thermal store incorrectly installed

[dgrs]

Dear All,

We have a flat that has electric only. When we renovated it, we took out the unvented cylinder and installed a thermal store which also 'powers' a wet central heating system. The plumber who installed it had never worked with a thermal store and was convinced it wasn't going to work. It does work well but I fear it's been installed incorrectly so working very inefficiently.

My recollection is that our store (from newark copper cylinders) has one coil inside for DHW. There is then simply a flow and return for the central heating which draws water directly out of the store i.e. not how the DHW is heated. The plumbers installed the pump on the return side so, when the central heating is on, the water is 'pulled' through the system. I've no problem with this.

However, two things bother. 1. They installed an expansion vessel, but if the above is correct it's not a sealed system is it? If it's drawing hot water directly out of the store this water is replaced by the inbuilt header tank and is therefore an open circuit. 2. Because the hot water is taken directly out of the store for the central heating, the flow pipe (which is not lagged at all) is essentially heated up all the time whether the central heating is on or not. This is so noticeable that a couple of the radiators actually get warm even if the heating is not required whatsoever.

The outcome is I think I have a system which is hopelessly inefficient. What do people think the best way forward is? I'm thinking I need a way of separating the central heating pipework from the store itself so think maybe a motorised valve is appropriate and then heavily insulate the pipework up to that valve. If I'm right and it's not a sealed system, then the expansion tank is totally unnecessary.

Thanks for any thoughts you might have,

Dave

 

[jam1979]

a thermal store is opposite to an indirect cylinder its mains water through the coil with the boiler flow and return and that's in the tank body that's what heats the water up as it goes through the coil and out to ur hot taps

 

[dgrs]

a thermal store is opposite to an indirect cylinder its mains water through the coil with the boiler flow and return and that's in the tank body that's what heats the water up as it goes through the coil and out to ur hot taps

I understand this is how the DHW is supplied. However, in our tank I believe the hot water for the central heating system is taken directly from the store of water in the tank.

To look at, the TS has the heat exchange bit for the DHW (with a mixer valve to have DHW to requirements). Then, on the other side of the TS there are two 22mm pipes coming directly out. One is the flow and one is the return. As I said I thought that they were drawing water directly out of the store...

Dave

 

[Masood]

Have you got a link to make and model of your TS? As you say, if there's an internal header tank, then it's not a sealed system and the expansion vessel is redundant. However, are you sure you're not confusing an internal pressure vessel or pocket with header tank? In which case, depending on the size of your system, the installer may have calculated that the internal vessel would have been too small and an additional vessel would be required.

Also, the fact that CH water is drawn from the store does not affect whether or not it's a sealed system - the water is not drawn and lost - it's circulated.

 

[dgrs]

Have you got a link to make and model of your TS? As you say, if there's an internal header tank, then it's not a sealed system and the expansion vessel is redundant. However, are you sure you're not confusing an internal pressure vessel or pocket with header tank? In which case, depending on the size of your system, the installer may have calculated that the internal vessel would have been too small and an additional vessel would be required.

Also, the fact that CH water is drawn from the store does not affect whether or not it's a sealed system - the water is not drawn and lost - it's circulated.

Thanks for your replies. Defo not confusing pressure vessel for header tank.

I should have done this before (sorry) but I've just called Newark Copper Cylinders who made it and are getting back to me. It looks like the central heating may be via a coil and hence a sealed system.

Whether the central heating is sealed or vented, I'm still left with the issue of the water circulating through the pipes. Would you all agree the best (only?) way of solving this would be to wire in a motorised 2 port valve which would open only when the pump is on?

All the best,

Dave

 

[chris watkins]

Insulate all the pipework around the store for at least one metre (more if poss on heating) with min 19mm wall thickness foam pipe lagging & see if that stops the rads getting hot, hopefully it is just creeping along the pipe otherwise pipework modes may be required.
What type of store do you have? Does it have the little tank built into the top or is it a dome? What heats the store is it just a 3kW immersion ??

 

[dgrs]

Insulate all the pipework around the store for at least one metre (more if poss on heating) with min 19mm wall thickness foam pipe lagging & see if that stops the rads getting hot, hopefully it is just creeping along the pipe otherwise pipework modes may be required.
What type of store do you have? Does it have the little tank built into the top or is it a dome? What heats the store is it just a 3kW immersion ??

It's a 290 litre TS with integral header tank and 3 x 3kW immersion heaters. Originally all three were on programmable timers but these all failed. To be fair, the timers were only rated to 3kW so was pushing it. A plumber came and hooked one immersion up to an economy 7 timer (this was the original idea), a second to the same economy 7 timer but as a 'boost' and the third one has a simple on/off.

At the moment only the one immersion is on (all the time) but because of the waste via the pipes and rads it's losing a huge amount of heat energy so is having to kick in a lot.

Do you agree 2 port motorised valve (with lagging up to it) would be the best solution?

Dave

 

[chris watkins]

Best solution IMHO would have been to stick with the un-vent hot water cylinder on economy 7 & some other form of electrical heating, but suppose you are stuck with it now?
What is the heating load of the flat ? If not sure can you give us an idea for the size & construction.
Newark only seem to do up to a 250L are you sure it is a 290L where about's are the immersion bosses located (one right at the bottom, one middle & ? )

You need to try & use the economy 7 as much as possible & only have the others on during the winter when the heating is required.

 

[dgrs]

I think Newark may have changed their range, but when this was installed (2010) I think most things were bespoke.

Immersion bosses are all in the lower third of the tank all above each other.

The flat is 860 square feet with two bathrooms and very well insulated. Heating very rarely required. In my opinion, the current issue is making it massively less efficient than it would be. We're heating up a lot of stuff by default that simply doesn't need heating.

One of the reasons for installing it was to replace electric rads (I don't like the type of heat) and the fact that TS don't require servicing.

Struggling to get anyone to agree a 2 port motorised valve would stop the central heating warming up by default.... I think if there's a way of stopping this waste happening it will improve the efficiency by a good 20% (just a feeling but it's constant waste at the moment). This would actually make it very comparable to the old unvented cylinder (which was much smaller).

 

[Masood]

Struggling to get anyone to agree a 2 port motorised valve would stop the central heating warming up by default.... I think if there's a way of stopping this waste happening it will improve the efficiency by a good 20%

I don't think that's your answer TBH. As Chris pointed out earlier, the heat through the flow pipe and rads is likely to be conduction, and a brass valve will not put an end to that.

 

[markfxy]

couldn't you just put a thermosyphon loop in to stop the heat loss!

 

[dgrs]

couldn't you just put a thermosyphon loop in to stop the heat loss!

This sounds a very good solution although one I don't really understand! I did a bit of googling but couldn't find a diagram to show how this would work. Would you mind helping me understand it?

 

[chris watkins]

There are two main questions here
1. How is the hot water circulation around the rads if the pump is not switch on - Gravity or Conduction we cant see the pipework runs so can't help much more ?
2. How efficient against how much it will cost for the energy used. The thermal store system will never be as efficient a directly heated cylinder & direct electrical heat emitters. If the flat has two bedrooms along with the bathrooms & is top end spec, recommended 170 - 210 Litres stored hot water directly heated using cheap rate over night electricity, water held at 60 - 65deg C. Against 290 L thermal store which also supplies heating, as soon as any amount of water is drawn store will need to reheat using full cost electricity, water held at 75deg C. Standing losses alone would make the system more costly to run.

 

[markfxy]

this diagram will show you the depth of the loop needs to be 10 times the pipe diameter