UFH Help
- Thread starter pwater
- Start date
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So flowrate, still a mystery to me as they are all very dirty and I have yet to find someone willing to swap them (they are on the pipes themselves), however I do have the auto balancing actuators, which seems to be keeping a decent temp difference between flow/return on each.
Each manifold has 9 loops, so 9 upstairs and 9 down.
I am wondering if the boiler is having an issue modulating the temp as the water demand isn't that high in general (on the manifolds maybe 3/4 loops are generally open at once), and its short cycling a bit?
Paul
Each manifold has 9 loops, so 9 upstairs and 9 down.
I am wondering if the boiler is having an issue modulating the temp as the water demand isn't that high in general (on the manifolds maybe 3/4 loops are generally open at once), and its short cycling a bit?
Paul
Per your 6 hr consumption, you are using 20.17 kwh/hr, = 17.74kw boiler output at 88% efficiency, if, say only a max of 5 loops open at any one time then each loop emitting a almost impossible 3.54kw/loop because you will need a flowrate of 3.38LPM at a dT of 15C to achieve this, something strange as well because the boiler if its outputting 17.74kw then no way should it be cycling.
Suggest when system is running normally, take a photo of the gas flowmeter and exactly 3 mins, 180 secs later, take another one and post back, also ensure boier is not cycling during this period.
Suggest when system is running normally, take a photo of the gas flowmeter and exactly 3 mins, 180 secs later, take another one and post back, also ensure boier is not cycling during this period.
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Hi
Thanks, so I kind of came up against 3 scenarios:
1. The boiler from cold getting up to temp (65ish) - 10988-454 up to 10989-129 - took around 20 mins
2. Boiler with just UFH on, wasnt making much noise, just seemed to be keeping temp - 10989-133 up to 10989-175 - 3 mins
3. Boiler with UFH on, and then the hot water kicked in (which is fed off the same heating circuit), sounded like it was working a bit harder - 10989-560 up to 10989-632
I did notice that when the hot water kicked in, the manifold temps went down by around 5-8 degrees, and didnt really recover properly until it went off, which may imply the hot water pump is pulling too much flow, meaning the return temps from the UFH are lower during that period and the boiler has to heat the return more?
The boiler pushes the water a short distance to a pipe that has the two manifolds, hot water, and rads for the top floor (never on), each of these has a pump, all are old CP53 on their lowest setting, and the hot water one is an evosta2, which is set on 'regulation with constant curve' on 1. So could be the hot water pump is pulling more water than it 'needs' and causing the boiler to work harder than it needs to when its on?
Sorry, maybe gone down a rabbit hole here...
Ta
Paul
Thanks, so I kind of came up against 3 scenarios:
1. The boiler from cold getting up to temp (65ish) - 10988-454 up to 10989-129 - took around 20 mins
2. Boiler with just UFH on, wasnt making much noise, just seemed to be keeping temp - 10989-133 up to 10989-175 - 3 mins
3. Boiler with UFH on, and then the hot water kicked in (which is fed off the same heating circuit), sounded like it was working a bit harder - 10989-560 up to 10989-632
I did notice that when the hot water kicked in, the manifold temps went down by around 5-8 degrees, and didnt really recover properly until it went off, which may imply the hot water pump is pulling too much flow, meaning the return temps from the UFH are lower during that period and the boiler has to heat the return more?
The boiler pushes the water a short distance to a pipe that has the two manifolds, hot water, and rads for the top floor (never on), each of these has a pump, all are old CP53 on their lowest setting, and the hot water one is an evosta2, which is set on 'regulation with constant curve' on 1. So could be the hot water pump is pulling more water than it 'needs' and causing the boiler to work harder than it needs to when its on?
Sorry, maybe gone down a rabbit hole here...
Ta
Paul
Gas consumption was 7.425kwh (assuming 20 minute warm up), which means the system contents are ~ 140L (assuming cold at 25C)
This gives a boiler output of 9.24kw which sounds more like it for the UFH heating.
If this again was over a 3 min period then the boiler output was 13.93kw, sounds OK with both UFH & DHW heating on although the water heating at ~ 13.93-9.24, 4.7kw seems a bit on the low side but not a problem really.
It was 3 mins, the hot water was just topping up I think, was only on for 10 mins overall that time.
So basically this all sounds quite 'normal'?
Ta
Paul
Just to hopefully close this off. I got some new thermostatic heads for the ufh manifolds today and they seem significantly better at holding a steady temp, this also seems to have made the boiler much happier and it seems to modulate down to 20/25% when a few ufh circuits are up to temp and humming away….
All seems much happier so far, many thanks for everyone’s advice!
All seems much happier so far, many thanks for everyone’s advice!
Two data points that may help:
1. I have had my system in for about 10 years now - with Ground floor all UFH and upstairs normal rads. 10 years is long enough that I have been able to experiment with one winter season running 24/7 - on the grounds that once you heat up the entire mass of the house, it doesn't take so much to keep it topped up - and there are less cold vortexes etc - and other winters running on timed. As a result, I have come to the conclusion (based on my gas usage) that I can't tell the difference between running 24/7 and just coming on/off when we are there (but see point 2 below) EXCEPT that when running 24/7, for the same apparent cost, we are warm 24/7..
HOWEVER this is the first winter I have used Vaillant V-Smart - which allows me still to run 24/7 but to different room temperatures over each 24Hr period. So I do 17C 23:00 - 07:00, 19C 07:00 - 18:00 and 20C 18:00 - 23:00. Great in theory - particularly as V-Smart is meant to do learning and weather compensation (so comes on earlier to try and hit the temp at period start) but it does no such thing. It has also been told that the heat profile is UFH, and then tells the boiler to increase flow temps > 90C - WTF? (luckily, I have hard set it to 60C at the boiler). So if anyone is thinking of using V-Smart, don't bother, it's a white box of poop and programable room stats would be cheaper/smarter.
2. I have a mix of Pex pipe in screed under natural stone tiles and spreader plates under natural stone tiles and under engineered wooden floor boards. With a flow of around 38C and return of 26C from the zone that is solid screed, I would say that the floor takes at least a day to warm up to > 22C, so that might be one of the effects you are seeing - in that you are expecting things to heat up faster than they probably will (in my experience).
PS. One thought - that you haven't mentioned - is if your boiler is anti-cycling like crazy? It could be that it is going all guns blazing, hits temp faster than it can modulate back down and then takes it's ball and goes home for 15 mins. I had to manually range my boiler down to 12KW* (the lowest it will go) in order to get a couple of mins burn out of it at a time - otherwise it was doing about 10 secs flat - and then anti-cycling for 15 mins, with predictable results at the UFH manifold.
*I also increased pump speed (i.e. flow rate) and pump over-run, just to pull the last drop of residual heat out of the heat exchanger - rather than it going up the flue.
HTH.
It should also be remembered that when running UFH only with a gas fired boiler that a bypass is almost all ways required to prevent the burner tripping on a excessive dT and constant cycling even if its minimum output is < than the UFH demand.
You can see below with a boiler flow temp of 65C, a UFH flow/return temps of 40C/30C that the boiler would have a return temp of 30C with a dT of 65C-30C, 35C, unless some by pass is used to reduce the dT to say 20C.
You can see below with a boiler flow temp of 65C, a UFH flow/return temps of 40C/30C that the boiler would have a return temp of 30C with a dT of 65C-30C, 35C, unless some by pass is used to reduce the dT to say 20C.
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