Compensation curve - compensating against what?

[DeanAlan]

Context:

• I have an Ecodan R32 8kw ASHP installed.
• Installer (Mitibushi platinum installer) set it up.
• Wet UFH installed by others.
• UFH control system by me - zigbee temperature sensors, home assistance, raspberry pi and 12 relays to control the 12 port manifold actuators and Call 4 Heat and UFH  manifold pump.
• I have the UFH set up as a single zone at the moment - to start with- with a daytime temperature target and night time a couple of degrees lower.

 

Question:

• The installer had the ASHP heating on its compensation curve which from my reading looks to be as efficient as possible in use of energy given outside temperature and inside temperature BUT the ASHP isn't sensing room temperature at all - just responding to Call 4 Heat. It has flow and return temperature sensors but that's it. Is this correct? Should I have it set in the other mode of fixed temperature (and what would that be)?

[JohnMo]

If the curve is set correctly the room temps manage themselves, with UFH the response is so slow feedback on room temp is pretty much meaningless for room compensation.  As the flow temp is constantly being adjusted but floor takes hours to respond, when it the control changes the settings and it just chases its tail.

 

Your thermostat just needs setting a degree or so over your target temp.  If room temps are getting to high, compensation curve needs lowering, if individual room are getting too hot the UFH loop flow needs to be reduced.

[DeanAlan]

Thanks @JohnMo still a little confused (bare with me, I'm smart honest 🙂 

What would it mean for the curve to be set correctly and what temperatures is it comparing and compensating against as it has no idea about my room temps, just the flow and return temps (plus outside temp).

 

Is the flow return temperature the temp being used to govern the ASHO when in compensation mode? For example if room temp target is 21 degrees and I have stat at 22 degrees should the cold end of the compensation curve be the flow return temp at say 30 degrees?

 

Seems hard to get chapter and verse on this stuff - is it written down somewhere in general and then in Ecodan speak?

 

Thanks for any and all assistance!

 

cheers,

-Dean

[JohnMo]

The basics are

 

For a given temperature difference between inside and outside the average heat loss will always be the same.  If you increase the temperature difference i.e. its colder outside, you need to add more heat to floor to compensate for the heat loss.

 

Your controller will measure flow and return and alter one or the other to a hotter set point as it gets colder outside, and less hot as the outside temp increases.

 

Now if the sun comes out and even though its cold outside, if it heats the house through thermal gain, the thermostat will trigger and tell the heating to go off.  Once the the houses cools the thermostat will then tell the heating to come back on again.

 

Now the problems come form having a thick screed and react times.  Our house has a 100m concrete floor and it takes about 6 hours to move a degree, so if I'm not careful the house temp can be all over the place.  Its a bit of a process to find what suits your house.

 

Trouble for most the controllers they are great for normal leaky houses, but low energy house with thick concrete floors it all a bit hit or miss with the control. 

[ReedRichards]

There's terminology.  If the controller works by adjusting the leaving water flow temperature (or perhaps it's the return water) according to the outside temperature it's called Weather Compensation.  A lot of heat pumps and gas boilers can do that but its more effective in reducing the running cost with a heat pump than a gas boiler. 

 

If the controller adjusts the water flow temperature according to the difference between the setting on the room (i.e. house) thermostat and the actual temperature in the room it's called Load Compensation.  For economy, the benefit of Load Compensation is that it enables the heat source to modulate down its output when the room temperature is close to the set temperature.  A lot of gas boilers can do this and some heat pumps, but in the case of heat pumps, only if you use the manufacturer's thermostat.

 

I'm not sure if this terminology is used outside the UK.  Consequently, foreign-made heat pumps may use their own terminology but for the same two types of control.       

Edited December 6, 2022 by ReedRichards

[DeanAlan]

Thanks

 

We have 50mm anhydride screed so little faster reacting that yours I imagine @JohnMo.

 

@ReedRichardsyes that is what I am thinking re the ASHP being able to turn itself down as it approaches the room setpoint but to do that a) it needs to know the room temperature - which in my case it isn't being given b) it needs it for individual zones that are on and calling for heat - once again not in my house.

 

I don't know if the Ecodan is doing Weather Compensation or Load Compensation. Just "Compensation Curve"

 

[PhilT]

28 minutes ago, DeanAlan said:

Thanks

 

We have 50mm anhydride screed so little faster reacting that yours I imagine @JohnMo.

 

@ReedRichardsyes that is what I am thinking re the ASHP being able to turn itself down as it approaches the room setpoint but to do that a) it needs to know the room temperature - which in my case it isn't being given b) it needs it for individual zones that are on and calling for heat - once again not in my house.

 

I don't know if the Ecodan is doing Weather Compensation or Load Compensation. Just "Compensation Curve"

 

Do you have the MELcloud app or any way of viewing and selecting the options? There are three - "Room", "Flow" and "Curve".

 

"Room" is full auto adaptation which uses both room temp and outside temp to "learn" how to manage power most efficiently to achieve and maintain target room temp, and takes some time, but is unfortunately not available without a Mitsubishi remote room controller, and Mitsubishi advise against using it for UFH anyway.

 

"Flow" is user selected flow temp

 

"Curve" (Weather Comp) is great for UFH if you put the work in to get it well balanced as JohnMo mentioned. I have radiators throughout and have been trying "Room" for a few weeks. I found it did work well mostly, but not quite as well as WC with manual intervention (the Mitsubishi central controller allows +/-6degC) to lower the curve when room temp is reached.

 

Do you know how to select and manage your "Curve" setting? It doesn't appear to be available on the MELcloud app, only on the central FTC6 controller.

[ReedRichards]

Quote

Wireless Remote Controller & Receiver PAR-WT50-E / PAR-WR51-E Up to 8 wireless controllers can be used per system - giving better control of a building, allowing different set points per room. Temperature display every 0.5ºC - allowing the temperature to be set to minimum increments for maximum user comfort. Load and Weather Compensation - This function allows the system to learn how the building is reacting to the heating system and adjust accordingly to get the best possible efficiency, whilst still delivering high user comfort levels. Hot water button (DHW) - allowing the hot water to be switched on and off if heating is required. 2-zone control - ideal for properties with 2 heating zones, i.e, radiators upstairs, underfloor heating downstairs. Holiday mode - enabling the user to quickly and easily set the system on to a lower energy saving mode with the touch of a single button.

 

This is from an Ecodan brochure explaining the capabilities of the Wireless Remote Controller and Receiver Accessory.  I did a copy and paste but the formatting was lost; the original is here: http://library.mitsubishielectric.co.uk/pdf/download_full/798   

[billt]

8 hours ago, DeanAlan said:

What would it mean for the curve to be set correctly and what temperatures is it comparing and compensating against as it has no idea about my room temps, just the flow and return temps (plus outside temp).

 

Is the flow return temperature the temp being used to govern the ASHO when in compensation mode? For example if room temp target is 21 degrees and I have stat at 22 degrees should the cold end of the compensation curve be the flow return temp at say 30 degrees?

 

It is compensating for changes in outside temperature, when the outside temperature drops the heat loss increases so the water flow temperature needs to increase to compensate.

 

A properly designed weather compensation system has two adjustments, the slope of the curve and the offset of the curve and it's a bit of a tedious trial and error job to get them to match the house characteristics properly - it's an open loop system.

 

The USAians seem to call it outdoor reset control.

 

https://www.pmengineer.com/articles/86699-outdoor-reset-control-no-quality-hydronic-system-should-be-without-it

https://www.pmengineer.com/articles/91930-how-to-use-outdoor-reset-controls-in-renewable-energy-heat-source-systems

[DeanAlan]

Thanks for the articles @billtand @ReedRichards

 

Fully integrated - with the ASHP controller understanding the target and actual room temperatures and outside temperature I can see what it is trying to do. Think it breaks down when there are multiple zones and simple Call 4 Heat request to the ASHP controller from the UFH wiring centre and stats.

 

In my case the UFH controller is my own Home Automation prototype based on Raspberry Pi, Zigbee room temperature sensors and relays to control the UFH actuators and call 4 heat request.

 

If I could find out how to talk to the ASHP controller in a more advanced way to work with its compensation curve then I think there is room for improvement but getting the details for that are unlikely. I guess if I could find the inputs to the ASHP controller for its dormant room temperature sensors (I think it can handle 2 zones) then I could manipulate what the ASHP is perceiving as its idea of zone temperature based on what my controller is doing with the ASHP manifold and the more zones it control (my manifold has 12 zones but I don't in anyway see them being operated independently - has that size due to loop length limitations)

[HughF]

I believe the ecodan supports control over modbus 485….. that’s your avenue into automated control.

[DeanAlan]

Nice! Thanks @HughFI can see more 2023 project (to complete before winter 2023 kicks in).

I'm a SW Engineer by trade so this is the only part of the build that I can truly help with beyond demolition work and cutting bits of Celotex.