Biasi Boiler ?

[Doctor Drivel]

As DD has realised, it is the engineering simplicity (in the case of the Intergas) and sheer performance (in the case of the Multi 24/80+) that keep me installing their boilers above all others. the Multi is pride of place in my office - as has been shown here. In fact DD, I would be interested on yiour thoughts of the Multi?

The multi has shades of the ACV HeatMaster - from Belgium, so maybe a Low countries approach, although the Range Powermax was like this.

The Multi plus is excellent no doubt. The DHW booster coil must be an added advantage in efficiency producing lower return temperatures and higher flowrates.

Good points

- looks like the primary heat exchanger can run at a very large temperature differentials. Most condensing boiler makers state 20C Delta T (temp differential between flow and return). This looks like it can be very wide indeed extracting as much heat as possible from the flue gases.

- CH and DHW can be run at he same time, although not a big problem when DHW only in other setups.

- High flowrates - although I'm not sure how long it will last and then run out of hot water. Does it drop to lower flowrates when the cylinder is exhausted of hot water?

- The bathroom rad comfort circuit. A nice touch. Maybe this can be used (adapted) for CH zoning.

- The HepVo trap on the unvented blow-off and combining the condensate and blow-off into one trap.

Iffy Points

- Uses an unvented cylinder.

- No catering for TVRs all around.

I like integrated thermal storage using this flue through cylinder approach. The ACV does this although uses a tank-in-tank unvented cylinder for DHW. However the CH come off the outer primary water thermal store. This means a Grundfos Alpha smart pump with TRVs all around can be used with no nuisance central room stat or efficiency lowering auto by-passes used. It seems the Multi needs a central room stat and cannot use a smart pump. Few boilers cater for TRVs all around which is now the norm.

The Atmos Multi has been around for while now and needs an update catering for TVRs all around. Since 1994, plate heat exchangers have improved no end and smart pumps have arrived. What must be catered for:

1. TRVs all around
2. Two CH zones, which half does. This would set this boiler on a higher level.

I think the ACV is the only integrated thermal storage unit around (well a thermal store/unvented cylinder hybrid), as the Range Powermax is now using an unvented cylinder.

A quality product no doubt. For the price I would also consider an ACV HeatMaster. Gledhill are a level down in quality.

 

[Doctor Drivel]

If one looks at the output of say a Stys, a Performa and an Intercombi (with the required mods to make it work at 24kW with 10 litres/min) then wonders how much - in the domestic market at least things have really improved in performance stakes.

Performance of combis has risen considerably in 5 years. To the point where a combi must be the first choice in assessment in typical British homes.

Remember here are infinitely continuous combis (heat DHW instantly) and the stored water assist combis.

The infinitely continuous combis now have a 40kW version, the W-B, giving around 15 litres/min. Unheard of 5 years ago, except for the 76KW MAN, which is special order in the UK and requiring a meter uprate. This increase in DHW flowrate is due to the introduction of small high efficiency plate heat exchangers.

Stored water combis now give the flowrate and a few models are wall mounted too: Glow Worm Extramax HE and Alpha CD 50. There are countless floor mounted stored water combis around too.

The modulating pre-mix burners now can modulate right down to decent levels giving a wide modulation range unheard of 5 years ago. This results in little burner cycling when serving CH when the boiler may be capable of outputting 40kW and the house only needs 6 kW. The burners can drop down accordingly.

Remember my position in this topic is purely from a reliability and simplicity stand point.

That is another point. Generally the higher the price the greater the reliability. Atmos are not cheap - and you get what you pay for. Amos need to uprate the Intercombi to around 16 litres/min with the same simple well thought out elegant engineering resulting in high uptime.

 

[Agile]

The modulating pre-mix burners now can modulate right down to decent levels giving a wide modulation range unheard of 5 years ago. This results in little burner cycling when serving CH when the boiler may be capable of outputting 40kW and the house only needs 6 kW. The burners can drop down accordingly.

Most premix boilers have a lower min/max ratio than many conventionally fanned boilers. premix are typically only 3:1 to 4:1 making them far less efficient when a 40 kW boiler is used in a normal 3-bed semi.

A 42CDI is 9.8-30 on CH so only 3.08 and a GW HXI is 12-28 so only 3.17. Thats typical of most current models!

Can you name any premix with a wider modulation ratio?

Tony

 

[Doctor Drivel]

The modulating pre-mix burners now can modulate right down to decent levels giving a wide modulation range unheard of 5 years ago. This results in little burner cycling when serving CH when the boiler may be capable of outputting 40kW and the house only needs 6 kW. The burners can drop down accordingly.

Most premix boilers have a lower min/max ratio than many conventionally fanned boilers. premix are typically only 3:1 to 4:1 making them far less efficient when a 40 kW boiler is used in a normal 3-bed semi.

Can you name any premix with a wider modulating ratio?

Look at what ECO-Hometec use. Made by MAN. They get down to around 3kW. I think Atmos and ACV do similar wide ranges.

 

[Doctor Drivel]

Dan,

From the Atmos web site:

InterSystem HE26 - Sealed system boiler for central heating and/or hot water via an indirect hot water tank.
Heating output up to 26 KW (90,000 Btu/hr).
Built in expansion vessel.
Built in circulation pump.
No bypass required.

No by-pass. Does this mean a Smart pump can be fitted?

 

[Dan Robinson]

Yes, you can change the pump of the system boiler to any you like - we have one running a 25-55 in Hitchin.

As long as the boiler has control... you just need an inch male iron to connect to copper on the return. You can also do this on the combi version as the Hot water mode does not use the pump - hence the combi can actually be installed as a multipoint with no neede to charge the heating circuit.

The Multi has had a few upgrades (nothing major though), and the Plus bit (extra hot water primary) coil knocks 11 minutes off the reheat time. I am setting up a couple of K2 temp sensors on various parts of my one at home 'cos I think there are a few more aspects of the performance that can be tweaked, but I need to know more about the absorption of heat before hand. The burner nolyt goes down to 7Kw; but as the secondary water is heated by any left over energy and acts as a form of thermal store that is not IMHO a major drawback.

I find the "easy-lift"handle a bit of a laugh as well - these things are far from easy to lift ;(.



VOTM - so you are either just monitoring my posts to be a pain in the a7se, or are a dual contributer. Both equally as pathetic as the other, and from that shltty picture, no I can't idenitfy it.

And I have working with gas for a fraction over seven years incase you are interested; I got my first ACS around 2000/2001, but I can't remember; nor do I care.

 

[Agile]

Its not really realistic to expect anyone to be able to identify that heat exchanger.

Its typical of many Italian made boilers. A Biasi M90 would be my first guess followed by one of the Vokeras if I was wrong but then I am not often wrong!

Tony

 

[Doctor Drivel]

Yes, you can change the pump of the system boiler to any you like - we have one running a 25-55 in Hitchin.

As long as the boiler has control... you just need an inch male iron to connect to copper on the return. You can also do this on the combi version as the Hot water mode does not use the pump - hence the combi can actually be installed as a multipoint with no need to charge the heating circuit.

What about the boiler control "interlock"? The burner would be cycling when the house is not calling for heat when eliminating a room stat and using a smart pump. It would require a flow switch on the CH return to turn the burner off when there is no flow. This can be wired into the room stat circuit. However the pump and burner would be switched out too, so the boiler has to be overridden to keep the smart pump on while the burner is off. An external relay can do this.

The Multi has had a few upgrades (nothing major though), and the Plus bit (extra hot water primary) coil knocks 11 minutes off the reheat time. I am setting up a couple of K2 temp sensors on various parts of my one at home 'cos I think there are a few more aspects of the performance that can be tweaked, but I need to know more about the absorption of heat before hand.

Absorption of heat?

The burner nolyt goes down to 7Kw; but as the secondary water is heated by any left over energy and acts as a form of thermal store that is not IMHO a major drawback.

It is indeed a form of thermal store, although not meant to be. When the house calls for say 3kW of heat the burner should be off and the pump still running, as the store of heat will be enough to cope. When the store depletes it can then recuperate at full belt. Atmos must look into this aspect and re-design the control system to suit. It can't take much to redesign it cut a new pcb, and introduce a smart pump.

VOTM - so you are either just monitoring my posts to be a pain in the a7se, or are a dual contributer. Both equally as pathetic as the other,

ignore him. No one takes any notice of him, so neither should you.

And I have working with gas for a fraction over seven years incase you are interested; I got my first ACS around 2000/2001, but I can't remember; nor do I care.

I did my first joint in 1967 - cutting a 1/2" iron thread. The next was a lead to lead joint. I remember the first wall hung boiler on the UK market - the Glow Worm Space Saver with cast iron heat exchanger, circa late 1960s/early 70s. Drayton TRVs have hardly changed in style since then either. Plastic pipe was not used, although the trade press said it was in the pipeline. I recall an experimental house built in the early 60s that had plastic pipe and most things plastic inside too, including the taps.

 

[Doctor Drivel]

Yes, you can change the pump of the system boiler to any you like - we have one running a 25-55 in Hitchin.

As long as the boiler has control... you just need an inch male iron to connect to copper on the return. You can also do this on the combi version as the Hot water mode does not use the pump - hence the combi can actually be installed as a multipoint with no neede to charge the heating circuit.

I noticed there are two sets of piping in the Intercombi heat exchanger. When heating DHW only the CH pipes will also get hot. OK the heat goes nowhere. Fitting a 3-way electric diverter valve and plate heat exchanger on the external CH pipes (OK the simplicity has gone) will use this unused heat and pre-heat the cold water before it reaches the main DHW heat exchanger. This must improve the DHW flowrate.

 

[Doctor Drivel]

We would cover Stevenage, but...cheap is not something I do I'm afraid. Our InterCombi list price (with flue, "make my life easier" bracket and delivery) is £954.35+VAT although there is a little movement on that.

A lot of movement. £677 + £34 for flue + VAT
http://www.tbsmerchants.co.uk/cgi-bin/build/product/PGAT.html

 

[Dan Robinson]

I am going to the factory where the Multi is made so if you have any specific questions then send them to me in an email.


TBS is in Daventry and either is part of Skaino (Part of the umbrella company with Atmos included) or have an arrangement direct with Atmos. It is up to them what they charge, and I quoted list prices. I am not going to sell a boiler at cost - there's no point and I have to cover my admin costs etc. .

I have had worse wind ups than VOTM can manage over the years - Now a tube of Deep Heat and a Rugby team initiation was probably the worst, VOTM is just annoying; but seeing as I am open about who I am and my experience in the trade; it seems largely pointless to use it as ammunition for sniping. Now if he/she/it knew something I hadn't/wouldn’t openly confess to then it is a different story.


Anyway, to more interesting things.

As far as the InterCombi twin pipe heat exchanger goes, this is why I wanted to get a copy of the video we were shown at the factory that showed the heat distribution during various cycles. From what I saw most of the heat is used, unless a very low hot water flow is being drawn. The heat exchanger operates as a single piece in whatever mode, and the boiler monitors the temperature of the HE block rather than the water temperature itself. Of course it monitors DHW temperature using a separate NTC for accurate delivery temperatures. I think the designer has gone for simplicity over some efficiency, and over the life of the boiler when you consider spares manufacturing, transport and engineers time it is a reasonable pay off.

Absorption of heat

I mean exactly where the heat is going and what the return temperature of the primaries is during a full recharge of the cylinder. The flow temperature during this is 80+ degrees, but I want to know how much of that is being taken into the secondary water.

It is indeed a form of thermal store, although not meant to be

I’m not so sure… During the initial call for central heating the boiler fires straight away at low rate, but the flow temperature drops nearly 30 degrees straight away. There is a programmed period of running at low rate regardless of demand/programmed KW restriction. Remember the secondary water is surrounding the primary heating jacket, although, my boiler is weather compensated it does seem to spend most of its time at low rate or in the pump-overrun cycle.

It has been limited to a heat load of 7.5kW. While I have been typing this (45 minutes or so) I ran the radiators and the flow temperature has been hovering around the high 40’s to low 60’s, but the missus has been using some hot water downstairs, though the boiler has not realised this. It has not yet gone to a high gas rate. When there is not demand the flow temperature is in the region of the mid 60’s and low 80’s depending on how recently it topped up the hot water.

I bow to your greater knowledge on the dynamics of thermal stores/heat banks (even if we do disagree fairly vehemently on the number of suitable applications .

The boiler will not drain its domestic hot water heat as it is designed to have a full tank load ready the whole time… One major update I have always felt needed was a night set-back on the hot water side. I do not know why the burner has a low rate of 7kW… it will go on my list of things to ask.

 

[Doctor Drivel]

I am going to the factory where the Multi is made so if you have any specific questions then send them to me in an email.

As you said, the Atmos Intercombi is trade off to maintain super reliability, although still very efficient. What is the Delta T of this boiler? It appears by design that it could have a very large delta T. Many makers do not want to extract as much heat from the flow as it drops the return temp too much - their primary heat exchangers are not designed for this and could cause early failure problems. That is why some of the DHW combi flow rates are not that brilliant on some combis. Nevertheless it looks like a simple mod on the Intercombi, even an external one by an installer, to claw back some heat and boost the DHW flow rate.

I boosted the flow rate of one system by using the water in a CH circuit a thermal store for DHW - approx 100 litre of it in hot rads. The rads went cold, however, the fast re-heat of a combi negated that somewhat.

The heat stored in radiators is used making the rads a large store of heat. they would cool rapidly and when switched to CH re-heat rapidly too. The rads will give 20-25C in summer and maybe even cool the house.

Using a plate heat exchanger, pump, flow switch and two check valves. The system should not have thermostatic rad valves, or few of them. On a combi system:

- a by-pass pipe between the CH flow and return at the boiler
- on this pipe a re-heat plate heat exchanger is fitted
- The pump is fitted between the plate and the return by-pass pipe tee to
the return.
- A check valve between the pump and the plate
- A check valve on the boiler flow before the tee to the by-pass pipe.
- A flow switch on the cold mains water before the pre-heat plate heat
exchanger.

The check valve on the flow pipe ensure no flow back into the boiler, although the internal 3-way valve (if one fitted) should do this. The check valve on the by-pass pipe ensures no short circuit in normal CH operation.
The cold mains water runs through the pre-heat plate heat exchanger. This pre-heated main water then runs into the combi as normal. When calling for DHW the combi diverts to DHW only to heat the incoming cold water; as per usual. The flow of mains water is detected by the flow switch and switches on the by-pass pump. This pumps water from the rads into the pre-heat plate heat exchanger. This will raise the mains water substantially and the combi tops up.

You can fill a bath up in a few minutes doing it this way. The rads cool down a lot. This doesn't matter as when the system switches over to CH, the boiler re-heats the rads ASAP at full burner, with loss in room temp so small it is not noticeable to the occupants.

The combi flow rate in summer, when the CH is off is better than an average flowrate combi as the water in the rads will be around 20 -25C when the CH is off. This stored 20C plus heat is used to pre-heat the cold mains water, which is around 10-12C, high than winter temperatures. Depending on the efficiency of the plate heat exchanger and power of the boiler, the flow rate may be very good, even in summer. Cooling the rads also helps to cool the house in summer too.

A simple and cheap way to vastly improve the output of a combi.

One question to Atmos is: Can the Intergas range be fitted with a smart pump and cater for TRVs all around? Remember in the UK a control interlock is required to switch out the burner which may require a CH flow switch. This may not be the case in many other countries - 70% of their production is exported. The boiler appears to run without being fully pumped.

The Multi would be better with a two full zone capability built in. It has the comfort loop which is not two full zones. Also a secondary circulation loop too could be built in, as is/was an Ariston combi.

A problem is delivering less than 7kW to CH, which is most of running time, with burner cycling. A full thermal store can do this with CH taken off the store, leaving the burner to independently of CH demand, only to maintain the store temperature. A semi split store cylinder can do CH at the bottom; temp maintained by weather compensation and promoting condensing and DHW at the top. To maintain the DHW output a DHW priority system would probably be needed to send all burner output to DHW; currently it is not a priority system.

Having an integrated heat bank (thermal store) is the best way with CH taken off this, or a separate CH buffer in the same cylinder, however totally separate to DHW so they operate independently in temperature. This eliminates boiler cycling and two CH zones can easily be taken of the same store. Having the CH and DHW stores together in the same cylinder unit makes the unit compact and all the heat is in one unit - thing of a combination cylinder of one unit with two separate water sections.

Makers don't like thermal stores because installers do not put enough inhibitor into them - this can be got around by having the store water separate from CH rads water. And also they can use their existing modulating boiler ranges to heat unvented cylinder inside the one box. Economics for themselves rather than producing the best system for the customer.

 

[Balenza]

What is the "comfort circuit" in the Atmos Multi ?.
And why does the flow and return connections to the coil in the UV cylinder appear to be connected to the return side of the pump in their schematics ?.
Are the schematics wrong or just plain confusing ?.
Is this coil the only means of heating the UV stored water ?.

 

[Dan Robinson]

The confort loop is just an extra tapping of the primary flow. The isdea is that you can hook a towel rail up to it and feed the return back in to thenormal heating return and whenever the boiler fires (for heating or hot water) is will heat up.

It can also be used for a secondary hot water cylinder, underfloor heating/other form of heating in a granny flat as you can wire up separate controls as needed - I think I was once told it would do up to 4Kw, but it does lower the hw rehet times a bit. Although not noticeably on a simple towel rail.

The manuals are not the greatest - which helps deter DIY'ers; and part of the reason why I like them. The schematic you refer to is actually for both versions of the Multi (normal and PLUS models), and should look this:

Hope it makes more sense now...

 

[Dan Robinson]

The coil is an enhanced way of heating the water. In the normal (and IMO pointless) version of the Multi there is no coil and the primary water is just circdulated inside the boielr and has twice the reheat time.

With the coil it runs the primary water throught the coil before going back to the HE which has the effect of halving the reheat time and promoting more condensing.

The diverter valve can modulate backwards and forwards depending on temperature readings and provide simultaneous heaitng and hot water or prioritise dpending on demand.

As mentioned with earlier post, if a small amount of HW is being used whilst the heating is on, the way it is heated means that the boiler will not bother to change modes as the HW will draw ome heat from the Primary anyway.

A complicated looking beast, that is actually deceptively simple. I have often chuckled att eh bemused ramblings of BG engineers who can't fathom these things.

But then a lot of them can't work out that a clogged condensate drain will throw up fan errors Present company accepted of course