Air in CH system and hot water returning to FE tank via the cold feed

[Tiggy1955]

I have a problem with air being sucked into my CH system creating airlocks in the radiators. The water is flowing back into the FE tank via the cold feed pipe. I can feel warm water coming through the feed pipe back into the tank as the tank water level slowly get higher. I can hear the overflow gurgling in the FE tank.

The system is 20 years old but the Worcester Bosch boiler is only 9 years old. All has worked perfectly well. I did have the classic blockage where the cold feed meets the hot return but the clogged pipes have been cut out and replaced.

I have fitted a new pump and it is set to the lowest speed. All of the radiators have been bled many times and balanced.

So the heating is working fine except that I have this problem of the air displacing the water back to the FE tank. The water it getting back into the tank a quite a rate - I would say about 2 litres per hour. This means that the rads need to be bled constantly.

Any ideas? Could it be an problem with the boiler itself?

 

[John.g]

The simple answer is efficiency. The pump efficiency peaks around the middle of the curve.

Yes, I saw Grundfos mentioning that but if that max setting of 3.0M isnt sufficiently high enough for your needs then you simply have to go over to fixed speed which is a pity really as you have lost all the benefits of PP control including much lower power demand).

 

[John.g]

That just gives you the working point when that particular pump is used. That may not be the same as the required working point.

Here's a example, using my system which has a UPS2:

The required flow rate and head are 8 litres/min at 2.2m. The actual working point, shown by the yellow dot, is 9.99 lpm at 3.43m which is where the pump curve and system curve (red line) meet. See graph below.

If a PP setting is used, it needs to provide the required flow/head not those obtained by the fixed speed setting.

The attached UPS2 file is corrupted,

View attachment 36462

Yes, exactly, if you need 8 LPM @ 2.2M head then the UPS2 will NOT do the job in PP mode at its max setting of 3M, it will only give 6.8 LPM @ 1.53M, just put 2.2 in cell L10 and 8 in cell M10 of my spreadsheet and just read the result off the graph. You would need a PP capability of around 3.3/3.4 to give you those required numbers.
I really couldn't recommend anyone to buy the UPS2 for this very reason. I will shortly post a modified spreadsheet using a Wilo pump on PP control to give your 8LPM @ 2.2M.

 

[John.g]

Unfortunately the spreadsheet is difficult to understand as you don't explain where the data comes from or what each column contains.

For example:
How did you obtain the Know Head and Known Flow?
Where does the UPS2 data at the top come from? It doesn't agree with the Grundfos published data.
What does "rem 7.9 lpm" mean (apart from the obvious litres per min)?
What does series 1 and series 2 refer to?
etc etc.

Here is a more detailed description of my spreadsheet which you may find interesting.

Most pump manufacturers PP control operate between a max and a min head where the minimum is the max/2 (see my post #234 above), for example in a pump that might have a PP set at 3M, the minimum is then 3/2 or 1.5M. Grundfos are a little different in that with the PP set at 3M then the minimum is ~ 1.2M (hard to read, page 11 of UPS file), but it doesn’t matter as the calculations method is the same for all the manufacturers and is very simple.

In the above case (UPS2.) 1.2M=0M3/h and 3M=2.15M3/h, I prefer to use LPM so 1.2M to 3M = 0 to 36 LPM. The calculation that the pump microprocessor carries out is completely proportional. So mathematically the calculated head = 1.2+(3-1.2)*LPM. For example if the LPM are 18 then the calculated head = 1.2+((3-1.2)*(18/36))= 2.1M, another example at 36 LPM the head is 1.2+((3-1.2)*(18/36))=3.0M (which we know is correct as 3M=36 LPM but just checking!) Spreadsheet: In column I (under LPM) I have started at 0 LPM and incrementally increased it in 0.1 LPM steps down through the column, (these values I copied across to column K to make it easier to build the trend.The caculation above is then done in the adjacent column J under H and gives the equivalent PP calculated head . Now the known (in this case, my own) LPM is 15 at a head of 2.9 M but as the pump starts ramping up at 1.2M (it possibly starts at 0) and because Flow is proportional to the sq.root of head then the ACTUAL flowrate at 1.2M is 15*sqroot(1.2/2.9), 9.65 LPM as shown in column L, so as the pump is ramping up this real flow rate will keep increasing and the calculated PP head will also keep increasing and when the real flow rate “catches up” with the calculated PP flow rate then the pump will stop ramping as the calculated power and the absorbed power will be equal, in this case at ~ 11.8 LPM @ 1.8M head. (the pump only looks at the power, it doesn,t measure head or flow) . Also see cells K134 & L134.

 

[John.g]

Yes, exactly, if you need 8 LPM @ 2.2M head then the UPS2 will NOT do the job in PP mode at its max setting of 3M, it will only give 6.8 LPM @ 1.53M, just put 2.2 in cell L10 and 8 in cell M10 of my spreadsheet and just read the result off the graph. You would need a PP capability of around 3.3/3.4 to give you those required numbers.
I really couldn't recommend anyone to buy the UPS2 for this very reason. I will shortly post a modified spreadsheet using a Wilo pump on PP control to give your 8LPM @ 2.2M.

Here you go, using a PP head of 3.3M will give you very close to your required 8 LPM @ 2M, it gives ~ 7.9 LPM @ 2.12M.

 

[John.g]

Correction: 2M should have read 2.2M.
Here you go, using a PP head of 3.3M will give you very close to your required 8 LPM @ 2.2M, it gives ~ 7.9 LPM @ 2.12M.

 

[doitmyself]

I really couldn't recommend anyone to buy the UPS2 for this very reason.

I have also come to the conclusion that the UPS2 PP option is a non-starter.

It is interesting that the Grundfos pump-sizing facility on their web-site never suggested the UPS2 if you specify PP operation; but it's recommended if you use fixed speed. I do wonder why they provided PP settings. The new UPS3 is much better.

 

[John.g]

I have also come to the conclusion that the UPS2 PP option is a non-starter.

It is interesting that the Grundfos pump-sizing facility on their web-site never suggested the UPS2 if you specify PP operation; but it's recommended if you use fixed speed. I do wonder why they provided PP settings. The new UPS3 is much better.

 

[John.g]

Yes, its strange alright because their old pumps were excellent long living products and some cheaper makes offer 5 or 6 PP settings, OK most of the lower ones wouldn't be used very often but the higher setting is often 4.5M or even 5M which will meet most normal sized dwelling needs.
As you say the UPS3 is better and even though it has only two PP settings, the higher one is 3.6M.
I have attached a different method of "sizing them up" which is easier to use I think than the previous Spreadsheet, I have done a few calcs using the UPS3 which are included.

 

[Ric2013]

I have also come to the conclusion that the UPS2 PP option is a non-starter.

It is interesting that the Grundfos pump-sizing facility on their web-site never suggested the UPS2 if you specify PP operation; but it's recommended if you use fixed speed. I do wonder why they provided PP settings. The new UPS3 is much better.

I have a UPS2 in my own house. I got it for free because the screws were missing on the terminal box. Actually, the head it provides is more than sufficient and one of the advantages of the UPS2 for me was that the fixed speed UPS on setting 1 was far far too high, but then I have quite an old boiler with negligable head loss across the heat exchanger.

That said, I do suspect that a high head would never be required for a properly designed system: if the velocity of the water in pipes be kept reasonably low, why would you need a 6m head? That said, easier to ensure in a new system than when modifying an existing system.

 

[John.g]

I have a UPS2 in my own house. I got it for free because the screws were missing on the terminal box. Actually, the head it provides is more than sufficient and one of the advantages of the UPS2 for me was that the fixed speed UPS on setting 1 was far far too high, but then I have quite an old boiler with negligable head loss across the heat exchanger.

That said, I do suspect that a high head would never be required for a properly designed system: if the velocity of the water in pipes be kept reasonably low, why would you need a 6m head? That said, easier to ensure in a new system than when modifying an existing system.

I suppose we should bear in mind that the UPS2 hasn't true fixed speed curves. Even speed 1 will give a constant head of 4M from 0 to ~ 6 LPM before the head starts falling, (any real fixed speed pump head starts dropping immediately on flow demand) which with modern zoning/TRV's etc will cater for over 6 kw of heat demand at a deltaT of 15C. and with the retro fitting of condensing oil/gas boilers the trend is to get a greater deltaT of 20C to enhance the condensing effect thus leading to even lower circulation rates. So in a house with even just basic insulation could very easily be running the UPS2 pump at the ridiculously high head of 4M on "fixed speed" for significant periods of time.
I havn't any pump curves for the older UPS pumps but I would think that they would have been operating at least 1/1.5M lower head?
Having said that the 3M PP head is a bit mean to say the least and certainly will fall short in a lot of instances as on PP control the head falls with reduced flow demand so to cater for both full heating flow rates and reduced demand it would have been nice if 3.5M to 4M was available, as was pointed out above, The UPS 3 has now got a 3.6M PP head. (AND has two CP (constant pressure) settings as well!)
This one may have been replaced in a lot of cases by the UPS 2.
https://product-selection.grundfos....tid=GMA&productnumber=97549426&qcid=501056454

 

[Ric2013]

At 6l/m the old UPS 15/50 had around a 3m head and the UPS 15/60 around 3.6m head.

The very old Selectric UPS 15/50 and Super-Selectric 15/60 has 7 and 9 foot head, at 6l/min respectively, so a little less. (I say 'has' in the present tense because I know at least one that is still running.)

All the above are on speed 1.

I suppose it would be useful to plot a little chart showing various types of pump curve all on the same axes, so comparisons could be made.

Why am I still up?

 

[John.g]

At 6l/m the old UPS 15/50 had around a 3m head and the UPS 15/60 around 3.6m head.

The very old Selectric UPS 15/50 and Super-Selectric 15/60 has 7 and 9 foot head, at 6l/min respectively, so a little less. (I say 'has' in the present tense because I know at least one that is still running.)

All the above are on speed 1.

I suppose it would be useful to plot a little chart showing various types of pump curve all on the same axes, so comparisons could be made.

Why am I still up?

Will put together one (chart) later today, I will include my own old Salmson NYL 33 which I installed in Sept 2000 set to speed 2 and was still running perfectly and quietly when I replaced it last November with a Wilo Yonos Pico 1-6 last November.

 

[tonyt]

A bit off thread but I love this forum! It's so good to see people discussing issues using reasoned and evidenced facts supported by experience rather then slagging each other off.

 

[Ric2013]

A bit off thread but I love this forum! It's so good to see people discussing issues using reasoned and evidenced facts supported by experience rather then slagging each other off.

That's because I'm a left-leaning liberal **** as they say on Youtube when I'm trying to make a reasoned point.

 

[John.g]

Will put together one (chart) later today, I will include my own old Salmson NYL 33 which I installed in Sept 2000 set to speed 2 and was still running perfectly and quietly when I replaced it last November with a Wilo Yonos Pico 1-6 last November.

Here it is, I wouldn't care to be running a few of these on even fixed speed 1, especially the UPS 3 .

 

[Ric2013]

Here it is, I wouldn't care to be running a few of these on even fixed speed 1, especially the UPS 3 .

Doesn't work on Libreoffice. Thanks though.

 

[John.g]

Doesn't work on Libreoffice. Thanks though.

Here's a snapshot of it & also a Zipped word copy.

 

[Ric2013]

I take it that's the old UPS and not the very old one, but it looks wrong. The UPS 15-50 starts at a 0 flow at 3.5m exactly, so how are you getting 3.76? Have you yet another IOM, as that differs from my data?

 

[John.g]

I take it that's the old UPS and not the very old one, but it looks wrong. The UPS 15-50 starts at a 0 flow at 3.5m exactly, so how are you getting 3.76? Have you yet another IOM, as that differs from my data?

You posted

I take it that's the old UPS and not the very old one, but it looks wrong. The UPS 15-50 starts at a 0 flow at 3.5m exactly, so how are you getting 3.76? Have you yet another IOM, as that differs from my data?

I got it from one of your files above... "Selectric UPS Old Style" page 1 shows speed 1 curve starting at 3.75/3.76M ?.

 

[John.g]

At 6l/m the old UPS 15/50 had around a 3m head and the UPS 15/60 around 3.6m head.

The very old Selectric UPS 15/50 and Super-Selectric 15/60 has 7 and 9 foot head, at 6l/min respectively, so a little less. (I say 'has' in the present tense because I know at least one that is still running.)

All the above are on speed 1.

I suppose it would be useful to plot a little chart showing various types of pump curve all on the same axes, so comparisons could be made.

Why am I still up?

Can you post any links (charts etc) to a UPS 25-50 Selectric, power outputs 40W, 65W & 95W. (installed in a new build house in 2005/2006), still running.
Thanks.

 

[Ric2013]

You posted


I got it from one of your files above... "Selectric UPS Old Style" page 1 shows speed 1 curve starting at 3.75/3.76M ?.

Can you look at the chart on my file again and tell me what you see? I make it between 3.5 and 3.6 and would like to know if this is human or electronic error.
This is how it appears on my screen:

 

[doitmyself]

Can you look at the chart on my file again and tell me what you see? I make it between 3.5 and 3.6 and would like to know if this is human or electronic error.
This is how it appears on my screen:View attachment 36507

I have to agree with john.g. The speed 1 line crosses the y-axis at 3.75.

 

[John.g]

Can you look at the chart on my file again and tell me what you see? I make it between 3.5 and 3.6 and would like to know if this is human or electronic error.
This is how it appears on my screen:View attachment 36507

(Internet down for past few hours so couldn't relpy)

A bit confused as to why you ask human /electronic error as this I presume is a grundfos data sheet that you posted?, I just copied the data from it into my own spreadsheet, if you can post the proper chart I can incorporate that data in the spreadsheet and re post.

 

[Ric2013]

It's okay John. I'm not very good at reading data from a screen for some reason and I was reading the digits 3.5 against the 3.75 line.

So ignore my comments above.

 

[John.g]

It's okay John. I'm not very good at reading data from a screen for some reason and I was reading the digits 3.5 against the 3.75 line.

So ignore my comments above.

No problem, if you do come across any info on that 25-50 selectric with those power settings I would appreciate it. (#70)