ASHP environmental yield- seems low?

[daunker]

Hi! I have an ASHP installed for a year and just thought I'd have a look at how it's performed. It's a vaillant arotherm plus 12kw. UFH in house, which has been kept constant 19 degrees all year (except when hotter outside of course!).

 

Attach a couple of photos. The installation is cumulative energy consumption for DHW and heating. Does the environmental yield seem low, I had thought the SCOP was supposed to be around 4 +/- depending on flow temps. Or am I misunderstanding things?

Thanks!

Edited December 8, 2022 by daunker

[SteamyTea]

If the top picture is thermal output and the lower picture electrical input, then yes, not very good at all, a CoP of:

 

7983 / 4474 = 1.78

 

If you have really only used ~8,000 kWh since it was installed, a 12 kW heat pump seems rather large.  At full output it means it has only run for 665 hours, but even at half output it is only double that, 1,330 hours.

 

Does it switch on and off a lot (short cycling) and do you know your flow temperatures and if there is a buffer tank fitted?

[Marvin]

Hi @daunker

 

As I understand it, a high SCOP is derived from keeping the water temperature coming out of the ASHP as close to the temperature of the outside air temperature as possible whilst still keeping the building at a suitable temperature.

 

A bit of a balancing act. We use the weather compensation option to do this.

 

[daunker]

39 minutes ago, SteamyTea said:

If the top picture is thermal output and the lower picture electrical input, then yes, not very good at all, a CoP of:

 

7983 / 4474 = 1.78

 

If you have really only used ~8,000 kWh since it was installed, a 12 kW heat pump seems rather large.  At full output it means it has only run for 665 hours, but even at half output it is only double that, 1,330 hours.

 

Does it switch on and off a lot (short cycling) and do you know your flow temperatures and if there is a buffer tank fitted?

Thanks!! So I have a 50L wall hung buffer tank. I've been researching and I think add the environmental yield to the power consumption and then divide by power consumption to get the COP. Still not good though (2.78!!). Does increase the annual heat demand to around 17,000kwh, does that still suggest it's oversized. The MCS installers said better to be a bit oversized as it is more efficient if it runs low and slow rather than full throttle, and also kinder on the unit with respect to lifespan. 

 

I'm not aware of it switching on and off regularly. Yeah temp for DHW is 55 and flow temp seems to be 45. I don't think I can change that. 

 

Thanks Marvin I think the arotherm plus has that inbuilt, to modulate depending on temperature. Clearly something not right though, and keen to get to the bottom of it. Thanks for prompts and starters will be speaking to the installers tomorrow 

[HughF]

Well, if the flow temp is permanently fixed at 45 degrees, it isn’t running under weather compensation. I wouldn’t trust your installers, they might well have stuffed up the install as easily as they stuffed up the flow temperature.

[Marvin]

As I understand it, the weather compensation setting has to be individually set to each property to work properly.

[HughF]

1 hour ago, Marvin said:

As I understand it, the weather compensation setting has to be individually set to each property to work properly.

Pretty much, yes... Although a good starting point would be 50@-2, 37@15 - the 37 being chosen to keep people quiet about 'the radiators aren't warm'

[joth]

14 hours ago, SteamyTea said:

If the top picture is thermal output and the lower picture electrical input, then yes, not very good at all, a CoP of:

 

7983 / 4474 = 1.78

It's possible Environmental Yield is the difference between thermal output and electrical input (i.e. is the energy savings made vs resistive heating). Which gives a slightly more reasonable 

(4474+7983) / 4474 = 2.78

 

Bloody ambiguous way of presenting the data, whatever 

[SteamyTea]

25 minutes ago, joth said:

It's possible Environmental Yield is the difference between thermal output and electrical input (i.e. is the energy savings made vs resistive heating). Which gives a slightly more reasonable 

(4474+7983) / 4474 = 2.78

 

Bloody ambiguous way of presenting the data, whatever 

Could be.

Display must have been written by a 12 year old marketing person.

[JohnMo]

1 hour ago, HughF said:

Pretty much, yes... Although a good starting point would be 50@-2, 37@15 - the 37 being chosen to keep people quiet about 'the radiators aren't warm'

You're been watching the freedom heat pump install video's, I watched them yesterday 

[HughF]

26 minutes ago, JohnMo said:

You're been watching the freedom heat pump install video's, I watched them yesterday 

I follow GH on LinkedIn, he blogged about this a few weeks back.  Not ideal numbers but good enough to stop people calling up the support number and complaining.

[Marvin]

-7°C this morning first thing and heating setpoint 43°C and inside 21-22°C.

36 minutes ago, HughF said:

Not ideal numbers but good enough to stop people calling up the support number and complaining.

Yes it's taken us a while to think about the room temperature rather than how hot the radiator is...

 

Also we would not have been able to adjust ours ourselves without understanding how it all works - and that's due to help from people @BuildHub

[ReedRichards]

3 hours ago, Marvin said:

-7°C this morning first thing and heating setpoint 43°C and inside 21-22°C.

 

 

-7°C must be very rare on the Isle of Wight, in which case you have probably gone off the end of your weather compensation curve and 43°C must be the maximum heating setpoint. 

[PhilT]

56 minutes ago, ReedRichards said:

 

-7°C must be very rare on the Isle of Wight, in which case you have probably gone off the end of your weather compensation curve and 43°C must be the maximum heating setpoint. 

This is the Vaillant Arotherm Plus WC - a choice of 14 curves of which Marvin's looks like it's been set to the 0.6 curve

[Radian]

7 hours ago, HughF said:

a good starting point would be 50@-2, 37@15 - the 37 being chosen to keep people quiet about 'the radiators aren't warm'

An important bit of psychology it would appear. I tried increasing the hysteresis by 0.5^oC to reduce boiler firing frequency but the occupants perceived this as a reduction in indoor temperature even though the average was identical. Cold radiators were the most often cited case for the prosecution.

[ReedRichards]

29 minutes ago, PhilT said:

This is the Vaillant Arotherm Plus WC - a choice of 14 curves of which Marvin's looks like it's been set to the 0.6 curve

So what does it mean when the curve reaches an impossibly high target flow temperature?  

[JohnMo]

9 minutes ago, ReedRichards said:

So what does it mean when the curve reaches an impossibly high target flow temperature?  

You are living in a barn and you have left the doors open, or your heat emitters are undersized.

 

But looks like a controller suitable for both a heat pump, but also a gas boiler.

[Bob77]

7 hours ago, joth said:

It's possible Environmental Yield is the difference between thermal output and electrical input (i.e. is the energy savings made vs resistive heating). Which gives a slightly more reasonable 

(4474+7983) / 4474 = 2.78

 

Bloody ambiguous way of presenting the data, whatever 

 

This is correct. The environmental yield is the additional heat generated on top of the electrical input. See this previous discussion.

 

FWIW my Daikin Altherma which has been running for a couple of months (but had a faulty flow sensor so was short cycling for the first month and never getting the DHW up to temperature) is reporting 1783 kWh generated (total, not additional) from 729 kWh input, or a COP of 2.45. That doesn't seem brilliant, but I probably haven't found the optimum usage pattern yet, and it has been quite cold for the last week. For the first few weeks when it was milder I was getting about 2.7 to 2.8 even with the flow problem.

Edited December 9, 2022 by Bob77

[HughF]

1 hour ago, Bob77 said:

 

This is correct. The environmental yield is the additional heat generated on top of the electrical input. See this previous discussion.

 

FWIW my Daikin Altherma which has been running for a couple of months (but had a faulty flow sensor so was short cycling for the first month and never getting the DHW up to temperature) is reporting 1783 kWh generated (total, not additional) from 729 kWh input, or a COP of 2.45. That doesn't seem brilliant, but I probably haven't found the optimum usage pattern yet, and it has been quite cold for the last week. For the first few weeks when it was milder I was getting about 2.7 to 2.8 even with the flow problem.

That’s pretty shocking COP from something as fancy as a Daikin. I’d expect better. Here’s a 5kW Samsung gen6 running with a pwm primary pump and the Samsung controller as the room temperature controller. Fantastic COP given the current weather.

 

http://emoncms.org/samsung5kw

 

It’s Glyn Hudson’s DIY install in north wales.

[Marvin]

3 hours ago, PhilT said:

This is the Vaillant Arotherm Plus WC - a choice of 14 curves of which Marvin's looks like it's been set to the 0.6 curve

Hi @PhilT

To clarify we have a coolenergy ASHP, and we set our own weather compensation curve to suit our own heat loss results.

[PhilT]

13 hours ago, Marvin said:

Hi @PhilT

To clarify we have a coolenergy ASHP, and we set our own weather compensation curve to suit our own heat loss results.

sorry daunker who made the original post

[Bob77]

On 09/12/2022 at 21:29, HughF said:

That’s pretty shocking COP from something as fancy as a Daikin. I’d expect better. Here’s a 5kW Samsung gen6 running with a pwm primary pump and the Samsung controller as the room temperature controller. Fantastic COP given the current weather.

 

http://emoncms.org/samsung5kw

 

It’s Glyn Hudson’s DIY install in north wales.

 

I am still fiddling with the settings. The installer told me he had left it probably too high because he "wanted to make sure your house was warm" after the building work we had done. And no doubt he didn't want us phoning him to complain the radiators were cold.

 

I've moved the weather compensation curve down a few degrees and also knocked the DHW temp down a bit. 

 

However we have had freezing fog and temperatures below zero for much of the last week so there has been a fair bit of defrosting going on! I'll see how much I can reduce the flow temperature before there is rebellion in the ranks...

[daunker]

On 10/12/2022 at 12:11, PhilT said:

sorry daunker who made the original post

Thanks! I've changed if to 0.4 and not noticing any deterioration in house temps at all, it seems to be running a better COP too, but was very poor over the real cold weather spell we've just had. 

Thanks @jothand @Bob77for that, yes now read this in Vaillants brochure but really appreciate you for posting. Seems unusual way but I guess makes sense once you wrap head around it.

 

having a lot of fun playing with controller settings if nothing else, although changing so much and the environmental temps are so variable that I'm not sure which changes are making the biggest impacts. Definitely heading the right way tho 

 

[George]

On 09/12/2022 at 12:07, joth said:

It's possible Environmental Yield is the difference between thermal output and electrical input (i.e. is the energy savings made vs resistive heating). Which gives a slightly more reasonable 

(4474+7983) / 4474 = 2.78

 

Bloody ambiguous way of presenting the data, whatever 

Would you think this is common? I've got a Samsung Gen6 and this could be a reason for the odd numbers (although there's something not quite right as on the weekly figures it'd be a SCOP of around 500!)

 

I have noticed SCOP dropping since I lowered all thermostats. But overall it's saving money so it's a bit of a tough call sometimes.  Ultimate answer would be to install a smaller heat pump.