ASHP PID query

[Marvin]

Would someone please confirm my understanding of how a PID system works on an (my) ASHP and if I understand correctly what changing the settings would do.

 

A proportional–integral–derivative controller (PID controller) adjusts the output rate to avoiding excessive over shooting or under shooting of the set point when changing the temperature to meet the set point.

.

The Kp setting would be the difference at which the controller would react (mine set at 5C)

The Integral setting would be how long before the controller would act (mine set at 200s)

The Differential would indicate something to do with the relationship between 2 PIDs? (mine is set at 0s)

 

As I tend to understand that the ASHP "runs" most efficiently when at the lowest temperature to achieve the desired result, and for at least 10 minutes a go, I was trying to understand how altering the PID settings would effect this optimum aim. My guess is the answer as what to do with it would be "Don't touch it"?

 

Thanks

 

Marvin

 

 

 

 

 

 

[dpmiller]

Good Q. I haven't fiddled with those tbh, rather using the temp difference and stop temp difference (inverter overshoot) to allow the system to ramp down a bit more smoothly.

 

In the installer menu the pump speed is configurable too, if you want to try altering the DeltaT outside that in U08- do you see the pump speed changing as the inverter throttles down?

[ProDave]

Which ASHP?

 

To be honest i have not encountered one with full PID control.  PID is something normally used in machine control or on furnaces etc where you are after both accurate and fast response.  That does not normally apply to an ASHP heating a house.

[dpmiller]

It's the Cool Energy with the Carel controller.

 

Edit: presume it to do with how the inverter winds up and down to reduce overshoot but it's not explained in the book of words.

Edited December 28, 2021 by dpmiller

[dpmiller]

... to explain a wee bit further, these units can be configured to control *either* on flow OR return temp depending on application, as well as having a tank thermistor. Control on flow seems to give a hard limit, whereas control on return gives a softer response with more of a DeltaT (suits me better)

 

While the controller doesn't have any in-house temp sensing- relying on dry stat contacts- it does have the full gamut of weather compensation trickery as well as low noise (fan control) modes and configurable defrost, pump speed,  etc etc. It also has an inbuilt 7-day programmer for flow temps.

[Marvin]

28 minutes ago, dpmiller said:

... to explain a wee bit further, these units can be configured to control *either* on flow OR return temp depending on application, as well as having a tank thermistor. Control on flow seems to give a hard limit, whereas control on return gives a softer response with more of a DeltaT (suits me better)

 

While the controller doesn't have any in-house temp sensing- relying on dry stat contacts- it does have the full gamut of weather compensation trickery as well as low noise (fan control) modes and configurable defrost, pump speed,  etc etc. It also has an inbuilt 7-day programmer for flow temps.

Yes... my main challenge is that I am trying to use the "weather compensation trickery" to only effect the heating/cooling and not the hot water.

[dpmiller]

Do you have v6.6 of the manual? It has a bit more info on the slopes.

[dpmiller]

Ok I've just delved into the hidden menu and can confirm that the DHW curve is minimal, running from 50 @ 0c ambient to 45 @ 30c ambient.

[Marvin]

2 hours ago, dpmiller said:

Do you have v6.6 of the manual? It has a bit more info on the slopes.

Yes.

 

2 hours ago, dpmiller said:

Ok I've just delved into the hidden menu and can confirm that the DHW curve is minimal, running from 50 @ 0c ambient to 45 @ 30c ambient.

After discussions with the boss, we think that we will turn off the weather compensation option and use the manual setting for the temp of the heating water.  

[dpmiller]

6 minutes ago, Marvin said:

Yes.

 

After discussions with the boss, we think that we will turn off the weather compensation option and use the manual setting for the temp of the heating water.  

if you had the super secret magic password, you could change the slope for DHW to disable WC for it...

:cough:

Prg- 9999- Fan configuration- last page (F18 I think)

 

?

[Marvin]

Thank you for this.I had the key but didn't know what it was for. I will have a go next week.

 

[ReedRichards]

Would one ever want to use Weather Compensation for DHW (it's not even an option with my LG ASHP)?  Maybe in summer I don't need the water I shower with to be as hot but I think I want to wash dishes in water at the same temperature all year round.

 

I have used a few PID controllers in my time but they have all been capable of learning.  So as long as the initial parameters are not too far wrong in the first place the controller will automatically improve on them, presumably in this instance in order to control the temperature better by minimising the undershoot/overshoot.    

[Marvin]

42 minutes ago, ReedRichards said:

 Maybe in summer I don't need the water I shower with to be as hot but I think I want to wash dishes in water at the same temperature all year round.   

Yes and as our place is expected to be cool in summer, we will probably want to have a shower at the same temperature, and the loss of heat from the tank would be about the same as its all insulated.

[ReedRichards]

If you skip to the "Tuning" section at the bottom of the page, this website gives instructions on how to tune a PID controller: https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=9013 

[joth]

15 hours ago, ReedRichards said:

Would one ever want to use Weather Compensation for DHW (it's not even an option with my LG ASHP)?  Maybe in summer I don't need the water I shower with to be as hot but I think I want to wash dishes in water at the same temperature all year round

 

Altering the DHW flow temp is less about the temperature of the water delivered to the taps, and more about adjusting the volume of heat energy stored in the tank.

If cold weather increases the demand on DHW in terms of L per day, then I guess weather compensation makes some sense, but for my setup I adjust based on number of people in the house as this seems to be the main contributor. The weather forecast is of some vague use to predict how much solar redirect I want to leave space for for tomorrow, or making use of any export generation as it's happening.

 

[SteamyTea]

Just done a quick chart about a heating curve.

Assumed 3 different power levels, half power, ideal power and double power, the numbers are for reference and not actual power.

 

 

Because heating starts rapidly, then slows, for any power input, it should be possible to initially run a heat source at lower power for a set time, then ramp up power later on.

This could be useful if using PV to supplement the grid supply as it would reduce imports.  It may also be useful to reduce cycling and frosting.

 

[dpmiller]

don't you need to consider the Delta as well tho, both across the source (the ASHP's internal heat exchanger) and the "radiator", whether it be UFH or wall panel?

 

The controller we're looking at here is smart enough to consider the compressor and gas combo's efficiency islands and will throttle back based on energy transfer-  it'll slow the compressor down, speed the water pump up, adjust the superheat levels and fan speed to keep the gas pressures sensible. 

[SteamyTea]

8 minutes ago, dpmiller said:

adjust the superheat levels and fan speed to keep the gas pressures sensible.

Is that how your HP controls temperature by keeping the pressure within fixed limits?

PV/T = C and all that.

[dpmiller]

2 minutes ago, SteamyTea said:

Is that how your HP controls temperature by keeping the pressure within fixed limits?

PV/T = C and all that.

 

All of the above, yes, kinda. Variable limits actually...

I think Carel and whoever wrote the GUI show a bit more of the inner workings of these than some of the more mainstream consumer brands tbh and I'm pretty nosey

The control system is modular with an internal ModBus between portions- Inverter, fan drive, analogue ins, EV stepper motors. The inverter and mainboard both have stored profiles for the compressor tying expected pressures vs power inputs etc, as an envelope that rest of the sensors and controls work within.

[SteamyTea]

3 minutes ago, dpmiller said:

All of the above, yes, kinda. Variable limits actually

Seems a simple way to control it.  It should stop the HP doing something that is impossible, i.e. reach a fixed output temperature when the input temperature is extremely low.

[Marvin]

Decided I'm not going to mess about with the PID settings. ? 

 

However the adjusting of the weather compensation will be done to suite our home requirements. The aim is to control the temperature in the buffer tank, bringing it closer to the water temp required to keep the house at the right temperature, whilst still cycling for at least 10 minutes of heating by spreading the temperature stops, if you know what I mean. This will be achieved by trial and error.  We're running at 35C set 37C top and 29 min and were quite hot. The weather compensation sat at 40C with the present external temperature.

 

 

 

 

 

 

 

[Marvin]

On 29/12/2021 at 11:27, joth said:

 

Altering the DHW flow temp is less about the temperature of the water delivered to the taps, and more about adjusting the volume of heat energy stored in the tank.

If cold weather increases the demand on DHW in terms of L per day, then I guess weather compensation makes some sense, but for my setup I adjust based on number of people in the house as this seems to be the main contributor. The weather forecast is of some vague use to predict how much solar redirect I want to leave space for for tomorrow, or making use of any export generation as it's happening.

 

We are trying to achieve this:

1. The minimum hot water tank temperature required to produce enough hot water to meet our daily needs.
2. An increase in the hot water tank temperature as a result of excess PV energy which can reduce the necessity of the ASHP heating the hot water tank the next day.
3. The heating of the hot water tank over 60C after the hot water tank being below this for a consecutive 10 days.

To achieve 2. we have installed a SOLiC 200 Model AF2.1

To achieve 3. we have a 10 day delayed relay, which is wired to reset if the hot water tank reaches over 60C, and heats the tank if this is not achieved.( and then resets)

To take advantage of cold bright days where excess PV is generated which can heat the hot water tank, we are aiming to keep the tank to our minimum hot water temperature requirement. Also the ASHP is less efficient at producing hot water in the colder weather. 

 

[ReedRichards]

19 minutes ago, Marvin said:

... we have installed a SOLiC 200 Model AF2.1

 

 

Is it battery compatible?  If , for example, you boil an kettle and the battery is supplying some or all of the power, when the kettle switches off the battery cannot drop its output immediately so discharges to the grid as it ramps itself down.  So you don't want that to be seen as spare solar power by your diverter and you probably need to have the diverter turn itself off for, say, 30 seconds every 10 minutes to check that the export is still there.  If it's not you were just draining the battery.

[Marvin]

On 28/12/2021 at 14:16, dpmiller said:

 you could change the slope for DHW to disable WC 

 

 

?

This is all about the set up of the Weather Compensation option on my ASHP

 

Yes. I have changed the hot water set point in the Weather Compensation to a constant temperature. Thanks @dpmiller.?

 

Whilst working on this I will adjust the heating temperature and outside temperature set points because once the outside temperature is above about 8C our home requires very little heat (we have run the buffer at 35C when the outside temp is 5C with no problem.)  

 

**** For those thinking they can do the same***These changes are in response to the location, BUILDING orientation, construction and use of our property and I would doubt that yours would be exactly the same.  

[Marvin]

13 minutes ago, ReedRichards said:

 

Is it battery compatible?  If , for example, you boil an kettle and the battery is supplying some or all of the power, when the kettle switches off the battery cannot drop its output immediately so discharges to the grid as it ramps itself down.  So you don't want that to be seen as spare solar power by your diverter and you probably need to have the diverter turn itself off for, say, 30 seconds every 10 minutes to check that the export is still there.  If it's not you were just draining the battery.