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Author Topic: Designing heating & hot water system for off grid new build  (Read 3016 times)
Rusty55
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« Reply #75 on: November 16, 2020, 08:17:55 PM »

Thank you all once again for the comments. It is really helpful and interesting to read all the discussions. I've tried to take a few comments/questions out of the many messages and can confirm the following ...

Off Grid or Not - this is not a debate for us as we love the idea of it and want the challenge of it .... so for better or worse ... that is settled.

Long term Planning - I'm 56 and will be living there with just my wife 95% of the time - all the kids are off the payroll. When we get to be infirm it will be difficult to live there for many reasons but I hope I will leave in a box. I also hope that by the time I am in that box the energy system will be pretty well automated.

Solar and winter - I sure Paul is right ... I don't expect it to work in winter ... so that is why I plan a) a Hugh Piggott 2kw (3.6m diameter) wind turbine (the site is really very windy indeed) and a b) a wood burning stove with back boiler. If all else fails, and thanks to the advice from you all, I will also have a smelly diesel generator. I will work tirelessly to address the reasons it is needed and try to eliminate them as I go along...

Costs - One thing I think that will revolutionise the cost of going off-grid is what is going to happen to batteries due to the mass-market move to EVs. There will be a surplus of part worn lithium batteries which will not be viable for EVs but still very useful for off grid setups. You can already by an old Nissan leaf for less than the lithium battery capacity would cost so I think in future this is going to make capacity a lot cheaper. Would be interesting to hear if you agree or not!

My location - I have looked at the solar yield for my location in detail and from multiple sources and it is roughly the same a Birmingham even though it is at a latitude North of Dundee. This is because the island is far enough west and has no high mountains so it is in fact a very sunny location even if it is very much further North. My plan is to have 3 separate ground arrays pointing SE, S, SW all at optimised angles for winter sun profile. Thankfully there are no mountains in the way. I'm increasing my solar from 5kw to 8kw based on your advice.

I have pretty much decided that the GSHP is a bit of a no-no even though the RHI is tempting me. It will demand too much power at a time when I might not have it (>1kw) so I'm now thinking of having a small vented thermal store (1000l) with a coil from the WBS boiler and 2 immersions - one low power and one high power. I will dump excess generation into this when I can. In summer I will generate more than I can use so the immersion, albeit inefficient, will not cost more than GSHP and it will be much easier to fix if it fails. It will also help iron out the lumps of available wind in the winter.

Also I haven't mentioned this yet (and I know this is going to bring on a whole load more debate!!) but eventually I want to use an old EV - both as a car and as a battery source. The island is small so journeys are very short. The car could be used to take on excess generation and also provide backup battery capacity. The problem is that no one has really invented a solution to this (commercially) - there is V2G and even V2H but it only works in conjunction with grid tied systems. There is one company I have found (SETECH) that professes to make a 6kw plug-in EV inverter and there is one company (Myenergi) have a product that uses dump load/excess to charge a car (Called Zappi) but again ... only works with a grid tied system. So we shall see... I'm definitely planning the EV as phase II though... makes me want to skimp a bit on the batteries now though...

Sorry if I'm boring you all ... if not ... looking forward to the feedback!


Cheers, Rusty.

 



 



 
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Rusty55
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« Reply #76 on: November 16, 2020, 08:21:50 PM »


2.
If you go with a MHRV and conditions are at all feasible look into the possibility   of  the  installation of an earth tube to feed the unit since  it will both warm and cool  at the appropriate times of year  for free.

Good Luck and please keep us posted on progress , that is what we all feed on 


Thanks Bxman. Do you mean sucking air into the MHVC system via a vent that goes underground? If so, I'd like to learn more about that. How long a run do you need to make it worthwhile? are there any other design considerations? Any links that I could learn from? Thanks again. R.
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A.L.
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« Reply #77 on: November 16, 2020, 10:11:01 PM »

hello again rusty55,

MVHR's have a limitatiom in that at low external temperatures the outgoing air can condense and freeze in the heat exchanger, because the incoming air cools it. The temperature that this happens at is typically -1/-5C, the more efficient the MVHR the higher the freezing temperature. One solution is to pre-heat the incoming air, this can be done by running the air through buried large diameter pipes but this is not cheap e.g.circa 3000. These systems seem to have fallen out of fashion, perhaps because of fears that mould growing in the underground pipes, they are sometimes impregnated with antimicrobial silver.

https://www.greenspec.co.uk/green-products/heat-exchangers/details/rehau-awadukt-thermo/

an alternative is to run brine through buried pipes and use a heat exchanger to transfer the energy to the incoming air.

https://sole-ewt.de/welcome/?lang=en   https://www.sole-ewt.de/PDF/en/Sole-EWT-Info-en.pdf

both of these can also be used to provide summer cooling.

an alternative to these is to fit the MVHR with an 'enthalpy' heat exchanger, this transfers water vapour in the outgoing air to the incoming air preventing condensing/freezing. This can be effective down to at least -8C

https://www.paulheatrecovery.co.uk/components/moisture-heat-exchanger/

this system does not provide summer cooling but selecting a MVHR with a 'summer bypass' and good house design is likely to make this a minor matter in our Scottish climate
« Last Edit: November 17, 2020, 12:06:05 PM by A.L. » Logged
camillitech
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« Reply #78 on: November 17, 2020, 06:01:28 AM »

Good plan with the EV Rusty, tis on my 'to do' list as all my journeys are on single track roads with absolutely no traffic and loads of wildlife  Wink
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http://lifeattheendoftheroad.wordpress.com/

'Off grid' since 1985,  Proven 2.5kW, Proven 6kW direct heating, SMA SI6.OH, 800ah Rolls, 9kW PV ,4xTS45, Lister HR2 12kW, , Powerspout pelton, Stream Engine turgo, 60 x Navitron toobs and a 1500lt store. Outback VFX3048 and 950ah forklifts for backup,
mr smith
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« Reply #79 on: November 17, 2020, 07:17:49 AM »

Sounds there is no turning you away from an off grid set up but this is my two pence.

My main concern from your plans is the WBS on an island with no trees. I run my house on timber and it is not easy even when I am surrounded by the stuff and work in the industry. When I get older I plan to fit a different system due to the work and time involved and possibility of illness etc.

I see there is the possibility of an electrical connection. Why not get connected then spend your retirement developing off grid systems to eventually get yourself in a position when it is only an emergency back up.

Good luck it sounds like a great adventure.
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biff
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« Reply #80 on: November 17, 2020, 11:22:32 AM »

Off-grid is good Rusty
        It takes a little while to figure it all out but it is well worth it. There are many more options and new ideas that were not about 15 years ago.
  We had a small 12v installation to start with. We had a gas fridge and despite Paul telling me that the gas fridge was an expensive waste of money, we kept it for a few years till finally, I converted a chest freezer to a fridge and saved a couple of hundred quid a year. We still cook with gas. Also , PV is a fraction of what it cost when I bought my first 2 x 80watt panels. I always kept and still keep a couple of generators, I never charge the bank with our generators, instead I have a separate DC  120v x 2kw charger which is permanently connected to the bank and extremely economic. I also moved up from 12 volt to 120volt because it could travel better and could take most combinations of PV panels with our Chinese controllers .
   However, 120vdc is not everybody,s preferred choice.
     Good Luck,
      Biff
 
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An unpaid Navitron volunteer,who has been living off-grid,powered by wind and solar,each year better than the last one.
kdmnx
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« Reply #81 on: November 17, 2020, 11:36:11 AM »


2.
If you go with a MHRV and conditions are at all feasible look into the possibility   of  the  installation of an earth tube to feed the unit since  it will both warm and cool  at the appropriate times of year  for free.

Good Luck and please keep us posted on progress , that is what we all feed on 


Thanks Bxman. Do you mean sucking air into the MHVC system via a vent that goes underground? If so, I'd like to learn more about that. How long a run do you need to make it worthwhile? are there any other design considerations? Any links that I could learn from? Thanks again. R.

I've seen a few of these systems. The point is that the ground temperature is about 10℃ all year round. So if you run the intake air through a long underground pipe you get cool(er) air in summer and warm(er) air in winter. Pipe length is obviously a key question, but other than "longer is better" it is very difficult to determine because the effectiveness depends on airflow rates and temperature differential. The ones I've seen have been a 4" pipe laid 3-4ft underground with a c. 50m run (limited by the length of the garden). If you've got an excavator and a man on site anyway digging the foundations then for the cost of an extra day of man/machine hire, it seems worthwhile to me!

My only comment on your plan would be to suggest simplifying your solar setup into two arrays instead of three. One SE, the other SW. It'd be cheaper this way (only two mountings/charge controllers/cable runs), you'd get more power at the edges of the day, and in the middle of the day both arrays would be generating anyway.
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bxman
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« Reply #82 on: November 17, 2020, 01:23:32 PM »

 hi Rusty

Looks as though  @A.L. has covered it for you,    better  than I could have done .


However you are still intrested look for " passive houses on Skye" you will find some one that knows about ground tubes,  (they are on their second one )

Regarding the the PV panels I think you will find that in Nov, Dec  & Jan the photons have to travel through just to much atmosphere to be of a lot of use,  except possibly around midday and  while your location may give you the same hours as us further South it will not produce as much power.

I have nothing much to boast of at the times of year I actually need it even 20 miles  South of Birmingham.
Cheers Patrick
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pantsmachine
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« Reply #83 on: November 17, 2020, 01:47:24 PM »


Nice wee 3kva lister genny on Aberdeenshire gumtree today. Offers around 950, any use to you?

https://www.gumtree.com/p/generators/3kva-generator/1390339856

Our 8kW array is outputting a very pathetic 4kWh per day at the moment. Sad

Are you going to be burning peat?
« Last Edit: November 18, 2020, 08:28:57 AM by pantsmachine » Logged

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jhinshel
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« Reply #84 on: November 18, 2020, 08:03:08 AM »

Rusty,
It will cost you atleast 20k to get a system that will charge a car and run the house. Probably more but that depends on lots of factors. I have lived off grid for 15 years in cornwall. I built all the systems and all energy is from renewables. We run a 30kwh nissan leaf and the house is a 200 year old farm house. It is possible but you will have to start with a good plan. Wind power is your biggest friend - find a 6kw used proven/kingspan/sdwind turbine or something similiar (this may sound over sized but if you want to run a car you'll need it) and the windest spot. If you have no wind resource, you'll need to find an alternative such as hydroelectric, biomass/biofuel.

Solar is cheap so you should plan to install a massively oversized system. This will produce far too much power at peak times but will help to smooth out the low output times. We have 12kw of solar PV.

Insulate the house - go overboard with this. The idea of excavating under the house and building a ground heat store with pipes sounds great. i'd try that but it would need careful design and modelling. It would be a great use of excess power.

If you manage to do all of the above, you'll have to develop deep understanding of how the system works. Ideally it will have a load of smart controls or else you'll have to occupy your time making sure things are working properly. You could get a stack or arduinos and rasperry Pis and learn how to programme them or find someone who is a whizz to automate stuff.

Note that grid electricity is cheap. Off grid electricity is always likely to cost more than this - think of economies of scale. If you have access to the grid there are ways to reduce the connection fee. Explore this as much as possible. Identify the lowest cost of connection. From the perspective of the EV, if you have nowhere else to charge the car other than your  home, go with the grid or plan to become an expert in all of the areas identified above.

Regards,
Justin

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off grid 4 years: 2.5kw pv,sunny island 5048, 2 mx 60s, proven 2.5 48v, home made charge controller, 1500Ah fork lift batteries, 60 evacuated tube solar heating, vigas 40 kw biomas boiler, 3000l thermal store
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