What boiler to go with Solar thermal and wood burner

[scottishjohn]

2 minutes ago, ProDave said:

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"

maybe it recovers quicker than some think ?

not sure what the difference is between the 2 descriptions --both store hot water,both are insulated 

i,m sure someone will enlighten  us

my last one had solar coil ufh coil in middle and dhw  at top and the i fitted blender on outside to mix mains hot and cold to get desired temp and not just use all the hot water which would then need alot  of cold adding at the tap 

[Alexphd1]

John 

https://www.mcdonaldwaterstorage.com/thermal-store-vs-unvented-cylinder

[Jeremy Harris]

7 minutes ago, scottishjohn said:

maybe it recovers quicker than some think ?

not sure what the difference is between the 2 descriptions --both store hot water,both are insulated 

i,m sure someone will enlighten  us

my last one had solar coil ufh coil in middle and dhw  at top and the i fitted blender on outside to mix mains hot and cold to get desired temp and not just use all the hot water which would then need alot  of cold adding at the tap 

 

 

There's an explanation earlier, but a thermal store will drop the max output water temperature continuously whilst water is being drawn off, so needs to have a higher starting temperature in order to allow the TMV to hold the mixed DHW temperature at the right level as it discharges.

 

An unvented cylinder will tend to deliver all of the hot water it holds at near enough the same temperature until it's empty.  In general, because heat pumps both don't like running at high flow temperatures, and because they generally have a lower output than a boiler (so they have a longer recharge time) they should be used with a UVC, as they are very unlikely to be able to get a thermal store up to the 65°C to 75°C needed.

[scottishjohn]

2 minutes ago, Alexphd1 said:

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. 

from my experience with 40 tubes I think really you need to run at least 2 tanks ,so anytime there is sun that can give 30+ it can dump it in to a tank --cos if your main tank is already hotter ,the solar just sits 

then be able to direct it to UFH or DHW as required.-ue plater heat exchanger  maybe --not actually interfere with ufh water circuit directly

Iran my underfloor as a test in february on this hosue ona sunny day --direct from panels at 25c

If that was a modern type of slab and good passiv type house -- 

storage is always problem with solar --you need alot of it and to be able to keep it at dif temps levels ,to get what heat when you can  --so retro fit always going to be a problem.

or do like i saw a house in switerzland  

2 storey typical tall steep angled roof --one complete gable end was a tank

so you would have nearly 30ft to stratify the temps -- 

they do have very clear sunny days even in winter ,which would help very much as it would be being topped up 

and in summer whole tank would get hot eventually 

my guess about 15000litre tank

not a retro fit job ,unless you got a gable with no windows. lol

but I just wonder with very low energy modern houses if it might be possible to do --

[scottishjohn]

3 minutes ago, JSHarris said:

 

 

There's an explanation earlier, but a thermal store will drop the max output water temperature continuously whilst water is being drawn off, so needs to have a higher starting temperature in order to allow the TMV to hold the mixed DHW temperature at the right level as it discharges.

 

An unvented cylinder will tend to deliver all of the hot water it holds at near enough the same temperature until it's empty.  In general, because heat pumps both don't like running at high flow temperatures, and because they generally have a lower output than a boiler (so they have a longer recharge time) they should be used with a UVC, as they are very unlikely to be able to get a thermal store up to the 65°C to 75°C needed.

so basically if it has an indirect coil its a thermal store if it does not its and UVC

 in that case the tank on my ecodan unit is an unvented cylinder,as the heating is done via a plate exchanger and an immersion in parent volume  

Edited February 11, 2019 by scottishjohn

[Jeremy Harris]

4 minutes ago, scottishjohn said:

so basically if it has an indirect coil its a thermal store if it does not its and UVC

 

 

No, not at all.  Both can have different coil arrangements depending on the application.

 

A thermal store holds a body of inhibited water which is heated to a fairly high temperature.  It then "instantly" heats cold potable water coming in to an internal or external heat exchanger at mains pressure.  The body of water inside the thermal store doesn't move or flow anywhere, it just sits there and stores heat.

 

A UVC is a mains water pressure fed cylinder where the water in the cylinder is the hot water source.

[ProDave]

1 minute ago, scottishjohn said:

so basically if it has an indirect coil its a thermal store if it does not its and UVC

An UVC has potable water inside it, so that is the water that comes out of the tap.  It is heated by a heat input coil that runs from the sealed primary circuit with inhibitor,  To use with a heat pump you should get one with a high capacity large area input coil.

 

You can have more than one input coil for different heat sources.

 

A thermal store has never changing contents, that just gets heated and cooled time and time again.  Hot water is delivered by passing cold mains water through he aheat ercchange coil at the top of the tank, or through a plate heat exchanger.

[A_L]

41 minutes ago, PeterW said:

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.

 

Only because of the design of current thermal stores. See tank B in attached pdf. A store charged to 60°C provides close to 120% of its volume at 43°C

TZS_10.pdf

[Alexphd1]

2 minutes ago, scottishjohn said:

from my experience with 40 tubes I think really you need to run at least 2 tanks ,so anytime there is sun that can give 30+ it can dump it in to a tank --cos if your main tank is already hotter ,the solar just sits 

then be able to direct it to UFH or DHW as required.-ue plater heat exchanger  maybe --not actually interfere with ufh water circuit directly

Iran my underfloor as a test in february on this hosue ona sunny day --direct from panels at 25c

If that was a modern type of slab and good passiv type house -- 

storage is always problem with solar --you need alot of it and to be able to keep it at dif temps levels ,to get what heat when you can  --so retro fit always going to be a problem.

or do like i saw a house in switerzland  

2 storey typical tall steep angled roof --one complete gable end was a tank

so you would have nearly 30ft to stratify the temps -- 

they do have very clear sunny days even in winter ,which would help very much as it would be being topped up 

and in summer whole tank would get hot eventually 

my guess about 15000litre tank

not a retro fit job ,unless you got a gable with no windows. lol

but I just wonder with very low energy modern houses if it might be possible to do --

 

Both tanks are a thermal store ie dhw runs through a coil in preheat then through the coil in main tank. Don't get any good for UFH direct from solar thermal but PV  will help.

 

A few people in Ireland tried various styles of large heat stores with varied poor results. 

[PeterW]

3 minutes ago, A_L said:

 

Only because of the design of current thermal stores. See tank B in attached pdf. A store charged to 60°C provides close to 120% of its volume at 43°C

TZS_10.pdf

 

Its one of those questions - have they not taken these designs into production as the costs would outweigh the benefits...? 

[newhome]

19 minutes ago, ProDave said:

A thermal store has never changing contents, that just gets heated and cooled time and time again.  Hot water is delivered by passing cold mains water through he aheat ercchange coil at the top of the tank, or through a plate heat exchanger.

 

Is that the same for UFH too (albeit the water comes off the bottom) or does the water from the TS circulate round the UFH? What happens with an UVC and UFH? 

[ProDave]

8 minutes ago, newhome said:

 

Is that the same for UFH too (albeit the water comes off the bottom) or does the water from the TS circulate round the UFH? What happens with an UVC and UFH? 

With thermal stores there are many variations some with heat exchangers and some without.

 

My own UFH runs direct from the ASHP. So the primary circuit with inhibitor is from the ASHP to the UFH and to the UVC heat input coil.

 

Some use a buffer tank with UFH in such a situation. I am not sure if that can be combined with an UVC or not.

[Nickfromwales]

11 hours ago, ProDave said:

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"

To not allow the OP to fear these things, its best to admit that you turned the stored temp down too low, and that is why you ran out  If you ran your setup at a higher set temp I doubt if you'd have ever had a problem as your cylinder is enough for a couple plus 2.4 children with ease, ( when fortified with an immersion to boost the stored temp as is supposed to be for 'normal use' ). 

 

11 hours ago, Alexphd1 said:

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.

This cascade setup is exactly what I would do if I had 'tinkering time' TBH, and should work really well with ST. As said you need a separate tank to raise to the lower stored temp to combat the main cylinder from not firing useful heat into it when the temp probes say the main cylinder is sitting out of the beneficial range, typically that which the ST is often producing in our less than sun-blessed country. I proposed a 2-stage setup like this for a client who wanted to go off-grid, triple cascade with a pair of TS's as sub low grade + low grade storage so nothing went to waste. These would have been boxed in and flooded with Vermiculite / other suitable full-fill insulation to retain whatever was produced. Problem is, that lot would need an outhouse / boiler room all of its own, around half the size of a domestic single car garage, so is just totally impractical in most instances. 

Low grade heat is of value, but you need to store shitloads of it to have any useful energy capacity, hence the mention of the 15,000 litres stored in a gable. Anything smaller would have been quite inconsequential. That said, I would likely come to my senses and fit as much PV as I could, dumping any excess into thermal storage, ( probably Sunamp as its simply the most efficient at retaining whatever you produce ), and accept that in the summer I'll need to buy near to zero electricity ( I'd 100% fit AC batteries ) and what I saved in the summer would offset ( not eradicate ) my winter energy costs.

Electricity is just a WAY more universal an energy to harvest and utilise, but this equation is hugely affected by, and the decision dependant on, a lot of factors; fabric choices, quality of glazing, airtightness with heat recovery, temperature ( and type ) of the space heating emitters, total annual energy requirements and on what do the divisible %'s go towards, and so on....and on....and on.

13 hours ago, Alexphd1 said:

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?? 

Regularly residing over 45oC will stave off most concerns, being boosted daily by PV almost wipes that out, other than winter times of course.

 

Thermal stores are a little mis-understood and are quite universal in their chosen applications;

A TS can be just like a buffer tank, and not do DHW at all, all the way through to multiple inputs / outputs and a DHW coil ( internal coil, or external pumped plate heat exchanger ) and can be heated by electricity via immersions, by gas / oil / HP via a dedicated, hydraulic input coil. The water inside a TS is primary grade water, the same as the water in your radiators, whereas the water inside an UVC is clean fresh potable ( drinking quality ) water, the water that actually comes out fo the hot outlets. DHW, therefore, in a TS is produced instantaneously, so look at a TS like a giant wet combi boiler, with heated water doing the job of the gas burner in providing the heat energy required for DHW production ).

 

TS's can be a static body of water, simply heated by a coil or immersion, or can be constantly circulating through the boiler and the central heating emitters as one huge unified body of water. 

In other mixed water solutions the heating circuit(s) could all be taken separately from internal coil(s) eg to keep glycol in an ASHP / GSHP install to a minimum volume by hydraulically separating the inputs and outputs, plus the heat inputs can also be introduced via a dedicated coil / coils say to separate ST from a gravity boiler system and so on.

 

When you start mixing heat sources and outputs things get quite flavourful with regards to controls, isolation and general associated complexity, so choose well ( particularly if you are going to ask a 'plumber' to come up with a way to get this to all harmonise. 

[scottishjohn]

this is why I am looking for a very flexible controller  as tried to do this with multiple analog thermostats and the hysteresis was always too great to be  very good 

I had my solar controller down to +6c over tank temp  and it turned on ,but again it was too simple to always doing what it should do 

I came to conclusion to get best you would need 3 tanks with different set temps +you had to be able to run solar input direct to floor through a heat exchanger  

for best use of solar energy 

 

SO  yes probable cost outweigh benefits,but as houses need less and less energy there could be a time when it would work .

this was the reason i was asking for total energy needed to heat a near passiv house per day -

then maybe tank size could be calculated.

and if a concrete unit built when house was and paart  of  floor  inside building any heat losses would go into fabric  of building

5" phonelic foam is what kingspan man told me was max it would sensible be to use --after that the extra savings in heat loss is so small it would never be viable .

 

 

 

 

 

Edited February 12, 2019 by scottishjohn

[ProDave]

My worst case heating week has been 95KWh of electricity, the week it was down to -14 one night and not above 0 in the day.  So that averages  13.7KWh of electricity per day. Assume a COP of 3 for the heat pump and that's 40KWh of heat per day, or equivalent of 1.7KW of heat into the house continuously.

 

That is a little under the estimated 2KW heating requirement so shows how incidental heat input is helping reduce the real figures.

[PeterW]

13 hours ago, ProDave said:

Some use a buffer tank with UFH in such a situation. I am not sure if that can be combined with an UVC or not.

 

Yep - I’ve installed a buffer in the circuit so have 60 litres of tank as a type of low loss header to allow the UFH to draw as much or as little as it wants in the way of water at 38c depending on the return temps. 

[joe90]

Yep, I’ve done the same, 60litre buffer tank with immersion in case of ASHP failure/servicing, in winter I run the ASHP full time at 40’ (heating) controlled by a tank stat. The UFH is controlled by a room stat that turns on the manifold pump when heating is required. That means we don’t have to wait fir the buffer tank to heat up when heat is required, the slab takes long enough to heat up anyway. I may be going on to E7 or E10 so will have to change this arrangement.

[scottishjohn]

29 minutes ago, joe90 said:

Yep, I’ve done the same, 60litre buffer tank with immersion in case of ASHP failure/servicing, in winter I run the ASHP full time at 40’ (heating) controlled by a tank stat. The UFH is controlled by a room stat that turns on the manifold pump when heating is required. That means we don’t have to wait fir the buffer tank to heat up when heat is required, the slab takes long enough to heat up anyway. I may be going on to E7 or E10 so will have to change this arrangement.

buffer tank would work for solar +ashp  as well,

when not doing dhw  or when solar  cannot get to temp of water already  in system DHW

not many days when you don,t get 30c in solar

the combinations are endless with suitable control circuits

[Ed Davies]

1 hour ago, ProDave said:

My worst case heating week has been 95KWh of electricity,

Which days were those? I'm just curious to do a like-for-like comparison against my oil burned here.

[ProDave]

4 hours ago, Ed Davies said:

Which days were those? I'm just curious to do a like-for-like comparison against my oil burned here.

It was the week between Friday 1st Feb to Friday 8th Feb.  I read my meters and record their readings on a Friday afternoon.  So I can't be more specific which days.

 

How can you accurately measure oil consumption by the day or week?

 

Heating bill so far this winter £164

[Hobbiniho]

23 hours ago, newhome said:

 

Costs for MCS installs up here are crazy numbers IMO. I only managed to get 1 ASHP quote and that was 14.5k. Given the cost of the parts it was several thousand to install and commission, way more than could surely be justified based on effort / time to install. Up here we seem to suffer from not having enough installers, a tendency for installers to concentrate on more lucrative commercial work, and the government providing interest free loans to pay for the installs. The final point is no bad thing of course but it means more people are applying to install renewables and demand outstrips supply. I wrote some Facebook messages on local groups when I was struggling to get ASHP quotes and was inundated with replies from others saying the same thing. The local ‘green’ consultants in the high street said the same thing and the woman from the Energy Saving Trust told me to widen my search area and try some in England and further north in Scotland. Great approach if something goes wrong and needs servicing. How likely would it be for someone to come to my house quickly to rectify? 

 

In addition the RHI scheme rewards those with leaky houses. A ‘D’ graded property stands to gain far more in RHI payments than an ‘A’ graded one so in theory their payback time would be less. 

 

 

 

i am having much the same problem with the property i am refurbing except i live on an island with only 4 MCS installers and i cannot get any of them to quote as they are more interested in doing new builds, i have had to go to neighbouring orkney which has 6 MCS installers and looks more promising but not got the quote yet, the interest free loan coupled with the RHI payments means that my system should pay for itself 

[Ed Davies]

1 hour ago, ProDave said:

How can you accurately measure oil consumption by the day or week?

 

I can't do it accurately but I can get an estimate from my log of a radiator temperature once a minute to get a reasonable approximation to the boiler run time. More details.

 

From 2019-02-01T17:00 to 2019-02-08T17:00 my software estimates the boiler ran for 175'897 seconds (29% of the time for the 7 days) which, assuming the same 19% overestimate of oil consumption I got lost autumn, would imply burning 85.5 litres of oil. Using the assumptions I made on that page that would be 904 kWh. So that's a tad over three times @ProDave's heat requirement assuming his 95 kWh gets converted to heat with a CoP of three.

 

My last oil delivery was 44.75p + 5% VAT per litre so just over £40 for that week's space heating.

[newhome]

2 hours ago, Hobbiniho said:

 

i am having much the same problem with the property i am refurbing except i live on an island with only 4 MCS installers and i cannot get any of them to quote as they are more interested in doing new builds, i have had to go to neighbouring orkney which has 6 MCS installers and looks more promising but not got the quote yet, the interest free loan coupled with the RHI payments means that my system should pay for itself 

 

I believe that @Stones used an MCS installed on Orkney so maybe he can recommend his (or not).