Underfloor Heating & Solar Panel

Joe,

I have that arrangement.

I have 3 inputs to the Thermal Store:
1. Solar - Evacuated Tubes 20m2
2. Solid Fuel Room Sealed Stove with 10kW Back Boiler
3. Condensing Oil Boiler

DHW is produced through heat exchange coils which are also loacted in the thermal store.

Mike.

Mike2006 - will have same system as that.
How is it working out? All relative I know, but are you going through much oil? Any idea if the solar is doing much of a job in the depths of winter?

Cheers

Thanks for the detailed response Mike.
We'll be installing ours in next couple of months.
Very interested in the control aspect and ensuring that all runs as efficiently as possible. Our plumber has installed a fair few so hopefully he'll be up to speed.

Mike2006 wrote: »

At the moment it is difficult to say because it is summer and I am not moved in yet but preliminary results look good.

The solar can take the the tank from 40 to 60 DegC in a few hours on an average day...

The big thing here are the controls. I have added lots of controls to the system myself to make it operate as efficiently as I can.

Im will try to explain how it works:

Inputs: Solar, Back Boiler, Cond Oil Boiler.
Solar: I have set it up to circulate once the temp of collectors is 6Deg or more than the thermal store.
Back Boiler: No control here. It is on when it is on and gives heat to the thermal store.
Oil: Only comes on in certain situations.

Temperature in the tank will always be between 50 DegC and 70 DegC.
I have set up some controls as follows using solar controller, pipe stats and relays etc..

1. 2nd available relay output on Solar Controller is used to control Oil Boiler. i.e. when the tank drops to 50 DegC, pull in boiler until tank is at 70 DegC.
but
2. Only if the Solar is not circulating. i.e. let the solar give all of its free energy to the store before using oil to get it up to temp.

This ensures that the oil only kicks in when really necessary...

Q. What if the rate of cooling is too much so that the solar can not hold the temp and it keeps falling (ie, UFH on and running a bath or showers etc..).
A. Pipe stat and relay tell the boiler to over-ride the solar controller if the temp drops below 50 and fire up the boiler until 58 DegC even if the solar is running.

Q:I have no heat dump so I had to make an allowance for what if I am avaw on holidays and the store gets up to over 90DegC and I am not there.
A: Another stat will over-ride 2 room stats in this case (both large areas) and run the UFH in those zones until the tank is back down to 50DegC. This will only ever happen if I am away for long periods of time because the solar would not get the store up to 90 DegC under any normal living circumstances.

Hope I have not confused the situation too much here.


I ran plenty of extra spare cables when installing each component because I knew that as I learn to live with the system, I will need to make extra control modifications that I may not have thought about yet..


I cannot name the thermal store supplier because of boards rules but if you PM me I can reply with it...

Mike.

Wow that is some system, I'm jealous

No bother...
Any questions along the way, just drop me a PM.

Mike.

Mike, would appreciate if you could PM me details as well.

Well,

I actually have a PLC as well but am doing lighting/interlock controls with that. Decided to keep it awy from the central heating system just in case something went wrong with it and I lost my central heating while I was waiting for a card/processor or something...
Must have a PM offline with you on that too...

Heating system:

1. Towel Rail dump is just as good as UFH. Essentially, you are just looking to dump heat, doesn't matter how this happens really... To be honest, with just the solar running, it is unlikely to happen all that often anyway...

2. Personally, I prefer to use temperature based on/off conditions rather than time because you are measuring the process variable directly rather than just going on time... I often see that the solar is only coming into its own by about 3pm or so if the tank is almost up to temp and the solar is 'charging' because it cannot contribute.. Then at about 3pm it can contribute and it gives it a great blast.. If you have your boiler brought in just before this, that contribution temp for the solar has been increased again and you may not get the benefit...

3. In my system the buffer tank should never get below 50 DegC (48 ish) so I would need to fully understand on what that water is doing (heating coils or just for UFH water) to see what your requirements are...


The only thing that I would look at is the timing of on/off conditions as opposed to temp based on/off.... The only place I would possibly have a timer is a run-on timer on the boiler circulating pump if you have a long run from the boiler to the tank.

I toyed with the idea of 2 tanks (CH and DHW). Its a really good system. Did you go for a tank-in-tank system or 2 separate tanks??
In the end I just decided to go with the 1 tank and hope that the specification of the tank does not lead to inefficiency when I just need DWH and no CH for long periods... I think it should be ok..

Once my plumbers leave the house, I fully intend on insulating every pipe in the hot-press to a high level. I am going to lagg it and then tape it up with alu tape much the same as you would see in a plant room. Insulate manual valves etc... to minimise heat loss locally.
Plumbers are just going to clean down all pipe-work using wire wool and I will do the lagging. Again, it requires a bit of patience and the attention to detail that only the owner/end user can provide!!

I will drop you a PM over the next couple of days re: PLC controls in the house...

Mike.

Tim,

Yes, my tank is dressed in the Cork colours alright...

I got the company who supplied it to size it for me and I ended up with a 1000L tank.

If you know how much UFH piping you were supplied you can calculate the capacity of your UFH system. For mine, I was supplied 2000metres of UFH pipe and 10 metres contains 1 litre of water so whole capacity is 200litres...

Full details of my controls are above within this thread. Rather than typing them all out again, take a look and if you have any particular question just drop me a PM or whatever...


Mike.

Re: back boiler:

The back boiler loop is pressurised (sealed) so it had 2 pressure safety valves on the loop. 1 local to the back boiler and another at the tank.

L driver wrote: »

Hello,
Sorry to jump on board, but would this system work well in a very well insulated house. I like the idea of mains pressure throughout the house without a booster pump. Also with external plate heat exchanger and ufh could the thermal store be ran at a lower temp say ~55c. Could an inline instantaneous electric heater be used for days that the solar doesn't bring the store up to temp, but there is no need to start up the boiler for 1shower or to wash the dishes? Great work on the controls btw

Well, I have 3 x solar panels, LPG boiler and 1000l buffer, and DH&C is on a Wilo pressure pump. Mains would be useless imho, and, but having to add pumped/elec showers, you're only complicating it. Put in a pressure pump (it's tiny), pressure regulator, and use whatever mixers/taps/showers that take your fancy. Simpler, imho.

I keep my buffer at 57 deg, tbh, to avoid cracking of lime issues at higher temps - we have really, really hard water around here.

Solar more than contributes - only on the worst days is it's contribution small. On anything remotely bright, it's not inconsiderable.

L driver wrote: »

Hello,
Galwaytt have you a separate dhw cylinder off the store so? Don't know why I asked that:o It must be a very efficient with the store running at 57c. What controls have you

No, no separate DHW cylinder: my DHW is supplied by the volume of the DHW coil within the cylinder.

Tbh, by control's are basic, and I'm planning to re-do them in the new year. Currently there is a room stat in each room, and a Horstmsann 37xl 3-channel timer on the heating itself.
Channel 1 - boiler to buffer - on 24/7, keeps the temp of the buffer at 57deg with no effort. It is effectively 'self-regulating', as the boiler is also very close - about 1m ! - so no big dead leg or losses.
Channel 2 - UFH for GF, basement, garage
Channel 3 - UFH for FF

Now, in reality, the clock, whilst a good one, isn't ideal. What I'm changing to is individial digital stat's with 7-day timers, in lieu of the existing ones, and setting 'step-back' temps for periods of no/low use.

I've no piped gas either - I have a 1t tank in the garden. Bottled cost would rob you afaik - much more expensive than a tank. You don't buy the tank anyhoo, so there is no cost - where are you getting the cost from ? Mine is leased - €100 p.a. or something, and they do annual inspection, maintenance and even paint it every few years ! Basically -I'm a lazy git

I use LPG because it's a fully modulating heat source, which suits UFH well.

You don't NEED 7-day stat's in each room, but imho, it does make sense - unless you have some sort of central plcc's which has full zone control to the same extent.

Using a clock - or time - to dictate heat makes no sense to me now. Far better to use temperature as the first control, and to refine it by time/room use. Doing it the other way around is less efficient.

By doing this, the system is 'on', or maybe we should say 'live' all the time, true, but if the room isn't calling for heat, the pumps won't run anyway - which is what you want.

I didn't size my thermal store, and I wouldn't. Let the installer do that - that's what he's getting paid for - design & fit. Otherwise you'll be the guy everyone will look at if there's an issue. Ditto for combining different systems: one system, one 'guy', one responsibility. Otherwise it's a mish-mash and it WILL go wrong (damhik....... )

Since I had the big mechanicals re-worked lately, house is much, much better.

Well,

I moved in October 1st 2010 and since then I have the living area stats set at 19.5DegC and the bedroom stats set at 18.5DegC and the UFH is on 24/7, (i.e. it is self controlled through the stats and not time controlled).

So far I have used about 1100 litres of oil. Prob a little bit more than I would have initially anticipated but looking at the bad weather we had and the fact that the house was always nice and warm and 24/7 hot water as well.

When the summer/bright weather comes in now I will use significantly less oil because the 20sqm of solar tubes will come into play so I may get away with 1000l more for the remainder of the year.

House size is 3600 sq ft, 2 storey with ufh both upstairs and downstairs.

Mike.

I have only lit the stove 3 or 4 times since we moved in because the room it is in was not fully finished etc...

I am hoping that the coldest 4 months which are now over (hopefully) have been covered by the 1st tank of oil so the warmer 8 months should be covered by the 2nd tank and solar contribution.

Year 2 should be better again because the house will have fully 'dried out' etc..


Mike..

JuniorB wrote: »

Mike2006 - will have same system as that.
How is it working out? All relative I know, but are you going through much oil? Any idea if the solar is doing much of a job in the depths of winter?

Cheers

Hi Mike,

Just came across this thread, have been intrigued about underfloor heating until I heard my neighbor screaming at the top of his voice over the winter. Basically he had this system installed after a major renovation and he is regretting the day ever since. His system has drank oil over the winter despite having the system on a constant and very low temperature.

I was led to believe underfloor systems were economical to run but clearly this is not my neighbors experience