Calculator recommendations????

[Riley]

Good afternoon I hope you’re well

I am trying to prove to a customer that their boiler is undersized. They have 20 radiators mostly doubles and a 220 L unvented cylinder. 18kw Worcester heat only boiler. Three years old.

I am trying to reverse calculate the heat requirements of the radiators that have been installed and I wondered if anyone had any calculator/app recommendations that might help with this?

Thanks

 

[Ric2013]

No, I meant 'zombie'. The walking dead. Decades old, inefficient by modern standards, and running off grandfathers' rights, but still in service. Saw the word in "Installer" magazine and thought it was a common term, but I think it is ONLY "Installer" that uses the term.

 

[Ric2013]

That’s why

Unvented required more heat / they have a bigger coil cap

If you look at gledhill 300l you will see the coil is rated at 25kw max for a re heat time for 45mins I think from cold

Thanks Shaun. Someone said 'any cylinder' so I assumed this included vented.

I wish I'd fitted a fast recovery in my last house: every time the boiler took an hour to reheat the water I sighed and wished I'd stuck to my guns and bought a fast recovery instead of listening to the idiot who told me my boiler wouldn't cycle. Another thing I've been told grr .

 

[chris watkins]

That’s why
Unvented required more heat / they have a bigger coil cap
If you look at gledhill 300l you will see the coil is rated at 25kw max for a re heat time for 45mins I think from cold

Vented or unvented an indirect hot water cylinder installed into a dwelling (heated by gas in this case) must be Part L compliment, this covers the re-heat times which must be 25 mins given the required boiler power is available.
Re-heat means 70% of its volume through 35 - 40 degC

 

[Ric2013]

Vented or unvented an indirect hot water cylinder installed into a dwelling (heated by gas in this case) must be Part L compliant, this covers the re-heat times which must be 25 mins given the required boiler power is available.
Re-heat means 70% of its volume through 35 - 40 degC

The cylinders I'm referring to are part L compliant, according to the manufacturers.
Thanks for your post - it explains a lot if re-heat times are quoted at 70% of the volume @35-40K in 25 minutes. Since we put the thermostat a third of the way up the cylinder, it's probably just below that 70%, after which the coil is half covered in heated water and heat transfer drops considerably.

What would be good would be a standard that requires a cylinder filled with 20°C water to satisfy a stat set at 60°C and located a third of the way up the cylinder, in 25 minutes, with a flow temperature to the cylinder coil of 80°C and sufficient flow to ensure the return is no lower than 70°C. You'd need to define the standard to allow for 75/55° operation too.

At least we know it would then work well, rather than just hit an arbitrary target (how do you measure the temperature of 70% of the water anyway?). But as someone who worked at the BRE when they were writing the Code for Sustainable Homes, commented 'we knew when we were writing it that it was ultimately a load of rubbish'.

 

[king of pipes]

I did a large town house with 20 rads they came out at 24kw on their own so chances are you are correct 30kw would be more like it . Kop