ACV or unvented? What specs? And other recommendations

[gdis]

Hi there,

I know that there are previous posts on this and I have tried to read them, but my technical knowledge is too limited and I want to make sure that I get to explain what I need.

I am going through a reasonably radical renovation of my house. It is going to be a 4 bed house with three bathrooms (two showers and one bath). There will normally be only 4 people living in the house, but we have people visiting quite regularly and we need to have sufficient hot water to deal with that. I would say that at the very most one can envisage two showers and the kitchen tap being used at the same time. The property will also have underfloor heating on the ground floor (60 square meters).

Our contractor has priced the work, but we will pay for the "external" gear (boiler, cylinder, manifolds, controls, etc.). We are going to place all this gear under the stairs on the ground floor (there is an external wall there) and we believe that we are constrained in terms space for the cylinder. We are told that the higher part of the space has to house the boiler, the manifolds, and related gear. This leaves the lower part of the space for the cylinder. We have also been told not to go for an horizontal cylinder as they tend to have problems. A plumber we had spoken to - who seemed to be reasonably switched on - had recommended to us the use of a "Smart ACV 160 unvented hot water cylinder". This seems to make sense to solve the space problem, but our contractor does not have experience with this tank-in-tank system and cannot vouch for it.

So, I would really appreciate it if you guys could help me with deciding the following:

1) ACV or unvented?

2) Either way, what size / model? For example, if I google Smart ACV 160 unvented hot water cylinder I get at least three different models!

3) What boiler should go with it? The contractor recommends using Worchester Bosch, which appear to be one of the two or three going manufacturer. I have read in one of the posts that - if one chooses an ACV tank - one has to choose carefully the boiler that goes with it.

4) If we go for an ACV cylinder, does it require previous experience? I have read on these posts that one has to be careful with handling the pressure.

5) We are also thinking of installing a Harvey’s twin tank water softener - any comment?

6) Anything else?

Apologies for the long posts (I believe that without the full picture it is hard to give advice) and the many Qs and many thanks in advance for your time and assistance.

 

[DP]

You need to select a boiler that will give you sufficiently high temperature water to heat the cylinder and variable temperature to heat radiators. Ideal boilers ( and one or two other makes) have two inputs to get the boiler working so you could run the boiler at say 70 degrees to heat cylinder when HW demand is on and 50 degrees when under floor heat demanded for example
Have you factored in thermostats cabling from rooms to manifold to give you temperature control of each UF area?

ACV 160 suggests cylinder has 160 litres capacity. You run two showers and kitchen tap, cylinder will soon have no water (I fitted a 300l cylinder for a customer, his two boys depleted of hot water in cylinder when they showered). Fortunately these cylinders recover very quickly

For installation of cylinder, installers needs to have UV certification. Cannot see any issues with pressures as long as installation is as per the book. ACV I understand has a jacket as opposed to a coil that a regular UV cylinder has for indirect heating. Cylinder orientation possibly better for ACV because it has a jacket?

Could be wrong, I don't think Worcester has dual inputs. A demand on boiler will give you primary flow at temperature set on boilerstat regardless of cylinder, radiator or UF demand. I could be wrong- don't fit WB

 

[Dan Robinson]

Wooshitter can be made to do this but why use an over priced schitbox?

If you're doing a radical renovation why not allocate space for the equipment needed? Shoehorned systems are a nightmare to service and an in-house builder's plumber is going to have his mind blown working out a Smartline as well as his speedfit.

To get the performance benefits of the ACV you'll need to massively oversize the boiler making it poorly performing on the heating.

 

[gdis]

Thank you both for your replies.

DP - could you suggest which boilers have dual inputs? Presumably this would be beneficial even if one went for an UV cylinder? And if there is a short answer to this Q: why not WB?

Dan - WB is what the builder recommended - i don't care and just want to choose the best option. As for space, I am afraid that's all we have; builder doesn't think it will be too tight.
Understand that working out the Smartline could be challenging, which is probably why the builder is against it!
Would the two input solution solve the problem that you mention in your last sentence?
Finally, given the circumstances (I haven't mentioned this, but the only source of heating will be gas - solar has been ruled out as there is not enough space to make it economically advantageous) what system would you go for?

Thanks again.

 

[St0rmer66]

ACV makes sense if you're space limited because at least it'll recover quickly. You'd still be space limited with a regular unvented tank but with slower recovery time.

You don't "need" 2 inputs but it would help efficiency. I'd suggest a "Hot Water priority" setup so that as soon as the cylinder starts to deplete the boiler comes straight on and starts replenishing ASAP.

Can't stress enough how much you need someone with experience of this though, most plumbers just tend to throw a combi at the wall in every situation.

 

[Razor900]

@Dan Robinson Bet he could fit a U16, SB18 and a Superflow under there

 

[Dan Robinson]

Until we get hte Superflow - this is standard fair for 4 bed houses in my portfolio. Cracking set up - pricing another one now with mixed emitters. Might want to get Chris to come down and do a piece .

 

[Razor900]

Chris is laid up Dan, I think you need an engineers visit

 

[Razor900]

Why the 24kW boiler, cylinder reheat??

 

[Roger928]

Nice work. But has to be over kill.
I've seen industrial plant rooms with less copper and cable trays and unistrut.
Whats that black yoke with the clocks.... on the right hand side?

 

[Dan Robinson]

Its a 30 actually - I wanted the 24, but he didn't believe me when i said it would be enough... Its being commissioned as a system not a combi too .

House heatloss 15kW (bigger than the OP's I'd guess), and cylinder coil rated at 19kW. HW Priority off the boiler with WC on the UFH.

 

[Dan Robinson]

Nice work. But has to be over kill.
I've seen industrial plant rooms with less copper and cable trays.
Whats that black yoke with the clocks.... on the right hand side?

ESBE Pump units - 7 UFH manifolds all fed direct from there - no pumpsets on the individual manifolds.

Rectangle underneath is a LLH.

 

[Razor900]

Nice work. But has to be over kill.
I've seen industrial plant rooms with less copper and cable trays.
Whats that black yoke with the clocks.... on the right hand side?

Dan does a lot of rather grand places in London - they can afford it

 

[Dan Robinson]

Chris is laid up Dan, I think you need an engineers visit

By the time I get the wiring done - he'll be on his feet or climbing up the walls.

 

[Roger928]

but our contractor does not have experience with this tank-in-tank system and cannot vouch for it.

Good quality cylinder and very fast recovery. The outer cylinder is mild steel. The inner stainless. Very easy to bleed as the vent is right at the top in the centre.
And its supplied with a tempering valve.
I don't think a standard immersion fits them though.