Ashp without a tank

[SteamyTea]

16 minutes ago, billt said:

 

ITYM "some" systems will do that.

 

The Vaillant arotherm+ 5kw has a COP of 3.41 at 50C, the 7kW has a COP of 3.65 at 50C, those aren't in the region of 3.9, but they are over 3.

 

Yes the 12kW just about gets to 3.9, but that's one of a range of 5.

You really need to quote the range of external temperatures they were tested at, and the flow rates are useful to know.

Temperature is not energy, the CPU on my Raspberry Pi probably gets to 50⁰C, but it wouldn't heat much water in a day.

[Christiano]

I've seen people saying that you may need to change your radiators/piping; it's potentially true but needs to be tested.

 

We did a test on our LPG (two boiler) system; turn the heating output right down so the radiators are getting less than 50c.

Leave it like that for a few days; are you all warm enough? If not, then you probably need to change radiators and/or piping.

[joth]

1 hour ago, Christiano said:

Leave it like that for a few days; are you all warm enough? If not, then you probably need to change radiators and/or piping.

And don't forget to be valid you need to run the test during cold weather, e.g. several day sustained period below 5º for most of UK. 

 

[J1mbo]

Map consumption to degree days over some time as a spot test is subject to a wide margin of error

[Christiano]

4 hours ago, joth said:

And don't forget to be valid you need to run the test during cold weather, e.g. several day sustained period below 5º for most of UK. 

Agreed.

[ReedRichards]

9 hours ago, Christiano said:

I've seen people saying that you may need to change your radiators/piping; it's potentially true but needs to be tested.

 

We did a test on our LPG (two boiler) system; turn the heating output right down so the radiators are getting less than 50c.

Leave it like that for a few days; are you all warm enough? If not, then you probably need to change radiators and/or piping.

 

Your LPG system  is probably set up for a larger temperature differential across the radiators than a heat pump would use.  So the best simulation would be to turn the heating right down but double or treble the pump speed if that were possible and safe to do (I suspect it's neither).

[Christiano]

On 16/12/2021 at 20:30, ReedRichards said:

Your LPG system  is probably set up for a larger temperature differential across the radiators than a heat pump would use.  So the best simulation would be to turn the heating right down but double or treble the pump speed if that were possible and safe to do (I suspect it's neither).

 

It’s also a bit late ‘cos the boilers have gone and we have a heat pump ?

 

I was wondering 2 things related to your comment though:

1) I wondered what the flow rate was on the boiler system compared to the ASHP. It seems the pump on the Alpha CB24 we had was a Grundfos UPS 15/60 which apparently has a flow rate of 3.4m3/hr which is about 55l/min. That’s over double the 24l/min we’re getting now. Does that sound right or would the boilers have operated the pump at a lower speed?

 

2) I’ve watched a few YouTube videos about balancing radiators which recommended a 10-11 degree temperature drop but I haven’t seen anything suggesting it’s the same or different for an ASHP. Is there a recommended differential for heat pumps? Does it change depending on the outside temperature? Or should I accept that it’s running okay so leave well alone?

Edited December 20, 2021 by Christiano

[ReedRichards]

The heat output from a radiator depends on its average temperature so if the differential is 5 C instead of 10 C then the average temperature will be 2.5 C hotter.  As heat pumps operate at lower water temperatures than conventional boilers do (or used to) then your radiators can be bit smaller if the differential is small and a 5 C differential seems to be what is favoured for heat pumps.  You can increase the differential across a radiator by partially closing the valves to reduce the flow rate but if the valves are fully open you have to increase the pump speed to up the flow rate and reduce the differential.  There may be more to it than this but if so I'm sure somebody will post to correct me.

 

If your system is running okay I would not worry about trying to make adjustments. 

[Christiano]

16 hours ago, ReedRichards said:

The heat output from a radiator depends on its average temperature so if the differential is 5 C instead of 10 C then the average temperature will be 2.5 C hotter.  As heat pumps operate at lower water temperatures than conventional boilers do (or used to) then your radiators can be bit smaller if the differential is small and a 5 C differential seems to be what is favoured for heat pumps.  You can increase the differential across a radiator by partially closing the valves to reduce the flow rate but if the valves are fully open you have to increase the pump speed to up the flow rate and reduce the differential.  There may be more to it than this but if so I'm sure somebody will post to correct me.

 

If your system is running okay I would not worry about trying to make adjustments. 

 

Thanks!