How would you fix this system?

Mike_Sheppard

I’d like to see what you guys would come up with for a solution to this system. Obviously the piping layout needs to be changed. But keeping the two boilers and the control, what is the best way you can come up with to make this work?

Drew this up EXACTLY as the system is piped now. System is over 10 years old. When I told them the entire thing was piped wrong they said “this system has been like this for a long time and no one has ever said it was wrong before.”

Details:
- Supply water cannot go above 160 or PVC in the building starts to leak. Every fan coil unit is piped in PVC.

- If the system sensor is on the supply side the boilers short cycle. Boilers come on, supply temp rises, boilers shut off.

- On cold days, if they don’t get 150 degree supply water the building doesn’t heat enough.

Have fun fixing this one......

Mike_Sheppard

Edit: ignore that I wrote diverting valve on that 3-way. Brain fart.

What do you guys think of this? Buffer tank is to stop the copper HX boilers from short cycling. The system 3-way is to better control the system temp. The thermostatic 3-ways at the heaters are made by the manufacturer (Lochinvar) to protect them from low return water. The Tekmar can be re-purposed to stage the two boilers on and off. A T775R can be used to modulate the 3-way system valve with outdoor reset.

EBEBRATT-Ed

a 4" 3 way mixing butterfly valve with a 0-10 volt or 4-20ma signal. You can drive the valve with a Johnson A350P (their cheap). Pipe the common port to the suction of the system pump. The inlet port gets piped to the supply water coming from the boilers. Bypass port get piped to a tee in the system return upstream of the boilers. Put the sensor to drive the valve in the supply to the building set at 150

The valve will limit the supply temp to the building. The valve will mix cooler return water in with the supply to control the building supply temp.

I would move the Tekmar sensor to the common boiler supply between the last boiler and the three way valve st at 150.

Control of the building loop will work fine. The boilers and teckmar operation will depending on load v boiler size. Any two stage or modulation on boilers?

Mike_Sheppard

No, both are on/off.

That’s why I incorporated the buffer tank. Without it there’s no way to stop the boilers from excessively short cycling.

clammy

How about proper piping of the two boiler so they both see the same return temps .i think I would only use 1 set of tee to tie into the primary loop and would make them 4 then reduce to 21/2 to each boiler . I would reverse return the boiler piping move the spriovent n expansion tank to the suction side of the pump . I put the tekmar sensor on the system supply . Just wondering how much 4 copper is there I ve used hi temp loop over a distance to feed a lower temp need work well and solved the issue you have a fun one there no doubt you will be getting it working peace and good luck clammy

Mike_Sheppard

@clammy they’re low mass boilers, the tekmar sensor can’t go on the supply. They’re also on off boilers, so one boiler fires and the system is running at half capacity.

One boiler fires, and the supply temp rises about 10 degrees in 30 seconds... putting the sensor on the supply would cause them to short cycle like crazy.

I don’t see any other way to correctly control the building supply temp other than how I drew it with the buffer tank and 3-way.

Steamhead

Mike, are you sure you really want this job? With that PVC pipe, I'd wonder what else the installers did wrong.

Mike_Sheppard

@Steamhead no I am not. I probably don’t want this job.

To be fair, they didn’t even believe me when I told them it was wrong. But if they’re going to call us monthly to come change settings to stop the high limits on the boilers from tripping.

As you can tell from the piping, boiler 2 sees higher temps than boiler 1. They keep setting the high limits at 160 because they’re trying to protect the system, but then they to run it at 150 and it trips their 160 high limits.

I wanted to at least show them how to fix it.

STEVEusaPA

If your first picture is correct, the boiler on the left has the circulator on the wrong side.

GroundUp

Well first of all boiler 1 is piped into the main backwards per the drawing, and secondly they should be piped into a sub-main like Lochinvar shows in their manual with a single pair of tees in the main to avoid boiler 2 catching the hotter water from boiler 1

Mike_Sheppard

@STEVEusaPA
@GroundUp

The first picture is indeed drawn exactly how it is currently piped.

Photo attached.

Gordy

Does the manufacturer I/O manual of the installed boilers have their method of piping for staged boilers. Are they staged even?

If they do, and you go through with this I would use their drawing. Both as reinforcement as to it being piped wrong, and the end result as it piped per manufacturer recommendations.

Mike_Sheppard

@Gordy yes, it does. It shows how to pipe them primary secondary (as I’ve drawn them) but they want them “first in last out” on the common manifold which I did not draw in on my picture.

The manual does not tell how to incorporate them into the system though. But I believe it is common knowledge that a low mass non-condensing on/off boiler needs some form of buffer to stop from short cycling.

Lochinvar does have a buffer tank application manual though that goes into more detail why a buffer tank is needed with low mass boilers like these.

Solid_Fuel_Man

Puke!

What kind of PVC? Corzan as in CPVC at least?

Where does it leak? I was involved on a job with 3 big Viessmanns with 3" copper in boiler room and CPVC there on out. The CPVC female adapters leaked where threaded over the male copper adapters. Went the other way around with the CPVC threaded into copper female adapters and it was better. That system was designed for 140 degree water though.

What about oxygen barrier? Is the entire system nonferrous? Doesn't look like it by those iron 3-piece B&G boiler pumps.

Can you add emitter or oversize to keep temps lower? Get rid of at least one of those inefficient chimney heaters and put in a modulating boiler and keep the chimney heater for backup if they won't spring for two new boilers. May be cheaper than a buffer tank and a 3" mixing valve with controls.

Although your buffer drawing looks good if you keep those boilers.

EBEBRATT-Ed

Weather the piping is right or wrong is secondary to me nothing will work without a 3 way. If the system has enough mass you shouldn't need a buffer tank......but with no modulation your probably forced into it.

We have a building that was done 15 years ago. All PVC and this is just a boiler/tower/heat pump system and the water is only around 100 deg. It sucks. I don't know how many times the building has flooded. Could have piped it in gold plated brass for what they have spent fixing leaks, flooding, damaged carpeting, computers.

The best part is the "Engineer" that designed it still has his offices in the building...they own the building.

Insert @Steamhead 's saying.............

hot_rod

Could I interest you in a two pipe buffer

1- when boiler(s) and load operate at the same time only the gpm difference goes into and thru the tank ex. 20 gpm boiler, 15 gpm load, 5 thru the tank, low flow velocity doesn't disturb stratification.

2- All or some of the boiler flow can go directly to the load. So if the tank is cooler than the boiler output, you do not need to warm the tank, boiler goes directly to load. As load satisfies, or slows buffer gets charged.

2 port tanks are generally less $$ and easy to source. A typical large DHW storage tank has ports like this, If it has a large top port, air elimination could be positioned there, although a dirt/air/ mag sep might be a good addition.

Mike_Sheppard

> @EBEBRATT-Ed said:
> Weather the piping is right or wrong is secondary to me nothing will work without a 3 way. If the system has enough mass you shouldn't need a buffer tank......but with no modulation your probably forced into it.
>
> We have a building that was done 15 years ago. All PVC and this is just a boiler/tower/heat pump system and the water is only around 100 deg. It sucks. I don't know how many times the building has flooded. Could have piped it in gold plated brass for what they have spent fixing leaks, flooding, damaged carpeting, computers.
>
> The best part is the "Engineer" that designed it still has his offices in the building...they own the building.
>
> Insert @Steamhead 's saying.............

I agree. I’m sure the system does have enough mass. The problem is that they are low mass boilers and the system is sensitive to supply temp. It is really hard, I’m going to say impossible, to maintain a steady supply temp with two 750k btu on/off low mass boilers in any kind of system without the use of the 3-way valve. But after adding the 3-way valve we have created the problem of a low water volume boiler loop. I have seen this issue many times when people try to use a 3-way on on/off low mass boilers, it just doesn’t work without a buffer tank. Thus, I can’t think of any other way to make these two boilers work in this system without the addition of a 3-way and a buffer tank.

Mike_Sheppard

> @Solid_Fuel_Man said:
> Puke!
>
> What kind of PVC? Corzan as in CPVC at least?
>
> Where does it leak? I was involved on a job with 3 big Viessmanns with 3" copper in boiler room and CPVC there on out. The CPVC female adapters leaked where threaded over the male copper adapters. Went the other way around with the CPVC threaded into copper female adapters and it was better. That system was designed for 140 degree water though.
>
> What about oxygen barrier? Is the entire system nonferrous? Doesn't look like it by those iron 3-piece B&G boiler pumps.
>
> Can you add emitter or oversize to keep temps lower? Get rid of at least one of those inefficient chimney heaters and put in a modulating boiler and keep the chimney heater for backup if they won't spring for two new boilers. May be cheaper than a buffer tank and a 3" mixing valve with controls.
>
> Although your buffer drawing looks good if you keep those boilers.

He did say it is CPVC. He said above 160 they start getting leaks all over the building. I didn’t inquire as to where specifically.

I’d love to change out the boilers. That is an option if they will understand this and consider it.

Mike_Sheppard

> @hot rod_7 said:
> Could I interest you in a two pipe buffer
>
> 1- when boiler(s) and load operate at the same time only the gpm difference goes into and thru the tank ex. 20 gpm boiler, 15 gpm load, 5 thru the tank, low flow velocity doesn't disturb stratification.
>
> 2- All or some of the boiler flow can go directly to the load. So if the tank is cooler than the boiler output, you do not need to warm the tank, boiler goes directly to load. As load satisfies, or slows buffer gets charged.
>
> 2 port tanks are generally less $$ and easy to source. A typical large DHW storage tank has ports like this, If it has a large top port, air elimination could be positioned there, although a dirt/air/ mag sep might be a good addition.

I am going to need a minute to think this one over. I’ve never seen it like this before.

Tell me if I’m understanding this. When the system doesn’t need as much heat, the 3-way is throttling and re-circulating most of the water back through the building. Meaning the flow would be reduced from the tank. At that time the boilers would have a chance to heat up the tank because they would be flowing more water. That was a terrible description but I think I got it lol.

I’m going to have to look into this one.

Would it be hard to find a tank like this with 4 inch connections?

clammy

I hear what ur say but with the tekmar on the return u will always over shoot. Seems either u don’t have enough flow through the system to get rid of the heat and or enough flow through boiler to let them run . I still see 5e need to tie the boilers into one set of tee w reverse return so they see the same return temp the way the boiler are pied into the system is wrong n only one boiler see s the work I hope that a 2 stage control if not forget bout Personally I feel they lived w it that long they are never going to spend a penny untill one will touch or repair due to it stupid penny pinching design I have seen pvc being used in office commercial building n they would cry there river n I would say oh well if you would have done it right u would be goi g through this crap All to save on piping . I hope they have some strainers on the system Has those water tube heat exchangers pass been check seen one cvpvc system clogged w plastic due to a crappy flush those saw dust plastic can make u crazy Cutting pvc tends to make lots of chips and the pipes static charge keeps it in place some thing to think bout the leaks most likely come from poorly supported pipe n pvc male adp to steel or brass usually at threads and the expansion on heated plastic does grow .i usually run from those places especially if it been going on for years easy way to tell is look at equipment and see ho many companies have been there Peace and good luck clammy

clammy

Here’s a trick if u want buffer gallons make primary loop of larger pipe and ps ur secondary off of it have ur air elimator make and expansion off it strap up ur sensor on the loop . Hang all up in the ceiling I used this on a oversized Lars that tripped hi limits so they raised them even higher in a attemp to stop the short cycling and limit lockouts didn’t work . We repiped it and add a large primary loop ps the boiler and secondaryocf it and all was good peace and good luck clammy

hot_rod

Copper tube boilers like that present a unique challenge when it comes to cycling. Some had 2 stage or modulating gas valves which would help short cycling. And regardless of what the manufacturers said in the past, they are not comfortable with low return temperature. You are wise to consider both return protection and some buffer, especially if the building is zones a lot.

Taco, Wessel, Lochinvar, State, really any of the tank manufacturers have large pipe size buffers available. Taco had a unique one in their booth at AHR, a bit higher tech than these Taco examples.

You can chose insulation types also, jacketed or non jacketed with spray insulation for example.

Tanks over 119 gallon capacity doe get $$, especially if ASME is required.

Lot of wood burners re-purpose LP tanks, if you want to be resourceful.

Mike_Sheppard

Thanks @hot rod_7

I will look into this. If they want to keep these boilers (they will) then I don’t see any other way to accomplish what they want to accomplish without the addition of the 3-way and buffer.

In reality though they will decided to do nothing and keep calling people to “fix” the high limits while complaining that they can’t get 150 degree water without ever passing 160..

mikeg2015

This is just like a boiler protection loop in reverse. You need a primary/secondary system to ensure loop water temp never exceeds 160F regardless of the boiler loop. Boiler loop, with buffer, can cycle between 150-180F to prevent short cycling.

hot_rod

Doesn't it always come down to how much they want to spend to make it as good as it can be.

With non-con boilers you could run a wide delta in the tank and really leverage some buff-ability.

if you know the load of the various zones you could run a simulation to show the owner how it could be improved.

The HDS program is nice for that

Mike_Sheppard

@hot rod_7 I am going to buy that program. I just bought Hydrosketch. I would have bought that one instead if I had known about it. Still going to buy it.