The challenge
1. Heating system for a large home - 7 beds + large open plan spaces. Very large extended family who come to stay throughout the year and plans for a lifestyle/career change to run B&B. Cannot downsize as Caribbean families get offended if you ask them to stay in hotel.
2. Novice with 1st eco project

Previous Bungalow
- 2 condensing boilers from previous owners attempt to have granny annex
- Very poor water pressures which I envision will get worse with moving
upstairs and multiple users at the same time. I have asked the water company and little can be done to improve.

Current Eco renovation / roof conversion
– 380mm rigid insulation in hybrid roof. 150mm EWI over 75mm cavity wall
– Sunspace and lots of triple glazed south facing windows with plans to have temp sensitive fans drive heated air to colder north facing rooms.
– Air-tightness will be addressed to the best of our ability with all the advice from GBF
- Took the opportunity to put in UFH pipe in the slab and beneath as a coild for potential interseasonal store, usining Vikings reasoning.

Current Need/problem – The heating system now and future proofed
Now – Condensing boiler but no ability to cope with ~6 months of high demand time throughout all seasons when family comes to stay. Heating may not be an issue as hopefully the insulation and air tightness will make meeting that demand easier via rads. Hot water demand will be a challenge are they are warm blooded types from the Caribbean.

Medium term – Solar thermal – Can’t afford now but envision a potential for a 40m2 solar thermal array and possible 80m2 Solar PV on flat roof. Like the solar/active house ideas.

Long term - Future woodburner with most heat to back boiler. I know, I know… but SWMBO and some caveman need for FIRE, means that I cannot rule out installing one in the future. Been trying to find out which one the AI PassiveHaus went for ( http://www.aipassivhaus.com/press.html ) Not sure which one they went for.

Have also been long at a 400 litre multi fuel stainless steel thermal store that can connect multiple heat sources simultaneously - such as gas/oil boiler, solar thermal, solid fuel appliances with condensing boiler providing top-up heat.

Controls
Would love a system that could be switched on by individual room when family / guests arrive, switch off at a set time at night, switch on again in the morning

Need recommendations on specs
1. Which multi-input tank/thermal store is most cost effective in terms of initial capital outlay?
2. Which woodburner? - Does anyone know which one the AI PassiveHaus went for ( http://www.aipassivhaus.com/press.html ), ?buffer tank, ?programmer etc)? I won't insatll now but need to install pipework and a system to accomodate in the furture
3. Would I need a buffer tank?
4. Which controller programmer
5. Should I use two seperate systems on 2 seprate condensing boilers at present? This would give the advantage of shutting off half the house when family are not about. Or should I go for one system?
6.When Interseasonal stores were fashionable I had envisioned linking the slab to the wood burner as I felt that this would prolong the heat output of the wood burner when space heating for large gatherings was the need and not DHW. Is that feasible? Is it a good idea?
7. What system would you design to cope with my inability to reduce the size and origins of my extended family? :)
If allowed specific brands and costs would be appreciated.

Be gentle... Thanks

If you have low (or uneven) water pressure/flow and you cannot predict your demand then you have a challenge on your hands.
How large a header tank can you put in your loft, this will buffer lack of flow and give you a consistent head (all be a low one).
Then you could have two thermal stores with some sort of heat exchanger in each one. Design each system to cope with 4/5 people each. Run just one when there is a few of you in the house, both when full.
If you want really speedy recharge times then a gas boiler or two, some electric immersion heating on top.
Design in a connection for a wood burner on your main thermal store, solar on the other one (assuming most of your guests will be staying between March and October).

But before all work out your water usage. You can't size anything without knowing what you need to heat.

Alternatively, move to the West Indies, I liked living there, was a large refinery on our island, now they are fitting a OTEC plant.

All sounds very expensive and complicated to me! If your hot water needs are much higher than your heating needs then you need to separate them.
We had the same ideas as you for our own passiv'ish new build, big thermal store, wood stove/boiler, back up gas boiler, thermal hot water all linked in etc, at what cost? prob heading for £10k plus!
All this kit needs maintenance over its life.
Keep it simple if you can. We went for a Rinnai tankless instant gas water heater which will supply up to 35l min. The cold water supply to the gas heater is pre heated through a Gledhill 180l PulsaCoil direct thermal store, this in turn is heated by the 2 immersion heaters run off spare capacity from our 4kw PV through a immersun device. Hopefully this will provide at least 50% of our hot water from the PV.
Apart from the cost of the PV, which we where having anyway and the outlay is covered by FIT payments, the rest of the kit cost less than £2k! and is virtually maintenance free, and runs its self, no time switches, logs to chop, how hot is my store, should I fire my boiler this morning, is the sun coming out later, will it get to hot, need to dump heat etc...
If your well insulated, heating is easy, little wood burner or small boiler and under floor at 21c, we are going for an air to air heat pump in our open plan main living kitchen space which also has the open stairs to the first floor bedrooms. Mitsubishi unit, COP 5.5, cost £650!

If you are intending to use the property for a commercial purpose you could investigate the non-dom RHI and if eligible use a pellet boiler and instantaneous hot water system,this would cover the install cost many times over during the 20 year scheme,but you need the plant area and the pellet storage area.

Simple is best especially in a commercial where you don't want down time, so I would definitely forget the thermal store back boiler idea and the multiple inputs, they are too complex and the condensing boiler that does the bulk of the work don't function well with them.

There are plenty of gas options in terms of water heaters, big storage combis from Viessmann etc.

We do a lot of boosted water supplies, upgrading the main may not be the solution, there is no guarantee that the UC won't downgrade the supply to statute minimum at any time in the future, or it may already be undersized in the road.

We have tried the accumulator tanks that CWatters refers to,but have reverted to holding tanks, feeding variable speed pumps where you can pre-select flow rate and pressure, much more reliable and bomb proof.

Posted By: montyfellrunnerRinnai tankless instant gas water heater

That was exactly what I was looking for but did not find! Oh well, I have what I have. When the boiler needs replacing that is what I may well replace it with.

Forget inter-seasonal storage.
If you must go the wood-burner route, then pumping as much as you can into an UFH system seems sensible to me.

Ah
Yes, then a large store.

Posted By: joe90Yes but cant you blend the water to a lower temp to put into the slab?

Yes you can. Or have a slab so large that you can only put in enough energy to get it up to a set temp.

Not very efficient or effect though. You only have to look at the thermal inertia figures to work it out.

@joe
blend the water to a lower temp to put into the slab ==> any ideas on how?

@steamy
How large is a large store? I can accomodate most things.

@markocosic
Thanks for the detail will try to see if I can cost that set up. Is there anyway to simplify it? Any idea on capital and maintainence costs?

@Monty
We are in exactly the same situation 'open plan main living kitchen space which also has the open stairs to the first floor bedrooms'
We have looked at Vikings no duct system (http://www.viking-house.co.uk/fine-wire-hrv.html) but not sure of the price £1000 or £2000. Your Mitsubishi unit, COP 5.5, £650! seems attractive.
What ducts do you need?
We had a chap come around specifically to get a price on a cost effective simple ductless system... I panicked when drilling through I beams started being mentioned.
Anyone with suggestions for air to air to heat solution for the open plan space (~444m3)?

Thanks

Posted By: Novice1We are in exactly the same situation 'air to air heat pump in our open plan main living kitchen space which also has the open stairs to the first floor bedrooms' We have looked at Vikings no duct system but not sure of the price £1000 or £2000. Your Mitsubishi unit, COP 5.5, cost £650! seems attractive.
What ducts do you need?
We had a chap come around specifically to get a price on a cost effective simple ductless system... I panicked when drilling through I beams started being mentioned.
Anyone with suggestions for air to air to heat the open plan space (~444m3)?

You appear to be confusing ventilation and heating Novice1, the air to air heatpump is for heating and not ventilation.

You really need to do heat loss calculations to decide what capacity of unit you require for your open plan area. It is then good to oversize it so that the fan speed on the internal unit can be kept to a minimum so that you keep the noise level to a minimum.