Advice - Hot water Coil in a thermal store, expansion requirements.

[ashling]

Hi, I need some help.

Stored hot water regs apply to 15 litres of stored hot water or above. So if you have a unvented hot-water system with less than 15 litres including the pipework, which incorporates a secondary recirculation pump. Do you have incorporate in to the design a expansion vessel or can you assume that the system will deal with expansion.

To add information the water is heated via a coil, in a thermal store. The cold supply to the coil has a non return valve in it, preventing any expansion. There is a mixing valve on the so that the hot water system only provides a maximum of 60 degrees at any of the outlets.

Any information would be appreciated, all work will be undertaken by a fully qualified individual. Just need some advice.

Please do not post read manufactures instructions or consult manufacture. I am looking to increase my understanding of this area and the regs concerning it.

Regards

 

[Neil K]

If it's a thermal store then the expansion vessel will go on the cold water mains before it goes IN. That is, if manufacturers instructions specify one to be fitted, and if they do then the expansion vessel would normally be supplied as part of the kit, along with the blending valve and other bits and bobs that will come with it. I have worked on ones which have no expansion vessel fitted though. Once your installer follows MIs then it should be fine.

 

[ashling]

Hi Neil K

Hi thanks for the post, but I`m looking or information, specific to what I`ve asked

 

[ashling]

Hi Neil K Thanks for Post

Hi I`m trying to increase my knowledge and understanding. Rather than relying on manufactures instructions.

 

[Best]

You surely won't have an unvented system with a secondary pump with a combined volume of under 15 litres??
Whatever you have, you just go by MIs. Any query simply contact the manufacturer.
The Albion Mainsflow thermal stores (rubbish imo) have a soft copper multi small bore coil inside them which the mains goes through. This coil needs protected especially if mains stopcock is very close to the store. Albion supplied a small potable stainless steel expansion vessel partly for this purpose.

 

[ashling]

Hi Best, thanks for your reply

It is a hot water coil, which is still classed as a unvented hot water store. I`m after a professional opinion based on the information.

 

[Mike Jackson]

A hot water coil isn't classed as an unvented hot water store. It may contain water at mains pressure but it is a completely different kettle of fish. As has been said above, manufacturers instructions are king. The manufacturer has developed and tested the unit and is best placed to advise on requirements for any expansion vessel.

 

[Mike Jackson]

Oh and my professional opinion is you are looking too deeply into the issue, we have to rely on the manufacturers to get things right for us.

 

[AWheating]

The hot water coil is just pipe work, not a store.

 

[Neil K]

I gave you information specific to what you asked and Mike has also elaborated on what I've told you and hit the nail on the head.

 

[Worcester]

Unless your TMV's are at point of use, your secondary circulation pump isn't going to pump anything...

Think about it ....

 

[SimonG]

Perhaps you can expand on why you need the info, because its not making any sense.

 

[Cello]

Hi, Ashling. I also wondered about expansion risks as I also have a thermal storage system. Obviously, sticking to MI is vital but it is reassuring to verify that your system is safe. For my system, I calculated worst-case expansion was 60 ml. I estimated the volume of the heat exchanger and used a value of the volume coefficient of expansion for water from the Internet. I assumed a temperature change from 5 to 70 degC. For the record, my system is fitted with a Worcester expansion vessel and I estimate its volume as approx. 250 ml. Hope this helps.

 

[Ermintrude]

It's negligible . The Albion ones have 4 8mm pipes coiled round cylinder.

When the store is hot and water enters it the tap is open.... So expansion comes out of tap.

When system is cold the whole system expands including the pipes as it heats up. The small expansion is partly for this and partly to stop wassahamma when TMv is working and coil is shaking around

 

[Worcester]

@Cello - do you understand why you can't have a pumped secondary in your example?

 

[Best]

It's negligible . The Albion ones have 4 8mm pipes coiled round cylinder.

When the store is hot and water enters it the tap is open.... So expansion comes out of tap.

When system is cold the whole system expands including the pipes as it heats up. The small expansion is partly for this and partly to stop wassahamma when TMv is working and coil is shaking around

Spot on!

 

[Cello]

Worcester. I really didn't understand why a secondary pump would be needed so I commented only with relevance to my own thermal storage system which does not have any pumps in the non-vented side. I was only trying to throw light on the expansion issue.