reverse return

jalcoplumb_7

This is a nice way to do a two boiler install. Need the proper controls.

Does it also serve an indirect for domestic hot water?

I would use a Tekmar 264 for a control.

Keith_8

reverse return

(2) HB Smith 28A-10 boilers in a school we service. The facility mamanger mentioned he was bringing an engineer in to address a flow imbalance between the 2 boilers. Seems that one boiler performs most of the work.

When I looked at it the 1st thing that I noticed is that the 1st boiler supplying the system was the 1st boiler getting the return back from the system.

Am I missing something or will changing this to reverse return solve the flow issue? Should I add balancing valves or do you think it's unnecessary?

The school is only about 3 years old. Is it possible that no one else thought of this before?


Keith

jalcoplumb_7

Two boilers.

This is a nice way to pipe the two boilers. With the proper control you can stage them and get equal run times.

Do the boilers also make domestic hot water?

I like to use a Tekmar 264 control.

Steamhead (in transit)

I agree

primary-secondary piping is the way to go here.

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Keith_8

Agreed

> This is a nice way to pipe the two boilers. With

> the proper control you can stage them and get

> equal run times.

>

> Do the boilers also make

> domestic hot water?

>

> I like to use a Tekmar

> 264 control.



I agree that primary secondary piping would be the prefered method. However that would require a major retrofit, boiler pumps and to be honest the boiler room is not condusive to much of anything. It's a 2nd floor mechanical room in the middle of the school with not much room to work.

In this case the customer is simply concerned about allowing the boilers to see similiar flow rates. That being said, in your opinion would the reverse return accomplish the goal?

As far as the boiler staging controls. In theory it is being staged and monitored by JCI and low- high-low burner controls. We will take a look at the history and verify that.

At another school we installed similiar boilers. 18 months later we got a call that one of the boilers was leaking. The cause of the leak was thermal stress on the 1st rear intermediate section. Upon further investigation it was determined that the controls company (not JCI) at times on a set back was allowing 60* water to enter a boiler that was trying to maintain 180*. Futher more the boiler was cycling 14 to 16 times an hour.

I don't think the design engineers ever realized the original school had a underfloor radiant system.
We are making the corrections this summer.

Keith

jalcoplumb_7

Piping.

Without knowing how the boilers are piped to the system I could not give a good answer.

Did they always have this problem? How old are the boilers? Could be a lot of things.

If it is piped in like the attached picture, then I would say yes the reverse return should help. But without knowing or seeing the system that is all I could say.

Good luck.

Al Letellier_9

reverse return.

Have installed many multiple boiler set ups with reverse return with no problems. As you mentioned, the first boiler feeding should be the last getting the water back. We did this long before P/S set ups and circuit setters were popular and more affordable (I've been around a while)./ Properly piped, reverse return will give good balanced flow thru the boilers but the only way to make certain is to install some circuit setters....they don't lie. Repipe your return and add a couple of circuit setters and you'll be OK. I agree that P/S is better, but sometimes in the real world it's just impractical to do.

hr

how will you protect against low return

temperatures without a P/S piping? You need a means to monitor and react to the possible low return temperatures. P/S can easily do that AND assure proper flow through either or both boilers.

hot rod

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hr

Or a hydro separator

would be another way to assure each boiler got the correct flow, and be separated from the system hydraulics.

A tekmar staging control could stage, protect, rotate, exercise the pair of boilers.

hot rod

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Keith_8

piping diagram

Yes, except for the fact that the base mounted pumps are on the supply and not the return side of the system the diagram you posted is accurate.

Al's suggestion of Circuit Setters is a fair compromise.

Hot Rod's point of protecting against thermal shock without P/S is fair. I'll call the facility people and have them look at the history and see if it's been a problem.

As usuall, The Wall is a great gut check.

Thanks guy's.

Keith