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Mitsubishi Ecodan & Raspberry Pi automations

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(@sunandair)
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@walkers-heatpump yes I get your curiosity…

in our case, the first start-off after setback for our machine appears to be the slowest to build heat so we’re increasing the time period then the following steps are a bit closer so the HP isn’t tempted to slow down too much. I guess as @derek-m states it’s about acting on the right information based on the individual house/HP relationship.

The challenge being: what is the right information? 😅

(And what’s best if you then throw Cosy Tarrif into the mix)


   
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(@sunandair)
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(Clarification on some new terminology used in the last few posts… incase anyone hasn’t seen these kind of acronyms)

Example:
“A basic controller has two inputs, the desired value or setpoint (SP) and the measured value or process variable (PV), along with one output (O/P). When PV = SP, O/P does not change.”

  • PV= Current Room Temperature (Process Variable)
  • SP = Set Point or Target Room Temp.(traditionally the Thermostat Setting)
  • O/P = Output or LWT (leaving water temperature) or Primary Flow. This is the temperature of the water leaving the heat pump.
  • RWT = Returning Water Temperature or Primary Return. This is the temperature of the water coming back to the Heat pump having warmed up the radiators or emitters.
  • DT = DeltaT or Diferential Temperature. This is the difference in temperature between “Output” pipe and “Return” pipe. This is a way of showing how much energy has been absorbed by the property at a given point in time…but is an ongoing process of energy transfer if the heat pump is continuing to operate at that speed and compressor output.

   
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(@sunandair)
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MELCloud shows Auto Adapt modulate to pass room temp by 1c.

Yesterday our heating was off all day then- Last night we cold started the heating by moving the target temperature 1/2 a degree above the existing room temp. Ie the room stat showed 18.5c at 19.05pm so we moved the target temperature up to 19c.

It took about 40 minutes to reach 19c whereupon it then abruptly switched itself off. 

2FED3FAC BE29 4736 9C35 E7137CC5C4DD

 

20 minutes later it switched itself back on even though the room thermostat was still showing the target temperature was reached (19c) however this time it appeared to quietly modulate it’s output over a 32 minute period, progressively lowering the LWT until the room thermostat reached 20c. However the target temperature was still set to 19c.

At 20.42 it switched itself off again for the rest of the night.

A20D920E 6732 4565 9E5D B844DB63E733

The small output of energy can be seen in this 24 hour internal temperature report:

21D77798 7111 4D65 8A20 8526F8EB910D

I have also posted this to show the reheating of our hot water tank which has been provided by our solar thermal panel. We are not requiring to use the HP to provide Domestic Hot Water, which should be the case for the remainder of the summer. This will have a direct positive impact on our COP sincerely our DHW cop is around 1:2.

i thought it interesting enough to post this since actions of Auto Adapt have been quite difficult to identify.

 

 


   
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(@derek-m)
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Posted by: @sunandair

MELCloud shows Auto Adapt modulate to pass room temp by 1c.

Yesterday our heating was off all day then- Last night we cold started the heating by moving the target temperature 1/2 a degree above the existing room temp. Ie the room stat showed 18.5c at 19.05pm so we moved the target temperature up to 19c.

It took about 40 minutes to reach 19c whereupon it then abruptly switched itself off. 

2FED3FAC BE29 4736 9C35 E7137CC5C4DD

 

20 minutes later it switched itself back on even though the room thermostat was still showing the target temperature was reached (19c) however this time it appeared to quietly modulate it’s output over a 32 minute period, progressively lowering the LWT until the room thermostat reached 20c. However the target temperature was still set to 19c.

At 20.42 it switched itself off again for the rest of the night.

A20D920E 6732 4565 9E5D B844DB63E733

The small output of energy can be seen in this 24 hour internal temperature report:

21D77798 7111 4D65 8A20 8526F8EB910D

I have also posted this to show the reheating of our hot water tank which has been provided by our solar thermal panel. We are not requiring to use the HP to provide Domestic Hot Water, which should be the case for the remainder of the summer. This will have a direct positive impact on our COP sincerely our DHW cop is around 1:2.

i thought it interesting enough to post this since actions of Auto Adapt have been quite difficult to identify.

 

 

The graphs that you obtained are typical of a control system whose response is actually slightly too responsive. I will formulate an explanation in a day or two, if that is okay.

 


   
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(@sunandair)
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@derek-m 

ok thanks Derek,when you’ve got a minute, no rush.... would be interested to hear your thoughts on what’s going on. Although admittedly it’s quite mild now. Also would be interested to hear thoughts on temp differential which is more often 7 rather than 5....

 


   
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(@derek-m)
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Posted by: @sunandair

@derek-m 

ok thanks Derek,when you’ve got a minute, no rush.... would be interested to hear your thoughts on what’s going on. Although admittedly it’s quite mild now. Also would be interested to hear thoughts on temp differential which is more often 7 rather than 5....

 

Your charts are quite interesting and are a good example of what appears to be happening within a heat pump system. The 3rd was quite a sunny day, and as you state the weather was quite mild.

The heat pump controller contains several control systems and equations, which hopefully work in conjunction with each other to maintain the indoor temperature within acceptable limits.

The first chart indicates that increasing the desired temperature setting from 18.5C to 19C is sufficient to restart the heat pump. It is obvious that the water pump starts running, since both the LWT and RWT, initially fall slightly, and then start to increase. The fall in temperature is probably due to the cooled water within the pipework and heat emitters, now being circulated around the system, and the fact that the compressor takes some time to increase the pressure and temperature of the refrigerant gas, to the point where thermal energy starts to be transferred from the gas to the water.

The LWT starts to increase, and is followed some time later by the RWT. The delay before the RWT starts to increase is due to the fact that the whole system has been shutdown for an extended period, so both the water within the system and the heat emitters will have cooled to the surrounding temperature. The initial thermal energy produced by the heat pump therefore heats the water, and most of this heat energy is then transferred to the heat emitters, which also start to warm. The rate at which the LWT increases is dictated by the amount of thermal energy being transferred into the volume of water, and the actual RWT. A good analogy would be moving a small block of wood across a table using an elastic band, where one's hand represents the LWT value, the wood the RWT, and the length of the elastic band is the Delta T. With one's hand touching the wood whilst holding the end of the elastic band, both LWT and RWT are the same and Delta T is zero. Moving one's hand away from the wood initially requires little effort, since the elastic band is slack, but as the elastic band becomes taut, moving one's hand requires more effort as the elastic band stretches. Eventually the block of wood will start to move, and the stretch of the elastic band will become reasonable constant. When one stops moving one's hand, the extension of the elastic band will cause the block of wood to continue moving, until there is insufficient supplied force to move it. This can be seen on chart 1 when the compressor stops.

A better example of what happens to the indoor temperature would be a person pulling a sled, over a frozen lake, using a bungee rope. The above description of the block of wood would hold true, but if the person stops suddenly, as the heat pump did, the extension of the bungee rope and the inertia built up in the sled, will cause the sled to continue moving forward, and it could even go past the person pulling it. Although it is not shown on the chart, this is what happened within the system. The indoor temperature represented by the sled, is moved from the starting point (18.5C), to the finishing point (19C), at which point the person (increasing net thermal energy supply) stops. But because the bungee rope needed to be extended to get the sled moving, and keep it moving, the person was required to go past the finishing point, so there is a strong possibility that the sled will also move past the finishing point. To get the sled back to the finishing point, the person would need to move slowly back past the sled, and without extending the bungee rope more than is necessary, gradually pull the sled to the correct location.

So, the reason why the Delta T may be higher under certain conditions is because there is a need for extra thermal energy, to not only to meet the present heat loss, but also to raise the indoor temperature, and therefore the temperature of the water and heat emitters.

To cause the indoor temperature to increase, the heat emitters, and water, need to be warmer than they would normally be if they were just maintaining a constant indoor temperature. Once the desired temperature has been reached, this additional thermal energy causes the indoor temperature to continue increasing for a period of time. The degree by which the temperature increases, above the desired setting, will be dependent upon the amount of excess thermal energy within the system, and the rate of heat loss. Under milder weather conditions the indoor temperature may rise higher above the desired value than under colder conditions.

I hope that the above answers most of your questions.

 


   
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 Spud
(@spud)
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Posted by: @mjr

I started letting a program on the Pi use the controls to make adjustments of the sort I was making manually (which I can't find any way to program into the ecodan controller), but it does goes to sleep if detects someone else using the controls. I've registered on the forum after lurking for a while because I saw a problem I thought I could answer.

Out of interest, how are you interfacing the pi to the eco Ecodan? Is there an API?

 


   
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