Intergas HRE X-Plan & ACV Smart Green 160 - poor recovery time

[Bob Wylie]

Hi everyone. Happy reading. Any advice/suggestions would be greatly appreciated.


Project Goals

Replace an S Plan setup and old cylinder with Intergas X plan and high gain cylinder. Giving a very rapid cylinder reheat time (circa 12 minutes) and embrace OpenTherm control from the Nest


Issues

The boiler seems to reach flow temp too quickly and cycles but doesn’t correlate to flow temp of 85 degrees, as expected


System equipment and setup

Intergas HRE 40 SB
ACV Smart Green tank-in-tank 160 cylinder
(131l stored domestic hot water, 31KW heat absorbtion
Intergas NTC cylinder stat
Intergas outside sensor

Nest (OpenTherm for heating, on/off for hot water)

28mm flow and return to primary flow and return of ACV cylinder
22mm flow and return to heating, via fernox TF1 filter (on the heating return)

Intergas x-plan

https://www.intergasheating.co.uk/app/uploads/2019/11/X-Plan-diagram-Rapid-HRE-Eco-RF-V3.pdf

Parameter 1 - 1
Parameter a - 6
Parameter 4 - 75 (31kw)
Parameter n - 85 degrees (flow temperature in DHW mode)
How water set point 65 degrees (maximum I can set)

https://www.intergasheating.co.uk/app/uploads/2022/07/HRE-Parameters-version-9-jdl-11.05.2021.pdf

I have two external sensors on the flow and return (DS18B20 to an ESP32) and another inside the drypocket (along with the intergas NTC)

My issue is that when heating the DHW store, with parameter 4 matched to the cylinder at 75%, the boiler soon ‘reaches temperature’ (state 1) sits there for about 30second to 1 minute then starts again.

The flow temperature I have on the DS18B20 is only around 61 degrees yet it keeps ‘reaching temperature’


To rule out any problem with circulation, the original flow and return in 22mm was replaced and upgraded to 28mm in the description above, but it’s made no difference.


If i drop parameter n to say 45% (19kw) the flow temperature I read gets up to 72 degrees. I believe it would keep rising but by that point, the set point on the DHW store is reached

What I don’t understand is why the boiler is ‘reaching temp’ very rapidly running at 31KW. I am not getting and because of the constant cycling, I am not getting the low time spent in DHW mode

I don’t yet have an IDS cable, I may buy one as I am intrigued to see what the boiler things S1 S2 readings are at that point

Pipework drawing for info:

 

[JonathanM]

Could it be to do with pump speed and flow rate? The manual for your cylinder says a 0.7 litre per second flow is needed for maximum reheat performance. That is 42 litres per minute, which is pretty high I think. There are some options in the parameters for setting pump speed. I can't tell from the graphs whether your boiler can even produce 42 litres per minute.

What is the maximum you have been able to set the DHW power output to without the boiler starting to cycle?

How long does it take to reheat the cylinder at 19KW? Is it acceptable?

 

[muggles]

A 31kW coil will only absorb 31kW when the cylinder is completely cold, although the boiler should be able to modulate to suit without cycling. Why did you go for the 40SB? Presumably the house doesn't need 40kW if it's surviving on a 160L cylinder?

Is it a long run from the boiler to the cylinder? There's not much residual pump head on the 40SB so if circuit resistance is too high it simply won't be able to shift 31kW round the system. In fact, if JonathanM above is correct and the cylinder needs 0.7l/s then that is in excess of what the boiler's pump is capable of producing

 

[JonathanM]

There's not much residual pump head on the 40SB so if circuit resistance is too high it simply won't be able to shift 31kW round the system. In fact, if JonathanM above is correct and the cylinder needs 0.7l/s then that is in excess of what the boiler's pump is capable of producing

Below is the info I have, but I'm no expert!

 

[muggles]

Yep, you seem to have interpreted that correctly. 0.7l/s gives 32.2kW at a dT of 11°C across the flow & returns, which is usually about what cylinder manufacturers will target.

 

[Bob Wylie]

Hi all.

I want to express my thanks for explaining to me what's going on. I had completely overlooked the effects of the appliance loss at that high flow rate.

The 40SB was put in about 5 years ago - and forgive me, I can't recall the reasons for the sizing of it at the time, but it looks like it's a perfect case of 'bigger isn't always better

I have it 'tuned' to around 53% power (22kw) and it seems to be giving me a reasonable reheat time (just over 13 minutes for the 130l stored water after showers) . Not what I had planned on when I wanted to capitalise on the 30-40kw but you live and learn!

I am just very pleased that I now understand exactly what's going on. Thanks again

Bob

 

[JonathanM]

I have it 'tuned' to around 53% power (22kw) and it seems to be giving me a reasonable reheat time (just over 13 minutes for the 130l stored water after showers)

I think 13 minutes is extremely good. I've read that the manufacturers tests are carried out under perfect conditions, with a constant 80C flow, so I would imagine it is difficult in real life to get it down to the 10 minutes claimed. Plus you are heating up to 65C, which is higher than the test standard, I think.

 

[Bob Wylie]

Yes it is. It's probably because it's not recharging the full 50 degree delta after only a shower or two, but certainly enough for our purposes. The goal was to effectively have almost continual hot water with one shower running but that was only going to work on paper

Again thank you all for your insights.