Storage heating - basic maths?

pbcpdeveloper

Scot_39 said:

 And note - you cannot get 1.5kW for 24 hours out of a 23.1 kWh standard E7 charge cycle input - 23.1kWh/24 = 0.96 kW max on average

Surely you would calculate over 17 hours, from the time the storage heater was fully charged until the time its starts to recharge again, which would give 1.35?

Scot_39

No - I don't think so re 17 hours vs 24.

Because many older NSH heaters begin to emit that input energy as heat almost immediately (hence often called lossy - as its not at the ideal or desirable time).

But it won't be linear over the day regardless - even if the most basic no output control model - and others going back decades - have adjustable air flow - manual or automated by time or temp over time - and many latest are fan assisted on timer and thermostat basis - when active.

Just making the point you cannot get 1.5kW Pnom on ave over day - thats 36kWh out - from a device with only 23.1kWh input (and that iirc at 240V not UK nominal 230V too).  

Another Edit - Thinking about it - over days rather than per day - it's possible the bricks might be capable of taking slightly more energy in heat charge if allowed - e.g. if dont discharge fully - but suspect the temperature cut outs and modern charge algortithms wouldn't allow too much more in any case.

One of many reasons many therefore wont use older nsh in bedroms as heat released overnight as charging would wake them up too early and people working // out all day do not find them a brilliant option - too hot for needs in am - or too cold by evening - again hhr and fan assisted can change dramatically that old lossy profile.

And even the most modern HHR panel probably still leaks a little.  (Some users here report their HHR Quauntums feel warmer to touch even if fan not operating to force distribute the heat at rated power)

And many in fact will be set to be releasing heat on coldest nights to maintain even lower overnight set temps - just as many find GCH will come on overnight if thermostats and timers enable it.

My parents used to drop thermostat several degrees to 12 just before going to bed - the GCH would often be back on in early hours just a few hours later - often before mum got up at 6am - on colder frosty or sub zero mornings.

Edit 
And in terms of warming up a cold house for getting up in the morning.
It's a hair and tortoise comparison - gas has higher power, higher speed, then derates or mark spaces, nsh a more slow and steady approach.

And remember even modern lot 20 NSH are low output power cf say a wet GCH setup.  If you want tge house warm at say 730 - it's going to take nsh maybe 3-4 times as long given the output power available.  GCH can often consume well into mid teens in kWh in first hour - to raise the radiator water and house temp - the equivalent electric home may only have 3-4kW of nsh output power available - so take 3 hours plus vs 1 hour.  Most of it in typical E7 charge window.

Polfers

Hi all - thanks for your interesting and informative responses.  I look forward to 10p off peak soon! :0) 

By the way, final configuration for the NSH's was as follows (bear in mind topsy-turvy house type):

Quantum :

- Ground floor front entrance hall, open to stairs: 0.7 KW

- 1st floor landing - 5 doors to kitchen diner, two bedroom, main bathroom, lounge - 1.5KW

- Lounge: 1.5KW

- Kitchen Diner: 1.5KW

Panel Heaters:

- 1st floor small bedroom/office 1.0KW

- 1st floor main bedroom 1.0KW

- 1st floor bathroom - 1.0 KW

- Ground floor bedroom 2.0KW

- On suite ground floor shower/WC 0.70 KW heated towel rail

We also have a 4KW capacity wood burning stove in the lounge.

The kitchen/diner and lounge are L shaped open plan

Normally, we are at home during the day - my wife is retired, and I'm semi-retired doing some work from home still. As such NSH's are more suitable than if we were both working away from the house during the day, as would be the case for many.

To answer the point raised re the dismissing of other options in preference of Night Storage Heaters (NSH's):

These were not dismissed lightly. We have spent over a year considering the options and their pro's and cons for our particular situation. We have also had surveys done in helping to asses matters, including the insulation possibilities, as well as using gas (we'd need LPG as no natural gas anyhow) and oil for heating. These were dismissed on ecological grounds and the cost if running them isn't that attractive, either, given their other drawbacks. They also require tanks to be installed and a propane tank is best buried in the ground - which is expensive, and access from a tanker (which has to have sight of the storage tank filler access), would not be possible unless surface mounted outside our front window (er, don't think so!), as the front garden is solid rock about 3 feet down, and there is no access at the back other than a 60 foot narrow path, so installation there was a non-starter anyhow. The reasons some solutions were dismissed may not have been the case had our situation been different (by situation I mean physical location, house type and available budget), but neither oil or gas for heating were likely to feature come what may.

We are in Scotland and where we live in the Cheviots, in the depths of winter, it can sometimes drop to -10 and -15 (not that uncommon), though typically, more like -3 to -5 excluding wind-chill. And it rains a lot in winter - so we get some lovely icicles!

The construction of our house was such that without some (for us), very expensive insulation solutions, the cost was  prohibitive, we were therefore not able to retro-fit the level of insulation that would have ensured an air source heat pump would have been a reliably efficient solution for us, added to which the cost, even with a grant, would have been too much for us to achieve on balance. We also had issues in terms of where the heat store tank could go as well as the back-up secondary tank. We have been able to insulate under the back floor of the house and to 300MM in the loft. We have double glazing (though of 1985 vintage, it is in good condition - we intend to replace in the future when affordable), and are fitting new composite doors front and back.

Air to Air heat pumps were not attractive for us as we would have found the noise, which is admittedly better these days, too intrusive.

Re the use of solar panels and batteries in combination with NSH's:  This means that during the day, we have largely free electricity from the Solar panels for running small appliances/lighting etc. meaning we don't use higher rate electricity from the grid of course. The batteries mean that if, because we are normally at home during the daytime, we use all the available solar generated electricity, the batteries are charged from the grid on the economy 7 night-time tariff. This means we can effectively access cheap rate electricity during the day generated from the batteries if need be - i.e. essentially, we keep electricity costs at no more than the off-peak rate for most of the time.

For water heating, we have a small wall mounted LPG boiler from Rinnai that is designed for instant hot water only. it uses two 45KG LPG bottles a year at a cost of £170 per annum, is ultra low NOx giving us a powerful hot water supply at low cost with minimal emissions.