compare boiler bypass to primary/secondary piping


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Old 04-26-10, 12:06 PM
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compare boiler bypass to primary/secondary piping

Can some one compare advantages and disadvantages(if there are any)of a boiler bypass to a primary/secondary piping.

Thanks again
 
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Old 04-26-10, 01:49 PM
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Let me start with p/s. The purpose of the closely spaced tees is for what we call hydraulic seperation which basiclly means the flow of one pump does not affect the flow of a second pump.
So you can runs a systyem pump and a boiler at with two different flow rates and they each operate well at their flow rates which again may be different for each pump.
Bypass piping move the amount of water the pump will move and the flow is divided up between the system and the boiler. For examle, if a pump is moving 10 gpm of water. You will have a boiler bypass adjusted maybe to move 5 gpm through the boiler and 5 gpm through the bypass. The system will still get 10 gpm. With a system bypass you have the same 10 gpm through the pump. You have the system bypass adjusted to get 5 gpm flow the boiler will recieve 10 gpm and the system will get 5 gpm. For mor information try these links for bypass piping and p/s.
 
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Old 04-26-10, 04:05 PM
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I think it should be mentioned that it's apples and oranges. Two different things in a sense.

Bypass piping is employed to protect the boiler, I would always choose a BOILER bypass because it won't upset the heat balance in the system, you will always have the proper flow through the heating loops.

With a SYSTEM bypass, you will also be protecting the boiler, but because as rbeck explained, the flow in the system is less, this can lead to uneven heating in the home.

Primary/Secondary piping can protect a boiler also, but only if the flow in the boiler is GREATER than the flow in the system, because in this case, some of the hot supply water will flow back into the boiler, warming the return to the boiler somewhat. It shouldn't be counted on for this purpose though, only that it is possible.
 
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Old 04-27-10, 05:48 AM
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Primary/Secondary piping can protect a boiler also, but only if the flow in the boiler is GREATER than the flow in the system, because in this case, some of the hot supply water will flow back into the boiler, warming the return to the boiler somewhat. It shouldn't be counted on for this purpose though, only that it is possible.
Good point Trooper.
In this case normally it would be a zoned system or an over sized boiler. This is where even mod/cons can short cycle as the boiler flow will be more than what the system requires. The return is preheated forcing us into modulation. As good as that sounds the problem with over sized equipment or micro-zoning is the minimum turn-down is not low enough.
 
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Old 04-27-10, 07:28 AM
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OK guys, I have another 2 questions then.

1. Can I save money on gas if I pipe with a boiler bypass and how.


2. The 7 zones on my current system are on a 2" manifold.

The new boiler(actually used) has a 1 1/2" supply and return.

Should I downsize from 2" right at the boiler connection so that only the boiler is 1 1/2" or should I downsize to include the bypass line? The question here is should the boiler pipe size and bypass pipe size be the same? Does it make a difference?


Thanks guys
 
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Old 04-27-10, 09:19 AM
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A boiler bypass should always be full size. Don't forget to put a valve on the boiler side of the bypass. That is the valve you adjust to get the proper delta-T. The bypass if there is a valve in it is always 100% wide open during operation. Pipe size is dependent on boiler size. Although usually not needed most boilers get piped with 1-1/4" pipe. If the required flow is above 7 gpm use 1-1/4" pipe or just use 1-1/4" because that is what most others do. If the boiler is over 160,000 use 1-1/2" pipe unless you are doing p/s which the boiler can be designed at a higher delta-T. With a large CI radiator system I would probably shoot for a higher delta-T like maybe around 40 or even higher depending how much connected load you have as compared to the boiler size/Heat Loss.
You can down size at the manifold.
 
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Old 04-27-10, 10:13 AM
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I was thinking of putting unions and valves on both supply and return before the bypass(after the boiler). The boiler is a 5 year old 300,000btu Buderus. My concern is that being that the system is 2" and the boiler is 1 1/2", the water would flow easier through the 2" bypass and it would take longer to heat my house.

That said, I should come out of the boiler with a
1 1/2" x 12" nipple followed by a reducing elbow 1 1/2" x 2" to get to 2". Then use a 2" ball valve followed by a 2" tee for the bypass tee. Does this sound correct?

Does the distance required before and after the tee make a difference as in the p/s piping?


Originally Posted by rbeck View Post
A boiler bypass should always be full size.
Full size to the boiler or system?
 
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Old 04-27-10, 12:03 PM
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300,000 btu boiler....wow. You have a monster of a home. Your home must between 9 and 10k sq ft? My fear here is that you got a good deal on a used boiler and did not pay attention to the heat loss or worst yet did not do a heat loss. If not this is going to cost you a fortune to operate. The more oversized the boiler is the higher the fuel bill is going to be not to mention increased maintenance costs.
If this is indeed the proper size you need a 2" bypass and 2" piping. The boiler side will work at 1-1/2" as you want a greater delta-T anyway. 1-1/2" pipe is good for about 25 gpm. The system is about a 30 gpm flow.
I would consider 1-1/2" valves before you go to 2" piping as the price changes considerably above 1-1/2". The bypass should be the sized for the maximum flow or 30 gpm in this case.
With a system this size I may rethink what I would do here. Are you using zone valves or pumps for your zones? A total of how many zones? What is the approximate sq footage of the home? What type of radiation do you have?
 
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Old 04-27-10, 01:08 PM
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Yes, monster home but also good a steal on a g334x/72.
Good boiler because it has 2 gas valves and it can be staged so its like having 2 boilers as far as fuel consumption goes.
I did a heat loss about a year ago and found that I needed a boiler a little bigger than the 20 plus year old 300,000 btu Weil Mclean or multiple boilers staged. I cant afford a new or multiple boilers right now so this has got to do. at some point I need to buy a controller that will stage the boiler. The Buderus controller stages but doesnt stage randomly so that both sides get even burn wear. Maybe start looking around for a good controller.

After reading your last comment, I think I may install 2" x 1 1/2" reducing couplings right ouside the boiler and go right to 2" from there, valves and all.

The house is about 10,000 feet. There are large areas that get heated only once or twice a year, if that. The boiler has 7 or 8 zones. One of the zones is radiant heat. I don't know if I'll ever use the radiant heat because I have 2 huge cast iron radiators that heat that area just fine.

Also, should the fittings/tees etc. be malleable or cast iron?


Originally Posted by rbeck View Post
300,000 btu boiler....wow. You have a monster of a home. Your home must between 9 and 10k sq ft? My fear here is that you got a good deal on a used boiler and did not pay attention to the heat loss or worst yet did not do a heat loss. If not this is going to cost you a fortune to operate. The more oversized the boiler is the higher the fuel bill is going to be not to mention increased maintenance costs.
If this is indeed the proper size you need a 2" bypass and 2" piping. The boiler side will work at 1-1/2" as you want a greater delta-T anyway. 1-1/2" pipe is good for about 25 gpm. The system is about a 30 gpm flow.
I would consider 1-1/2" valves before you go to 2" piping as the price changes considerably above 1-1/2". The bypass should be the sized for the maximum flow or 30 gpm in this case.
With a system this size I may rethink what I would do here. Are you using zone valves or pumps for your zones? A total of how many zones? What is the approximate sq footage of the home? What type of radiation do you have?
 
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Old 04-27-10, 07:24 PM
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I would use malleable fittings. Good luck in this endeavor.
 
 

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