Plate heat exchanger or internal coil

[Enfield250]

Hello!

My thermal store needs replacing due to an internal leak.

I don't know wether to go for a store with an external plate heat exchanger or another one with an internal coil.

Has anyone got a preference for one type or the other?

The cost of both is similar.

Thanks

 

[Agile]

Most installers would recomend that you fit a non thermal store system!

Tony

 

[45yearsagasman]

If I'm honest I would skip any idea of a new thermal store and fit unvented cylinder(Megaflow type).A good combi in place of the th/store is another alternative.Consider also the age of your boiler.

 

[Enfield250]

Thanks,

For the replies, but I have hot water sauna cabin that requires 11ltrs/min.
A downstairs bathroom at the back of a single storey extension.
I have a system boiler that is only 2 yrs old.

When I had the boiler installed the plumber recommended keeping the thermal store, because of the shower cabin.

Cheers!

 

[Agile]

You have obviously set your mind on another thermal store.

As as customer you can ignore professional advice as its you that are paying.

However, I should be interested if you were able to explain the advantage of a thermal store over an unvented cylinder?

Tony

 

[Enfield250]

Agile,

The advantage as I see it is;

1. Can be a DIY job.

2. No annual maintainance required.

3. Does not need building regulations approval.

4. Does not require electrical supply unless immersion heater is required.

A part from those four, I can't think of anything else.

Of course the main disadvantage is the price, a thermal store for some reason is about twice the price of an unvented cylinder.

Cheers.

 

[bobthebender]

As above.external exchanger with pump and flowswitch.
google DPS Hi-Flow.
I am about to do same.

 

[Enfield250]

Thanks, Thermal man.

That's given me a better idea, I shall probably go for the DPS Pandora.
The other one I had in mind was the Eco-Equipped Copper Thermal store.

Cheers!

 

[Onetap]

Get one with a plate heat exchanger and a coil for the CH to avoid sludge build up. Have the boioer heat he store directly. Fit a Smart Pump on the CH and have TRVs all around. Have two stats to avoid boiler cycling. Have the store venetd and the CH circuit can be presurised using a cheap pressure vessel kit.

Thermal stores are not direct equivalents to unvented cylinders. They are much more and much superior.

Oh dear TM, you sound like Water Systems/Drivels latest incarnation.

A coil and a PHE? Please explain.

And thermal stores make the DHW unnecessarily hot, causing the precipitation of most of the dissolved limescale. They prevent condensing boilers operating efficiently, they are pointless with a modulating boiler and, unless you have a wood burner or solar themal, are utterly pointless and are usually specified by the clueless.

 

[mysteryman]

...and any half-decent combi will give 11 litres/min.

It is crazy to heat up a large thermal store to take central heating from it. You lose all controllability, as well as the other snags mentioned.

 

[Enfield250]

thanks for the info,

However the thermal store is just for DHW and is only 180ltrs max.

The DHW is not over hot 65c max.

I did before I changed the boiler 2 yrs ago look at a combi, but, to work my hot water sauna I ned 11ltr/min at 55c.

The combi's I found were all rated at 35c. and I would need a 30kw combi to provide enough flow, whereas the system boiler is only 12kw and up until now has provide both heating and enough hot water for my needs.

Cheers!

 

[Agile]

You would be better off with a gas instant water heater.

That will run a shower all day long.

Your store will only run for about 15 minutes at 11 li/min until the 12 kW boiler is unable to keep up. It needs about 30 kW as you know.

Tony

 

[Enfield250]

Until this leak happened the present store of 140ltrs, would be enough for 4 of us to shower in the morning.

The boiler would run from 6 to 6.30 to charge the store, this would provide enough for the day until tea time when another 30 mins refresh did the evening.

Now the leak is cooling the store I need to refresh more often.

 

[Onetap]

It was clear what I wrote. The coil is for the CH take off only. It prevents sludge build ups when teh system is neglected.

Right. So you have the heat transfer from the primary (CH) fluid to the secondary (DHWS) water via a tertiary (thermal store) fluid. What fouling factor do you allow for in sizing your heat exchangers?

The above is 100% incorrect. Thermal stores using plate heat exchangers can be run a around 63C store temeperature. The DHW temp is controlled by a blending valve.

You are Water Systems/Drivel.

The blending valve is necessary because the thermal stores heat the water to whatever temperature the store is at. The temperature of the stored unblended HW is uncontrollable and most of the limescale drops out of solution. The outlet should be a 60 degC, with local blending at the oulets if necessary. You will disagree with that, but those are the HSE recommendations; you can argue with them.

The thermal store stores heat; it will not have much heat stored if you run it at 63 degC and the minimum usable HWS temperature is 40 degC. They're usually run at 80 degC+.

The Range Powermax boilers were a combined thermal store with a gas fired boiler in order to provide mains pressure hot water. No-one makes anything similar now because they became obsolete when the Water Regulations were changed to allow thge use of unvented hot water storage heaters. Thermal stores are obsolete technology, unless you need to store heat (wood burner, solar) for later use.

 

[transam]

Thermal stores will never allow a condenser to run at its best effiency , if u already have one installed thats one thing , but installing one on a new install , no would'nt bother ! there is a large estate up the road form here that had themal stores installed from new , they are gradually being taken out !

Some combi manus used to use the themal store principle for hot water !

Used to ??