7 day immerson controller

tommy-g_3

Thanks for your replay Rich in not sure what sort of thermostat is on it, its certainly not one I can set but I can't image that the immerser just stays on for 7 hours. But our water is still roasting at 8 pm.

I'm not sure if the e7 switchs over by teleswitch or timer. We had a new meter installed 3 months ago that appears to be set to GMT. So my worry would be changing the time would mean we'd end up using peak power.

Richie-from-the-Boro

tommy-g wrote: »

Thanks for your replay Rich in not sure what sort of thermostat is on it, its certainly not one I can set but I can't image that the immerser just stays on for 7 hours. But our water is still roasting at 8 pm.

I'm not sure if the e7 switches over by teleswitch or timer. We had a new meter installed 3 months ago that appears to be set to GMT. So my worry would be changing the time would mean we'd end up using peak power.

- your new meter will be digital, a bit like this one :

- you can adjust the stat both up and down, not sure why you'd want to do that, and I'm not going to teach you

Look the E7 cylinder is totally different from what you call an immersion heater, an immersion heater heats the top 20% of the water only and does a losey job even at doing that. Additionally an immersion heater insulation is lousy at insulating compared to an E7 cylinder.

An E7 cylinder heats from the bottom of the tank and heats the whole volume of water in the tank from bottom up, additionally the insulation value surrounding the tank compared to an immersion heater will keep the whole or the half tank you have left piping hot for much longer. That half a tank you have left will be sitting on top of the half a tank of cold water at the bottom [see #01]

So if you start tomorrow night with half a tank of well insulated very hot water at the top of the tank your costs will be only the cold bottom half of the tank where the thermostat is. tommy-g, its really no cost advantage unless you are away for more than a few days to turn off or restrict the kWh you put into your hot water cylinder.

Whilst its true that off uses zero kWh, if you do switch off / reduce the hot water heating your starting point will be a whole 100% [140+ litres] of cold water that needs heating so unless you use hardly any ever hot water from the cylinder even for washing up purposes I can't see how you would benefit. But I can see how your lifestyle would be inhibited by having to boil multitudes of kettles for different purposes.

If you want to TEST how much you save or even are inconvenienced simply switch the thing off for a week or whatever !

__________

[#01] Liquid, such as water, is heated from the bottom, the layer of water closer to the heat source expands and hence becomes less dense compared to the water layer above it. Expanded water is less dense than the surrounding water and therefore it rises. The cooler regions of the water in the upper part of the flask, being denser, sink. This movement of liquid due to a difference in density sets up a convection current.

So the heated [ hot ] water pushes up and forces the cooler water down over the thermostat which in turn is heated until the whole volume of the tank reaches your pre determined setting then the stat switches the leccy off. Its a bit atomic science and the random motion of atoms and all that, but sufficient to say that's why the top down element is rubbish at heating a full tank of water.

tommy-g_3

Thank-you very much for your detailed reply Richie, most appreacheted.

Yes that's very similar to what our new meter looks like and it has a sticker on it giving the E7 operating times. You are absoulty right I can't be assed with the idea of boiling kettles for water.

If I've picked up right what you are saying, regardless of how long the immersor is powered it will only heat to a set point then switch off?
So on a day like today (like most weekends) when we have been away all day and night therefore not used any water from the tank. It will only heat for a short spell to bring it back up to x temperture, and given the tank is fairly well insulated it shouldn't have lost much heat so it won't need much power to bring it back up.

Am I right in thinking that if were to switch off on Friday and Saturday nights it would probably use 3x the power to heat up on Sunday night? Therefore they'd be next to no saving anyway?

Richie-from-the-Boro

tommy-g wrote: »

Thank-you very much for your detailed reply Richie, most appreacheted.

Yes that's very similar to what our new meter looks like and it has a sticker on it giving the E7 operating times. You are absolutely right I can't be arrassed with the idea of boiling kettles for water.

If I've picked up right what you are saying, regardless of how long the immersion is powered it will only heat to a set point then switch off?

So on a day like today (like most weekends) when we have been away all day and night therefore not used any water from the tank. It will only heat for a short spell to bring it back up to x temperature, and given the tank is fairly well insulated it shouldn't have lost much heat so it won't need much power to bring it back up.

Am I right in thinking that if were to switch off on Friday and Saturday nights it would probably use 3x the power to heat up on Sunday night? Therefore they'd be next to no saving anyway?

- yes to everything but the last question
- assuming you were away or used no hot water at all Fri & Sat and switched it off for 24 hours
- the stored water would lose little in just 24 hours, but then it would cost equally little to leave it on - wouldn't it ?
- it would be better expressed by saying a cold tank needs 100% of something, an already hot tank off for 24 hours only 10% of something

I calculated it precisely yonks ago, the figures are here on this forum but I can't be arrassed looking for them.

With night store heaters it works with the same principal. A night store heater [damper closed fully charged] switched off for two days will still be warm to the touch. A night store heater switched off [damper closed fully charged] for one 12 hour cycle will prolly still be far too warm to touch ! Space heating with night store heaters, as with all heating systems takes a day or three to bring the 'fabric temperature' of the room concerned up to a reasonable level, once at that level its 'maintaining' your desired comfort level. At this time of the year you could prolly get away with switching your big storage heater off for a day or two, then back on again to re-charge from nearly cold. This is because the ambient temp of each day can be a huge 5 or more degrees of fluctuation until the weather decides to remain permanently cold and the fluctuations in temp reduce.

Owain_Moneysaver

Richie-from-the-Boro wrote: »

I wonder if there's any need for this in the first place, the O/P has an old economy 7 quartz I assume with only two options / (1) OFF / (2) TIMED only + a clock + a boost.

- forget the [bottom element] boost
- set the clock wrong by +4 hours

The supplier teleswitches you over at say midnight and off at say 7am .. .. but your clock won't throw till 4am real. So the top element is switched to isolate and the bottom element is not live because your clock has not thrown the solenoid.

At 4am real the bottom element starts charging then at 7am real the supplier teleswitches you off, that circuit however is still open but no longer live and the boost is still isolated till 11am of the clock but because that circuit is not now live you will have received only 3 hours of cheap rate.

Your clock however is still running till 11am of the clock [3pm real] and will deny you a 'boost' facility even if you want it because it thinks it under the control of the teleswitch until 11am of the clock.

No, because the Horstmann E7 timer will be connected to a permanently-live on-peak circuit. That's why it has the clock in it, which must be kept in sync to real time so the heater operates at off-peak.

If the immersion were connected to the off-peak fuseboard it woudln't need a timer.

tommy-g_3

Richie I think Ive got it. Say the unused tank looses 10% heat per day. So 10% Friday 10% Saturday and 10% Sunday when it switches on on Sunday night it needs to heat from 70% as opposited to 90% so makes no real difference.

victor2

Depends on how well insulated it is. Say it loses 50% per day. Then you'd be heating it from cold if switched off or from 50% every day if left on.
The best thing to do is try both ways, reading your meter before and after each one.

jalexa

tommy-g wrote: »

... I think Ive got it. Say the unused tank looses 10% heat per day...

I can't say how much your particular vintage of cylinder loses but if it is a Part L compliant cylinder (mandatory since April 2011) then the losses are stated on the label.

From memory, with typical factory insulated pre Part L cylinders, I recall about 2kWhrs/day but that doesn't include adjacent pipe losses. Certainly much less than 10%. Open to be corrected on that.

Owain_Moneysaver

tommy-g wrote: »

Heatrae Sadia 'megaflo' cylinders are between 1.19 and 1.89 kWh heat loss per 24 hours, depending on size (large sizes lose more).

So if you're paying 6p per kWh for off-peak rate, you'll lose about 12p for the first day.

As losses are proportional to the difference between the water temp and the outside air temp, the losses on the second and subsequent days will be lower because the water is cooler.