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.

383200 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.

782The 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.

383So 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 sub-panel 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.

782What formula are you using? Can you give me a link or type it up here?

3,056Longest 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 UPS15-58 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?

782What is the significance of 1.5 and .04? What are they computed from? At what flow is this head loss for?

3,056The 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..

782For 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.

3,056Used 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.

782Example: Determine the head loss of the circuit shown in Figure 5-14, 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.

4,158What 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.

78215k in each loop if I remember correctly.

That would be 3gpm at 10 degree delta, 1.5gpm at 20 degrees.

4,1583gpm at 20* DeltaT. 30000 divided by 20 x 500

7823gpm 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?

3,056It'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 delta-t.

383So, 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.