Calorifier

[Gibbo]

The only ones not agreeing with the calculator are Chris W and your good self

 

I'm actually getting tired of your bullshit.

 

You either have a serious comprehension problem or you are mentally confused.

 

Show me where I have said I do not agree with the calcuator.

 

You can't

 

Because you dreamt it.

 

Gibbo.

 

PS. Your edit (after you realised your mistake) was too late.

Edited November 13, 2008 by Gibbo

[chris w]

where you said...

 

 

The only one not agreeing with the calculator is Chris W

 

Do you agree with it? If so, good!

 

cheers,

Pete.

See my post above your last one. C'mon do the maths for my settings and prove me wrong. Here's your chance.

Edited November 13, 2008 by chris w

[ChrisPy]

This is way above the PRV pressure (either psig or psia) so how come the PRV is not blowing? Without the EV, the PRV dribbles everytime the water is heated.

refer post 218

 

............... in other words, live in the real world. you need to get out more.

[chris w]

refer post 218

 

............... in other words, live in the real world. you need to get out more.

 

So you agree my maths shows that it shouldn't work (I knew it) and now you are claiming the reason it does work is due to mysterious "other" things that you assume is the cause like "long pipe runs" and "things that other people will come up with" - very scientific!!!. (ref your post #218)

 

Well I don't have long pipe runs: the NRV is fitted right before the calorifier, the EV is right at the output of the calorifier and it's only a very short distance to the hot water taps. My maths shows too that it shouldn't work by a big margin not just a small tweak.

 

It's also strange that the EV manufacturers also recommend the exact pressure to which I have set my EV, viz: between the WP cut-out pressure and the PRV pressure.

Edited November 13, 2008 by chris w

[smileypete]

Show me where I have said I do not agree with the calcuator.

Well, do you agree with it, or not?

 

Personally, I wish I never posted the link to the d*mn thing!!!

 

 

See my post above your last one. C'mon do the maths for my settings and prove me wrong. Here's your chance.

Right, phone up the manufacturer of your calorifier and ask for their technical support department. Then ask what's the recommended expansion vessel size for the calorifier. Job done!

 

cheers,

Pete.

Edited November 13, 2008 by smileypete

[PeterF]

Apologies for the delay in replying, but there was a need to do some paying work!

 

As others have pointed out, your arguement still does not work.

 

In simplest terms, the pressure on each side of the diaphragm has to be the same - otherwise it will move in one direction or the other until the pressure is equalised. It does not matter which laws apply to the two fluids, as long as they are the appropriate ones.

 

Out of interest, do you have a stockcock which can isolate the calorifiern and a pressure gauge on the calorifier? If so, it would be interesting to do some tests to see what actually happens when the isolated system is heated up.

 

Also, are there any ASME VIII people (if we are going to look at this, at least get it done properly) out there who would like to work out the increased volume of the calorifier itslf as the pressure increases? I did some calcs, but the answer seemed to be too small (I'm not a vessel design person).

 

Chris G

 

Chris G,

 

I did some basic calcs and the expansion of the calorifier itself has some impact from 2 viewpoints.

 

1. The increase in pressure from cold at say 30psig to hot at say 45psig if the calorifier was designed for 45psig would expand by less than 0.1% on volume, this is because the design stress from PD5500 (rather than ASME VIII) is around 51Mpa and Young's Modulus is 115GPa, four orders of magnitude difference so little actual expansion. Thus I agree with your view that it is very small. Even at the point of yield copper will only expand by 0.5% linearly (1.5% on calorifier volume), which is when it will be permanently deformed.

 

2. The calorifier itself expands by about 0.33% in volume during heating up from 20°C to 85°C compared to the water expanding by about 3%. Makes an effect but hardly a dominant one.

 

i.e., if a 60l calorifier requires 1.83l of extra water volume from 20°C to 85°C (from my physical properties tables water expansion = 3.04% over this temperature range), then 0.24l is taken up by the calorifier warming up and expanding and the increased interla pressure also causing it to swell further (but elastically, i.e. it will return to originla size on depressurisation). Therfeore, expansion vessel has to take up 1.59l of water, a small change. Therefore, expansion lies elsewhere.

 

 

Other effects.

 

1. There may well be air trapped at the top of a horizontal calorifier because the internal tube will not be exactly at the top. I have previously reported I used to have a horizintal calorifier without an EV. The calorifier had the outlet tube slightly to one side so had a large amount of stored air and never dribbled from the PRV. I had an NRV direct on the calorifier inlet. The hot taps did not drip and I had not found any plumbing leaks.

 

Now some people argue that this air pocket should dissolve with time on line into the water. Hwoever, I believe that this may well be a fallacy because as you warm water up the solubility of air in water reduces. Also, the water as supplied is already contains a lot of air, especially on a boat where we tend to use a hose pipe to balst the water into a tank, mixing it well with air first. Sometimes water arrives from the water treatment plant saturated with air, how has at times run off a glass of water and seen small air bubbles forming on the inside of the glass. Why do so many creatures go to feed in the arctic waters when they are so cold - because they are so cold they have a high level of dissolved oxygen so plankton etc. can flourish. Back on topic, we charge the calorifier with cold water which contains lots of air and then heat it up which drives off the air. OK argue Henry's law back at me in that the water in the calorifier is under pressure and the pressure will hold more of the air in solution at the higher pressure. Yes agreed, but reduction in solubility due to increased temperature is a larger effect than the increase in solubility due to increased pressure. Additionally, oxygen is soluble in water but nitrogen is much less soluble in water and close to 80% of the air is nitrogen. I am happy to believe that a horizontal unit may well contain some air permanently at the top but a vertical one probably will not.

 

2. There is also the plastic pipework that many of us use now, but this is such a small volume as to be insignificant, at most there would only be 2l of liquid in this so offering limited expansion potential.

 

3. Water compresibility - forget it, increasing pressure from 30 to 45psig would reduce water volume by 0.005% or 0.003litres in our 60l calorifier example (less than a teaspoon).

 

PeterF.

Edited November 13, 2008 by PeterF

[chris w]

Chris G,

 

 

2. There is also the plastic pipework that many of us use now, but this is such a small volume as to be insignificant, at most there would only be 2l of liquid in this so offering limited expansion potential.

 

3. Water compresibility - forget it, increasing pressure from 30 to 45psig would reduce water volume by 0.005% or 0.003litres in our 60l calorifier example (less than a teaspoon).

 

PeterF.

 

So, and especially if one has a vertical calorifier as I do, ChrisPy's assertion that it's all down to the plastic pipes seems a bit far fetched?

 

Chris

 

 

Right, phone up the manufacturer of your calorifier and ask for their technical support department. Then ask what's the recommended expansion vessel size for the calorifier. Job done!

 

cheers,

Pete.

That's exactly what I did. 8 litre EV precharged to 35psig.

 

Now show me the maths. Rather than throwing mud around, why do you not simply do your maths and show why my system works yet (using my maths and ChrisPy's maths) it shouldn't. Throwing your toys out of your pram is not the answer.

 

I would genuinely like to know what the missing maths factor is... I really would. I'm not trying to score points - I want to know from an engineering perspective.

Edited November 13, 2008 by chris w

[Gibbo]

Well, do you agree with it, or not?

 

I haven't considered it. I haven't tried it. I haven't even clicked the link for it.

 

I have no idea what size EV is needed for any particular tank. Not a damned clue. I just asked the bloke in the office next door who runs a heating company and he's gonna work it out for me.

 

Gibbo

[Batavia]

1. The increase in pressure from cold at say 30psig to hot at say 45psig if the calorifier was designed for 45psig would expand by less than 0.1% on volume, this is because the design stress from PD5500 (rather than ASME VIII) is around 51Mpa and Young's Modulus is 115GPa, four orders of magnitude difference so little actual expansion. Thus I agree with your view that it is very small. Even at the point of yield copper will only expand by 0.5% linearly (1.5% on calorifier volume), which is when it will be permanently deformed. I got about 0.1% for this, treating the calorifier as an axially unconstrained length of pipe, but this seemd a bit small and consequently I was reluctant to float the figure in case it was wildly out. Good to know that there is a vessel designer out there!

 

Your arguments are impeccable and I would suggest that a passing NRV might have some role to play, given that we are rapidly running out of other options, apart from "air in the system". I have experience of air dissolving in white oils under pressure, but it takes (a) reasonable pressure (say 10+ barg) and ( time for it to happen - and I have no experienec of water/air combinations (water being something we generally try and keep out of the way).

 

Chris G

 

So, and especially if one has a vertical calorifier as I do, ChrisPy's assertion that it's all down to the plastic pipes seems a bit far fetched?

 

 

I would genuinely like to know what the missing maths factor is... I really would. I'm not trying to score points - I want to know from an engineering perspective.

 

You should not have spurned my offer of a tutorial....

 

The other Chris (who agrees with the other, other Chris)

[ChrisPy]

So, and especially if one has a vertical calorifier as I do, ChrisPy's assertion that it's all down to the plastic pipes seems a bit far fetched?

so sad that you continue to rely on misquotes.

do I have to remind you about Bridget and the 'wrongly' magpies?

[chris w]

So no maths from any of your "team". Sad isn't it.

 

You don't do the maths, because you are also puzzled as to why the result comes out like it does!

 

You have my figures - just work it out and post it. What a chance to prove me wrong.

[Batavia]

So no maths from any of your "team". Sad isn't it.

 

You don't do the maths, because you are also puzzled as to why the result comes out like it does!

 

You have my figures - just work it out and post it. What a chance to prove me wrong.

 

The basic maths for the accumulator and expanding water have been done to death by several people - and the calcs show that there must be other, as yet un-modelled, things going on to explain what has been reported as having been observed. Various other factors have been identified and some of these have been shown, by calculation, to make only an insignificant contribution to the elasticity of the system and hence its ability to absorb presure increases.

 

The world is waiting, with baited breath, for the (ideally witnessed) results of your experiments and measurements, in my case to see what happens from fitting a tight stopcock at the inlet to the calorifier (which will show, in your case, if a passing NRV makes a contribution) and to see at what pressure your TRV actually lifts.

 

Chris G

[chris w]

The basic maths for the accumulator and expanding water have been done to death by several people - and the calcs show that there must be other, as yet un-modelled, things going on to explain what has been reported as having been observed. Various other factors have been identified and some of these have been shown, by calculation, to make only an insignificant contribution to the elasticity of the system and hence its ability to absorb presure increases.

 

The world is waiting, with baited breath, for the (ideally witnessed) results of your experiments and measurements, in my case to see what happens from fitting a tight stopcock at the inlet to the calorifier (which will show, in your case, if a passing NRV makes a contribution) and to see at what pressure your TRV actually lifts.

 

Chris G

At last, someone agrees with me that we are missing a factor in the maths. ChrisPy's attitude was that he had already done the maths and was too above us all to show us the result in public. That's because the result doesn't work.

 

I too am looking forward to my experiment. It may well indeed be a change in PRV pressure to that stated on the label or a leaking NRV. However, I just don't believe that the science of this depends on sub-standard NRV's and incorrectly labelled PRV's. None of the other possible identified factors have been shown by calculation to have any significant effect on the result.

 

There is no shame in the fact we don't know the answer yet........ that's what engineering is about. I find it strange that some so-called "experts" on this topic go on the defensive rather than being curious.

 

Chris

[PeterF]

When I worked for ICI designing chemical processing plants, if we were using NRVs to prevent backflow and needed to calculate the reverse flowrate we had some conservative rules. If we had 1 NRV then we assumed that the reverse flow was the full flow that would occur should the NRV be stuck open. If we used 2 NRVs in series (which had to be of different type and manufacturer to avoid common mode failure) then we would assume that we had a flow area equivalent to 5% of the fully open flow area of one of the NRVs to allow for leakage due to failure to shut off tight and the other NRV was stuck open. I know this is different to plumbing and the consequences of getting this wrong is rather dire on a chemical plant, hence a very conservative approach. I am currently designing and starting up some reactors that inject pure oxygen into a hydrogen / natural gas mixture and combust this at 300 - 600psig (20 - 40barg). We have about 4 layers of protection on the oxygen supply as reverse flow of hydrogen back up the oxygen supply pipe is real no no.

[Batavia]

When I worked for ICI designing chemical processing plants, if we were using NRVs to prevent backflow and needed to calculate the reverse flowrate we had some conservative rules. If we had 1 NRV then we assumed that the reverse flow was the full flow that would occur should the NRV be stuck open. If we used 2 NRVs in series (which had to be of different type and manufacturer to avoid common mode failure) then we would assume that we had a flow area equivalent to 5% of the fully open flow area of one of the NRVs to allow for leakage due to failure to shut off tight and the other NRV was stuck open. I know this is different to plumbing and the consequences of getting this wrong is rather dire on a chemical plant, hence a very conservative approach. I am currently designing and starting up some reactors that inject pure oxygen into a hydrogen / natural gas mixture and combust this at 300 - 600psig (20 - 40barg). We have about 4 layers of protection on the oxygen supply as reverse flow of hydrogen back up the oxygen supply pipe is real no no.

 

Likewise for the piping systems that I design - and practical experience demonstrates time and time again that all designs of NRV that I have encountered do fail in service, with a greater or lesser frequency - which depends on both the service and the quality of the materials and construction.

 

Also, it is important to remember that we are dealing with pretty mickey mouse TRVs and NRVs on most boats - certainly not devices built to the standards that one would encounter in a piping system designed to ANSI B 31.3!

 

Chris G

[Guest TerryL]

Likewise for the piping systems that I design - and practical experience demonstrates time and time again that all designs of NRV that I have encountered do fail in service, with a greater or lesser frequency - which depends on both the service and the quality of the materials and construction.

 

Also, it is important to remember that we are dealing with pretty mickey mouse TRVs and NRVs on most boats - certainly not devices built to the standards that one would encounter in a piping system designed to ANSI B 31.3!

 

Chris G

I quite agree that's why I think a pumped boat system is better without a NRV or at least a good quality one.

[Mac Man]

Jabsco (Cleghorn Waring), also recommend fitting an expansion vessel (such as an accumulator tank normally used after the water pump), to the hot water side of the system, either on the cold water inlet side of the calorifier after the non-return valve (if one is present), or on the hot water outlet side of the calorifier. They sent me a nice diagram with my new waterpump, but unfortunately it's not on their website.

 

 

Sorry to open up this can of worms again, but can anyone advise me which type of expansion vessel to use on the input to the calorifier (after the NRV)?

Should I use the type for a sealed heating systems (usually painted red) or should it be the portable type (usually painted blue or white), the latter which I intend to use as an expansion tank adjacent to the water pump?

 

Thanks Keith

[chris w]

Sorry to open up this can of worms again, but can anyone advise me which type of expansion vessel to use on the input to the calorifier (after the NRV)?

Should I use the type for a sealed heating systems (usually painted red) or should it be the portable type (usually painted blue or white), the latter which I intend to use as an expansion tank adjacent to the water pump?

 

Thanks Keith

You can't go by the colour unfortunately. You need to get one that is specified for HOT water (take a look on Ebay to see the options). I have a 10 litre (red - hot water) expansion tank on my calorifier and a 2 litre (red - cold water) version on my water pump.

 

Chris

[ChrisPy]

You need to get one that is specified for HOT water (take a look on Ebay to see the options).

Chris

why is that important?

- the expansion vessel is on the cold water side,

- we have demonstrated that in operation only a relatively small amount of hot water will be forced out of the calorifier into the expansion vessel where it mixes with cold water.

[chris w]

why is that important?

- the expansion vessel is on the cold water side,

- we have demonstrated that in operation only a relatively small amount of hot water will be forced out of the calorifier into the expansion vessel where it mixes with cold water.

IF the expansion vesel is put on the cold water side, that's correct. But, for example, mine is on the hot water outlet from the calorifier which is the recommended position for an expansion vessel.

 

Chris

[smileypete]

IF the expansion vesel is put on the cold water side, that's correct. But, for example, mine is on the hot water outlet from the calorifier which is the recommended position for an expansion vessel.

 

Maybe recommended, but it doesn't make sense.

 

When you open a hot tap, the now cold water in the expansion vessel comes out before the hot water from the calorifier, wasting water.

 

And it's 'vessel' NOT 'vesel'...

 

cheers,

Pete.

[Guest]

Maybe recommended, but it doesn't make sense.

 

When you open a hot tap, the now cold water in the expansion vessel comes out before the hot water from the calorifier, wasting water.

 

And it's 'vessel' NOT 'vesel'...

 

cheers,

Pete.

Interesting thought.

[alan_fincher]

On the type of pre-plumbed Surecal calorifier I have just fitted, the only place you can put an EV is on the hot take off.

 

This is because the cold feed in incorporates an NRV, right up against the cylinder, so there is nowhere between NRV and syclinder that you could tee into for the EV,

 

Surejust clearly show they expect the EV to be on the hot outlet, despite the reservations that Pete, (probably quite correctly), has about it.

 

When I get to use ours in anger, I'll get a better idea how much cold comes through before the hot, (although obviously some of the cold that comes out is from the pipework, not the EV).

 

Alan.

[Guest]

On the type of pre-plumbed Surecal calorifier I have just fitted, the only place you can put an EV is on the hot take off.

 

This is because the cold feed in incorporates an NRV, right up against the cylinder, so there is nowhere between NRV and syclinder that you could tee into for the EV,

 

Surejust clearly show they expect the EV to be on the hot outlet, despite the reservations that Pete, (probably quite correctly), has about it.

 

When I get to use ours in anger, I'll get a better idea how much cold comes through before the hot, (although obviously some of the cold that comes out is from the pipework, not the EV).

 

Alan.

Yes much the same as mine. I am about to fit an EV in the hot side, to prevent wasting water (the prv currently dribbles when the engine is running). But Pete makes a valid point that an EV may waste water too.

Edited January 24, 2009 by Guest

[Mac Man]

Hi,

 

Sorry to open this can of worms again but can someone give me advice on which type of EV to fit on the calorifier? Can it be one of the type used on domestic boilers (usually painted red) or should it be the same type used adjacent to the water pump - 'portable water expansion vessel' (usually painted blue or sometimes white)?

 

Many thanks. Keith