Space heating & DHW in all electric house

[sammiepammie]

Hi,

 

Considering options for space heating/ DHW for a 4 bed house. Build end ‘50s, detached, 140m2 over 2 floors, South England.

Filled cavity walls, loft insulation, all current (DG) windows will be replaced with new DG PVC units over the next few months. 

No gas connection, no wet system in place - so all electric (panel heaters & old electric UFH) and an electric HW cylinder.
We installed a 10kW wood burner in the large open plan living room a few years ago and added a 7.4kW PV system this year with 10kW batteries and an Eddi hot water diverter.
 

Prior to solar install, we used about 7000kW per annum - and that is being pretty tight with heating and hot water. I think this year we’ll end up around 4500kWh import. Octopus Agile incoming and fixed export.

Solar has covered all electricity/DHW requirements this year from April to October, surplus (3000kWh) was exported.

I have calculated the heat requirements (via city plumbing site) for the open plan living at around 5.1kW. The total for the whole house would be about 11.5kW - does that sound about right?

 

Considering A2A to get the house to more comfortable temperatures without having to feed the wood burner all day long.

We also need to replace the old hot water cylinder with a bigger one to suit a family of 4(2 adults & 2 teenagers).

 

Plenty of space for outdoor units, currently no ceiling boards downstairs so pipes/ducts not really an issue there either until we (finally) board this up. Hoping to fit the new HW cylinder in the loft- and get rid of the cold water storage tanks.

 

I’m not sure how many units we would and where to place them? the downstairs is pretty much all open plan (60m2) apart from the hall/wc. The stairs are in the middle of the open plan living room so the warm air will likely flow upstairs. The kids bedrooms upstairs (10m2 ish each)needs warming in afternoons, nothing else upstairs needs heating really dusting the day.

 

grateful for any advice!
 

 

 

 

 

 

[SteamyTea]

Welcome.

 

Quite difficult what to suggest without a lot more detailed analysis.

 

A2AHP is a relatively cosy effective form of heating, and cooling.

Do you know your energy usage for DHW?

Do you know how much insulation is under the UFH, you may be making the worms and moles warm.

[sammiepammie]

Haha, yes, like warming up the soil - I don’t know if there’s much insulation under the UFH so assume non. We only use it during cheap or negative pricing sessions really, its expensive to keep running all day long (11kW/hr for 3 zones when its cold)

We use about 5kW for DHW per day- all is used in the mornings only really - the current tank will be empty with no time to reheat for the next shower. The cylinder is only 100l currently - so, 3x short warm + 1x coldish unfortunately….it wasn’t a problem until the kids started showering in the mornings too. I sometimes shower at night if we have enough PV to heat the water but prefer mornings.

[SteamyTea]

5 kWh a day for DHW for all of you really quite low.

A larger cylinder may help a bit, but as you can top up with PV a lot of the year, you may get a marginal benefit.

I use about the same and I live alone.

[sammiepammie]

Yes, we need double the size cylinder really. Thinking either just standard electric cylinder or maybe a mixergi or even sunamp. 

[SteamyTea]

39 minutes ago, sammiepammie said:

Yes, we need double the size cylinder really. Thinking either just standard electric cylinder or maybe a mixergi or even sunamp. 

I use a 200 litre E7 cylinder (vented) with no problems at all.  Even when I have had 4 people in the house it has coped (I just up the temperature).

There is a lot of stuff about Sunamps on here, read up on them and make your own mind up.

I cannot comment on the Mixergi, but they are really just a tank of water, and we know the thermal properties of water very well.

[sammiepammie]

Thanks steamy tea, that’s helpful. 200l should be fine for our needs. The sunamp would be easier to place in the house, a bigger cylinder would need to go in the loft i think

[MrPotts]

If you need 200l then make sure you are actually getting 200l as this is often quoted as the size including the heating coil.

[RobLe]

Consider upvc 3G instead of 2G.  Supply only is £170(3G) instead of £120(2G) for an opening 1m x 1m window*, and it’ll get the u from 1.2 down to 0.7.  It’ll be a bit quieter, and even less cold feeling nearby.  Likely installation actually costs more than the units themselves anyway.  When they’re being fitted, get some decent air tightness foam in the gap between frame and brick; usually there’s sealant on the outside and just a bit of trim glued inside.
 

*https://www.modernupvcwindows.co.uk

[Nickfromwales]

21 hours ago, sammiepammie said:

Yes, we need double the size cylinder really. Thinking either just standard electric cylinder or maybe a mixergi or even sunamp. 

You'll need a second job to be able to afford a Sunamp (aka Thermino) nowadays..... Prices have gone into orbit, and when compared to an UVC you can get 3 or 4 for the price of 1 S.A. unit 

 

You'd be much better off with an UVC, especially with the PV, and I'd defo double the size of your current capacity to maximise on solar storage/revenue and to get you to a higher % of self-consumption. Also, with a modern UVC you'll be very well insulated and have minimum losses compared to an older/less efficient one. You can have deeper baths and longer showers then too  

[sammiepammie]

8 hours ago, RobLe said:

Consider upvc 3G instead of 2G.  Supply only is £170(3G) instead of £120(2G) for an opening 1m x 1m window*, and it’ll get the u from 1.2 down to 0.7.  It’ll be a bit quieter, and even less cold feeling nearby.  Likely installation actually costs more than the units themselves anyway.  When they’re being fitted, get some decent air tightness foam in the gap between frame and brick; usually there’s sealant on the outside and just a bit of trim glued inside.
 

*https://www.modernupvcwindows.co.uk

Yes, have considered that but thought maybe only for the east & north facing windows. The frames were a lot bulkier if I remember correctly (VEKA Halo). The biggest windows are on the south side and we enjoy a fair bit of passive solar heating here in winter (& overheating is not problematic in summer).

[sammiepammie]

Hmmm, but then we need to heat up a whole big tank in winter….when there is no solar. I liked the idea of the Sunamp but the payback as you say is likely very long - I thought it would be about double the price of an UVC. 

[JohnMo]

7 hours ago, sammiepammie said:

Hmmm, but then we need to heat up a whole big tank in winter

No you don't, direct cylinders will have two immersion heaters, so you can heat all or part of the cylinder.

 

For the price difference for a normal direct cylinder and sunamp, you could heat a normal cylinder for free for a decade.

[SteamyTea]

8 hours ago, JohnMo said:

For the price difference for a normal direct cylinder and sunamp, you could heat a normal cylinder for free for a decade

I just did the sums.

A 200 litre cylinder heated from 30°C to 60°C, with electricity at £0.12/kWh will cost ~£306/year.

Evan at full price electricity, or heating it up twice a day, would still work out about the same as a Sunamp.

[sammiepammie]

Thanks both, that’s helpful math! My sums came to approx 10-12 kW/day to take the water from mains temp (10-15C ?) to 60C- so at 12p/kW that would be £450 ish or £900 on full price electricity. Agree that the sums don’t add up…

any ideas on the A2A and in particular where the indoor units should go?

[JohnMo]

12 hours ago, sammiepammie said:

My sums came to approx 10-12 kW/day to take the water from mains temp (10-15C

But it is unlikely you would ever have to replace the whole contents. Thermostat is low down, the rest of the cylinder will be at a higher temperature. Bottom of our cylinder can read 12 at the thermostat, but it's actually 45 at the top of the cylinder. My average input to a 210L by immersion is 4.5kWh.

[sammiepammie]

Ah, that makes sense. Although I think we might finish a full tank with 4 of us…anyway, will have a look at UVCs and forget about the Sunamp.

[JohnMo]

11 minutes ago, sammiepammie said:

Although I think we might finish a full tank with 4 of us

Possibly will, but the kWh used, no matter if UVC or Sumamp would be pretty much the same on a daily basis.

 

You have more flexibility with an UVC, you just heat to different temperature, to alter capacity. A Sumamp has defined max capacity based on PCM melt temperature, so less flexible on that basis.

[SteamyTea]

57 minutes ago, JohnMo said:

You have more flexibility with an UVC, you just heat to different temperature, to alter capacity. A Sumamp has defined max capacity based on PCM melt temperature, so less flexible on that basis.

That is an important point.

I limit the charging time to 1.5 hours, so 4.5 kWh(ish), I don't run out of hot water. 

When there was 2 of us in the house, and once I had trained my lodger not to stand under the shower until it ran cold, I limited the time to 3 hours, but raised the temperature up by 5°C to 52°C top of tank temperature.

Never ran out and could get two bathfuls and a shower out of that.