Delta T 60 C versus Delta T 50 C: self condensing boilers

Calahonda52 · 27-11-2017 08:14PM #1

Have come across a few boiler upgrades where the boiler is operating at the self condemning setting and the rads are not providing enough heat.
What is the solution?
max out the boiler and then not have it self condensing?
?
Thanks as always

Wearb · 27-11-2017 08:48PM

Bigger or extra rads. Assuming that the supply pipework can supply enough heat.

Cheapest option is to up the boiler temperature to a point that supplies enough output. A condensing boiler still provides good efficiency even when not in condensing mode.

Dardania · 27-11-2017 09:00PM

The extreme solution is better insulation, to prevent heat loss.

With this self condensing range, is it with a weather sensor? As I think I saw on a boiler years ago with with weather sensor that changes the flow/return temp based on outside temp, that you can change how aggressively it tries to condense e.g at 0C outside you could change the return temp to be 65C or 70, depending on heat loss from the house.

Or the new nest thermostats (v 3) have OpenTherm protocol, which does this function also of changing return temp dependent on outside weather temp - could help achieve best possible efficiencies for most of heating season, and only go to less efficient for really cold weather

Calahonda52 · 28-11-2017 07:38AM

Thank, there is no Outside weather sensor.
With the temp dial maxed out the max flow is about 77 C so its never going to get to a delta T of 60

New rads is not an option at this stage..

Can you buy non condensing boilers these days or has Brussels put pay to that?

Dardania · 28-11-2017 08:34AM

Another way to deal with it would be to reduce the temp demand in certain rooms (e.g. hallways, bedrooms etc.) so as to prioritise what heat can be generated to those rooms that need it most.

Do the rads have TRVs? If so, can you turn some of them down in "sacrificial" rooms? Or if no TRVs, can you fit them?

antoinolachtnai · 28-11-2017 05:19PM

If the problem here is that the house doesn't have enough radiators to deliver the heat at the lower temperature, it is very unlikely that turning off radiators is going to help. In fact that should make it worse.

Boilers in general have to be condensing unless there is some brilliant reason why it is impractical. If the boiler is already in, the easy fix is to add a few radiators of course.

Two other possible solutions:

1. The obvious thing to do is just to run the heat for a longer period to attain the target temperature.

2. This yoke should increase the output of a radiator to some degree by forcing air through it (hard to say how much and I only suggest it for this specific situation, I don't think it will generally have much effect on fuel efficiency generally).

https://purchase.ie/product/all-products/radiator-booster

Dtp1979 · 28-11-2017 07:37PM

Calahonda52 wrote: »

Have come across a few boiler upgrades where the boiler is operating at the self condemning setting and the rads are not providing enough heat.
What is the solution?
max out the boiler and then not have it self condensing?
?
Thanks as always

What is this self condensing setting you speak of?
If the new boiler stat is set to 70 then the rads will eventually get to 70. Condensing boilers should be slightly undersized if anything to ensure they’re chasing the heat. It sounds like the jobs your coming across have the boilers too undersized

Calahonda52 · 28-11-2017 08:20PM

The plumber told the homeowner that having it set at about the middle setting was the one that would allow it condense.

However there is a physics issue here: if the boiler can not deliver an average of 80 degrees C to the rads, the delta T will never be 60, regardless of what you do with the rads in terms of switching empty rooms off etc.

Wearb · 28-11-2017 08:37PM

Calahonda52 wrote: »

The plumber told the homeowner that having it set at about the middle setting was the one that would allow it condense.

However there is a physics issue here: if the boiler can not deliver an average of 80 degrees C to the rads, the delta T will never be 60, regardless of what you do with the rads in terms of switching empty rooms off etc.

What if there was only a temperature drop of 10 / 11 across the rads?

Tom44 · 28-11-2017 09:49PM

The main purpose of a boiler is to heat a house, not to satisfy a mathematical equation.

Up the output.

It's only losing out on the full benefit of constant condensing if it's to big in the first place.
The loss on efficiency is minuscule and only when the boiler is approaching high temperature.
It's in condensing mode till then.

Customers want heat.
Not the pleasure of looking at a plume while been cold

Up the output and see a satisfied customer.

Simple.

antoinolachtnai · 28-11-2017 10:10PM

I thought you said that the max you can get it to is 77? And that is not enough to heat the house?

Calahonda52 · 29-11-2017 08:07AM

antoinolachtnai wrote: »

I thought you said that the max you can get it to is 77? And that is not enough to heat the house?

Correct by two

https://www.theradiatorshop.ie/content/8-radiator-sizing-guide

shows the " mathematical equation "
"Delta 60 (Δt 60ºC) is the British Rating System whilst the newer European Rating is Delta 50 (Δt 50ºC ). Many radiator shops still sell radiators by only mentioning the output of the radiator at Delta 60. But Delta 60 assumes the water entering the radiator is about 85⁰C, and todays condensing boilers supply water at lower temperatures."

antoinolachtnai · 29-11-2017 08:44AM

And I take it that the boiler is cycling (i.e, turning off as the circulation water hits some temperature)?

If that is the case, the radiator loop is just undersized. Adding two or three radiators would probably be the easiest way to sort out.

Calahonda52 · 29-11-2017 01:13PM

antoinolachtnai wrote: »

And I take it that the boiler is cycling (i.e, turning off as the circulation water hits some temperature)?

If that is the case, the radiator loop is just undersized. Adding two or three radiators would probably be the easiest way to sort out.

Correct re the normal cycling.

So the "mathematic equation" , dismissed by Tom44 is correct:

antoinolachtnai · 29-11-2017 03:39PM

It is somewhat theoretical, alas.

jimf · 29-11-2017 06:44PM

what circulating pump is on the system is it man enough for the job

Dtp1979 · 29-11-2017 07:28PM

jimf wrote: »

what circulating pump is on the system is it man enough for the job

The term is person nowadays Jim.

jimf · 29-11-2017 07:33PM

it wouldn't be the first time a new boiler was fitted dtp and the old 15year old person left on the system

or is that only a local to me thing

Calahonda52 · 30-11-2017 09:11AM

the circc pump is not the issue, doesn't matter how much water is circulated, if its at 75 in and 65 out of the rad, then the delta T is 50.
The rad surface area is too small so as suggested earlier the heat loss in the rooms needs to be reduced.

Tom44 · 30-11-2017 10:06PM

Im not been dismissive of the calculations, but if the radiator size is to small for the rooms then a boiler will never heat the house, even if you double the size of boiler.

Condensing boilers are the most efficient, no matter what. Setting it to the maximum output (nozzle) only looses full condensing efficiency mode as it reachs top temperature.
Surely a condensing boiler in condensing mode for 80% of it's cycle is better efficiently than your preference to source / fit a non condensing, standard boiler ?

I have never failed to heat a house if the radiators were large enough and the boiler was close to spec.
That scenario is only difficult if the boiler is grossly undersized.

Which is common when customers double the size of their house and expect a pre 2000
900000btu boiler to still heat it.

Calahonda52 · 01-12-2017 07:38AM

Tom44
Thanks for this.
The boiler in question is a Vitodens 100 and as far as I can see, the max flow temp is about 77, with the dial maxed out.

Dtp1979 · 01-12-2017 07:48AM

Calahonda52 wrote: »

Tom44
Thanks for this.
The boiler in question is a Vitodens 100 and as far as I can see, the max flow temp is about 77, with the dial maxed out.

Why anyone would set the stat to 77 is beyond me.
Either these jobs your coming across are poorly insulated or the rads are way undersized and the customer was expecting miracles from their new condensing boiler.

Calahonda52 · 01-12-2017 08:15AM

Either/or/and

Let me restate the basic proposition here again as clearly I am not making myself clear.

A house has a heating system working perfectly from a heat perspective.
The rads provide plenty heat.
The boiler delivers flow rate water at 85C to the rads, which were sized on a Delta T of 60C

The boiler breaks down and needs to be replaced.

Is there a boiler, branded as a condensing boiler, available that will deliver a flow rate water at 85C to the rads?
[Whether it is operating in condensing mode or not is irrelevant at this point]

Dtp1979 · 01-12-2017 08:47AM

Calahonda52 wrote: »

Either/or/and
Let me restate the basic proposition here again as clearly I am not making myself clear.

A house has a heating system working perfectly from a heat perspective.
The rads provide plenty heat.
The boiler delivers flow rate water at 85C to the rads, which were sized on a Delta T of 60C

The boiler breaks down and needs to be replaced.

Is there a boiler, branded as a condensing boiler, available that will deliver a flow rate water at 85C to the rads?
[Whether it is operating in condensing mode or not is irrelevant at this point]

You’re talking about a gas boiler I assume. Ariston clas boilers can be programmed to give out 82. But again, why anyone on earth would set a boiler stat to 75 or even 85 is beyond me.

01-12-2017 11:34AM

65c is the industry standard anything higher risks burning drunks and small children which I have both seen, the drunk sadly being my dad who fell asleep on a rad and done some serious damage very quickly, I have also seen where a mother put her child down on a bed beside a rad and the child rolled on to the rad receiving terrible burns again very quickly.

Google surface temperatures and 3rd degree burns to see how many seconds it takes to burn skin at temperatures over 65c.

02-12-2017 08:25PM

Just to add to the original post, modern gas boiler are designed by computers with software based on well designed heating systems as they don’t have a “ sure that’ll do” program for Ireland a lot of the efficiency programming skills on the boiler can cause a new boiler problems ie.. the pump/burner may modulate down to a slower pump speed or smaller flame, the boiler can cycle on/off every 3-5 minutes, this is mainly due to oversized boilers and heating pipe work that’s too small to take the heat output of the boiler which allows the boiler to reach temperature quicker than the rads

Delta T 60 C versus Delta T 50 C: self condensing boilers

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