Heat exchanger for new boiler on legacy open vent system

LordWest · May 19, 2021

Hi,

We are planning to replace a 50-year old boiler for the communal heating-only (no hot water) of a residential block of 12 flats with 60 radiators. We have an open vent system. Our heating engineer recommends the GB162 100KW, WITHOUT a plate heat exchanger, because he says that heat exchangers are unreliable. The specs of the GB162 require a sealed system, and from what I have read separating the two networks is advisable. What advice do you have regarding a plate heat exchanger vs no plate heat exchanger in relation to a legacy open vent system?

Thanks,

Gasmk1 · May 19, 2021

i would separate the systems with plate heat exchanger.

ShaunCorbs · May 20, 2021

Plate the system and keep the old open vent

SJB060685 · May 20, 2021

As above use plate separation. Have the boiler loop on a sealed system and keep the old system open vented. That way you save pressurising the old system which could find leaks and also save the boiler from an almost certainly fouled to a certain degree original heating system.

LordWest · May 20, 2021

Thanks all. How can I ensure that the new plate heat exchanger does not get clogged up? Beside a good magnetic filter, any other reccomendations?

What do you think of the Magnaclean CMX, which can also filter the water with replaceable filters?

Or the spirotech dirt and air separator?

SJB060685 · May 20, 2021

I personally think spirotech are much better products and have a whole host of products for various requirements.
I would install some kind of dirt/air separation on the open vented system as like I said a 50 year old plus system will have a certain amount of fouling in it. The plate will always be at risk of fouling but more often than not if they get clogged they can be flushed through before seeking a complete replacement, not always though.
Again on the boiler side some kind of dirt/air separation but providing that small loop is flushed after install and properly water treated, you shouldn't get any problems.
The boiler side should have an auto top system installed as well.

gmartine · May 20, 2021

For those with a commercial ticket wouldn't you want some built in redundancy, ideally cascade a couple of smaller units not to mention the other advantages of cascading?

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ShaunCorbs · May 20, 2021

A fine strainer filter and regular cleaning or replacement of the gause

LordWest · May 20, 2021

Thanks all.

I agree that 2 boilers would makes sense. But I am dealing with an irrational co-director who would not appreciate this, and need to resolve more pressing issues for now. Though, I will still propose it.

The SpiroTrap Dirt Separator with magnet seems interesting. Has anyone had experience with that for protecting a plate heat exchanger?

Timmy D · May 20, 2021

Plate for sure. Even 2. With 2, one can be removed for cleaning while leaving the system operational.

You either get “disposable” plates and bin it once clogged past it’s cleanable state and renew.

Or a phe with seperatable plates/gaskets which can be disassemble/cleaned/new gaskets/reassembled. This cleaning can take up to a day and is where a second phe is beneficial.

LordWest · May 20, 2021

ok thanks. Other than protecting the boiler, is there any other reason for using a plate echanger as opposed to not using one to separate the network?

Also, how do the waterways of the plate heat exchanger compare to a commercial boiler's waterways, such as the GB162?

Timmy D · May 20, 2021

LordWest said:
ok thanks. Other than protecting the boiler, is there any other reason for using a plate echanger as opposed to not using one to separate the network?

Also, how do the waterways of the plate heat exchanger compare to a commercial boiler's waterways, such as the GB162?

Protecting the boiler is the priority. I can assure you that if you don’t, you’ll need new boilers within 5 years on the system you’ve described.

The 50 year old boiler will have a cast iron heat exchanger that were built like a tank.

They could put up with all the crap in the system. A new boiler won’t handle an old system like that and you’ll never flush it clean enough to do without the plate.

Not long ago I’ve had to remove a 3 year old 65kw boiler for the same reason. It was installed directly (with a magnetic filter) to the old system. 3 years was as long as it lasted!

I got an exterior area roofed and created a boiler room. Downsized the boiler to two smaller ones (redundancy), added a low loss headed, magnetic filters, strainers and plate heat exchangers to ensure the customers investment is protected.

This is the 3rd install I’ve done like his for this customer as he now understands the benefit of spending that extra to prolong the life of his equipment.

Few pics if you’re interested.

SJB060685 · May 20, 2021

Timmy D said:
Protecting the boiler is the priority. I can assure you that if you don’t, you’ll need new boilers within 5 years on the system you’ve described.

The 50 year old boiler will have a cast iron heat exchanger that were built like a tank.

They could put up with all the crap in the system. A new boiler won’t handle an old system like that and you’ll never flush it clean enough to do without the plate.

Not long ago I’ve had to remove a 3 year old 65kw boiler for the same reason. It was installed directly (with a magnetic filter) to the old system. 3 years was as long as it lasted!

I got an exterior area roofed and created a boiler room. Downsized the boiler to two smaller ones (redundancy), added a low loss headed, magnetic filters, strainers and plate heat exchangers to ensure the customers investment is protected.

This is the 3rd install I’ve done like his for this customer as he now understands the benefit of spending that extra to prolong the life of his equipment.

Few pics if you’re interested.

View attachment 61320 View attachment 61318 View attachment 61319 View attachment 61321 View attachment 61322 View attachment 61323 View attachment 61324 View attachment 61325 View attachment 61326

I like the reverse return to llh from boilers 👍

Timmy D · May 20, 2021

SJB060685 said:
I like the reverse return to llh from boilers 👍

Fun making that llh.

SJB060685 · May 20, 2021

Timmy D said:
Fun making that llh.

I know how to calculate the size of a LLH but never tried making one. Would leave to specialists if needed one.

LordWest · May 20, 2021

@Timmy D : That is an impressive piece of work.

Other than redundancy, is there any other benefit from having two boilers (say 50kw) instead of one (100kw)?

SJB060685 · May 20, 2021

LordWest said:
@Timmy D : That is an impressive piece of work.

Other than redundancy, is there any other benefit from having two boilers (say 50kw) instead of one (100kw)?

Obviously redundancy means if one fails there's a back up but with a decent control system the boilers firing can be prioritised or staggered, so the loads are equally shared throughout a season, hopefully prolonging the life of the boilers. Further more if you only need part load, say on a warmer day only one boiler will be firing but in extreme weather two can be called upon.

Timmy D · May 20, 2021

LordWest said:
@Timmy D : That is an impressive piece of work.

Other than redundancy, is there any other benefit from having two boilers (say 50kw) instead of one (100kw)?

Thank you.

I changed career at 33 and did that install after 3.5 years.

There are things I’d do a little different now but as they say, every day’s a learning day.

The install performs as expected and the buildings demand is met.

Redundancy is the primary reason, if one one boiler, could the building cope with no heating/hot water for potentially a few days.

Other concerns could be the flue. Just quoted a job where they wanted 2 x 80kw boilers. This meant more difficult flueing than if we put in 3 x 48kw/64kw.

Also cost, commercial boilers cost more to install/maintain.

Forgetting about gas pipe volume limits, 2 smaller boilers may keep the instal in the domestic range, rather than commercial.

Like I’ve said above it all comes down to the buildings requirement/non requirement for an uninterrupted boiler supply.

One block of studio flats we look after has 1 x 100kw commercial and 2 x 30kw domestics.

Chuck · May 21, 2021

LordWest said:
Other than redundancy, is there any other benefit from having two boilers (say 50kw) instead of one (100kw)?

In addition to the points others have made, you usually get a lower minimum output, which means less short-cycling when demand is low.

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Heat exchanger for new boiler on legacy open vent system

LordWest

Gasmk1

ShaunCorbs

Super Moderator

SJB060685

Plumbers Arms member

LordWest

SJB060685

Plumbers Arms member

gmartine

Enjoying the efficiency benefits of cascade boilers - Modern Building Services

ShaunCorbs

Super Moderator

LordWest

Timmy D

LordWest

Timmy D

SJB060685

Plumbers Arms member

Timmy D

SJB060685

Plumbers Arms member

LordWest

SJB060685

Plumbers Arms member

Timmy D

Chuck

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