How to optimise your combi boiler

FlyingFish · 5 Dec 2022 at 08:14

Surely it's all a moot point anyway.

A space will require a certain amount of energy to reach a certain temperature depending on that spaces heat loss. We use heat loss calculators in the trade to adequately size the source of heat (radiator) to maintain a temperature in a given space, taking into account all the other variables.

Altering (lowering) the flow temp into that radiator will only extend the period it takes to get that space to it's temperature. The closer the difference between two different temperatures (air temp & rad temp) the poorer the heat transfer. The energy usage will still be the same. You don't get nothing for free.

The only way you will use less energy is by being colder. Assuming boiler, rad, insulation etc are up to spec.

Now if you are running it longer and it doesn't get to temperature within its timed period, then yes you will use less, because the job doesn't get done.

dirtychinchilla · 5 Dec 2022 at 08:17

FlyingFish said:
Surely it's all a moot point anyway.

A space will require a certain amount of energy to reach a certain temperature depending on that spaces heat loss. We use heat loss calculators in the trade to adequately size the source of heat (radiator) to maintain a temperature in a given space, taking into account all the other variables.

Altering (lowering) the flow temp into that radiator will only extend the period it takes to get that space to it's temperature. The closer the difference between two different temperatures (air temp & rad temp) the poorer the heat transfer. The energy usage will still be the same. You don't get nothing for free.

The only way you will use less energy is by being colder. Assuming boiler, rad, insulation etc are up to spec.

Now if you are running it longer and it doesn't get to temperature within its timed period, then yes you will use less, because the job doesn't get done.

A condensing boiler will be more efficient when condensing. That requires a certain return temperature. The return temperature is a factor of the flow temperature and how that energy is consumed. By increasing the dT, you not only use more of the energy but your boiler will condense. Your demand doesn't change regardless of how much heat you use, so achieving 70/60 or 60/50 say, will deposit the same amount of heat, but enable your boiler to condense and use less energy getting to the appropriate flow temperature. Ideally, I'm going to get my house to be doing 50/30.

FlyingFish · 5 Dec 2022 at 08:25

Exactly?

Hotter radiators will have a larger temperature difference to ambient air, so more efficient heat transfer.
And that will go hand in hand with maximising the temperature difference between flow and return, due to the better heat transfer at the radiators.

Relentless81 · 5 Dec 2022 at 08:45

eddyr said:
Assuming you're using TRVs, you could try keeping the flow temp at 60C but setting TRVs on your rads a little higher and seeing how you get on.
Aim is to get the same amount of kw into the rooms as you were getting at 70C flow that you found comfortable but achieve it at 60C, means you've got to let more in at the lower flow temp.

Yeah tried it, doesn't work, all rads have trvs and we have smart trvs in the bedrooms.

Unless I set the boiler to 70 the house will take hours to hit the target temp, at 70 it'll hit it fine. Even 5c less running it at 65 it struggles.

It's cheaper at 70c too, not by a massive a amount but the difference is there

FlyingFish · 5 Dec 2022 at 08:53

Relentless81 said:
Unless I set the boiler to 70 the house will take hours to hit the target temp, at 70 it'll hit it fine. Even 5c less running it at 65 it struggles.

It's cheaper at 70c too, not by a massive a amount but the difference is there

Funny that

Who'd of thought.

jpaul · 5 Dec 2022 at 08:55

FlyingFish said:
Hotter radiators will have a larger temperature difference to ambient air, so more efficient heat transfer.

not necessarily, you'd have greater radiant heat which penetratates wall behind (not useful) say, versus, at lower temp, predominately convection which would slowly distribute heat, more efficiently, around the room.

e: losses off of the pipes, even though insulated, would be greater too.

e2: https://www.heatgeek.com/benefits-of-low-temperature-heating-systems/
Another notable effect of lower temperature heating within the room is the reduced heat gradient. When the room is heated by a cooler emitter a higher amount of radiant heat is used which, as mentioned, travels in straight lines.
hmmh - interesting they suggest radiant heat is more efficiently used at lower temp, and convection heating should always be deprecated.

eddyr · 5 Dec 2022 at 10:21

Welshman said:
but what if your TRVs are already opened to the max and temps are still shoot at 60C flow??? mine works way better at 70C and thats where its staying

Other consideration is radiator balancing as dirtychinchilla said.
You may be inadvertently strangling the flow to a few rads relative to others. So the higher flow temp gets more heat in to the rads underperforming.
Or other scenario is the higher temp allows some rads (getting preferential flow) into getting their room to temp and then shutting off by TRV, which then gives the other rads their opportunity to get more heat. Commonly a rad or two get hot very quickly while the others are still tepid. Might find a rad somewhere that has the lockhsield has been opened to far. Radiators close to the boiler/pump is common, shorter pipe runs means a lower resistance to flow to those.

Relentless81 said:
Yeah tried it, doesn't work, all rads have trvs and we have smart trvs in the bedrooms.

Unless I set the boiler to 70 the house will take hours to hit the target temp, at 70 it'll hit it fine. Even 5c less running it at 65 it struggles.

It's cheaper at 70c too, not by a massive a amount but the difference is there

If it works it works.
There can be many variables especially in large or older houses where upgrades and changes have been done here and there over the years to either the heating or building, that there is only so much you can do without going the while hog and adjusting the installation!

jpaul · 7 Dec 2022 at 10:10

dirtychinchilla said:
Well, balancing with the valves we normally have in the UK doesn't work very well for precisely the reason you've stated - you balance for a certain condition, which is full load. When your system goes into part load, the balancing is out.

Something like the Altecnic pressure independent valves are perfect. Danfoss also do some (who I would say are better, but you can't put your own heads on them) and so do Drayton (who are ****). The solution in the middle is the Danfoss R-AN valve, on which you can pre-set a specific flow rate, as you can with these pressure independent valves, but you don't get any pressure independence.

Feel free to put it in the other thread. I'll reply there too.

well yes, it was a rhetorical question, but my elderly relation would be wasting their time with tado type valves when something like a PIV valve with manual control would be a more economic(cheaper?) investment,
danfoss ones look like they are £30 a pop https://www.bes.co.uk/danfoss-ras-b-angled-dynamic-trv-with-lockshield-10mm--25235/ so cheaper than tado

they had a new system combi installed recently, but, usually heat 50% of house, if there aren't visitors.

dirtychinchilla · 7 Dec 2022 at 11:11

jpaul said:
well yes, it was a rhetorical question, but my elderly relation would be wasting their time with tado type valves when something like a PIV valve with manual control would be a more economic(cheaper?) investment,
danfoss ones look like they are £30 a pop https://www.bes.co.uk/danfoss-ras-b-angled-dynamic-trv-with-lockshield-10mm--25235/ so cheaper than tado

they had a new system combi installed recently, but, usually heat 50% of house, if there aren't visitors.

Agreed. I'm not personally bothering with any of the smart home stuff for heating either. I don't see a cost benefit to it for the occupancy profile of our house. So I think yes, the PITRVs would be a much better investment in efficiency and comfort. They will be more difficult to install, but the PITRVs will improve efficiency and comfort, whereas Tado etc are designed for comfort and reducing heat demand in unoccupied rooms. For an elderly relative, they also have a learning curve that PITRVs simply don't have.

jpaul · 16 Dec 2022 at 13:50

had a maintenance call this week on the logic ideal+ I have - due to full condensate trap not syphoning out it's contents (flame lockout)
I now know what the bubbling sound was > https://housewarm.co.uk/how-to-clean-ideal-boiler-condensate-trap/

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Interesting hybrid use of pitrv's and tado - have 2 pitvs on upper/lower storey circuits (if you have that)... so that tado heat calls managed

flow control valves on a home-run TRV system

I'm looking at some distribution manifolds that have flow meters/flow limiters built in.

forum.heatinghelp.com

While it may not be absolutely critical to use a manifold with flow balancing, it is a good idea. This ensures that all radiators recieve adequate flow during rapid outdoor temperature changes. It also helps prevent excessive system flow and corresponding higher than necessary btu input from the boiler. Having a balanced system before the TRV's results in the most stable conditions for the boiler and the longest runtimes. You should also use a pump that features a proportional pressure curve. Such as "auto adapt" on the Alpha circ, or the "proportional pressure mode" on vr1816 Taco circ. These pump modes have technology built into them that is designed to keep the TRV's modulating somewhere in the middle of their flow rate command spectrum. What this does is allow continous, but moderated input from the boiler, further discouraging an over accelerated firing rate.

The physical design of most TRV's does not match the flow balancing capabilities of the balancing valves on a manifold. It is important to have a well balanced system prior to the TRV's to obtain optimal results from an overall system standpoint.