System Boiler - Unvented cyclinder - Modulation

[adam_no_understand]

Hello,

I am buying a new entire heating/hot water system for a 1920's 4 bedroom, 2 bathroom house which will also be fitted with solid wall insulation. I have radiators, I don't have underfloor heating and I would like an indirect unvented cylinder for mains pressure hot water for the showers.

What I think I know (please correct if I'm misguided):
- 150L tank should be big enough - most of the time just 2 people in the house
- ~15 radiators - 20kw gas system boiler should be over sized
- I'm probably going to want to "heat on demand" so using a room thermometer is probably the way forward rather than low and slow weather compensation with otuside thermometer
- I need to set the unvented tank temp to 60 degrees
- S looks like most standard plumbing to not be overly complex. My boiler when heating my house should modulate using the thermostat and be fairly efficient
- When my tank is in use my boiler controller will need to request hotter water (60 degrees) so override the modulation of the thermostat - this is called hot water priority?
- If I oversize my radiators even if heating to 60 degrees the return temp of 15 radiators in my cold house is likely to be ~ 40 degrees so good for condensation anyway?


What I've no clue on:
- How the unvented tank actually works
- It has an electric heater in it, I'd rather only use this as backup by default I assume it's generally off?
- When someone turns on the tap it has a sensor which will tell the boiler controller to open the valve and start producing more hot water?
- The boiler controller has a timer to heat the tank at certain times of the day? Or does it have a minimum temp setting and when the thermometer on the tank drops it will heat it back up?

- How direct hot water will work with modulation on an S plan?

- Is it really worth having automated TRV's like Tados in a house like mine or if it's better just balance the system oversize the radiators and pray for efficiency gains?


What I would really appreciate some advice with:
- I haven't been able to talk to my contractors plumber yet, but I've been told he can fit anything but is a valiant installer so will get an extended warranty if I go valiant.
I have therefore chosen a Valiant ecotec plus 620 with a Gledhill ES Indirect Stainless 150L Unvented Cylinder. I don't know what comes with these items and whether I need to purchase controls and/or wifi control seperately

At this point I could change everything. I just want to be environmentally friendly, have a low gas bill while hopefully being warm with a nice shower pressure

Appreciate you taking the time to read the post

Thanks,
Adam

 

[Madrab]

- ~15 radiators - 20kw gas system boiler should be over sized

Depends on the size/type of rads - to give you an idea - a medium sized rad @ 600x1000 K2 (T22) is ~1750W, so 15 of them would need ~ 26Kw.

- When my tank is in use my boiler controller will need to request hotter water (60 degrees) so override the modulation of the thermostat - this is called hot water priority?

No - PDHW - means that when HW is called for, the Ch system shuts and the boiler goes into max temp (~80deg) hi fire mode to heat the cylinder as fast as possible

should modulate using the thermostat

No - modulation means that when the flow/return temps reach set limits, the boiler turns itself down and modulates to maintain those temps. The room stat will shut the boiler down once it reaches it's set temp and then turn it back on when it drops below that set temp

If I oversize my radiators even if heating to 60 degrees the return temp of 15 radiators in my cold house is likely to be ~ 40 degrees so good for condensation anyway?

Balancing a system ensures return temps are suitable to maximise boiler condensing, it rarely just happens. You want you CH system to heat your house so it isn't cold but still want the retun temps low enough to maximise condensing.

How the unvented tank actually works

If it's an indirect cylinder then the programmer calls for heat > the valve to the cylinder opens> hits a switch>that turns the boiler on. Immersion heater is only used if the boiler fails, to provide emergency HW

a sensor which will tell the boiler controller to open the valve and start producing more hot water?

The cylinder will have a cylinder stat that calls for heat when needed.

- The boiler controller has a timer to heat the tank at certain times of the day? Or does it have a minimum temp setting and when the thermometer on the tank drops it will heat it back up?

Both, usually working together

Is it really worth having automated TRV's

Depends on how much control is required

I don't know what comes with these items and whether I need to purchase controls and/or wifi control seperately

comes down to personal choices, your engineer should be able to advise, they usually come separately