Are complicated controls/thermostats/hydraulics needed for ASHPs at all?

[Gary68]

Its probably the same as you are achieving through HA but for those who don't use automation and have an Ecodan with Melcloud who want to boost heating at a cheap fixed time it is possible through the app.

 

If you go through to the orange heating screen in the app and press actions then timer you can can create a schedule that turns on the heatpump at the fixed flow temp your controller is set to for a certain period then reverts to weather comp at the end of that period.

[jack]

4 hours ago, joth said:

PAW-AW-MBS-H supports H generation onwards, via the CN-CNT port.

 

Thanks. I did look into the modbus module when buying the ASHP, but it was several hundred quid + the prospect of me having the figure out how it all interfaced with Loxone. Seemed like too much effort at the time - I may revisit at some stage, but I already have too many projects on the go!

 

4 hours ago, Johnnyire said:

Is it not a simple solution to just increase the temperature on the loxone schedule during this period of low cost tariffs?

 

Unfortunately (well, unfortunately for this approach), the time constant on our slab is too long for this to work. At the current flow temp settings in mild winter weather, it I turn the heating on, it takes just under three hours to show any change in temperature (+0.1 degrees). The temperature will continue to slowly rise for another three or more hours after the heating is turned off.

 

I think the solution is just to bump of the flow temp across the weather compensation curve and experiment with how the house reacts.

 

3 hours ago, joth said:

Just to riff on this a bit more, what I've effectively done now is create a WC curve that allows my heatpump to put in a day's worth of energy requirement in about 4 or so hours runtime. I have octopus go so having Loxone boost  the room target temp between midnight to 4am pretty much ensures the ASHP just runs during cheap rate, and again a bit sometime during the day if solar gains are low. This works well enough I'm not so motivated to mess with direct control of the UFH flow temperature 

 

Thanks. If I understand you correctly, that's what I was proposing above when I said:

 

20 hours ago, jack said:

Depending on the rate at which my slab can absorb energy, the solution may be to just increase the flow temperature across the weather compensation curve. That might be enough to get me over the line. The problem I have is modelling all of this. I may just need to try it out when it gets colder.

 

There'll be some experimentation involved, but it's an interesting project, plus I can start working on it now even before I'm back on the cheap overnight rate.

[joth]

@jack got it that all makes sense. Sorry you've ended up explaining each point 5 times lol.

Our UFH is in just 75mm screed which is pretty good to freewheel a constant temperature through the day, but also fairly fast responding when we do heat it so boosting the room setpoint does work ok for cheap rate. It's a fairly simple regression analysis to work out the daily kWh input needed for a given outdoor temperature, so sooner or later ASHP will have learning thermostats that solve this in a nicer way.

 

[joth]

4 hours ago, Gary68 said:

Its probably the same as you are achieving through HA but for those who don't use automation and have an Ecodan with Melcloud who want to boost heating at a cheap fixed time it is possible through the app.

 

If you go through to the orange heating screen in the app and press actions then timer you can can create a schedule that turns on the heatpump at the fixed flow temp your controller is set to for a certain period then reverts to weather comp at the end of that period.

interesting point. I've always been put off playing with this on the basis the schedule is entirely driven from the cloud so an outage will leave it in an odd state. (And, it's in competition with the FTC6 built in schedule function and the schedule in my HA). you're right though this is the easiest way to set variable flow temp.

(The other would be to abuse the zone 1 vs zone 2 settings, have them both plumbed to a single set of emitters but switch between which one calls for heat based on time of day. No good for me though as I need the dual zones for its intended purpose, as i have different zones for UFH vs FCU)

 

[Adrian Walker]

29 minutes ago, joth said:

interesting point. I've always been put off playing with this on the basis the schedule is entirely driven from the cloud so an outage will leave it in an odd state. (And, it's in competition with the FTC6 built in schedule function and the schedule in my HA). you're right though this is the easiest way to set variable flow temp.

(The other would be to abuse the zone 1 vs zone 2 settings, have them both plumbed to a single set of emitters but switch between which one calls for heat based on time of day. No good for me though as I need the dual zones for its intended purpose, as i have different zones for UFH vs FCU)

 

 

Have a look at what @TerryE is doing with regards to Octopus and planning his heating and hot water based on the very cheap rates that they publish 24 hours in advance. 

[SteamyTea]

18 minutes ago, Adrian Walker said:

 

Have a look at what @TerryE is doing with regards to Octopus and planning his heating and hot water based on the very cheap rates that they publish 24 hours in advance. 

And a weather forecast, though energy usage and weather are generally closely related.

[siletto]

And how would you combine these forecasts and WC controls with cooling?

 

I plan either fancoil and/or UFH cooling, maybe a cooled ceiling type system, but controlling the cooling demand per room, and non-zoned UFH heating seems not to have so many off-the-self thermostat options.

 

Making a simple Arduino, or Home Assistant or PLC thermostat system is not too far from me, but then I'll lose the TPI learning feature, I am not experienced enough to program this algorithm.

Edited November 20, 2023 by siletto

[JohnMo]

3 minutes ago, siletto said:

non-zoned UFH heating seems not to have so many off-the-self thermostat options.

Simple thermostat is all you need (thick screed 0.1 hysterisis, thin screed any thermostat will do), if single zoned with a heat pump on weather compensation, you can actual run without a thermostat. Mine has done nothing for weeks, outside temperature has ranged from -3 to +14

 

Basically if the house becomes hotter due to solar gain etc, the heat input into house reduces due to floor to room dT reducing. The return flow to heat pump stays slightly warmer, heat pump reduces input to maintain dT across flow and return. Your WC curve needs to be setup well for this to work in practice.

[Beelbeebub]

26 minutes ago, siletto said:

And how would you combine these forecasts and WC controls with cooling?

 

I plan either fancoil and/or UFH cooling, maybe a cooled ceiling type system, but controlling the cooling demand per room, and non-zoned UFH heating seems not to have so many off-the-self thermostat options.

 

Making a simple Arduino, or Home Assistant or PLC thermostat system is not too far from me, but then I'll lose the TPI learning feature, I am not experienced enough to program this algorithm.

You can use off the shelf algorithms like the PID library.

 

My current mini project is to control my UFH flow temp (from a thermal store) by controlling a thermoelectric UFH zone valve on the cold return from the blending valve. The idea is to sense the outside air temp (from a temp probe in the heat recovery air inlet) and calculate a desired slab temp (assumed to be the return flow from the slab). The system then controls the valve on/off to achieve a desired flow temp to the slab that is 5C higher than the desired slab temp.

 

My tip.is to use a M0 Arduino rather than the old atmega type  

 

I favour a seeeduion model, with their "grove" shield on top. This makes all the sensors plug and play.  Use DS18b20 temp sensors and M5Stack relays 

 

DM me if you want any info.

[JohnMo]

@BeelbeebubOr just use one of these off the shelf items to control from a buffer 

https://www.ebay.co.uk/itm/126168847679?hash=item1d603fd53f:g:dzwAAOSw93JlRK6R&amdata=enc%3AAQAIAAAAwJE0AgmF7NYnmL%2Bb3NHl2nvvJs%2BbcZvTFN%2BOBVKGewKstjeKAYl2eR3SSF2IJmsxwJYj09wDR9tEYcC1gFA%2Blp2Q5jIZ4TqaTTGhDjMjQuo6yjexVnRtNY0jqE%2BLMSSMxYRgwEFD5E3kVXPIa%2BDEcgcwiYhvsOH8C6%2BCc4Gb6M1KyeGASY4cuRXY2VK6cr0%2FBZSNOPYEQ7HEs1LuEpFlzPFOgQfLpBBaxK8a9yearpCZWrEPzaT5vybPfl8mZhHgaw%3D%3D|tkp%3ABk9SR4r5ub_9Yg

 

 

Clima500.pdf

[Beelbeebub]

23 minutes ago, JohnMo said:

@BeelbeebubOr just use one of these off the shelf items to control from a buffer 

https://www.ebay.co.uk/itm/126168847679?hash=item1d603fd53f:g:dzwAAOSw93JlRK6R&amdata=enc%3AAQAIAAAAwJE0AgmF7NYnmL%2Bb3NHl2nvvJs%2BbcZvTFN%2BOBVKGewKstjeKAYl2eR3SSF2IJmsxwJYj09wDR9tEYcC1gFA%2Blp2Q5jIZ4TqaTTGhDjMjQuo6yjexVnRtNY0jqE%2BLMSSMxYRgwEFD5E3kVXPIa%2BDEcgcwiYhvsOH8C6%2BCc4Gb6M1KyeGASY4cuRXY2VK6cr0%2FBZSNOPYEQ7HEs1LuEpFlzPFOgQfLpBBaxK8a9yearpCZWrEPzaT5vybPfl8mZhHgaw%3D%3D|tkp%3ABk9SR4r5ub_9Yg

 

 

Clima500.pdf 939.75 kB · 1 download

but where's the fun in that? 😁

 

 

[siletto]

2 hours ago, JohnMo said:

Simple thermostat is all you need (thick screed 0.1 hysterisis, thin screed any thermostat will do), if single zoned with a heat pump on weather compensation, you can actual run without a thermostat. Mine has done nothing for weeks, outside temperature has ranged from -3 to +14

 

Basically if the house becomes hotter due to solar gain etc, the heat input into house reduces due to floor to room dT reducing. The return flow to heat pump stays slightly warmer, heat pump reduces input to maintain dT across flow and return. Your WC curve needs to be setup well for this to work in practice.

So you don't think advanced TPI algorithms do much good with heat pumps?

[JohnMo]

2 hours ago, siletto said:

So you don't think advanced TPI algorithms do much good with heat pumps?

From my perspective - no, tried with the gas boiler, it had built-in algorithms room temperature just yo-yos. Those algorithms were also controlling flow temperature. On an ASHP you are just giving an on off signal.

 

Room compensation comes with some ASHP, but that is only any good with radiators as it requires a short response time.

 

For me - Either a small hysterisis thermostat and almost fix flow temp (very small WC curve) to switch on/off the ASHP or a well set WC curve are the only things that get my vote.

[siletto]

15 minutes ago, JohnMo said:

From my perspective - no, tried with the gas boiler, it had built-in algorithms room temperature just yo-yos. Those algorithms were also controlling flow temperature. On an ASHP you are just giving an on off signal.

 

Room compensation comes with some ASHP, but that is only any good with radiators as it requires a short response time.

 

For me - Either a small hysterisis thermostat and almost fix flow temp (very small WC curve) to switch on/off the ASHP or a well set WC curve are the only things that get my vote.

Thanks for the reply!

 

What's your thought on combining it with separate room control possibility for cooling?

 

Adjustable cooling is mandatory in every room, as We don't feel like operating the whole cooling system nonstop, just on demand for some hours on the hottest days.

 

The Innove "airleaf" fancoil is the most attractive for me, but IR remote control would be the best, missing from every cabinet type fancoil.

[RobLe]

Present ASHP monoblocs are best installed with WC, which is basically a feedback loop controlling the flow temperature by adjusting the compressor and fan and pump power based on a temp sensor outside and a controller in the hose.  I honestly don't why they bother with the feedback loop?  Why not control the ashp output power (ie compressor/fan/pump speed) based on the outdoor temperature?  The reason I suggest this, is that makes the system agnostic as to radiator sizing.  Sure more rads running together or UFH will be more efficient - but this requires WC changes, which a regular plumber can't be bothered with. 

 

So with this idea when installing, maybe you'd figure you need a 9kW ashp say, plumb it in.  Call for heat like with a gas boiler it's probably replacing in the uk - and it delivers 9kW if it's -5C outside (where the unit is, no need for wires), or 3kW if it's 15C or whatever.  On top of this, as has been suggested, a thermostat for fine tuning (which you likely have anyway)- it won't kick in and out too much as the system power is only a little more than needed at any one time.  And another control wire for DHW - this would just go full wack until 60C flow is achieved, then off.

 

I just don't get why present units use weather compensation, which adds a whole bunch of complexity to give constant flow temperature, which isn't actually useful - we need constant power!

 

Nb: for ref, we have a diy gshp, constant power 2.5kW unit controlled with a thermostat.  No fuss.

 

 

[HughF]

On 20/11/2023 at 13:41, RobLe said:

Present ASHP monoblocs are best installed with WC, which is basically a feedback loop controlling the flow temperature by adjusting the compressor and fan and pump power based on a temp sensor outside and a controller in the hose.  I honestly don't why they bother with the feedback loop?  Why not control the ashp output power (ie compressor/fan/pump speed) based on the outdoor temperature?  The reason I suggest this, is that makes the system agnostic as to radiator sizing.  Sure more rads running together or UFH will be more efficient - but this requires WC changes, which a regular plumber can't be bothered with. 

 

So with this idea when installing, maybe you'd figure you need a 9kW ashp say, plumb it in.  Call for heat like with a gas boiler it's probably replacing in the uk - and it delivers 9kW if it's -5C outside (where the unit is, no need for wires), or 3kW if it's 15C or whatever.  On top of this, as has been suggested, a thermostat for fine tuning (which you likely have anyway)- it won't kick in and out too much as the system power is only a little more than needed at any one time.  And another control wire for DHW - this would just go full wack until 60C flow is achieved, then off.

 

I just don't get why present units use weather compensation, which adds a whole bunch of complexity to give constant flow temperature, which isn't actually useful - we need constant power!

 

Nb: for ref, we have a diy gshp, constant power 2.5kW unit controlled with a thermostat.  No fuss.

 

 

If there's an indoor sensor, then that's load compensation... Weather comp is purely outdoor sensor based.

[joth]

On 17/11/2023 at 15:52, joth said:

On 17/11/2023 at 11:47, Gary68 said:

Its probably the same as you are achieving through HA but for those who don't use automation and have an Ecodan with Melcloud who want to boost heating at a cheap fixed time it is possible through the app.

 

If you go through to the orange heating screen in the app and press actions then timer you can can create a schedule that turns on the heatpump at the fixed flow temp your controller is set to for a certain period then reverts to weather comp at the end of that period.

interesting point. I've always been put off playing with this on the basis the schedule is entirely driven from the cloud so an outage will leave it in an odd state. (And, it's in competition with the FTC6 built in schedule function and the schedule in my HA). you're right though this is the easiest way to set variable flow temp.

(The other would be to abuse the zone 1 vs zone 2 settings, have them both plumbed to a single set of emitters but switch between which one calls for heat based on time of day. No good for me though as I need the dual zones for its intended purpose, as i have different zones for UFH vs FCU)

 

Thanks again for this @Gary68.  I had another go with it, and actually got something working very nicely  (in terms of performance in practice, most definitely not for elegance of design).

 

1/ Loxone uses dry contact inputs to control call for space heating (UFH and FCU zones based on room stats and house occupancy), and also sets the "Smart grid - On recommendation" inputs to FTC (based on excess PV generation, or octopus Go cheap rate)

2/ The ecodan FTC local controller has a schedule to disable DHW reheat at certain times of day (basically for evening CO2 peak, and after bedtime up until the overnight cheap-rate starts).

3/ The MELCloud app has a schedule setup to flip UFH into Target Flow temp mode (t=40degC) during cheap rate, and back to Weather comp mode at the end of cheap rate. Bonus: I have created seasonal schedule, so it can finally automatically enable cooling mode from May to Oct, no longer needing the twice annual mode flip.

 

It's sad but I need all three control systems, as each is doing something that can only be done via one of those interfaces, pretty much as listed above.

 

Other challenges I had to overcome

- the actual flow temps can't be set in the MELcloud schedule, so you just have to hope that what was last set manually  still takes effect when the schedule turns to that mode

- the local controller does not support automatic day light saving (no NTP support is very sad for a wifi connected device in 2024).  I always forget to manually set it to BST, which messes up the DHW cycle. So as a workaround I leave it always in GMT, I have set the controller cooling/heating seasons to match DST as best I can (basically March to Nov) and I do the mental arithmetic to configure the "summer" schedule to correct it for DST. Going to stick a big reminder label to the unit about this, as I will always forget this!

- the MELcloud app crashes if you try and enable seasonal schedule. I debugged the javascript and manually crashed over the problem line (spoiler: they misspelt "noXss" as "noxss" in a dictionary lookup) so managed to enable this feature. I attempted to report to mitsubishi but their web feedback form also crashed on me, LOL.  If anyone needs pointers I can try and write up the steps a bit more.

- our bamboo flooring does not like to go up to 40degC, so I have Loxone monitor slab temp in those rooms and close off the corresponding manifold actuator when it exceeds 26C. The majority of the GF is porcelain so this emits well during this cheap rate boost period.

 

Last night was cold enough to need heating on, but not cold enough to hit defrost cycle, and it's the smoothest blast of continuous cheap rate lecy I've managed to eek out of the thing, with no cycling:  over 2kW sustained through the whole period up until DHW reheat cuts in at 3.30am. (In weather comp mode it only draws about 0.5kW even when it's subzero outside; great for maximizing COP but not so good for getting max value out of the overnight cheap rate)

 

 

 

 

Here you see the bamboo flooring modulating very nicely at 26C, while porcelain floor is still ramping up temp throughout the boost heating period: