Primary/Secondary piping and boiler preperation

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Old 10-30-08, 04:44 AM
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Primary/Secondary piping and boiler preperation

Hi,

I am new to this and need some help piping (re-piping) and working on an 80 year old system..

I started doing some work on my 6500sf house that includes 2 boilers/seperate systems, a 300,000 btu gas/hot water and a 150,000 oil/steam boiler and figured this would be a good time to split up the one zone hot water system into 6 zones and also get rid of the 150,000 btu steam system and keep only the radiators that I would convert into 2 zones.
I added an extension to the house for a new kitchen to replace an older kitchen that was not proportionate to the rest of the house. I built the kitchen with tubing in the floor slab for radiant heat.
I did a heat loss and come up with 300,000 btu for the whole house, they realy did oversize in the past.
I figured to do the piping now and replace the boiler at some later time with either multiple staged boilers or even maybe a condensing or multiple condensing boilers. At this time I am not sure of the boilers including make/model/manufacturer so all I want to do is the piping and preperation so that when I am ready all I will be doing is disconnecting the existing boiler and installing the new boiler(s).
While looking for primary/secondary piping schematics I ran into this site and saw something here http://i202.photobucket.com/albums/a...s/bolier08.jpg similar to what I envisioned with some minor differances. Here are some questions that came up with for starters.

1. Is it correct/proper to connect the expansion tank on the return side? Is this something a manufacturer would have different ideas on or object to?
2. What size should the expansion tank be, how do I size it? Guestimates would be appreciated here guys.
3. What is the outcome of an undersized and/or oversized expansion tank?
4. What size pipe should the primary pipe/manifold be for a 300,000 btu system?


Also on figure http://i202.photobucket.com/albums/a...s/bolier21.jpg, I noticed only 1 drain valve on the return side before a ball valve, is this common to save on material instead of doing the one drain valve on each zone? Does this affect the filling of water or removing of air from any one zone?

Also, the current 300,000btu boiler has 3 large 20+ gallon tanks that are connected to the boiler with a 3/4" pipe. These are probably expansion tanks because there is no other sign of any expansion tank on the system, are these neccessary.

Any help/advice is appreciated.
 
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Old 11-25-08, 11:05 AM
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Hi To answer some of your questions; 1. I have always seen the expansion tank on the supply side do to it having the air scoop/vent attached at the top, witch would remove the air prier to suppling the loops. 2. The sizing of a expanision tank is the same for some heating systems. The out put of the boiler isn't as important as the "temps" being reached and the amount of water in the whole system. 3. No problem with an oversized exp. tank and an under sized tank would do "the job" partly. Removing excess pressure from expanding water do to heat expantion. 4. Depends on the size pipes going to each zone. I would think an 1 1/2 to 2" pipe would handle most large systems. Also, the more drains (one for each loop)and valves the better for servicing. Important...In both schematics, they don't show any air vents but the one on the mail return line. It would help alot if you would have one auto vent on each loop at its highest spot of the loop on the floor that it's heating. Hope that helps some. Sorry for any porr spelling, it's not my "strong point". Beer 4U2
 
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Old 11-25-08, 07:09 PM
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1. The 'proper' place for the expansion tank is upstream of the circulator so that you pump away from the tank (or, the 'point of no pressure change') (the Bell & Gossett website has some excellent literature that explains all of this in great detail)

The drawings you cited would be correct, because both pumps are pumping AWAY from the point at which the tank connects to the system.

2. Your expansion tank has to be large enough to accept the expanded water. Yes, size by WATER VOLUME, and TEMPERATURE EXTREMES. The manufacturers websites have calculators for the purpose. However, you will have to do some work in estimating the volume of water in your system. When you drain the system to do the work would be a good time to verify your estimates. Drain into a 5 gallon pail ... count the pails full ... to estimate, you need to measure up the piping, then a bunch of multiplication from the numbers found on charts found on internet that tell you how much a pipe holds. When you know how much water, use the manf sizing calculators.

As an example, if your system had 100 gall of water at 70, when you heat to 180 you would have almost 104 gall. Your tank would need to be able to accept that 4 gallons without substantial pressure increase on the system.

I'm guessing your tank is going to end up being the '90' size... or perhaps two 60s ... the three tanks you mentioned, are they in the ceiling joists above the boiler ?

3. An undersized tank will be a problem. You will have large pressure swings on the boiler from cold to hot. You will most likely open the relief valve, venting the excess pressure all over the floor. Nothing worse than a boiling hot hydrogen dioxide spill.

Oversized won't hurt anything except your wallet, and your floorspace. The more tank you have, the less pressure swing.

4. Inch and a half is good for maybe 250 MBH ... that's probably 'pushing it' a bit ... Two inch figure on 450 MBH ... so the piping that is common to ALL zones is going to be 2".

3/4 - 40 MBH
1 - 75
1-1/4 - 140

You should check out this link ... there's all kinda tables and stuff of all this info ...

Tech index at Comfort-Calc.net

to save on material instead of doing the one drain valve on each zone?
Sure! Why not ? Great idea...

Saves three valves... and moving the hose all over the place... just hook up the hose and select the zone you want to purge. Schweet ...
 
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Old 11-25-08, 09:06 PM
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the three tanks you mentioned, are they in the ceiling joists above the boiler ?
Yes.

Sure! Why not ? Great idea...
Saves three valves... and moving the hose all over the place... just hook up the hose and select the zone you want to purge. Schweet ...
Three? How about close to 10 zones so 9 valves is what you save and the fittings. Or you can use the location where the valves would have went to temp gauges to monitor return temperature on every zone.


When using the 1 drain system, do you need to close the other zones when purging a zone?


Also...Being that the expansion tank is located on the return side connected to the air scoop is it OK to add another air separator of some sort somewhere else on the system or even multiple air separators?
 

Last edited by zizanio; 11-25-08 at 09:25 PM.
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Old 03-10-09, 04:28 PM
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wondering

i'm wondering about having the primary loop to a secondary loop take offs to the radiators, i read that it should be supply tee then second return tee is 4x the diameter away which at 1.5 size pipe would be 6" right but this is my question

i was told to put all my supplies at the top of my header then all my returns at the bottom, so this type of configuration would not work, how would i line up all the supplies then the returns????

I'm building a black pipe system p/s system from an old gravity system that was partially torn apart, new black pipe cause copper is still over priced

thank you.
 
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Old 03-10-09, 05:25 PM
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I would not use a loop unless you have many different water temperature loops. I would do it this way if most loops require the same water temps.
http://www.comfort-calc.net/primary-..._tutorial.html

Pipe sizes are as follows
http://www.comfort-calc.net/pictures/Piping_chart.JPG

Multiple boilers
Multiple_boiler Installation
Also do not use auto vents at the high points of the system and return side of the circulator. They can suck air as well as vent. Remember the higher you go the lower the pressure is. You lose 1 psi per every 2.31 ft or 28".
 
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Old 03-11-09, 03:24 AM
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I guess i'm looking at doing it like in diagram 4 on that site where I can use all my returns on one side and supplies on the other, I'm really kind of confused on how to build my piping
 
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Old 03-14-09, 02:58 PM
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trying this out







thought I'd throw some fittings together but i have some questions about distance as you can see in my photos the tee in the bottom left how that will be my supply and the tee next to it will be the return, do you recommend more spacing say the 12" minimum distance and please critique my plumbing and tell me what i should change?

i am planning on changing to shorter nipples at 1.25 under the ball valves also

my main secondary and primary pipe is 1.50 inches and the branches are 1.25 all throughout the house except for a couple of small copper lines fed off the main branches

thank you
 
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Old 03-14-09, 10:41 PM
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That won't work right... both tees need to be in the same orientation... and there needs to be straight pipe ahead and after the tees... like this:

http://www.comfort-calc.net/pictures...r_P-S_Tees.JPG
 
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Old 03-15-09, 06:14 AM
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Okay I thought i'd just save space but i'll reconfigure the pipe and repost

It should be fine if i were to slope the return tee's to feed from behind the supplies?

and would it be still good if i were to still install the cushion tank just after the supply from the boiler on the secondary loop or should i install it on the primary up with all the valves?

thank you
 
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Old 03-15-09, 07:07 AM
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Are the P/S tee spacings that critical for a single CST P/S system? The tee's are more critical when using multiple P/S CSTs for multiple heat loops to provide hydronic isolation; but for a single set of CSTS does it make any difference? Just asking.. ?

Pete
 
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Old 03-15-09, 08:31 AM
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Probably not Pete, but the way that one is set up now, that circ pump being in line with the flow will upset the flow.

Nowisn, what pipe size is going to your heating loops? Do you really need to come off the manifolds with that size pipe? At some point you are probably going to have to reduce the pipe size... the sooner you do that, the cheaper the whole installation becomes. Just the price difference between 3/4" and 1-1/4" ball valves is pretty significant.

Your zones are going to be pumped with circulators, correct?
 
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Old 03-15-09, 08:52 AM
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the piping is throughout the house is a two pipe gravity system which all 1 inch and a quarter, I'm converting by adding a p/s loop which is secondary through the boiler and the primary which is the feed to the house.

the secondary loop is the same size as the boiler ports which are 1 inch and a half then i'm downsizing to match the braches which are 1 and a quarter
 
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Old 03-15-09, 11:37 AM
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How are you going to circulate the zones? Individual pumps?

Something about the pump mounting has got me bugged... I seem to recall Grundfos not wanting the electric box on the bottom... but I could be wrong... check the install sheet for the pump.

You're not using a decent air separator?

Where/how are you mounting the tank?

Consider:

 
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Old 03-15-09, 12:37 PM
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Sure looks like the tees for the boiler secondary loop are more than 5" apart from the centerline of the branches.
No air separators and if not using zone valves the circulator is not required where you have it. The circ in the primary pipe is only required with the use of zone valves.
I would also have the ball valves on the supply side above all the zone valves, circ's and everything else for ease of service. Also add a drain on for servicing on the primary pipe. You air vent is not going to be as efficienct as it would be on an air seperator as the seperator will cause agitation to seperate the air from the water as the water slows down in the seperatore. The water slows due to a larger space than the pipe has. Better air seperation.
 
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Old 03-15-09, 12:42 PM
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I haven't actually decided on putting the tank in the primary or seconary boiler loop but then I decided to put an air scoop with a vent and the tank below off the left hand side of the boiler supply line, I'd go with a spiral vent but there like 200 bucks here and not worth it

the pump does concern me as well but not to many options on placement except for removing the union and placing the pump vertically

And the electrical box can be moved on that pump, manufactures don't like putting the eletrical connections on the bottom due to leaky water making its way in

maybe someone could suggest a different piping config

Oh i was going to zone it off indiviually but not now, thats why you see the unions there for future concideration and the ends of those primary supply and return lines will be just capped with temp stata on them at the end of there lines

there will be some additional nipples and tees with drain coks for each branch as i ran out of stuff and this is only a mockup, its just screwed together
 
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Old 03-15-09, 12:49 PM
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You want the larger water volume to go through the air separator to get rid of more air.
It should be in the primary just behind the circulator and the tank will connect to it.
Fig 4 is showing zone valves. The primary pipe does not have to be straight but everything in the proper order.
http://www.comfort-calc.net/primary-..._tutorial.html
 
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Old 03-15-09, 01:51 PM
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in that diagram 4 does the circ pump have to be before the return

I have my pump just before all the supply tees, It is like the diagram kind of but the pump is after the supply and return from the boiler.

I can make room for a separator if I can find a supplier who has any
 
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Old 03-16-09, 08:01 AM
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does the circ pump have to be before the boiler s/r tees or behind them or does it matter???
 
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Old 03-16-09, 12:02 PM
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Does not make a lot of difference. We still have not determined if you are using zone valves or circ's for the zones. Are you installing an indirect water heater?
 
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Old 03-16-09, 12:09 PM
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there are no zone circs and all the supplies are in one row and returns in the other, i'm using ball valves to balance my flow,
i'm piping it like in calcs site diagram 4
 
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