I’ve got a 2 up, 2 down plus small bathroom extension, brick end terrace. Floor on ground floor very well insulated, loft insulated. Also – not complete yet, but will be 40/50mm insulation on all walls on top of lime plaster and with lime plaster over top The house has a gas supply but no gas boiler.
Heating consists of underfloor – (just put in), in 2 ground floor rooms and radiators in upstairs rooms and in bathroom extension.
A system fuelled by a woodburner supplemented by solar thermal and also electric in emergency e.g. illness.
We were quoted for an unvented system with a Dunsley boiler, solar thermal panel and a 180L thermal store with solar coil. Thermal store to be connected to DHW system and heating system.
We couldn’t afford it all so asked for the above system that was quoted but without solar panel– and still have thermal store with solar coil for when we could afford it.
When it was installed I tested running the heating system using the heat store which I heated in advance with the woodburner. The heating didn’t come on and I then found out that the company they have not connected the THS to the heating.
I tried heating the THS with the immersion heater – it doesn’t heat all the water in the tank and doesn’t provide enough hot water for a bath. The THS has a 3kw immersion heater in it.
When we raised this, the company said it was impractical to connect the THS to the heating system because the heat in the THS will very, very quickly drop and the woodburner can’t replenish heat in the THS – efficiently. (This was the first time they had mentioned this despite connection being in the quote). At one point they said it might run the heating system for 20 to 30 minutes, but the next time they said it wouldn’t work.
We wanted a system which provided the option of instant heating , even if limited (we thought through the THS) and emergency backup – through the immersion heater, but we are now left with a system which only ever provides heat when the wood boiler is burning – exactly what we wanted the THS to prevent.

Is there anything that can be changed or added to the system so that we have the option of instant heating e.g. for half an hour in the mornings and/or emergency backup if we can’t fire the woodburner e.g. if ill etc.

Is there any pointing in having a 180L heat store for DHW if it is heated just with solar thermal and excess woodboiler heat ?– I didn’t want to rely on electric for any part of the system (except in emergency) and the company are saying that you are supposed to keep the THS to temperature because if it loses all its heat, having to heat it up again is very inefficient/would use loads of fuel?
Is there a more appropriate kind of cylinder if DHW is mainly heated by wood boiler and solar?

Hi Chrisj - sorry if I've misunderstood something but from your description I don't see what is supposed to heat the underfloor heating and the rads as the system is now.

I don't really follow woodburner stuff but aren't they supposed to have vented plumbing so it doesn't all explode if there's a power cut?

Difficult to comment without figures of heat load and wood stove size - however
The firm who are saying the TS is too small to support the heating are correct (as was alluded to in posts above) however IMO this should have been pointed out at quotation stage and either a workable solution proposed or they should have backed out rather than install something that was not quoted for on the basis that the quoted work was not feasible. IMO the firm have a liability as they should not have quoted for a system that could not work and then installed a system that both was not quoted for and falls short of the requested requirements. A very unprofessional job.

So where to from here
For emergency heat I would consider a gas convector heater with a balanced flue (preferably through the wall) They work over here, I'm not sure about the UK regs. OK they only heat one room but can throw out an amount of heat and you leave the doors open, and hey its for an emergency.

I have a 300lt DHW tank that has a 3kw immersion in the bottom, this heats the tank to 65 deg. without problems. (Its on our version of E7 and we get about 10 hours power a day) The 300lt. tank supports 2 houses with DHW and we have yet to run out of hot water when using the electricity (normal mode is via a wood burner) So I would expect your TS to be heated by the immersion, but don't expect the TS to run the heating. As to why the immersion heater is not heating the TS, its difficult to say but I would start looking to see if there was some gravity circulation happening to take the heat away from the TS

An option could be to use the TS as a buffer (rather than an accumulator) to be fed by the wood burner and the solar (when you get it) and then the heating and DHW would be run off the TS. And yes you would need the wood burner going when you wanted the heating on. Over night would be an issue but I don't see a way around this with the kit you have got.

Of course if you had the gas convector then on cold nights this could be left on, on a low thermostat setting - and then you have your emergency several times a week in the cold bit of the winter.

there is another solution to the emergency situation and to support the shortfalls of your current system - this would be a gas boiler.........This could be plumbed into the TS and with the correct thermostat controls would only function when there was a heat demand and there was nothing (or not enough) from the wood burner. The TS then would have three inputs, solar, the wood burner and the gas boiler and with sufficient conjuring, mirrors and thermostats it could work. (I don't like complicated systems). With this system the TS even more becomes the balancing point for the whole heating and DHW system.

I'm with Ringi on this one! I wish we had a gas supply in our area - no storage of oil or wood needed, with the associated upfront costs. Gas boilers are small and cheap in capital costs by comparison with almost any other heater.

Go for the PV option on your roof - a more flexible energy source. Add an Immersun-type controller for your immersion heater

You say that you don't get enough hot water for a bath from a 180 litre cylinder. Does your 3kW immersion heater not heat the whole tank, is it not near or at the bottom?

As P-in-H says, your designer/installer should bear some/most of the responsibility for the system not working properly and it might be worth pressing them for compensation - maybe enough to fit a gas boiler ??

Thanks very much for the comments.
Yes, do think it’s unprofessional.
Thanks for the information that a 3kw immersion should heat the whole store. I understand that the immersion heater is located halfway up the TS – maybe this explains why it can’t heat it all.
Peter, in terms of adding a gas boiler, at the moment the woodburner boiler heats the rads and UFH directly and any excess heat goes to the TS – this is the most efficient way of using the boiler.
If a gas boiler was added to the system, could the woodburner still heat the rads and UFH directly, while solar and gas would heat the TS? Or would everything have to go through the TS first?

So the wood burner is connected to the TS but the TS isn't connected to the UFH. So it seems nothing is connected to the UFH?

Did they design the system? If so I think you have a case against them for bad design. If you designed it then perhaps not, although shame on them for not telling you the design is wrong.

If you have mains gas available consider getting a gas boiler installed - perhaps using the connection on the TS intended for solar. Even an oil boiler should be cheaper to run than peak rate electricity.

I don't understand why you have such a complicated system for such a small property.
I wouldn't have bothered with the cost of underfloor heating, unless there were other reasons to take the floor up.
a simple log burning stove of say 10kw total heat output with 6 kw to the back boiler linked to a neutraliser would have been sufficient. the 4 kw from the stove would heat most of the down stairs anyway. Two radiator circuits one for kitchen and bathroom and other for rest of house would have worked fine with the kitchen/bathroom prioritised would work well. super insulated 180 litre hot water cylinder and you are done.
I have designed a few of these for myself and friends and they work very well. Not expensive either. run on wood or less green but very cheaply on coal

but why would you want to in a small property?
all you are doing is creating the need for a large space for a thermal store and taking up space that could be better used for other things.
Charging a large thermal store from a small stove isn't practical. installing a large stove in a small house isn't practical.
in my view this needs thinking through. Thermal stores can be a source of all sorts of problems an in many applications are not appropriate.

Nick
I know its not everybody's green ideal but if you bank a good quality air tight stove down on coal over night the low heat output will keep most heavyweight properties quite warm. Our heavy construction and good insulation stays about 18degC over night in the depths of winter. Getting up to a cold house isn't an issue. Where neither a THS or solid fuel with back boiler and radiator set up performs is if you go away for the weekend or have a winter holiday and leave the house empty. We have an air source heatpump with our solid fuel set up. This has some advantage as you can set the house to a low temperature whilst you are away. We also use the heatpump for summer domestic water load. On economy 7 we get lots of hot water for very little cost.
The Ecodan feeds into the neutraliser and with some relays we have it working with the solid fuel controls. Very pleased with the combined performance. The cost of the whole set up is very reasonable and no thermal store.

I wasn't suggesting coal is green in any way. I am suggesting its cheap though. I buy my coal at summer prices. 4 ton of quality house coal for £820. Considerably cheaper per kwh than any other form of heating. I also burn lots of wood which is green and I have an air source heat pump which is green. So I can be green and black. This time of year we burn wood on the occasional evening when it feels a little nippy. We are 280m up in the peak park so cool. We cant get planning permission for solar or PV. We have no gas mains. When it is below freezing we run on coal for ease and more kw. The air source is poor at low ambient so we don't use that when it is so cold. The house was built in 1764 so very thick walls. We have done lots of insulation so now have an EPC of D. Not too shabby for such an old house. we are as green as we can be with the restrictions of the property.

hi JonG. As far as I know I have the only Ecodan/solid fuel combination in the UK. Mitsi are not aware of any others. We had a few issues integrating the two systems. The Mitsubishi commissioning guys really didn't have a clue with what I was trying to achieve. In the end my electrician and I resolved the problems and got the system operating how we wanted it.
I don't have a wiring diagram or current schematic of the system but I can talk you through the system.
Basically we are operating the solid fuel side with a neutraliser. We have a Rayburn solid fuel stove and a multifuel stove feeding into the neutraliser. We have two radiators circuits. Each radiator circuit has its pump switched by a strap on cylinder stat on the nuetraliser. The bathroom/kitchen circuit is set at 70degC. The other circuit is set at approximately 78degC. The DHW cylinder has a spring open 2 port valve. On power failure the cylinder acts as a heat dump. The cylinder is a conventional pre-insulated type with an additional 6 inches of wrap added for super insulation.
The Ecodan feeds in to the neutraliser with its own pump. Since the Ecodan operates at low water temperature relays are needed to activate the two radiator circuit pumps when the Ecodan is in heating mode. In domestic hot water mode the pumps need to stay off. They do this on their own as the Ecodan doesn't heat domestic hot water beyond 60degC so the strap on stats don't close in this mode. The wiring isn't hard but it did take some sorting out. not helped by my Ecodan being supplied with a faulty pc board in the first place.
We have had the solid fuel system set up for 10 years and we are very pleased with it. the Ecodan has been installed for 18 months and it is a useful addition. The cost of the Ecodan addition was relatively small since we only needed to buy the unit and plumb in the relatively short length of pipework to the nuetraliser and do the wiring. I think it cost me about £4k to add the Ecodan. We also added anti- freeze to the system to protect the Ecodan in winter.
The Ecodan is great for summer domestic hot water. I run on economy 7 so we run the Ecodan for two hours at night and get a nice full cylinder of hot water. The super insulation ensures it stays hot into the evening. The cost of this summer domestic hot water is very cheap at about 6p/kwh. Even running the Ecodan flat out for 2 hours would only be 36p/day. I think we get a typical COP of 2.5:1 for domestic hot water in summer. The Ecodan needs to run for a couple of hours for domestic hot water to get a full tank. The issue being that the relatively low Ecodan water temperature of circa 60degC does not gravitate very quickly to the DHW cylinder. I have tried running for just an hour but the water wasn't quite warmer enough by evening so we now do two hours instead. No big issue in the scale of things. I could improve the DHW solution by fitting a pump but it just adds complexity I don't need. It works ok and with the COP benefit of the Ecodan over the immersion heater we still win.
Hope this helps

The ecodan is pressurised by virtue of the conventional f&e tank as it is on the same circuit as the solid fuel devices. We have far more radiator surface area than we need for the solid fuel heating. At conventional 75degC mean water temperature we have circa 18kw of radiator capacity. The Ecodan is an 8.5kw model. I think we actually have a building heat loss of circa 12 kw at -4degC in theory, but the heavy weight structure acts as to smooth out the peaks so the smaller output Ecodan works ok. To be honest, when it is that cold we are on solid fuel anyway so we don't run the Ecodan.
The cylinder has a large coil and it seems to work ok on domestic generation. I was concerned about stop starts on the Ecodan during domestic hot water mode only but it doesn't seem to be too much of a problem. The last few days I have been using the Ecodan for only an hour over night to do hot water and we have had enough for two of us to shower in the evening without running the Ecodan again. Used only for an hour the Ecodan runs constantly with no shut downs. We have the Ecodan set at 58degC for domestic hot water

JonG. I am surprised at your comment about the drop in performance of the glycol.
The ethylene gycol is high performance grade that should be able to deal with high temperature. No difference to the temperatures experienced in the block of a vehicle. I would be interested to know a little more about this.
Glycol only drops performance of heat transfer by about small amount. I am not sure of the relevance of this as it is what Mitsubishi recommend. Noted about the leak risk wrt to f&e tank. something to keep an eye on and monitor with a tester.
The system is set up such that if the system is running on Ecodan and someone lights a fire in the stove the Ecodan will switch off due to the high temperature return. This drops the pump out on the Ecodan so it wont pump off the system and therefore protects the HE.
The neutraliser has a smoothing effect on temperature in our heating system. The only high temperatures we see in the system are from the gravity circuits and these don't go over 75degC which is the switching temperature for the pump circuits.

Hi JonG. I don't disagree with you on any of this but I have tried to keep the system simple. I didn't want to strip out the installation that works so well for the solid fuel side. As I can see it, the only drawback is the non food quality antifreeze but you understand my reluctance to go that route on a cost basis and frequency of replacement due to the degradation issue in my system.
If I was starting from scratch I think I would go the high performance plate route to separate the Ecodan and twin coils in the DHS cylinder. if I ever had to replace the copper cylinder I may well do that mod anyway. Thanks for the comments.