So a challenge for the forum.
I've a friend whos looking for the best solution for HWS , with the restrictions on any external changes the choices are very limited (no PV, ASHP, Solar thermal)
Space heating the goal would be insulation, the idea of E7 thermal store came to mind , but seems better to invest in insulation, airtightness etc, (lets leave that for now)
for HW my first thoughts would be a main pressure cylinder with 2 immersions high Standard/low E7, which is the obvious standard solution.
anyone got some better ideas
here's the brief

Hot water design

Aim: Adequate cost-effective hot water provision to suit house being enlarged from 3-5 bed.

Current design is:
• All electric (no other fuel to property)
• “Economy 7” dual tariff meters
• HW cylinder is 1500 x 450 Economy 7 vented
• House heating supplied by two storage radiators (not sufficient!!)
• Bathroom shower is currently “Aqualisa Quartz Smart – gravity pumped” – good.
• Shower room shower is unknown (hidden behind tiles and not working properly).

Factors to consider:
• No change to external appearance of house permitted (alternative heating sources not practicable).
• New house heating will be provided by electric under-floor (to ground floor) and by electric skirting radiators (first and second floors).
o Hot water provision will be independent from house heating
o House heating will be mostly in use outside “Economy 7” hours.
• Expected use of house is single person, part-time (typically one cloths wash, one dish wash, five showers per week). However want to have solution that will adequately cope with typical household of four people (for when guests visit or for when house is sold).
o Want capacity for at least three “good power” showers in the morning (current tank can provide for two only). Bath infrequently used.

Layman’s thoughts:
• Will need to move hot water tank anyway
o Option to change to more efficient type of system?
• Ideal solution will probably have limited or nil hot water storage capacity (to minimise unnecessary heating)
• When second floor is added, showers on first floor will not need to b

What is the electricity supply, single or 3 phase?

Owlman single phase , instantaneous would be good but i was under the impression they'd need 3 phase to get a decent system

Posted By: jamesingram
• New house heating will be provided by electric under-floor (to ground floor)

Will the occupier(s) be at work during the daytime? If so then I think UFH might be a mistake.

Is there enough insulation in the floor or headroom to add more?

Bottled propane 'multipoint' instant heater - Rinnai or similar. Cheaper and greener than electric. Less capital cost than a pressurised cylinder.

I am with Will above, Rinnai on LPG bottles......

basic Maths error, 8 m3 should be 1.6 m3 in my post above, so even less....

And just for some secondary information, I have just ordered a replacement 200lt cylinder for £252.
Quick look for an E7 indirect unvented cylinder and the price is £525, so over double the price.

Water source heat pump sounds the best option. Urban rivers usually suffer from heat pollution, so extracting a bit of heat from it will be doing them a favour.

You can either bury a loop in the water bank or bed, or extract water, put it through a heat exchanger and then put it back. The former is simpler if you can get permission.

You then have the option of a thermal store (doesn't need a legionella cycle), or high pressure cylinder (which does, but you can time that to run on E7).

With the thermal store, you can either run it a high temperatures, or at a lowish temperature (e.g. 40) and use on-demand top-up for DHW if necessary (e.g. a 9 kW "amptec")?


Another alternative is E7 direct heating with a thermal store, but you need good controls to get the thermal store "charge" right (so that you don't overheat or underheat it).

But on the heating they will assuming a none too well insulated building

We have a similar dilemma (albeit with PV) and have opted for a SunAmp thermal store.

They reckon a 3kWh unit is equivalent to 90-138 litres storage which should be more than enough for a single occupant and have potential for a couple more showers in reserve.

I don't know much about E7 but if I understand it correctly you could 'fill up' overnight at times of low demand and then have a decent amount stored overnight.

The newer units have 'dual ports' which means they can feed DHW and Space Heating if this was an option (although that might mean a larger 6kW unit is required).

Not cheap (or renewable in this setup - until the grid is decarbonised...) but the storage losses are ridiculously small and it's a modular system so can be added to later if required.

Dimensions are about half a kitchen unit (580mm x 380mm), height varies with the kWh capacity.

finnian, any brands you could point me to , thanks

Last A/A HP I heard was pretty intrusive! Louder than I had thought. Louder than I'd want on a quiet evening!

I don’t think you need a thermal store with a WSHP, just hot cylinder

<blockquote><cite>Posted By: jamesingram</cite> ASHP is out as nowhere to site it (cold loft with adequate ventilation ? pretty sure thats out as it'll pull heat out the house over time).
</blockquote>
Maybe more do-able than you'd think - even with no ducting to external at all. Depends on how big the attic is and whether the roof itself is a sufficiently good conductor, ie. uninsulated preferably,to keep the attic air temp from dropping lower than a degree or two below external.
The Ariston Nuos for example consumes 700W average at a claimed COP of 3 or so, which means that the heat extraction from the loft air is 1400W. You could easily check what effect this would have on the air temp by putting a 1.5 kW fan heater in the attic for a few hours when the external temp is expected to be steady and measuring the temp rise.
An advantage of it working without ventilation is that the air would become dehumidified so that there would be less chance of needing frequent defrost cycles during cold weather.
I've got about the perfect situation for it here, so if I haven't persuaded you I think I've at least persuaded myself.