ASHP standby power consumption, monitoring, turn off and back on because of power cut.

[PhilT]

quote from a supposedly reputable manufacturer "...power consumption in standby mode should only be measured by use of a Watt hour meter to give a true figure, due to the nature of an inverter driven unit. Measuring current with a clamp meter and then calculating using P = V I pF will give higher readings than the system is actually consuming..."

 

so to get a representative measurement you would need to switch absolutely everything off except the HP and watch your main meter reading over at least an hour.

[Marvin]

29 minutes ago, PhilT said:

quote from a supposedly reputable manufacturer "...power consumption in standby mode should only be measured by use of a Watt hour meter to give a true figure, due to the nature of an inverter driven unit. Measuring current with a clamp meter and then calculating using P = V I pF will give higher readings than the system is actually consuming..."

 

so to get a representative measurement you would need to switch absolutely everything off except the HP and watch your main meter reading over at least an hour.

Yes like this set up with a separate meter altogether :

 

Edited October 19, 2022 by Marvin
clarification

[SteamyTea]

49 minutes ago, PhilT said:

quote from a supposedly reputable manufacturer "...power consumption in standby mode should only be measured by use of a Watt hour meter to give a true figure, due to the nature of an inverter driven unit. Measuring current with a clamp meter and then calculating using P = V I pF will give higher readings than the system is actually consuming..."

While true, there is a difference between showing under 20W and 200W.

It is too easy to say that because something is not 100% accurate it is not worth doing.

There are also statistical methods that can reduce the uncertainty.

Edited October 19, 2022 by SteamyTea

[Radian]

1 hour ago, SteamyTea said:

While true, there is a difference between showing under 20W and 200W.

It is too easy to say that because something is not 100% accurate it is not worth doing.

There are also statistical methods that can reduce the uncertainty.

Sorry to say the power factor may be such as to make VA look ten times as much as real (actual) power. A clamp really isn't good enough. A revenue grade meter like @Marvin uses is perfect but a bit of an overkill. Any meter that displays PF (possible example) should also report real power.

Edited October 19, 2022 by Radian

[Kevm]

18 hours ago, Radian said:

Sorry to say the power factor may be such as to make VA look ten times as much as real (actual) power. A clamp really isn't good enough. A revenue grade meter like @Marvin uses is perfect but a bit of an overkill. Any meter that displays PF (possible example) should also report real power.

 Can you explain why a clamp meter doesn't work?  I assume these meters measure current and then work out power from an assumed 240v? 

[SteamyTea]

18 hours ago, Radian said:

Sorry to say the power factor may be such as to make VA look ten times as much as real (actual) power

In very rare circumstances.

To get an idea as to how much energy is being used, they are adequate in this circumstance, especially if the crankcase heater is resistive, or acting as a resistive load.

7 minutes ago, Kevm said:

Can you explain why a clamp meter doesn't work?  I assume these meters measure current and then work out power from an assumed 240v? 

It is because with AC, the current and the voltage are out of phase.

When voltage is crossing the zero voltage point, current is infinite.

To find out true power there is a lot if calculating to do during each cycle to find out, at any given point, what the actual power is.

Root Mean Square is one method that is fairly easy as it, in effect, makes all the numbers positive. So less calculations to do.

Another method is to take the area under each curve during a cycle, then multiple those areas. That is the integration method. Hard work if calculated manually.

What usually happens with cheap clamp in meters is that a power factor gets assumed, often between 90 and 95%.

So the meter over reads sometimes, and under reads others. But on average, it evens out.

[Radian]

2 hours ago, SteamyTea said:

To get an idea as to how much energy is being used, they are adequate in this circumstance, especially if the crankcase heater is resistive, or acting as a resistive load.

I've not been paying particular attention to what's being measured because it's best not to assume the type of load. Some of these compressors use DC PWM to double-up the motor windings as heaters and that would sure as heck give a misleading reading.

[SteamyTea]

14 minutes ago, Radian said:

I've not been paying particular attention to what's being measured because it's best not to assume the type of load. Some of these compressors use DC PWM to double-up the motor windings as heaters and that would sure as heck give a misleading reading.

Probably all explained here.

https://www.tek.com/en/documents/application-note/power-analysis-pwm-motor-drives

[Radian]

In an AC inverter driver the rectification and capacitive smoothing stage upstream of the PWM switching transistors typically has a power factor of around 0.65 or less.

[Marvin]

Well I'm still trying to avoid damaging our ASHP along with who knows how many of the 47,000 other ASHP owners in the UK. 

I assume the likes of @Conor and @richo106 and others who have the same ASHP as us are aware....

 

 

[joe90]

Mine is timed fir daytime usage but unsure I am doing harm this way, found this https://heatpumps.co.uk/2013/08/13/stand-by-power-and-air-source-heat-pumps/

[Adam2]

On 19/10/2022 at 16:28, Radian said:

Sorry to say the power factor may be such as to make VA look ten times as much as real (actual) power. A clamp really isn't good enough. A revenue grade meter like @Marvin uses is perfect but a bit of an overkill. Any meter that displays PF (possible example) should also report real power.

Thanks for the link, also listed I saw this one which looks to be easier to use as I think you can probably more easily put the clamp around the live or neutral vs having to always disconnect. BUT - are there options which allow a clamp around the 3 cores in a typical LNE supply that will provide accurate/reliable readings?

[Radian]

1 hour ago, Adam2 said:

are there options which allow a clamp around the 3 cores in a typical LNE supply that will provide accurate/reliable readings?

No. Current transformers need either L or N but not both as their magnetic fields cancel each other out. You can get 13A plug-in type adaptors if your ASHP is terminated in a standard 13A plug but that's extremely unlikely.

[Marvin]

10 hours ago, Radian said:

No. Current transformers need either L or N but not both as their magnetic fields cancel each other out. You can get 13A plug-in type adaptors if your ASHP is terminated in a standard 13A plug but that's extremely unlikely.

Hence the overkill 

[dpmiller]

still waiting for the weather to cool enough to see the crank or chassis heaters being called

[PhilT]

Just did another check over 2 hours with everything else switched off. Main meter readings give 40W per hour total which is 15W for the compressor heater (per data sheet) and by difference must be 25W for the control system. Model is Ecodan R32 11.2kW

[SteamyTea]

24 minutes ago, PhilT said:

Main meter readings give 40W per hour total

Now it isn't.

W is the power and is multiplied, not divided, by time.

 

[PhilT]

1 hour ago, SteamyTea said:

Now it isn't.

W is the power and is multiplied, not divided, by time.

 

yes sorry picking up bad habits. Power draw = 40W. Daily = around 1kWh 

[Marvin]

On 18/10/2022 at 15:40, SteamyTea said:

At 2 kWh a day, that is, at current rates, about £250/year.

 

Now I have no idea what you could realistically get for your ASHP on eBay, or how much a new one with a decent compressor would cost.

But I would be considering it at today's energy prices (though I think they will come down).

Which ASHP with a decent compressor were you thinking of? Daikin? Mitisibishui? Valliant? ( yes they all have the same challenge that they need a warm compressor....
 

[SteamyTea]

7 hours ago, Marvin said:

Which ASHP with a decent compressor were you thinking of? Daikin? Mitisibishui? Valliant? ( yes they all have the same challenge that they need a warm compressor....
 

I wasn't thinking of any particular make, just one with the lowest overall standby load.

[PhilT]

Our you could get the one with the best performance/price irrespective of standby power draw and switch it off for 4 months of the year, if you have suitable alternatives for DHW

Edited October 26, 2022 by PhilT

[Marvin]

3 hours ago, PhilT said:

Our you could get the one with the best performance/price irrespective of standby power draw and switch it off for 4 months of the year, if you have suitable alternatives for DHW

Good idea. 4 months? I live on the Isle of Wight. We'll turn it on sometime this month.....

[Marvin]

On the Samsung ESH ones the crankcase heater kicks in when below 10C!!

[Marvin]

On 24/10/2022 at 11:34, PhilT said:

Just did another check over 2 hours with everything else switched off. Main meter readings give 40W per hour total which is 15W for the compressor heater (per data sheet) and by difference must be 25W for the control system. Model is Ecodan R32 11.2kW

For your information. I think the 112 is the 11.2kW model

 

 

Manufacturer	Model	Numbers	Date of manual	Page on manual	comment
Mitisibishui	Ecodian	PUHZ 50, 85, 112,140	?	2 and 7	Turn on at least 12 hours before operation.

                               

 

[dpmiller]

So I finally have an instance of the heater coming on. Displayed external temp was <9C and the crank heater was noted to come on for a short time during startup and as the unit ramped to capacity. The chassis (anti-ice) heater was called for a while too *after* startup

 

I can't be sure whether these events occurred purely at the 9C threshold or if coil or evap temp was relevant too so will continue to monitor. Certainly the unit didn't appear to be sitting with the crank heater on for hours on this occasion...