Earth Notes: Reconnecting the Heat Battery (2025)

Updated 2025-03-10.
Summer solar hot water from our PV again. #solar #DHW #PV
Before the heat pump was installed at the end of the Sunamp Thermino 150ePV heat battery was disconnected. All DHW was been provided by the heat pump and its DHW cylinder. As of we are starting to get sunny days where we could capture some 'excess' PV generation that would otherwise spill back to the grid, and instead divert it via the myenergi Eddi to the Sunamp Thermino, and everything was reconnected and ready! This arrangement should provide almost all our DHW locally for about six months of each year, and the heat pump should have almost nothing to do other than covering DHW cylinder losses and the odd run of dark days.

2025-02-21: Getting Started

DM arrived at ~ to start the reconnection works.

20250221 Thermino reconnection first sketch
Initial sketch (by DM) after a couple of hours of discussion. Bottom left box is the Thermino 150ePV. Tall DHW cylinder on the right. Mini expansion vessel and pressure relief valve top left. Intasol on the left half-way up. Also see the Thermino and heat pump systems diagrams.
20250221 heat battery reconnection work end of day

We spent maybe a couple of hours looking at the manufacturers' instructions (MI) and the various system schematics to hand including my diagrams of how I think things ought to end up. We have come up with a sketch that we agree on of how things ought to work, and a shopping list of 6 isolator valves and a pressure-relief valve (PRV).

A feature of this setup is that the Thermino 150ePV and Intasol can be isolated, and normal vanilla DHW operation with the heat pump only can be restored.

At I powered off the heat pump at its dedicated supply panel until .

The water was off too, for a shorter period, while pipework was reconfigured.

The plumbing was not quite completed today. The various isolation valves in place have been set to the 'vanilla' heat-pump only DHW configuration.

Electrical and networking, and outside tidy-up/screening, works remain to do.

(We did get a separate plumbing problem under the kitchen sink fixed by DM in passing today, as a bonus of having a grown-up on site...)

2025-02-27: Round Two

20250226 Thermino pipework landscape DM
Thermino 150ePV heat battery DHW pipework schematic (by DM ). Bottom left box is the Thermino. Tall DHW cylinder on the right. Mini expansion vessel (and pressure relief valve, not shown) top middle. Intasol in the middle half-way up. See original PDF. Also see the Thermino and heat pump systems diagrams.

DM arrived with colleague a little before to continue the works. I turned off the heat pump and the Eddi H1 heater output by the DHW tank, but left the Eddi itself powered up initially. The Eddi now thinks that the DHW tank (and Thermino) is hot, and so may think that pasteurisation is done, so today's rogue data should not be a test case for pasteurisation detection! The sun was strong enough to be starting to divert to the DHW cylinder. There is a bit more energy being spilled to grid than would otherwise be the case. (But the Enphase battery and dishwasher absorbed most of the generation by the time work stopped a little before .) I powered down the Eddi at at the breaker to leave an 'unusual' footprint gap in the data.

At work stopped for the day. All valves are set so that we have DHW direct from the tank. Power is back on to the Eddi and heat pump. Plumbing, electrics and networking will be finished tomorrow.

2025-02-28: Round Three

DM arrived a little after to finish off. I powered down the Eddi and the heat pump at .

Water was routed through the Thermino and Intasol at .

20250228 bypass valves red and black set to use Thermino heat battery
Correct setting of red/black bypass valves to use the Thermino. For the new normal DHW arrangement, red valves should be off and black valves on to use the heat battery. (Conversely, red on and black off to bypass the heat battery.)

At the replacement network cable to pekoe tests OK (without a crossover adaptor this time, slightly mysteriously).

We discovered again that the neutrals have to be split at the Thermino because we have two RCDs at the distribution board, and if not split at the Thermino those independent board neutrals connect, and the breakers pop.

Having resolved that, the Thermino is powered for now from a wall socket in the cupboard, with the Eddi h2 brought to the Thermino "modulated live" and to the other side of the the heating element subsystem. I forced a boost to heater 2 on the Eddi without popping the breakers again.

The positioning of the Thermino makes it possible to see its front panel indicator LEDs by opening one of the cupboard doors. That is an easy way to find out how full the heat battery is without any RPis!

20250228T1507Z pipework largely complete

DM plus colleague left at .

The heat pump was powered up at and the DHW re-enabled under "Operation". The tank is at 18°C, about 5°C warmer than before the PV diversion today.

20250302 view of Intasol and expansion vessel

The bath tap is running a bit slower than before, which is to be expected given the extra stuff in line. I may ask DM to replace with 22mm the pipework from the output of the Intasol to help boost flow rate; it is the most critical section since cold will be being mixed in with water from the Thermino. Minimising volume in the other runs is probably the best thing to do.

(Also, I am told that the bathroom sink hot tap now takes significantly longer to run hot.)

20250228T1658Z monitoring RPi back in place

The Thermino logs on pekoe are being generated again.

A short test running the bath hot tap and observing the logs suggests that the Intasol is correctly routing water through the currently cool Thermino to the DHW tank.

There are various bits of tidy-up still to be done, including various bits of cable routing, and insulating all the new 15mm pipework, and fitting the the PRV (pressure relief valve), but plumbing and electricals and networking seem to be functional.

The weather forecast has several sunny (though chilly) days ahead. Today's PV generation was over 10kWh. Diversion of similar generation may avoid the heat pump making much or any DHW, even while space heat is still required.

Basically the heat battery is ready to go! Hurrah!

202503 heatBatteryInputDailyRecent
Boost (h1 cylinder pasteurisation) and diversion (to Thermino) in .

2025-03-02: Slight Lag

Today I did some temporary lagging of the more important new pipework with random spare bits and pieces of grey foam insulation (though for 22mm pipe) that I had to hand. This was a mixture of lagging from my pre-heat-pump DHW pipework, and off-cuts discarded during the heat pump installation, largely scavenged from the Octopus post-installation waste pile.

More important here means normally carrying water above room temperature. So to and from the DHW cylinder, and from the output of the Thermino and Intasol en route to hot taps. Also around the cold water inlet to the Thermino as that leaks heat.

2025-03-03: It Moves

A pasteurisation cycle ran for ~1h / 2.7kWh, starting at , powered from the grid and the Enphase battery.

~ PV diversion started, to the Thermino, because Eddi heater output 2 (the Thermino) takes priority when no pasteurisation cycle is due.

20250303 h1 pasteurisation overnight h2 heat battery diversion during day
A DHW cylinder pasteurisation cycle from grid and Enphase battery overnight (h1b) in grid "supergreen" time, followed by some PV diversion to the Thermino heat battery during the sunny daytime (h2d). (I think that the demand spike at ~ plus three following smaller spikes may have been a warm wash for bedding — water heating then three spins — timed to finish at breakfast.)

As of , from sh script/myenergi/eddiDaySummary.sh: 

#Eddi daily stats summary in kWh; partial if h lt 24
#UTCISOdate,h,h1d,h1b,imp,exp,h2d,h2b,hph4
2025-03-03,18,0,2.715,5.724,2.047,0.874,0,3.084
20250303 boost imports and spilled exports flat
Imports and exports matching the above period. Imports for h1b boost are capped at ~8A (~2kW), and exports are capped at ~400W before PV diversion to the h2d heat battery.

2025-03-06: Do It Right

DM was here before , with colleague.

Though I have a number of ideas to tweak and improve things (get water to the hot taps faster and with greater flow) today is a final fix and tidy day: PRV, insulation, plinths, etc.

In the "do it, do it right, do it better" view we are at about stage two! I do not want to move on to stage three before we are definitely doing it right.

The network cable was sorted ~.

Shortly after, DM replaced the CombiPhos, which is beyond me to do.

DM measured the DHW flow rate with and without the Intasol/Thermino in circuit to get an idea of how much difference any pipework rearrangement might make. ~9l/min with the heat battery stuff in circuit, ~12l/min without.

DM left by ~.

On the Intasol the temperature dial (biggest knob) should be near maximum so as not to mix down the DHW from the tank (which would be a CoP tragedy), it seems. Tested for science at the kitchen tap and with a hot bath...

20250306 end of works
Pipework at end of works .

2025-03-08: Climbing To Zero

At I estimate the Thermino to be ~0% full, ie it could nominally just directly supply ~50°C DHW. It started today a little below ~-20% and took ~2.4kWh to get up to 0%, and ~3.5kWh to fill by a little over 1/3rd to ~15%. At reconnection on it was ~-50% full, ie ~19°C room temperature. 100% full represents ~7kWh of DHW available above 50°C.

Given that inlet mains water temperature is currently ~10°C, anything above that in the Thermino reduces 'lift' demand on the heat pump, even as (tepid) water is fed through the tank rather than used directly.

I have the Intasol output temperature set probably a little below 50°C now.

2024-03-09

The next morning at ~ the heat pump consumed under 0.5kWh likely mainly to make up for overnight DHW cylinder losses. Then a shower at ~ was covered entirely from the Thermino, taking it nominally back a little below 0% full (maybe ~2kWh used). Then washing up of pots and pans taking it to a little above where it started yesterday (maybe ~1kWh used).

In the evening from there was another ~0.5kWh DHW heat pump consumption, likely mainly tank losses again.

Main Outstanding Thermino Actions