Explanation of thermostat vs control temp

[vulcancontinental]

Is that available to general public do you know? I've heard about it and understand it, but would be nice to have a read through.

Don't think so but caught a copy and made my own version.

 

[vulcancontinental]

Don't think so but caught a copy and made my own version.

Having said all that I'd take the hit if any on stainless because Ali is not looked after properly.

 

[JonathanM]

Having said all that I'd take the hit if any on stainless because Ali is not looked after properly.

Great video.

EDIT: Was copper ever used for boiler heat exchangers. I'm sure many years ago (pretty sure 2000), our plumber told me that some modern boilers had copper heat exchangers. I'm not sure whether he meant condensing boilers, or standard boilers. Was copper ever used at that time?

EDIT2: When you say looking after Al properly, are you talking about dissolving the oxide, like in the video?

 

[vulcancontinental]

In order of conductivity it's copper best (but cannot resist condesate), aluminium then stainless steel.

A washed copper heat exchanger plus a secondary recuperator and a modulating fan speed tied to the gas valve I'm told can achieve efficiencies in use equal or even better than many current condensing boilers. Look up Vokera Syntesi or Line 735 if interested. Those constructions are too expensive now.

Ali running at non-condensing temperatures will not build up oxides or very little; running cooler as is now becoming norm and condensing continually the flueways will block with oxide hence our change to stainless. Similar wall thickness ali is 13 times more conductive than stainless.

Following on from another thread here regarding a Worcester boiler the speed of shut down from ignition intrigued me as I am following an installation in FaceBook plagued with what they call micro-firing experienced with a very expensive high modulation (1:17) boiler. With exceptional low modulation, compensated system flow temperatures but switching from DHW reheat at high temp to modulated flow temps the boiler is cycling every 10 seconds as it hits setpoint almost immediately.

All current Vokera boilers have adjustable anti-cycle up to 20 minutes. As I mentioned earlier the parameters are comprehensive and adjustable.

Some models like the Unica Max with active combustion control modulate down from ignition fan speed slower than those with simple pneumatic gas valves, the others are quite quick, incredibly quick in the case of the Vibe Max.

I did a video first with the 35kW Vision Plus in heating start up from warm, around 40°C, with secondary flow from the plate heat exchanger we use to remove heat during testing turned off so heating output is through a 3m loop of pipework and one side of the plate heat exchanger only.

Watching the fan speed you could calculate the power of the boiler.

It is the same procedure with the 35kW Unica Max and then the Vibe Max 26C which follow. The Vibe Max has a ramp up of fan speed at the end because the boiler closed down after reaching setpoint. It is a pre-production model without a modulating pump which production models do have.

All were range rated to 10kW.

 

[Harry Bloomfield]

Don't think so but caught a copy and made my own version.

Does that suggest that if the aluminium boiler is regularly run at none condensing temperatures, as it would when called daily to run at 75C flow for heating an HW cylinder, that the efficiency would decline less?

 

[JonathanM]

Thank you, such great info again.

When I get my new boiler, I will run at low temp, so need to think about Al. Intergas use Al, I think, with some copper as well.

"we created a revolutionary aluminium and copper heat exchanger that can reach the demanded temperatures faster than any other boiler"

How is fan speed related to modulation. Is it directly proportional?

Is that the test you did the other day in response to a post on here?

 

[vulcancontinental]

Does that suggest that if the aluminium boiler is regularly run at none condensing temperatures, as it would when called daily to run at 75C flow for heating an HW cylinder, that the efficiency would decline less?

It simply means ali is more conductive. If continually running at low temps, and central heating accounts for around 85% of operating time, the efficiency will be better until the increasing deposit of oxides inhibit flue flow and heat transfer.

 

[vulcancontinental]

Thank you, such great info again.

When I get my new boiler, I will run at low temp, so need to think about Al. Intergas use Al, I think, with some copper as well.

"we created a revolutionary aluminium and copper heat exchanger that can reach the demanded temperatures faster than any other boiler"

How is fan speed related to modulation. Is it directly proportional?

Is that the test you did the other day in response to a post on here?

Intergas is different, it has other shortcomings (in my opinion).

The fan pulls the gas from the gas valve, the faster it turns the greater the input of fuel and the advantage is it is pulling combustion air into the burner at the same ratio so fuel/air mix remains optimum.

The catalyst was the other post was regarding the Worcester short cycling and a facebook thread.

 

[JonathanM]

The fan pulls the gas from the gas valve, the faster it turns the greater the input of fuel and the advantage is it is pulling combustion air into the burner at the same ratio so fuel/air mix remains optimum.

When reading the fan speed, is there an easy way to convert that to output %?

 

[Harry Bloomfield]

When reading the fan speed, is there an easy way to convert that to output %?

There might be several minutes lag, but if you have a Smart Meter, the Indoor Display can very accurately indicate a boilers power input, if it is the only gas consumer running.

 

[JonathanM]

There might be several minutes lag, but if you have a Smart Meter, the Indoor Display can very accurately indicate a boilers power input, if it is the only gas consumer running.

I've been waiting eight months now for OVO to send me an IHD! They're blaming global supply chain issues, related to semi-conductors I think.

 

[vulcancontinental]

When reading the fan speed, is there an easy way to convert that to output %?

Look at the manufacturers instructions, there's usually a graph or image something like this. Obviously all models will be different. Speed on the Y axis, output on the X axis.

 

[JonathanM]

Intergas is different, it has other shortcomings (in my opinion).

The fan pulls the gas from the gas valve, the faster it turns the greater the input of fuel and the advantage is it is pulling combustion air into the burner at the same ratio so fuel/air mix remains optimum.

The catalyst was the other post was regarding the Worcester short cycling and a facebook thread.

Your SS heat exchanger looks very cool.

Something occurred to me, watching the video. You touched on this before. It says the dT between the exiting flue gases and the return water, in some other brands, can be up to 29C. So, for example, with some boilers, does this mean that if the return comes back into the boiler at something very low like 27C, the flue gases would never get below 56C? If the dew point of the water vapour in the flue gases is 55C (as often quoted), then even at that very low return temperature, there would be no condensing?

EDIT: although that dT is when running at 80/60 - presumably that makes a difference? Do you have the dT for, say, 60/40 or 50/30? And I've often wondered, what is the typical temperature of flue gases when they first hit the heat exchanger?

 

[vulcancontinental]

Your SS heat exchanger looks very cool.

Something occurred to me, watching the video. You touched on this before. It says the dT between the exiting flue gases and the return water, in some other brands, can be up to 29C. So, for example, with some boilers, does this mean that if the return comes back into the boiler at something very low like 27C, the flue gases would never get below 56C? If the dew point of the water vapour in the flue gases is 55C (as often quoted), then even at that very low return temperature, there would be no condensing?

EDIT: although that dT is when running at 80/60 - presumably that makes a difference? Do you have the dT for, say, 60/40 or 50/30? And I've often wondered, what is the typical temperature of flue gases when they first hit the heat exchanger?

I think it's how much of the exchanger is at a low temperature. The flue gases or water vapour that don't touch a cool surface will not be cooled so it's time, surface area, and how much surface area is cool enough. Flame temp can be 1000⁰C.

Best to get figures from manufactures literature as they present them in the best way possible. Some don't give flue temps.

 

[JonathanM]

I think it's how much of the exchanger is at a low temperature. The flue gases or water vapour that don't touch a cool surface will not be cooled so it's time, surface area, and how much surface area is cool enough. Flame temp can be 1000⁰C.

Best to get figures from manufactures literature as they present them in the best way possible. Some don't give flue temps.

Great, thanks.

Sounds like the cooling may not always be uniform.

Never thought that level of detail would be in the manuals, but I've found some straight away.