Underfloor Heating & Solar Panel

Dempo1

Dempo1 wrote: »

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

I have an oil boiler and UFH, solid fuel boiler (only fired once every few days, it provides about 5% of the hot water)
Useage so far this winter 800 litre fill in september, 500 litre fill two weeks ago, house 180m2, high levels of insulation plus MHRV.

I found it works best if you set it on for a few hours a day, my on times are 06:00 - 09:00 & 16:00 - 20:00

wclarke20

JuniorB wrote: »

Have a similar set up as Mike. Hosue only 3100 sq ft. Buffer tank set to 55 degrees. Stats in every room. Set to 18-20 degrees.
Moved in last week in Nov. Heat was on since start of Nov.
Just ordered my 3rd .... yes 3rd 1000 ltrs of oil 5 mins ago :mad:
Plumber due on site tomorrow and he'll have a fair few questions to answer!

3rd fill!! , that’s crazy. Why do you think that is? Mike mentioned the house drying out etc but 3 fills is a bit much?

Wonder how an air source heat pump replacing the oil boiler would work out instead?

Dempo1

wclarke20 wrote: »

3rd fill!! , that’s crazy. Why do you think that is? Mike mentioned the house drying out etc but 3 fills is a bit much?

Wonder how an air source heat pump replacing the oil boiler would work out instead?

Mother of god, that sounds really costly to run, no wonder my neighbour is having panic attacks!

paddy147

Can solar panels be installed and then the hot water used in some way to heat the rads in the house,just to take the chill out fo the air?

is this possible?

galwaytt

Dempo1 wrote: »

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

The issue is not UFH in the above, I'd say, but more the quality of the installation and/or set up.

Consider: if your house has a heat load of, say, 50kW sq/m, then whether you deliver that energy by UFH or rads is irrelevant, and the running costs should be nigh-on the same.

That it isn't leads me to believe your neighbour is losing his heat to.....the foundations, the walls........or the system is poorly set up..........or the actuall running of it is set up funny (on/off/on/off etc)

I've had UFH since 1993, and I'd never go back.

JuniorB

The plumber was out the weekend. He's installed 10 or more of the same set up in the last couple of years. He agrees there's an issue!
He's coming back today with his electical guy to have a look at the setup. The electrics were done by the builder's electrician on instuction from the plumber/supplier.

House is well insulated. Air tightness test result of 2.5. MHRV commissioned in last few weeks. Stats set to 18/20 generally. UFH downstairs/Alu-rads upstairs.

Looked back through my central stat controller - gives me logging info for last month. On average the kitchen/living room underfloor heating have been on for 10 hr per week. Bedrooms have been 28/30 - they have rads, set by stat to come on 2 hrs each day both morning and night if required. Have a store room and sun room that have been on for 50 hrs per week:eek:. Very small areas though.
3 rooms in house not being used/not finished so stats/heat have been off in them for last 2 months.

Did a bit of investigating the weekend.
Have 2 stats in the buffer tank - one 1/3 way up - the other 2/3 way up or so.
Oil boiler was off (due to no oil!). 600 ltr Buffer tank was at 17/19 degrees on Fri night. Lit a good fire and within a couple of hrs that brought it up to 26/31 degrees or so. (not sure if back boiler is configured/functioing correctly either but will sort that when the oil is sorted!)
Checked at 9am Sat morning - 29/30. Happy enough the tank is retaining heat anyway.
Turned off all stats in house. Fired up the boiler. The buffer didn't 'call' for any heat. Have a timer connected to buffer that can be set for hot water. Turned that on and the tank called for heat from the boiler. Took 50/60 mins for water to get up to 55 dgrees. I assume this is normal enough.

Turned on some stats. Boiler kept firing. Left on for half an hour or so. Intermitently turned stats on/off for rest of day. Boiler fired every time they were on - didn't seem to matter what temp the buffer was at.

Will wait and see what the plumber and his buddy find today. Will be happy enough if it's a 'configuration' issue and not a 'structural' issue

My understanding with ref to solar - solar will only contribute to the heat in the buffer when the temp goes above that off the tank. So if the tank is 40 degrees and the solar is 30 degrees then there will be no benefit.
Sayng that my solar collector was up to 30 degrees on saturday with not much sign of the sun so might not be too long before it's contributing.

JuniorB

Ref the 55 degrees setting on the buffer. It was 65 until a month or so ago. Plumber explained that it was only up to 65 to provide hot water at that temp. Underfloor needed 30 degree and rads 40 degress as far as I can remember. So turned it down to 55. Think he should have reduced down the 'lower' stat too but not sure if he did. This may have caused some knock on issues but it hasn't been set that long so can't see it being fully to blame. We'll see !

JuniorB

Update: 'bottom' stat should have been reduced to 45 degrees when he reduced the 'top' stat to 55. Condenser boiler was set too low as well and was cycling away to it's heart's content!
Will reset them this week and I'll monitor the oil usage for a few weeks. Prob wont really know unless we get another cold snap. I wont be wishing for that!

galwaytt

JuniorB wrote: »

600 ltr Buffer tank was at 17/19 degrees on Fri night. Lit a good fire and within a couple of hrs that brought it up to 26/31 degrees or so. (not sure if back boiler is configured/functioing correctly either but will sort that when the oil is sorted!)
Checked at 9am Sat morning - 29/30. Happy enough the tank is retaining heat anyway.
Turned off all stats in house. Fired up the boiler. The buffer didn't 'call' for any heat. Have a timer connected to buffer that can be set for hot water. Turned that on and the tank called for heat from the boiler. Took 50/60 mins for water to get up to 55 dgrees. I assume this is normal enough.

I'm glad someone has identified that something is indeed wrong : it certainly seems to.

My 0.02.
Your buffer should never be that low (17/19 degrees). It should be kept at a constant temp all the time, irrespective of weather or demand. It's purpose is to keep a 'pot' (sic) of energy to hand, at all times, for you to draw on, whether for floor's, dhw etc etc. The job's of your input sources is to keep it there, and which one does it - solar or dhw, is dictated by their ability to deliver (solar during the day, say, boiler at other times.....)

For this reason, get rid of the clock for your dhw - you're effectively running the boiler flat out, to heat the buffer, to heat your DHW, when you should only be drawing off a small qty of heated DHW, and letting your boiler 'top up' the system. It is a contradiction to have a temp-sensitive system, governed by time. IMHO, anyhoo.

Not sure about your tank, but a good quality modern tank, topped to proper design temp (say, 60 degrees), should, in the absence of drawoff, lose only......1 degree (?) over 24hrs...

JuniorB

Thanks for your reply GalwayTT.
It was at 17 degrees because the oil had ran out !!

Mike2006

Sorry Folks, just back online now....

In my opinion, if you do not have A-rated insulation levels then stay away from UFH. The heat needs to be reatined and the only way to do that is through high level of insulation.

Controls are very important as well and you need to understand exactly how your system works before you make any adjustments etc... Your electrician should spend an hour or 2 explaining every element of your system to you. For example, if you turn up the temp on your buffer stat to say 70 DegC and your boiler is only set to 65 DegC then the boiler will be 'called for' 24/7 and you will use 1000litres of oil pretty quickly. So you need to understand your system.
I have UFH both upstairs and downstairs. Already, I have made changes to my system and one potential big saving I can make is to change my stats upstairs to 24/7 controlled stats. I have a 35mm screed upstairs and this reacts to temp changes within an hour which I didn't expect so I could make a significant saving by timing my stats as opposed to having them maintain a temp upstairs all day and night.
This would not work downstairs because I have a 75mm screed and this would take a lot longer to 'charge' and react so it is more economical to leave it run 24/7.
I did not fully understand this before I built but now I do. Hindsight and all that.. Plus, I thought my stats were time programmable but it turns out that they are not, so I will have to change them 1 by 1 as I see fit...

Mike.

galwaytt

Mike2006 wrote: »

Sorry Folks, just back online now....

In my opinion, if you do not have A-rated insulation levels then stay away from UFH. The heat needs to be reatined and the only way to do that is through high level of insulation.

Controls are very important as well and you need to understand exactly how your system works before you make any adjustments etc... Your electrician should spend an hour or 2 explaining every element of your system to you. For example, if you turn up the temp on your buffer stat to say 70 DegC and your boiler is only set to 65 DegC then the boiler will be 'called for' 24/7 and you will use 1000litres of oil pretty quickly. So you need to understand your system.
I have UFH both upstairs and downstairs. Already, I have made changes to my system and one potential big saving I can make is to change my stats upstairs to 24/7 controlled stats. I have a 35mm screed upstairs and this reacts to temp changes within an hour which I didn't expect so I could make a significant saving by timing my stats as opposed to having them maintain a temp upstairs all day and night.
This would not work downstairs because I have a 75mm screed and this would take a lot longer to 'charge' and react so it is more economical to leave it run 24/7.
I did not fully understand this before I built but now I do. Hindsight and all that.. Plus, I thought my stats were time programmable but it turns out that they are not, so I will have to change them 1 by 1 as I see fit...

Mike.

In general all good, but don't nail your colours to 'A-rating' - that's a bit too vague. Yes, by all means insulate the wazoo out of it, but ratings and u-values are being tossed around like confetti tbh - there's more to it than that.

For instance, a friend of mine lives in a B1 rated house with UFH, and it runs very well. U-value of the wall is 0.26, airtightness is 3.25. It's because other issues come into play.

Regarding the controls and individual prorgrammable stats: + 1000

I have to re-do mine(analogue), now: which ones did you use, btw ?

Mike2006

Agreed, re A rating. I was just trying to get the point across about insulate, insulate, insulate...

I used Henco stuff. I upgraded from the analogue stat to the Digital stat but I didn't read enough of the small print. I saw day/night mode etc... and incorrectly deduced that there was time control on it, but there wasn't. You have to manually press a button to change modes which is no good for me. So I will upgrade once I find a suitable replacement.

Mike.

fclauson

Don't want to ask a dumb question - but have you also check for an oil leak.

Had this on a system a few years ago - very slow oil weap rather than leak - detected it by the very strong smell

Worth checking that are you are actually burning all you pay for.

Rayzor1

Hi all,Just wondering if anyone can help.I've just had installed underfloor heating to a new build on ground floor and first floor.Total 4500sq ft.I have heatmiser electronic stats in all rooms and have them set to 20C now so as to dry out the house.The house is well insulated,I have the condenser boiler in the garage along with my 500Litre buffer tank which is also heated by 60 solar tubes.The solars are set by there controller to activate when the temperature is 6C above the bottom stat in buffer tank.My problem is that since installing the system about 3wks ago I've used 600 litres of oil:(.The boiler seems to be running for 1min then idle for 1min then fires again.At present its only running from the limit stat thats on the boiler and as soon as the temperature drops a hair in the buffer it fires up again.because it's always on the solars aren't getting a chance to work unless I turn off the boiler which I had to do as I ran out of oil.Can anyone advise on the placement of high/low limit stats and what temperatures to have all set to as it's madness to say the least at present.surely the boiler shouldn't run like that as it seems uneconomical.Its the first underfloor heating system my electrician has wired so its new to him but the crowd that supplied it to me keep trying to fob me off by saying use a timer for the oil boiler,Any suggestions would be greatly appreciated.

Cheers,

Ray

You need a pair of stats on the tank, one near the bottom and one near the top.
They are wired so they only fire the boiler when both are below the preset temperature, the boiler stays on until they both exceed the preset temperature.
Now when hot water is drawn from the buffer the botton stat will drop below it's preset temperature but the boiler doesn't fire until the top one trips.
Doing this means that the boiler has a single long burn then stops until the contents of the buffer have been used.

Mike2006

It sounds to me like your UFH pump/s is/are calling the boiler.
i.e. every time a stat calls for heat in any room, the boiler starts.

For a 4500 sq ft house, a 500 litre buffer sounds small. You will probably have about 300 litres of water in your UFH loop so your buffer would be drained of 40 degree water pretty quickly in that instance. This will cause your boiler to cycle more regularly as well.

Get the controls looked at quickly. You can use the temp probe from your solar controller to pull in the boiler instead of having to use 2 stats and it will be more accurate as well. There should be a spare relay output on your solar controller which your electrician should be able to configure.

Mike.

Rayzor1

thanks for input lads.yes the buffer did seem to drop temp pretty quick when all the zones were looking for heat.my room stats have 4 programmable time settings per 24hr period so when I have house dried out I plan to reduce temp in certain rooms which should mean they won't call for heat as often as I'll increase there heat to suit when timed boiler is firing.I was thinking of running boiler for about 2/3 hours in the morning set about an hour before we get up to heat house to say 20C then have it stop till about 4pm and continue to run till about 8 or 9pm.This I hope should limit oil consumption and provide heat and hot water when required most.The solars should stop the tank getting cold as on bad days now they're getting about 25/30C.The way the system is set up is when any stat calls for heat it sends a signal to the garage to turn on pump at boiler.Its only when buffer tank drops temp that the boiler kicks in.Another problem I have is that if the boiler is off and the house calls for heat it sends across water which could be cold and further reduce heat of floor.:(
Can you recommend where to get these high limit and low limit stats.I have 3 places on buffer to put them top,middle and bottom.At present the top and bottom are being used from my solar controller.I have a spare relay on the solar controller which I'll read up on and see how I can incorporate it into system.can you tell me the temp I should have all the stats at in buffer/boiler etc.the underfloor provider said I should have the buffer heated to 70C while the plumber said 55C.the plumber said the mixing valve at the manifolds for underfloor should be set to 45C so as to heat the floor quickly.I think once I get these items sorted it should be ok,You'd think all this info should be with instructions of underfloor instead of trying to figure it out yourself.

Mike2006

Rayzor...

Your problem is with your electrician. He did not/does not understand how the system is supposed to work so he has wired it up stupidly....

Firstly, with UFH, you really should leave it run 24/7. But you will need to set up correctly before you do this, otherwise you will not be able to keep oil in the tank...

To try to explain this from first principles, it is the heated water in the buffer that heats the UFH loop, therefore when a stat calls for heat, it is the UFH pump associated with that loop/manifold that should be called for, not the central heating/boiler pump. This needs to be changed.

It is the temperature in the buffer that calls for the boiler to fire (not a stat or UFH pump). You have 2 options here:
1. Install 2 stats on your tank. 1 to fire the boiler when the temp drops and the 2nd to stop the boiler once the temperature in the buffer has reached its setpoint.
2. Use the existing temperature sensor which is already in the dry pocket of your buffer and wired back to the solar controller. This is done by using the spare relay output on the solar controller. Set up the relay to energise at whatever temp you want to fire the boiler at (say 50 DegC) and de-energise when the temp in the buffer gets to the desired temp (say 65 DegC). Switch a live to the boiler through this relay and now you are sorted.

I have my blend valve at my manifold set at 38DegC. I would think that 45 is a bit hot, especially if you are drying out floors... I am open to correction on this though...

I heat my buffer tank to 65Degc. The tank is rated for 110 DegC so I will see during the summer how well my solar performs...

If you are turning your boiler on and off based on time and your stats call for heat when your buffer is 'cold' then the water going through the UFH loop could potentially cool down the house..

If you have your boiler on 24/7 controls, this is not an issue (until you run out of oil..). If you wish to remain on timed based running of heating, then you would need to interlock your UFH pumps to the temperature in the tank. This can be done easily enough, but it is a solution to a problem that should not be an issue if you were running your system correctly.

Print out sections of this post and give it to your electrician. If he understands what I am on about then he will be able to make the mods required to make this work. If he doesn't, get rid of him...
It is all simple stuff so he should be able to do it....

Mike.

Rayzor1

Thanks for all your help mike,You certainly know your stuff.I have a 50mm hemi hydrate screed which is supposed to be controlled like radiators as in quick response times so thats why plumber said set manifolds to 45C.Your right of course about initial heat as too much straight away can crack the screed.I hope to use the timed boiler fire up just so as to limit oil burned unneccessarily when not at home.By setting my stats during the day when oil is not firing to a lower temp it should stop the house calling for heat during the day and sending across cold water(I hope):).I'll do this for night time also.The UFloor heating supplier had said to wire heating pump in garage to underfloor controller above the mainifolds(I have 3 manifolds)so when the stats called for heat the heat pump would come on and send hot water over through heating loop in buffer.The boiler at present directly heats buffer but obviously is over working with start stop motion.The pump at the manifolds always seems to be on but then maybe the stats are not satisfied.(I must turn off all stats and see if manifold pump stops:rolleyes:.what way do you suggest the heat pump is wired.Should it be controlled by stat in buffer so when The buffer hits just say min 40C the heat pump kicks in sending over warm water but if it not at 40C it knocks off and in turn doesn't send across cold water which could cool down slab.The manifold pump could still probably kick in and just pump existing water around the open zones.Plenty of food for thought!! Plumber is back later so I'll see what he says and I might try the heating supplier and run it by them.Thanks again.

Mike2006

Rayzor,

Before I send a long reply, how are you heating your hot water for taps/showers etc?

Mike.

Rayzor1

Mike,
Thanks for getting back so soon.I have a 500L duel coil buffer tank.Oil heats the top and solar supposed to heat the bottom.I have a 1000L storage tank beside the buffer/Boiler which has a pump set to 3bar that supplies hot/cold water to house.Obviously it T's off,cold runs to house and hot runs through centre of buffer and comes out hot at top and then across to house through a mixer valve to prevent very hot water running to house.The buffer tank is supposed to allow 22L of hot water flow per min.problem I have with this is the garage is about 15m away from house and it takes forever to get hot water in house.Am thinking of getting plumber to install a hot water loop but then this may drain heat as well.Probably another days work or thread.

Mike2006

Ok, your hot water is supplied from/through buffer tank as well. Sounds like you have a heat exchange coil in the buffer?? Therefore if you time control your boiler, you run the risk of not having hot water when you want it..
Why don't you time control the stats in each room instead? This will let the boiler heat the buffer when needed but the stat won't call for heat until it hits the specified time. This would be a lot more efficient.
Your location of hot water is a problem alright. Every 1 metre of 22mm pipe holds approx 380ml of water, so you have to 'drain' about 7.5 litres of water from your system before you get any hot water and then you leave a further 7.5 litres of hot water in the system as well when you are finished.

A hot return loop is a solution alright, but I don't think that it is a great solution in your case. Your buffer tank is relatively small so if you have your hot return 'pulling' the loop the whole time it is going to cause you more inefficiencies. I installed a hot return loop on my shower but I used a live from the light switch to pull in a contactor to start the pump so I am only pulling the loop when I turn on the light switch (which I always do when I am going for a shower anyway). You could have the hot return loop pump on a timer and have it pulling at certain times during the day when you 'know' you will need hot water (i.e. shower time, wash-up time after dinner) and then just wait for the loop all other times. I would not run the loop 24/7 if I were you.

My guess is that your UFH supplier was either not aware of the fact that you have a buffer tank or else he didn't understand how it works either...

As I explained, I would suggest having the solar controller call for the boiler/central heating pump. The type of sensor that is supplied with the solar controller (PT100 RTD or PT1000) is a lot more accurate than 2 stats and can be easily re-configured if you like. It is correct that the boiler directly heats the buffer. What is wrong is the order in which it is heating it. It is heating it when any of the 3 UFH pumps run instead of when the temp in the buffer tank runs low...

You don't want to be going around the house twice a day changing temperatures on stats... That is not living !!!

Mike.

Rayzor1

Very impressed mike,you know your stuff.If only you worked for my heating supplier.I actually got the underfloor,Buffer and solars from the one supplier so they know exactly what I got but the lads I was dealing with aren't up to speed.I believe there is one lad that works for them that knows what he's talking about but its impossible to get him,always busy.Is this what you recommend then.
1/ room stats on timers so as to call for heat only when in the house ie. morning and night.when zone calls for heat motorised valve opens and manifold pump starts.At present now this happens but heat pump in garage also comes on and if buffer is not hot it'll cool down the floor with cool water being pumped across,If its set that the solar stat only turns on the heat pump when its a certain temp(what temp?)can the manifold pump work away happy days pumping around the zones that are looking for heat with existing water in zones even though heat pump is off in garage.I know it wouldn't increase temp but shouldn't cool it down much either.just in case stats ever look for heat when buffer is not hot.
2/ Boiler set on timer to come on 1hr approx before heating starts and then stay on an hour or so to get temp up and come on evening also for few hours.If I'm in during the day and need heat I can set it to constant if required or solars my be contributing more also.It would be off all night also unless needed.
3/I think I'll still need the high and low limit stats to give me a 20C approx differential to stop the boiler over cycling.If the house is calling for heat the buffer drops temp fairly quick so the 20C differential should help me out instead of boiler firing all the time.
4/At present the solar pump kicks in from relay #1 at 6C above bottom stat in buffer,Should I then use relay #2 to kick in heat pump when top stat in buffer reaches say 40C.this will ensure this pump doesn't pump water across for manifolds unless its hot,The downside is that if the house is not calling for heat and the buffer is up at above 40C the heat pump will be pumping across to manifolds and looping back,Although thats not the end of the world as I have a 0C heat loss pipe(Supposedly)
5/Your dead right about hot return loop being a drain on the buffer when not needed.I plan to set this as you said on a timer for when needed most and I have option of putting timer to constant if required.
6/just a thought,Had asked the plumber today about installation of backboiler,There is an industrial one you can get now that can go in a garage etc and can feed it with logs etc,I plan to get this if the oil bills work out to be colossal as I have access to solid fuel.didn't want it in the house though as hate the ashes/Cleaning etc.

I'd appreciate if you could run your eyes over this and give some feed back.If all is ok I'll get onto electrician tomorrow to start refiguring it.
Cheers,

Ray.

Mike2006

A bit long winded, but here we go........

1. Use the 24/7 timer function on your Heatmiser room stats to ‘call’ for heat to the Alu-rads upstairs when you will need it. I would recommend 1 hr before needed. i.e. if you get up at 6am then have the stat set to come on at 5am etc.. Same again at night. Bed at 11pm, set to come on at 10pm. This will give you a good saving.
Downstairs, since you have UFH on a heavy bed of screed, I would leave the stats set at a constant 19.5 DegC all the time. If you don’t regularly use any of the rooms (e.g. formal dining room or whatever) turn the stat down to 15DegC here. Same for ‘guest or spare’ bedrooms upstairs.

You need to understand the concept of the buffer tank and how it is supposed to operate. Lets forget about how the buffer tank is heated for the moment and just zone in on what it does. The buffer tank supplies your heating system (UFH and Alu-rads) and your domestic hot water system (taps/showers) with the hot water they need to operate. The room stats, UFH pumps, UFH manifold solenoids and solar system are all linked to the buffer tank and NOT the oil boiler. They have nothing to do with the oil boiler. When a stat looks for heat, it opens the corresponding solenoid on the UFH manifold and starts the UFH pump associated with that manifold and the warm water for the loop is taken from the buffer tank. Full stop. Thats is where the brains of the system ends. It does not know if there is cold or hot water in the buffer. It is possible to interlock all of this out with a stat and relay but that would be a wrong move and a waste of €100.
What needs to happen is for the buffer to be ALWAYS at its required temperature. Therefore, you can not have your oil boiler set to timer because you do not know how often your stats will be taking warm water from the buffer tank, so it has to be always ready. This is the general operating principle of how buffer tanks work. If you did not have a buffer tank (i.e. just a standard copper cylinder arrangement), you could have your oil boiler on timer and it would work as you want it to.
If you put your buffer on timer and let it cool down then you are heating it from scratch every time as opposed to just raising the temp by 15 degrees every time to keep it topped up.
Here is the proof:
ΔQ = mcΔT where where ΔQ means change in energy (or energy required in this case), m is mass of water, c is specific heat capacity, and ΔT change in temperature.
Water's specific heat capacity (energy needed to raise 1kg by 1 degree K or C) is 4200J Kg-1 K-1, so, if we put your numbers in:
Firstly from 15DegC (cold) up to 65 DegC
Q = 500kg x 4200J Kg-1 K-1 x 50°C (50 degress celcius)
Q = 105000000J, or, 105000KJ, or 105MJ of energy. = approx 29 kWh = €5.54 (Electricity)
Now from 50DegC to 65 DegC
Q = 500kg x 4200J Kg-1 K-1 x 15°C (15 degress celcius)
Q = 31500000J, or, 31500KJ, or 31.5MJ of energy. = approx 8.7 kWh = €1.67 (Electricity)
I have used electricity units as the conversion is direct. But you get the idea...

2. Do not use your oil boiler on timer setting as explained above. Interlock your live feed to the oil boiler through a relay. This relay shall be energised/de-energised by piggybacking the contacts on the solar pump. The result here is that when the solar is contributing (pump running) then the live feed to the boiler is killed through the relay. Only when the solar is finished contributing to the system can the oil boiler fire again.

3. You don’t need 2 stats or even 1. The temperature sensor on your solar controller which is most likely a PT1000 covers all temperatures from -40 to + 150 DegC.You can get teh 2nd relay to switch on and off anywhere in this range. I have mine set to switch on (fire the boiler) at 50 DegC and switch off (stop the boiler) at 65 DegC. I have a 1000L buffer tank and this is the range that works for me.

4. Yes, get relay 2 to maintain the temp in the buffer to whatever range you choose, regardless of what the UFH is doing. Reasons are in 1. Above.

5. Timer here is the best option for you.

6. If you want to add a back boiler in the future you will need an extra coil in your buffer tank. You may or may not have a spare coil available...


Mike.

BMD

Hi,

I'm just getting to grips with my system (HRV, UFH, oil burner, soild fuel back boiler and solar). In addition to this all my rooms have a south facing window and my air-tightness is around 3 (still waiting for final test).

My insulation levels are fairly standard; 38mm dry lining and 70mm cavity insulation, triple glazed windows etc. 300mm insulation in the attic and ceilings dry lined. The house is 2900 sq ft.

Over Christmas, I was using ~€50 a week for oil (about 66 litres) and was lighting the fire about every 3 days. This would equate to an oil consumption for the year of €1300 based on having the heating on for 6 months (October/November to March/April). When we moved in November (mild weather) we didn't need any heat for a couple of weeks due to the solar gain.

I was just wondering what these figures sound like...is my system working well or should I expect it to be more efficient.

BryanF

BMD wrote: »

Hi,

I'm just getting to grips with my system (HRV, UFH, oil burner, soild fuel back boiler and solar). In addition to this all my rooms have a south facing window and my air-tightness is around 3 (still waiting for final test).

My insulation levels are fairly standard; 38mm dry lining and 70mm cavity insulation, triple glazed windows etc. 300mm insulation in the attic and ceilings dry lined. The house is 2900 sq ft.

Over Christmas, I was using ~€50 a week for oil (about 66 litres) and was lighting the fire about every 3 days. This would equate to an oil consumption for the year of €1300 based on having the heating on for 6 months (October/November to March/April). When we moved in November (mild weather) we didn't need any heat for a couple of weeks due to the solar gain.

I was just wondering what these figures sound like...is my system working well or should I expect it to be more efficient.

your house is still drying out and you adjusting to using the system efficiently, so your bills will not settle down for a while.

• standard levels of insulation for a 290m2 house, what is your BER result coming out at?
• did you use the ACD's to be allowed put in the lower thermal bridge factor?
• you haven't finalised the air-tightness test, is there construction still on-going? this may have something to do with the high bills..

BMD

Haven't got the final BER done yet but it was calculated to be A3 based on spec before the build.

Re the air-tightness, our spec is for less that 3. The initial result was 3.7 but the builder has some more work to do to get this below 3 (the initial test was done a bit early).

I'm not familiar with ACDs.

I assume from your response that the running cost of €50 a week is on the high side. What would you consider to be efficient for this type of system

fclauson

Mike2006 wrote: »

...You could have the hot return loop pump on a timer and have it pulling at certain times during the day when you 'know' you will need hot water (i.e. shower time, wash-up time after dinner) and then just wait for the loop all other times. I would not run the loop 24/7 if I were you.

Mike - I thought of putting a flow switch on the h/w loop so that when a tap is turned on the pump runs (say for 10 mins so it does not cycle on/off/on/off) so you get h/w faster than you would have had running the tap - but slower than if the pump was on permanently

I would then put a timer on the pump so its on as you suggest at "know" need times

Francis

CotBC

Since I was involved in this thread over a year ago, and got some good information from Mike, I figured it might be of interest to provide an update on how my own system is performing.

The background is that that we moved into our new build at the start of December 2010, so just over the 1 year mark at this point. House is 306m2 (3,300 sq ft), timber frame, UFH on ground and first floors, 250mm wall insulation (0.18 nominal u-value), 150mm floor insulation (0.15 nominal u-value), 400mm attic insulation (600mm in one annex (I had some extra rolls!), triple glazed windows (0.9 average u-value). Heating system comprising of a 750l buffer tank with 5 coils (2 x solar, 2 x DHW (1 preheat and 1 final heat) + 1 for back boiler), 2 solar panels (6m2 aperature area), 15kW insert fire with back boiler (2/3 to boiler, 1/3 to room), MHRV and an oil boiler.
Heatmiser stats in all rooms with a central LCD control panel (so useful!), a Horstman timer controller for the recirculation loop and the towel rails, and an M type controller for the heat inputs to the buffer tank. Tank is located in the garage with about a 10m run back to the house.
I don't have the air tightness test repeated yet, nor the BER rating so can't give figures for those.
House has a significant amount of North and East facing glass (the price I pay for maximising the sea views!), has a 5 person household and is heated for 24/7 occupancy.

Heating systems basically operate in line with what Mike has advocated many times on this thread.

Buffer tank inputs are all controlled by the M controller, with the oil boiler only being called on when the tank temperature drops below a preset level and then only when time lockouts are not in effect. The reason for including time lockouts was because I found during the summer that there were often cases when the tank temp would drop just below the trigger temp in the morning (after showers, etc.), and thus switch on an oil burn, where, if it had waited for an hour or so, the solar panels would be providing the necessary heat input. There are many ways to facilitate such an interlock, but the M controller has the timer function available as part of each function block, so it was an easy and effective option for me.
On a related topic, I did invest in a VBus to LAN adapter, so that I can log the system performance on a computer. Once I had put in the time to get my excel file automated, it only takes a couple of minutes to copy and paste the daily text file into excel and see the system performance for the day. By allowing me to monitor the system performance over extended periods of time and adjusting settings accordingly, that piece of kit has easily paid for itself in the first year in terms of oil saved! The dedicated datalogger is the other option there, but I was trying to keep the costs down at that stage. The other advantage of the LAN adapter is that I have the program backed up on the computer and I can make any changes from there which is certainly easier than trying to navigate through the menus on the controller. It also makes it easy to have separate programs, so it looks like I will have a Summer and a Winter program (mainly just the timer lockout previously referred to which is not in place for the winter months, and a slightly different trigger temp for the boiler).
Note that it is better to set a static IP address on the router for the LAN adapter just to simplify things.

So, getting back to how things have been going!
Bottom line is that I filled the 1,100l oil tank in November 2010 before we moved in, and it lasted until November 2011 when I had to put in 919 litres to fill it again. That was despite the fact that we burned through over a third of the tank in the first 6 weeks due to a combination of the house drying out, UFH settings not optimised, very cold weather and not least because the electrician had wired it up wrong so that it was short cycling constantly. After I re-wired the boiler control by inserting an aux. relay which is switched by the M controller, it only operates as required by the temperature in the upper section of the buffer tank. The only reason for using an external relay for the oil boiler was because the potential max load conditions of everything being switched were getting uncomfortably close to the max rating for the controller, so better safe than sorry.
A side benefit of having the M controller switching it is that I can see from the data log how long and how often the oil boiler runs each day.
This winter the oil consumption maxed at just under 50l per week during the cold spell in December, which was higher than I would have expected, but it is keeping house temperatures at levels for 24/7 occupancy, and in fact some of the preset temperatures were higher than they needed to be and have been dialled back since then. At the moment it's averaging around 30l per week consumption, and that's with very dull weather so the solar input is negligible most of the time.

It's important to note that we do light the fire most evenings, and that does give a nice amount of warm air into the building. Even with only the theoretical 5kW being transferred to the room (5.5m x 4.5m), it is a very warm room after a 4 or 5 hour burn ("cozy" for the wife, too hot for me!). The HRV does it's bit to distribute the heat by pushing it out the door of the room, but unless I maxed the fan speed, there is no way there would be sufficient air transfer to handle the heat load. For reference, increasing the fan speed on the HRV does make it audible upstairs when anywhere close to the ceiling inlets/outlets (it's located in the attic). The temperature in the room will drop a couple of degrees over night, but it will still be the warmest room in the house in the morning (door left open over-night). We bought 10 cubic meters of firewood last summer and it looks like we will go through most of it. That is more than is strictly necessary, but we like the "comfort factor" of having the fire lighting, and the fact that it is a renewable fuel makes it worth the effort for us. I cannot stress enough how important it is to get dry seasoned wood for burning. After we moved in we got a load locally which was supposed to be seasoned, but the reality was that it was far too green and would have needed another year to dry out properly. The result is that it did not burn hot enough in the stove and caused a lot of tar build up under the boiler with the resulting drop in efficiency and the soot builds up on the glass door at a frustratingly rapid rate. Last summer we bought timber that was 2 years cut, but we had to pay a premium for it, and it is increasingly difficult to get. These were large blocks (400mm length), which have the added benefit that 2 or 3 of those keep the fire going for a good long burn without having to keep checking on it. If you are seriously looking at the stove option, you will need to factor in the construction of a timber shelter large enough to allow buying the timber a year in advance so that it's properly seasoned before burning ... aim for <20% moisture. On that subject, I did get a moisture meter for approx. EUR20 after our initial experience, which showed that the original timber had moisture levels in the high thirties and some of it well over 40%.

The back boiler input to the buffer tank is a bit of a mixed bag! One negative with my arrangement where we have the buffer tank in the garage, is that the pipes from the back boiler have quite a long run to the tank. That would not have been much of an issue except for the fact that the manufacturers specified that ONLY copper piping could be used, so despite lagging those pipes as much as we could, there is still significant heat loss on the transfer to the tank. Originally, the system was setup having a standard pipe stat by the boiler which switched on the circulation pump when the back boiler water temp hit 60C and switched off when it dropped below 40C. After monitoring the way that was performing for a while (by monitoring the tank temperatures), I changed out the pipe stat and replaced it with a PT1000 sensor and again used the M controller to take over these functions. Program was setup to use a DeltaT trigger mechanism instead of fixed temperatures, with the circulation pump being switched on when the back boiler temperature is 15C higher than the middle of the buffer tank and off again when the temp difference drops to 5C (coil for back boiler is in the bottom section of the buffer tank). This allows it to automatically compensate for the initial high heat losses until the pipes heat up, and then keep the system running at good efficiency levels. Over the course of an evening, it will generally raise the temp at the very bottom of the tank by about 5C and the middle of the tank by 10C to 15C (that's heating approx 500l of water).

Finally, on the sizing of the buffer tank. This is one I don't have any good answer on. As I mentioned we went with a 750l tank based on the recommendation of the supplier. I tend to think of it as a 500l tank on the bottom and 250l on top ... there is a baffle in the middle to help with the stratification. I did put in 4 x PT1000 sensors for monitoring the tank performance and I can say that the stratification or layering of the temperatures does work very well. A typical Winter situation would be to have the bottom of the tank at 20C, the next sensor at 45C (top of the bottom section), the next sensor at 50C (bottom of the top section) and the top of the tank at 60C ... hope that makes sense! You will see some mixing at the mid levels during an oil burn, but it quickly settles down again.
One thing I did find last summer is that 2 or more consecutive long sunny days causes problems as the tank reaches max capacity and we do not use anything near enough hot water to take sufficient heat from the tank to compensate for the solar input. On the plus side, the 6m2 solar tubes I got can very effectively heat 750l of water when the sun is shining ... we just can't use that much and have no further storage. While I am on the solar subject, I will say that I found trying to select the solar tubes a very frustrating experience ... it is challenging to say the least to try to cut through the sales blurb and to get the relevant data from all the suppliers to make a realistic data driven comparison.
I am going to have to include a heat dump mechanism before this summer, which unfortunately will probably be a water flush. I did some trials last year by turning on the heated towel rails, but they did not take anything near enough heat out of the tank. The other downside with using the towel rails was that the last thing I wanted to do was add any more heat to the house, as we struggled last summer to keep the temperatures low enough in the house ... that on a very dull and relatively cold summer. Don't underestimate the potential for solar loading in rooms if you have large south facing glazed areas (we did not have curtains hanging on the relevant windows at the time), and be sure to disable the heat recovery function on the MHRV during the summer months!
So for the tank size, you will get any number of opinions on this but for me it's a trade off between having a big enough buffer during the summer to take the solar input vs. not having a huge (expensive) body of water to have to heat during the winter months. Therein lies the challenge...

OK- that was longer than I had planned - apologies if I went off on too many tangents.
Anyway, for those of you starting out in all of this - Good Luck!
I'm not sure if any of the above actually helps or just confuses the situation more, but it's my 2 cents worth based on my own experience.

BR,
Tim