The Boy That Cried PV Extension

[Countrypaul]

How long do your showers take (not just you as someone may take much longer)? You can then caculate how much it takes per shower and whether it is better* to store HW with associated losses vs importing 2/3 of the shower energy.

*Better subject to definition of cheapest, most environmentally sound, keeping others happy, or whatever most suits your pov,

[Stinsy]

@ Stinsy. Yep, our low(ish) demand is why it dawned on me that a basic tank possibly makes more sense. Charged from PV for ~7months of the year, and cheap rate when PV gen is lower.

Even in summer it is better to export your excess solar and heat your DHW with cheap-rate electric.

[AGT]

Hi Mart,

It’s really one 2.5mm radial circuit for a 3kW immersion nothing spurred.

[Stinsy]

How long do your showers take (not just you as someone may take much longer)? You can then caculate how much it takes per shower and whether it is better* to store HW with associated losses vs importing 2/3 of the shower energy.

*Better subject to definition of cheapest, most environmentally sound, keeping others happy, or whatever most suits your pov,

Tank sizing is difficult.

You get lower standing losses if you heat 250L to 45℃ compared to heating a 125L tank to 80℃.

How much DHW is consumed by a shower is highly variable. Some people have 5-min tepid showers while others thake 15-min seering-hot showers.

You also have to size for the worst day of the year. You might be a couple who use very little DHW but then your two daughters come home from university and your needs 10x.

We are a family of 5. We currently have a combi that is only used for DHW. I plan to swap it for a DHW cylinder and bin the gas meter. However sizing is tricky. I assume our combo is horribly inefficient at producing DHW test below is our consumption. Averages at 3kWh of gas per day, so maybe 2kWh/day of DHW.

[Krill]

Those are frankly ridiculously low usage figures. I'd question how you are going to make any economic sense (even cutting out the standing charge) for any change prior to the gas boiler literally breaking.

For context there's just me and the wife at home and I use between 70p and 90p per day (one bath, one shower) and I can't make any numbers add up (nor do I have space for a cylinder anywhere, I used the space that the previous one was in to fit a standard bath in a shower room, so it's like we are in similar positions).

[Mart]

Thanks guys. TBH our showers are very quick, probably 3-5min max, so an inline heater wouldn't import huge amounts. At the same time, I suppose we could experiment with lower tank temps in the summer to minimise losses. Not too concerned about the winter, as mentioned we will need a bit of supplemental heating, maybe oil rad in that room anyway.

Hadn't thought of worst case with visitors, perhaps higher temp heating of tank would cover that, so long as we don't go too small. That would work well with the lower temp too, giving us the necessary headroom.

I mentioned perhaps 80% efficiency for our 25yr old combi, as being generous, but I assume in the summer, with a cold boiler, and heat lost to house through pipework, it may be 50%?

I'm not yet on paid export. The first bi-directional meter was faulty, so had to be changed, and EDF are helpful but slow doing all the FiT paperwork for the changes, so I can't do a final reading yet, for the change from them on deemed export, to Octopus on actual. Also low gen through winter now, so will revisit in spring. If the export rate stays high, then after I switch, I'll do all water heating, and BEV charging on cheap rate, whilst maximising export.

Sparkie / neighbour is off on holiday for 3 weeks in a couple of days, so last night was a great time for me to mug him for advice and free labour. I feed their cats, feral greenhouse cat, hedgehogs and fox, whilst they are away, so they 'owe' me, though tbh I don't mind at all. He suggested putting in a .... can't remember the name, may have said the word 'splitter' .... but effectively sounded to me like a small consumer unit / garage unit. Take the 30A supply, split it through two 16A fuses, one for the tank, and one for the loft ring main.


But, looking at the airing cupboard again, can't see a tank fitting without removing the combi, and still perhaps extending the cupboard forward. Not a problem, but does mean I can't really make the tank change first. Still need to see how the winter goes, and how much additional heating I need to add to get heat into the corners. I'm guessing it's fine, but need to see how January goes I suppose.

Wifey is actually pleased about possibly switching from gas oven to electric. Apparently there is far more choice of double ovens in leccy. So dropping gas completely may well be on the cards in the next year or so. Great to have so many options, but downside means I'll of course need to overthink everything, then overthink it all again.


At least I can't really go wrong with the oil rads experiment this winter. So I can see if heating to the 'edges' of the house is adequate, and how much extra leccy that uses, and importantly how much day rate leccy, as the batts (and PV gen) may be needed just for the A2A units and normal household demand.

[Moxi]

Mart

For those rooms that are on the periphery wouldn’t a small dehumidifier do you better than oil rads? You get the benefit of a heat pump, dryer air and lower temps so less heat loss but sill sufficient to warm the room up to a sensible level for a low occupancy room ?

We have just started to use our dehumidifier on the landing again for winter and it’s noticeably comfortable upstairs.

Moxi

[Mart]

Thanks Moxi, I've been pondering the same. We have a small (200W I think) unit, which is great for finishing off clothes after a shorter spin in the tumble dryer.

Also, 200W is pretty much what the smallest room, and furthest from the stairs (heat rising from A2A units) needs. I've been trialling our old and pretty rubbish 1100W oil rad in there. But I only use the 400W element, and even then after 20 mins it has to modulate on and off every 5mins, due to unit thermostat .... so around 200W.

I think you guys have explained that a de-humidifier has a small COP bonus? I never managed to quite follow the explanation, but certainly worth taking advantage off.

[AE-NMidlands]

I think you guys have explained that a de-humidifier has a small COP bonus? I never managed to quite follow the explanation, but certainly worth taking advantage off.

I think it is because (on top of the waste heat from the work being done by the use of electricity) you get the heat released when the water vapour condenses... as long as you throw out the ice-cold water which accumulates. Otherwise (I reckon) that water just takes some of the the heat back out of the room again as it warms up to the ambient temp.

[Stinsy]

Those are frankly ridiculously low usage figures. I'd question how you are going to make any economic sense (even cutting out the standing charge) for any change prior to the gas boiler literally breaking.

For context there's just me and the wife at home and I use between 70p and 90p per day (one bath, one shower) and I can't make any numbers add up (nor do I have space for a cylinder anywhere, I used the space that the previous one was in to fit a standard bath in a shower room, so it's like we are in similar positions).

Agree our gas consumption is small compared to others. We are a family of 5 (2 adults and 3 kids). Handwashing is with cold water in our house. The kitchen sink has a boiling water tap which we use for dishes.

Swapped the gas hob for induction a few years back and would strongly encourage others to do the same.

No one in our house showers daily. Have been tempted to fit an electric shower and game cheap-slots whenever it is used. But I always avoid installing infrastructure that’d become useless or a burden at the whim of a cephalopod.

An additional complication is that we have an enoumo bathtub that is used very infrequently indeed. However I’m not sure I’d want to be the person who tells SWMBO that she’ll have to wait a couple of hours for a tank to heat up. So that really does require a big DHW tank to be maintained 24/7/365 that we wouldn’t use from one week to the next…