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Flow temp - Central Heating...


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Hi,

 

I am trying to find the most economical value for the Central Heating flow for my 9kw LG Therma V system (Split). Current setting is 38 degrees - however the house does appear to be a little cool. I'm using a Nest Thermostat as the main control but not convinced that it is up to the job. It's located in the hallway, it can frequently be reading 20 degrees and switch the ASHP off yet the rooms can be reading between 16-18 degrees (I have Z-Wave TRVs installed in all rooms).

 

What sort of temperatures do others run their systems at? Is it better to leave it running for longer at a lower value, or a potentially higher value for a shorter period of time?

 

Any suggestions appreciated.

 

Andrew

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13 minutes ago, Sketching said:

That was my next option - turn up the thermostat, however, I was also looking for some feedback as to what flow temperatures people are running their ASHP installations at?

Radiators or under floor heating?

 

How well insulated is the house?  Old or new etc?

 

 

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Turn down the radiator in the hall or turn up the thermostat in the hall.

 

Is this a new system for this winter?  If so it hasn't been balanced yet. Balancing means adjusting the flow rate of water through each radiator so all the rooms heat up at about the same rate, and at the moment the hall heats up way quicker then the other rooms and the thermostat in the hall turns the whole lot off. You want the hall to heat up slower than all the other rooms so its radiator wants a very low flow rate.

 

Once that is sorted out, you will have to experiment with the flow temperature.  Only when it gets colder, if you find it struggles to heat the house, increase the flow temperature a bit.

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13 hours ago, Stones said:

@Sketching

 

Do you have the heating set to a timer - as you would a gas or oil system, or are you letting the heating come on/off as it needs 24/7 ?

Hi,

 

I've got a Nest Thermostat installed, with a schedule of -

 

09:00    19 degrees
19:00    20 degrees
23:45    19 degrees
 

This is repeated every day, so in theory it shouldn't be changing the state on/off much at all unless the house starts to cool down. My understanding of ASHP was that they were best left running 24/7?

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12 hours ago, ProDave said:

Turn down the radiator in the hall or turn up the thermostat in the hall.

 

Is this a new system for this winter?  If so it hasn't been balanced yet. Balancing means adjusting the flow rate of water through each radiator so all the rooms heat up at about the same rate, and at the moment the hall heats up way quicker then the other rooms and the thermostat in the hall turns the whole lot off. You want the hall to heat up slower than all the other rooms so its radiator wants a very low flow rate.

 

Once that is sorted out, you will have to experiment with the flow temperature.  Only when it gets colder, if you find it struggles to heat the house, increase the flow temperature a bit.

 

The hall radiator doesn't have a thermostat on it (balancing radiator?), however, the hallway itself is normally quite cool - i'm always surprised that the Nest is reporting the temperatures that it does. It's not in sunlight so I don't see how it should be 'over reading', if anything I would expect it to be under reading... The hall covers both the ground and the 1st floor - 1st floor TRV is set down at 18 degrees so don't think that radiator would actually come on at all.

 

The system was installed last February, just before lock down.

 

I guess one way to tackle this would be to use a seperate thermometer to read/record the temperature and then start to compare?

 

I was just concerned that I was running the system either too hot or too cold. Flow temp of 38 degrees, house thermostat of 19/20 degrees but getting something that feels right seems to be difficult.

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The issue is this one and only thermostat turns the whole lot off when that is satisfied which is wrong.  By "turn down" I don;t mean adjust a TRV, I mean turn down the lockshield valve on that hall radiator to slow the water flow rate through it which will make it a bit cooler and less heat into the hall.

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Definitely worth getting some thermometers, checking they all agree with each other, and fitting them around to see what the temperatures are really like. 

 

I had a Nest for a while and found it rather poor at measuring an accurate room temperature. It has multiple sensors inside (7 I think?) and supposedly does a whole load of jiggery pokery to improve accuracy but frankly it just didn't work too well and I got the impression that Google aren't that invested in the thermostat side of things. Online searches suggested it being a common problem for some, and even cases of apparent self-heating from the WiFi chip. Google replaced mine (despite it being second hand and out of warranty!) but the replacement wasn't much better. The stabity of control was also rather poor and not a patch on my old CM927 whose TPI control kept a rock solid temperature with no over/undershoot. 

 

Ended up selling it, which was a real shame as it looked smart and the control dial was a joy to use.

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On 18/10/2021 at 22:03, ProDave said:

The issue is this one and only thermostat turns the whole lot off when that is satisfied which is wrong.  By "turn down" I don;t mean adjust a TRV, I mean turn down the lockshield valve on that hall radiator to slow the water flow rate through it which will make it a bit cooler and less heat into the hall.

 

Looking at lockshield valves online and then what is installed on the radiator... is this actually a valve?

RHS.jpg

LHS.jpg

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