Condensing system boiler options in an S-plan?

[ms1012]

Probably better if I leave you to continue chatting to Upgrade ME as you seem to prefer to ignore my advice!

Your advice is very much appreciated, hence why I also pressed the thank button for your earlier response! Depending on who you ask my 20% is conservative, Danfoss claims up to 40% improvement from WC Guess it's the double-edged sword of marketing lies and internet.

I came into this thread thinking upgraded controls would be required to make more efficient use of boiler. From what's being said here, and from what Vaillant are saying, it sounds like the boiler will modulate well enough on its own (well enough, improvements are possible, but small). That leaves other advantages that UpgradeME also stated, such as being able to use HW boost, setting HW and CH temps seperately. However, I like my Honeywell stat, so leaving things as they are sounds fine. Which still leaves me to pick a boiler. Worcester only do the 30 kW DCi system boiler, Vaillant seems to have a wider range. I'll get back to the installer and ask why he's pushing for the 30 kW over say the 24 kW.

 

[ms1012]

you expect to know more than the experts ( which does not include the nupties who oversize boilers ). Obviously you are intellectually superior to anyone who works in the heating industry. Just be aware that not boiler engineers are nupties though.

I don't know more than expert, I don't want to know more than experts, but I do want to know enough so that I don't get caught out by a numpty who doesn't know how to size a boiler!

 

[D_Hailsham]

A condensing boiler that's not condensing should be as efficient as a regular boiler, right? So that's 80% instead of 90%?

A modern condensing will be about 88% efficient, even when it is not condensing. This rises to about 92% when it is condensing.

Have a look at the boiler data at Sedbuk.

 

[ChrisR]

88% efficient, even when it is not condensing. This rises to about 92% when it is condensing

A bit better than that I'm sure - sedbuk is about seasonal efficiency - like an urban cycle rather than comparing specific speeds. Correct me if I'm wrong.

The whole weather compensation issue is a mess at the moment.
Companies like Viessmann are making silly claims like 20%, half the information you get that was tested was years ago, and some systems are hated by users and get disabled.
CIBSE claimed weather compensation saved 2%. But apples and apples??
Yes boilers modulate themselves down - some can go further than others.
If you set the boiler max temp yourself to say 75º, it'll be condensing (when the return is below about 56). You can do that for all but the coldest weather. A WC boiler would be running at a lower temp than that for longer, but the savings are small and really unknown.
Some of my customers with fancy systems report NO savings. Maybe they're using more hot water -?
I refuse to install a system with only an external sensor, which Viessmann promote. Dumb if you ask me. Opentherm room sensors for me, please.

Yup. Lots of dumb installers. Lots of dummies in the manufacturers too, who just trot out what's in the glossies. And they only make what the marketing men tell them will make most profit - they aren't there to save you gas.

Lots of dumb users too. I'd want a separate zone in each room. Then as user I'd leave all the doors open.

 

[mysteryman]

It is astonishing to read here of people who think they know better than the manufacturers and testing agencies.

The Germans and French think we are absolutely bonkers to be so resistant to the forms of control which they have been using for decades!

 

[mehran]

I hate to have to weight in on this but...

outside sensors allow you to take in account one more factor that affect your heating. nice and simple your house will need more heat when it cold outside. it better to have it than not. there is saving.

all this debate is about 'who can suck a lemon harder'

get WC, get opentherm, get both... it's all good

 

[UpgradeME]

It is astonishing to read here of people who think they know better than the manufacturers and testing agencies.

I've worked in Product Development for electronic equipment for over 10 years. I've visited many different manufacturers globally and seen many 'support' desks 1st hand. In my experience the front line people know very little about the products, only what they are "told" or read on their Intranets.

I fully understand the development process which can easily be applied to CH controls. I've contacted Vaillant to clarify some of the technicalities of the VR65/392/430 controls, the initial response was poor, actually very poor, so I've asked some specific questions in the hope it will be escalated to someone that understands (technically) how their products work.

Searching on this site, doing some real-world research (bearing in mind 'research' is what I do professionally) reveals that very few people actually know how these controls work...

If I get some technical answers from Vaillant on how they work, I'll post here (and/or my own thread) on how they operate.

Has any installer here been on the Vaillant "Domestic Controls" training?* Do they give any detailed information on how their controls work?


* http://www.vaillant.co.uk/installers/training/courses/domestic-controls-training

 

[UpgradeME]

I think that you are overthinking and that worries me because you expect to know more than the experts ( which does not include the nupties who oversize boilers ). Obviously you are intellectually superior to anyone who works in the heating industry. Just be aware that not boiler engineers are nupties though.

Tony,

Would you class your good self in the category of an "expert" in the heating industry?

If so, perhaps you could answer the questions rather than having a snipe at the posters asking sensible / technical questions?

I learned a long time ago that not all "experts" are as good as expected! With that in mind and my background in product dev. I often delve deeper when making technical purchases to find the 'best' products for my needs.

After reading many threads on this forum, I'm rather surprised so many posters have a 'chip on their shoulder' (why??), this is a DIY forum where people come to get advice to "do it themselves" afterall don't they??

 

[mehran]

UpgradeME, the chips come from the RGI only forum that is hidden on diynot from normal users.

which then spills on to this forum.

in a nut shell, viessmann uses a outside sensor only approach(with no measurement of internal temperature), which makes ChrisR go completely of the rails.

I use both internal and external controls on my install. others do only internal others only external somehow this makes some of us what to fight with each other.

 

[UpgradeME]

in a nut shell, viessmann uses a outside sensor only approach(with no measurement of internal temperature), which makes ChrisR go completely of the rails.

I use both internal and external controls on my install. others do only internal others only external somehow this makes some of us what to fight with each other.

- For me, it's about getting the best price / performance combination. I won't be swayed by marketing 'hype' unless it can be backed up with technical data. So far, no-one can give me such data.

Logically, I agree with you! Having both an internal AND external measurement of temperature (if used correctly) has to be the most effecient. The question I would like to know is if the additional efficency of the external controls justify the additional costs?

 

[D_Hailsham]

88% efficient, even when it is not condensing. This rises to about 92% when it is condensing

A bit better than that I'm sure - sedbuk is about seasonal efficiency - like an urban cycle rather than comparing specific speeds. Correct me if I'm wrong.

Sedbuk efficiency is calculated from two figures: The full load efficiency and the part load (30%) efficiency. Full load is measure with the boiler running at 80°C/60°C - so well above the condensing temperature. Part load is measured at 50°C/30°C. Take the Baxi Solo HE A 18 as an example:

At 80/60 the input is 20.18kW and the output 17.81kW, giving an efficiency of 88.25%. At 50/30 the output is 19.27KW, giving an efficiency of 95.5%

Another thing to be aware of is that some manufacturers, particularly continental, use net efficiency not gross. (The Baxi example above is gross.) Net efficiencies produce efficiency figures of above 100% at part load. For example the Greenstar 40cdi Regular:

At 80/60 the input is 42kW and the net output is 40.8kW, giving a net efficiency of 97.1%. At 50/30 the net output is 43.3kW, giving a net efficiency of 103%.

Furthermore, the way Sedbuk efficiencies have been calculated has changed, so the A-G gradings have been dropped. The database just shows the (new) SAP2009 Annual efficiency and the (old) SAP2005 Seasonal efficiency, which was the basis for the A-G grades. The new efficiencies are lower than the old. You can read an explanation on the Sedbuk website.

The whole weather compensation issue is a mess at the moment. Companies like Viessmann are making silly claims like 20%

I agree that the WC issue is a mess - in the UK that is, but can't comment on Viessmann's claims

Yes boilers modulate themselves down - some can go further than others.
If you set the boiler max temp yourself to say 75º, it'll be condensing (when the return is below about 56). You can do that for all but the coldest weather. A WC boiler would be running at a lower temp than that for longer, but the savings are small and really unknown.

The main difference between a WC boiler and a non-WC boiler is that the non-WC boiler will modulate to maintain a constant flow temperature while the WC boiler modulates to maintain the appropriate flow temperature for the weather conditions. The modulation of a non-WC boiler is effectively nothing more than a fancy way of range-rating the boiler. A non-WC boiler will tend to cycle more.

 

[Agile]

There is a lot of misunderstandings about boiler efficiency and controls.

The efficiencies usually quoted for boilers are the urban cycle or seasonal efficiencies to be expected to be achieved in practice.

The efficiency of a condensing boiler is higher when non condensing than a non condensing boiler. That statement, although true, will be difficult for many to accept because of their lack of understanding of boiler design.

You will find little information on exactly what boiler controls and only the designer is likely to know that. For commercial reasons, as well as the lack of information, you will not get much of a reply to those questions.

Its made more difficult because installers have their own ideas about whats best and often are very strongly defend their own views.

A typical condensing boiler is 12% more efficient when fully condensing but that requires a return temperature below 40C.

So its easy to see that a control will not gain 20%.

Like Chris, I know that an outside only sensing will not give a good internal control because it does not know whats going on inside. It will also give poor results when the outside temperature changes rapidly as when the sun rises/sets.

The Worcester control for example allows setting of the inside/outside proportion used for the controlling the boiler which seems the sensible way to do it. Manufacturers try hard to make their controls unique to their products!

Then there are users! About a third get the W/C disabled because they cannot understand how to use it.

A friend of mine has installed UFH with 26 different zones all individually temp and time controlled. When he moves in soon I will see if he leaves all the doors open!

But this is all irrelevant when installers want to fit boilers which are twice as powerful as required. For those who dont know, that is not just a matter of the boiler working less like a 200 mph car running at 30 mph.

Tony

 

[Agile]

Has any installer here been on the Vaillant "Domestic Controls" training?* Do they give any detailed information on how their controls work?

Manufacturer's courses are aimed at the average installer and are primarily to explain what controls are available and how to fit them.

You have to remember that the average installer is not knowledgeable about electronics and would have difficulty in explaining the difference between analogue and digital and would not know what DAC or ADC relates to.

Alex, who posts here, is an advocate of ( ext sensor mainly ) W/C and its amusing when he asks technical questions at those events and clearly the trainer often does not even understand his questions.

Tony

 

[UpgradeME]

The main difference between a WC boiler and a non-WC boiler is that the non-WC boiler will modulate to maintain a constant flow temperature while the WC boiler modulates to maintain the appropriate flow temperature for the weather conditions. The modulation of a non-WC boiler is effectively nothing more than a fancy way of range-rating the boiler. A non-WC boiler will tend to cycle more.

Hi,

Do you know much about how the VRT392 works? From what I have read, I *assume* that it maintains the appropiate flow temperature to achieve / maintain the set room (or DHW) temperature, based on the current indoor (or tank) temp!? i.e. In a similar way that WC does for external temp?

Do you know if that's correct or how it works? (I've emailed Vaillant but not yet got a (sensible) reply).

 

[UpgradeME]

First of all, thanks for taking the time to reply Agile!

You will find little information on exactly what boiler controls and only the designer is likely to know that. For commercial reasons, as well as the lack of information, you will not get much of a reply to those questions.

The questions I've asked Vaillant have no commercial value, other than to help sell the product! I hope they don't go down that route as a 'get out' as any 'competitor' that wanted to copy the product or know minute detail could easily just reverse engineer the software on the chips!

A typical condensing boiler is 12% more efficient when fully condensing but that requires a return temperature below 40C.

So its easy to see that a control will not gain 20%.

I 'assumed' the efficiencies were gained by not having to heat the water that high in the first place... i.e. by modulating the boiler "appropriately for the conditions" so it could maintain the room/tank temp using lower heat output) rather than just cycling on/off and modulating by return water temp alone.

Like Chris, I know that an outside only sensing will not give a good internal control because it does not know whats going on inside. It will also give poor results when the outside temperature changes rapidly as when the sun rises/sets.

This is a good point and where experience comes into play with these devices! They won't tell you that on their marketing material!