geoffdg

What boiler to go with Solar thermal and wood burner

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16 minutes ago, scottishjohn said:

yes it was  you JS 

so actual heat input for 24hrs is around  38-40 kw 

that's fine thank you 

 

 

 

No.  The heat input when it's -10 deg C is about 1.6 kW

 

The 38 kWh figure is the heat energy required.

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1 minute ago, JSHarris said:

 

 

No.  The heat input when it's -10 deg C is about 1.6 kW

 

The 38 kWh figure is the heat energy required.

1,6 kw prhr x 24hr =38kw 

that is real worse case scenario as not many days inyear when you see -10c 

average winter temp here from epc calcs  is  +3c.

ok another question --total energy used in last year  for heating ?

 

 

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18 hours ago, scottishjohn said:

first question must be --how good is build --is it near passiv --or old leaky thing

can you get mains gas?

Hi John,

It will be a pretty standard build, just complying with building regs. Unfortunately there is no gas in the village, we could get LPG but the neighbours have an agreement with the oil supplier for a discount.

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13 hours ago, geoffdg said:

Hi John,

It will be a pretty standard build, just complying with building regs. Unfortunately there is no gas in the village, we could get LPG but the neighbours have an agreement with the oil supplier for a discount.

NO.

Ive had LPG and it is worse or sometimes better than oil,depending on world pricing and deal you can get  --but both are so much worse than mains gas.

so  spending more on the insulation level should be first goal as that will drop your energy usage now  and forever 

doing that is the first and best thing you can do for your house

,how you heat  it is secondary .

 

 

 

 

anyway --look at getting insulation better and look very hard at ASHP +RHI payments you can get -use that to heat UFH and a thermal  store for dhw.

 

as already stated getting multiple heat sources will only work well if you are into serious control systems 

 

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8 minutes ago, scottishjohn said:

anyway --look at getting insulation better and look very hard at ASHP +RHI payments you can get -use that to heat UFH and a thermal  store for dhw.

 

Ok so ... ASHP can’t get to thermal store temperatures. You need in excess of 65-70c to have a decent thermal store capacity and that gets to near 1:1 CoP which gets expensive. 

 

Also, if you want to use RHI on an ASHP deal, do the bare minimum as your payment is based on the design heat load so if you put too much insulation in, you won’t get the payments to cover the cost of the ASHP install. 

 

 

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Does a thermal store really need to hit 65-70 degree?

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2 minutes ago, Alexphd1 said:

Does a thermal store really need to hit 65-70 degree?

 

Isn't this to kill the bugs?

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57 degree for a normal tank for bacteria plus it's a thermal store water is heated on demand (like a combi boiler). 

 

Nick, is this correct?? 

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1 hour ago, scottishjohn said:

1,6 kw prhr x 24hr =38kw

 

No. Please find out what a watt is; you clearly don't understand and you're just reinforcing an all-to-common confusion.

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Nothing to do with legionella since the water in the thermal store remains inside the store, it only provided heat via a heat exchanger of some sort. The higher temps are needed because as soon as heat is removed from the store to heat the DHW, it starts to cool down, so you want higher temps to maintain a consistent DHW temp for a long period before the store gets too cool to work. 

10 minutes ago, Alexphd1 said:

Does a thermal store really need to hit 65-70 degree?

 

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Thermal store, as soon as you start drawing heat from it, the temperature starts to fall, so to get a sensible capacity of actual usable heat, the temperature in the stoer needs to be a lot hotter than the water temperature you actually want. otherwise you will only get hot enough water for a very short time.

 

On the other hand, an unvented cylinder delivers water at it's stored temperature and continues to deliver that temperature until it is almost empty.

 

So a heat pump works well with an UVC but not very well at all with a thermal store.

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I tried various temp with my themal store and found 67 was my sweet spot.  A little less and it lost heat to quick but heated up quicker.  A little more and it held its heat longer but then took longer to get to this temp. 

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1 hour ago, scottishjohn said:

1,6 kw prhr x 24hr =38kw 

that is real worse case scenario as not many days inyear when you see -10c 

average winter temp here from epc calcs  is  +3c.

ok another question --total energy used in last year  for heating ?

 

 

 

 

As @Ed Davies has already mentioned, you're mixing up units.

 

The Watt is a unit of power.

 

The Watt hour is a unit of energy.

 

 

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31 minutes ago, PeterW said:

 

Ok so ... ASHP can’t get to thermal store temperatures. You need in excess of 65-70c to have a decent thermal store capacity and that gets to near 1:1 CoP which gets expensive. 

 

Also, if you want to use RHI on an ASHP deal, do the bare minimum as your payment is based on the design heat load so if you put too much insulation in, you won’t get the payments to cover the cost of the ASHP install. 

 

 

funny how my ecodan plumbed unit works fine -heats DHwater to 55c -

or you telling me mitsubishi don,t know what they are doing ?

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13 minutes ago, Alexphd1 said:

@scottishjohnIs that not a unvented cylinder?

yep,mains pressure DHW

ecodan  ASHP and  a plumbed cylinder +controller package --does UFH +DHW .

ashp runs high temp for DHW only when it needs  for anti legionella -all automatic

you set temps for both UFH +DHW on controller

Edited by scottishjohn

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Just now, scottishjohn said:

funny how my ecodan plumbed unit works fine -heats DHwater to 55c -

or you telling me mitsubishi don,t know what they are doing ?

 

Read my response carefully then comment please. 

 

To get anything like a decent capacity - such as 200 litres of usable hot water - you need to use either a UVC of 300 litres at 55c, or a thermal store of around 425 litres due to how they heat the water. That’s a big ass TS to get not a lot of DHW capacity.

 

I expect the Ecodan you’re using is one of the PUTZ units that has its own controller. If you read the technical manual ( I have) and also look at the control algorithms (I have) and then look at the on off cycle of the compressor vs auxiliary heater (I’ve done that too..) you’ll find that it uses a secondary aux heater to get to 55c so your CoP is around 2.1 at best when it’s 17c outside. (Somewhere around page 32 of the manual). At 7c outdoors it’s 1.6, -5c it’s around 1.2. 

 

For reference, that’s a pretty crap score and makes your ASHP solution for hot water roughly 30% more expensive than mains gas ... but what do I know ..??

 

ASHP is not designed to heat to those temperatures unless it has either an auxiliary heater - ie an immersion element - or uses a type of compressor that can create high output temperatures which is at the direct cost of flow volumes. Lower flow volume = longer recovery time. 

 

So yes, Mitsubishi do know what they are doing, but I suggest you read the manuals and understand how they actually work before commenting please. 

 

 

 

 

 

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15 minutes ago, Alexphd1 said:

@Declan52 what are you heating your store with?

I use a pellet stove. 

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1 minute ago, PeterW said:

 

Read my response carefully then comment please. 

 

To get anything like a decent capacity - such as 200 litres of usable hot water - you need to use either a UVC of 300 litres at 55c, or a thermal store of around 425 litres due to how they heat the water. That’s a big ass TS to get not a lot of DHW capacity.

 

I expect the Ecodan you’re using is one of the PUTZ units that has its own controller. If you read the technical manual ( I have) and also look at the control algorithms (I have) and then look at the on off cycle of the compressor vs auxiliary heater (I’ve done that too..) you’ll find that it uses a secondary aux heater to get to 55c so your CoP is around 2.1 at best when it’s 17c outside. (Somewhere around page 32 of the manual). At 7c outdoors it’s 1.6, -5c it’s around 1.2. 

 

For reference, that’s a pretty crap score and makes your ASHP solution for hot water roughly 30% more expensive than mains gas ... but what do I know ..??

 

ASHP is not designed to heat to those temperatures unless it has either an auxiliary heater - ie an immersion element - or uses a type of compressor that can create high output temperatures which is at the direct cost of flow volumes. Lower flow volume = longer recovery time. 

 

So yes, Mitsubishi do know what they are doing, but I suggest you read the manuals and understand how they actually work before commenting please. 

 

 

 

 

 

thats the beauty of buying good quality  tank  270 litre i think 

I don ,t need to know and as i have the  solar type unit i can heat dhw for  free  80% of the year .

and it has an immersion element as  well which it uses when it decides  to .

I,m happy with the system -

 i don,t have mains gas ,so it was the best simplest all round choice

I already said early mains gas is the cheapest .

I have no idea of recovery time as  I have never run out of hot water with 2 bathrooms 

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32 minutes ago, scottishjohn said:

Also, if you want to use RHI on an ASHP deal, do the bare minimum as your payment is based on the design heat load so if you put too much insulation in, you won’t get the payments to cover the cost of the ASHP install.

why do you assume I don,t know that

maybe you need to find a more co-operative EPC man  ,then you get max payment 

Edited by scottishjohn

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I am pretty sure (though they don't make it clear) that the Ecodan cylinder in an UVC not a thermal store, so it only has to heat to target temperature not higher.

 

With a 270L tank I am surprised you have not run out of hot water. Obviously the ladies in this house use more water than your household as after 2 "ran out of hot water" incidents, I added an electric modulating water heater as a "reserve"

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5 minutes ago, scottishjohn said:

as i have the  solar type unit i can heat dhw for  free  80% of the year .

 

I'll be picking your brains for sure if I get these 3 solar thermal panels repaired and up and running.

 

My homemade 1m2 ST panel worked amazingly well so I'm a believer in the technology. 30degC ambient, over 80 at the output:

 

SAM_6122_zps488cad1c

 

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Will be interesting on how we get on, we have a 500l TS heated by ashp/pv  plus a 500l TS preheat with thermal/log gasification . If preheat store temp rises above main tank then preheat starts to heat up main tank. We will get a good idea on how well solar thermal actually works.

For what it's worth this a trial and error project, wouldn't think twice on major changes if doesn't work ie change tank to a sunamp or even sticking in a oil boiler. 

 

Our thermal controllers aren't wired in yet we but stuck a plug on the grundfos pumps yesterday for two hours. It raised the preheat tank from 8 to 20 degrees.

Edited by Alexphd1

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