iBoost causing tank overflow?

zeupater

evomatt wrote: »

Taken from south stafs water

1. a bath uses much more than a shower. A full bath uses up to 80 litres of water whereas a 5-minute normal shower uses about 35 litres, saving 45 litres of water. A 5-minute power shower uses about 60 litres, which still saves 20 litres of water when compared to a full bath

So a 10 minute shower would use about 70lt.

There is already a hole in the bottom of the tank which im guessing is there so you can put the immersion at the bottom of the tank.

Hi

That of course is 35litres of water at a shower delivered temperature of ~40C, therefore mixing 10C mains with proportionally diverted immersion heated DHW at a high 70C would result in a mix of 1:1, therefore a 10 minute shower would actually only use 35litres of DHW ... replenishing the 10minute shower 35litres of DHW from 10C to 70C would consume somewhere around 2.4kWh (1.16*0.035*60), therefore a 35 litre 5 minute shower as per the water company's figures would be around 1.2kWh.

As a sanity check for the above let's look at the energy required for the shower from an alternative source. A 9kW electric shower running for 10minutes would consume 1.5kWh (9*10/60) if the thermostat doesn't cut out ... the difference between the 2.4kWh and 1.5kWh obviously being due to the restricted flow rate on the electric shower ...

As can be seen from the above, the figures actually do stack up ....

HTH
Z

Sterlingtimes

In our first 4 months, the iBoost has clocked up 124 kWh. I have been urged by correspondents here not to over-egg the efficiency of heating the water by gas. So I may presume that I have saved 248 kwh of gas. At £0.03 per kWh including VAT, my saving in the four months is £7.44. Not encouraging!


Yet the immersion thermostat has been set too high by the solar installer causing problems with the power shower. I suspect even lower diversion now.


Perhaps, with the summer coming the diversion will be more encouraging. The shower uses 17 kWh of gas a day. So it would require 8.5 kWh of diverted electricity to provide fully for our shower use. I would be surprised if we met 50% of that by solar diverted electricity during the summer months.


The savings really are tiny and I am disinclined to invest in major modifications.

Martyn1981

Hiya Sterling. I guess only time will tell, but remember that potential diversion will rise greater (proportionally) than generation.

Say you generate 6, and consume 4, then potential diversion is 2.
Generate 8 (up 33%) and consume 5, potential diversion is 3 (up 50%).
Generate 12 (up 100%) and consume 6, potential diversion is 6 (up 200%).

So if your average generation from Apr to Aug is between 12.5 and 14.5kWh per day, then you may (may?) have around 8.5kWh of potential diversion, depending on your daily consumption of generation. Quite a dramatic increase. Hopefully, the smoother and more predictable generation in those months will mean that you don't get too many bad days back to back, so what is missed in one (bad) day, may be made up in the following (good) day by PV rather than your boiler.

Whether or not that equates to approx 17kWh of gas, I don't know, but it would be interesting if you update as time goes on. But that's potentially 150 days * 17kWh (gas) = 2,550 @ 3p = £76 for those 5 months.

I think the reasoning of 50% efficiency may only apply to the non-heating months, when the boiler is running less and therefore less efficiently, and all heat loss in the house, from the boiler and pipework is also wasted. However, efficiency in the heating months may be higher, since all 'waste' heat inside the envelope of the property is no longer wasted, so perhaps (I'm not sure) your heated month savings, so far, may actually be worth a small amount less.

Mart.

pinnks

My experience is that I turn my gas off in April at some point when I can finally turn off the heating and turn it back on in October when we need the heating again. Over the intervening period my diverter provides all our hot water except on the very worst rainy days. Given that we used to use £50 to £70 of gas for hot water over that period, the maths is easy. Over the winter months it is less easy to estimate but as a well-known supermarket says, "Every little helps".

Sterlingtimes

Martyn1981 wrote: »

Say you generate 6, and consume 4, then potential diversion is 2.

Mart.

Thank you, Mart. The truth is that if I hadn't got one then I would have wanted one. The greatest benefit of this has been the red light outside the airing cupboard that gets everyone running for action.

It will be interesting to see what happens over the summer months. I remain optimistic.

zeupater

pinnks wrote: »

My experience is that I turn my gas off in April at some point when I can finally turn off the heating and turn it back on in October when we need the heating again. Over the intervening period my diverter provides all our hot water except on the very worst rainy days. Given that we used to use £50 to £70 of gas for hot water over that period, the maths is easy. Over the winter months it is less easy to estimate but as a well-known supermarket says, "Every little helps".

Hi

I think that's probably somewhere in the right ball-park ... we'll probably collect ~1300-1500kWh.t into the DHW over a year which is limited more by usage than collection, so that's somewhere around £60/£70 of gas displacement before allowing for boiler and system inefficiencies .... up to £100ish saving/year shouldn't be considered impossible with a decent size cylinder, say 210/250litres+, but it'd be much harder to achieve as the storage capacity reduces due to an increased frequency for top-up from the GCH when the buffer is depleted ....

HTH
Z

pinnks

Looking at my records my May to September gas is now zero compared to about 1900kWh prior to having a diverter. Add a bit of April and a bit of October and you have something over 2000kWh. So, about £75 in actual fact. That seems to be replaced by about 400kWp leccy. The apparent difference between the amount of gas needed and the amount of leccy will be in part due to the 20m return pipe run which cannot be lagged.