How quickly does LLH create heat

[Zencap]

Hi
We have had a LLH installed after major issues of UFH robbing heat from CH. now installed want to ensue working as expected.
All 3 systems (CH,UFH,Hot water) work when on together now, which is progress, however despite the boiler flow to LLH being roasting it takes a fair amount of time for CH flow to get up to a “hot” temp out of the LLH, then if you switch UFH on as well, the same and in turn cools CH flow etc… for a period.
I recognise the LLH vessel will have cold water entering via returns thus cool it but thought it would get up to temp v quickly given size?

 

[John.g]

I remember your problems last January.

Are you saying the temperature from the LLH to the rads is slow to rise?, does the flow (boiler) temperature into the LLH rise rapidly from cold, say 10 to 15 minutes, CH only on, (10 rads?), You answered that, the boiler temp does rise rapidly.
Can you take a few temps from the LLH flow and returns?. Photo of the LLH & pump(S)

 

[Scott_D]

Can you post some pictures?

 

[Zencap]

Attached photos. Flow from boiler into LLH is near instant whether 1 or all 3 on. When just one is on, the flow from LlH to CH, UFH OR HW takes time maybe 15 mins to really warm up? Is that right, normal, think so just want to check or should it be as quick as boiler to LLh? Obviously if just CH is on and hot, then UFH kicks in, the heat is diluted in CH and again takes time for UFH flow to get hot.

 

[John.g]

If say the CH only is on and the flow rate through the secondary (CH) side is exactly the same as the primary (boiler) side then the heat up time will be exactly the same as if you had no LLH, if say the flow through the secondary side was/is higher than the primary side then the temperature of the secondary side flow (to the CH rads) will be reduced due its dilution from the secondary side return (from the rads) and depending on the ratio of secondary to primary flow rates will lead to the rads giving reduced outputs. These flowrates are dependent on the primary and secondary pumps head/flowrates.

What model pumps are these and settings?, is the pump on the primary (right hand) side the only pump associated with the boiler, ie, a heat only boiler (which has no internai pump).
What is the vertical pipe from the top of the LLH?.

 

[Zencap]

Hi thanks John.
See attached photos of all pumps.
All are set at max except for the hot water flow which is at min.

 

[Zencap]

Hi thanks John.
See attached photos of all pumps.
All are set at max except for the hot water flow which is at min.

Sorry also the pipe out top of LLH is auto air vent

 

[Zencap]

Hi thanks John.
See attached photos of all pumps.
All are set at max except for the hot water flow which is at min.

John any further thoughts on this based on the pumps?

 

[ShaunCorbs]

When you have only the rads on any other pipes get hot except the mains into the llh ?

 

[John.g]

John any further thoughts on this based on the pumps?

You shouldn't require running the circ pumps at full speed especially with the UPS3 as it gives a head of 6.4M under all your flow requirements, it will result in a higher boiler return temp which impacts on efficiency, also higher pump electrical consumption.
I would buy a heat gun or even more accurate, a clamp on thermocouple thermometer to take the boiler and the individual circuit flow&return temps, you can then easily see the lowest head required for your system and also the performance of each circuit plus the lowest boiler return temperature.

 

[Zencap]

When you have only the rads on any other pipes get hot except the mains into the llh ?

Hi Shaun, no they don’t, only just to the pumps (for UFH and HW) but obvs pumps not on so stops there. Tiny distance.

 

[Zencap]

You shouldn't require running the circ pumps at full speed especially with the UPS3 as it gives a head of 6.4M under all your flow requirements, it will result in a higher boiler return temp which impacts on efficiency, also higher pump electrical consumption.
I would buy a heat gun or even more accurate, a clamp on thermocouple thermometer to take the boiler and the individual circuit flow&return temps, you can then easily see the lowest head required for your system and also the performance of each circuit plus the lowest boiler return temperature.

Ok so think reduce the pump power for CH and UFH down one level? Or maybe just the UFH?

Also do you think the flow from boiler (and return) changed to 28” vs 22” would mean greater flow to LLH thus more “hot” water to be pumped round?

 

[ShaunCorbs]

Hi Shaun, no they don’t, only just to the pumps (for UFH and HW) but obvs pumps not on so stops there. Tiny distance.

None of them return heat up do they ?

 

[John.g]

Ok so think reduce the pump power for CH and UFH down one level? Or maybe just the UFH?

Also do you think the flow from boiler (and return) changed to 28” vs 22” would mean greater flow to LLH thus more “hot” water to be pumped round?

I would suggest changing the boiler, CH & UFH circ pumps to speed 2 (5.2M), you should then ensure the UFH loop flowrates are as before.
You really require a few temperature sensors to get the proper picture, you might purchase say 6 or so spring clip on dial thermometers and you can monitor all the flows and returns together or one of the two types mentioned above.

What do you mean by 28" vs 22"?.

 

[Zencap]

None of them return heat up do they ?

Not sure what you mean, you mean on the returns? No if so. If Ch on only pipes that get warm/ hot are the CH.

 

[Zencap]

I would suggest changing the boiler, CH & UFH circ pumps to speed 2 (5.2M), you should then ensure the UFH loop flowrates are as before.
You really require a few temperature sensors to get the proper picture, you might purchase say 6 or so spring clip on dial thermometers and you can monitor all the flows and returns together or one of the two types mentioned above.

What do you mean by 28" vs 22"?.

Wil invesitagte temp sensorrs

I mean the size of pipe to and from the boiler - it is only 22 inch, should it be 28” copper pipe and thus allow great flow to the LLH?

 

[John.g]

22" should be fine, bags of pump power available.