How long can I put heat into heating circuit before boiler overshoots................

[marshian]

Probably one for @SteamyTea or @John Carroll

 

If I have a fixed flow rate of 0.5 m3 / Hr thro a heating circuit

 

A heat loss of 1.0 kWh shared across all the heat emitters in the circuit

 

A boiler which (after initial fire and ramp down) is putting 4.0 kWh into the circuit

 

The circuit starting temp of 20.5 deg C

 

And when it reaches 32 Deg C (boiler overshoot temp)

 

Just trying to get straight in my head what length of "run time" I should expect

 

I know if I have a heat loss of 1.0 kWh and a heat input of 4.0 kWh then I should expect the boiler to run for less than 25% of the available time.

 

So ideally 1 x 15 mins in an hour but I'm trying to work out if 15 mins in an hour is possible mathematically based on the ability of the circuit to take that heat or if mathematically the likelihood is two burns of 6 ish mins

 

Circuit volume is 130 Litres if that helps?

 

 

[SteamyTea]

Would need to knock up a spreadsheet, I am sitting in a cafe at the moment, maybe when I get home.

[marshian]

1 minute ago, SteamyTea said:

Would need to knock up a spreadsheet, I am sitting in a cafe at the moment, maybe when I get home.

 

Enjoy the people watching 😉

 

Thank you if you do have chance

[SteamyTea]

On 24/03/2025 at 16:57, marshian said:

Thank you if you do have chance

Not had a chance, sorry.

 

But I think you are right about a 15 minute total runtime per hour.

What will affect the frequency is the temperature difference between flow and return temperature, as that is what sets, in part, the energy needed.

 

[marshian]

2 minutes ago, SteamyTea said:

Not had a chance, sorry.

 

But I think you are right about a 15 minute total runtime per hour.

What will affect the frequency is the temperature difference between flow and return temperature, as that is what sets, in part, the energy needed.

 

Yeah at a flow temp target of 28 it will keep the burn going until flow rises to 32 before shut off

 

boiler seems happy with maintaining a 7 Degree delta between flow and return - it apparently doesn’t have a return temp sensor and all the firmware is based on flow temp

 

during the coast after the burn return temp typically drops to around 8 deg below target temp

[John Carroll]

On 24/03/2025 at 16:51, marshian said:

Probably one for @SteamyTea or @John Carroll

 

If I have a fixed flow rate of 0.5 m3 / Hr thro a heating circuit

 

A heat loss of 1.0 kWh shared across all the heat emitters in the circuit

 

A boiler which (after initial fire and ramp down) is putting 4.0 kWh into the circuit

 

The circuit starting temp of 20.5 deg C

 

And when it reaches 32 Deg C (boiler overshoot temp)

 

Just trying to get straight in my head what length of "run time" I should expect

 

I know if I have a heat loss of 1.0 kWh and a heat input of 4.0 kWh then I should expect the boiler to run for less than 25% of the available time.

 

So ideally 1 x 15 mins in an hour but I'm trying to work out if 15 mins in an hour is possible mathematically based on the ability of the circuit to take that heat or if mathematically the likelihood is two burns of 6 ish mins

 

Circuit volume is 130 Litres if that helps?

 

 

Maybe look at it from two opposite ends.

One is to assume no anticycle time  and a very small HEX of say 5L and a dT of 5C  between firing on/off, a 1 kw "rad" would, more or less output this under these conditions. The other extreme is (by using anticycle logic) is to allow the whole system contents of 130L to fall to 25C, the dT through the HEX when firing is almost  7.02C, 4*860/60/0.5/16.66, (6.88), so when the rads/HEX return rises to 25C  then the HEX will shut down as its discharge temp will be 32C, by allowing the system contents to fall to almost "cold" conditions of 20/20.5C will give a system buffer of 130*5/860, 0.756kWH and a OFF time of ~ 45 mins to give a cycle time of 1 per hour!!, of course the rad output would require to be doubled as the average output will only be ~ 50% with the flow temperature rising and falling, bif effect at very low flow temperatures.

Anyway have a look at this.

 

Buffer mars Rev0.xlsx