@uk_pete_2000 Adding the GW04 mainly makes it easier to change the timer which is largely redundant now!! 🤣 . I am looking at how to send commands to the HP via modbus to change the values that I think might make a difference, manually at first and maybe a bit further down the line with some sort automation with weather prediction via a locally run AI.

I have used the wavesure poe modbus to ethernet adapter  I had a bear of a time setting it up as all the software is windows based and I am on a mac but finally got there. I couldn’t get the modbus integration to work at first (mainly layer1 issues, note to self always double check your wiring!!) and ended up spiralling into modbus2MQTT and then Node Red (total failure on my part and way too many weekends wasted because it was just the wires that were not working!) once the wires were good it was then indentation problems in the configuration.yaml file, literally line by line to get it aligned properly! And then bingo bango it actually worked! I used this project on github as my start point and they have very handily included a ton of register values from the Chofu manual. I have added this to the WC ready reckoner that @AllyFish posted (thanks @AllyFish this has been key to getting me to this point).

All of this and I am still yet to calculate the COP of the system! I need to add some better power monitoring, however seeing as my water pump is belting out a near constant 4,400rpm at least my flow rate is fairly stable at 35l/min (I think not sure how to read the flow meter! Picture attached either 35 or 28!)

Hope this helps and if you do go down the modbus route attached are my settings for the wavesure.

Regards

Si.

@stuartornum Thanks for this I will take a look at this tomorrow when I am less Shirazlled!! I am deffo not a coder but smash it into copilot enough times I might just be able to get it to work for me lol!!

@grantmethestrength thank you for this information.

@uk_pete_2000 no worries I am really standing on the shoulders of giants here and just trying to get it to work for me so happy to share.

Posted by: @grantmethestrength

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Picture attached either 35 or 28!

They are not very clever, are they! I think that is reading 28, partly because I can cross check mine against the Midea controller's reported flow rate (assuming that is correct...).

Another reason for thinking you read off the bottom of the 'float' is the way the markings are laid out. The only way to get a reading of five (or less) is to use the bottom of the float, and when the float is at the top, the only reading available, 42, corresponds to the bottom of the 'float'.     

This thread is great!

What do people mean by efficiency?  It's a word that's often quoted in relation to heating systems, but do people really understand what it means?

In my world, Efficiency = Useful energy out / energy in.

For a heat pump the equation would become:

Efficiency = "Heat into my house" / ( "Electrical Energy" + "Energy from cooling the outside air" )

A refrigeration system works by needing to condense the refrigerant against a cold fluid.  The compressor increases the pressure, which also increases the gas temperature.  The high temperature as is sent to a plate heat exchanger and gives up it's energy to the heating system water, that condenses the gas.  The condensed high pressure gas is then rapidly depressured over the expansion valve and that gives a low pressure, cold gas.  The cold gas is warmed up by the air and the loop starts again.

If the return water from the heating system is too hot to condense the gas, the expansion valve will close off and the compressor discharge pressure will go up.  The higher pressure gas will condense at a higher temperature.  The compressor will require extra electrical energy because it's operating at a higher pressure ratio (discharge pressure / suction pressure).  The heat pump controls can fiddle with the compressor speed to try and reduce electrical energy usage, but the root cause of the increased electrical usage is the return water temperature from the heating circuit.

Running a system with a low flow temperature (ASHP leaving water temperature) will give a low return water temperature, which will minimise the required compression ratio and therefore minimise electrical power input.  BUT, you still need to get the heat into the house.  If you need a high flow temperature to get the energy into the house then you will need more electrical energy because your return water temperature is high.

You pay for electrical energy, so you will have higher bills if you operate with a high flow temperature.

However...the compressor in an ASHP is a variable speed, positive displacement device.  Every revolution of the compressor will "squash" the same amount of gas.  If you have a small ASHP, you have a small compressor.  The small compressor will run at high speed to "squash lots of gas" when it's running at high power outputs (made worse if you're also operating at high flow temperature).  A large ASHP will have a large compressor that would operate at a lower speed to get the same power output, which in theory would use less electrical energy.

Try driving your car on a motorway at 70mph in 4th gear, you'll use more fuel that driving in 5th gear because your engine is running at higher rpm.

The most efficient system is the one with the lowest RETURN water temperature, which will minimise the required compression ratio and use the minimum electrical energy.  That will give you the maximum efficiency.  Sizing the ASHP to operate at is slowest compressor speed would make sure you're using the lowest amount of electrical energy - so bigger might be better!

Regards

Bob

Posted by: @grantmethestrength

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I am looking at how to send commands to the HP via modbus to change the values that I think might make a difference, manually at first and maybe a bit further down the line with some sort automation with weather prediction via a locally run AI

I think you ought to know that DESNZ is working on an approach to control appliances in the home using remote signalling.

At the very least they intend Off/ON commands to be sent across the internet to turn off heat-pumps when national demand is high.

But they are also working on a 'common' standard which will allow a more Smart control method using Modbus for HPs that offer it.

The strategy is called Demand Side Response, and was part of a large public consultation "Delivering a Smart & Secure Electricity System" in May/June '24.
The proposals for HP controls are in Part-1, titled Energy Smart Appliances.pdf

The working party is in progress, and is mainly looking at cyber security matters.
That's a high-level requirement because the Tariff Optimiser(s) have a database which ties together

• who owns what appliances
• your energy supplier's billing system and tariff
• data derived from your smart meter

Third-party DSR-Agents will be permitted to 'sell' you a service by which they turn off in-home appliances and credit your electricity bill with compensation.

I was a respondent, and challenged a substantial number of the proposals on technical and ethical grounds.

Typically, such consultations attract less than 100 submissions, almost exclusively from companies in the energy sector.

Posted by: @bobtskutter

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What do people mean by efficiency? 

Slight side track, but I am inclined to think that with heat pumps we should avoid the word and concept of efficiency, because the idea of something that is 300% energy efficient risks becoming an oxymoron. It implies you get something (and that something is energy) for nothing, which in a way you do, but of course you don't, it still has to come from somewhere, eg the outside air for a heat pump. I prefer the concept of performance, which of course is already in heat pump jargon, hidden away in the COP. It may also be an easier concept for a novice to grasp, if the performance of a heat pump is 3, you get back three units for each unit of energy you put in.  

Posted by: @transparent

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I think you ought to know that DESNZ is working on an approach to control appliances in the home using remote signalling.

At the very least they intend Off/ON commands to be sent across the internet to turn off heat-pumps when national demand is high.

You will own nothing, you will be in control of nothing, and you will be happy...

Brave New World just around the corner?

@transparent is absolutely right to bring this to our attention. It was clearly meant to be slipped in through the back door (almost literally) when no one was looking.

Posted by: @bobtskutter

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Sizing the ASHP to operate at is slowest compressor speed would make sure you're using the lowest amount of electrical energy - so bigger might be better!

Ah... interesting conclusion!

I don't think that will work because compressors can't operate at very low speed.
They are designed to be used over a range which might be capable of dropping to 35% of maximum output, but not lower.

An 8kW unit might be able to operate as low as 2.8kW, but not below.

So if I fit a larger 11kW model, my lowest possible output would be higher, at around 3.8kW

Feel free to scribble over my graphic and re-post it with your own thoughts.
I can tidy it up later.

@transparent  that's a great diagram to share, it shows the design trade off that go into system specification.

Suppose we required 4kW of power to maintain a stable temperature in my house (or garage in my case 😉 )

Assuming the proposed drawings are for heat pumps with a small (8kW) compressor and a larger (11kW) compressor.

The proposed 11kW model would be operating at the bottom end of it's modulation range (36%), therefore with the slowest compressor speed and minimum electrical input - so maximum efficiency.

The 8kW unit would also work, and it would be operating at 50% of it's modulation range so potentially spinning faster than the 11kW unit and using more electrical energy.

If there was a much smaller 4kW unit it would be running flat out - which is potentially not a good situation to be in for electrical input power.

However, we do need to put our "reality hats" on.  What is the realistic long term minimum power requirement? If it really is 4kW, then the 11kW unit might be a good choice.  But if the outside air temperature warms up then the power required to maintain a stable indoor temperature might drop to 3kW, at which point the 11kW unit might start cycling and the 8kW unit looks best.  Would a (properly designed and installed) buffer tank help in this situation?

I also suppose the large 11kW unit might defrost less because it has a larger capacity to store ice in it's air:air heat exchanger.  Would this help maintain a more stable flow temperature?

I think if I was looking to choose between the two proposed units and had a 4kW "design" power requirement - I would choose the 8kW unit because it gives me some turn down (lower modulation) before going into cycling mode.  Purely from an engineering point of view, the 8kW unit looks best.  I would not select a 4kW unit if the design power requirement was 4kW.

Regards

Bob

@jamespa I have been quietly following all of this in amazement at some of the statements, especially about over-sized HP’s being more efficient. The comments by @jamespa are absolutely correct. Let me provide a parallel view. Imagine you are trying to heat a large metal cooking pot on a fire outside on a winter’s day and you want to keep a constant water temperature. With the right size fire the metal pot will heat up to the temperature at which balance is achieved between the heat input and the heat output from the pot which will be sustained for a constant outside temperature. If we only have a big on/off flame, we can overheat the pot by, say, 1C more and then let it cool -1C down before applying heat again. The bigger the flame the more on/offs. The average required temperature will be sustained (with hysteresis) but the actual heat energy applied to the pot will be the same regardless.
The same applies to a house. The flame is the floor in a UFH system and the pot is the room above with its internal air and its walls to the outside temperature. A UFH system with insulated floating screed floor, tog 1 carpet and 20cm pipe spacing has a fixed System Performance Factor (SPF) of 3 W/m2K. A certified Passivhaus must meet a space heating limit of 10W/m2 at peak demand. A 500 sqm Passivhaus will therefore lose 5kW at this limit. To supply constant 10W/m2 @ SPF 3 requires a delta-T of 3.33C (3 x 3.33 = 10) or MWT 23.3C for 20C room temperature (25.8C flow). If this 24 h heat load is concentrated over 12 hours and the room then left to cool for 12 hours, double the heat output is required for 12 hours, therefore the delta-T must be doubled (6.66C) with flow of 29.2C. The 24h heat loss @ 20C average room temperature is the same however you heat it. Therefore, assuming fixed outdoor temperature, you can heat constantly @ 26C flow or for 12 hours @ 29C flow with slightly worse COP. The size of the heat pump is irrelevant as long as it can supply peak 5kW load and cater for lower loads efficiently. However, a 13kW heat pump would need to demodulate down to 5kW before cycling. Below this peak demand, it will struggle. The situation with an average house losing 60W/m2 will be 6 times worse with wide COP difference. Furthermore, to say that heating constantly at 23C room temperature costs 3 times more than 12 hour concentrated heating at 20C, and therefore constant heating at 20C should not be used is frankly ridiculous.  And WC is useless......🤨