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Author Topic: Air or ground source + solar  (Read 8890 times)
tony.
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« Reply #15 on: May 17, 2010, 01:22:02 PM »

couldnt the PV /offset the GSHP/ASHP energy consumption. i assume that you have a large thermal mass,being a old barn, with stone walls and possibly concrete floors.

tony
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neilydun
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« Reply #16 on: May 17, 2010, 02:21:27 PM »

Yes the PV would offset the energy consumption of either, but I have read of huge electric bills from air source pumps, and during the coldest periods, not a lot of heat being generated by them.
If this is the case they are not really for me, but I only know what I have read on the net, and wanted to get as many people`s opinions before I make a descion.
I do like the idea of being able to extract heat from the ground, for little cost, but would an air source and solar themal combined do the job just as well, without having to dig up my garden?
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martin
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« Reply #17 on: May 17, 2010, 03:09:38 PM »

The Law of Sod prevails-  when you most need heat (midwinter) you'll be getting diddly squat out of the solar, an ASHP will be clanking away full tilt at it's most inefficient (COP of "1" is not unusual at that point) , so you're using electricity to effectively  "directly" heat your home, might as well have a few electric fires.... Ground source will work better in winter, but installation is pricey, upheaval to install considerable......... Undecided
If you're already "exporting", everything depends on the deal you have with your power company, but I'd suggest with the size of array that you have, you're probably pretty much "evens" in import/export, so I'd tend to avoid heat pumps altogether..........
The other thing to bear in mind is that if you're miles from nowhere, if the mains connection fails and you're dependant on heat pumps, you'll be pretty parky, whereas with wood........... Wink

Having "done the sums" several times for this sort of thing I will utter complete heresy - if you  have an existing oil boiler in good nick, you may be better off to keep it and supplant where needed with wood/solar..........(keep the oil boiler for "emergencies") - solar for DHW Spring to Autumn, wood to take over in the colder months........
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neilydun
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« Reply #18 on: May 17, 2010, 04:02:19 PM »

Thanks for your thoughts Martin.
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daftlad
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« Reply #19 on: May 17, 2010, 04:11:08 PM »

How much is wood costing you (in time as well as money). If it is free then maybe sticking with that or expanding it slightly would maybe be the best option.
The main advantage of Masonry stoves is that they are very efficient 90+ percent and a lot of there heat is given out as radiated heat which would be better for you because it would not travel straight upstairs (which is what hot air does).
Often barn conversions don't have so much thermal mass because they are insulated on the inside of the walls.
ta ta
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I WILL KEEP BANGING ON ABOUT MASONRY STOVES
neilydun
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« Reply #20 on: May 17, 2010, 04:38:02 PM »

Hi daftlad, Ive no insulation on the inside of my walls, they are solid and thick, up to 2 feet thick in some places. When we bought the place the walls were full of damp, so I hacked off the plaster, D.P.M injected and then rendered.
I gather up my own wood, so in a way its free, except I have to travel for it, petrol and chains for my saws, and then there is my time??? Maybe it cost more than I thought !
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billi
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« Reply #21 on: May 17, 2010, 08:37:41 PM »

Hi neilydun

An old Barn needs a woodburner  Grin ,  and there are good , very efficient ones on the market


I helped about 4 years ago to install this one in an old  cottage in Ireland  , in combination with a 1000 litre thermal store and 10 m2 solar thermal panels



I still think that is the ideal combination for people who have access to firewood , to go for wood burning and solar thermal as a combination , and as Martins says use the "Dirty" sources as a emergency (like oil ,gas, heatpump  Lips Sealed )

Sure if you have the space and the calculations are right (compared to a ground source heatpump costs  ) then i would go for an outside log burner that take meter lengths  of (un)splitted wood  and a 5000 litre store  (just a geustimate ) and cover the remaining 25 m2 with (some or all) solar thermal panels on your roof ... to reduce work /firing-up


Billi

« Last Edit: May 17, 2010, 08:46:10 PM by billi » Logged

1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
brackwell
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« Reply #22 on: May 18, 2010, 09:53:54 AM »

Hi Neilydun,

You ask the $1000 question as the saying goes and to be honest i do not think the definitive answer to this exists.  In many cases people quote examples/facts without any hard data to back this up and it may be out of date figures or figures chosen to suit their argument.    People talk about it being useless/expensive in winter but where is the facts to counteract the professional/manufactures saying it is OK. down to -15C.   To be honest only listen to those who have one.

My feeling is that using a solar thermal ( i have one ) for the hot water is the clear sure bet . It has to be a good investment whichever way you look at it and soon you will be able to get say 400 against your elec bill and my hobbyhorse is that you tie this in with a electric inline heater as a insurance policy against poor sun.

Ken
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martin
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« Reply #23 on: May 18, 2010, 10:06:33 AM »

or the "prejudice" may come from those of us who've seen innumerable people to whom heat pumps have been grossly oversold, and talking to those who have had them installed and really wish they hadn't! Wink
I'll reiterate - I've "done the sums" many times (using real life performance, not hyped claims), and I have never been able to make them "add up" unless you have something like a hydro plant churning out gobbets of power (which few of us are fortunate enough to have) Roll Eyes
« Last Edit: May 18, 2010, 10:12:19 AM by martin » Logged

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neilydun
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« Reply #24 on: May 18, 2010, 10:45:05 AM »

Yes, everyone seems to agree that solar themal is the way forward. If this is the case do I fill my roof space (approx 25 Sq M) with them? and keep my existing oil fired system?
Altough I like the idea of a woodfired burner I don`t really want to spend any extra time collecting wood, and the supply which I have at the moment is limited, as is a space to fit a woodburner.
If, for example, I were to fit 25 Sq M of solar thermal and it was mid winter, 0c outside temp, but a bright sunny day, what temp could I hope to achieve ?
I have approx 85 Sq M of underfloor to heat and hot water.
Does anyone have any toughts on the RHI ? and the rates they have set out ?
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dhaslam
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« Reply #25 on: May 18, 2010, 11:26:26 AM »

This winter was very good for solar thermal because it was frosty with  clear skies.    November was the worst month but then it was warmer.

This graph in kWh  is for just under six square metres.  From a system four times larger there would be enough heat most days to warm the floors.  Output is greater if the system is set up to transfer heat at lower temperatures.      To get the full benefit you ideally would need to add some seasonal storage.   In any case you would need to dump a lot of heat in summer, more that 75% of the heat produced most days.   


* WinterSolar0910.jpg (90.4 KB, 900x681 - viewed 325 times.)
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
djh
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« Reply #26 on: May 18, 2010, 11:52:14 AM »

do you have that data as a CSV file? Just for fun.
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Cheers, Dave
Countrypaul
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« Reply #27 on: May 18, 2010, 03:47:07 PM »

or the "prejudice" may come from those of us who've seen innumerable people to whom heat pumps have been grossly oversold, and talking to those who have had them installed and really wish they hadn't! Wink
I'll reiterate - I've "done the sums" many times (using real life performance, not hyped claims), and I have never been able to make them "add up" unless you have something like a hydro plant churning out gobbets of power (which few of us are fortunate enough to have) Roll Eyes

Martin,

Is there an element of those that have had problems shouting loudest in this case, and those that are happy, keeping quiet and busy with other things so not looking round discussing things etc?

I am sure that they will have been grossly oversold, especially by salesmen on commission one way or anothertoo much "won't be my problem when it doesn't perform cos I'll be gone by then.."

Paul
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billi
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« Reply #28 on: May 18, 2010, 06:32:41 PM »

Quote
Yes, everyone seems to agree that solar themal is the way forward. If this is the case do I fill my roof space (approx 25 Sq M) with them? and keep my existing oil fired system?

I wouldnot rush , if you are the character that likes thinking of ideas ....
There are lots of ideas/thoughts  to be combined to a clever heating idea
But you could end up like me , to have too many ideas without a plan  norfolk


Anyhow a customer of mine here (ireland)  asked me 10 years ago to built a lined Pond , so i did built his pond ( me am a Pond builder since i am 2 years of age  Wink )

He asked me to bury  ca. 800 metres of 1 " Pipe underneath the Pond/liner  for his heatpump idea

He has about 20 m2 solar thermal on the roof and the controller/ plumbing  control the flow ...

So if solar is doing enough for hot water and heating (in a 750 litre store ) , the controller sends the extra heat from the solar panels back under the pond, or in his case under the foundation into an earth store as well  , the heatpump just connects to the warmest source first , so measures  the temp under the pond , if that is colder , it switches to the stored heat under the foundation  and back to the pond 

Sounds complicated , but  all i want to say is that a heatpump can benefit from the overproduction of bigger solar thermal Idea if that heat from summer/or sunny days  is captured some how !

Billi 

thats the pond


* bischi.jpg (116.41 KB, 1134x448 - viewed 298 times.)
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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
dhaslam
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« Reply #29 on: May 18, 2010, 07:11:40 PM »

do you have that data as a CSV file? Just for fun.

Xls file attached.   CSV  format doesn't seem to be allowed by the system

There doesn't  seem to be much data available on long term underground storage.  I will bury some temperature sensors into  mound and monitor the temperature  over the year.  It will be another few weeks before it is setup but I want to have it start heating before the end of June.  This winter has given more confidence that the  temperature can be topped up even in winter months.     

The greenhouse overnight store is   not working that well in warmish weather.     The exit air is getting up to  about 16C by the end of the day and dropping to around 10C  by morning.  So the store is varying by about  six degrees  but perhaps adding only about one degree to the greenhouse temperature.    The heat transferred is something like 2.7kWh, assuming that the two fans are moving 300cu metres of air per hour and average differential of 3 degrees.   But the greenhouse has practically no heat retention,   U-value is about 4 and surface area 32 sq metres so  over  nine hours the heat loss should be about 1.2kwh per degree differential but there is also  some ventilation loss as well.      I think it should work better in very cold weather when the temperature difference is greater.  Fitting auto vents has reduced the input temperature to the mid 20s C most of the time.   There is no temperature control on the fans yet, just time. 


             OutMin In_Min    Min Exit   MaxExit
09/05/2010      3       5                    Before fans used
10/05/2010   4   6.5      8      
11/05/2010   1   5      9      16
12/05/2010   2   6      10.6      15
13/05/2010   5   8            
14/05/2010   5   6      10.2      
15/05/2010   6   9            
16/05/2010   5.5   6         12      
17/05/2010   6   7        12      
18/05/2010   8   10.5        10.8      




* SolarOutput.xls (16 KB - downloaded 179 times.)
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
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