Unvented or vented ?

[scottishjohn]

2 minutes ago, SteamyTea said:

There was a press release from SunAmp a year or two back about barging in a huge heat battery to Bristol.

I suspect it just just puff.

worth a conversation with them at some point -- my other idea of 10,000litre tank would weigh over 10tons

 

[Jeremy Harris]

A 10,000 litre water tank, with a max temp of 80°C and a min usable temp of 30°C would store about 583 kWh, a bit over 1/3rd of our requirement, without allowing for heat loss.  Realistically, we would need a seasonal heat store that would hold around 1,800 to 2000 kWh, allowing for heat losses that couldn't be usefully utilised.  That means a water store of around 30,000 to 33,000 litres, heated to about 80°C at the start of the heating season.

[Ed Davies]

6 minutes ago, JSHarris said:

allowing for heat losses that couldn't be usefully utilised. 

 

…unless the tank's inside the thermal envelope, of course.

 

But, more generally, any plausible “inter-seasonal” store really has to start with the notion that a significant proportion of the heat will be harvested during the winter half of the year. It should only be discharging at a significant rate during the worst few weeks of the winter, say the worst 6 or 7 weeks in the period from the middle of November to the end of February. That is, of those 14 or so weeks you'd hope that about half have at least the odd bright day or two meaning your net losses over the week would be small.

[scottishjohn]

If I can find it ,cos it was a long time ago ,will look 

kingspan /thermomax technican dept did a calculation for me some years ago on this house ,which is crap compared to a modern one. and they were given the heat loss calc for the house at that time .

numbers i do remember were a heat loss  of 1.7c per week from the tank

the end result of that was 6x20tube panels with 20,000litre storage to get 100% of all heating requirements+dhw

for your numbers to come out at more  than 50%  more storage on a very energy efficient house seems strange,as the heat loss of this house must be close to double of yours as the annual energy bill is--all electric  at around 14000kw--£2kish 

 taking what they said as a guide you can see why I considering to store the energy for the small amount you are talking about.

I will try to talk to them again ad give them a target of 2400kw  ,and see what numbers they come up with .my thoughts are to  cascade sunamps so you charge one up fully and then swop to next one 

It probably fall down on costs anyway --but it,s worth a bit more digging first 

Edited July 6, 2019 by scottishjohn

[Jeremy Harris]

36 minutes ago, scottishjohn said:

If I can find it ,cos it was a long time ago ,will look 

kingspan /thermomax technican dept did a calculation for me some years ago on this house ,which is crap compared to a modern one. and they were given the heat loss calc for the house at that time .

numbers i do remember were a heat loss  of 1.7c per week from the tank

the end result of that was 6x20tube panels with 20,000litre storage to get 100% of all heating requirements+dhw

for your numbers to come out at more  than 50%  more storage on a very energy efficient house seems strange,as the heat loss of this house must be close to double of yours as the annual energy bill is--all electric  at around 14000kw--£2kish 

 taking what they said as a guide you can see why I considering to store the energy for the small amount you are talking about.

I will try to talk to them again ad give them a target of 2400kw  ,and see what numbers they come up with .my thoughts are to  cascade sunamps so you charge one up fully and then swop to next one 

It probably fall down on costs anyway --but it,s worth a bit more digging first 

 

 

1.7°C heat loss per week from a 20,000 litre tank is 39.67 kWh/week heat loss, about half the heating requirement for our house in winter.  The heat loss rate isn't linear, though, it's proportional to the differential temperature between the tank contents and outside, so the heat loss rate will start high (when the tank is hot) then reduce as the tank contents cool (see Newton's Law of Cooling: https://en.wikipedia.org/wiki/Newton's_law_of_cooling).

 

For a 20,000 litre tank that starts off at 80°C (about as hot as you would want it to be really) and ends up at 30°C (about as cool as it can be and still be of use for heating) then the heat stored over that 50°C range would be 1,166.67 kWh.  That's less than would be needed to heat our house through winter by about 37%, and our (electric) heating costs around £130 a year (at E7 rates).

 

You can do a rough assessment of the heating energy you use from taking your heating bill and working back to get the amount of energy, making an allowance for hot water energy (for us, hot water uses more energy than heating over the course of a year.

[scottishjohn]

its not for this house -so no point --its for new house and as it ain,t designed yet ,  nothing to be concrete with

which was why I asked for your ACTUAL figures.

I know my elec is high ,but not just because of heating ,but i run a big pond pump and things 24/.7-- that will be close to 400w pr hr --all adds up 

 

Edited July 6, 2019 by scottishjohn

[SteamyTea]

Surely, when looking at interseasonal heat stores, and assuming you are not after a truely passive system, then everything shoudl be compared to a heat pump.

A heat pump is really just taking advantage of stored energy anyway.

 

[scottishjohn]

8 minutes ago, JSHarris said:

1.7°C heat loss per week from a 20,000 litre tank is 39.67 kWh/week heat loss, about half the heating requirement for our house in winter.  The heat loss rate isn't linear, though, it's proportional to the differential temperature between the tank contents and outside, so the heat loss rate will start high (when the tank is hot) then reduce as the tank contents cool (see Newton's Law of Cooling: https://en.wikipedia.org/wiki/Newton's_law_of_cooling).

which again is why thermal stores ,as they are sold are not good --never enough insulation on them and never the best type 

that is osmething ilearned with my thermal store .befoore ihad the ASHP

I used phonelic pipe lag sections around the 500mm tank -made BIG difference to heat loss ,,but increased my boiling problem with the solar .LOL

300litre tank was no where close to being correct size for 2x20 evac tubes,my guesstimate is 500 litres min --so you don,t get boiling problem ,but even then you end end up with having lots of hours in the day when the solar temp is same as tank --so it stops working --storage is the be all  of solar  and ,with cascaded systems to get best from it,

this is why if viable on cost i think the sunamp could solve a lot of problems 

 

[scottishjohn]

lest suppose solar can only give 30-40c in some parts of year --then add an inline pv powered heater to lift it to sunamp threshold -----

lots of ways to make both work together using free pv to top it up  --but storage costs will always be the killer

[Jeremy Harris]

20 minutes ago, SteamyTea said:

Surely, when looking at interseasonal heat stores, and assuming you are not after a truely passive system, then everything shoudl be compared to a heat pump.

A heat pump is really just taking advantage of stored energy anyway.

 

 

Very true.  Once you've got your heating bill down to the level ours is, then there's no way a thermal store is ever going to recover it's installation cost before it dies from old age.

[SteamyTea]

Right, got the correct data this time.

I think this interseasonal storeage is a statistical problem.

There are just not enough times when it is cold to replenish a store sufficiently to be of any use.

The below chart is shows the amount of time that a concrete brick is either above external temperature or below it.

The trend lines, withing the 1 standard deviation limit, show that as the external temperature gets hotter, there are more times that the block is hotter still.  The reverse is true for the cooling side of the equation.

There are the odd outliers that pop into the 'the other side', but these are probably rare weather events i.e. snow (had some twice), rain (it can cool things quickly), extra sunny days (had a few last year), very windy days (again, there has been a few, not many this last 12 months).

 

 

Edited July 6, 2019 by SteamyTea

[SteamyTea]

2 hours ago, JSHarris said:

You can do a rough assessment of the heating energy you use from taking your heating bill and working back to get the amount of energy, making an allowance for hot water energy (for us, hot water uses more energy than heating over the course of a year.

You can do the same with heating degree days (HDD).

It is only good as a rough guide, but may be useful when looking at storage.

 

[scottishjohn]

3 hours ago, JSHarris said:

 

Very true.  Once you've got your heating bill down to the level ours is, then there's no way a thermal store is ever going to recover it's installation cost before it dies from old age.

how much better do you need the house to be before all electric heating --mats etc remove the need fora big UFH install + complications of heat pump if you working ROI 

can,t be far away?

 

[Jeremy Harris]

5 minutes ago, scottishjohn said:

how much better do you need the house to be before all electric heating --mats etc remove the need fora big UFH install + complications of heat pump if you working ROI 

can,t be far away?

 

 

Even an ASHP may not recover it's additional capital cost from the energy saving cost reduction through life.

 

We're lucky, in that I bought a relatively cheap ASHP and installed it myself.  It saves us around £300 a year in electricity cost, and the installed cost came to a bit over £2,000, so it needs to last for about 7 years before it starts to save us any money.  If it had been installed by an MCS installer it would have cost around £4,000 installed, so would take the best part of 14 years to break even, and I suspect it may well be due for replacement at around that time.

 

There's a reasonable case for doing as @TerryE has, and just fit a cheap immersion heater in a Willis tube for heating a low energy house.  Capital investment probably well under £100.

[scottishjohn]

normal UFH I presume ,but water heated by willis -with or without thermal store?

 and pv ?

Edited July 6, 2019 by scottishjohn

[Jeremy Harris]

7 minutes ago, scottishjohn said:

normal UFH I presume ,but water heated by willis -with or without thermal store?

 and pv ?

 

AFAIK he's not got any thermal storage in the heating system other than the concrete in the passive slab.  The Willis heater just sits in series with the UFH pipes as the heat source.  Don't think he's got any PV yet, either.  DHW is from a pair of electrically heated Sunamp PV units, run in parallel.

[joe90]

On 05/07/2019 at 16:34, JSHarris said:

but Sunamp reckon that the element will last for the life of the unit,

 

Does that mean the life of the unit is not that long?

[Jeremy Harris]

Just now, joe90 said:

 

Does that mean the life of the unit is not that long?

 

I do hope not.  When I was talking to their technical chap, back when we bought the Sunamp PV, the life of the unit was being estimated at around 20 years +, based on the accelerated ageing testing on the PCM they were doing.  I'm not sure what they are quoting for the UniQ range though...

[joe90]

1 minute ago, JSHarris said:

 

I do hope not.  When I was talking to their technical chap, back when we bought the Sunamp PV, the life of the unit was being estimated at around 20 years +, based on the accelerated ageing testing on the PCM they were doing.  I'm not sure what they are quoting for the UniQ range though...

 

Sorry I was back to the constructive pessimism thread??????

[SteamyTea]

5 hours ago, scottishjohn said:

how much better do you need the house to be before all electric heating

Looked at this a few years back with someone else over at the other place.

Think we decided that anything less than 2.5MWh for heating and it was not worth while.

One of the reasons that I have stuck with basic storage heater on E7.

[TerryE]

5 hours ago, JSHarris said:

We're lucky, in that I bought a relatively cheap ASHP and installed it myself. 

 

As Jeremy says, I can only make the payback work if I do the install myself (around 5-6 years).  If I use a typical provide and install quote then this would go up to nearer 15 than 10 years, and with the expected life of an ASHP being around 10 years, this makes no sense at all.  Of course this equation and payback would all change if I had a lower-spec energy efficient house.

[scottishjohn]

I think though to be fair you can,t really do a true ROI on heating when  all systems need replacement at some time ,

but what you can do is compare with initial and replacement  costing of a gas boiler and mains gas ,as that is generally the cheapest system ,

and see which one works out best  over say a 15 year term .

I personally would be suprised if an ASHP does not last that long at least ,judging from aircon systems  life

[Ed Davies]

10 hours ago, scottishjohn said:

but what you can do is compare with initial and replacement  costing of a gas boiler and mains gas ,as that is generally the cheapest system ,

and see which one works out best  over say a 15 year term .

 

Probably true for a building-regs house but likely not for an efficient one. By the time you've paid the gas standing charge and for a boiler service you've taken a noticeable chunk out of the electricity cost for a house like @TerryE's, never mind the depreciation on the boiler and the cost of the gas.

[TerryE]

On 07/07/2019 at 00:18, scottishjohn said:

... initial and replacement  costing of a gas boiler and mains gas, as that is generally the cheapest system ,

and see which one works out best  over say a 15 year term...

 

As Ed says, definitely not true in our case. No BGas installation fees; no daily standing charge, no boiler maintenance charge, and that's before we do any other side-by-side comparisons.  (The annual maintenance on my last BGas boiler was over £300).  Because my house is very energy efficient, the Willis does the job fine; it's tiny and doesn't need an area of external wall for its install. 

 

We have about a 6-year payback if I self-install and self-maintain an ASHP, and if I reckon on a 10 year working life then this is just about viable -- but there's no cost-benefit case for a professional install.  One nice side-effect of having the Willis as a fallback is that the ASHP isn't "mission critical".  If it were to break down in peak mid-winter and I needed to order a part or even replace it, then the only real impact would be that my electricity bill would go up by maybe £10 or so per week for the outage.

Edited July 8, 2019 by TerryE

[scottishjohn]

9 hours ago, TerryE said:

then the only real impact would be that my electricity bill would go up by maybe £10 or so per week for the outage.

so the difference between full electric heating by willis and ashp is £10 a week in the winter .

thats beginning to sound like that maybe ASHP is or could be redundant due to intial cost verus willis cost ?

 so maybe the claim that graphene heatings panels are a viable  alternative in a near passiv house is not far off  with PV +batteries

if one 3kw? willis can power all UFH?

what are are your wall ,floor +roof insualation values?

 

Edited July 9, 2019 by scottishjohn