Air to air split heat pumps for UK spring and autumn heating

[Radian]

13 minutes ago, RichardL said:

but the AC units heat the rooms up so quickly I reverted to a nominal 18º during waking hours increasing for the evening then off overnight (similar to how I have central heating setup for the rest of the house).

 

I'm reluctant to leave things to cool too much as a room feels different if it's left to cold soak as you put it. Maybe I'll experiment by dropping the set back by a degree a week and monitor the power. Difficult doing long-term tests when the weather is as mental as it has been recently.

[SteamyTea]

3 hours ago, RichardL said:

Normally rooms drop to 15º min overnight with no heat, but in the cold snap I had one morning where they went down to 12 inside!

That is quite interesting.

 

I have storage heaters and I limit the time they can store energy to between 3 AM and 7 PM.  So 3 hours.

The other 21 hours of the day, they are discharging.  The mean temperature did drop a couple of degrees over the cold spell (just working out the data now).

But not too much and I only used the fan heater about 4 times for an hour at a time.

 

 

[SteamyTea]

4 hours ago, RichardL said:

Normally rooms drop to 15º min overnight with no heat, but in the cold snap I had one morning where they went down to 12 inside!

That is quite interesting.

 

I have storage heaters and I limit the time they can store energy to between 3 AM and 7 PM.  So 3 hours.

The other 21 hours of the day, they are discharging.  The mean temperature did drop a couple of degrees over the cold spell (just working out the data now).

But not too much and I only used the fan heater about 4 times for an hour at a time.

 

 

[RichardL]

1 hour ago, SteamyTea said:

That is quite interesting.

 

I have storage heaters and I limit the time they can store energy to between 3 AM and 7 PM.  So 3 hours.

The other 21 hours of the day, they are discharging.  The mean temperature did drop a couple of degrees over the cold spell (just working out the data now).

But not too much and I only used the fan heater about 4 times for an hour at a time.

 

 

Re 12º - The nature of that bit of the house & our location TBH -  it has external wall insulation - but persistent cold inbound from the Brecon Beacons and the timber frame part of the house takes on a chill relatively quickly.

I guess 'no heat' is different on A2A too - i.e. once its off its done and the rooms start to cool immediately whereas radiators/central heating going off at 22:30 there will be residual warmth in the pipes/water etc.

[SteamyTea]

Right.  Here is the last two weeks data.  I know that I live in the warmest part of the country, but for here, it was artic.

 

Work out at 4.6 kWh/m² for that periods space heating.  As my heating season is about 12 weeks, that will be 28 kWh.m².

Not too bad, especially as the mean temp was only a gnats over 1°C down.

 

[Radian]

4 hours ago, RichardL said:

I guess 'no heat' is different on A2A too - i.e. once its off its done and the rooms start to cool immediately whereas radiators/central heating going off at 22:30 there will be residual warmth in the pipes/water etc.

 

That's true to a certain extent and it may be more significant in a TF house but in a masonry building the more massive elements are what freewheel the heat. Air has a very low SHC so is easy to heat and quick to cool down. Keep it hot and blowing around for long enough and the heat in the air will transfer to the materials with a higher SHC. Infrequent use of A2A is not going to do that. It's why I spoke of there being a different feel to a room with A2A. The room may feel warm as you walk around but when you sit down on a chair or pick something up from a desk it feels a little cooler than you might expect. I've only been studying these effects since the beginning of December when the weather turned colder as my A2A units were only installed in November and I'm still learning about it.

[SteamyTea]

11 hours ago, Radian said:

Air has a very low SHC so is easy to heat and quick to cool down

It is higher than timber, brick and stone.

You are talking about volumetric heat capacity.

 

You can order the list by mass or volume.

https://en.wikipedia.org/wiki/Table_of_specific_heat_capacities

[Radian]

7 hours ago, SteamyTea said:

You are talking about volumetric heat capacity.

If I said VHC only you would have understood (I'm being tongue in cheek)

I'll give it a go from now on.

[markocosic]

On 20/12/2022 at 12:28, Radian said:

 

I see you're using Tasmota to monitor the power draw using MQTT I imagine. 

 

Tasmota > MQTT > HomeAssistant on a Pi

 

Took an afternoon to setup. Tuya converting the smart plugs then firmware upgrading them was the tedious part. If you buy pre flashed plugs it'd be an absolute piece of cake.

 

A2A is on a proper utility meter but this didn't give the 10 sec interval data to see things waking up and sitting down again etc.

[SteamyTea]

1 hour ago, markocosic said:

A2A is on a proper utility meter but this didn't give the 10 sec interval data to see things waking up and sitting down again etc.

You could count the LED pulsing and use that data.

 

[JohnMo]

6 minutes ago, SteamyTea said:

could count the LED pulsing and use that data

There's an app "my electric meter" that does just that

[SteamyTea]

Just now, JohnMo said:

There's an app "my electric meter" that does just that

Yes, but you would have to glue a spare phone to the meter.

My monitor just needs a small washer glued over the LED, and it logs a timestamp every time the light pulses.

[markocosic]

 

@SteamyTea  The £10 plugs satisfied the high res curiosity for the A2A and a few other widgets - I have the utility grade meter read every minute along with some other mbus sensors for other purposes.

 

I do still need to pay with a Shelly and the induction hob though. I'm curious to document how that cycles at part loads / compare with other models. (gut feel is cheap hobs funny modulate down at all well)

 

[SteamyTea]

31 minutes ago, markocosic said:

gut feel is cheap hobs funny modulate down at all well

My induction hob pulses, like the old resistance hobs.  I think they all work like this.  

[markocosic]

Definitely not @SteamyTea - some modulate at a high frequency (like an inverter driven compressor) where others switch at a low frequency (like a fixed speed compressor cycling)

 

Even within the same hob/ring the behaviour can differ. The (IKEA) hob I have have appears to turndown from 100% to say 50%, then modulates from 50% to 0% on some rings; whereas on others it appears to modulate down the whole way.

 

Most noticeable on the little mocha pot when making coffee.

 

The cheap shite plug in sits in the table jobbie on the other hand just switches at a low frequency for anything less than 100%.

 

I would guess something to do with the cost of the power electronics to work at different outputs. Perhaps @Radian would know more?

[Radian]

For cost-effectiveness most hobs use a Single Ended Parallel Resonant Inverter to generate the EM field. It's generally optimised for a fixed frequency (resonance) somewhere above audible range. To modulate the heating effect this HF signal is then gated with a lower frequency PWM signal. Because it's all solid state control this can still be cycled on and of quite fast to effect a linear control using the shorter time constants of metal cookware. The difference between cheaper and more expensive models seems to be just how high this PWM frequency is?

[SteamyTea]

11 minutes ago, Radian said:

For cost-effectiveness most hobs use a Single Ended Parallel Resonant Inverter to generate the EM field. It's generally optimised for a fixed frequency (resonance) somewhere above audible range. To modulate the heating effect this HF signal is then gated with a lower frequency PWM signal. Because it's all solid state control this can still be cycled on and of quite fast to effect a linear control using the shorter time constants of metal cookware. The difference between cheaper and more expensive models seems to be just how high this PWM frequency is?

Looks like English but can't make sense of it.

Does it basically just turn it on and off to limit the power, or is the power limited by reducing the current input to thee induction coil?

[Radian]

35 minutes ago, SteamyTea said:

Does it basically just turn it on and off to limit the power, or is the power limited by reducing the current input to thee induction coil?

No written languages are good at capturing techie stuff like this. We have multiple different frequencies to consider - one is turning on and off the mains current  in an inductor at a higher frequency than the mains itself, this will have to be a fixed frequency to get resonance. Then this needs to be turned on and off to effect power control. Changing the drive frequency into the resonance circuit would modulate the cooking power but way too much energy would be dissipated in the drive circuit.

 

I think the main difference comes down to how the temperature is monitored for feedback. Cheaper slower hobs probably have less sophisticated sensing.

[SteamyTea]

4 minutes ago, Radian said:

turning on and off the mains current  in an inductor at a higher frequency than the mains itself, this will have to be a fixed frequency to get resonance.

So basically there are two circuits, one increases the mains frequency (50Hz) to the resonant frequency (400Hz maybe).  This produces a fixed power output.

The other circuit switched that resonance circuit on and off.  This then pulses the pan with energy.  More time off than on, the lower the temperature, more time on than off, the higher the temperature.

Yes?

[Radian]

18 minutes ago, SteamyTea said:

So basically there are two circuits, one increases the mains frequency (50Hz) to the resonant frequency (400Hz maybe).  This produces a fixed power output.

The other circuit switched that resonance circuit on and off.  This then pulses the pan with energy.  More time off than on, the lower the temperature, more time on than off, the higher the temperature.

Yes?

 

Wow, this has gone some way off topic!

 

Yes. The resonant frequency is always kept above audio frequencies - usually somewhere between 25kHz and 60kHz. I made a wireless power transfer system to charge our robot cat (he just drives on and off a flat plate) but that's running at over 1mHz. At such high frequencies the inductive reactance of that single loop of copper tube is not a short circuit but allows around 10W of power transfer from a 12V 1A power supply.

 

21 hours ago, markocosic said:

A2A is on a proper utility meter but this didn't give the 10 sec interval data to see things waking up and sitting down again etc.

 

10 second update? How about 0.02s 😁

 

That's a GIF of my real-time monitor for my DIY PV diverter. Every vertical slice is a mains cycle.

The little blue triangle  at the bottom is ~450 Joules going in and out of the virtual buffer in the utility meter.

The magenta dots are +/- Watts going through the meter (a few cycles with a 2kW dump load going either on or off).

Average watts (as billed for) is the green trace kept just below the zero line.

The black dashed horizontal zero line marks 1 second intervals.

The dashed vertical line that appears now and then is when the utility meter LED blinks.

[SteamyTea]

22 minutes ago, Radian said:

Wow, this has gone some way off topic!

Yes, but I now know that a stuffed toy can flick a switch with cat like reactions.

 

[Radian]

5 minutes ago, SteamyTea said:

Yes, but I now know that a stuffed toy can flick a switch with cat like reactions.

 

 

Mouser is approaching his 40th birthday. I kid you not.

 

[SteamyTea]

2 minutes ago, Radian said:

40th birthday

Wish I was.

I have so much advice for 40 year olds. 

Seems strange that when I was 40 I was lecturing undergraduates, no idea what has happened to them, except 1. But most will be getting close to 40 now.

[Sparrowhawk]

2 hours ago, SteamyTea said:

Wish I was.

I have so much advice for 40 year olds. 

This is my 40th year so go for it. I'd welcome it - though perhaps a new thread so as not to derail this one

 

[markocosic]

6 hours ago, Radian said:

The difference between cheaper and more expensive models seems to be just how high this PWM frequency is?

 

There's something more subtle going on.

 

For the same make/model of hob and the same pot the behaviour differs between rings of differing dimensions.

 

At high power all the rings PWM "quickly" (no discernible change in heat input to pot)

 

At lower power (say <50%) some rings switch to a low frequency PWM (of the order 3 second cycles) whereas others continue to do high frequency PWM all the way to the minimum setting.

 

This image from a Quora post seems to describe the behaviour.  What's the technical limiting factor that forces a ring to switch from "FM" to "PWM" though?

 

 

https://www.avdweb.nl/Article_files/Tech-tips/Panasonic-HV-inverter/Technical-Guide-Microwave-Ovens-with-Inverters.pdf