Mitsubishi Ecodan not switching according to Cost Boiler selection

Sorry. I don’t think any of the Ecodan owners who usually see this forum have a hybrid hp.
You will probably find an answer to this and your other question on the renewableheatinghub.co.uk forum, there are lots of knowledgeable people there.

Good morning! Thank you for information, this is new to me - i will create an account there and post the questions. They are quite advanced, the system was built to take advantages of price variations on different energy market as well as backup if any of the sources have problems. I leave the topic open, maybe there are also people here that can guide me. 

Please pop back if you find out ​@Sorin it might help other community members in a similar situation 😊

Hi ​@Sorin 

Out of complete ignorance of your particular system I've read the instructions contained in your link and it says the costs of electricity and gas are stored on the SD card. Do you know what is programned for each of those?

Your electricity price (approx) would be either 22 or 0.22 (for pence or pounds) and your gas would be either 6 or 0.06. This will give you a energy cost of 22/3.2 = 6.8p / kWh for the HP with a COP of 3.2 (mentioned in the document) and 6/0.9 = 6.6p / kWh for gas (where 0.9 or 90% is a typical condensing boiler efficiency) which means the gas is cheaper all the time so it won't switch to the HP. As the temperature drops the COP will fall so your price per kWh on the HP will continue to rise and it will never be the cheaper option in this case.

For it to work dynamically (selecting the cheaper energy) the electricity price would have to be around 20p a unit. With a COP of 3.2 the HP cost would be 6.25p (cheaper than gas) or 7.1p when the COP is 2.8 at very low outside temperatures (more expensive than gas).

Any thoughts on what I have said here?

Peter

Does Peter E’s response help ​@Sorin?

Hi Peter. Perfectly logical. Thank you for looking into the document also and explaining the thought process. The values are stored on SD card and in the menu of the programable controller inside the unit.

To your question: :what is programmed for each of those”

The programmed values are close to the the ones in my example from the post. Also (good remark) the efficiency of gas boiler is a parameter ( currently set up to 100% but it allows values from 50% to 150%. I have a condensing gas boiler that declares around 105% efficiency at some water temperatures under 60? is i remeber well.). I do not wish to have the last p saved … therefore approximation in decent limits is acceptable.

The issues is that the HP never switches to gas, even for a 1000x higer electric energy price (specially entered for testing purposes). It always runs on electric power. The installer is not experienced with hybrid setups, maybe i find here someone that solved the same issue.

​@Sorin thanks for coming back to the discussion. I run a discrete hybrid system (separate gas boiler and air to air heat pump) but I run it (manually) against the Agile Octopus electricity price (dynamic half hour pricing) and that is cheaper except during the peak (4pm-7pm) when I run the gas boiler or more often a wood burner to save using gas.

Given the current prices of electricity and gas it is always going to be cheaper to run gas with your system but you could choose an artificially low electricity price to get the HP to take some of the heating load and save gas.

However, it seems your actual issue is something else causing it not to switch to gas; most likely another setting buried in one of the menus something like HP Override set to On possibly. I'll try and get a User Manual and have a dig through to see if there are any settings that could be causing this. I'll come back either way.

In researching hybrid systems it seems these are popular in the USA where they run the heat pump down to 0C/32F and a gas heating system (both air ducted systems) below that when the COP drops to a low value and you start getting very frequent defrost cycles.

Peter

I don’t know if there’s some misunderstanding here 

The Heat Pump itself doesn’t run on gas and so will never ‘switch’ .. or do you mean that the whole system never switches to your gas boiler?

Hi ​@BPLightlog

We can wait until ​@Sorin comes back but my reading of the issue is that the HP runs when electricity is cheaper (with the COP) and provides a ‘handover’ signal to the gas boiler when it isn't. That is why the HP has both prices stored in the SD card. I might be wrong but I think the HP is not handing over even when very high electricity prices are entered so I'm figuring that the gas boiler handover signal has been inhibited for some reason, possibly by a setting in one of the menus. I can't find a user manual atm. I have seen Sorin’s request on another forum though so I'm in the right ball park.

Another possibility is the HP can't see the gas boiler (if it's designed to look for it) so it will keep on going rather than shut off and give a handover signal. We need a manual.

Hello! The HP is the electronic brain that decides to switch. It has a simple relay interface connected to the thermostat entry of the gas boiler turning it on/off when needed. This is working and could be tested from HP LCD interface when i tell to operate only on boiler. But i need the ‘Intelligent’ functions to kick in. Thank you!