The deltaT on ASHP is sometimes 1 deg - sometimes 8 - same day!

Ive scoured the forums here for an hour on this… nothing seems relevant.
A friend has a Nibe HP (10 years old) in the large , well insulated house they bought last year.
Have found the elec bills very painful - > £10/day

So with my emonCMS experience - i wired up loads of sensors to look.

I’m hoping that tweaking down HW temps and adjusting the Curve will do the business.

But -that deltaT variation…

The one HP does HW too, with a valve. (hence the spiky parts on the graph)

The NIBE controller is SMO10 and HP’s outside F2015 - both no longer sold.
There is a 300 litre buffer tank in the CH - 3 pipes: bottom: 1 connection to RETURN of both HP and CH; top 2 pipes, in series between HP FLOW and the CH pumped FLOW

I’m no expert in heating or plumbing, but I’d guess that the low dT at 2am is caused by either some valves that aren’t open or some pump that isn’t running. In effect, the HP is supplying heat to the buffer tank, but the central heating system isn’t taking heat out of it. Based on that one chart, it seems like the heating has turned off for the night, but didn’t tell the heat pump.

Some questions to ask:

  • how is the heating controlled? is it on a timer?
  • radiators or underfloor heating? or a mix?
  • do radiators / UFH have their own thermostatic valves?
  • single zone or multiple zones?
  • how is the hot water triggered? can it run convinced to run less often?

Thanks for that input. Your suggestion makes sense.

Your Questions:
how is the heating controlled? is it on a timer?

  • it’s purely the NIBE SMO10 controller. (12 year old system - no longer buyable) It has no timers - but does allow an overnight set-back

radiators or underfloor heating? or a mix?
Pure UFH - up and down.

do radiators / UFH have their own thermostatic valves?
Thermostats in all rooms - but all set to high. Maybe I need to watch the actuators next time the HP fires up - make sure they truly are open The NIBE does not know about the room sensors… they seem to be wired only to the actuators and not the ‘system’.

single zone or multiple zones?
As above - the controller-brain is single zone. But rooms do control their own actuators.

how is the hot water triggered? can it run convinced to run less often?
By the SMO10 controller. It has a HW sensor in the HW tank. You set the max and the min temp you want. That does work - emonCMS shows it!
But -no way in the controller to set time of day.
Note: the system has a HW loop - so the HW pump circulates from the HW tank round the house and back. (nice for instant hot water in the tap at the far end of the house… but means HW is losing heat to the house all year… the expensive high-temperature heat, at that!

There is a seperate time-clock hardware: labelled ‘Heat Loop’ - so I guess the main controller SMO10 does not know about that…

EmonCMS bottom graph - in red - shows the HW pipe temp 1m upstream from the tank. It very slowly drops in temp, until the HP fires, never for long, the higher-peaks of Red/Green in the top graph.

Is it running on weather compensation? or on a fixed target flow?

WC is always the way to go.
You would assume that if there is a setback option, that it would be WC.

A DT of between 3 to 5 is usually expected on a heat pump system.
If you’re getting a tight DT, then the heat isn’t going anywhere and coming straight back.
Is there some closing of radiators at all?

Is the tight DT only shown overnight?

Is there any information on the Nibe to suggest daily COP or electric in and heat out?

Do they have any design docs for the system? MCS room by room calcs or anything that we could use to make sure unit is sized correctly?

What size heat pump is it?

Weather compensation - yes, the Nibe controller majors on that - the first settings in the panel are which curve, and a one click way to modify it.

What size heat pump is it?
I need to double check - 8kw probably.

A DT of between 3 to 5 is usually expected on a heat pump system
If you’re getting a tight DT, then the heat isn’t going anywhere and coming straight back. Is there some closing of radiators at all?

It’s claimed that the UFH actuators are always fully open. But I perhaps need a way to prove that. There are no radiators.

Design docs - I’m awaiting those.

Apologies, thought I saw mention of rads.

I think the best way to run it would be actuators open and drop the curve / flow temp as low as you can and just use the room stats as limiters. But hopefully if you nail the curve you shouldn’t need them to kick in.

So as you said, leave the temp sensors high and make sure all the system is open.

Heat pumps are flow machines… more space for the water/heat the better, ie open system.

Is there any way you can monitor elec in and heat out? Is there a electric meter?
Was this an old RHI install as I think those installs required a meter installing.

I have Shelly monitoring the elec usage right now via some CTs- until I move the emonPi closer and use CTs in that.
I’ll ask if it is an RHI install.

Did you know you can get the Shellies to write to MQTT and use a Node Red flow in your Emonpi to write the output to EmonCMS? I have a couple doing that (i also use Node Red to control some Shelly switches).

Multi zone then (it can’t be both!) - all the central point is doing is deciding if the pump needs to run, i.e. one of the actuators is open and heat required.

As a slight aside, don’t think that theses controllers cannot be replaced. All they are doing is closing a circuit to open/close the actuator. That can easily be replaced by a simple Wi-Fi relay and then you can get greater control using something like HomeAssistant.

Running all the time! Very expensive. I’d be doing that on demand i.e. I’m having a shower in a few minutes, turn on the pump! You would have hoped that it only ran on a timer at least! Again. a WiFi relay can be set to control that.

I have reduced the temperature of my tank significantly recently and the saving is quite amazing.

Thanks for the tips @Rachel @borpin .
This NIBE system is at a friend’s house. He seems to have lost interest in trying to tweak it to save money, sadly: so I’ll be removing the EmonPI sensors shortly.

I contacted NIBE - on that model they pump in the outside compressor cannot be prevented from running all the time… even when compressor is not running. (something Brian you mentioned somewhere here as bad thing to be heating the outside metal-lump all the time from the CH flow).

I did manage to get the HW set lower which will save him something.
But I still feel there is something wrong in the design.
Not got to the bottom of why the deltaT HP flow and Return sometimes is only 1 degree for 20-30 minutes.
And the plumbing of the storage tank seems weird. it has 3 connections: (which is one of the modes in the Nibe installers manual). But seems to be acting more like a LLH than a buffer tank… to my semi-engineering thinking.
You can lead a horse to water…etc

Thanks anyway folks.

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Hi @Rachel - can you point me to a good dummies guide for doing that with the Shelleys.
I tried 3 or 6 months back: but couldn’t get NodeRed set up right. I’m a savvy guy with tech normally:but got stuck on that.

EDIT- -I just spotted this recent guide, which may help me:

Glyn posted an article the other day about connecting up the new Shelly H&T using NodeRed. Just search Shelly and it should be the top article. Its basically the same way i do it, so should be fine for other devices.


thx, yes saw that now. Appreciated.