Hello all,
Hoping you kind folks could answer a few of my queries regarding my proposed hot water/heating system.
I have bought a pile of stones in a field in Sicily which once upon a time ago was a house, I have one room habitable and a second one soon to be finished. In the next few weeks I intend to install a hot water and space heating system. It is a temporary set up until I finish more of the house, so temporary meaning several years.
Plan as follows:
Morso Squirrel wood burner (4kw) with 8000btu back boiler in one room for space heating and to heat 300lt direct vented thermal store with combination F&E tank located in neighbouring room on gravity circuit. 1.5kw Heat leak rad in room with the TS.
Additional solar heating to be added next year.
Wood burner will run 24/7 in the winter.

Questions:
1. How/where to vent the primary circuit? Outside? Direct to the f&e tank or will the TS self vent to the f&e tank in the unlikely event of boiling? Does it require a T&P valve or tundish?
2. I presume 8000btu is roughly 2.5kw to water is this correct? I want to be able to drive the wood burner hard often, if the TS has reached temp will the little Morso be able to get the heat leak rad hot? Would I be better off with a smaller heat leak rad and space heating the second room with rads on their own gravity circuit?

The aim is create a simple gravity system to space heat two rooms and provide hot water.

Also, we are off grid, only solar for power.

Many thanks in advance.

Kieran

The thermal store

Many thanks green paddy for such a detailed response. Funnily enough Italked to mark at Newark (before I read your post) and he did explain the internal pipe work for the thermal store. I have read here somewhere that it is not advisable to use the internal expansion and fill pipe work for venting purposes, so if anybody else could chime in on this point it would be appreciated. Mark suggested that he would expect to see the primary pipe work extended and vented into the top of the f&e tank, which is how I had planned to install the vent.

I was starting to think on the same lines as your suggestion of using separate gravity fed rads, thank you for your real life observations.
Tell me GP, do your gravity rads have oversized tappings? Or are they standard half inch?

In terms of insulation, it is a typical Sicilian farm house built on solid bedrock with 600mm thick random rubble walls. We are trying to use only natural traditional materials, all lime render and a coppo tiled roof. We have used 32mm thick sarking boards as insulation and will decide after this first winter wether to add sheep’s wool between the rafters internally and lathe and plaster. The coldest it gets here is 0 degrees at night and that is not the norm usually around 4-5 for a few months a year.

Kieran

Posted By: KieranfMark suggested that he would expect to see the primary pipe work extended and vented into the top of the f&e tank, which is how I had planned to install the vent.

The pipework can be vented into the header tank, but you still need an overflow from the header tank. In the UK the overflow needs to be taken outside to a visible spout, or else through a visible tundish inside. You can easily get an overflow if the ballcock valve in the header tank goes wrong (don't ask me how I know!) or in the worst case you might get boiling water expanding or venting into the header tank and then overflowing.

What GP said about insulation. :)

Not sure it would matter. There'll be no relevant back pressure diff between a 22 and 28 over that distance. Do whatever's easier. Check how the vent will pass through the lid of the F&E - question for Tom (NCC).

Make sure you have an isolating valve in the cold feed to the header tank (refer to my previous answer :)

What's the thing that looks like a small expansion tank? i.e. what's it's purpose?

Forgot to say...... yes the tank plumbing came fitted with said isolation valve on cold feed 😀

Thanks Ed. All input appreciated. Although this is an old thread I delayed the install so need all the help I can get at the moment.

Kieran

Posted By: WillInAberdeenOur system has both an expansion tank and a pressure safety valve at this point, don't know if this is overkill.

Its definitely not overkill and absolutely essential! If the expansion vessel loses its pressurised gas or the internal diaphragm fails, there will be nothing to absorb pressure fluctuations and eventually a pipe will rupture or a joint come apart.

Posted By: WillInAberdeenThe expansion tank is for when you open a hot tap and run a lot of cold water through the coil to be heated, then close the tap.

Thanks for the explanation

Many thanks for the replies and your patience.
I will try and clarify a few things.
Firstly, the system I have designed is largely driven by a tiny budget and the will to learn new things. My basic plumbing skills are sound, making good tidy connections in copper and plastic. My knowledge of thermal dynamics and plumbing systems is limited.
I understand the Morso stove is far from ideal, but it’s what I have right now. I purchased the TS primarily as a future proof hot water only system but would like to try to utilise it for space heating one room (adjacent to the room with the stove. In addition to the Morso I have bought materials to construct a DIY flat plate solar thermal collector. The solar system intended is a drain back with the collector Containing a 20m 10mm copper coil.
We get a lot of warm winter sunshine here but I have no idea how efficient my solar system will be.
We are a family of three, 2 showers and a toddler bath a day and washing up dishes From now until April I will light the wood burner mid afternoon or run it 24 7 depending on the outside temps. I am hoping the diy solar and Morso will achieve this. The original schematic I posted utilises what I consider to be a beautifully simple and safe primary wood burning circuit. I like simple and safe. However, after a year of pondering and the inclusion of the solar I was wondering if there maybe a better way to use the TS to also space heat the bedroom?
To answer GP’s questions:
1. My solar controller has sensors at top and bottom of tank. I do also have a stat pocket available half way up TS.
2. I had an extra tapping because I am concerned about the primary return height from TS to Morso and wanted the option to use a higher port if needed.
3. Yes I can run the heat leak rad directly from the primary but was thinking that it maybe beneficial to run it directly from the TS in the hope it would get some heat into the radiator quicker. Is this logical or possibly I am mistaken.
4.i asked for spare ports purely to keep my options open in the future as I modify and improve my systems.
5. I only really need one rad in the bedroom and I suppose I was hoping the heat leak rad could work. I don’t really understand how the gravity rad you have suggested would work? I would really appreciate if you could explain the idea in more detail, I don’t understand how it would differ from the proposed heat leak direct from the TS.
6. I will have to ask mark at Newark. It appears that the pressure relief valve is only for the TS unless it is plumbed to the coil internally.
7. I had not considered this and yes I think you are spot on. Will add to shopping list.

Any advice and suggestions much appreciated.

Kieran

Are you sure you actually need a a heat leak rad? Im sure you need a gravity feed to a heat sink, but this can be a radiator OR a hot water tank. As youve already got a gravity loop to the TS I dont think you need the rad unless you want a gravity powered radiator for heating. If thats the case bare in mind that the rad can get extremely hot. We have both a pumped and gravity connection to the stove but the gravity loop goes to the hot water tank, no rad, and Im pretty sure that was the config that the stove manufacturer advised.

If you have to go for a totally gravity powered system how are you going to ensure that the TS is prioritised over the rads if the rads are connected to the primary loop from the stove? I would have thought that the rads would need to be tapped off the TS part way down so they only warm once you have heated enough DHW??

Ive no experience of a split gravity loop but looking at the OPs original sketch, Im still not certain it would prioritise DHW. If the bottom of the TS was at 30 degrees and the rad was at 20 then surely the cold water from the rad would flow into the stove ahead of the cold flow from the TS. This would set up circulation through the rad ahead of the TS????

Posted By: Kieranfmy understanding is the heat link rad direct from the primary would start to flow after the primary flow had started to slow down, ie top of TS hot because of the difference in pipe size from 28mm to 22mm.

It is not the pipe size, a small pipe will just restrict the flow across the whole system. It is the temperature of the TS that will stop the gravity flow. As the temp of the TS increases the flow will decrease. When the TS temp reaches the stove temp then flow will stop. If there is another loop lower than the TS then as the TS temp rises close to the stove temp then flow will start on the lower loop which will increase as the flow to the TS slows due to the increasing temp of the TS.

Typically the pipe work on a gravity system would aim to keep the cross section area of the pipe work (roughly) the same across the system. so a 28mm pipe would divide in to 2 x 22mm or a 22mm and 18mm and a 22mm would divide into 2 x 15mm, of course when the pipe work goes on the return then the dia. increases as the pipes come together finishing up at the stove with flow = return.

Gravity systems work very well but have to be designed (pipe gradient also plays an important part). The typical modern CH system usually pays no attention to gravity circulation and if the flow is too slow then the pump speed is cranked up - you can't do that with gravity !

Kieran,

let's try these for size...

1. keep the heat leak, coming off the flow from the stove low down versus the TS feed, which I would connect at the top of the TS. No mid point feed to the TS. Take a radiator connection from near the top of the TS and return it at the base of the TS. That rad feed would be a gravity circuit, going to the top of a tall vertical radiator, in a room presumably not too distant, as needs to be below water level in attached F&E tank. Fit a TRV to that radiator, so you can can control its output (unlike the heat leak).

OR

2. Forget the heat leak. Take a vent to the roof, swan necked over. Lovely simple, safe system, that can't over pressurise. The little Morso will be bouncing and bubbling long before you get to 90oC at the TS. Fit the gravity rad as above. With stoves I always go openvented, but then I've seen the aftermath of failed relief valves, so I'd take an open line to the roof (safe place physically above the system high point) in any case.