[long! read only if you're bored/have time] mod/con boiler if i don't want one

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  #121  
Old 03-21-13, 04:21 PM
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in other words, sizing for the largest zone is ok?
Maybe, but what I'm really saying is that those calculations are seldom if ever done for a normal residential hydronic system. There are now 120 posts on this thread, so I kind of forget where we started. Did your current or previous system work satisfactorily? Why are you computing all these pressure drops? If it's to fine-tune the pump selection, I doubt that it is all worth it.

Most installers pick a circulator from experience and move on, and it most always works. Many new boilers come with a circulator, and the boiler manufacturer obviously knows nothing about the system piping that the boiler will be installed in.
 
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  #122  
Old 03-21-13, 04:33 PM
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Note Honeywell zone valves have a cv of only 3.5 and an efp of 50.

So taco is a good choice.
 
  #123  
Old 03-21-13, 04:34 PM
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gilmorrie,

i have a regular non condensing gas fired boiler that is 32 yo with a taco 007 recirc and two zones with valves. i'm just going thru the options right now trying to be ready for when i need to do a replacement.

since i like to understand how things work and not in a rush I'm trying to make an educated choice and not end up with a system that is oversized or not optimized or not suitable.

this forum is full of knowledge and i'm taking advantages of it

as thread progresses i learn new things and that results in more questions hopefully it's educational for other people as well.

now back to the topic i wanted to go with a single recirc and 2 zone valves. i thought vavles were cheap, but they cost as much as a recirc! so now i wonder if should have 2 recircs with IFC for two of my zones. instead of a recir and pair valves? the price is about the same but i would get a full flow per zone when 2 zones are open.
 
  #124  
Old 03-21-13, 04:43 PM
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i thought vavles were cheap, but they cost as much as a recirc!
In the short term, yes. Cradle to grave cost of ownership, I would think a zone valve wins due to the decreased use of electricity. There ARE pumps out there now that are very miserly on electric usage, but they aren't cheap.

I don't think this has been touched on with all this talk of pump curves... BUT:

Remember that the SYSTEM has a curve ALSO. It is an inverse shape to the pump curve. At ZERO FLOW, there is ZERO HEAD. Remember that the MORE FLOW, the MORE HEAD.

Matching a pump to a system requires hitting a MOVING TARGET.

In this graphic, a 'system curve' has been added to the pump curve. It shows that the INTERSECTION of the two curves determines what the flow rate will be.



The system curve can be calculated using the formulas in the following book, but there are places on-line where you can find the same formulas.

Diver, if you want to be totally ejumicated, and have about $200 available to spend on that education, I would highly recommend you purchase John Siegenthaler's 'bible' of hydronic design.

Modern Hydronic Heating: For Residential and Light Commercial Buildings: John Siegenthaler: 9781428335158: Amazon.com: Books

Study this and earn your degree!
 
  #125  
Old 03-21-13, 05:29 PM
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NJ Trooper,

That point was missing in this story. I have a pool and I went thru the same process there as well. From having no understanding to how it all work, to going deep into pool chemistry and dynamics of the pumping. Dynamic head is always a function of the flow and in the calculation i've seen so far for hydronic system it was liner feet multiplied by 0.04. I was a bit puzzled, since there was no flow specified. I think 4 gpm was implied.

I think the approximations that I've gone with are good enough for my purpose.

Electricity wise I'd think it should be somewhat similar when it comes to recircs vs zone vavles.

When only one zone is open it's one recirc moving water around in a system with 2 recirs and in a system with 1 recirc and 2 valves. So the electricity cost is the same.

When two zones are open two recirs will provide enough flow to satisfy call for heat from two zone in half the time as compared with one recircs and 2 open valves. Provided the boiler has enough capacity of course. So it's twice the electricity but half the time. Am I wrong in my thinking?

As for the book, I'd love to read it, but it's too much
 
  #126  
Old 03-21-13, 05:38 PM
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Desired delta T thru a mod con is subjective, and is not a one number fits all.

I typically will look at what is connected to the heating side and base my system piping and flow rates from there.
For instance, if I have a mid temp load and a radiant slab, I would want to size the loop flow rate to take advantage of the lower return water temps coming from the slab. This will condense the boiler and save fuel. I would likely look for a delta t at design of 40 F.
Would I use that same pump for DHW generation... NOPE
I would increase the flow rate so as to get a delta t of around 20, maybe a bit more maybe a bit less. Depends on the tank. DHW production would suffer with a 40 degree delta T.

You will never want, or expect to get a 10 degree delta t thru a Geonini Heat exchanger, they are just too restrictive in the water ways. A fire tube, no problem.
A low delta T is not desirable from several points, it's expensive to obtain, maintain and it can move the boiler out of condensing range.
 
  #127  
Old 03-21-13, 06:04 PM
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TO heating, your last post is referring to a 40f delta-t in the system? I never heard of a 40f delta-t in a radiant system. How's that work as far as comfort?
 
  #128  
Old 03-21-13, 06:27 PM
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if a boiler piped as a secondary loop to the zones and PF-50 boiler requires 4.6 gpm flow for 20 delta T, would there be a problem if a primary loop (zones) run at lower rate of flow? this will result in reverse flow in the closely spaced tees. any problem with that?
 
  #129  
Old 03-21-13, 09:16 PM
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Delta T

TOHeating,

Been reading this very informative thread.

Can you answer a question for me? I realize the delta t needs to be high enough to get the return water below 130 if you want to operate in the condensing mode. I am missing something here but on my WAY oversized Alpine 150 the difference between output temp and return temp is less than 10 deg most of the time as read on the LCD on the boiler. I have also read the numbers on black friction tape wrapped around the pipes and get similar readings. How do you get/measure a 20 or 30 deg D/T?

I like your handle, its my initals


Thanks,

Tom O. Hale

Tom
 
  #130  
Old 03-22-13, 05:45 AM
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Note Honeywell zone valves have a cv of only 3.5 and an efp of 50.

So taco is a good choice.
here is this crazy guy with a CV of 23.5 and EFP of 2.5!

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i'm starting to think that maybe a recir for each zone might be better.
 
  #131  
Old 03-22-13, 06:24 AM
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Diver,
The reverse flow between the tees happens in p/s everyday normally from oversized mod/cons. The beauty of p/s is hydraulic separation. This means the flow of one pump does not affect the flow of another pump. With that said it does not mean that both pumped system work as thought. Although it is not always a bad thing.
A3holerman,
Try derating the boiler. Let me know the hours of operation, # cycles for heat and DHW under the "Status" screen and I will help you. Also include the manufacture and model # of the IWH.

The problem with over sizing a Mod/con is reversed flow between the tees. This causes the boiler to short cycle. A properly sized boiler means the required system flow rate closely matches the boiler flow rate. Add multiple zones to that and it gets worse. Yes,it does modulate but if the delta-t is wide it goes to high fire until the delta-t gets closer. Now the fan is searching for a good rpm to modulate but is changing constantly. So it short cycles. Believe me I do enough job site visits to prove that. I am tired of seeing 3 minute average run times when 20 or more is much better. The other thing you loose by over sizing a mod/con boiler is the whole lower end of input. Take an 80k boiler with a 5:1 turndown. That means it turns down to around 16k. With a het loss of 60k means we operate below 50% of the heat loss about 65% of the heating season. So most of the heating season would be at or below 30k. How much of this time do we operate at 50% of this or 15k? Not sure but if there is two or more zones I bet most of the time. Now look at a 150k boiler with a 5:1 turndown and the same het loss. It goes down to 30k. Now add in the multiple zones and we lost the most efficient time of operating the mod/con boiler, add to that the flow between the tees to pre-heat he returns and ..........wow!
 
  #132  
Old 03-22-13, 07:23 AM
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rbeck,

as always thanks for valuable information. The system Iím ďdesigningĒ seems to be sized properly. PF-50 has a DOE output of 46K and my heat loss is about 34k. My radiation is a bit over 50k. I know radiation amount is somewhat irrelevant, I just included it here for reference purpose.

Here is a table for flow rate thru the boiler and recirc selection:

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The recommended flow rate for 20 deltaT puts a flow thru PF-50 at 4.6 GPM. Recommended recir selection for delta T makes the flow a bit higher, so letís say itís 4.6. Since the boiler loop itself it not included in this table, letís use 4.6 GPM.

I calculated my best zone to have about 4 gpm flow , the other one will be a bit less. So even at best scenario my system flow is 4 gpm and boiler loop is 4.6 gpm. So it looks like I will end up with a constant, albeit a small reverse flow. Is it anything to be concerned with? Should I go for a bigger system recirc?

also, is there an easy way to detect a reverse flow?
 
  #133  
Old 03-22-13, 07:59 AM
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Rbeck thank you

Rbeck,

Thanks for the input.

My installer/plumber did a nice job on the installation by the looks of it. The problem was he has no idea how to set up this type of boiler. When asked if he made any adjustments to the programming he said "NA I just leave it as the factory defaults" Thats when I took it upon myself to try and learn how to set it up properly.

I have the fan turned down to 4500rpm, but my understanding is that this really only effects how fast it ramps up to temp. The heating temp is set at 160 and with the ODR it is running around 140-145deg with the OAT here at 29-33deg F.
That seems to keep the boiler running almost continuously modulating from min fire to 10-15% above that. With those temps I am seeing return temps 5 or so degrees below output temps after it has stabilized as read on the LCD. Don't understand where the Delta T temps at 20-30deg people talk about come from.
There are a total of 3 zones in the house now not counting hot water.


The IDH is a Superstor SSU-45. The new heating contractor I hired just finished installing a mixing valve so we can run the tank at 140 or so and have 120 or so coming out of the tank. The HW setup on the boiler is set at 5000rpm and a temp of 180deg.

The problem as I see it is: With these outside temps 140-145 deg water seems to keep the house warm with various zones coming and going keeping the boiler running most of the time near or at min mod. With return temps well above 130 I am not in the condensing mode. As the days warm up and hopefully when I get the ODR curve set right and it lowers the water temp so as to get in the condensing mode, it will start short cycling again.

Just ordered my copy of "Modern Hydronic Heating", anxious to get into it.

Looking forward to any thoughts or comments.

Tom
 
  #134  
Old 03-22-13, 09:06 AM
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Diver that 7 ft and 4.6 gpm is decieving, no? Look at the 005. At 7 ft is about 7 gpm?


Also I assume the 7 ft will increase when you add valves, flow check,...etc.


I believe r beck may have stated just put 007 circs all around?


 
  #135  
Old 03-22-13, 09:20 AM
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it is deceiving. i looked at other recircs recommended for boiler loop and they all seem to give a bigger flow that table implies.


i think i will go with a 3 speed Grundfos_ups15-58fc - three speed option gives very wide performance range and ability to adjust the flow if needed.

maybe low/med speed for boiler loop, med/high speed for zones and IHW. with check valves integrated it seems to make sense to go with recirc controlled zones instead of zone valves. do you still think that recircs instead of zone valves would cost more to operate?
 
  #136  
Old 03-22-13, 09:25 AM
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IMO I would go with 3 00R three speed pumps for 76 bucks each.

0015-MSF2-IFC - Taco 0015-MSF2-IFC - 00R 3-Speed Cast Iron Circulator - Integral Flow Check, 1/20 HP

Indirect on hi so you get better then the 8 gpm min required.
It would seem the boiler circ on med to get you the 15f delta tee.
And the system on lo, although med might be good if not noisy.


Again I am not pump guy but IMO the 3 speed gives best options.



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  #137  
Old 03-22-13, 09:42 AM
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lawrosa, i meant to look into this one as well, but forgot. i will take a look, thanks!

i really like an option of 3 speed. if sizing is a bit wrong, there is flexibility to adjust it. i'm surprised it cost pretty much the same as one speed.
 
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Old 03-22-13, 09:49 AM
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Also I am not a grunfos fan. I rather spend my money on a american based company such as taco rather then give it to denmark....

Just my opinion of course....
 
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Old 03-22-13, 11:12 AM
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lawrosa,

i looked at both of them and compared the pump curves. the high speed curve is similar in both, but lower end is lower for grunfos. meaning grunfos has a wide range. another plus for grunfos - lower amperage, taco one is more powerful pump overall.

but i think they both are suitable for my application.
 
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Old 03-22-13, 12:17 PM
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I did not compare. The ups 15-58 right? The taco looks better IMO....

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dotted line is IFC

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  #141  
Old 03-22-13, 12:37 PM
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it depends on definition of better it's more powerful and it will move more water under the same head. but it will also consume more power. if i don't need more power then it would be a waste.

taco graph is a bit misleading since it's not "square" - units on vertical grid go by 2 and on horizontal one they go by 1.

here is slightly adjusted "square" graph:

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for the record, i'm not opposed to taco pump
 
  #142  
Old 03-22-13, 12:57 PM
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OK I did not compare amps.

Dont think you will notice the .23 or so difference in amps on your electric bill....LOL..... About 27 watts difference on Hi.





Grunfos
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Taco

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  #143  
Old 03-22-13, 01:26 PM
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not sure where 0.01 amp came from.

grunfos: 0.75, 0.66, 0.55
taco: 0.98, 0.82, 0.71

20 watts on average difference. 2-3 recircs running at the same time (boiler + IHW, boiler + 1(2) zone(s)) = 40-80 watts extra. it will add up

edit: hey, you changed your post!
 
  #144  
Old 03-22-13, 01:37 PM
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i'm not overly concern about electrical cost of running a recirc per se.

as i mentioned before the high end of the flow produced by either pump doesn't seem to be a very important spec for my particular case since they both can produce higher rate that i could possibly use.

however, the lower end of the flow range is different with two of this recircs. grunfos will be able run lower flows since it's less powerful pump.

maybe (and i'm not sure here) i would need that slower flow rate to run the system more efficiently. and that might result in much more savings. with taco i won't have that low end, since it's more powerful.

just a thought.
 
  #145  
Old 03-22-13, 01:51 PM
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Yes but what fits this scenario best?

Which puts my worst zone at 9.72 feet of head and at 3.5-4 gpm. which is exactly where i should be at, correct?
You can run the taco on lo @ 4.5 gpm .71 amp.

The grunfos on med @ 6 gpm .66 amps

See what I mean....

( People are going to think we are nuts analyzing this stuff to minute detail.)...LOL
 
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Old 03-22-13, 03:00 PM
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You can run the taco on lo @ 4.5 gpm .71 amp.

The grunfos on med @ 6 gpm .66 amps
if those numbers are correct, i'd think grunfos would be better - lower amps, more flow - bigger bang for your buck. and there is still possibility to run faster or slow. with taco you're already at the very end of the range, you can only go up. more up than grunfos though.

( People are going to think we are nuts analyzing this stuff to minute detail.)...LOL
i think they already gave up on this thread
 
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Old 03-22-13, 03:10 PM
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Yes but do you want 6gpm through the loops? I think thats too fast no?

Again not a pump guy... Just throwing stuff out there to you so you make an educated investment/purchase..

Its exciting to me and I have that peerless on my short list too.

Im still partial to the s 34. This seller is only an hour ride from me so I would pick up. Cheap because they sell for $1800. I would couple it with a ss 35 indirect as I suggested to you.

( When I win the lotttery )



Slant Fin Sentry s 34 DP Natural Gas Hot Water Boiler | eBay


Look at my dinosaur.


[IMG][/IMG]
 
  #148  
Old 03-22-13, 03:25 PM
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yeah, 6 gpm on grunfos on medium speed is only 2 at slow speed, so there is no 4 gpm at 10 feet head.

but wouldn't 6 gpm thru the zone be good? the heat exchange will definitely improve. i'd think it wouldn't be bad to the fin baseboards, would it?

how old it the dinosaur? the fire box on the bottom is all open! does it spit fire here and there ?
 
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Old 03-22-13, 03:49 PM
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but wouldn't 6 gpm thru the zone be good? the heat exchange will definitely improve. i'd think it wouldn't be bad to the fin baseboards, would it?
Dont know... I assume not as you will get noise and possible pipe wear??? This is what you need to ask to others. 4 gpm is what is in all the text books.....


how old it the dinosaur? the fire box on the bottom is all open! does it spit fire here and there ?

No. There is a door under there with site window just on top of the cast iron burners. Cant see it.

That dirt/burn mark looking spot is just that...Dirt from grummy hands relighting the pilot every year...

Well the Relay was installed or replaced in 84'. That has a date inside. But I believe its older then that. 1950 home had grate heater in floor. After the grate heater was removed this was installed. When???? I dont know.

Im thinking late 60's

Well water too.......
 
  #150  
Old 03-22-13, 04:10 PM
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4 gpm is what is in all the text books.....
It's not 4 gpm - it's 4 ft/sec maximum flow velocity, which depends upon both flow rate and the cross-sectional area of the pipe.
 
  #151  
Old 03-22-13, 05:05 PM
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according to this calculator for 0.75" ID pipe the 4 ft/sec flow velocity equals 5.5 gpm.

thanks, gilmorrie!
 
  #152  
Old 03-23-13, 06:00 PM
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The system flow rate is normally calculated at 20f delta-t. To determine system flow rate Divide heat loss by 10,000. So a 60k heat loss would be 60,000/10,000=6 GPM. The boiler flow rate is what they suggest. This is when zone valves may be a better idea. Multiple pumps can cause too much flow through the boiler.
When the flow in the system is different than the boiler flow that is a good time for p/s even if it is a cast iron boiler.
 
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Old 03-25-13, 08:24 AM
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Rbeck,

Iím very interested in the zone valve vs recirculator conversation. I understand the problem with overpumping and return water coming back not cold enough.

Letís say we have two zones. In the scenario when only one zone is calling for heat the flow rate in that particular zone will be the same in zone controlled system or recirculator controlled system Ė you have one recir running a zone. Technically with zone controlled system the flow will be lower since there is additional head from the zone valve, but letís ignore it for now. So if recirc is big enough we will be overpumping in each system. If it's sized properly, we're good.

When you have two zones calling for heat in zone controlled system the flow thru each zone dropped in half (letís pretend zones are equal) and for recirculator controlled system the flow stays the same. So only in this scenario (which might or might not be happening often) the zone controlled system will be better when it comes to overpumping. If overpumping was happening when only one zone is on.

I assume a system has to be design that there is no overpumping when only one zone is open. In which case valve vs recir overpumping argument is a moot point. However it will make a difference in a system that is not designed properly.

Originally I was inclining towards having zone valves for my future system (see here), but now I think otherwise.

Pros for recircs:

- simpler system: for 2 zone one will have 2 recircs with IFCs, otherwise a recirc + 2 zone valve
- cheaper: 2 recircs cost less than a recirc + 2 zone valves
- same flow when one or 2 zones are calling for heat
- someone mentioned that zone valves are less reliable
- 2 speed recircs will give flexibility regarding the flow rate per zone

Cons:

- NJ Trooper thinks that it will cost more electricity wise, but Iím not sure if I agree. When two zones are open a single system recirc will run more or less twice as long as two individual zone recircs, so it should be the same. Please correct me if Iím wrong on this assumption.
 
  #154  
Old 03-25-13, 09:01 AM
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When two zones are open a single system recirc will run more or less twice as long as two individual zone recircs, so it should be the same. Please correct me if Iím wrong on this assumption.
I don't think that's a correct assumption Diver...

The zones are running in parallel with each other, both producing heat at the same time.

What is your reasoning that the pump would run twice as long?

Also, remember that a zone valve consumes what? maybe 10 watts of power? compared to a typical wet rotor circulator which might consume say 100 watts.
 
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Old 03-25-13, 09:39 AM
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The zones are running in parallel with each other, both producing heat at the same time.


the heat will be delivered by half the flow for each zone, so the output will be lower. but not in half though:

Attachment 10632

so it will only run 5% longer: (610 - 580) / 580

if boiler is big enough to satisfy 2 zones, then i agree, you will consume less electricity.

zone valve power consumption goes on top of the recirc, so it will balance things are bit, but probably not enough to make recirc system consume the same amount of power.

you convinced me, it will take less power. not sure if i wan't zone valves yet, but i agree on one negative for all recircs system.

i assume having a dedicated recirc for IHW is still preferred since the flow rate should be higher there and zone valve in that loop is not desirable due to increase in the head?
 
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Old 03-25-13, 07:47 PM
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the heat will be delivered by half the flow for each zone,
No... circulators don't work that way.

If one zone is open and pumping say 4 GPM, when the second one opens it doesn't pump 2 GPM through each one.

That's what a 'pump curve' and a 'system curve' and the 'operating point' is all about.

When the second or third or fourth zone opens, the pump is moving water against LESS HEAD (zones in parallel present less head to pump) and the flow from the pump increases.

A pump with a flat curve like the 007 will pump say 4 GPM into one zone, maybe 7 into 2 zones, maybe 10 into 3 zones... to a point of course, but absolutely not half, or a third, or a quarter. It just don't work that way!

This graphic illustrates. The three curves starting at zero are what the system might present to the pump with one zone (the left curve), two, or three open. Note the intersecting points with the pump curves. This is the 'operating point', where the system curve intersects the pump curve. That's how much will flow.



i assume having a dedicated recirc for IHW is still preferred since the flow rate should be higher there and zone valve in that loop is not desirable due to increase in the head?
Correct. But, with a zone valve with a high Cv rating and priority on the DHW, they can be made to work just fine. I personally would run a dedicated circ on an indirect to get max performance.

Boy, we did a good job hijacking Ntonkin's thread, didn't we? ( hint, hint )
 
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Old 03-26-13, 05:50 AM
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Follow up to this post by NJ Tropper:

I understand the system curve vs pump curve relationship a little bit better now. I agree that the flow won't decrease that much as i initially implied. Another thing that works for zone valve system is the fact that even if a flow drops form 4 gpm to 1 gpm heat delivery doesn't suffer much according to the table I posted earlier.

so it appears that one recirc and 2 zone valves would deliver almost as good as 2 dedicated recirs. i was wrong.

it will be hard to provide a good flow rate for IHW with the same system recirc since the rate thru IHW has to at least twice the rate of the zones. if zones operate in the 1..4 gpm range, the IHW requires 8+.

some of the zone valves have very high CV and almost no extra head. White Rodgers valve has a CV of 23.5 and only 2.5 feet of EFP! Looking at this valve i wonder why would anyone consider any other valves with CV of 3.5 to 8???

what are the pros/cons for zone valve 24 VDC vs 115 VAC voltage??
 
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Old 03-26-13, 05:56 AM
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rbeck,

thanks for the formula for the flow rate as function of the heat loss. i assume this flow rate is for the boiler, not the zones?

i implied p/s piping in all my latest posts talking about recircs vs zone valves.
 
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Old 03-26-13, 01:02 PM
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You're welcome diver. These formulas work for both system and boiler.
 
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Old 03-26-13, 02:30 PM
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I believe you guys are talking about the "Universal Hydronic Formula" ?

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