Cylinder Jacket

[nb Innisfree]

We did some experiments with measured amounts of water, 1 litre, 2 litres and 4 litres (at the tap). We just took the first amount from the tap, didn't wait for it to get hot. Anything above about 4 litres had the detrimental effect described.

 

Sounds like we'd better put 15mm back where we have the 22mm pipe if that is going to help.

 

Ignore my last post, I got my sums wrong

 

With 22mm pipe you would draw 3pints off so I can't see that being much of a contributory factor but as you say cold water coming into the cal could be.

 

Can't think of anything else, sorry

[Smelly]

How big is the copper run off the top of your calorifier? In the absence of any water movement i'd wonder whether you've effectively got a radiator attached to the top of the cal that's dissipating heat. It might go to explain the small quantities of water bit; if you were charging enough copper to radiate the heat more effectively away from the tank then might you continue to get radiation of heat once they're charged.

 

If that's feasible even a relatively short run of plastic, along with some lagging, at least as far as where the pipe descends to floor level would insulate it to a good extent.

 

If there's a decent run of copper, maybe into the kitchen, does it stay hot after you've run hot water off?

 

As an aside, our hot water runs into 22mm speedfit pipe after a 900mm flex pipe, we've never had any probs; speedfit is rated way above that in temp terms. i can't remember exactly how much but I remember a reassuring glow when i checked the pipe spec.

Edited August 17, 2009 by Smelly

[LEO]

Hi,

 

Have you insulated the pipes running to and from the calorifier? and also any exposed brass/copper work on top of the cylinder.

 

I found I got more hot water in the mornings from the short squat calorifier positioned on the swim in a previous boat than the taller one positioned on the base plate in the current one, both were insulated by spray foam.

 

Evening use of even hot water adversely affects the availability of hot water in the mornings in both instances.

 

Leo.

[Ray]

The only metal at the top of the cylinder is that which contains all the couplings - the output from the calorifier, the connection to the PRV and the connection with the mixer. Not more than about 9 inches in total and much of it brass couplings/elbows. Everything else is in unclad 15mm or 22mm pipework.

 

Beta have confirmed that the thermostat is doing right, opening at around 70 degrees, whereas SureCal say that the water isn't getting hot enough during the day to overcome the natural cooling that is bound to occur (slowly) overnight.

 

Someone has said that the calorifier will lose about 1 degree per hour. If the temperature starts at 70 degrees at (say) 6pm, it will naturally be down to 57 degrees by 7am the following morning. If that 1 degree loss per hour is nearer 1.5 degrees, then we're down to around 50 degrees by 7am. If the injection of cold water, to replace the hot drawn off for washing up during the evning, were to reduce the ambient temperature by another couple of degrees not long after the angine stops, that 50 degrees could be down as low as 45 degrees.

 

We've actually measured the morning temperature at a little under 40 degrees.

 

Increase the engine temperature to around 85 degrees and/or reduce the heat loss, by whatever means, to 1 degree per hour and the morning water temperature could still be hovering around 70 degrees.

 

If a cylinder jacket could reduce the heat loss by just 0.2 degrees, the morning temperature would be 6 degrees higher.

 

Or perhaps I simply have the maths wrong.

 

All I know is that the water temperature in the morning is too cool for me to shower/wash up after breakfast, and the latter is unhygenic.

Edited August 18, 2009 by Ray

[LEO]

The only metal at the top of the cylinder is that which contains all the couplings - the output from the calorifier, the connection to the PRV and the connection with the mixer. Not more than about 9 inches in total and much of it brass couplings/elbows. Everything else is in unclad 15mm or 22mm pipework.

 

 

Hi,

 

I still try to insulate these fittings as much as possible, and the HW pipework, as has been stated previously - a small amount out of the HW tap equates to a fair volume from the calorifier.

 

Do you have a big brass immersion heater blanking off fittings exposed.

 

Leo

[denboy]

since i fitted a pressure reduction valve to my pump set at 1.3 bar instead of the 3 bar its supposed to be i have found that water stays hotter longer,might be worth a try

[Ray]

A Pressure Reducing Valve like this?

 

I must admit that I thought of trying this idea as well. How did you settle on 1.3 bar?

 

We haven't got an expansion tank on the outlet, nor non return valve on the cold water input. We suspect that the accumulator is doubling as the expansion tank. I wonder if this makes any difference?

 

We don't think that the calorifier has an inbuilt NRV as the PRV (Pressure Release Valve) only trips when we test it.

Edited August 18, 2009 by Ray

[alan_fincher]

We haven't got an expansion tank on the outlet, nor non return valve on the cold water input. We suspect that the accumulator is doubling as the expansion tank. I wonder if this makes any difference?

 

We don't think that the calorifier has an inbuilt NRV as the PRV (Pressure Release Valve) only trips when we test it.

Ray,

 

I believe this is one of she standard pre-plumbed SureJust/SureCal units, cased in blue covered foam ?

 

Unless they have changed them, I believe all have a non-return valve on the cold input.

 

It's not entirely obvious, as it is buried in the fitting you make the connection to.

 

Curiously it is no longer referred to in the manufacturers brochure, but web sellers of these calorifiers, (e.g. KingsLock chandlery), list it as having this feature.

 

You should be able to prove it by disconnecting the cold feed pipe. If there is a NRV present, then the calorifier contents will not drain out when you try this.

 

If I'm right, your accumulator cannot act as an expansion vessel. SureJust are quite clear in the documentation for these calorifiers that you need to fit a hot water expansion vessel. Presumably this is because they know that the NRV prevents pressure being relieved via the cold inlet and an accumulator.

 

What surprises me is that your PRV doesn't leak as the water heats. I believe the Horizontal ones do have air space at the top that may allow some expansion, but I'd not expect this to be the case with a vertical one.

 

I'm tempted to think that if your PRV doesn't open, it is just a further symptom that the water isn't being heated enough in the first place.

 

Personally I'd be fitting a higher temperature stat to the engine, (and keeping the old one to put back in the event of any warranty issues). It's hard to understand why a modern engine should not have a stat of 80 degrees plus by default, (even our BMC has that).

 

I'm also persuaded that you really should have an EV - but that argument has been done to death on here many times. Personally we have accumulator (cold side) NRV (cold feed) and EV (hot side), and it works a treat.

[RLWP]

Someone has said that the calorifier will lose about 1 degree per hour. If the temperature starts at 70 degrees at (say) 6pm, it will naturally be down to 57 degrees by 7am the following morning. If that 1 degree loss per hour is nearer 1.5 degrees, then we're down to around 50 degrees by 7am. If the injection of cold water, to replace the hot drawn off for washing up during the evning, were to reduce the ambient temperature by another couple of degrees not long after the angine stops, that 50 degrees could be down as low as 45 degrees.

 

We've actually measured the morning temperature at a little under 40 degrees.

 

Increase the engine temperature to around 85 degrees and/or reduce the heat loss, by whatever means, to 1 degree per hour and the morning water temperature could still be hovering around 70 degrees.

 

If a cylinder jacket could reduce the heat loss by just 0.2 degrees, the morning temperature would be 6 degrees higher.

 

Or perhaps I simply have the maths wrong.

 

There is a bit of a problem with the maths in that this isn't a linear relationship. Heat is lost by temperature difference, the bigger the difference the faster the loss. So a cylinder at 85C will lose heat faster than one at 70C. Whether that's enough to make a difference is another matter.

 

I'm a bit puzzled by your NRV and expansion vessel. If the NRV is on the cold inlet and the expansion vessel after the NRV I'm happy. I was just wondering if the expansion vessel was pushing hot water back down the cold inlet when a cold tap was opened...

 

Richard

[Ray]

Alan

 

It is a SureCal vertical calorifier and may well have an NRV on the input. All I know is that we haven't added one externally on the supply side of the cylinder.

 

I've been toying with the idea of fitting the expansion vessel and even got the costs somewhere here. Originally the outlet via the PRV drained into a pot under the stern gland but that was a pain to empty without removing the engine room floor so I re-routed it to drain into a plastic milk bottle mounted on the bulkhead wall. I've never found any liquid in the milk bottle except when we test the PRV manually.

 

Like you I'd expect to see some "expanded" water in the bottle if there was an NRV on the inlet.

 

The water is getting hot enough when the engine is running as we can easily get two showers out of the tank if we shower as soon as we moor up.

 

BTW our documentation for the calorifier only states that an expansion vessel is recommended.

 

Richard

 

We don't have an expansion vessel. The only capabilities for expansion is for the water to back up to the accumulator as it isn't escaping via the PRV but I'm not aware of noticing the cold feed getting warm as a result of this although there about 10ft of 15mm pipe for the expanded water to sit between the calorifier inlet and the nearest tap.

 

-----

 

I'm going to try a pressure reduction valve on the inlet and see if that makes any difference. I'd been wondering if the pressure on the inlet was forcing the cold too high up the cylinder and cooling the warm water before Den said anything so it is probably worth a try. If it doesn't make any difference we've only lost £20 and can always adjust the outlet pressure back to the equivalent of what it is now.

 

-----

 

Thanks for all the ideas on this. We haven't ruled out the possibility of changing the thermostat either but that may well be a last resort.

[RLWP]

You have no expansion vessel, but your PRV doesn't open. You know that the water is going up to 70C.

 

Have you got a massive amount of air trapped in the calorifier? That would allow for expansion, hold not much water which would cool down quick and be easily "diluted" with cold.

 

Richard

[nb Innisfree]

You have no expansion vessel, but your PRV doesn't open. You know that the water is going up to 70C.

 

Have you got a massive amount of air trapped in the calorifier? That would allow for expansion, hold not much water which would cool down quick and be easily "diluted" with cold.

 

Richard

 

Only way to check this would be to see if air exits hot outlet? it would be forced to do this as there is no other route for escape, how air could be getting in though is a mystery. If it is, an auto air valve on cal outlet would cure this, I have one (for other reasons) and it works fine, totally reliable and trouble free.

 

Could it be that when hot water is drawn off in the evening a negative pressure is created in cal, pulling air back in from hot outlet?

Edited August 19, 2009 by nb Innisfree

[Ray]

We've measured the coolant water temperature after we stopped the engine. that was just 70 degrees after a couple of hours cruising.

 

I don't think there is air in the cylinder as the water outlet is at the very top and we always get water, not air, when we open the taps.

 

That's what makes me think that there isn't an NRV on the supply (and we haven't put one there).

 

Admittedly though it is very seldom that we cruise for long periods without someone running some hot water off. This would zero the pressure and, by then, the temperature is probably up to 70 degrees and doesn't get any hotter, so no more expansion.

 

The milk bottle drain is a recently modification and we haven't done any significant cruising since we fitted it. We did used to get some water in the pot under the stern gland and we thought that was from the PRV when the overflow was routed there.

 

We do have the odd blip of the water pump during the evening and this could be the water contracting and drawing more into the cylinder. Because it is only occasional, it implies that the accumulator is being used as an expansion vessel, with no NRV on the feed to the cylinder. I have got a spare NRV and could fit that in the feed to prove the point.

[RLWP]

Ray, would it be possible to post some photographs of your installation?

 

Richard

[mayalld]

Having browsed through the information on this thread, it doesn't strike me that we are seeing anything particularly odd.

 

Any figures that you have on cool-down rate will be a fudge, an average.

 

When the tank is hotter, it will cool down faster than when it is colder.

 

The upshot of this is that if you start with a full hot tank, run off 10 litres (replacing it with cold), and leave for 10 hours, you will end up at one temperature. If you run off the 10 litres at the end of the 10 hour period, you will end up with colder water.

 

As others have said, a jacket is not going to make much difference.

 

The things that might help are;

• Hotter thermostat (provide you have an adequate skin tank)
  
• Pressure reduction on the cold water inlet to try and keep the hot and cold water stratified.
  
• A larger tank. If you have a 55l tank, then 5l of washing up water is almost 10% of the hot water used.
  

A 250l tank, 80 degree stat, and a prssure reduction would make things much better.

[alan_fincher]

The things that might help are;

[*]Hotter thermostat (provide you have an adequate skin tank)

A hotter thermostat will not put the skin tank at any greater risk of not being able to cool the engine.

 

I remain surprised if Beta expect a modern industrial engine to run as cold as 70 degrees - it just doesn't sound right, unless there is some oddity with Beta engines not yet explained in this thread.

[Naughty Cal]

Cant comment on the Beta but our Volvo runs at around 65-70 degrees at canal speeds. It does climb to around 80 degrees when given a work out though.

[alan_fincher]

Cant comment on the Beta but our Volvo runs at around 65-70 degrees at canal speeds. It does climb to around 80 degrees when given a work out though.

But it's not keel / skin tank cooled, is it ?

[Naughty Cal]

But it's not keel / skin tank cooled, is it ?

 

Nope.

[Proper Job]

A hotter thermostat will not put the skin tank at any greater risk of not being able to cool the engine.

 

I remain surprised if Beta expect a modern industrial engine to run as cold as 70 degrees - it just doesn't sound right, unless there is some oddity with Beta engines not yet explained in this thread.

70 deg C - I dream of being able to get up to 70 deg C

 

I must get one of those thermo whats-it thingies and see if I can get up to 60 deg some time

[mayalld]

A hotter thermostat will not put the skin tank at any greater risk of not being able to cool the engine.

 

Actually, it will.

 

Let us set a few parameters here;

 

We have a pressurised system, in which the coolant will boil at 110 degrees. If the coolant boils, the engine will sieze in a fairly short time.

 

The engine with the stat closed, not dumping any heat will reach stat temperature fairly rapidly

 

With an adequately sized skin tank, the tank will then be sufficient to keep the coolant at its regulated temperature.

 

With an inadequate skin tank, the tank will cool the coolant somewhat, but not as much as the engine is heating it when running the engine hard.

 

This will result in a steady rise in temperature, even when the stat has opened. perhaps 1 degree for every 10 minutes cruising hard.

 

If the stat opens at 70 degrees, you have 40 degrees before the engine is a goner, so 6 hours 20 minutes.

 

If the stat doesn't open until 80 degrees, then you only have 30 degrees to play with, so 5 hours.

[RLWP]

Actually, it will.

 

Let us set a few parameters here;

 

We have a pressurised system, in which the coolant will boil at 110 degrees. If the coolant boils, the engine will sieze in a fairly short time.

 

The engine with the stat closed, not dumping any heat will reach stat temperature fairly rapidly

 

With an adequately sized skin tank, the tank will then be sufficient to keep the coolant at its regulated temperature.

 

With an inadequate skin tank, the tank will cool the coolant somewhat, but not as much as the engine is heating it when running the engine hard.

 

This will result in a steady rise in temperature, even when the stat has opened. perhaps 1 degree for every 10 minutes cruising hard.

 

If the stat opens at 70 degrees, you have 40 degrees before the engine is a goner, so 6 hours 20 minutes.

 

If the stat doesn't open until 80 degrees, then you only have 30 degrees to play with, so 5 hours.

 

 

The engine isn't doing any more work at 80C than it is at 70c. If the tank can dissipate the waste energy at 70c it will dissipate it better at 80c - bigger temperature difference.

 

Richard

[mayalld]

The engine isn't doing any more work at 80C than it is at 70c. If the tank can dissipate the waste energy at 70c it will dissipate it better at 80c - bigger temperature difference.

 

Richard

 

If the skin tank is inadequate, the coolant will eventually boil.

 

It is self-evident that if the skin tank first starts attempting to dump heat at 70 degrees, it will take longer to reach boiling point than it will if it first starts trying to dump at 80 degrees.

[RLWP]

If the skin tank is inadequate, the coolant will eventually boil.

 

It is self-evident that if the skin tank first starts attempting to dump heat at 70 degrees, it will take longer to reach boiling point than it will if it first starts trying to dump at 80 degrees.

 

Alan said

 

A hotter thermostat will not put the skin tank at any greater risk of not being able to cool the engine.

 

I agree. You are saying that an inadequate skin tank is inadequate. I agree. Two completely different things. Simples

 

Richard

[colin stone]

I remain surprised if Beta expect a modern industrial engine to run as cold as 70 degrees - it just doesn't sound right, unless there is some oddity with Beta engines not yet explained in this thread.

 

Concur. Perhaps there is no thermostat at all??