Biasi Boiler ?

[Balenza]

Aaaah, thats more like it.

So does any heat transfer occur through the wall separating the HW tank from the primary water in the second surounding channel through which the hot flue gasses flow ?.

In other words will the UV store of water heat up if no primary water is ever passed through the immersed coil inside ?.

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.

I think this answers my question.

 

[Dan Robinson]

Yes but it would take twice as long - hence I think the non-PLUS version of the boiler is pointless:

Interestingly the 32 and soon to be released 38kW versions of these boilers have the same HW performance as the 24kW.

We have only ever fitted one 32kW, and I still think that again it is over kill. A house that needs that amount of space heating by definition is probably going to need even more HW than a Multi on its own can provide.

Still, some peopel won't be told

 

[Doctor Drivel]

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.

Like a heat bank/thermal store. They are simple and very efficient when using plate heat exchangers (heat bank). The NU-Heat version has the plate heat exchanger inside the cylinder, so it is also preheated and less energy escapes to the surrounding air.

Heat banks shine when using:

- plate heat Xs,
- lower store temps,
- effective water spreading inside the cylinder to maintain stratification,
- a modulating DHW (plate) pump or a modulating diverting valve
- a decent control system which promotes very low boiler return temperatures and greater efficiency
- an outside weather compensator raising and lowering the lower store temperature.

A world away from the old immersed DHW coils. All that is lost on many here.

The multi is simple well thought out engineering that promotes simplicity and reliability using less expendable components. This comes at a price. As I have previously written, cheap plate heat exchangers can transform a system - they made the combi an acceptable very cheap product that is now the biggest seller (some combis are so cheap they are throw away items - unheard of 15 years ago to do such a thing), and have also transformed the thermal store into a very efficient setup.

By some thinking, plate heat Xs can transform existing systems - the e.g of using the rads as a thermal store boosting DHW flowrates on a combi is easy and cheap to do. A cheap 10 litres/min combi can be transformed to give flowrates that a combi costing £600-800 more would give.

 

[Doctor Drivel]

Interestingly the 32 and soon to be released 38kW versions of these boilers have the same HW performance as the 24kW.

Do they drop the burner output to maintain the same DHW reheat levels? It would have made more sense to have inserted larger DHW coil to take advantage of the extra power available. Maybe cost cutting so they can use only one coil in all models.

We have only ever fitted one 32kW, and I still think that again it is over kill. A house that needs that amount of space heating by definition is probably going to need even more HW than a Multi on its own can provide.

The multi should do two bathrooms, although filling two baths simultaneously may be a struggle. The re-heat time fast enough, so staggered or semi-staggered baths should be fine. Two simultaneous showers from it is clearly not a problem.

 

[Doctor Drivel]

Yes but it would take twice as long - hence I think the non-PLUS version of the boiler is pointless:

When heating DHW the pump is acting as shunt pump only. As you say pointless when the coiled version available.

 

[Balenza]

So why does ACV have a shunt pump fitted.?.
Is this due to the tank in tank technology they use ?.

 

[Doctor Drivel]

So why does ACV have a shunt pump fitted.?.
Is this due to the tank in tank technology they use ?.

Yes. The HeatMaster is long and thin with a longer primary heat exchanger than the Atmos Multi, so more water to heat exchanger surface area. The heat exchanger runs through the two tanks. Heat transfer to the inner secondary water tank is very fast as it is totally immersed in the outer thermal store tank. So getting the heat all around it via a shut pump increases the secondary water tank heat up rate. It also keeps the heat at the top and cooler water at the bottom which promotes condensing efficiency.

 

[Balenza]

So does the ACV heatmaster have CH water channels up the center similar to the Atmos design ?.
I don't think their schematics show the inner cross section detail of the heat exchanger as clearly as the Atmos detail.


Looking at the Atmos Multi the priniciple looks the same as the Heatmaster except the ACV engineers have shrouded the entire UV tank in another shell giving another tank in effect and split the lower area of this tank with a divider plate which helps separate the lower cooler water from the upper hotter water.
Then used a pre heat coil enroute to the UV cylinder immersed in this lower cooler section of primary water to promote the condensing operation in DHW.
So even though the top section may be at a temperature well above a boilers capability to condense (60-90c) due to this design ACV have used condensing is pretty much guranteed.

 

[Doctor Drivel]

So does the ACV heatmaster have CH water channels up the center similar to the Atmos design ?.

I don't think it does. From memory here: The heat exchanger is finned stainless steel for maximum exchanger/water contact. It is removable and replaceable (a big job though) , which the Atmos Heat X appears not to be.

Looking at the Atmos Multi the priniciple looks the same as the Heatmaster except the ACV engineers have shrouded the entire UV tank in another shell giving another tank in effect and split the lower area of this tank with a divider plate which helps separate the lower cooler water from the upper hotter water.
Then used a pre heat coil enroute to the UV cylinder immersed in this lower cooler section of primary water to promote the condensing operation in DHW.
So even though the top section may be at a temperature well above a boilers capability to condense , due to this design ACV have used condensing is pretty much guranteed.

The design is simple and excellent indeed. It is roughly the same price as the Multi and I consider the stainless steel HeatMaster a superior product - yes Dan A smart pump can be on the CH circuit and TRVs all around as the CH is off the thermal store section. Also it is easy to zone up the CH too. A tee on the CH flow at the unit and two smart pumps with non-return valves.

However it is tall and thin and may not fit in many homes - although also designed that way to fit through the average domestic door. Depending on space the Atmos may be a better option.

It condenses nearly 100% of the time. A well thought out unit indeed and well worth buying. The inner DHW tank can be low pressure by taking off the unvented controls.

I looked at it and though it can be converted to a 100% heat bank, Connect the outer thermal store pipes to the inner secondary water tank pipes and effectively make it all one body of primary water. Off the inner tank, take off a pump and plate heat exchanger and run cold mains water through this. The return from the plate runs through the bottom coil which then feed the inner tank Then it can be DIYed.

Alternatively, have inner tank fed via a small F&E tank, separating the inner and outer water. The input to the plate is the DHW outlet and return is the cold feed. Then the inner is at low pressure. the bottom coil and inner tank vastly reduce problems of stratification. Just raise the DHW inner tank temperature. Very simple to do.

All for the cost of some pipe and fittings, pump, plate Heat X and blending valve...and a little know-how.

 

[Dan Robinson]

I certainly wouldn't want to di a HE swap out on a Multi; and I think they have made amajor gaff by not selling the underslung pipe work kit. A new one is coming, but unless you do them regularly or are as familiar with as I am then plumbing all the controls and vessels is a reall pain.

I will when I get time look at the ACV's; they do sound impressive -but what Kw are they? the Veissman 333 is the closest I have seen in terms of performance, but doesn't quite cut the mustard.

 

[Doctor Drivel]

I certainly wouldn't want to do a HE swap out on a Multi; and I think they have made a major gaff by not selling the underslung pipe work kit. A new one is coming, but unless you do them regularly or are as familiar with as I am then plumbing all the controls and vessels is a real pain.

I will when I get time look at the ACV's; they do sound impressive - but what Kw are they? the Veissmann 333 is the closest I have seen in terms of performance, but doesn't quite cut the mustard.

The ACV Heatmaster is scaled down commercial job for the domestic market. Many of these are fitted in commercial premises though. The ACV modulates from 35kW to 10kW. The tables below, the first figure is the 35kW and the second the 85kW model (needs a meter upgrade). So it will deliver @ 45C, 38 litres/min for 10 mins then drops to 15 litres/min. Impressive. Recovery is v fast @ 37 mins for the two tanks of 189 litres from cold - in reality it will much faster after a bathfill as the store never goes full cold. The 85kW version gives 72 litres/min for first 10 mins and then drops to 60 litres/min - yes 60 litres for ever, infinitely continuous. More a commercial jobbie, but great for houses with 4 or more bathrooms if you have the flowrates.

First figure is the 35kW model and second figure the 85kW model:

Litres in first 10 minutes,
40°C: 419 850
Litres in first 10 minutes
45°C: 381 722
Litres in first 10 minutes
60°C: 224 459
Litres in first hour
40°C: 1312 3177
Litres in first hour
45°C: 1080 2717
Litres in first hour
60°C: 692 1778
Continuous flow 40°C
Ltrs/hr: 1057 2793
Continuous flow 45°C
Ltrs/hr: 898 2394
Continuous flow 60°C
Ltrs/hr: 578 1583

The burner does not cycle as the CH is taken off the the outer thermal store tank - so if a Smart pump(s) only wants to deliver 2kW to the house it can without the burner clicking in and out. I regard it as a 98% combi as the CH pumps(s) and expansion vessel have to be fitted outside the unit, so not 100% inside the box. Not sure if it can be open vented, the secondary unvented cylinder can be.

It has an integrated weather compensator.

The thermal store side can be heated by an external boilers when the HeatMaster burner is down, and when up contribute to a large multi-boiler heating system.

Last time I looked it was £2,300 inc VAT from a dealer, and you have to supply the external CH pump(s) and expansion vessel.

Specs:
http://www.acv-uk.com/heatmaster35.htm
Manual:
http://www.acv-uk.com/pdf/HeatMaster 35-85TC.pdf
The manual explains the operation very well with nice diagrams too.

I want one in my house

 

[Dan Robinson]

Very interesting - I will save the web site for future perusal - Still think the Multi kicks ar7se for most 4 bed domestic dwellings though .

I'm bug gered if I am lifitng my underfloor heating to run a pipe for 85kW though!!!

 

[Doctor Drivel]

Very interesting - I will save the web site for future perusal - Still think the Multi kicks ar7se for most 4 bed domestic dwellings though .

It is good, however not the best. I rate the ACV in design and performance a class on its own.

I'm bug gered if I am lifitng my underfloor heating to run a pipe for 85kW though!!!

The DHW performance is certainly impressive that is for sure - 60 litres/min infinitely continuous when the store is cold, 72 litres/min when hot.

I wonder what the 85kW costs? Then the U16 meter too - can be LPG. No oil burner version like other ACV commercial products. Must be great for small hotels and the likes.

BTW,the tank in tank is fastest reheat of any cylinders. However a plate heat X and a bronze pump off a boiler takes some beating. Plate Heat Xs have been used instead of coils, by Glow Worm in their Extramax and Ultramax stored water combis to reheat the internal cylinder.

 

[Dan Robinson]

85Kw on domestic LPG?

Like our discussions on Thermal stores etc., It is a case of need/cost/hassle/gain.

 

[Doctor Drivel]

85Kw on domestic LPG?

I think it will be commercial LPG

Like our discussions on Thermal stores etc., It is a case of need/cost/hassle/gain.

Not really. Firstly, the best solution to fit the problem. Then whittle it down with your points. Most start the other way around.