Noisy Immersion Element In Thermal Store

[martinwinlow]

Hi,

I have a 400 litre thermal store (TS) with 2 immersion elements fitted one at 9kW and the other at 6.  The plan was to use these to heat the TS up to 85 deg C or so on Eco7 electricity.  The house is upside down and the TS is on the ground floor, sitting on 100mm of foam insulation and then on a concrete slab house foundation surrounded by bathrooms and bedrooms.  Despite a good 100mm of spray-on foam insulation to the TS, concrete walls and what not, the immersion heaters are very noisy at night.  I have reduced the output to 2 x 3kW temporarily but during the winter this is not enough heat to keep the UFH going during the night (even on set-back) and completely heat the TS ready for the next morning.

The immersion heaters are pretty basic ones and I have looked at trying to replace them with quieter ones.  I gather there are 'low watts' ones with incalloy sheaths and so on.  Question is, are they really much quieter?

Alternatively, bearing in mind the water in the TS is static, ie it is not circulated and therefore there is a limit to how much limescale can come out of it (it is also thoroughly doused with inhibitor) would an electric boiler of at least 15kW o/p be a guaranteed way of heating the TS quietly if the electric boiler is located next to the TS?

Thanks in advance.

Regards, Martin Winlow.

 

[SPECIAL LOCATION]

Noisy "element"?????

Or is it noisy water overheating..  ??

pressure issues... ??

water hammer effect ??

Elements noise?  what sort of noise????

 

[steptoe]

my guess is kettling,

by the way, you dont have any inhibitor in the water surrounding the immersion heater elements, that is normal mains water, the heating system is in a coil within the tank the immersion is in,

or, at least it should be,

the immersion heater heats up the heating system indirectly.

 

[ProDave]

Actually no Steps

A Thermal store is different. The water in the tank is static (i.e never replenished) and it's the water from the tank directly that circulates around the heating system.

For hot water, that is heated by a heat exchange coil in the TOP of the tank. Mains pressure cold water into the bottom of the coil, hot water out of the top.

So you get mains pressure hot water without having to have a pressurised tank and all the complications that go with that. (thermal store tanks are normally just fed from a small header tank)

The noise is probably just kettling as already stated, localised boiling of the water in contact with the element.

Are they really 6KW and 9KW elements?  That's a lot of power from one element.  All the ones I have seen have just had three 3KW elements making 9Kw in total.

You should consider changing to economy 10 tarrif. That gives a very useful 3 hour mid day top up to boost the heat in the tank ready for the evenings use and will probably ease the demand on your hot water.

Swapping to an external boiler to heat the tank won't stop the noise, they too make the same sort of noise. BUT it might enable you to move the source of the noise to somewhere that does not matter.

 

[steptoe]

ah,

thanks Dave,

good job Im not a plumber,  :|

 

[ProDave]

Where I was working today the guy was not a plumber either.

I was doing a load of "odd jobs" to finish off a self built house.

One was to wire the ground source heat pump.  Didn't actually finish that as at the last minute he told me he still has to flush it all through so the GSHP has to come out again. So I told him I'll wait to do the connections when it's "finished"

But looking at his plumbing, there's a flow and return from the GSHP that goes to a small cylinder, but teed off from the same pipes is the feed to the UFH.

I can't see how that's going to work as looking at  his plumbing, one pump is pumping one way, but the other pump is pumping the other.

I agreed to wire it for him when it's finished, but I can't guarantee that it's going to work.

This is yet another of those jobs where the (probably mythical) "previous electrician" didn't come back to finish it.

 

[martinwinlow]

Hello all,

Thanks for the replies.  ProDave... you have it almost right... but the  TS' UFH is indirect as well as the HW.  As it stands, I am only using one 3kW element from each immersion heater via solid state relays (silent) but in really bad weather and/or high demand the 15kW would give a good margin.  But as you say, a lot for 'normal' use.  To raise 400 litres of water from 30 deg C to 85 deg C takes 400 x (85-30) x 4187 joules (Specific Heat Capacity of water) = 92114000J... divided by 3,600,000 (number of J in a kWh) = 26kWH.  

At a rate of 6kW (2 X 3kW elements) that's 26/6 = 4 and a bit hours.  However, I have the UFH on as well at night - albeit set back to 18 deg C - which, (according to my heat loss calculations) at the industry standard -2 deg C outside temp, adds roughly another 7kW of drain on the system.  Hence the need for all that power.  It is a good size house but importantly has a very pretty but draughty as hell structural oak frame on the front.

I am sure the TS noise is kettling but the question of whether so-called 'low noise' ie low watts or more accurately 'low watts per area of element sheath' immersion heaters are going to help, remains.

I suspected that electrical boilers would suffer from this too... and then there is the mechanical noise of the relays that normally control the heaters to contend with.

As for the GSHP, they normally only supply either the HW or UFH at one time, not both togeather which might explain why the pumps are pumping in different directions. Perhaps that's not what you meant.

Anyway, thanks again.

MW