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Author Topic: Advice on Self Build  (Read 7532 times)
Smirker
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« on: November 24, 2012, 08:23:00 PM »

Hi All,

We are about to embark on a self build and are getting bogged down as to whether we should go down the heat pump route (Earth Save ASHP for UFH and Ecocent for DHW) or if we should stick to installing an efficient boiler to run UFH and provide adequate hot water? We intend to insulate to 0.15U Value or below with triple glazing and be as air tight as possible.

I realise that the capital outlay will outweigh the savings that we will get in the short term but we are willing to invest for the future as gas/electric prices are only going to increase.
 
We intend to install some form of solar tech (PV only or PVT if the budget will stretch) which will provide some of the DHW/electricity.

Really finding all the conflicting opinions confusing and we obviously want to make the right decision.

Does anyone have any views on the Genvex Combi as well as Earth Save Products integrated systems?

Thanks,

Jim
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desperate
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« Reply #1 on: November 24, 2012, 08:53:19 PM »

Hallo Smirker welcome, speaking as a non HP expert........

If you have mains gas available it will undoubtedly be the cheapest option for the short term at least, although not necessarily the lowest carbon option, you will be exposed to future gas price increases with no options.
If you go down the HP route you will more than likely need a small amount of back-up particularly for the hot water, but it does future proof your heating against those price increases, of course electricity is going to increase as well but if you can generate some of your own with PV that will help out.

My gut feeling..........with your UFH, good insulation levels and glazing, go HP route.

Desp
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Smirker
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« Reply #2 on: November 24, 2012, 09:14:35 PM »

Thanks for the reply,

A bit of a headache trying to decide what to do for the best facepalm. We would like to use some renewable tech but not if it is going to cost a fortune. A compromise has to be reached and we will prioritise insulation/airtightness so space heating demand should not be huge. DHW is a different matter. 2 adults and three growing children so the demand will be high. Best to spec a 250l Ecocent or gas boiler maybe in addition to solar thermal?
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Richard Owen
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« Reply #3 on: November 24, 2012, 09:21:39 PM »

I'd make a thermal store with lots of tappings, the heart of the system.

Then, if your chosen technology doesn't quite deliver, it isn't going to be a major drama to add something else.


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44 Yingli 230Wp panels feeding into 2x Solar Edge SE5000 inverters.
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10kW heat pump.
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Smirker
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« Reply #4 on: November 24, 2012, 09:44:42 PM »

Ok, an interesting take. A thermal store would be a good option as we are thinking of some solar thermal as one of the inputs which could then be supplemented by an efficient condensing boiler.

Our friends who self built a few years ago went down this route and are happy with the results. Our only issue might be space for the tank.
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dhaslam
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« Reply #5 on: November 24, 2012, 09:54:15 PM »

If you are getting an air source heat pump you should  buy a  good  reliable make.    The more expensive ones have a larger air throughput  that allows them  to work down to about -15C  and at more normal temperatures they can still produce quite a lot of heat.    With care you can top up DHW  with an immersion  for the last 10C which saves running the heat pump at excessive temperatures.    I don't see how the Ecocent can add anything because it means either cooling the house or bringing in outside cold air  which would be duplicating the main heat pump.  There is a small  net gain by condensing  moisture from the air in the house but a modern house won't have  high humidity.   An ASHP running cost can be very low  if off peak electricity is used.    When building you should allow  sufficient space  in the centre of the house for a good big   thermal store.  If it is centrally located any heat loss  will be retained in the house.     It can be used to even out   solar gain over a few days  as well as to allow flexible running times for a heat pump.    As Richard says a heat store allows other heat sources to be added.        
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brackwell
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« Reply #6 on: November 25, 2012, 09:27:16 AM »

Comparing running costs between gas and heat pump then there is very little in it but soon you will be able to get RHI for a GSHP (the ashp is still in the air) and this will then make the GSHP a no brainer. The fitting cost on a new build when the JCB is already there etc makes this cost effective. Always assuming you have the space.

The thing you should really consider are passive solar heating of the building along with significant internal thermal mass in order to provide stable internal temps and reduce overheating in summer.

Ken
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Smirker
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« Reply #7 on: November 25, 2012, 03:14:18 PM »

Thanks for the input. It shows how little I know about all this stuff, I had not considered thermal mass etc.

To address the points made in the last two posts; GSHP we had pretty much ruled out as we only have a narrow but fairly long plot 9.5x45m approx and did not think we would have enough room to lay the pipe work. A good point is made about the Ecocent unit in that it will drain heat from the building in order to provide DHW. It would seem then that a better route might be to install a thermal store with several inputs, we will need therefore to look at our plans to see where we could site one as I have seen how big they are plus we will need a place for UFH manifolds etc.

Is GSHP feasible in the allotted space we have? In which case this could be used to run UFH and hot water to an extent.

Passive solar heating will play a part as we have significant south facing glazing incorporated into the design.

Views on whether it's worthwhile to install solar thermal?

Does anyone have a view on the Genvex Combi, a good investment or not?

Thanks to everyone who has given advice, it's good to hear the views of people who are not necesarily selling something.
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bornagain
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« Reply #8 on: November 25, 2012, 04:36:36 PM »

Hi,

Please find my two-pennies worth....

We completed our new build in Oct 2011, its around 190m2

It is built of ICF and has similar spec as your proposed house.   Walls U=0.15, floor <0.1, roof <0.1

We have solar thermal with quite a large Thermal Store. 500L

We have no heating at all upstairs and UFH  downstairs.

All the internal walls are blockwork, the ground floor is;- 300mm EPS: 100mm concrete: around 110mm of screed.   The UFH pipes sit on the concrete. The first floor is beam and block with screed on top.  This all adds upto loads of Thermal Mass.

The windows and doors are all 3G, we have a lot of glass facing south.

Vent Axia Sentinel Plus MVHR unit.

There is a small room sealed woodburner in the living room which has a back boiler that thermosyphons into the Thermal Store .   The woodburner does not get lit very often (ie hardly ever), but it is really lovely to light it on a cold winter evening.

We have PV that has generated around 3600 kWHr but I think the overwhelming majority of this has gone back into the grid - the Yorkshireman in me fancies an Immersun - but I think that the right thing to do is to export as much as possible.

The Thermal store is heated by the Solar Thermal, the backboiler and by a couple of Economy 7, 3 kW Immersion heaters.

We have no oil or gas, and our total fuel bill (if we ignore a little bit of timber) is around 670/yr (circa 7500 kWHrs)

PV is yielding around 1700, so we have a net energy bill of around -1000/yr.

We could have used less energy, but my wife likes the house warm 21 C.

I am an Engineer and I tried really hard to convince myself that we could do with an Air or Ground Source Heat Pump - but no matter how I did the calcs, it just didn't pay.  In retrospect, I was correct.   Spend your money on insulation.

Let us all know how you get on...

Regards

P.
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Smirker
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« Reply #9 on: November 25, 2012, 09:02:45 PM »

Great concise response, thanks genuflect The more I read the more it becomes apparent that we will be best to insulate to a high level and go down the solar thermal/thermal store backed up by a gas boiler (we have mains gas available). We too will be installing UFH downstairs. My only fear is that we wont have that much thermal mass in our building, being a timber frame. We have to minimise our wall thickness as it is a narrow site. The overall dimensions are the same (190msq), I am looking forward to the reduced energy bills from a better level of insulation and the feed-in from the solar.

The rational is that with a thermal store we can always add a ASHP at a later date if gas prices sky rocket. It makes no sense to bypass gas but run a heat pump with expensive electricity.

Are you happy with the MVHR unit you installed?

How does your UFH run out of interest; from the thermal store? I am lucky in that my wife likes it a bit more freeze so our heating bills should be less so should be quids in. hysteria
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acresswell
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« Reply #10 on: November 25, 2012, 09:33:25 PM »

You may not be able to put much thermal mass in your walls, but don't forget that you can add thermal mass to the ground floor!
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Building a new home in North Worcestershire
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Smirker
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« Reply #11 on: November 25, 2012, 11:46:24 PM »

Thanks, will bear that in mind. Block and beam with added insulation so that will provide decent thermal mass in fact. Like the Blog by the way.
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brackwell
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« Reply #12 on: November 26, 2012, 10:47:18 AM »

Bornagain,

P could you expand your thoughts/calculations a bit further  " I am an Engineer and I tried really hard to convince myself that we could do with an Air or Ground Source Heat Pump - but no matter how I did the calcs, it just didn't pay.  In retrospect, I was correct."    I am an engineer and when i have done calculations of running costs i come out pretty evens.

Ken
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bornagain
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« Reply #13 on: November 26, 2012, 06:03:28 PM »

Brackwell,

Assume that we use a typical amount of electricity for normal, day to day use   3500   kWHr/yr
                     
All remaining electricity is used for DHW & Heating                  4000   kWHr/yr
                     
Assume a CoP of 4 (which is pretty optimistic)                     
                     
Energy required to drive a heat pump                                  1000   kWHr/y
                     
Actual Energy Required to Drive Immersion Heater                             4000   kWHr/yr
                       
Energy "saved" by Heat Pump                                                      3000   kWHr/yr
                     
This energy is all E7 electricity which costs 5p kWHr and therefore costs                150   /yr
                     
If we Use a CoP of 3, then the saving drops to around 133/yr                     
                     
So, in order to save at most 150/yr I need to buy a heat pump, install it, and then maintain it. Then buy a new one is (say) 15 years.

Feel free to spot the deliberate mistake - but if you can't then I'm sure you will agree that unless E7 electricity gets a lot more expensive, you don't need a heat pump.
                  
Regards

P.
« Last Edit: November 26, 2012, 06:14:38 PM by bornagain » Logged
bornagain
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« Reply #14 on: November 26, 2012, 06:12:49 PM »

Smirker

The UFH is connected via a 4 port valve installed like the arrangement on the Accumulator Tanks website -goto the downloads page and download the last circuit diagram.

I bought my tank from Accumulator tanks, it appears to be a one man band, but he knows his stuff and gave a bit of support over the phone when I came to pipe it all up.

The solar thermal installation onto two coils seems to work particularly well, although the solar thermal company who installed it took a lot of persuasion - ultimately, Akvatherm are a big European outfit who know what that they are doing.

http://www.accumulatortanks.co.uk/Circuit%20diagram,%20AKVAir%20Solar%20Plus%20range.%20For%20guidance%20only.pdf

good luck

P.

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