boiler circulator question

Reply

  #1  
Old 08-18-09, 06:24 PM
Member
Thread Starter
Join Date: Aug 2009
Location: usa
Posts: 6
Received 0 Votes on 0 Posts
boiler circulator question

I am in the process of installing a new weil mcClain cgt 5 gas boiler pre packaged with one circulator after the three way valve. The current setup is using two circulators on the return side for zoning 2 zones. I was planning on making 3 zones from the outlet of the boiler using zone valves and using the single boiler circulator a 007 taco for circulation. Would the one circulator be able to funtion properly or should I use circulators to control zoning on the outlet of the boiler? Any help is appreciated.
Thank you, Steve
 
Sponsored Links
  #2  
Old 08-18-09, 07:22 PM
Member
Join Date: Jul 2009
Location: Toronto
Posts: 1,174
Received 0 Votes on 0 Posts
Kinda hard to answer that question with out knowing the head loss on each of the zones.
Taco 007 is a pretty universal pump so it should work.
But "should" may not cut it.
 
  #3  
Old 08-18-09, 07:33 PM
Member
Thread Starter
Join Date: Aug 2009
Location: usa
Posts: 6
Received 0 Votes on 0 Posts
Exactly I dont want to over work the circulator and not get the propper flow if all three zones are calling for heat at the same time. Which is one reason I want to split zone1, no sense in heating the full upper level if its not occupied at night when jus the bedrooms are being used. Whats the best way to calculate head loss, I have a pretty good estimate of all the pipe lengths, and rise is about 6-7 feet
 
  #4  
Old 08-19-09, 05:21 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Something to understand is the fact that the pump has LESS work to do when MORE zones are open. Pumping into ONE 3/4" pipe is much more restrictive than pumping into THREE 3/4" pipes!

Check out the 'pump curves' on the various pumps (google and you shall find), and read up on that aspect.

The pump will pump more water with more zones open due to the less restriction.
 
  #5  
Old 08-19-09, 07:58 PM
Member
Join Date: Nov 2005
Location: USA
Posts: 2,459
Received 0 Votes on 0 Posts
What Trooper said. Plus...

You can't really overwork a 007. In fact, by splitting the zones you will probably stress it and the boiler more because the loads will be small. The boiler will cycle more, and so will the pump. Longer cycles are good.

Having said that, also keep in mind that the cgt5 is probably 2-3 times larger than you need to heat the house, so it will be prone to short cycling from the get-go. I wouldn't split your zones.

The tankless coil is also about the most inefficient (i.e., most costly) way to heat domestic hot water.

You might be better served by ditching the tankless coil and going with an indirect water heater on a separate zone.

As for how to pipe the boiler with a circ and zone valves, I would pipe it exactly as shown in Figure 19 on page 23 of the manual:

http://www.weil-mclain.com/downloads...ilermanual.pdf

What's very important is to have the expansion tank connected to the system on the inlet side of the circulator. If you look at the figure, it shows exactly that. That's "pumping away" and is good hydronic practice.
 
  #6  
Old 08-20-09, 03:30 PM
Member
Join Date: Oct 2008
Location: USA
Posts: 2,916
Received 7 Votes on 7 Posts
Originally Posted by NJ Trooper View Post
Something to understand is the fact that the pump has LESS work to do when MORE zones are open. Pumping into ONE 3/4" pipe is much more restrictive than pumping into THREE 3/4" pipes!

Check out the 'pump curves' on the various pumps (google and you shall find), and read up on that aspect.

The pump will pump more water with more zones open due to the less restriction.
Not 'zactly

Yes, the pump will produce higher flow with less restriction.

However, the max power produced by a centrifugal pump is when the restriction or pumping head is low - and flow rate is high. So, the pump/motor will work harder with three zones open than with one zone open. Power = flow rate x pump head.

Theoretically, a pump produces zero power when it operates at shut-off head, against a shut valve. Since flow is zero, flow x head = zero. (But don't run a pump at shut-off head.)

But I wouldn't worry at all about "overworking" a Taco 007 in the situation described.
Doug
 
  #7  
Old 08-20-09, 05:22 PM
rbeck's Avatar
Member
Join Date: Jul 2007
Location: Pennsylvania
Posts: 2,456
Received 2 Votes on 2 Posts
A pump will move more gallons through 3 pipes just due to more places for the water to go. If two zone valves out of 3 closes the velocity increases. As you increase flow you increase resistance and flow slows down.
 
  #8  
Old 08-20-09, 06:03 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Doug's eggspanation is of course, correct... I chose my words poorly. Of course if you are moving more water, more work is being done, and that equates to more power being drawn.

The point though was that the pump will move more water when three zones are open, versus one zone open, for all the reasons stated by all the esteemed gentlemen...
 
  #9  
Old 08-20-09, 06:10 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Oh... forgot something... I know how these guys just LOVE the old 'rules of thumb', but here's a quick and dirty one for ESTIMATING the head loss of a circuit. (most accurate for 3/4" pipe)

Take the total length of the circuit. Let's say 66 feet.

Multiply by 1.5 = 99 feet

Multiply again by 0.04 = appx 4' of head

do this for each zone, and size the pump for the WORST CASE, because if it can pump that one, it can pump them all.

And remember that the total head that the pump sees goes DOWN as additional zones open, NOT UP. In other words, TWO zones with 4' of head each does NOT equal 8' of head when both are open. It's more like 2' of head. Add a third zone of 4' and you are down to like 1.5' total pump head.
 
  #10  
Old 08-20-09, 06:20 PM
Member
Join Date: Jul 2009
Location: Toronto
Posts: 1,174
Received 0 Votes on 0 Posts
Umm, it's only half if the flow drops in half once the second zone opens.
Usually, you will not double the flow thru a single zone if it's the only one open.
If you use a flatter curved circulator, like a 007, there is not enough available head to double the gpm. They say you can often get away without using a differential pressure bypass with a flatter curve circ.
 
  #11  
Old 08-20-09, 07:14 PM
rbeck's Avatar
Member
Join Date: Jul 2007
Location: Pennsylvania
Posts: 2,456
Received 2 Votes on 2 Posts
The reason you do not double the flow is the velocity and resistance goes up so flow goes down.
 
  #12  
Old 08-20-09, 08:03 PM
Member
Join Date: Nov 2005
Location: USA
Posts: 2,459
Received 0 Votes on 0 Posts
And resistance goes as something like the cube of the flow rate..., or something like that....
 
  #13  
Old 08-20-09, 08:28 PM
Member
Join Date: Oct 2008
Location: USA
Posts: 2,916
Received 7 Votes on 7 Posts
Originally Posted by rbeck View Post
A pump will move more gallons through 3 pipes just due to more places for the water to go. If two zone valves out of 3 closes the velocity increases. As you increase flow you increase resistance and flow slows down.
True. And when two out of three zone valves shut, the pump/motor will produce less power, "work" less hard, and draw fewer amps.
Doug
 
  #14  
Old 08-20-09, 08:46 PM
Member
Join Date: Oct 2008
Location: USA
Posts: 2,916
Received 7 Votes on 7 Posts
Originally Posted by NJ Trooper View Post
Of course if you are moving more water, more work is being done, and that equates to more power being drawn.
Yes, at a given head, higher flow will require more power. But conceivably, you could move more water, at a sufficiently reduced head, and the power (work) could be less.

But, for typical piping systems and a centrifugal circulator, higher head and reduced flow will result in lower power or work.

I'm a little slow, so it took me a little while to understand why a pump with its discharge flow throttled would result in lower power. It's tempting to think of a pump, with its discharge throttled, as "struggling," beating its head against a wall, like driving a car with the emergency brake on. Actually, pumps/motors love being throttled - it makes their lives easier Beer 4U2
Doug
 
  #15  
Old 08-20-09, 09:27 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
I'm not sure I'm understanding myself! You guys are confusin' me...

I didn't say the flow would double... I was talking about the head that the pump is looking at... the amount the flow increases does, as TO said, depend on the pump curve. If pump curves were LINEAR (they are not!) and the SLOPE of the curve exactly matched (and they never do!) the difference in one or two (or three or four) zones open, then the flow _MIGHT_ double, triple, quadruple... etc, but yes, it (the difference in flow you get) absolutely depends on the pump curve.

The fact remains that the more zones open, the more flow (to a point) you will get through the PUMP.

The numbers I gave were by no means exact, merely rough examples in order to illustrate a point.

Now... if the pump were a BATTERY, and the zones were RESISTORS... naaaaahhhh, Xiphias don't want me to go there! Beer 4U2
 
  #16  
Old 08-20-09, 09:38 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Let Siggy do it!

Here's a good article with lots of pictures!

Column - Plumbing and Mechanical
 
  #17  
Old 08-21-09, 02:36 AM
Member
Join Date: Jun 2009
Location: Fairbanks Alaska
Posts: 92
Received 0 Votes on 0 Posts
Aw heck, just when I decided to eliminate the system bypass it comes up again.
 
  #18  
Old 08-21-09, 06:30 AM
rbeck's Avatar
Member
Join Date: Jul 2007
Location: Pennsylvania
Posts: 2,456
Received 2 Votes on 2 Posts
That is not really a system bypass for the function of the system bypass. That is a place for water to flow when some zones are closed. The pressure differential valve opens and closes to balance flow in the system. As zones valves close the PDB valve opens to a degree depending of how many zone valves are open and closed. It moves anytime a zone valve changes position.
 
  #19  
Old 09-16-09, 05:48 PM
Member
Thread Starter
Join Date: Aug 2009
Location: usa
Posts: 6
Received 0 Votes on 0 Posts
Id like to thank everybody for their help here. Got the boiler all plumbed up per weil
mcClains diagram with 2 zone valves. Everything works great. Had acouple issues. inducer had a very loud bearing noise and got one under warranty. Another issue was the three way zone valve. On a cold start up the three way zone valve will remain closed(for DHW priority) and isolate the expansion tank from absorbing system pressure when heating up from cold. I just removed the zone motor to open the valve to let pressure reach the tank. What did I miss here? Plumbed exactly as diagram here

http://www.weilmclain.com/downloads...ilermanual.pdf
EDIT I TOOK A CLOSER LOOK WEIL MCCLAIN CHANGED THEIR DIAGRAM A TEE FITTING IS NOW ADDED ABOVE THE CIRCULATOR WHICH GOES TO THE EXPANSION TANK MY MANUAL INSTRUCTED TO INSTALL TANK ON RETURN LINE BEFORE THE THREE WAY VALVE. Google image cgt 5 boiler and old pics and new pics will come up. Thanks weil McClain.
 
  #20  
Old 09-18-09, 10:13 AM
asm660's Avatar
Member
Join Date: Aug 2009
Location: Punta gorda Fl.
Posts: 62
Received 0 Votes on 0 Posts
Umm just my two cents
A taco 007 Can not pull water or push water through an open or closed system
 
  #21  
Old 09-18-09, 03:24 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 3 Votes on 2 Posts
Originally Posted by asm660 View Post
Umm just my two cents
A taco 007 Can not pull water or push water through an open or closed system
I think you get change back? please explain what you mean...
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: