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Author Topic: System Planning Advice  (Read 2351 times)
linesrg
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« Reply #15 on: March 11, 2019, 05:44:31 PM »

Bikerzz,

Having a system which uses an Immersun which diverts Solar PV to two immersions in a heat store I'm coming around to thinking this isn't the most efficient thing to do.  In fairness others have made this point elsewhere on this forum.

For the sake of argument say you use your Solar PV diverted to heat water then let's say this is an 80% efficient process.  If you take this same amount of energy and use it to charge batteries and you have roughly the same level of efficiency.  This is a simplistic argument so absolute accurate figures aren't essential.

If you have a heat pump then let's say it has a COP of 3.0, using the energy stored in the battery you get much more energy back overall then using an Immersun to heat water in a heat store.

Regards

Richard
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nowty
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« Reply #16 on: March 11, 2019, 07:33:45 PM »

Yes 12kwh a year in oil does seem a lot, any idea what that would cost in Electricity from a ASHP? At a COP of 3 and 0.15p electricity isnt that only £600?

A GSHP may give you a COP of 3 in Winter (mine does), but you aint gonna get a COP of 3 with a ASHP in winter when you need the heating the most.
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Bikerzz
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« Reply #17 on: March 11, 2019, 07:51:13 PM »

Thanks people. I have rang council about solar PV and ASHP being allowed in a conservation area and awaiting a call back.
However going back to ASHP and 12MWH, £600 in electric sounds like a bargin, even compared to how cheap oil is at the moment (which can only get worse)
Im very open to suggestions, however none of you have really put me off a ASHP yet, a £1k electricity bill each year maybe less with some solar, sounds fine to me...... Im not going to go throw away the oil boiler until it breaks or oil get stupid expensive again, so dont worry I wont make any hasty decisions.
I will look into Thermal stores and unvented cylinders, however with many sources of heat I guess a TS is more appropriate (and the fact Im not sure living out here on the end of a water main gives me the best water pressure, and Im up a hill)
« Last Edit: March 11, 2019, 08:17:40 PM by Bikerzz » Logged

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rogeriko
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« Reply #18 on: March 11, 2019, 09:48:28 PM »

In the winter dont forget your ASHP will continuously freeze up outside and then it will run full power in reverse to defrost itself. Despite what the manufacturers say you wont get a cop above 2 when its cold and damp outside. If you need 10kw of heat to continuously maintain your temperature thats 5kw of electric 24h per day which will cost 540 pounds per month. Please forget the theory, these are the facts.  (I install heat pumps)
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Countrypaul
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« Reply #19 on: March 11, 2019, 10:35:26 PM »

In the winter dont forget your ASHP will continuously freeze up outside and then it will run full power in reverse to defrost itself. Despite what the manufacturers say you wont get a cop above 2 when its cold and damp outside. If you need 10kw of heat to continuously maintain your temperature thats 5kw of electric 24h per day which will cost 540 pounds per month. Please forget the theory, these are the facts.  (I install heat pumps)

If he would need only £600 per year for direct electric heating, there is no way he will need anything like £540 per month even in January!

Whilst an ASHP might not be the most efficient solution in winter, it is likely to be better than direct electric heating most of the time in this country except perhaps during a very bad spell such as the "Beast from the East" last winter. Relying on an ASHP for most of the time but having the oil boiler available for any really bad spell could be an acceptable compromise. 
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Bikerzz
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« Reply #20 on: March 12, 2019, 07:26:49 AM »

Thanks Roger I understand.

As Paul said - Im my non understanding mind (Im still learning), running a ASHP 90% of the time with water at 20-30c for just UFH must be the most efficient I can get? Then boiler for bad winter spells?

I also have unlimited supply to lithium batteries but that's for another topic.
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biff
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« Reply #21 on: March 12, 2019, 09:19:59 AM »

           "I also Have an unlimited supply of Lithium batteries"
       Shocked Shocked Shocked  I Say ,
                     Biff
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Bikerzz
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« Reply #22 on: March 12, 2019, 09:27:29 AM »

           "I also Have an unlimited supply of Lithium batteries"
       Shocked Shocked Shocked  I Say ,
                     Biff

Not ones I can hand out sadly. Its what I do for a living 12v and 48v automotive dev engineer
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gnarly
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« Reply #23 on: March 12, 2019, 10:36:05 AM »

Is 48v automotive really coming? Itís only been 10+ years!

I would take heed of rogerikoís comments that ASHP specs donít reflect real life amd they switch to full price resistance heating when they going gets tough (and freeze / defrost cycles that donít actually produce much overall heat).  But you have the perfect solution if you are keeping your oil, you just have a control problem where you need to use the ashp when not so cold out, and the oil on the coldest days.
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Bikerzz
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« Reply #24 on: March 12, 2019, 11:25:49 AM »

Cheers.

Sounds like I need a full system expert in..... good luck finding one! (Warwickshire - anyone?)
Im going to be here 30+years so I dont mind if payback is 20 years but I want to do it right and once.

Cheers
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Bikerzz
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« Reply #25 on: March 15, 2019, 11:11:19 AM »

Is 48v automotive really coming? Itís only been 10+ years!

I would take heed of rogerikoís comments that ASHP specs donít reflect real life amd they switch to full price resistance heating when they going gets tough (and freeze / defrost cycles that donít actually produce much overall heat).  But you have the perfect solution if you are keeping your oil, you just have a control problem where you need to use the ashp when not so cold out, and the oil on the coldest days.

It already is here. You can buy 48v systems on a few vehicles today. MHEVs they call them.

I honestly have no clue what to do about heating the house. A plumber coming next week, see what he says. (I will of course take with a pinch of salt)
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Countrypaul
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« Reply #26 on: March 15, 2019, 11:28:17 AM »

I made the consious decision when renovating to decouple the heat generation from the heat emission within the house. We went with UFH for the heat emission as almost all forms of heating would drive that (Air to Air heat pump excluded, and if you really wan to use night storage heaters they wouldn't either), and by using a thermal store I figured that I could combine multiple heat sources relatively easily and update the heat souce in future should a new technology appear.

I'm not sure that most plumbers would think that way, more likely they want to put a system in without the flexibility you may want in the future.  Even teh heat calculations carried out by the plumber are likely to be very rudimentary and include a large margin to ensure it is warm enough regardless of whether that costs more to operate than is should or not.
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Bikerzz
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« Reply #27 on: March 15, 2019, 12:09:10 PM »

Thank Paul

Basically Im willing to invest in anything that will payback in 20 years, if I plan on living here for 30 years ish.  Yes I have to be slightly flexible as Mrs might add to the size of family and maybe we convert the loft etc....

However starting the major renovations this year and UFH seems a no brainier, its just what pipes should be put in where and what electrics etc.... Do I leave space for a Thermal Store or Unvented cylinder in utility room?  What Size?

I will probably add Solar PV (Id consider thermal but I think PV is the way to go now), and I battery bank is a no brainier really for my position.

If Im putting UFH in on an oil boiler I really need at least a 120L buffer store if I dont go for a larger TS.
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DonL
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« Reply #28 on: March 15, 2019, 02:17:53 PM »

I was just a bit concerned about the negative advice on ASHP's. I have one and my experience has been entirely positive with very low electricity bills.
I recall a report I read a few years back in which they compared actual results for ASHP's and GSHP's. The difference was pretty small but the spread of results on both was enormous. So, in my view, the most important thing is to get the design right with the lowest practical design temperature for your heat emmitters to get the best COP (I replaced conventional radiators with larger units operating at a lower temperature).
The other main source of problems is people operating the system wrongly. To get the best COP and low radiator temperature it needs to be set up so that it runs most of the the time to maintain house temperature with the water temperature varying inversely to the outside temperature. People expect to run it like gas fired central heating and leave it off all day and then turn it on in the evening expecting to get a warm house, and when that doesn't work they turn up the water temperature, the COP drops and the bills go up.
I'd go so far as to say that if the house is unoccupied for a lot of the time I wouldn't choose a heat pump.
So: Insulate
Draft proof
Insulate again
Have a properly sized and designed heat pump
Run it the way it should be run.
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Bikerzz
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« Reply #29 on: March 15, 2019, 02:27:39 PM »

Thanks Don

Im thinking if I could run the the UFH off a ASHP that would be great! Low temp constant, not sure how in winter I could move over to boiler/TS, but might be a simple way.
Run the hot water off Solar PV and boiler in the winter.

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