We have the pre-plumbed 300 litre tank (EHPT30X-UKHDW), which came with both an upper and lower sensor.
The FTC6 seems to use the upper sensor to trigger the DHW heating cycle (when it drops more than “DHW max temp drop” below the target temperature), and the lower sensor to determine when it can stop.
Weirdly, although both are visible on the thermistor reading screen, only the lower one (THW5B) is reported via melcloud. The upper one is also not available via the Modbus adaptor. However, after a bit of digging around in the CN105 protocol, it is available there – as different bytes in the same command response that contains the readings from the lower sensor and the flow and return temperatures.
Thanks @marko - lots of rads replaced with install (Mainly K2’s).
Definitely exploring next steps / options - one of them being whether to remove the buffer tank - it’s only 12l and not sure if it’s really adding any value!
Also working on gradually opening locksheilds on rads to try and get a better balance.
Interesting - when you say switched - can you give a bit more detail and explain why you think it’s made the difference?
Maybe some more details about your system? Really conscious of comparing like for like etc! Or at least understanding the differences and impact out possible outcomes
The diagram below shows the change - alterations are in orange.
Basically the flow from the HP now can go directly to the CH circuit; I was finding the flow temperature to the CH was the temperature of the buffer and that was about 5 Celsius below the flow temperature from the HP.
Now the flow temp to the CH is within 1 degree of the HP and that means I can lower the HP flow temperature by 5 degrees! That’s made a huge difference to the COP but the house is still the same temperature.
I also fitted some more sensor pockets and isolation valves when I had the system drained down to avoid having to drain the whole lot if I have to any future alterations. A spring check valve was also added on the HP flow as per the Caleffi diagrams.
That is very interesting. Do you have any before and after data to show how much improvement in Cop you gained?
What was the reason for having a three pipe set up rather than two pipe? Doesn’t the flow take the path of least resistance and preferentially go into the buffer?
[Edited to show the source of the quote - Moderator (RW)]
Improving numbers since I changed but slightly slowed by the fact that I was away a week last month and for a couple of days just now so today’s COP is having to heat the house up from 16 (but my thermal store is at 85C so no DHW needed from the ASHP).
I went with three pipe 'cos it was one less than I already had and so was easier plus looking at the stuff on YouTube and input from John Cantor.
Surprisingly, the vast majority of the flow goes to the radiators; only the difference in the two pump rates goes to the buffer (to the extent I can hear the spring one-way valve bouncing 'cos it’s so slow.
