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Mike-P

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  1. So I have only one setting the way mine was plumbed & wired. That is heating. It does either heating, water or both in that setting with the standard S plan arrangement. I switched off the weather compensation to enable us to run it at 50 degrees when we want to heat the water and 40 when we don't. I am currently experimenting with how to get the best efficiency, comfort and hot water when needed.
  2. We had an ASHP installed a few weeks ago and are still working out how to get the best operation. We went through a period when it was tricky to get hot water and it turned out to be a number of things. Our system is installed in an S plan rather than the standard Y plan. In other words, it can be run as a standard boiler that allows space heating and DHW heating to be on at the same time. The ASHP is only configured to 'space heating' and had weather compensation on. This resulted in us trying to heat the DHW with the heat pump running at 37 degrees. The pump and valve circulating the water round the coil in the cylinder are on as soon as the water heating is turned on, however, the heat pump might be pushing cold water for 5 or 10mins if starting from cold. During this time our ASHP is cooling the water in the cylinder rather than warming it. If we are running both heating and DHW heating from cold it takes much longer to start pushing water that is hot enough to warm the cylinder, extending point 2 above. We had an immersion that was set to do a legionella cycle once a week by turning on the ASHP (not an immersion) but that was pushing weather compensated 37 degree water through the cylinder, in an effort to get water to >60degrees it was taking our previously hot cylinder and cooling it down to about 35. In our system we have the heat pump just circulating the R32 into a plate heat exchanger and back. The cylinder coil and UFH closed systems are heated by that heat exchanger. The cylinder is 200l with large coil. The rooms are controlled using heatmiser stats like yours. There are 4 adults in the house, a 3 bedroom that is powered by a 10kW Midea ASHP. Currently we are getting water at about 46degrees by doing the following (solving the corresponding issues above); Turned off the weather compensation mode and set it to a programmed temperature. 40 degrees when we have the space heating programmed and 50 degrees when the DHW heating is programmed to be on. we have the DHW heating set to periods that directly follows the space heating times. I plan to add a clip on temp switch to the R32 loop to make sure that the circulating pump for the heating and DHW only runs when the R32 is > eg 35degrees. when we run the ASHP at 50 degrees we have the room stats programmed to be a couple of degrees lower having the effect of shutting off the heating and pushing all of the hotter water through the cylinder coil. the legionella cycle is deactivated. I had gone into the detail here in case some of this is relevant to your situation. Factors I've been trying to consider include efficiency of timing the water heating, might be a mistake, but trying not to heat the water overnight or early morning when the outdoor temp is coolest, also running the heating and the DHW heating for a period to get the cylinder up to 40s then blasting (!) it with 50 degrees to give it a final top up of heat. I'd like to set it so that the valve for the cylinder only opens if the water in the R32 loop is warmer than the cylinder but not sure how to do that without bashing out a Raspberry Pi controller (I'd be grateful for some advice on that one if there is a simple way without me writing some Python and hacking together a load of electronics). Alternative would be to dig up the concrete again to connect the cylinder sensor to the outdoor unit and run it on a Y plan but I think the current S Plan gives more flexibility and potential for efficieny. Some things I noticed with your system; you appear to have 5 pumps! your boost timer seems to be connected to a pump rather than the immersion. I haven no idea why you might do that. It looks like you have an Ecodan pre-plumbed cylinder with active heating. I don't think it uses a coil unless you have the solar version. It actually pumps the water out of the cylinder, through a plate heat exchanger and back into the cylinder again. Mitsubishi recon this heats the cylinder quicker, and maybe they are right. So the stuff on the bottom right of your cylinder in the picture is the pump, scale trap and heat exchanger. If your cylinder is hotter than your heat pump is running then it will for sure cool your water down very quickly. Also note: if the cylinder pump comes on when the heat pump is not on for some reason it will have the same effect of cooling down your hot water rather rapidly. Our ASHP only comes on when a heatmiser stat calls for heat or water heating. Yours coming on and off without a call seems weird. Are you using the wireless neo air stats? they have a 'safety' mode that turns the boiler on (I think from memory for 7 mins per hour) if the signal from a stat is lost (including a flat battery). If you are using those wireless ones you can turn off the 'safety' feature at the wireless controller. (given that it is pre-plumbed and designed to be used with your heat pump and the big box of electronics on your cylinder it seems odd that you would be having those problems unless sonething has been configured incorrectly.) I'd be inclined to periodically check the pump below the TF1 to see if it is coming on when the heat pump is either off or running cold. That would quickly chill your hot water!
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