Does it matter if boiler is slightly over sized?

[benaround3]

[...] The Veissman 100 W compact would seem to modulate from 13kw max to 1/3 of that, ie 4.3kw.

I don't think it can go that low - the MI's say 7.9kW.

Mathew

Thank you for pointing me to that.I am using the below, which may be different as it is described as "compact". It says that the boilers modulate down by a third, which may apply to the bigger ones as well, so they may not all go down to the same value.

http://www.viessmann.co.uk/etc/medi...e.Par.12469.File.File.tmp/DPGOCT2011_web1.pdf

 

[benaround3]

You can set the parameters on the Intergas as you can with some others, however because of the design the Intergas will condensate whereas the other will not.

Alec once again mentions Compensation controls, but they are found wanting with an oversized boiler.

All you need to stop the boiler cycling, is a simple in-line stat controlling the low temperature.

So, the compensation controls the room temperature, and the in-line stat says wait till the temperature is
a bit lower, could be air temperature or return temperature.

Are you saying the Intergas has an advantage? If so I will go for it. How do I get an in-line stat? Will my Heating Engineer fit this or does the Intergas have one? I am thinking of an OV by the way.

 

[MJN]

It says that the boilers modulate down by a third, which may apply to the bigger ones as well,

It only applies to the big one.

so they may not all go down to the same value.

They do - the MI's say so (and are more likely to be correct than the marketing material).

Mathew

 

[JohnD]

I am using the below, which may be different as it is described as "compact"

Ah, the "compact" is the non-combi one which you use with a cylinder, I got one of those because it is simpler and has less to go wrong.

It will occasionally run at full power if I have been away, when it is heating the rads from cold, or in cold weather when it is heating a cylinder of very cold water, then it modulates down as the heat requirement eases off.

I used to work away a lot, so have oversized rads which with an oversized boiler can heat the house faster from cold.

 

[doitall]

You can set the parameters on the Intergas as you can with some others, however because of the design the Intergas will condensate whereas the other will not.

Alec once again mentions Compensation controls, but they are found wanting with an oversized boiler.

All you need to stop the boiler cycling, is a simple in-line stat controlling the low temperature.

So, the compensation controls the room temperature, and the in-line stat says wait till the temperature is
a bit lower, could be air temperature or return temperature.

Are you saying the Intergas has an advantage? If so I will go for it. How do I get an in-line stat? Will my Heating Engineer fit this or does the Intergas have one? I am thinking of an OV by the way.

See your other thread.

Having the sensors in the block means it can and does condense even for hot water.

 

[D_Hailsham]

I can well believe it. It is very common in consumer electronics - the very same innards will be shared amongst a variety of models throughout a range and will be selectively crippled as part of production in order to produce the desired lineup.

I can vouch for that. When I left school - many years ago - I went to work for a company within the Philips group. I learnt that TVs were made on a single production line and then tested to a high standard. Those which passed were put into cases with a Philips badge one the front. The failures were then re-tested to a lower standard, if they passed they went into a case with another name on it (I think it was Sobell). Failures were sent back for rectification.

The same happened on the semiconductor production line - different batches from the same production line would be given different type labels depending on the results of the quality control tests.

 

[Dan Robinson]

Exactly what Intel and AMD do with their processors.

Car manufacturers do the same as well. They are catering for different corners of the same market.

 

[benaround3]

You can set the parameters on the Intergas as you can with some others, however because of the design the Intergas will condensate whereas the other will not.

Alec once again mentions Compensation controls, but they are found wanting with an oversized boiler.

All you need to stop the boiler cycling, is a simple in-line stat controlling the low temperature.

So, the compensation controls the room temperature, and the in-line stat says wait till the temperature is
a bit lower, could be air temperature or return temperature.

Are you saying the Intergas has an advantage? If so I will go for it. How do I get an in-line stat? Will my Heating Engineer fit this or does the Intergas have one? I am thinking of an OV by the way.

See your other thread.

Having the sensors in the block means it can and does condense even for hot water.

Thanks but you have gone a bit fast for me. Is the "sensor in the block" the same as an in line stat? If it is then I think I get it. Something integral with the boiler that measures the water temp as opposed to the air temp can ensure the boiler is only on when the water is cold enough to allow condensation mode. I did look at my other thread but it didn't help.

 

[doitall]

No the inline stat is different. One would need to make something up with whats available.

The room stat/ compensation controls the room temperature, you need a simple stat, that makes on temperature fall like a frost stat, in the heating return pipe.

What it means is the return can never go above a set temperature.

I would have thought Alec would be the best guy.

 

[ALEC1]

the boiler will cycle excessively...but they all do that when you use on-off controls, for the simple reason that they are working to a fixed flow temperature...

You are better off using compensation controls that adjust the flow temperature to match demand..

Whilst modulating controls will undoubtedly be better in this regard, they are still limited by the lower output power of the boiler which, in so many cases even with highly regarded models, is way too high for many a modern home.

[Edit: Apologies, missed D_Hailsham's post where he's already covered this]

Mathew

My point entirely is that the search for the low end modulation is misplaced..as boilers with compensation controls deal with the lowend very well any way. Correctly sizing boilers is the key, and with a house with a 4.2 kw boiler perhaps another fuel should be used...

 

[Agile]

Ah, the "compact" is the non-combi one which you use with a cylinder, I got one of those because it is simpler and has less to go wrong.

The ONLY extra component their combi has is the DHW flow switch!

Apart from the DHW pipe!

Tony

 

[peekay53]

for the house you have described i myself would fit a intergas combi range rated down to minimum for heating remember intergas are condensing in hot water mode also and ideally when a boiler is condensing it is running effiently just my opinion and sure someone will try to shoot me down well good luck in your search
peekay53

 

[JohnD]

The ONLY extra component their combi has is the DHW flow switch!

Apart from the DHW pipe!

Tony

What, no heat exchanger and no pressure vessel? no pressure gauge and no filling loop? No aquablock? No internal pump? No diverter valve?

 

[D_Hailsham]

My point entirely is that the search for the low end modulation is misplaced..as boilers with compensation controls deal with the low end very well any way.

The only way any boiler can deal with a heat requirement which is below the low end is by reverting to on-off mode. This automatically reduces the efficiency of the boiler, mainly due to the effect of the start up routine the boiler goes through each time it lights. The smaller the ON time, the greater the reduction in efficiency.

 

[Agile]

Most boilers lose heat when the burner is off and this inefficient.

The Intergas HE has considerable latent heat and I suspect it may be more efficient than other types when forced into on/off modulation.