Solar DHW no CH circuit

[pmarston]

Hi All,

Complete newbie here, though have read a few of the topics avidly!

I'm not sure how unusual our circumstances are, but I'm having difficulty working out quite what my best course of action is, as non of the examples/case studies I ever read seem to touch on our situation.

We live in an old farm house/croft in a Scottish glen (a but'n ben as they say) 2up 2 down, it's 1.5 storey (i.e. the upstairs is the roof space - there's no loft) (See image 1). While we have mains electric, we're on a septic tank and water is from a well further up the hill (i.e. gravity feed). There is no CH (the place used to be used as summer holiday accomodation) so heating is electric fan heaters etc!!!  This year we are going to insulate through out, replace the rotten DG and install solar for the DHW.  Next year we'll put in GSHP and UFH and eventually we'll put in a wind turbine.   


Image 1

Everything I read assumes that people have mains water and some form of CH - I don't see any need to combine the CH with the DHW if we're going to use GSHP - they can be (need to be?) independent as they operate at different temperatures etc.  Another problem is that the place is small.  The bathroom is where the front porch used to be, houses the DHW tank and has a header tank in it's own little roof.  I'd like to move that tank upstairs onto the landing (see image 2) to sit on the other side of the stairs, under where I plan to have the solar panel (on south facing roof) and we'll use the freed up space in the bathroom for a shower (hurrah!).  So for a start, do I have to have a header tank (as you can see there's not much room!)?  If so I'll have to have a horizontal tank I guess?  I'll be using an electric immersion heater for supplimentary during the winter, but I assume I only need one coil since the only other heat source will be the solar panel?


Image 2

Despite not finding other similar examples, does this sound like I'm thinking along the right lines to folks?  What have I not thought of (there's always something!)?  Does anyone have a better idea (especially based on experience!)?

Cheers,

Phil

[martin]

my first thought is "wot, no woodburner?"
Then you mention gshp - installing them ain't cheap, particularly to bung the underfloor heating piping into an existing building (and what nobody ever points out is that you do get "free" energy, but the energy you put in is the most expensive sort - electricity)
My initial feelings would be - solar - woodburner with back boiler - wind turbine - then you've cut the need for an immersion heater except for emergencies

[pmarston]

Thanks Martin - the energy will be "free" once the turbine is in wont it? 

My feeling about a wood burner is that I'll still have to buy logs (we already have a small one at one end of the house and while it's handy supplimentary heat in winter they're hardly convenient).  I'll also have to feed it manually (unless I want to spend more than on a GSHP and have a hopper fed wood chip system) and so I'll only have heat when I've done that. 

I don't want to have to stoke a stove just to have a warm house (especially the bathroom) on a chilly June morning like today.  Maybe I'm missing something or maybe I'm just lazy? 

Electricity may be bad for the environment when sourced from a coal fired power station and may cost a fortune when you don't generate it yourself and believe me we know having spent a couple of winters here already, but it is also very clean, convenient and easy! 

[O MidKnight]

Hi pmarston

How fab  - did my beloved doctor and myself pass by you on our recent 3 week tour of Scotland?

Which roof is south?

How about a ground mounted solar panel so they will thermosyphon up to the cylinder? Reduce the need for electricity.

If not and room is short then a small well insulated extension/boiler room to hold the proposed solar cylinder/pumps/under floor heating control items etc? You could consider a combination cylinder in the house which has its own cold header tank and is quite compact. Not really suited for lots of baths if mains water pressure is a bit on the low side.

Horizontal  specials cylinders are not as efficient as verticals  plus may not be as reliable. I once fitted (20 very odd years ago) 6, one after the other for a customer. Each one had a leaking coil. In the end a twin coil vertical was fitted. Must have been a spate of Friday    specials. Talk to the GSHP guys in case an extra coil might be of use at a later date - and who knows what energy source may be just around the corner.

Well water - any problem with excess deposits in the pipes/cylinder?

[pmarston]

Thanks for your comments O MidKnight,

How fab   - did my beloved doctor and myself pass by you on our recent 3 week tour of Scotland?

We're on the Eastern edge of the Cairngorm National Park (outside edge) - were you anywhere near there?

Which roof is south?

The South facing roof is the one with the dormer windows in the picture above.

How about a ground mounted solar panel so they will thermosyphon up to the cylinder? Reduce the need for electricity.

The ground mount idea doesn't sound good - we're keen gardeners, there's a perfectly good roof and electricity isn't that degree of an issue anyway.

If not and room is short then a small well insulated extension/boiler room to hold the proposed solar cylinder/pumps/under floor heating control items etc?

We do plan to locate the HP part of the GSHP in one of the out buildings, but putting the hot water tank out there (or in a it's own extension) isn't really an option though under other circumstances I could see the attraction of a plant room.

You could consider a combination cylinder in the house which has its own cold header tank and is quite compact. Not really suited for lots of baths if mains water pressure is a bit on the low side.

I did  wonder about a hot water tank with its own header tank, but figured it wouldn't be small enough to fit in the limited space available (height = 80cm (min) to 180cm (max) over 120cm from wall to stairwell) see image

There's three of us so I was figuring on a tank at around 200 ltrs give or take.  But we also have a huge enamel cast iron bath so a small header isn't an option really.  Though do we need a header at all - I don't know plumbing regs, so I don't know if we have to have a header tank off a well or just off anything for that matter?

Horizontal  specials cylinders are not as efficient as verticals plus may not be as reliable. I once fitted (20 very odd years ago) 6, one after the other for a customer. Each one had a leaking coil. In the end a twin coil vertical was fitted. Must have been a spate of Friday specials.

Why are horizontals not as efficient?  Is it the way the water stratifies?  Does it matter more or less if the tank is only for DHW? and does it matter more or less if it's being heated by solar?  Given that your horizontals were 20 odd years ago, Friday specials or no,t I would hope things have improved since then .... ?

Talk to the GSHP guys in case an extra coil might be of use at a later date - and who knows what energy source may be just around the corner.

I have spoken to the GSHP guys (Kensa - sorry Ivan ) it was them that advised against tying the two systems together since DHW operates at much higher temps than is optimum for UFH and GSHP.  That seems to ring true since one of my neighbours has installed a combined DHW/UFH system heated by GSHP and it's costing them a lot more than they expected, because the GSHP is having to bring the temps way up for acceptable DHW so I guess the COP works out rubbish!  Or do you have a tip off about the future .... ?

Well water - any problem with excess deposits in the pipes/cylinder?

I've no idea about deposits in pipes or cylinders - if it helps, we drink the water straight out of the ground unprocessed or filtered (it's been tested by the local authority as safe) and there are no green copper deposits on our sinks or bath despite the water being slightly acid.

So I'm still wondering whether I need a header tank?
Whether a horizontal cylinder would be OK if I did (not sure a vertical one would fit anyway)?
Something I haven't mentioned yet is what pressure I need for a decent shower - subjective I know, but I don't even know how our pressure compares to mains - there must be rules of thumb?!

Cheers,

Phil

[O MidKnight]

Phil Hi

Alas we were on the west coast.

Sorry no help so far.   

Horizontals will be more reliable today. Although they are quoted as being less efficient because of the way the water stratifies - they used to enjoy  having  huge heat exchange coils. I do not think it really matters if they are a little bit less efficient. My own twin coil cylinder for example is not a solar dedicated one - yet it works reasonably well.

How about an unvented horizontal cylinder - if such a beast exists? You would have to pay for an annual inspection though. If available check the rules to see if this can be supplied by your  water  supply pump/expansion vessel.

Over to the more knowledgeable for no cold water header tank options. These may include a storage tank in your outbuildings, pump, and  expansion vessel to maintain the pressure. Plus pressure switches to trigger the pump back into life when the water pressure drops.

[dinitro]

hi Phil

ever considered air source heat pumps rather than your immersion?

also why not have multiple smaller cylinders...although this would work out more expensive the new
solar controllers can charge them turn by turn.  This could also be put to use in that if say you had a series of
3 the last one could be a combined GSHP solar.

regarding mains pressure... I don't know if this is an option but if you could site a tank a groundlevel you
could run a booster pump.  If this is coupled with a thermal store coil in your lead tank you will have pressurised
cold and hot water.


dinitro

[pmarston]

Hi Guys,

Thanks for the advice - it is all sounding a bit complicated though - I'm sure someone said on one of the other threads to keep it simple and that certainly sounds good to me.

I don't like the sound of unvented - I've read Ivan's explanation (warning)  and that doesn't sound like a simple route to follow - I'm not even sure what the advantage would be? 

I haven't considered air source heat pumps at all - believe me if you'd ever felt the bitter North wind off the arctic up here in the winter neither would you!   It'll be much warmer under ground and consistently so.

We don't currently have a well pump - the well is actually up the hill behind us and feeds us by gravity. I don't know what the head on it is or the pressure, but the rate is 10 litres per minute.  It doesn't have any purification unit either.  On the principle of keeping it simple it would be kinda nice to keep it that way too.

All I want to do is heat my DHW using solar, but I don't know what's the best tank to choose for my circumstances? 

Phil

[Loir]

It would be very useful to know the head on your water supply. I am sure a chap with your ingenuity  can figure out a way to measure how much higher than your house your water supply is.

Do bear in mind that you can put the HW cylinder wherever you want; upstairs, downstairs or in the roof space. The pressure (and if it's good enough for a shower) just depends on the head of water going into it. This could be a CW tank somewhere high in the house.

But it could be the head on your cold water supply if you KNOW what it is and it's within the spec of the HW cylinder. This would make it an unvented cylinder (kind of) and you would not need a cold water tank.

A cylinder with one coil is what you want. But it does not cost a lot more to have two coils and you might want a wood burner or another heat source in the future.

You might also want to read up on wind turbines and dump loads in the forum. Can be a useful source of heat for hot water!

Loir

[wyleu]

I'm not sure how unusual our circumstances are, but I'm having difficulty working out quite what my best course of action is,

Sell the child on E-bay and move to Spain on the proceeds

[pmarston]

Loir - the idea of a second coil "just incase" sounds appealing and I like your suggestion on wind turbine dump loads, however, I was planning on being able to sell back to the grid - what with electricity always getting more expensive and suppliers starting to pay a reasonable rate for buy back, things should only get better on that front over the 20 years life span of the turbine.   

I've calculated the head from the well as being in the region of 30m 

Something I don't fully understand is what purpose(s) the CW tank serves - the only time a house I've been in didn't have one was when there was a combie boiler.  Is it OK to connect the supply direct to the hot water tank?  Would it have to be unvented even from a well supplying the water by gravity (i.e. not pressurised)?   

wyleu - sounds like an idea, but I don't fancy Spain and her mother would probably be un-impressed! 

Cheers,

Phil

[wookey]

The purpose of the cold water tank is twofold. 1) it provides insurance against unreliable mains supply (which used to be a problem about 100 yrs ago, but is generally moot these days, and presumably irrelevant to you?) 2) it isolates your system pressure from the mains system pressure. Your system pressure becomes that of the height of the CW tank, not that of the supplied water (i.e ~5m in a typical house, which is 0.5 bar). For a long time I think such a tank was required by the regs which is why they are standard in in the UK, but not most of the rest of Europe.

If your head is 30m then you have about 3bar pressure, which is about the same as a lot of people's mains.

I'm getting out of my depth a bit now, but I presume connecting this direct to your tank would make it a pressurised tank and invoke a whole lot of regs you want to avoid. You may be able to avoid those on a technicality due to not being mains-connected but you'd still need to have the extra safety bits. I'll shut up now and wait for an expert to comment further on tankage as I'm still swotting up on all these tank flavours and pros/cons. High pressure water is _much_ better for showers so considering schemes/kit that will let you keep that is well worth it (e.g a thermal store with a heat exchanger, rather than using the actual hot water in the tank). Such a store has low-pressure internal water (simple, cheap, safe), but lets you have high-pressure hot and cold water (good, costs money for the fancier tank).

[wyleu]

The one big advantage of the dear old cold water tank is you will have water if the utility companies supply is interuptted whilst your neightbour with an unvented system will not.

It comes down to how reliable you feel your supply is.

[pmarston]

Thanks wookey ... and so the picture builds ...

I did wonder whether there was some aspect of isolation going on, both from a failed supply and the pressure of the supply, which would actually both apply to us - TIP: never leave a tap with a leaky hose running all night when you're on a well, it took three days for the well to refill to a usable depth!

The 3 bar thing sounds like it might be around about right, though the water from tank must only be about 0.2bar by that reckoning! 

I definitely don't like the sound of a pressurised tank (ref back to Ivans web site advice http://www.navitron.org.uk/thermalstore.htm), though high pressure water is very appealing as I'm diing to have a shower again - it's getting to be 2 years since I've had one! 

Can you explain further about

Such a store has low-pressure internal water (simple, cheap, safe), but lets you have high-pressure hot and cold water (good, costs money for the fancier tank).

or can you point me in the right direction to research it further?   

Hi wyleu, sounds like good general advice, though no body round here gets their water from a utility co.  (Nice reduction in the council tax too )  Our supply is as reliable as the weather (on average) and on my memory to turn the tap off!   

[pmarston]

Hey wookey ignore my dumb request for more info   I've just re-read Ivan's FAQ on mains pressure tanks v thermal stores and realised I'd already read about them!  A thermal store is also known as a vented mains pressure tank - doh 

Now it sounds like our pressure must be short of 1 bar since our flow rate is 10 litres/minute.  So now I'm confused again.

Having re-read the FAQ it sounds like both systems kind of work like a combi boiler - they transfer heat to the water you'e using as you use it.  It sounds like the vented system would certainly help me out of the need for a header tank IF I have enough pressure, but if I don't have the pressure I'll be stuck with a rubbish shower.   

I think I'me vearing towards a horizontal cylinder with a similar tank mounted piggy back.  At least if I don't like the pressure I'd be able to pump it!