Solar thermal integrated into ASHP

[JohnMo]

Not much progress had to order some more unistrut bits, that weren't available locally.

 

So the solution to panel install is simple but requires a couple of hinges. The support structure will hinge down, I can support structure, install panel at ground level. Then lift up the assembly and bolt in place.

 

[Andehh]

Enjoying this project, keep it up!! 

[JohnMo]

Thanks.  Will keep updating, solar pipe insulation has just arrived, so can start running some pipe externally.

[crispy_wafer]

I've seen a few snippet's from your project pictures, looks ideal habitat for wildcats, do you ever catch a glimpse? 

[JohnMo]

5 minutes ago, crispy_wafer said:

I've seen a few snippet's from your project pictures, looks ideal habitat for wildcats, do you ever catch a glimpse? 

No wild cats (as far as I can tell), but see red squirrels, had Mallard ducks nesting this year. Had about 20+ swans on loch.

[JohnMo]

Insulation arrived, (high temp UV resistant) so have installed the pipes through the wall and joined to flex hoses. Pipes have a continuous fall of 40mm per metre back to the drain back unit.  Will glue the joints when I have leak tested. 

 

Drain back unit filled with water (circa 8L)

Edited July 18, 2023 by JohnMo
More details

[JohnMo]

Little more progress, now have the support frame hinged and in a lowered position to aid install of the panel. Panel is circa 35kg. Just need a second pair of hands.

[JohnMo]

Close up of the hinge point 

[JohnMo]

Panel now in place - piping and temperature probe next.

 

[JohnMo]

Pipework all installed, couple of minor leaks sorted, system levels checked then piping insulated.

 

Operating - Will coincide a legionella cycle within the ST controller with a timed heating cycle of DHW by the ASHP, and see how it goes. This will take return water from DHW heating, and add heat via the close coupled tee.

 

For UFH I will run the ST as follows

 

Panel temp 10 degrees above return flow temp back to heat pump, this allows for a temp transition cross the PHE within the drain back unit. With a Hysterisis of 6 set. This is simulating bottom of cylinder temp.

 

Will heat the return flow via a CCT to a max of 35 degrees. This is simulating the top of cylinder temp.

 

Wet and very cloudy here today, rubbish solar day.

[Wil]

Love the tinkering. Can you post a rough schematic of how you’ve put this inline with the ASHP.

 

I’m struggling to see what you’re doing unless literally running the ASHP return through the secondary of the solar PHX?

[JohnMo]

21 minutes ago, Wil said:

rough schematic

Please see attached

[Wil]

Forgive my questions, but:

1. Doesn’t the ST panel flow in at the bottom and out at the top?

2. If you put a Three port diverter on the return from the heating/ DHW to the ASHP, you could save the energy of the primary side PHX pump and let the ASHP pump do the work moving water through the PHX. * When your PHX temp is higher than the ASHP return temp*

 

Rough scribble:

 

Edited July 27, 2023 by Wil
Clarity on second point

[JohnMo]

This is the manufacturer drawing of the install - below

 

The pump to the panel is flooded, so has to suck from the bottom and out the top, it cannot pull down as it would immediately get full of air. At shutdown all panel water drains back to drain back unit. At startup the water is pushed up through the panel from to top. Doing the other way round may have issues with the drain back system and would fall through the panel too quickly.

 

 

 

There is little no flow through a CCT as it provides hydraulic separation.

 

I didn't want flow through the circuit when ASHP is in cooling mode. With the pump I can control the flow rate through that part of the system also, pump at the moment is set to min speed, so when it's running only draws something like 5w. If it's adding an average of a kW when running, that's not bad. The main pump to the panel is set at speed 2, so draws about 30w as it's bigger pump.

 

 

 

[JohnMo]

Apart from rubbish weather, my first trial was not successful. Main issue is timing things to occur together, biggest issue is shading and timing hot water heating.  Have moved everything to 2pm. And will try again tomorrow.

 

The other issue was the legionella program working slightly different from what I expected, so that required a little fine tuning. Which I have done.

 

See what tomorrow brings

[Wil]

On 27/07/2023 at 13:20, JohnMo said:

This is the manufacturer drawing of the install - below

 

The pump to the panel is flooded, so has to suck from the bottom and out the top, it cannot pull down as it would immediately get full of air. At shutdown all panel water drains back to drain back unit. At startup the water is pushed up through the panel from to top. Doing the other way round may have issues with the drain back system and would fall through the panel too quickly.

 

 

 

There is little no flow through a CCT as it provides hydraulic separation.

 

I didn't want flow through the circuit when ASHP is in cooling mode. With the pump I can control the flow rate through that part of the system also, pump at the moment is set to min speed, so when it's running only draws something like 5w. If it's adding an average of a kW when running, that's not bad. The main pump to the panel is set at speed 2, so draws about 30w as it's bigger pump.

 

 

 

Looks like you’re well covered, of course in a drain back system the pump needs to run that way around! 

 

Hope the experiments work out better for you with your alterations!

[JohnMo]

DHW heating summer is not working too well so far. If the sun's out the PV heats the cylinder by the time the ASHP is ready to heat. Or it's been raining, so solar is pretty rubbish.

 

Need to do some thinking about summer use.

[SteamyTea]

3 hours ago, JohnMo said:

DHW heating summer is not working too well so far. If the sun's out the PV heats the cylinder by the time the ASHP is ready to heat. Or it's been raining, so solar is pretty rubbish.

 

Need to do some thinking about summer use.

What heat pump you got and how large is your PV now?

I have a spreadsheet that needs more data.

[JohnMo]

Maxa i-32V5 6kW

 

PV 3.2kW in south eastern direction (quite a bit off shading until 10am) at 45 degrees, and 3.4kW in south western at 90 degs (vertical).

 

ST southwest at 45 degrees 

[SteamyTea]

12 hours ago, JohnMo said:

Maxa i-32V5 6kW

 

PV 3.2kW in south eastern direction (quite a bit off shading until 10am) at 45 degrees, and 3.4kW in south western at 90 degs (vertical).

 

ST southwest at 45 degrees 

I shall have a look at what my spreadsheet churns out when I get some time.

Pulling kitchen part at the moment, been years since it was properly decorated.

[JohnMo]

So got the control scheme sorted, so preheat will be added to ASHP return when in CH and DHW modes, but not in cooling mode.

 

This is the control scheme I am using (below), but without the diverter valve P3. It's not required for the drain back system. Temperature probe 4 is used to control the diverter valve and start and stopping of pump P2.

 

Placing the temperature probe 4 on the ASHP supply pipe and setting a control permissive of 25 degrees, will keep the P2 pump switched off unless the output of the heat pump is above 25 degrees. If ambient is above 25 it's likely the ASHP will be on cooling duty, so should get very little if any heating when not required.

 

This solution also allows pump P4 to run if the panel is hot to give some cooling.

 

This solution should work all year round without any controller changes, between summer and winter.

 

Then it's just a matter of fine tuning the set points.

[JohnMo]

Slight update, this really hasn't been working too well, was fine for DHW in the summer, but so good at the moment.  But found if I operated to two pumps together in manual test mode, I could deliver 1 to 2kW to the heat system. So have radically changed the control scheme to simplify things. Now just have two probes, 1 downstream of CCT's and the other on the top of the panel.  The two pumps are wired to run together.

 

Using a simple swimming pool control scheme.

 

Ran out of sunlight today to test properly, so will see if the sun comes out tomorrow.

[Iceverge]

Do you adjust you panel angle for the lower winter sun?

[JohnMo]

55 minutes ago, Iceverge said:

Do you adjust you panel angle for the lower winter sun?

Not made any changes so far. It's at 45 degrees.  But production window seems to be quite small, about 3 hours as to many tree in the way.

 

Solar startup temperature is 8 degrees above heat pump return temp, by the time the panel water has gone through plate exchanger, its running with a dT of 3 to 4 between the PHE and ASHP return temp. Have heating side pump, which is between CCT and PHE running at min speed (0.19m3/h) and according to the heat meter it's delivering around 0.8kW in to the heating system.

 

[Iceverge]

0.8kW would be plenty for our house if it was continuous. 

 

Have you any evacuated tubes to tie onto it for the lower winter temps?