combi vs conventional

[John Rumm]

In fact go to the Pottern site and use their search page. Search for combi and the powermax does _not_ come up.

[MBQ]

Go to usenet and IMMs gone silent too!

MBQ

[Tony Bryer]

My Glow-worm Cxi came with a flying lead on which (at a minimum, non Part L complying of course) you needed to put a 13A plug. I'm not sure whether this counts as 'wiring'

[IMM]

The IMI Powermax, the old version. The new "Potterton" Powermax is a combi, and classed as one. Look up Powermax in sedbuk.

[IMM]

They don't understand.

[Andy Hall]

It may be by Sedbuk, but there are numerous other mistakes in their database

If you look at the Potterton web site or more specifically download the brochure, they don't use the word combi or anything like it in the description, going for descriptions like "packaged system in a box"

If you look at the cut away view of the thing it's basically a conventional boiler and water cylinder in one box with a high recovery coil.

Hardly rocket science.

.andy

To email, substitute .nospam with .gl

[Lurch]

On Tue, 22 Jun 2004 01:25:32 +0100, "IMM" strung together this:

Yes it does, it was wired both at the factory and upon installation. A combi does need wiring to work.

Bold statement coming from one so clueless.

[Matt Beard]

Quoting directly from the Potterton Powermax Brochure at:

"The Potterton Powermax HE combines a condensing stainless steel heat engine, unvented Duplex stainless steel domestic hot water cylinder, pump and programmer in a single package ? virtually ?a system in a box'."

If this isn't a CPSU then what is? It even has an optional immersion heater in the cylinder!

Note: The cylinder comes in three sizes, 80litre, 115litre and

150litre

I think that Potterton have decided not to use the term "CPSU" because most people think that they either want a "combi" or a "standard" boiler and so get scared about "alien terms". This one walks like a duck and quacks like a duck... maybe it is a duck!

Interestingly Potterton claim that 48lpm is enough to "fill a bath in

5 minutes" which suggests that they think that a bath requires well over 200 litres.

Matt

[Tony Bryer]

The quality of the data is not wonderful. In our QSEDBUK program (see sig) we have a routine called 'Massage' which cleans up the makers names, or you'd have 2 Maxols, 3 Pottertons and 4 Baxis. There are a whole lot that have a minimum output of 0 - which in one sense is true - but the field is AIUI meant to hold the output when the boiler modulates down to its lowest setting.

[Tony Bryer]

Using the definitions in SAP, a storage combi is much like a boiler/pump/cylinder system in one box. In a CPSU the burner heats a thermal store which has a heat exchanger coil running through and DHW is heated as it runs through this coil. IOW in a storage combi, the water in the store comes out of the taps; in a CPSU it doesn't.

[Matt Beard]

Looks like I stand corrected!!

Matt

[timegoesby]

I have been assessing this Alpha combi and the new Powermax, as I like packaged heating and hot water. I find these idiot proof as I don't have to think out the system or control wiring. The Alpha is indeed a two stage flow combi, so you never run out of hot water. I confirmed this with Alpha. The Powermaxes have large storage unvented vessels which make it unlikly to run out of hot water. The reheating times on both are very good, which leads me to believe they will be reheating water fast as you use it. This very fast reheating must extend the cylinder size as such.

Sedbuk does class both as a combi. I am leaning towards the Alpha.

[IMM]

Bean, you haven't a clue.

[IMM]

Which is a combi.

SEDBUK make the classification, not the makers. Potterton's marketing people are attempting to put the Powermax in a category of its own. Those who know these things can see through this. You can't.

But they put it in one box and matched the cylinder/boiler/controls to maximise efficiency.

[IMM]

A combi. I have explained what a CPSU (Combined Primary Storage Unit) is. The only one available now is the Gledhill Gulfstream 2000. You may get some old IMI Powermaxes that have not been sold yet.

Yep. And the Gledhill has an auto electrical backup, called the Switch, that comes in within a second or two.

[IMM]

A CPSU has BOTH the DHW and CH taken from the thermal store, or heat bank. The Worcester-Bosch HighFlow, and Vokera, have heat banks and are classed as combi's because only the DHW runs through the heat bank.

[Andy Hall]

Be careful on that. It can only, by definition heat the water as rapidly as the energy going in - in this case 25kW - not very exciting. If the cylinder runs out of hot water, it is going to give a fairly poor performance equivalent to a low to mid range combi.

There is no functional difference between the Potterton product and a standard boiler plus fast recover cylinder.

The only reason it can claim to have "continuous" hot water is on the basis that the cylinder doesn't run out. It certainly is not heating the water as fast as it is being used. 30-48lpm needs more than 25kW to provide it. The manufacturer does not state the temperature rise in these figures either which suggests some "marketing" of the figures.

Sedbuk has it wrong. Potterton does not claim that for their product..

.andy

To email, substitute .nospam with .gl

[Andy Hall]

A combi is generally accepted to be an instantaneous water heater and heating boiler.

In this case they didn't look closely.

Of course Potterton are trying to differentiate their product. This is because it is nothing more than a packaging exercise. There is nothing clever about it. Functionally, it is much more like a system boiler with added cylinder in the case than anything to do with a combi.

It doesn't need to be done this way to achieve that. It is a packaging exercise. There is nothing in it, as its spec shows, that makes it more efficient than any other condensing boilers. Also, there is quite a bit of specmanship in the claims bing made regarding performance.

There's nothing wrong with a clever packaging exercise, but this is not a revolutionary new invention.

.andy

To email, substitute .nospam with .gl

[IMM]

But it still does not run out of hot water, a fact you can't seen to comprehend, which any conventional cylinder/boiler setup will run out. The Alpha is approx 19 litres/min of water at 65C, and when the cylinder is exhausted the flow reduces and approx 11 l/min is delivered FOR EVER. So a very large bath can be filled reasonably quickly. The recovery rate of the cylinder is zippo too.

Nonsense!!! Potterton engineers (who are far more expert than some smart arse DIYers) have matched the boiler/cylinder size/coil/recovery rate, etc, to maximize efficiency. They have also simplified the electrical side of it too. All in one box and a doddle to fit.

That depends on how much is being used. Someone having a normal flowrate shower may not be emptying the cylinder faster than the boiler is re-heating, so infinitely continuous hot water.

Sedbuk has it right!!! See my explanation of what a combi and CPSU is.

Their marketing department can what they like. The BRE is there is tell us the real story, not maker marketing, which you suck in and blow out.

An explanation for you....

Firstly, a combi is a "combination" of the heating and water system in one case, eliminating external tanks and cylinders, and generally supply hot water at high main pressure. To confuse a little, some can run at very low pressures and even off tanks. Generally most are fed from the mains. It is generally a matter of mounting the boiler and connect up the pipes. The expert designers have done the hard work for you and put all in one case.

There are three types of combi:

1) The Infinitely Continuous Combi -

Heats cold mains water instantly as it runs through the combi. It never runs out of hot water. This is the most common type of combi, generally having lower flowrates than Nos 2 & 3 below. The largest flow rate instant combi is a two bathroom model, 22 litres/min ECO-Hometec. Being a condenser it is very economical too.

Unvented Cylinder Combi -

An unvented cylinder is a similar to a conventional cylinder but run off the high-pressure cold mains. A combi with an integral unvented cylinder has approx 60 litre cylinder heated to approx 80C, with a quick recovery coil that takes all the boilers output. A fast acting cylinder thermostat ensures the boiler pumps heat into the cylinder ASAP with a recovery rate from cold around 5-8 mins (Ariston claim 8 mins). The 80C water is blended down to about 45-50C. e.g's, Ariston Genus 27 Plus, Glow Worm, Powermax, Alpha CB50.

3) Invinately Continuous/Unvented cylinder combi -

The Alpha CB50 is a combination of both having atwo stage flowrate, of high flowrate when using the stored water with an automatic flow regulator switching in to reduce flow to an invinately continuous flowrate of approx

11 litres/min. Heat Bank Combi -

Incoming water is instantly heated running through a plate heat exchanger (as is most instantaneous combi's) that takes its heat from a "domestic hot water only" store of water at approx 80C (instantaneous combi's take the heat from a heat-exchanger heater via the burner). A fast acting thermostat ensures the boiler pumps all of its heat into the store ASAP with a recovery rate about 5-8 mins from cold. The 80C water is blended down to about

45-50C. They are generally two stage flow rates, in that when the thermal store is exhausted it reverts to what the bunrer can produce, which isapprox 11-12 litre/minute. e.g. Vokera & Worcester floor standing models (standard washing machine sizes).

N.B. The heat bank is a variation of a thermal store, but is "not" a thermal store in the conventional sense in that a coil carrying cold mains water runs though a store of hot water kept at about 80C. Heat-banks are far more efficient and give higher flowrates than conventional coiled thermal stores. The stainless steel plate heat-exchangers do not scale up so easily.

5) Combined Primary Storage Unit (Not classed as a combi, but a derivative of a combi, but still a one box solution, so still in the same family)

These are a combination of a large thermal store, or heat bank, and boiler in one casing. The units are large (larger than standard washing machine size) and floor mounted. The heating is taken off the thermal store, which in many cases the DHW taken off the store using a plate heat-exchanger (heat-bank). Unlike the Heat-bank in 3) above the thermal store supplies heating "and" DHW, giving the "combined" to the title. They are available from 1 to 2.5 bathroom models. Gledhill do an excellent condensing version, the Gulfsream 2000.

2) 3) 4) & 5) have high flowrates. No. 1 "generally" has low flowrates but there are always exceptions and some can be high - e.g. the ECO-Hometec infinitely continuous combi, actually has a very high flowrate.

Nos 2), 3) 4) & 5) use stored water, but in different ways. Unlike No. 1 "some" versions will eventually run cold, but that takes quite a time, hence some are referred to as "two bathroom" models, having the ability to fill two baths with very fast recovery rates. As hot water is being drawn off the high rating burner is also reheating. Very rare do these combi's run out of hot water in average use. When taking one shower the burner may be re-heating faster than what can be drawn-off. No. 3) above uses stored water but will not run out of hot water (high and low flowrates). Most versions of N. 4) above are two stage flowrate models (high and low flowrates) and will also not run out of hot water.

There are combi models that give hot water and heating simultaneously as Combined Primary Storage Units do. Most don't as they are hot water priority.

[...Jerry...]

IMM,

We ALL know what you meant to say, that combi boilers do not require as mush wiring as other boilers, but that is not what you originally said and all you are doing is digging yourself in deeper - do yourself a favour and just admit that you got it wrong.