What size boiler needed

[sherylryan]

The above gives a manifold demand of 21.85kw so the boiler output must be there or there or there abouts the same since it can't reach its SP and cut out, I suppose the manifold temp of 48.6C isn't bad control since we don't know how accurate the TMV SP index is, you might reduce it to 30C sometime to see reduced manifold output and boiler cut out

For interest, you can see the bypass flow required to increase the boiler return temp from 37C to 45C.

The position of the EV connection is effectively into the pump suction in your boiler and it the new original seems to be into the pump discharge with the pump pumping into the return, probably OK in both cases.

Boiler return 37C (no bypass)
View attachment 76763


Boiler return 45C (with bypass)
View attachment 76762

So should we put a bypass in somewhere? there was one on the side of the boiler teed into the flow and returning back into the bottom of the boiler ? The nozzles they have had in this boiler are 0.55 80 s 2.11kg/h and a .50 80s 1.87 kg/h. Thank you for your spreadsheets they are very informative.

Another question, sitting here reading the installation manual, with the nozzle currently in the burner, it refers to blast tube T3 to be installed, we currently have a T5 installed, would this cause an issue?

 

[John.g]

I wouldn't have it as my top priority just now but can think about best way to achieve it, would be inclined to try a "Tapstat" with the sensor on the boiler return set to 45C (or whatever min return temp required).

How long is it taking the UFH to get the room (kitchen?) temp up their desired temp, at the moment the room/ambient dT isn't particularly bad, so roomstat should be cycling fairly often?, and the rooms with rads??.
Do you intend to increase the boiler output??.

The installed blast tube should be as recommended, I have a feeling that the reason for the small nozzle with the extremely high pump pressure is to get the emissions right, a, say, 0.65 nozzle with a more modest pump pressure of 10bar + the T3 should give the same boiler output and probably less flame impingment on the baffles.

 

[sherylryan]

I wouldn't have it as my top priority just now but can think about best way to achieve it, would be inclined to try a "Tapstat" with the sensor on the boiler return set to 45C (or whatever min return temp required).

How long is it taking the UFH to get the room (kitchen?) temp up their desired temp, at the moment the room/ambient dT isn't particularly bad, so roomstat should be cycling fairly often?, and the rooms with rads??.
Do you intend to increase the boiler output??.

The installed blast tube should be as recommended, I have a feeling that the reason for the small nozzle with the extremely high pump pressure is to get the emissions right, a, say, 0.65 nozzle with a more modest pump pressure of 10bar + the T3 should give the same boiler output and probably less flame impingment on the baffles.

Its taking 1 hour to get the floor temp up 3 degrees differential in the kitchen and it has a cycle time of approx 3 hours.

Yes I intend to increase the boiler output, but I'm unsure whether 35kw is enough output for UFH, & Rads. I will also get blast tube changed to instruction manual specs.

 

[sherylryan]

Its taking 1 hour to get the floor temp up 3 degrees differential in the kitchen and it has a cycle time of approx 3 hours.

Yes I intend to increase the boiler output, but I'm unsure whether 35kw is enough output for UFH, & Rads. I will also get blast tube changed to instruction manual specs.

If we have
21.85kw ufh kitchen
11.50kw ufh Laundry
16,50 Kw Radiators/Trench
3 Kw DHW
A total of 49Kw a 35 kw boiler is not going to perform very well is it if they all demanded heat at once.?

 

[John.g]

Yes, but there are lots of ways of skinning a cat, if the kitchen has a cycle time of 3hrs, 1 hr on time so kitchen average requirement is 21.85x0.33=8.3kw, ideally the UFH should give this output continuously and the manifold output can be reduced by various means, reducing the mixing temperature for example so assuming Laundry similar at 11.5x0.33=3.8kw, then continuous UFH demand is ~ 12.1kw, the rads might cycle in a similar fashion, so you may well find that 35kw output is quite sufficient.? You measured your oil consumption at ~ 23LPD or ~ 10kwh/hr so not a mile away from the above?.

 

[sherylryan]

Yes, but there are lots of ways of skinning a cat, if the kitchen has a cycle time of 3hrs, 1 hr on time so kitchen average requirement is 21.85x0.33=8.3kw, ideally the UFH should give this output continuously and the manifold output can be reduced by various means, reducing the mixing temperature for example so assuming Laundry similar at 11.5x0.33=3.8kw, then continuous UFH demand is ~ 12.1kw, the rads might cycle in a similar fashion, so you may well find that 35kw output is quite sufficient.? You measured your oil consumption at ~ 23LPD or ~ 10kwh/hr so not a mile away from the above?.

You are very knowledgeable. Thank you.
Ok so heres what I think I need to do from our conversations:

• Reinstall original pump
• Install another EV
• Turn TMV down on kitchen manifold
• Install new pump set on Laundry manifold
• Upsize boiler back to 35kw
• Replace blast tube to correct one, as per instruction manual
• Install bypass?

And hopefully we will have a system the will operate efficiently.

 

[John.g]

I would suggest replacing the boiler PRV (safety valve) as well, it may be lifting before 3bar.

The laundry manifold seems to be performing spot on, it gives a mixing temp of 45C with a boiler temp of 70C, what is the TMV setting index?, you could reduce that by say 5c to test that the TMV is working OK.

Have you the spec on the original circ pump model etc.

Laundry manifold
Boiler/manifold flow temp 70 c
Manifold mixed flow temp 45
Manifold return temp 35
Total flow 16.5 LPM
Blr circ pump flowrate, 4.71LPM (Manifold output, 11.50kw,) Pump RPM 1080.

 

[sherylryan]

I would suggest replacing the boiler PRV (safety valve) as well, it may be lifting before 3bar.

The laundry manifold seems to be performing spot on, it gives a mixing temp of 45C with a boiler temp of 70C, what is the TMV setting index?, you could reduce that by say 5c to test that the TMV is working OK.

Have you the spec on the original circ pump model etc.

Laundry manifold
Boiler/manifold flow temp 70 c
Manifold mixed flow temp 45
Manifold return temp 35
Total flow 16.5 LPM
Blr circ pump flowrate, 4.71LPM (Manifold output, 11.50kw,) Pump RPM 1080.

Oh yes forgot about the PRV valve. So you think we should put a pump set on the laundry like the kitchen one? (Instead of the one attached)

This is the pump they moved from inside the boiler, also they have attached this pipe between flow and return. Do you think I should turn this on to get retune temp up?

So the only explanation we have as to why the boiler doesn’t reach serpoint when heating the kitchen manifold is because the manifold output is > or = to the boiler output?

 

[John.g]

Oh yes forgot about the PRV valve. So you think we should put a pump set on the laundry like the kitchen one? (Instead of the one attached)

NO, what I said is that this TMV/pump set seems to be working perfectly well even though I would like to know how it "works" (see queries in attached that you can answer). Can you see what the TMV is set to just now?.
If it's working OK why change it?.

This is the pump they moved from inside the boiler, also they have attached this pipe between flow and return. Do you think I should turn this on to get retune temp up?

I don't think this will work because the circ pump is on the flow so the boiler return pressure is > than the flow (where it leaves the boiler) so the bypass flow will be the wrong way?.

So the only explanation we have as to why the boiler doesn’t reach serpoint when heating the kitchen manifold is because the manifold output is > or = to the boiler output?

Yes, IMO, so just reduce this (kitchen) TMV setting to say 30C or whatever is required to get the mixed flow temperature down to say 35C/38C.

 

[sherylryan]

NO, what I said is that this TMV/pump set seems to be working perfectly well even though I would like to know how it "works" (see queries in attached that you can answer). Can you see what the TMV is set to just now?.
If it's working OK why change it?.

I don't think this will work because the circ pump is on the flow so the boiler return pressure is > than the flow (where it leaves the boiler) so the bypass flow will be the wrong way?.

Yes, IMO, so just reduce this (kitchen) TMV setting to say 30C or whatever is required to get the mixed flow temperature down to say 35C/38C.

The laundry TMV is set to 45 c.

I have this morning turn the kitchen TMV down to 38 c and mixed water is still getting to 46 c. I am wondering if the pump pressure and speed of water is literally seeping through the valve.

Below is a better pic of the manual bypass, it actually tees of the flow before water even gets to 2 way valve and joins into the return pipe from DHW cylinder, which then tees into UFH return pipe.

Sorry for all the questions, hope your brain is not as confused as mine

 

[John.g]

The laundry TMV is set to 45 c.

So the SP is 45C and the actual is 45C= perfect control, don't dream of changing it.

I have this morning turn the kitchen TMV down to 38 c and mixed water is still getting to 46 c. I am wondering if the pump pressure and speed of water is literally seeping through the valve.

Turn it down to 30C, see what effect it has, if any.
I would think something wrong with the TMV as the laundry is under similar working conditions and working perfectly, why was a decision made to replace them with this kitchen type? which ironically is not working.

Below is a better pic of the manual bypass, it actually tees of the flow before water even gets to 2 way valve and joins into the return pipe from DHW cylinder, which then tees into UFH return pipe.

Sorry for all the questions, hope your brain is not as confused as mine

Yes, that might work, but don't really know its purpose, would prefer to eventually see a temperature controlled one installed in the correct position.

View attachment 76784

 

[sherylryan]

So the SP is 45C and the actual is 45C= perfect control, don't dream of changing it.

Turn it down to 30C, see what effect it has, if any.
I would think something wrong with the TMV as the laundry is under similar working conditions and working perfectly, why was a decision made to replace them with this kitchen type? which ironically is not working.


Yes, that might work, but don't really know its purpose, would prefer to eventually see a temperature controlled one installed in the correct position.

The kitchen pump had started leaking and they recommended this, as the same as the laundry is obsolete now.

I will turn Kitchen TMV down and if this doesn’t work I will get it replaced.

The purpose of that pipe was the plumbers quick fix to get return water up in temp, as he didn’t want to investigate any of the other issues and thought he would just keep adding pieces to the system in the hope it would fix everything.

Thank you

 

[John.g]

Just crack it open gradually until it raises the return temperature to 45C or so.

You might also have a look at this and comment.

 

[sherylryan]

Just crack it open gradually until it raises the return temperature to 45C or so.

You might also have a look at this and comment.

Just crack it open gradually until it raises the return temperature to 45C or so.

You might also have a look at this and comment.

Yes correct, hot flow pipe from boiler.

The other pipe is the return to boiler/cold return.

the little pipe on the end of the manifold, is an unused pipe (yes cowboys instaledl our system)

Attached is diagram on how isotherm is suppose to work

 

[sherylryan]

Yes correct, hot flow pipe from boiler.

The other pipe is the return to boiler/cold return.

the little pipe on the end of the manifold, is an unused pipe (yes cowboys instaledl our system)

Attached is diagram on how isotherm is suppose to work

I cracked open that manual pass valve and you wouldn’t believe it the boiler got up to temperature (well boiler step point was 60c but boiler flow reached 72c) and the expansion vessel off the hot water cylinder was dripping. So I believe the expansion vessel in the boiler is either not working or to small when running the kitchen UFH manifold.