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Vaillant Arotherm Settings for New Installation

 
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Air Source Heat Pumps (ASHPs)
Last Post by bontwoody 1 year ago
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bontwoody
 bontwoody
(@bontwoody)
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Joined: 3 years ago
Posts: 805
Topic starter 25/04/2024 1:55 pm  

@drew-pa 

It is set on pure weather compensation at internal temperature of 22C. The unit runs 24hrs with a setback overnight. Theoretically that should be good for COP even if the electricity usage could be higher than running it for a shorter period.

I cant really drop the desired temperature or curve as the BIL's wife likes it warm. It was running at 20C initially but that didnt seem to help the COP greatly.

Your COP figure looks lovely. What sort of flow temperature are you using to get that high?

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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 Drew Pa
(@drew-pa)
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Joined: 3 years ago
Posts: 73
25/04/2024 6:37 pm  

Dropping the curve won’t drop the temp, it just adjusts the time it takes to get there. (Well in my simple mind lol). 

Our present heat curve setting is 0.3. That’s been set by Vaillant using the adaptive heat curve setting. Next time the system fires up I’ll check what the flow temp is for you.  

drew


   
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bontwoody
 bontwoody
(@bontwoody)
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Posts: 805
Topic starter 25/04/2024 6:50 pm  

@drew-pa 

Thanks Drew

that isn’t how I understand it. To me the curve sets the “gradient” on the weather compensation chart. The desired room temperature moves that gradient up or down the flow temperature axis. 

I’ve put gradient in inverted comments as I know that it isn’t a straight line. 

I might be wrong but coming from a system where I enter the min and max flow temps for different outside air temperatures, it makes sense in my mind. 

In that case, if too low a curve is selected, a room might never reach the desired temperature. 

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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 Drew Pa
(@drew-pa)
Estimable Member Member
Joined: 3 years ago
Posts: 73
25/04/2024 7:06 pm  

You are correct.  I just tend to over simplify things.  We’ve never had it not reach temperature; it seems to just take longer the lower the curve number is.  With the Vaillant system there is no option to adjust the temps individually so the curve is the only option we have to play with.  It may be worth trying to lower yours to 0.6 and seeing how it goes.  

simplistically, with ours the higher the number the higher the electrical bill.

Drew 


   
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bontwoody
 bontwoody
(@bontwoody)
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Joined: 3 years ago
Posts: 805
Topic starter 26/04/2024 1:59 pm  

@drew-pa Ah thanks. Good to know I dont have a misconception about it.

On Energy Stats Uk ( https://energy-stats.uk/vaillant-arotherm-weather-curve-information/) Mick Wall gives a rough way of setting the correct curve.

A more detailed equation (TFlow = a * (HC * (Tset - Tout))b + Tset) is given on the Open Energy Monitor forum. ( https://community.openenergymonitor.org/t/vaillant-arotherm-owners-thread/21891/83?page=5)

Ive used that to reproduce a more accurate table of flow temperatures for curves at desired room temperatures at -3C OAT

I will paste it below for anyone interested in the future.

image

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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