Hot water and heating control with my Mitsubishi Ecodan Air-Source Heat Pump (ASHP)?

Forum|Forum|4 years ago
October 25, 2021
81 replies
18264 views

Hi there,

I’ve been looking at some of the data coming from my EcoDan system.

Something you can see here just looking at the tank temp maroon line at the top (chart is last 24 hours of time). At around midnight the HW temp falls to about 40 degrees which triggers the pump to bring it back up to 50. The temp then falls back across late night / early morning. Given I know no one is going to use the HW until 7am, is heating up at midnight a waste? It seems like that intially, but then you have to factor in that the tank temp would still fall further if not reheated at midnight.

Wondering if I could / should stop the HW heating up at midnight? (Of course if I had a nighttime elec tariff this could be a better strategy)

Best answer by Speps

You can do two things to stop this.

Firstly is to look at and adjust the reheat temperature, which is the temperature below the set point that the tank will heat up. These graphs don't tell the whole story but it looks like yours is very aggressive, 5 degrees or less? Try 10 or even 12 degrees.

Second thing you can do is to adjust the hot water timer so it doesn't go on overnight.

I use this timer to stop the hot water from reheating in the morning, as otherwise a few morning showers will stop the central heating and interferes with the heating schedule. But I would not suggest this for your fix as there will be times you empty the tank before bed and need it in the morning.

I've attached my graph of the same. By chance it also shows a leigionella boost. Its strange your graph doesn't show the boiler set point?

Another warning not to take these graphs as 100% accurate for temperature, as I had a shower last night and it was definitely warmer than the 20 degrees it says my tank was.