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ivan&alice

Hot water circuit design

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As I have to replace my calorifier and I have a new stove with a backboiler, I have been re-thinking my hot water system and I thought I'd ask the forum for comment.

 

I'm considering a re-circulating hot water system to reduce wasted water as we wait for the hot taps to get hot, as I'm circulating water for the rads anyway.

 

I know that rads usually have a "coolant" and corrosion inhibitor in the water they circulate, so using "fresh" hot water for this purpose poses a problem that I propose to solve by using copper finrads or simply bare copper pipe.

 

I would use a large 22mm bore pipe for the hot water feed, with the hope that it would circulate some with gravity alone. I'll also raise the calorifier up a metre off the ground to increase water pressure. If I insulate the top feed (in red) (that I would run nice and high right in my roof) and I don't insulate the return feed or rads (in orange, to show cooling) I'm hoping that this would drag the water around.

 

If not, I plan to include a pump in parallel with a non return valve on the return feed, so that I can turn it on to circulate the water faster if necessary.

 

For super redundancy, I want a custom made calorifier that has three coils - one for the engine, one for the Eberspaecher and one for the backboiler. This way I can heat water (and hence boat) with either diesel, coal or just from cruising. I'll also add an immersion heater that I can drive from solar in the summer.

 

Any thoughts on this idea? Some questions:

  1. Will the NRVs inhibit the gravity circulation?
  2. Is there a problem with copper pipes work hardening (and eventually splitting) on the boat due to vibration?
  3. What's the benefit of having each heating circuit independent? Or what if I shared a coil between the Eber and the backboiler?
  4. Can the three circuits share a header tank?
  5. Safety considerations for the backboiler in particular - do I need PRVs on that circuit?
  6. Will my idea to have a pump and NRV valve in parallel work? I don't want to have to waste power circulating water if I don't have to.

 

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You really are determined to fight convention and eliminate any tried and tested narrowboat practices aren't you. Nothing wrong with bucking a trend now and then or thinking outside the box, but every trend and every box? :icecream:

 

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37 minutes ago, Sea Dog said:

You really are determined to fight convention and eliminate any tried and tested narrowboat practices aren't you. Nothing wrong with bucking a trend now and then or thinking outside the box, but every trend and every box? :icecream:

You're right, I should be asking what is the correct way to plumb a calorifier.

Edited by ivan&alice

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I think you're running tap water through the radiators with no inhibitor or antifreeze? Doesn't sound like a good idea. What happens when it's cold and you're away?

  • Greenie 1

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4 minutes ago, Onewheeler said:

I think you're running tap water through the radiators with no inhibitor or antifreeze? Doesn't sound like a good idea. What happens when it's cold and you're away?

Hmm, good point. But isn't that the same problem with normal hot and cold pipes? What is the difference if it runs through a radiator?

 

Yes if we went away for long we'd have to have the system on a timer or drain it.

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9 minutes ago, ivan&alice said:

What are you talking about? What trends am I bucking?

I don't know the correct or best way to plumb a calorifier. That's why I am asking. If that bothers you, you don't need to comment on every post.

See the ice cream thing? I put that there as an indication of the somewhat tongue in cheek nature of my comment. :)

 

If it helps, I do indeed resist commenting on many of your posts, mostly because I've gained the impression that many of them start with your 'from scratch', frequently off the wall idea (not always a bad thing) rather than looking for the tried and tested method (often a good thing).  It was the appearance of another post which was rather (to me  at least) "off the wall" which cause me to smile and share my observation with you, thinking it make you smile too.  Clearly, my idea was also "off the wall"! :D

 

Enjoy your plumbing - always one of my favourite bits as it gives such instantly rewarding results when it's done right.

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Just now, Sea Dog said:

See the ice cream thing? I put that there as an indication of the somewhat tongue in cheek nature of my comment. :)

 

If it helps, I do indeed resist commenting on many of your posts, mostly because I've gained the impression that many of them start with your 'from scratch', frequently off the wall idea (not always a bad thing) rather than looking for the tried and tested method (often a good thing).  It was the appearance of another post which was rather (to me  at least) "off the wall" which cause me to smile and share my observation with you, thinking it make you smile too.  Clearly, my idea was also "off the wall"! :D

 

Enjoy your plumbing - always one of my favourite bits as it gives such instantly rewarding results when it's done right.

Oh sorry, I didn't know the meaning of the ice cream thing. I apologise I got the wrong impression.

 

You're perhaps right that I need to think more about what the "tried and tested way" is rather than thinking from scratch. I'll keep this in mind in future.

 

 

  • Happy 1

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I think this but others will know more

1. Yes - only the one in the circuit

2. Not if they are properly fixed

3.If one fails does not effect the others and different pressure/temp requirements - engine is pressurised, back boiler vented to air?

4.Not a good Idea

5. Better to have back boiler vented to outside air  pressure maybe a failsafe PRV in my opinion with a high header tank.

6. You don't seem to have any way of controlling the pump and it will act as its own one way valve. Depending on the pump.

I don't think thermo -syphon will work on its own unless you are very lucky and if you use a small circulating pump you can use smaller bore pipe.

you might well need a circulation pump on the boiler primary as well. All depends on the physical layout.

 

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Just now, ivan&alice said:

Oh sorry, I didn't know the meaning of the ice cream thing. I apologise I got the wrong impression.

 

You're perhaps right that I need to think more about what the "tried and tested way" is rather than thinking from scratch. I'll keep this in mind in future.

 

 

No worries Ivan. :)

 

I have quite a wide house and the long run between the boiler and far end bathrooms means the hot water takes an age to come through. It always seems such a waste but practically speaking there is little that can be done without a nearer source. On the boat, the hot water is virtually instant in comparison, although on blessed with a centrally located calorifier. Have a look at @tonybTony Brooks' web pages at TB Training - I'd be surprised if there isn't a very clear layout there. 

 

Good luck! :)

 

 

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10 minutes ago, ivan&alice said:

Hmm, good point. But isn't that the same problem with normal hot and cold pipes? What is the difference if it runs through a radiator?

 

Yes if we went away for long we'd have to have the system on a timer or drain it.

Radiators are designed to transfer heat and so will freeze more easily. Pipes can be insulated. You'd have to insulate them anyway if you propose a recirc system. That alone will increase heat loss and battery drain under normal operation. Radiators are also usually steel so will corrode. Dunno about finrads. It would be a right PITA to have to drain the whole system and refill it regularly and bleed it all.

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Impractical.

 

To use direct circulation of domestic hot water, every single component and part thereof has to be bronze or pure copper.  Even brass will fail due to dezincification.

That includes all pumps, valves, fittings, unions, radiators and pipes. Horrendously expensive and difficult.

The heat losses alone would make it inefficient energy wise. Insulation will only conserve heat up to a point, there are always losses.

Tell be how your expansion tank up against the ceiling is to be fill and vented. (and prevented from freezing)

Put the idea where it belongs, back in the box. 

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12 minutes ago, Boater Sam said:

To use direct circulation of domestic hot water, every single component and part thereof has to be bronze or pure copper.

Why is this - does the hot water corrode the pipes away faster? What about plastic pipes like I currently have?

As far as I'm aware hot water recirculation is becoming fairly common on land - do all these systems use bronze or pure copper?

15 minutes ago, Boater Sam said:

The heat losses alone would make it inefficient energy wise.

But considering that I'm using the system for heating, the heat will be lost into the cabin, which is what I want! And in summer, I could turn off the recirculation and then simply use it like a "normal" non-recirculating system.

17 minutes ago, Boater Sam said:

Tell be how your expansion tank up against the ceiling is to be fill and vented. (and prevented from freezing)

I'm not sure what you mean here - are you saying that having the expansion tank higher than usual will make it more likely to freeze? Surely the warm air in the cabin will rise and make it warmer?

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Why passing fresh water through your heating is a bad idea.

 

Copper and steel in contact will create a galvanic corrosion cell, so to prevent corrosion you must use corrosion inhibitors, to avoid frost damage it is normal to add antifreeze to a boat closed system as well.  Hence the use of coolant.

 

Steel rads will always rust internally the rust will jam up your thermostatic (eg shower) valves.

 

Corrosion also needs oxygen, on a closed system, the small amount of oxygen in the water is soon used up (it makes a film of rust), fresh tap water contains dissolved oxygen, so if you pass hot fresh water through your system you will constantly be bringing fresh oxygen to the exposed steel surfaces inside the rads which will greatly encourage corrosion.


In a hard water area you will deposited scale inside your rads.

 

As an aside, and if I remember correctly - If you use plastic pipe for closed heating systems you must use barrier pipe not the cheap stuff (if you can get it), the purpose of the barrier is to prevent (or greatly reduce) oxygen diffusion through the pipe walls into the recirculating water, otherwise corrosion of steel rads and boiler heat exchangers will be a big problem.

 

 

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Basically everything Chewbacka has just said.

 

If you constantly replace the water inside your radiators with new stuff, (rather than letting the same stuff recirculate all the time), you are going to have massive problems with corrosion, and that will not just cause problems in the bits that corrode, because the result of that corrosion will get circulated and cause problems elsewhere.

 

Bin this idea, and stick with convention - things are generally done the way they are for good scientific reasons.

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I think the heat exchanger in the Eberspacher is aluminium, probably not a good idea with no inhibitor and copper pipes in the system.

 

There may be some merit if you think the waste of water is enough to warrant it to fit a pump in the hot water to taps pipe and    keep that circulating just for the taps but in that case it will take ages to heat up because you would be putting hot recirculated water into the cold,m bottom of the calorifier.

 

All seem too much like overkill to me, why not just heavily insulate the hot pipes so they stay hot.

 

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Above you (Ivan) said “far as I'm aware hot water recirculation is becoming fairly common on land”.  Are you thinking of combi boilers??

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10 minutes ago, Chewbacka said:

Above you (Ivan) said “far as I'm aware hot water recirculation is becoming fairly common on land”.  Are you thinking of combi boilers??

If so they do not circulate domestic hot water.

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18 minutes ago, Tony Brooks said:

If so they do not circulate domestic hot water.

And the domestic water is separated from the radiator water which contains corrosion inhibitors.

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I think it's a non starter. If I understand correctly, your plan is to use the calorifier as a heat store so it will have to be up to temperature before you get heat to the radiators. Normally there will be one circuit for the calorifier and another for the heating. There will surely be times when you want as much heat as possible to the radiators without wasting energy heating the domestic water. The conventional method starts to heat up the radiators immediately rather than having to heat a full tank of water first. 

 

If the main goal is to reduce water loss while waiting for the hot to reach the tap, why not look at creating a hot 'ring' with its own pump and short tails from this to the taps. The pump could just be run for a few moments to get the hot around the ring. Not sure if this is viable or not and it would need an nrv in parallel like you have in your diagram. 

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Before designing a hot water circulation system consider -

 

Even lagged pipes will loose heat, so to keep the tank hot will require more heat in. This may not be a problem.

 

Circulating the water requires a pump, which will take a amp or so, so if you run it for 12hours that could be 15Ah.

 

For me the heat lost and power used is a bigger concern than a few litres of water saved per day.  

 

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It is a common idea that you can prevent fresh water in pipes exposed to cold from freezing by insulating them.  You can't.  You can delay it, but if the cold lasts long enough or is deep enough it will still freeze eventually.  If you insulate well then you can prevent freezing in short or light spells of cold weather.  If you can be certain that this is all you will see, eg by frequent visiting, then fine.  But the main principle is that insulation (short of NASA standards) will not absolutely prevent freezing.

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I feel like there is a crucial point that I'm not making well: There are two systems I need here, one is heating and one is hot water. Installing a hot water based central heating system will require circulating hot water anyway. Lost heat is not "lost" - losing heat into the boat cabin is the goal of the central heating system!

 

Since I'm circulating hot water, I'm wondering if I could find a way to use fresh water in the rads so I can use the same circuit for my hot water taps.

 

Yes it will save a few litres of water, which is appealing because water is my biggest problem on our boat. You also get the convenience of turning on a tap and getting instant hot water - I find I don't use hot water in most cases (e.g. washing hands) simply because I have to wait a few seconds and waste water. So instead I just use cold. Last pro, it's half as many pipes because you don't have two systems in parallel (heating and hot water).

 

But the main reason I'm looking for a solution is this: my old (now defunct) system had the Eberspaecher and rads on one coil, the engine circuit on the other. I could use heat from either the engine or the Eberspaecher to drive the rads. I want to add my back boiler to this system so I can distribute the heat from the stove around the boat. If I can get a hot water recirculatory system for free, why not?

 

3 hours ago, Chewbacka said:

Copper and steel in contact will create a galvanic corrosion cell, so to prevent corrosion you must use corrosion inhibitors, to avoid frost damage it is normal to add antifreeze to a boat closed system as well.  Hence the use of coolant.

 

Steel rads will always rust internally the rust will jam up your thermostatic (eg shower) valves.

 

... bringing fresh oxygen to the exposed steel surfaces inside the rads .. will greatly encourage corrosion.

 

3 hours ago, alan_fincher said:

If you constantly replace the water inside your radiators with new stuff, (rather than letting the same stuff recirculate all the time), you are going to have massive problems with corrosion, and that will not just cause problems in the bits that corrode, because the result of that corrosion will get circulated and cause problems elsewhere.

Isn't the corrosion problem solved quite simply by not using steel radiators? I'm thinking of using copper finrads or just bare copper pipe, with heavily insulated plastic pipe to carry the hot water to the rads and taps.

 

3 hours ago, Chewbacka said:

Above you (Ivan) said “far as I'm aware hot water recirculation is becoming fairly common on land”.  Are you thinking of combi boilers??

No, I'm talking about recirculation. Basically instead of having a pipe that comes out of your hot water cylinder and ends in a tap, you have a circuit that leaves the top of the cylinder, circuits around the house and then rejoins at the bottom of the cylinder. Taps are then spurs off of this circuit.

 

Sometimes this is achieved with a pump, but it can also be done with gravity, by insulating the top pipes and not insulating the return pipes. This does cost a bit of heat. The water doesn't have to move very fast for this to work.

 

I don't know of any system that combines heating and hot water like I'm suggesting, and there are obviously some really good reasons for that - I'm just wondering if any of them might be solvable!

 

2 hours ago, Tony Brooks said:

I think the heat exchanger in the Eberspacher is aluminium, probably not a good idea with no inhibitor and copper pipes in the system.

 

There may be some merit if you think the waste of water is enough to warrant it to fit a pump in the hot water to taps pipe and    keep that circulating just for the taps but in that case it will take ages to heat up because you would be putting hot recirculated water into the cold,m bottom of the calorifier.

 

All seem too much like overkill to me, why not just heavily insulate the hot pipes so they stay hot.

I know very little about galvanic corrosion. The current system has a copper calorifier and Eberspaecher, what's the difference with my suggestion?

 

Yes, I can just have two parallel systems heavily insulated, and that's probably what I will end up doing. My suggestion saves piping, ensures that tap water is immediately hot, and requires one fewer coil in the calorifier.

 

3 hours ago, alan_fincher said:

Bin this idea, and stick with convention - things are generally done the way they are for good scientific reasons.

I realise there are good reasons for running heating and hot water as parallel systems, but I don't think it's a Bad Thing to want to know what they are, is it?

 

1 hour ago, stegra said:

There will surely be times when you want as much heat as possible to the radiators without wasting energy heating the domestic water. The conventional method starts to heat up the radiators immediately rather than having to heat a full tank of water first. 

I think this is the best reason not to go this route, and this explains why the Eberspaecher and the rads are on one circuit.

 

1 hour ago, Chewbacka said:

Circulating the water requires a pump, which will take a amp or so, so if you run it for 12hours that could be 15Ah.

I want to try get the water to circulate with gravity only. I'd use large bore pipes and raise the calorifier. The pump is for in case that idea doesn't work, it's plan B.

 

OK, I accept - everyone has explained why I can't do it this way and that I should do it the conventional way.

 

What IS the conventional way of installing a hot water and central heating system, making use of heat from the engine, Eberspaecher, solar and back boiler?

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10 hours ago, ivan&alice said:

I feel like there is a crucial point that I'm not making well: There are two systems I need here, one is heating and one is hot water. Installing a hot water based central heating system will require circulating hot water anyway. Lost heat is not "lost" - losing heat into the boat cabin is the goal of the central heating system!

 

Since I'm circulating hot water, I'm wondering if I could find a way to use fresh water in the rads so I can use the same circuit for my hot water taps.

 

Yes it will save a few litres of water, which is appealing because water is my biggest problem on our boat. You also get the convenience of turning on a tap and getting instant hot water - I find I don't use hot water in most cases (e.g. washing hands) simply because I have to wait a few seconds and waste water. So instead I just use cold. Last pro, it's half as many pipes because you don't have two systems in parallel (heating and hot water).

 

But the main reason I'm looking for a solution is this: my old (now defunct) system had the Eberspaecher and rads on one coil, the engine circuit on the other. I could use heat from either the engine or the Eberspaecher to drive the rads. I want to add my back boiler to this system so I can distribute the heat from the stove around the boat. If I can get a hot water recirculatory system for free, why not?

 

 

Isn't the corrosion problem solved quite simply by not using steel radiators? I'm thinking of using copper finrads or just bare copper pipe, with heavily insulated plastic pipe to carry the hot water to the rads and taps.

 

No, I'm talking about recirculation. Basically instead of having a pipe that comes out of your hot water cylinder and ends in a tap, you have a circuit that leaves the top of the cylinder, circuits around the house and then rejoins at the bottom of the cylinder. Taps are then spurs off of this circuit.

 

Sometimes this is achieved with a pump, but it can also be done with gravity, by insulating the top pipes and not insulating the return pipes. This does cost a bit of heat. The water doesn't have to move very fast for this to work.

 

I don't know of any system that combines heating and hot water like I'm suggesting, and there are obviously some really good reasons for that - I'm just wondering if any of them might be solvable!

 

I know very little about galvanic corrosion. The current system has a copper calorifier and Eberspaecher, what's the difference with my suggestion?

 

Yes, I can just have two parallel systems heavily insulated, and that's probably what I will end up doing. My suggestion saves piping, ensures that tap water is immediately hot, and requires one fewer coil in the calorifier.

 

I realise there are good reasons for running heating and hot water as parallel systems, but I don't think it's a Bad Thing to want to know what they are, is it?

 

I think this is the best reason not to go this route, and this explains why the Eberspaecher and the rads are on one circuit.

 

I want to try get the water to circulate with gravity only. I'd use large bore pipes and raise the calorifier. The pump is for in case that idea doesn't work, it's plan B.

 

OK, I accept - everyone has explained why I can't do it this way and that I should do it the conventional way.

 

What IS the conventional way of installing a hot water and central heating system, making use of heat from the engine, Eberspaecher, solar and back boiler?

Pray tell me where you will buy a bronze 12v DC pump from?

 

Years ago there were copper radiators/towel rails made for use on direct hot water systems when back boilers were common. The back boilers were also copper or glass lined cast iron and they still corroded eventually Hot water full of fresh oxygen in a mixed metal system will cause galvanic corrosion like you would not believe possible.

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10 hours ago, ivan&alice said:

OK, I accept - everyone has explained why I can't do it this way and that I should do it the conventional way.

 

What IS the conventional way of installing a hot water and central heating system, making use of heat from the engine, Eberspaecher, solar and back boiler?

 

I doubt there is a single "conventional way".  Also solar water heating is far from conventional on a boat and as  far as that is concerned do you intend to use solar for just hot water, space heating, or both? If you say space heating or both then you add another level of complication involving heat exchangers and pumps.

 

The most common and simplest way if we ignore solar for a while would be a three coil calorifier with the stove only space heating via the air but I can see no reason why a stove and Eberspacher can't both use the same calorifier coil providing you fit sufficient bleed points at any air traps. If you ensure at least one calorifier coil has a decent bore then the stove could circulate by gravity, especially if its the top coil of a vertical calorifier. The  Eberspacher is pumped so both should co-exist as long as you turned the Eberspacher off before it potentially overheated from the stove and cut out. Personally I doubt you can get reliable gravity solar circulation on a narrowboat because the collectors (of whatever sort) would give too much air draft if angled to permit gravity circulation so there will need to be a another circulating pump. If you want just solar hot water then given a large enough header tank plus a natural drain down solar collector then the solar could share the stove/Eberspacher coil but you will need to ensure the solar pump is controlled to make sure you don't pump hot water through the collectors. However that would contribute little, if anything, to space heating. If you wanted to add then you would need a heat exchanger in the initial vertical pipe leg at the back of the stove so the solar heated the "stove water" thus allowing it to gravity circulate but the solar would still need a pump I think.

 

Anything is possible but as electricity is often the thing boats are most short of I would have thought that minimising the number of pumps running for long periods was of some importance. Your ideas are far from conventional when all put together. Forget solar hot water and it all becomes a lot simpler. If you do go Lithium batteries then once they are well enough charged why not switch the solar electricity to a 12V immersion heater. That way you get space for an extra solar galvanic panel.

 

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15 minutes ago, Boater Sam said:

Pray tell me where you will buy a bronze 12v DC pump from?

 

Years ago there were copper radiators/towel rails made for use on direct hot water systems when back boilers were common. The back boilers were also copper or glass lined cast iron and they still corroded eventually Hot water full of fresh oxygen in a mixed metal system will cause galvanic corrosion like you would not believe possible.

I see - so to minimise corrosion you need:

 

1. Use only a single metal in the system

2. Avoid using steel

3. Minimise oxygen in the water (such as by avoiding fresh water)

4. Add a corrosion inhibitor to the water

5. Avoid hot water if possible

 

Is there anything else that can be done?
 

Note that my old system has 12V pumps, steel tanks, a copper calorifier and an Eberspaecher which @Tony Brooks said has an aluminium heat exchanger. So is the corrosion inhibitor the only thing keeping this system from falling apart?

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