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Is a pool heat exchanger suitable for a communal heating system?

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LordWest

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Hello all and Merry Christmas,

We are in the process of planning the replacement of our 50-year old heating boiler serving a residential block of 12 flats with a total of 60 radiators. It is a vented single-pipe heating system, which has not been properly maintained, and we only recently installed a commercial magnetic filter to filter out as much sludge as we can prior to the replacement. We will be installing a 100kw boiler. I know that we could also install two 50kw boilers, but this is a matter for a different post. A heat exchanger will protect the new boiler from the old vented system. Our installer suggested that we use the following pool heat exchanger, because it has 2 inch connections matching our 2 inch pipes and also has larger waterways so that it does not get clogged.

POOL HEAT EXCHANGER NORDIC B300 88KW (300KBTU/H)
Pool Heat Exchanger NORDIC B300 88kW (300kBTU/h) - https://nordictec-store.com/b-line-pool-heat-exchangers/171-pool-heat-exchanger-nordic-b300-88kw-300kbtuh.html

How suitable is this pool heat exchanger for our purposes? I am concerned that it may not be as efficient as a normal heat exchanger. Also, the suggested heat exchanger is 88kw, yet the new boiler will be 100kW.

I can order a normal heat exchanger with 2 inch connectors and to address the clogging issue I could use a CMX inline filter like this one here from Addey: MagnaClean CMX® | ADEY - https://www.adey.com/product/magnaclean-cmx The medium and large models can also be used inline.

I would appreciate your feedback.

Below is information for the pool heat exchanger:

POOL HEAT EXCHANGER NORDIC B300 88KW (300KBTU/H): €319.99 VAT included
Pool&Spa Heat Exchanger B300
Nordic Tec B-Serie
Nominal Capacity: 88kW
based on 60 °C difference between heating and heated medium (water to water),
with counter-courent work

Material: Stainless steel 316L
Heat Exchange surface: 0.64 m²
Connections: 2x 2" & 2x 1 1/2"
Important Note: If one of media is glicol, the capacity will be only 85-90% of nominal one
Pool&Spa Heat Exchanger B300

Nordic Tec B-Serie
Technical Details:
Nominal value 88kW (power/capacity) is based on 60 °C difference
between heating water and pool water (calculations are different for other media).
If there is other temperature difference, the capacity is following:
60 °C = 100%
50 °C = 85%
40 °C = 70%
30 °C = 55%
The nominal flowrates values are also required to achieve the declared capacity.

Nominal flowrates: 42/325 l/min (one of opportunities)

nordictec-store.com

Pool Heat Exchanger NORDIC Tec B300 88kW ( 300 kBTU/h )

Swimming pool heat exchanger B300 90 kW- full catalogue of pool heat exchangers by Nordic Tec with quick delivery in every European country.
nordictec-store.com nordictec-store.com
 
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Plates don’t like dirty system so you might need a cleanable one with individual plates this won’t be cheap
 
Good for metal particles but not good for everything else
 
That’s perfect strange adey don’t spec it on there website
 
It is listed on their website under "Commercial and Industrial:

Commercial | ADEY

ADEY Solutions delivers central heating system protection and maintenance for plumbers using MagnaClean magnetic filter technology removes black iron oxide from new and existing domestic and commercial central heating systems
www.adey.com www.adey.com
 
LordWest said:
It is listed on their website under "Commercial and Industrial:

Commercial | ADEY

ADEY Solutions delivers central heating system protection and maintenance for plumbers using MagnaClean magnetic filter technology removes black iron oxide from new and existing domestic and commercial central heating systems
www.adey.com www.adey.com
Click to expand...

Sorry I mean the filter part it’s in the manual but you would of thought it’s a selling point
 
Speak to UK Exchanges Ltd, they can make plates for any output/connections you need. They have a large selection off the shelf.

If you call them, they will also spec the required plate for your supply/demand.

I’ve used them a few times. Reasonably priced, great service.

I know you said the design is for another post, but I’d seriously be considering 2 boilers and a low loss header instead of 1 boiler.

Like this. Multiple boilers/LLH/plates for heating/hot water.

80F76FE2-2472-49A3-8EF4-BF9791C3AA46.jpeg
94F3AFC3-1AFA-4CB0-9F4E-DF206350C6BB.jpeg
0774F269-816D-44D1-949B-BB8FE11368C4.jpeg
A9E4428D-751B-4D8D-8D81-317B6B37D315.jpeg
A50F55D6-7FC2-478A-B034-DCE8F3E0E7A6.jpeg
74664ED8-278E-42DA-8E24-F959F3B351A5.jpeg
 
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Regarding PHE, because you need both the HW flow & return temps to be the same as the boiler flow&return then you need a very high output HX, around 550kw IMO with 3M2 hearing surface, a Nordic BA 60/50 might be suitable and give 100kw output. The BA -27-30, 175kw, 0.96M2 will only give ~ 33kw if my basic calcs are anyway correct.
If you email Nordic and state your requirements, ie boiler output, boiler flowrate&flow & return temps and heating flowrate& flow&return temps then they will suggest the exact fit for your system.

1640894139681.png
 
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Thanks Tim and John,

I am aware of UK Exchanges Ltd, which they seem to have a good reputation. They are certainly on my list.

Nordic has an interesting blog on their website about sizing.

How to choose a heat exchanger to connect a gas boiler?

Many Customers ask us how to size the right heat exchanger to connect a gas boiler with installation. We got a simple converter of heat exchange area of the exchanger to a nominal power of a boiler in kW. Feel free to check and use it!
nordictec-store.com nordictec-store.com

According to Nordic, for every 10kW of boiler output you need a heat exchanger surface of 0.3m2. Thus, a 100kW boiler would need a heat exchanger with a surface of at least 3m2, and they have advised me on what heat exchanger to get, preferably a brazed one.

The issue I am faced with is as follows. Our heating system has been badly maintained and I want to avoid the heat exchanger getting clogged. We recently placed a commercial 2’’ Magnaclean filter, but I am concerned that this will not be enough. I am faced with 3 options:
  1. Install a brazed heat exchanger, which in principle is ideal and the most efficient. However, they usually come with waterways of 1.8-2.2 mm depth and can be clogged, despite having a magnetic filter. Magnaclean’s CMX commercial MIDI and MAXI filters can work as inline filters and if suitable then I could possibly use them with a brazed HE. The CMX come with 50 micron replaceable filters, which will certainly limit any clogging. But I am not sure if this will impact the flow into the return of the heat exchanger.
  2. Install a shell-and-tubes heat exchanger (sold for pools by Nordic), which will not be as efficient as a brazed HE but will not clog easily. Our installer prefers this method for our circumstances.
  3. Install a gasketed HE, which can be cleaned easily. Danfoss Sondex makes a gasketed HE that has 4.3mm depth in the waterways and thus would clog less and it is cleanable. However, they are also more expensive, and in theory they can leak.
Thus, this is the dillema I have.

Tim is correct that two boilers would be preferable to one, and the instalation he has done as shown in his photos are admirable. The reason we are likely to use one boiler is because the heating boiler is installed in the basement and ideally we would use existing flue. We would place a liner in the flue and the distance from the boiler to the top of the chimney stack is about 23 meters and they are a few 45 degree angles on the way up. A 100kW GB162 V.2 boiler allows us to have a flue up to a theoretical 50m high. Once you incorporate the turns, then this become less. If we use two 50kw GB162s then the theoretical distance becomes shorter and we may even have to use a slightly wider diameter liner. Thus, using one boiler enables to use a smaller diameter liner to ensure it passes through the flue and also we will not be close to the limit once we incorporate 45 degree turns. Note that this is not for a concentric flue, but just for the output. The air input will be from ventilation in the basement.

We have a separate WB 35kW CDI boiler for the hot water. The flue is in the front basement lightwell, but it would be a challenge to also have the heating boiler flue(s) in the basement lightwell, and in case I am told we are not supposed to. This is a conversion of two terraced houses in a conservation area and the building is grade ii listed.
 
A shell&tube heat exchanger might require multiply times the heating surface of a PHE but (thermal) efficiency doesn't come into it except the exchangers have no external lagging/insulation.
 
Not sure I should comment, because I am just a DIY guy, but wouldn't a small buffer tank, or large vertical LLH work? The return from the rads would come in at the bottom, and the return to the boiler could come off half way up. If the water is not moving too fast, then most of the sludge should settle to the bottom. It would not give complete isolation, but combined with a decent filter on the boiler return, maybe that would be enough?
 
Hi John, That is why I was thinking a small buffer tank might work better, as the water would move more slowly, and give more chance for anything large to settle out. Plus you would not want the two returns across from each other like in the picture in your link, but rather staggered something like this:
BufferAsLLH.jpg

I suppose a stainless tank around 90+ litres could be had for a few hundred pounds. Of course it would take up space, and you would have to up-size the expansion vessel accordingly (OP is going to seal this system, correct?). Another challenge might be to find a small tank with large enough connections, although some places will make whatever tank you want. In this case a tall thin tank would work best, basically just a larger volume vertical LLH.
 
There's that advantage all right, but the whole system has to be looked at, think its a vented single pipe system, whatever system is decided on and even with it cleaned out and depending on a successful result it may be deemed best to install a LLH or that buffer tank of a PHE or a shell&tube Hx, depending on installation space available.
 
Indeed, I guess I assumed that when a professional is doing the install, they would automatically go for a sealed system, it did not occur to me that they might want to leave it vented. Along with inhibitor, sealing the system should stop the corrosion that is generating the problem in the first place, which is always going to be worse on a vented system. Without going too far off topic, I agree with the whole system approach, I am bit surprised you can run 12 flats with 35kw for hot water. I'd be tempted to go with a larger buffer and size the boiler for both, although separate systems also have their advantages.
 
I noticed you mentioned a 23m flue, may I ask how tall is the building? Or more importantly, what is the height difference from the lowest pipework in the basement to the top of the highest radiator? 10m is around 1 bar, and you can run a sealed system at that pressure, or maybe a bit above, so it could be your system is already operating at the pressure you would need for a sealed system, since the boiler is in the basement. You would probably need to go a wee bit higher to make sure the rads on the top floors fill, but not much more.
 
Re Original query,

A Nordic B3600 Swimming Pool Heater, 1060kw, 6.4M2 might do the job for you, I'm assuming the heat flux at 2850 w/m2.degC, Nordic will advise.


1640963719149.png
 
@John.g

In reply to my pool heat exchnzger query, Nordic suggested the pool heat exchanger B2400 at 704kw, as it has a surface of 4.47 m2, not too far from the required 3m2 for the 100kW boiler . However, Nordic's stronger preference is a brazed heat exchanger Ba-95-40 which is 1000kw and has a surface of 3.8m2, which is cheaper but more efficient. As discussed before, my concern is of a brazed HE clogging as our system is old and had been poorly maintained. Keep in mind that one of our requirements is to have 2'' connections, as this is what our single pipe system has.

@siricosm

The height difference from the lowest pipework in the basement to the top of the highest radiator (on 5th floor attic) is about 22 meters.

​

 
LordWest said:
@siricosm

The height difference from the lowest pipework in the basement to the top of the highest radiator (on 5th floor attic) is about 22 meters.

​

Click to expand...
This means you have over 2 bar of pressure in the lower parts of your unvented system already. So sealing it would not require a dramatic increase in pressure, but perhaps a discussion for a different thread.
 
The required 3M2 to give 100kw output is based on a PHE, the required surface area of a S&T to give the same output (100kw) with the same flowrates and flow&return temps and LMTD is far higher than using a PHE because the more turbulent flow in a PHE gives a far greater (IMO) heat flux, so to compensate, the surface area of the S&T must be far higher, this is why they say its more efficient, all this means is that you have a smaller Hx, they both give exactly the same input/output., ie 100% efficient. If you have the space to install a S&T if you think it's easier to clean (and it is) then I would install it.
I am a little surprised that Nordic sized the S&T at 4.47M2 (704kw) but they have the requirements?. I would be far happier with a 6.4M2 (1060kw).
 
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siricosm said:
This means you have over 2 bar of pressure in the lower parts of your unvented system already. So sealing it would not require a dramatic increase in pressure, but perhaps a discussion for a different thread.
Click to expand...
Shouldn't increase the pressure too much, don't know what the system contents are, say 400/500 litres, a large 100 litre EV would ensure the pressure kept to 2.25/2.3 bar on heat up, boiler would require a PRV if not already fitted.
 
I appreciate the benefits of converting the vented heating system into a sealed one, but I do not want to take the risk of leaks in the old pipework and radiators. If this were for my house only, then I would take the risk. But the heating system serves 12 flats (including my flat) and I do not want take the risk nor for the increased policy policy premiums that may result from damage from the leaks.

Going back to the heat exchanger, I will discuss again with Nordic the right size for my circumstances. John you are correct that plate HEs are indeed mroe efficient because of turbulent flow conditions.

Assuming (i) we recently installed a 2'' Magnaclean filter, and (ii) our system has not been well maintained over the years and clogging the HE is a possibility, which of the three options below woudl go for?
  1. Install a brazed heat exchanger, which in principle is ideal and the most efficient. However, they usually come with waterways of 1.8-2.2 mm depth and can be clogged, despite having a magnetic filter. Magnaclean’s CMX commercial MIDI and MAXI filters can work as inline filters and if suitable then I could possibly use them with a brazed HE. The CMX come with 50 micron replaceable filters, which will certainly limit any clogging. But I am not sure if this will impact the flow into the return of the heat exchanger.
  2. Install a shell-and-tubes heat exchanger (sold for pools by Nordic), which will not be as efficient as a brazed HE but we will get a larger size and will not clog easily. Our installer prefers this method for our circumstances.
  3. Install a gasketed HE, which can be cleaned easily. Danfoss Sondex makes a gasketed HE that has 4.3mm depth in the waterways and thus would clog less and it is cleanable. However, they are also more expensive, and in theory they can leak.
 
I would stay with the Vented system if it has served well with no air ingress problems over the past 50 years. (like my own)

I would also go for option 2, like your installer, have a good look at the attachments again as I would strongly suggest the 6.4M2, 1060kw Hx as your rads, if based on the normal "50deg" will still give 72% output and if oversized originally (by a factor of 1.39) then you will still get 100kw. If you opt for the 704kw Hx then you will only get ~ 70kw.

Finally, a Happy and Healthy 2022 to you and yours and everyone.

John



1640994888651.png
 
John,

Happy New Year and many thanks for your analysis. I will enquire about the B3600.

Do you have any views on options 1 and 3 I listed above, compared to B3600 (Option 2)?
 
Option 1, depending on how clean you can get the system is probably a better choice than option 3 despite option 3 having bigger waterways and the ability to split it for cleaning, my experiences of this type (3) of PHE was on a number of ships I sailed on, they needed very careful re assembly with the correct torque settings for the tie bolts etc after cleaning, the rubber gaskets frequently were torn on splitting them and any new gaskets had to be glued on, if you go down this route then who will disassemble, clean and re assemble them properly?.
Option 1, if you are prepared to treat the Hx as a throwaway item should it get plugged is far less trouble IMO but of course may prove very expensive in the long run.
My preference is still option 2.

Of course, as suggested above, by others, you could go for a LLH, with suitable filtration, both magnetic&particle, of the boiler return, you might find that the boiler Hx might last for years and its replacement cost may not exceed and may even be far less than the maintenance cost of either of the PHEs.
 

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