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Posted
3 hours ago, jamesdiyer said:

The heating circuit is always going to be lower flow than DHW due to the increased pressure drop,

 

Not necessarily. There are multiple factors at play:

 

  • Heat demand
  • Delta T
  • Flow rate
  • Flow velocity
  • Pump rating
  • System control settings

At the moment you're trying to test and commission the system at an ambient temperature of about 20C. At this temperature your radiators are not going to be able to dump the heat into the atmosphere, which is why I'm slightly surprised you are seeing a delta T of 5C at full load right now, unless the system is modulating its output and therefore its flow rate.

 

Also, with Vaillant heatpumps, output to dhw is managed according to a measured delta T so Flow rate will vary too.

 

Posted

And I confirm those two valves connecting to heating inside after 3way are dn20 so 16mm internal. They shouldn't have been there. 

 

So we will take those out and see then see about upgrading the 25mm plastic. Then the elbows. Then see if the full pipe need be re run in 35 copper/40pñ

Posted
8 minutes ago, SimonD said:

 

Not necessarily. There are multiple factors at play:

 

  • Heat demand
  • Delta T
  • Flow rate
  • Flow velocity
  • Pump rating
  • System control settings

At the moment you're trying to test and commission the system at an ambient temperature of about 20C. At this temperature your radiators are not going to be able to dump the heat into the atmosphere, which is why I'm slightly surprised you are seeing a delta T of 5C at full load right now, unless the system is modulating its output and therefore its flow rate.

.

 

 

It was -2C here yesterday morning. 

 

But yes it's modulating a lot and I'm not doing delta 5 much. It's trying to run aroun 25-30C temps and then cycling. 

Posted
1 hour ago, jamesdiyer said:

 

It was -2C here yesterday morning. 

 

But yes it's modulating a lot and I'm not doing delta 5 much. It's trying to run aroun 25-30C temps and then cycling. 

 

It's looking like you've got multiple things going on with the system and you need a proper design in place that looks at the system as a whole. 

 

Best wait for the Vailant person and see what they say.

Posted
35 minutes ago, SimonD said:

 

It's looking like you've got multiple things going on with the system and you need a proper design in place that looks at the system as a whole. 

 

Best wait for the Vailant person and see what they say.

Yes agreed. 

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