Calorifier

[smileypete]

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)?

 

It depends if your calorifer has a non return valve in the cold feed, and what the opening pressure of the calorifier's safety relief valve is.

 

If you're not sure of the above, fit a white/blue/£££ marine one intended for potable water supplies, and with a maximum working pressure of 4 bar or more.

 

cheers,

Pete.

[Mac Man]

It depends if your calorifer has a non return valve in the cold feed, and what the opening pressure of the calorifier's safety relief valve is.

 

If you're not sure of the above, fit a white/blue/£££ marine one intended for potable water supplies, and with a maximum working pressure of 4 bar or more.

 

cheers,

Pete.

 

Hi,

There will be a NVR in the cold feed, at th moment all there is a twin heating coils calorifier connected to the engine and the Eberspatcher and a safety valve in the top of the calorifier. The setting of this I think is 35psi? There is no other pipework.

I'm in the process of fitting out the plumbing from scratch. So far got the pipe run from the pump (which is not connected and waiting for a 5L portable water vessel) to the sink mixer tap, with hot and cold feeds from the sink to the bathroom. Thats all I've done so far. At the moment working on fitting the shower tray and pump out drain plus vanity unit.

Any advise is welcome.

 

Cheers Keith.

[chris w]

Any advise is welcome.

 

Cheers Keith.

Once you fit the expansion vessel, set its pump-up pressure to the same pressure as your water pump's cut-OFF pressure, usually around 2 bar (say 28-30psi). Double check your PRV setting as most are around 3 bar (~42psi).

 

Chris

[Rojja]

Once you fit the expansion vessel, set its pump-up pressure to the same pressure as your water pump's cut-OFF pressure, usually around 2 bar (say 28-30psi). Double check your PRV setting as most are around 3 bar (~42psi).

 

Chris

 

Hello Chris,

In the above statement, if you mean 28psi with the water side depressurised, has me confused (easily done), so I'd be pleased if you would explain why.

Thanks in advance.

Roger.

[chris w]

Hello Chris,

In the above statement, if you mean 28psi with the water side depressurised, has me confused (easily done), so I'd be pleased if you would explain why.

Thanks in advance.

Roger.

I went into the formal mathematics of this some weeks ago if you care to do a search. To summarise (and assuming you have an NRV in place between the water pump and the calorifier), most effective use of the expansion vessel is when its internal pressure (as pumped up via a bicycle pump) is equal to the water pump's cut-OUT pressure (which is usually around 2 bar).

 

Just for completion, for the water pump's accumulator this should be set at the water pump's cut-IN pressure (usually around 1.5 bar). The mathematics can be found in the same place. Both of the vessels' pressure should be set with the water system depressurised (ie: water pump OFF, taps open).

 

The difference in these two optimum pressure figures shows why using a single expansion vessel to act as both the calorifier expansion vessel and the water pump accumulator will not result in optimum performance from either and will always be a compromise. The same argument applies if no NRV is used as well (even if 2 separate vessels are used).

 

Chris

[Rojja]

I went into the formal mathematics of this some weeks ago if you care to do a search.

 

Snip

 

Chris

 

Chris and all,

Talk about mssing the bleedin' obvious, I apologise for not 'seeing' the previous postings in this thread!

I'll go away now and get some new glasses.

Cheers,

Roger.

[ChrisPy]

yes, I think that we can all agree that after hundreds of posts on this subject, and the inevitable angst associated with that process, CW is now as well-versed in the mathematics of EVs as any of us.

 

I also have the greatest respect for a Zahada survivor.

[Mac Man]

I went into the formal mathematics of this some weeks ago if you care to do a search. To summarise (and assuming you have an NRV in place between the water pump and the calorifier), most effective use of the expansion vessel is when its internal pressure (as pumped up via a bicycle pump) is equal to the water pump's cut-OUT pressure (which is usually around 2 bar).

 

Just for completion, for the water pump's accumulator this should be set at the water pump's cut-IN pressure (usually around 1.5 bar). The mathematics can be found in the same place. Both of the vessels' pressure should be set with the water system depressurised (ie: water pump OFF, taps open).

 

The difference in these two optimum pressure figures shows why using a single expansion vessel to act as both the calorifier expansion vessel and the water pump accumulator will not result in optimum performance from either and will always be a compromise. The same argument applies if no NRV is used as well (even if 2 separate vessels are used).

 

Chris

 

 

Thanks Chris, info very useful. Mac Man (Keith)

[Ray]

I've found this EV and this mounting bracket which would solve a space problem. We have a 55l Calorifier.

 

Am I correct in thinking that I only need to:

1. turn off water pump and open the hot tap

2. fit the EV in position and install a T junction in the hot water outlet

3. connect the two

4. shut the taps

5. set the pressure on the EV

6. turn the water pump back on

7. check for leaks

 

Any idea what fitting I'd need to connect the (new) pipe to the EV?

[RobinJ]

I've found this EV and this mounting bracket which would solve a space problem. We have a 55l Calorifier.

 

Am I correct in thinking that I only need to:

1. turn off water pump and open the hot tap

2. fit the EV in position and install a T junction in the hot water outlet

3. connect the two

4. shut the taps

5. set the pressure on the EV

6. turn the water pump back on

7. check for leaks

 

Any idea what fitting I'd need to connect the (new) pipe to the EV?

To set it up correctly you will need to know existing pressures (pump, PRV etc.). EV needs to be set to just above cold pump cutoff pressure and below PRV release pressure.

Don't forget that with the taps open, when you cut the pipe, all the water will run out!

Depending on what it is expected to be fitted to (e.g. Combi?) it will probably be either 1/2" or 3/4" BSP fitting, a tap connector should fit?

[alan_fincher]

Ray,

 

An alternative is something like this.....

 

http://cgi.ebay.co.uk/5-litre-expansion-ta...%3A1|240%3A1318

 

More expensive, I know, but the mounting bracket is included, as is a termination that simply allows you to plumb straight on to it with a 15mm push fit fitting. Hard to see an easier installation, if you plumbing is plastic.

 

Personally I feel 5 litres EV is enough for a 55 litre calorifier, but if you want to be completely within Chris W's 10% figure, then they also do an 8 litre model at a couple of quid more. (They are getting pretty big by then!).

 

Robin's point is correct about retrofitting - you are likely to be cutting a hot water pipe lower than the calorifier water level, so unless you have a valve that cuts off output from the tank, you'll need to drain it, to stop it's contents emptying through the cut pipe.

[chris w]

Personally I feel 5 litres EV is enough for a 55 litre calorifier, but if you want to be completely within Chris W's 10% figure, then they also do an 8 litre model at a couple of quid more. (They are getting pretty big by then!).

You're incorrect in your assumptions Alan.

 

It's all to do with Boyle's law which you may be overlooking. It's not just about having a vessel that's large enough to accomodate the expansion, the resultant pressure (after expansion) has to be below that of the PRV or it's pointless putting an expansion vessel on the calorifier anyway because the PRV will still blow.

 

 

Here is the maths for the above statement:

 

 

Take a 5 litre expansion vessel to begin with. Over the temperature range that one is likely to heat water, the expansion will be about 3% maximum. For your 55 litre calorifier that equates to an expansion of 1.6 litres.

 

The expansion vessel pressure needs to be set at the water pump cut-OFF pressure which is typically 2 barg. For Boyle's law we need to work in absolute bar (bara) so we need to add 1 to all the pressure figures.

 

So, for a 5 litre expansion vessel, initially full of air at 2barg (3bara), and then being filled with 1.6 litres of water (ie: 3.4 litres of air now left),

 

we have 5x3 = 3.4xP

 

therefore P = 4.4barg = 3.4bara which will blow your PRV, which is typically set to blow at 3barg

 

However, if we increase the size of the vessel to 8 litres,

 

the equations become: 8x3 = 6.4xP

 

Thus P is now 8 x 3/6.4 = 3.8 bara = 2.8 barg which is BELOW the pressure of the PRV, so the expansion vessel is correctly doing its job.

 

Hence, for a 55 litre calorifier, the minimum expansion vessel size should be 8 litres.

 

Chris

Edited February 4, 2009 by chris w

[alan_fincher]

You're incorrect in your assumptions Alan.

 

It's all to do with Boyle's law which you may be overlooking. It's not just about having a vessel that's large enough to accomodate the expansion, the resultant pressure (after expansion) has to be below that of the PRV or it's pointless putting an expansion vessel on the calorifier anyway because the PRV will still blow.

 

Chris

OK, but that's not my practical experience.

 

I've got the PRV draining through a long plastic pipe into the bilge under the stern tube.

 

The water in the calorifier is reaching the expected temperatures, but nothing is being expelled through the PRV.

 

I can only guess at the internal design of the calorifier, but being a horizontal one, I suspect it could have a pocket of air trapped in the top, higher than the hot take off.

 

So on reflection, I guess it's possible that trapped air is giving me a margin more expansion beyond the quoted capacity of the EV.

 

So I accept that maybe if I had a vertical calorifier, with no trapped air that the EV might be insufficient.

[chris w]

OK, but that's not my practical experience.

 

I've got the PRV draining through a long plastic pipe into the bilge under the stern tube.

 

The water in the calorifier is reaching the expected temperatures, but nothing is being expelled through the PRV.

 

I can only guess at the internal design of the calorifier, but being a horizontal one, I suspect it could have a pocket of air trapped in the top, higher than the hot take off.

 

So on reflection, I guess it's possible that trapped air is giving me a margin more expansion beyond the quoted capacity of the EV.

 

So I accept that maybe if I had a vertical calorifier, with no trapped air that the EV might be insufficient.

1. Do you have a Non-Return Valve (NRV) before the calorifier?

 

2. Do you have an accumulator on your water pump?

 

Also, it may be that your expansion is not quite 1.6 litres, your PRV may have a slightly higher blow point, your expansion vessel may be slightly more than 5 litres in reality.

 

The point is that a 5 litre expansion vessel (as the above maths shows) could be highly problematic if used on a 55 litre calorifier.

 

Chris

Edited February 4, 2009 by chris w

[alan_fincher]

1. Do you have a Non-Return Valve (NRV) before the calorifier?

 

2. Do you have an accumulator on your water pump?

Yes and yes.

 

........although I'm currently trying to work out if the accumulator is actually staying pressurised to what I want it to be.

 

Presumably with the NRV fitted, (assuming it works!), the accumulator is irrelevant as to whether the PRV will leak or not ?

[chris w]

Yes and yes.

 

Presumably with the NRV fitted, (assuming it works!), the accumulator is irrelevant as to whether the PRV will leak or not ?

Quite correct - I was trying to ascertain if your acumulator is also acting partly as a hot water expansion vessel. It won't be if there is an NRV fitted.

 

I can only reiterate what I said above. If your 5 litre expansion vessel is working correctly that's great, but there is an amount of quantity/pressure tolerance and luck involved at that size, as the maths shows.

 

Chris

[Ray]

Chris/Alan

 

Thanks, as always. And thanks to Robin for indicating the obvious which I'd overlooked, about getting the water level down before I break the connection when the taps are open.

 

I've checked the eBay bits and also spoken to Surecal. The 8 litre on eBay is about £2 cheaper than a new one from Surecal and they're both from the same place. I suppose I could bid for the eBay one and try to get it below the BIN price.

 

That puts the Screwfix one at around half the price of the Surecal one(s) and all I need to do is add the connector to the tank and call in (as I pass the door on the way to the boat) to buy it. Is the quality likely to be that much different?

[chris w]

Chris/Alan

 

Thanks, as always. And thanks to Robin for indicating the obvious which I'd overlooked, about getting the water level down before I break the connection when the taps are open.

 

I've checked the eBay bits and also spoken to Surecal. The 8 litre on eBay is about £2 cheaper than a new one from Surecal and they're both from the same place. I suppose I could bid for the eBay one and try to get it below the BIN price.

 

That puts the Screwfix one at around half the price of the Surecal one(s) and all I need to do is add the connector to the tank and call in (as I pass the door on the way to the boat) to buy it. Is the quality likely to be that much different?

Don't forget, on the Screwfix one, you need to factor in the cost of the mounting bracket and any adaptors to get the output connector to what you require on your actual system.

 

Chris

[Ray]

Chris

 

the Screwfix Tank is £18.10 and the Mounting Kit is £7.82. I presume that I only need a tap/push fit connector at about £3 to complete the job (about £28).

 

If I bought the Surecal tank I'd need to pay (almost) £40 plus £8 postage and then need a straight push fit connector at about £3 to connect that to pipe run from the T piece.

 

Don't get me wrong. I'm not adverse to paying the extra but, given that it is a presurised vessel and, thus, has to be to a set build standard, will I get any real benefit?

 

Even if the local Screwfix branch don't have it is stock, I could pay an extra £5 and have it delivered by Friday, whereas Surecal are suggesting 2-3 days delivery. Screwfix trade centres will usually get stock with 24 hours and that saves the £5 (and I can cycle to Screwfix in a few minutes).

[alan_fincher]

Ray,

 

Some points to note:

 

The Screwfix one says "Suitable for heating and cooling systems", but whether "heating system" is the same as use in your hot water supply, I'm not really sure.

 

More worryingly though it says "3 bar maximum". Pressure Relief Valves vary, but many are 3 bar, which means your EV might only be sound up to the stated operating pressure of the PRV. That doesn't sound to have any safety margin in it to me, if they really mean "3 bar max".

 

Personally I'd spend enough to get one that would withstand considerably more pressure than the PRV is intended to operate at, just to have a comfort zone if it were not too well calibrated.

 

It does hack me off though when carriage makes up such a large part of the cost of something I need to buy, (but to be fair, they are pretty heavy....).

[Guest]

I plan to use this one (8 litre one), any comments?

 

http://www.toolstation.com/shop/Heating/Ce...0/sd2708/p29704

Edited February 4, 2009 by Guest

[alan_fincher]

I plan to use this one (8 litre one), any comments?

 

http://www.toolstation.com/shop/Heating/Ce...0/sd2708/p29704

Well at least that one looks good for 4 bar.

 

IIRC you have the same 55 litre Surecal calorifier as I've just fitted, so if this isn't suitable for potable water, the NRV should prevent any water being forced back into the cold system. Also IIRC, the PRV is 3 bar, but worth checking it's less than 4 bar!

 

They don't give a lot of detail, but I assume you can adjust the pre-charge with a foot pump or bike pump ?

 

Looks like it's probably something like 3/4" BSP, so if you want to get down to 15mm plastic plumbing, and don't already have the bits, that could push the cost up. As could a proper bracket if you need one.

 

The EV I'm using came with all that, slightly mitigating it's higher price.

 

On the other hand the similarly sized accumulator at the front of the boat was just lashed in with bent coat hangers when we got it, but a simple cradle in scrap 2" x 2" softwood, and an old bungee strap was just as effective as paying for a proper bracket! (Better in fact, as it can be removed in seconds, if required).

[Jparry]

I plan to use this one (8 litre one), any comments?

 

http://www.toolstation.com/shop/Heating/Ce...0/sd2708/p29704

I think that type is normaly used on sealed heating systems I dont know if it would make any difference long term but expansion vessels used for water systems are white or blue Joe

[chris w]

I think that type is normaly used on sealed heating systems I dont know if it would make any difference long term but expansion vessels used for water systems are white or blue Joe

My 8 litre expansion vessel (certified for hot water systems) and my 2 litre accumulator (certified for cold water systems) are both RED.

[Jparry]

My 8 litre expansion vessel (certified for hot water systems) and my 2 litre accumulator (certified for cold water systems) are both RED.

I did say normaly I should have said usually but the one in the link is made for central heating systems or boilers as shown on their web site

Joe