My installers have almost completed a Vaillant aroTherm 12kW ASHP along with a Newark 300l cylinder to which we have both a solar thermal coil connection and another for the ASHP. The solar thermal panel (Viessman Vitosol 300TM) is connected to a Resol controller, and for this to function it needs a temperature probe in the top.of the tank.
The ASHP also needs a temperature probe in the top of the tank, and this one is currently occupying the space.
And then there’s the emonPi3 with the optional DHW probe I asked for (installed but not yet up and running).
There is a second temperature probe pocket at the bottom of the tank, but this won’t help me, as all three probes need to be in the top pocket.
I’ve checked out posts here, where one suggestion was to share a probe with multiple devices. I’m not keen to do this, not least as it may invalidate warranties. It also seems rather complicated.
Has anyone else had the same problem and found a good solution? The only one I can think of is to have a custom made pocket which accepts three probes. I’ve left it with my installers for now, but it does seem to me that the requirement of a two probe pocket (at least) can’t be that uncommon.
For me the heat pump probe should be about 1/3 up from the bottom, not at the top, unless your heat pump uses 2 probes then it’s top and bottom or can set to one at bottom only. Using the top only of your cylinder effectively decreases the total capacity of the cylinder so a waste of a big cylinder.
That’s a good point,although you’ve got me thinking perhaps the solar thermal probe should go in the bottom pocket to keep the panel circulating heat into the DHW tank when the sun is shining, and the ASHP probe somewhere higher up. Still, as there are only two pockets, top and bottom, I still need to get the emonPi probe in with another, and I’m guessing this should be at the same height as the ASHP probe, or doesn’t this matter? I’ll have to check installation instructions for the RESOL controller.
My Joule cylinder has two pockets, one around 60% of the way up and another (unused) right near the top.
The ASHP sensor is in the lower of the two pockets at 60% of the way up. This works well, I think if the ASHP sensor were too low down, the tank would sense cold water too early and reheat when there was still significant hot water left in the tank.
Even at 60% up the tank, there can still be a good amount of hot water at the top of the tank when the sensor is reading 30C implying the tank is cold.
When you say two pockets at top and bottom of the tank, roughly how far up are they? Right at the top/bottom, or 1/3rd and 2/3rds, or something else? If you only have one pocket about the half way point, that’s the pocket I’d use for the ASHP.
For me, the ASHP probe at around 2/3rds up the tank works well. If it’s right at the top, the tank will be almost empty before it triggers a reheat. I think anything from around 60% to 75% of the way up the tank should work well assuming only one sensor for the ASHP DHW.
I don’t have the same problem as my 300 ltr Gledhil installed in 2014, 6 years prior to the heatpump. It has pockets large enough for 2 probes at 1/3 and 2/3 these are used by heatpump, The solar thermal installed at the same time uses sensors at the top and bottom of the panel for control. However I did want to monitor the temperatures at 1/4, 1/2, 3/4 and top to monitor what was happening to the stratification within the tank when the solar thermal was in use. I also have a modern very efficient (installed with the thermal store) Scandinavian wood burner linked in, which I used in the spring and autumn (this was our hot water source in the winter when there wasn’t enough sun for the solar, it also ran the radiators up stairs). We solved the problem by putting the probes under the insulation on the hot water outlet and the solar and woodburner return pipes. I realise the temperatures might not be 100% accurate on the returns when there in use but for my purposes it works. Sorry to the people who will be appalled by the wood burner it’s not used much now and my cars been electric since 2017.