Accumulator/expansion tank sizing

[Caladh]

I will be replacing and fitting a new 40l calorifier and can’t find information about sizing an accumulator tank. I’m not sure whether I need an expansion tank fitted as well. My fresh water pump is a ParMax 2.9 Jabsco - they say it doesn’t need an accumultor. My current system has neither but the Surecal replacement calorifier advises to have both. Can anyone advise about sizing please ? Ta

 

[PaulRainbow]

I will be replacing and fitting a new 40l calorifier and can’t find information about sizing an accumulator tank. I’m not sure whether I need an expansion tank fitted as well. My fresh water pump is a ParMax 2.9 Jabsco - they say it doesn’t need an accumultor. My current system has neither but the Surecal replacement calorifier advises to have both. Can anyone advise about sizing please ? Ta

Surecal give the expnsion tank sizes on their website, the tank should be 10% of the calorifier capacity, or see here: Surejust > Advice and Troubleshooting

The Surecal calorifiers are fitted with non-return valves in the cold inlet fitting, this stops hot water coming out of the cold tap when you first turn the tap on. It also means there is no-where for the hot water to expand, so it's important to fit an expansion tank. The Surecal warranty is also void if you fai to do so.

I think you'll find a 2 litre accumulator will work fine for you.

 

[VicS]

I think this will help

https://www.jabscoshop.com/files/Accumulator and Expansion Tank Instructions ZPWL4 doc595.pdf

 

[Caladh]

Surecal give the expnsion tank sizes on their website, the tank should be 10% of the calorifier capacity, or see here: Surejust > Advice and Troubleshooting

The Surecal calorifiers are fitted with non-return valves in the cold inlet fitting, this stops hot water coming out of the cold tap when you first turn the tap on. It also means there is no-where for the hot water to expand, so it's important to fit an expansion tank. The Surecal warranty is also void if you fai to do so.

I think you'll find a 2 litre accumulator will work fine for you.

Thanks Paul - always giving good information on the forum.

 

[PaulRainbow]

Thanks Paul - always giving good information on the forum.

My pleasure

 

[VicS]

I think this will help

https://www.jabscoshop.com/files/Accumulator and Expansion Tank Instructions ZPWL4 doc595.pdf

Sorry it does not answer your question about the size of an accumulator but does tell you what the pressure should be and how to size the expansion tank.

Actually the Par max pump has an internal bypass and does not need an accumulator .... In the description they say , "Includes bypass feature to provide smooth, quiet flow. No need for accumulator tank"

 

[Caladh]

Sorry it does not answer your question about the size of an accumulator but does tell you what the pressure should be and how to size the expansion tank.

Actually the Par max pump has an internal bypass and does not need an accumulator .... In the description they say , "Includes bypass feature to provide smooth, quiet flow. No need for accumulator tank"

Yes Vic I am aware of that and when changing the pump 2 years ago I got rid of the accumulator that was there! ....dohhhh.....However the pump has worked flawlessly since BUT Surecal indicate that I need one for their calorifier. For the sake of my sanity I'll will refit one as it's not a big increase in the overall budget.

 

[VicS]

Yes Vic I am aware of that and when changing the pump 2 years ago I got rid of the accumulator that was there! ....dohhhh.....However the pump has worked flawlessly since BUT Surecal indicate that I need one for their calorifier. For the sake of my sanity I'll will refit one as it's not a big increase in the overall budget.

I've read your original post again ... properly this time I hope

If you have a calorifier it's an expansion tank you need , to absorb the expansion which occurs when the calorifier heats the water. Otherwise the pressure relief valve on the calorifier is likely to open every time the water is reheated ( unless there is sufficient air trapped in the calorifier to absorb the pressure )
At least this is so if you have the non return valve in the supply to the hot water system shown in the diagram in my link

if there is no non return valve an accumulator will absorb the pressure, assuming you have an accumulator. If there is no accumulator either the calorifier prv will open. The downside is that there wil be occasions when warm water is delivered by the cold water taps .... perhaps at times, but briefly, very warm/ hot water.

If the Par Max operates satisfactorily without an accumulator I would merely install an expansion tank sized to suit the new calorifier and install the nrv if there is not one already

I don't understand why Surecal say you need an accumulator as well as an expansion tank if you have a pump which does not need an accumulator.

If you still have the old accumulator tank perhaps you could use it as an expansion tank ??????

 

[PaulRainbow]

Sorry it does not answer your question about the size of an accumulator but does tell you what the pressure should be and how to size the expansion tank.

The link in post #2 provides all of this information, from the actual manufacturer of the OPs calorifier. It also states that the Surecal tanks come pre-set.

 

[PaulRainbow]

I've read your original post again ... properly this time I hope

If you have a calorifier it's an expansion tank you need , to absorb the expansion which occurs when the calorifier heats the water. Otherwise the pressure relief valve on the calorifier is likely to open every time the water is reheated ( unless there is sufficient air trapped in the calorifier to absorb the pressure )
At least this is so if you have the non return valve in the supply to the hot water system shown in the diagram in my link

if there is no non return valve an accumulator will absorb the pressure, assuming you have an accumulator. If there is no accumulator either the calorifier prv will open. The downside is that there wil be occasions when warm water is delivered by the cold water taps .... perhaps at times, but briefly, very warm/ hot water.

I already explained why the expansion tank is needed, as have Surecal. I also explained that the Surecal calorifiers are fitted with no-return valves and failure to fit an expansion tank invalidates the warranty.

The PRV is not there to routinely act as a pressure relief device, it is there as a safety feature and is a legal requirement. For routine expansion due to heating the water, an expansion tank is required when using Surecal calorifiers.

If the Par Max operates satisfactorily without an accumulator I would merely install an expansion tank sized to suit the new calorifier and install the nrv if there is not one already

It's my experience that the system is smoother with an accumulator, even the Par Max pumps. Surecal calorifiers are all fitted with PRVs, see above.

I don't understand why Surecal say you need an accumulator as well as an expansion tank if you have a pump which does not need an accumulator.

They say you must have an accumulator:

"An accumulator tank is usually necessary, we would advise the installation of an accumulator tank as it will help look after the pressure pump and provides a small volume of water to use before your pump kicks in. "

If you still have the old accumulator tank perhaps you could use it as an expansion tank ??????

He needs a 5 litre tank, seems unlikely that the old accumulator will be big enough.

 

[VicS]

Yes Vic I am aware of that and when changing the pump 2 years ago I got rid of the accumulator that was there! ....dohhhh.....However the pump has worked flawlessly since BUT Surecal indicate that I need one for their calorifier. For the sake of my sanity I'll will refit one as it's not a big increase in the overall budget.

I have now looked at the instructions for fitting Surecal calorifiers on their website. It does not say anything there about needing an accumulator but is does state than an expansion vessel should be fitted.

Perhaps fit an accumulator as well if the Par max does not deliver a steady enough flow for a shower.

 

[RupertW]

I have now looked at the instructions for fitting Surecal calorifiers on their website. It does not say anything there about needing an accumulator but is does state than an expansion vessel should be fitted.

Perhaps fit an accumulator as well if the Par max does not deliver a steady enough flow for a shower.

Our accumulator rusted through about 5 years ago so I bypassed it then got professionals to fit a new tank amongst other jobs over Winter. It took me about a month to notice they had carefully left it bypassed too and it’s been prettily sitting there since as it works fine for hot and cold water although the pump does come on after 5 seconds of taps running rather than 15. But at least there is no sudden pump running every few hours when no taps are. I suspect we have so much piping that it is naturally expanding a tiny bit in each pipe as the pressure pump builds.

 

[PaulRainbow]

I have now looked at the instructions for fitting Surecal calorifiers on their website. It does not say anything there about needing an accumulator but is does state than an expansion vessel should be fitted.

Perhaps fit an accumulator as well if the Par max does not deliver a steady enough flow for a shower.

Obviously smoking some strange substance.

 

[Caladh]

All very enlightening!

 

[PaulRainbow]

All very enlightening!

This thread is a great example of someone with no actual knowledge of the subject matter Googling answers. It has a tendency to cause confusion. All of the "if it has a PRV", "if it has a NRV", "if it needs this", or "needs that". From someone who didn't even consult the manufacturers website during the course of his Googling, until post #11, and even then incorrectly stating that there is no mention of needing an accumulator, despite my direct quote in post #10

Surecal are my go to supplier of calorifiers, expansion tanks and accumulators. So, just to summarise:

Your calorifier will:

• Be fitted with a pressure relief valve, as required by law.
• Be fitted with a thermostatic mixer valve on the hot outlet. This allows the engine or the immersion element) to heat the water to a high temperature, but have water at the hot tap at a temperature that cannot scald.
• Be fitted with a non-return valve in the cold inlet. This is fitted to a specially machined inlet fitting, if you change the pushfit fitting to a hosetail, you lose the non return valve.
• Need an expansion tank. 5 litres is the correct size for you calorifier.
• The accumulator is optional, in all installations. With a pump that has no bypass the pump will cut in and out and the water at the tap will surge. Pumps with bypass circuits should not surge at the tap, but the pump will usually run all of the time the tap is on. The accumulator stops the surging at the tap, reduces the pump cycling of non bypass pumps and stops the bypass pumps continuously running.

The above relates to current Surecal products, not every product is the same and older systems vary a lot. For instance, ASAP "Hotpot" calorifiers are actually Surecal. They come in a Surcal box and are painted blue, with "Surecal" labels. There are a couple of differences though. The cold in and hot out fittings are not pushfit, they are barbed hosetails, annoying when you are fitting to a pushit system and you have to go and buy fittings. Also, the cold inlet fitting does not have a non return valve, so you get hot water coming from the cold tap when it is first turned on. I'll stick with Surecal.

 

[Hoolie]

Another additional benefit of a thermostatic mixer valve is that you get more hot water than your calorifier contains. For example if your calorifier is at 80deg, your hot water supply is set at 50deg and the cold water is at 20deg your hot water system will provide double the volume in your calorifier. Hence why we have only a 15litre calorifier for 30litres of hot water.

 

[RichardS]

Another additional benefit of a thermostatic mixer valve is that you get more hot water than your calorifier contains.

Unless you quantify the relative temperature of the hot water at the end point, it rather sounds as if you are defying the laws of thermodynamics.

Richard

 

[Hoolie]

In my example above I suggested 50deg at the hot taps, derived from equal volumes of water at 80deg and 20deg. Hardly advanced physics. Even better if you can settle for 45deg.

 

[pvb]

In my example above I suggested 50deg at the hot taps, derived from equal volumes of water at 80deg and 20deg. Hardly advanced physics. Even better if you can settle for 45deg.

I've no idea what precise temperature my thermostatic valve is set to; I simply adjusted it until the shower wasn't too hot. Even with our quite small 20 litre calorifier it certainly ensures an adequate supply of hot water - my wife and I can both shower in the morning (separately!) and not run out of hot water, and my wife spends ages in the shower.

 

[RichardS]

In my example above I suggested 50deg at the hot taps, derived from equal volumes of water at 80deg and 20deg. Hardly advanced physics. Even better if you can settle for 45deg.

Apologies. somehow I missed the temperature data, although I'm still not sure that you'll ever be able to "get more hot water than your calorifier contains." The best you can ever do is get exactly the amount of hot water your calorifier contains .... albeit mixed with more or less cold water.

Richard