Hi!

[Jeremy Harris]

20 minutes ago, Dreadnaught said:

 

Yes, I was thinking about that. Assuming that the UFH water circuit is a closed loop, would you bypass some of the water around the Sunamp and re-blend the unheated water with heated water from the SunAmp outlet using a thermostatic blending valve? Sorry for my basic description, I know next to nothing about plumbing.

 

 

The standard Sunamp PV has an integral thermostatic mixer valve that does just this.  You decide on the output temperature you want and just adjust the valve to deliver that temperature, and as long as there is enough charge in the unit to maintain the set temperature it will.

[Dreadnaught]

22 minutes ago, JSHarris said:

The standard Sunamp PV has an integral thermostatic mixer valve that does just this.  You decide on the output temperature you want and just adjust the valve to deliver that temperature, and as long as there is enough charge in the unit to maintain the set temperature it will.

 

Ah, I see. 

 

So all the new 3rd-generation Sunamp would need to add is separate circuits for DHW and UFH so that they don't mix (and no doubt lots of other goodies that I can't even imagine). 

 

And now I also understand @Nickfromwales's point about the different phase-change materials (PCMs). They are simply to cope with different sources of energy. The lower temperature PCM is for heat derived form an air-source heat pump (ASHP), which cannot generate high temperatures without sacrificing COP (or using a complex multi-stage heat pump). 

 

I am also aware that, with a SunAmp that does contain both high- and low-temperature PCMs within, then the low-temperature PCM can be used to preheat water that then feeds into the high-temperature PCM, and then this higher-temperature water can be blended down to the target temperature.

 

So in my scenario, using E7 and PV, a high-temperature PCM Sunamp would be the choice unless I anticipate possibly adding an ASHP later, when having both PCMs might be desirable.

 

Anyhow, it seems @Nickfromwales has some good news up-his-sleeve about some thing for early March!

Edited February 14, 2018 by Dreadnaught

[TerryE]

3 hours ago, Nickfromwales said:

I'd reconsider the Willis heater and await the arrival of the 3rd generation SunAmp heat battery if I were you.

 

Nick, I feel that you are missing a fundamental point here.  The SunAmp uses PCM cells to get a lot of thermal capacity in a small form facts -- about 4½kWh in the standard box.  The slab is a thermal store with well over 10x this thermal capacity at less than ½°C temp drop, and it is there anyway.  IMO, there's little to be gained by using a SunAmp as a heat battery for the whole slab.  Where is does make sense is possibly for a DHW preheat buffer, but really only when we have baths. 

 

I just tweak my version of the "Jeremy Spreadsheet" to increase the house temp to our actual average (21°C) and drop the Jan/Feb temps to actuals rather than forecast.  So the prediction of this 3 year-old model was Feb average consumption of 47kWh / day.  Our actuals this month vary between 42-55 kWh with an average 47.5 kWh /day , which I think is just amazing.

 

It's bloody cold at the moment, the 24hr average temp is around 3°C so we are needing 21kWh @ low tariff + another 6kWh top-up late afternoon at peak tariff to maintain a warm house environment.  This space heating element costs £1.51 (cheap) +0.83 (peak) (+5%VAT) at our current OVO tariff.   Our slab could probably take more than 3kW, but I've only got the one 3kW heater.

 

A big caveat for @Dreadnaught: for this sort of heating architecture to be viable you need to do the sums for your design and you then need to make damn sure that your house as built achieves the sort of passive class performance that you designed for.  Acres of glass make a big difference to the figures; ditto bridging failures in the thermal envelope; ditto material airtightness failures.  But get it right and you won't need upstairs heating at all, so no radiators cluttering walls, just a warn ground floor.

 

This all being said, we'll be laying the insulated return pipe from the services room to the end of our garden shed (the probably place for ASHP should we decide to install one) this weekend as the paving guys are starting the drive and paving the following Monday.  That way we won't have any digging to do if we do decide to install an ASHP.

[TerryE]

BTW with an ASHP you have three different "grades" of water: potable; + inhibitor for the UFH loops; + antifreeze for the ASHP.  You need to use PHEs between these; though I believe you can use a combined inhibitor / antifreeze mix for a combined UFH + ASHP flow, though no doubt JSH or NH will correct me if I am wrong.

[Dreadnaught]

12 minutes ago, TerryE said:

The slab is a thermal store with well over 10x this thermal capacity

 

Oh, very good point. Just store the energy in the slab. Obvious now you say it.

 

12 minutes ago, TerryE said:

you then need to make damn sure that your house as built achieves the sort of passive class performance that you designed for. 

 

Truly excellent point. Not at all sure how to do this. I assume PHPP and an eagle-eye on the builders will not be enough. Have more to learn.

 

By the way, @TerryE do I understand your arrangement correctly that you generate DHW from your Willis heater (at least as for showers)? I think that can't be so but I was confused about your comment of a SunAmp being only useful in your case for baths.

Edited February 14, 2018 by Dreadnaught

[TerryE]

@Dreadnaught, we live at NN7 so you are close enough for you to come over for a visit and walk around / talk some of the issues.  Just PM me if you want to.  I am sure that other members can do likewise.

 

I know that I've made this point on other threads, but the devil is in the detail on ensuring that the house as-built achieves the as-designed goals.  We are retired and our build was on an adjacent plot split off from our previous garden -- and so we could keep an extremely close eye on all of the quality issues.  This isn't the case with people how have to hold down a job and don't live next to their build.   Here you have to put a lot more trust in the trades teams. 

 

Doing a self-build is extremely stressful , IMO and having a bad builder or tradesmen cut corners is the last thing that you want to face, especially if you only find out when it is too late to fix the issue cheaply.  So my view is that you make damn sure that you pick the right builder / supplier with an excellent track record.

 

As to my "bath" point, I don't use the Willis for my potable hot water at all, just the slab.  I have a pair of SunAmp PVs which I heat overnight.  This is absolutely fine for normal use, but we have a big bath and a full one on top of normal daily use is enough to require use to top-up the SunAmps after this with peak rate top-up.

[Guest Alphonsox]

32 minutes ago, Dreadnaught said:

 

Oh, very good point. Just store the energy in the slab. Obvious now you say it.
 

 

We're using exactly the same technique, with a small buffer tank heated by a 3kW immersion rather than a Willis. This allows us to store a bit more cheap energy for use during the day.

One other thing to consider is what the payback time for the PV is likely to be if you have an E7 supply. If all your DHW and heating is off-peak then the PV may not be cost effective.

[Dreadnaught]

11 minutes ago, TerryE said:

walk around / talk some of the issues

 

What a kind offer. I will PM you.

 

12 minutes ago, TerryE said:

devil is in the detail

 

I am slowly learning that. Much more to learn.

 

12 minutes ago, TerryE said:

Doing a self-build is extremely stressful

 

It is indeed a rather intimidating prospect having read some of the blogs and threads, although thus far is not deterring me, although I am rather apprehensive. Ben Adam Smith of the House-Planning-Help podcast seems to be going down the route of doing as little himself as possible for his newly-started build. I now can understand why.

 

14 minutes ago, TerryE said:

my "bath" point

 

Makes sense. Thank you. 

 

[Visti]

Great summary @TerryE. Our estimates are very close to yours at 44kWh/day using Jeremy's spreadsheet, but as you say it's all dependent on the build actual! Your average of 8.6p/kWh for Feb is pretty good. E7 I take it? or E10?

 

To clarify, you use the grid for the Heating via the Willis, and PV for your DHW which is stored in the Sunamp units. Is there any cross over? And what made you decide on that configuration as opposed to all PV, or all grid?

 

 

Edited February 14, 2018 by Visti
units

[Dreadnaught]

3 minutes ago, Alphonsox said:

One other thing to consider is what the payback time for the PV is likely to be if you have an E7 supply. If all your DHW and heating is off-peak then the PV may not be cost effective.

 

Very good point. I am tempted to plan for PV but not install it until an economic case becomes clear. Two complications about this decision are: (i) the possibility of recovering VAT at the time of build, should that sway the choice; (2) I am expecting the cost of PV to continue falling, especially as material science continues to advance.

[Guest Alphonsox]

1 minute ago, Dreadnaught said:

 

Very good point. I am tempted to plan for PV but not install it until an economic case becomes clear. Two complications about this decision are: (i) the possibility of recovering VAT at the time of build, should that sway the choice; (2) I am expecting the cost of PV to continue falling, especially as material science continues to advance.

 

Pretty much what we have done, The VAT on PV is only 5% so not a big sum in the big scheme of things. We may go for a DIY install at some point in the future but we're not rushing.

[Dreadnaught]

8 minutes ago, Alphonsox said:

The VAT on PV is only 5%

 

Oh, of course. Less of a factor.

[Triassic]

1 hour ago, Alphonsox said:

 

One other thing to consider is what the payback time for the PV is likely to be if you have an E7 supply. If all your DHW and heating is off-peak then the PV may not be cost effective.

We’re planning in roof PV, so you also need to consider the saving on roofing materials.

[Jeremy Harris]

4 minutes ago, Triassic said:

We’re planning in roof PV, so you also need to consider the saving on roofing materials.

 

 

For us, we saved around £2k in roofing materials plus maybe another £500 in roofing labour by having in-roof PV, so that does alter the cost balance a fair bit in favour of PV, even with the lower FIT rate.  The export tariff is index linked, too, and no matter what they do with the FIT it doesn't impact the export payment part.

[Dreadnaught]

6 minutes ago, Triassic said:

We’re planning in roof PV, so you also need to consider the saving on roofing materials.

 

1 minute ago, JSHarris said:

we saved around £2k in roofing materials plus maybe another £500 in roofing labour

 

Very good points. My word, these assessments are complicated! 

[TerryE]

9 hours ago, Visti said:

To clarify, you use the grid for the Heating via the Willis, and PV for your DHW which is stored in the Sunamp units. Is there any cross over? And what made you decide on that configuration as opposed to all PV, or all grid?

 

Our planning department turned down the installation of PV in our pre-planning advice: PV on the principle elevation was "not in keeping with the preferred cottage style".  The house is SE facing, so the principle elevation is the only one where it makes sense to install PV.   So we use grid electricity for all energy (apart from a couple of back propane gas rings on our cooking hob, just in case of power cuts.

 

Our village has a wind-farm and 3 largish PV installations within a 3 mile radius, so we it makes sense to buy our green electricity through the grid.  We've learnt so much from Jeremy's experience, but he's reworks his system at least three times, each a stepwise improvement and he isn't living in his house full time yet!  So our intent has always been to use the 1st year to complete the house inside and out and gain experience of living in it (including collecting hard performance data on the house as built) before doing any optimisation of the heating system etc.. 

[AliG]

Will any rooms other than the bathroom benefit from the return loop and how often will the bathroom be used? If the answers are no and not much I would question the value of it.

 

We have one and I run it four times a day as it wastes quite a bit of heat and electricity. We felt we needed one though as the kitchen and master en suite are 30M from the hot tank. When it is running or just running you get instant hot water, when  it has been off for a few hours you get instant warm water and a 2 minute wait for hot water (it is a 28mm loop due to the large number of fittings connected). At some point I may try to get a more accurate reading on its energy use to see if I should run it more. In fairness a smaller loop would use a lot less energy.

 

15m of 15mm pipe holds around two litres of water, so if you are running a shower or filling a bath you should get hot water through in less than 30 seconds. I would probably just go for this.