Heating setup - Pump speed, flow temps and balancing.

[dhutch]

Having had the bulk of our central heating replaced I'm keen to make sure it setup well.
- How do you select pump speed.
- How do you set and measure flow and return temps.

Viessmann Vitodens 100 35kw system boiler, running 18 rads mainly on TRVs, two towel rails.

I understand for condensing boilers the lower the return temp the better for efficiency, 55deg often being mentioned as a threshold, with systems being designed for a 20deg drop, 75/55 or 70/50 etc. Which goes against most plumbers instinct of turn everything to max and call the job finished.
Most boilers control/display flow temperature but not return. Intial tests with some clip on pipe thermometers I have show a discrepancy between the boiler and the pipe in the order of 20deg!

Pump speed can be changed, which controls the return temp for a given radiator bank size, slower speed lowering the temperature, and flow noise, if also making it harder to balance.
Lower rad temps reduce total heat output.
Our boiler can use weather compensation, or opentherm control to adjust the flow temp to keep it as low while also ramping it up when more heat output is needed, which seems reasonably sensible.

Can any recommend a good way to measure flow and return temperatures? Has anyone spent and time setting up a central heating system well?

Cheers, Daniel

[Peanut Gallery]

In on this thread, with similar questions!

I have one of these clipped onto either side of my system boiler

https://www.ebay.co.uk/itm/2X-0-120-C-PIPE-CLIP-ON...

(that is an ebay link to 2 dial temperature gauges that are held onto the pipe with springs)

What I have noticed so far is the bypass valve really should be replaced - I am just returning a lot of heat to the boiler un-necessarily. (S-Plan with a slightly open tap instead of a proper bypass valve)
https://www.wolseley.co.uk/product/danfoss-randall...

[Alucidnation]

Weather comp the system.

Problem solved.

[Black_S3]

IR thermometers are less than £10 and perfect for quickly checking flows and return.

Simply put you want the pump set as low as you can get away (too slow and you end up with too much of a temp drop and too fast ends up with not enough) with & the flow and returns as close to an 11degree c drop on every rad (by tweaking the lockshields) & at the boiler as possible.... then set the boiler temp to 65 (so the return is never above 55) and only up it on a really cold day if you think the heating isn’t coping.... easier explained properly by a YouTube vid...

It’s a lot of arsing about which is why installers seem to just whack everything to full, check the rads are so hot you can’t touch them and bugger off.

Edited by Black_S3 on Thursday 2nd May 14:43

[Black_S3]

Peanut Gallery said:

What I have noticed so far is the bypass valve really should be replaced - I am just returning a lot of heat to the boiler un-necessarily. (S-Plan with a slightly open tap instead of a proper bypass valve)
https://www.wolseley.co.uk/product/danfoss-randall...

Nothing wrong with using a gate valve, just shut it off so it’s only letting enough through to take stress off the pump when the 2 ports shut...

[Peanut Gallery]

Black_S3 said:

Peanut Gallery said:

What I have noticed so far is the bypass valve really should be replaced - I am just returning a lot of heat to the boiler un-necessarily. (S-Plan with a slightly open tap instead of a proper bypass valve)
https://www.wolseley.co.uk/product/danfoss-randall...

Nothing wrong with using a gate valve, just shut it off so it’s only letting enough through to take stress off the pump when the 2 ports shut...

Thank you, that is what is there, I'm just conscious that when the boiler is trying to get the hot water tank to 60, even the slightest amount of bypass and the boiler is stopping due to return temp being high.

It is a very basic 10+ yr old boiler, so does not throttle down the flame, just shuts off when the return temp gets to whatever is set (+-65)

On shutting both valves due to temp or time, the boiler then cools itself running the pump through the gate valve. - Takes a while, but gets there.

Hugely appreciated to have someone tell me I am not loosing my marbles!

Regarding using an IR thermometer, I hear sticking a small square of black insulation stuck on your rads / pipes can give a better result.

(Sorry for the thread hi-jack!)

[Black_S3]

Peanut Gallery said:

Thank you, that is what is there, I'm just conscious that when the boiler is trying to get the hot water tank to 60, even the slightest amount of bypass and the boiler is stopping due to return temp being high.

It is a very basic 10+ yr old boiler, so does not throttle down the flame, just shuts off when the return temp gets to whatever is set (+-65)

On shutting both valves due to temp or time, the boiler then cools itself running the pump through the gate valve. - Takes a while, but gets there.

Hugely appreciated to have someone tell me I am not loosing my marbles!

Regarding using an IR thermometer, I hear sticking a small square of black insulation stuck on your rads / pipes can give a better result.

(Sorry for the thread hi-jack!)

Shut the gate completely, with the system cold, turn on heating, watch which 2 port opens, carefully (esp if it’s plastic) manually shut the 2 port, open the gate valve a tiny amount and feel for the other side of it getting hot... turn the heating on and off and listen to the pump to check it doesn’t sound stressed as the 2 port closes... (it’s worth having a spare gate valve handy if it hasn’t been turned in a while as turning it might cause it to start weeping - even if you get to this point consider just swapping the internals of the valve as if it was fitted before other pipes were soldered you could have to force them apart a bit and potentially end up with a plumber in resoldering a cracked join.... if there’s play in the pipes just swap for an auto valve)

If that doesn’t get it you can try slowing the pump speed so the water takes longer to go through the coil in the water cylinder or have a look and see if there’s any other ways of slowing the water down on return from the cylinder?

I believe the pumps should switch off fairly shortly after the 2 ports shut and leave the expansion vessel to cope with static water getting hot? Hopefully a gas man can answer this one for you...

Re the IR therms, yeah... you have to pick what you point them at, they don’t like copper much but brass seems fine... it’s obvious when the material it’s pointed at is no good as it reads miles off like 20 degrees when something’s uncomfortably hot to hold.

[biggiles]

Worth getting a load of those stick-on LCD thermometer strips. We have wet UFH and I have them stuck to every outbound and return pipe, so it's REALLY easy to see where the heat is going. Cheap as chips and much easier than using my IR thermometer each time.
I assume you can get them for rad temperature ranges, but they're certainly easy to find in the 10-40 range you need for UFH systems.

[dhutch]

Peanut Gallery said:

In on this thread, with similar questions!

I have one of these clipped onto either side of my system boiler

https://www.ebay.co.uk/itm/2X-0-120-C-PIPE-CLIP-ON...

(that is an ebay link to 2 dial temperature gauges that are held onto the pipe with springs)

Yeah, that's the sort of thing I have. They appear good quality but are not new.

We're a system boiler rather than S or Y plan. New in 2012 believe from paperwork left by previous owners, but certainly has variable size flame. No bypass valve as far as I'm aware.

Alucidnation said:

Weather comp the system.

Problem solved.

Weather comp (Viessmann sensor) rather than a OpenTherm compatible thermostat (Drayton Wiser or similar) or do you mean either?

[dhutch]

Black_S3 said:

IR thermometers are less than £10 and perfect for quickly checking flows and return.

Simply put you want the pump set as low as you can get away (too slow and you end up with too much of a temp drop and too fast ends up with not enough) with & the flow and returns as close to an 11degree c drop on every rad (by tweaking the lockshields) & at the boiler as possible.... then set the boiler temp to 65 (so the return is never above 55) and only up it on a really cold day if you think the heating isn’t coping.... easier explained properly by a YouTube vid...

It’s a lot of arsing about which is why installers seem to just whack everything to full, check the rads are so hot you can’t touch them and bugger off.

Yeah, sounds about as expected, although I thought 20deg is typically used now rather than 11deg. Would the Viessmann installation instructions cover much detail here? Might dig out an online copy if I can.

Daniel

[Black_S3]

I’ve always gone by 11ish... 20 does make more sense as it allows boiler to run at 70 and still condense but in practice maybe very difficult to achieve as much as that?

[dhutch]

Fair, we will see.

I need to call the plumber to chat over the invoice, a few other bits, and to chase a quote for further work we want him to do, so I will ask him is thoughts as well slightly ask why he has turned the boiler up the max and walked away, given the rest of the job has been bob-on and he seems a competent bloke.

We have 18 rads and two towel rails, with a decent number of the rads being largish (main rooms have a paid of 600x1800 twin convectors each) with 'only' and 35kw Boiler so I am hoping we can get a reasonably temperature drop with the pump on a slow-med setting, and then back the flow temperature up in cold weather one way or the other.

I might get a pair of decent clip-on thermometers from RS (£15) and go from there. I notice they do magnetic ones you can stick on the corner of a rad to. Think dad still has his mates ebay-spec IR temp gun too so might get him over with the for a day.

Struggling to find nice inline/inflow thermometers at all, and what I have found are expensive (£40+fittings) and or would need messing about with a tee-piece and reducers to couple it all together, so given copper is a brill conductor it all seems a bit fruitless,

Clip on https://uk.rs-online.com/web/p/temperature-gauges/...
In flow https://uk.rs-online.com/web/p/temperature-gauges/...

Cheers again.

Daniel

[MJNewton]

The IR thermometer, held up close to black insulation tape, will give you all the accuracy, repeatability and responsiveness you need. No need to overcomplicate things, particular given the risk of undermining one or more of these important properties.

[dhutch]

Yeah I like the idea of a square of black insulation tape to give you a standard reading, set emissivity and location, each time.

I also like the idea of having a pair of gauges I can watch in real time and leave in there, especially if varying the temps with weathercomp/opentherm. So will pick up a pair of the clip-on spring pipe gauges too.

[MJNewton]

Yes, for long-term monitoring/information some clip-ons/inlines would be good (even just for geek value!); I've just found them to be poor for balancing purposes as it's enough of a pain doing multiple rounds of all your rads without the added hassle of clipping/waiting/unclipping thermometers. I don't think they have sufficient resolution to do the job either ('properly').

Edited by MJNewton on Friday 3rd May 12:29

[Sheepshanks]

Black_S3 said:

It’s a lot of arsing about which is why installers seem to just whack everything to full, check the rads are so hot you can’t touch them and bugger off.

That's exactly what our CH fitters did. They dismissed condensing like it was some kind of nonsense, and said the bpiler should be set on max. When I pointed to bit in the instructions that say set it on 1.5 (out of 6) they looked gobsmacked.

I got them to fit bigger rads than their calculator showed, but I think they thought I was bit mad.

Balancing only works when flow and ambient temps are fixed. Modulating boilers and TRVs mess it up.

[MJNewton]

Sheepshanks said:

Balancing only works when flow and ambient temps are fixed. Modulating boilers and TRVs mess it up.

??? Not at all.

Balancing is, as the name suggests, all about ensure that you get the same relative flow to each radiator, regardless of size and distance from the pump. With radiators plumbed in parallel a properly balanced system will mean that each radiator presents the same resistance to flow and so, even when TRVs start close, the remaining in-circuit radiators will maintain the same performance as before (with the boiler modulating down given the reduced total heat loss of the system). The radiator with the closing TRV will undergo temporary 'unbalancing' but only for a limited time before it either closes off fully (taking it out of the equation) or leads to slight cooling of the room when it will begin to reopen. Boiler modulation and TRV cycling are both perfectly acceptable events for steady state balanced operation.

All you need to know on the subject (and more besides; it can be a bit heavy going) can be found here.

[dhutch]

Sheepshanks said:

That's exactly what our CH fitters did. They dismissed condensing like it was some kind of nonsense, and said the boiler should be set on max. When I pointed to bit in the instructions that say set it on 1.5 (out of 6) they looked gobsmacked.

I got them to fit bigger rads than their calculator showed, but I think they thought I was bit mad.

Yeah, our boiler even has a mark on the knob for the 'recommended temp' about 2/3 of the way round which I set it to a few times and each day its still back to max.

I also pushed to install larger rads, and I understand that 70/50 only gives out 75% of the rated output, as the ratings are given at hotter temperatures. Despite clearly being switched on there was a still a decent amount of 'computer says no' in terms of straying from what the plumbing supplies place calculator says was required. If we where specing a whole house from new I might have pushed hard, or done the whole system design myself, but as it is I think we have got reasonably large rads, including the ones we havent replaced, and I am somewhat banking on compensated flow temps meaning we run with good condensing most of the time.

Sheepshanks said:

Balancing only works when flow and ambient temps are fixed. Modulating boilers and TRVs mess it up.

I understand that TRV's add a dynamic element to balancing, and good pipework layout/sizing (which the plumber did seem to have a good eye for) is also part of it, however even with TRVs some balancing with the lock-shields has got to be a good thing?
Boiler is not current temp compensated, and the modulated flame means the output temp appears to be rock steady, so from that view point we should have a reasonable good start in terms of balancing up the flows between the rads to ensure the return temps are all there or there about equal.

We dont have a by-pass valve, and almost all of the rads now have TRVs, but we have two towel rads and once we decide where the thermostat is going to go we can make sure the rad in that room is left on full.


Daniel

[MJNewton]

dhutch said:

We dont have a by-pass valve, and almost all of the rads now have TRVs, but we have two towel rads and once we decide where the thermostat is going to go we can make sure the rad in that room is left on full.

Be mindful that many boilers require pump overrun i.e. the ability to dissipate heat by keeping the pump running after the demand has ceased. This can only be achieved if there's somewhere for the water to circulate which, with zone valves closed (assuming an S-plan configuration), means the radiators aren't an option and so either a bypass or another solution is generally required (e.g. diverting it through the cylinder to capture the 'waste' heat).

Edited by MJNewton on Friday 3rd May 15:43

[Sheepshanks]

MJNewton said:

With radiators plumbed in parallel a properly balanced system will mean that each radiator presents the same resistance to flow and so, even when TRVs start close,....

TRVs closing has to have some effect though - the overall system resistance will increase.

The other variable these days is the pump might change speed as the system resistance changes - it definitely will on a built-in pump on a recent boiler.