Martyn1981 wrote: »
1,200kWh of gas would need about 1,000kWh of leccy (if boiler is 80% efficient ... If losses from boiler efficiency and pipes are closer to 40% (in non heating months), then 1,000kWh of leccy is closer to 1,400kWh of gas.
nigelpm wrote: »
I've no doubt you could divert around 1,200 Kw/h in a good year but not useful if you only make use of 75% of it.
Sterlingtimes wrote: »
We all have a tendency to justify our own purchases. For me, the iBoost was thrown into a job price. However, I will not be fully convinced until I have the first summer's data. Problem here is that as an eco-dad, I fail in imposing behaviour on the Sterling family.
1961Nick wrote: »
From the little bit of research I've done it seems that the best way to make use of one of these units is to combine it with a destratification pump. Lowering the central heating tank stat & maxing the immersion stat will only go so far. A destrat pump could probably double the energy storage of the existing tank & enable a lot of water to be drawn over night before the boiler kicked in. It might even be possible to make it until sunrise the next day without any boiler assistance.
zeupater wrote: »
.... probably not if your annual demand for showers alone is 131 tonnes of 60C DHW consuming over 17kWh/day of heat provision energy - without a really large (/massive) heat store you'd never have a buffer for dull days, but with a really large (/massive) heat store and a destrat pump you'd rarely have any hot water anyway .... 17kWh would just about boil a 200l cylinder from cold, and tomorrow you'd need to do it again, come rain-or-shine ....
To supply that level of shower energy whilst providing a buffer for dull days and supply a decent proportion of DHW from pv you'd probably need a 1000l cylinder and divert from an 8-10kWp array to multiple immersion elements ... but, of course, there's always the possibility that the EST DHW calculator is wrong, assumptions used have been overestimated, or the OP has very old & very inefficient gas boiler - in which case the money for a heat-pump tumble dryer could probably be put to better use ...
1961Nick wrote: »
Who said anything about buffering for dull or rainy days?
We use about 100 tonnes of 60C DHW for showers pa plus about 10 tonnes for everything else.
During the summer months we average 10kw per day spare which would go a long way towards meeting the DHW needs. The problem is getting as much of that energy into the existing tank as possible while there's a solar surplus. A destrat pump would ensure that happens. Without it the immersion stat maximum setting would soon be reached & the surplus energy would be exported.
1961Nick wrote: »
Who said anything about showering at 60C? I said we use about 100 tonnes of DHW (not DW) for showering. The mix rate is pretty hard to calculate because the percentage of HW from the cylinder increases the longer the shower is run (I'm making the assumption that the energy cannot be replenished as quickly as a power shower can use it).
You keep asking whether I'm sure about something. Well I am sure that on a peak summer's day, I have too much surplus energy to heat a domestic HWC in it's current configuration. A destrat pump would solve some if not all of that problem. Another method would be to fit an immersion heater lower down the tank, but as mentioned earlier on this thread, it's not easy because of the profile.
For clarification....I'm investigating the possibility of using as much of the surplus solar energy as possible. I'm not trying to provide all of my DHW needs from solar as that would be impractical & very costly.
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