What size boiler needed

[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.

 

[John.g]

Do you mean the expansion valve on the HW cylinder is dripping, if so, this, or a failing HW cylinder EV has got nothing to do with the boiler EV or PRV, what is/was the boiler pressure gauge reading when this dripping occurs?.

 

[sherylryan]

Do you mean the expansion valve on the HW cylinder is dripping, if so, this, or a failing HW cylinder EV has got nothing to do with the boiler EV or PRV, what is/was the boiler pressure gauge reading when this dripping occurs?.

Yes expansion valve on HW cylinder was dripping, with that bypass valve open hot water was feeding down the pipe to where the EV is on cylinder. Nothing else was calling for heat other than Kitchen UFH with manual bypass open. Boiler pressure was 1.5 bar, pump was 1.35 bar, flow temp was 72 degrees. (Hope that makes sense)

Another question, our original nozzle was a .65 80 s 2.47kg/h, if I'm reading these specs correct on the side of the burner does it indicate the nozzle size must be 2.8 - 4.5 kg/h and is the output of this burner 33-54 kw, should it couldn't be downsized to a 26kw?

 

[John.g]

If that bypass valve is feeding HOT water into the HW cylinder then it will have to be from the HW cylinder hw outlet which will be at higher pressure when the cylinder is heating or is hot with no HW draw off, if tied into the boiler system primary system flow pipe it cannot feed hw as the primary/boiler system pressure is only 1.5bar. If it was connected from the cold mains then that will lift the cylinder expansion valve but the pipe would be cold.?

Nozzle Sizing: From below. a 0.65 nozzle will give a burner output of 31kw @ 12.5bar which will be 31*(14/12.5)^2, 32.81kw @ 14bar, a boiler output of 28.87kw @ 88% boiler efficiency.

Your present 0.55?? nozzle will give a burner output of 26kw @ 12.0bar which will be 26*(14/12.0)^2, 28.10kw @ 14bar, a boiler output of 24.73kw @ 88% boiler efficiency.

 

[sherylryan]

If that bypass valve is feeding HOT water into the HW cylinder then it will have to be from the HW cylinder hw outlet which will be at higher pressure when the cylinder is heating or is hot with no HW draw off, if tied into the boiler system primary system flow pipe it cannot feed hw as the primary/boiler system pressure is only 1.5bar. If it was connected from the cold mains then that will lift the cylinder expansion valve but the pipe would be cold.?

Nozzle Sizing: From below. a 0.65 nozzle will give a burner output of 31kw @ 12.5bar which will be 31*(14/12.5)^2, 32.81kw @ 14bar, a boiler output of 28.87kw @ 88% boiler efficiency.

Your present 0.55?? nozzle will give a burner output of 26kw @ 12.0bar which will be 26*(14/12.0)^2, 28.10kw @ 14bar, a boiler output of 24.73kw @ 88% boiler efficiency.

Ok so you get a burner output and a boiler output from one nozzle calculations?

In below photo, pipes in red were hot, pipe going into EV was cold

 

[John.g]

Yes, the table gives (presumably) burner output, the only assumption that will marginally affect the boiler output is its efficiency so 85% to 92% should cover it, the calculation for pressure is universally used, ie flow is prop to the sq.root of pressure, I should have shown that as ^0.5 and not ^2, but I did use ^0.5 in the calculation.

Can't really comment on that by pass except to suggest finding out exactly where the connections are teed in.

 

[sherylryan]

Yes, the table gives (presumably) burner output, the only assumption that will marginally affect the boiler output is its efficiency so 85% to 92% should cover it, the calculation for pressure is universally used, ie flow is prop to the sq.root of pressure, I should have shown that as ^0.5 and not ^2, but I did use ^0.5 in the calculation.

Can't really comment on that by pass except to suggest finding out exactly where the connections are teed in.

Thank you for the calculations they are very handy.

I am totally stumped over the whole system 😂😂😂 but have quite a bit more knowledge now thanks to you.

 

[John.g]

This Laundry Manifold/TMV is a mystery to me as all the indications are that the return temperature to the boiler is the mixed flow temperature but havn't figured out if this is thermodynamically possible.
You might please take the (4) temperatures where indicated and also take the return temperature to the boiler; at the boiler.

 

[sherylryan]

This Laundry Manifold/TMV is a mystery to me as all the indications are that the return temperature to the boiler is the mixed flow temperature but havn't figured out if this is thermodynamically possible.
You might please take the (4) temperatures where indicated and also take the return temperature to the boiler; at the boiler.

View attachment 76807

Ok, will do. I’ll get back to you.

 

[sherylryan]

This Laundry Manifold/TMV is a mystery to me as all the indications are that the return temperature to the boiler is the mixed flow temperature but havn't figured out if this is thermodynamically possible.
You might please take the (4) temperatures where indicated and also take the return temperature to the boiler; at the boiler.

View attachment 76807

Boiler set point 60
Boiler flow temp 72
Boiler return 59

Ufh at points 2 72 into mixing valve 50 going into pump.

Point 4 45 degrees
Point 8 57 degrees

Wow temps are all over the place. Return is high into boiler as that manual bypass is open.

I have attached a graph of the laundry manifold with boiler flor and return temps taken when boiler was set at 35kw. (Blue is boiler firing flow , Red is pump only pumping)

 

[John.g]

Sorry for confusing you, its the temperatures at 1,2,3&4 in this attachment I would like.

 

[John.g]

Have added another one below, point 5, so measurements at points 1,2,3,4,5. (thanks for your patience)

 

[sherylryan]

Sorry for confusing you, its the temperatures at 1,2,3&4 in this attachment I would like.

Oh sorry, I’ll check again

 

[sherylryan]

Sorry for confusing you, its the temperatures at 1,2,3&4 in this attachment I would like.

Oh sorry,

Have added another one below, point 5, so measurements at points 1,2,3,4,5. (thanks for your patience)

Awesome, sorry have been away for back tomorrow and then I’ll have temps. Thank you.

 

[sherylryan]

Oh sorry,

Awesome, sorry have been away for back tomorrow and then I’ll have temps. Thank you.

Ok so I have checked all temperatures and what a shambles, they are

Boiler flow 76.5 degrees
Boiler Return 46.3

Temp 1 - 60
Temp 2 - 46
Temp 3 - 38
Temp 4 - 34
Temp 5 - 48

 

[John.g]

Yes, it's working as I thought it might, apart from temp 1 at 60C which should be the same as the boiler flow at 76.5C or vica versa. The TMV is controlling (first mixing) the temp at 48C = temp 5, this is then (second) mixing with the manifold return of 34C to give a final mixed manifold temperature of 38C, there is only a dT of 4C across the loops so do your calc, LPM*60*dT/860, to give the loop output, kw.
The TMV mixed flow temp of 48C is returning to the boiler which is very good from a balanced corrosion and efficiency point of view, obviously if you require the manifold flow temp of 38c increased then you have to increase the TMV setting.

Its quite a clever control system IMO especially for a oil fired system as it obviates the need for recirculation if the manifold return was returned to the boiler.