heat pump and pv diverter

ewan.costar · 18 Jan 2023 at 00:22

Hi,

I've got both a solar pv and an ashp system.

The solar system also has 2 batteries and it's configured to fill the batteries first and then export to the grid when they are full.

I don't think it matters, but the pump is an LG Therma V R32 monobloc.
From what I understand (I'm not an electrician or have any kind of technical background), the heat pump is connected to the cylinder in the attic in 2 different ways:

it pumps hot water into the cylinder through the coil. that only takes the temperature inside the tank to between 45 and 50C.
there's 2 wires from the pump to a box next to the cylinder (one for power and one for data). the box contains a circuit breaker and a contactor that decides whether energy is sent to the immersion heater to top up the temperature.

It's all working fine, except that I've still got an iboost+ (or similar) pending to be fitted. We've been back and forth with the installer for almost a year now.
The installers have tried the solic200 and the solar iboost+ so far without success. They designed the system with this (without specifying the model) and i didn't even know this existed before they mentioned it to me.

They've sent me a few electricians. Every new guy tells me a different thing about compatibility with the heat pump and even some times they manage to break things that were already working when trying to make it work. i've lost trust on them.
We have a bad relationship at the moment and I'd rather get this installed and working if possible rather than having to battle for a refund that may take a long long time.

the original design said that the diverter would be wired into the lg box and use energy that would go into the grid to heat the water.
however, now that i've looked into it, it doesn't make a lot of sense to me.

despite all the conversations with engineers and my own research, I'm not really an expert by any stretch of the imagination, so I would then like to ask you for your experience with similar setups. I've got 2 main questions:

is this set up even possible? if so, do you have any details setting it up that you can share? what i understand is that when paired with the heat pump, the immersion heater would only work if lg sends the signal and there's excess energy being produced. this doesn't seem very practical to me, but maybe i'm not understanding how it really works. the electricians tell me that i can also press the boost button on the iboost, but it wouldn't really work unless lg decides it has to be on anyway. actually, the way they've tried to set it up (iboost between the contactor and the tank) means that the iboost will not even be on until lg tries to start the heater. it has not direct feed most of the time.
if this is possible, do you reckon it's worth doing? my dhw is usually set between 48 and 50 depending on the time of the year. it's enough even when 2 people have a shower at the same time. i have a night tariff that i use to charge batteries overnight already in winter and i can schedule the pump to heat the water so that it's ready when we get up. i have no idea about the financials about both options, but again, i'm looking for a practical solution unless using iboost is much cheaper than the current set up.

I called iboost and solic manufacturers, and also LG. they all have told me that they have clients using the 2 things together, but wouldn't give me any hints/help/recommendation on how to set them up. they just don't want to offer any help with something they don't make themselves.

any help would be greatly appreciated.

thanks!

BUDFORCE · 18 Jan 2023 at 06:21

ewan.costar said:
the way they've tried to set it up (iboost between the contactor and the tank) means that the iboost will not even be on until lg tries to start the heater. it has not direct feed most of the time.

This might be your issue, I need to add I am not an electrician so some of this is my best guess.

The way solar iBoosts work is they put a CT clamp on the neutral cable on your main supply (before your consumer unit) and all that does it detect any excess current going out. It then sends a signal to the iBoost to draw the same amount of current as whatever the sensor is detecting is going out.

The iBoost is just a variable resistor really from off to 3kw (or whatever) - but it needs to have a constant switched on feed for it to work. If it has a constant feed, whenever you generate excess it'll dump that into your hot water tank up untill whatever temperature you have your thermostat set to (this is the thermostat on your element) and then stop, at which point the iBoost will display "tank hot" or similar.

I know nothing about heat pumps, but if your heatpump switches off the feed to your iBoost, it wont work.

How you sort that, I dont know.

ewan.costar · 18 Jan 2023 at 09:23

thanks for your reply!

it seems the guys didn't design this very well. i had countless issues with them during the setup and they changed their mind a few times until the installation was completed.

not a big deal for me really. it's just that they were adamant that this would work and tried to charge me for it.

1pudding1 · 18 Jan 2023 at 10:26

Budforce has covered it all mainly. We have a heat pump, and have had solar PV and an iboost installed for the last 7years or so. All worked fine. The iboost had no connection or interaction with the heat pump or solar install at all. It wouldnt matter if they werent there. All the iboost cares about is electricity being exported, and then diverting that by switching on an immersion heater on a hot water tank when it detects export. Its now been complicated on our install because we added batteries last year, which also wants to detect exported electricity and then use it to charge the batteries. So what can now happen is the battery inverter and iboost fight and conflict with each other as they both use CT clamps to detect export to turn themselves on. You can get a iboost CT clamp with a higher export allowance I think of 150-200W before it will turn on the iboost so it doesnt battle with a solar battery system.

ewan.costar · 18 Jan 2023 at 10:49

thanks @1pudding1

yeah, following the previous message i was thinking whether to give up on the iboost thing all together or have the heater completely separate from the pump.
the problem with the latter is that the thermostat in the cylinder is wired to the pump and the tank doesn't really have (that i know of) a self-stop option.

imagine a very sunny day in summer where i have lots of excess. batteries are already full and if my understanding is correct, the diverter would simply keep warming the water until it's too hot and steam starts coming out through the valve at the top.
unless there's something i'm missing or missunderstanding, this wouldn't really be a good option either.

1pudding1 · 18 Jan 2023 at 10:57

Yeah you might be right actually, the iboost and immersion heater could be using a cylinder thermostat linked to the heat pump. I havent looked into and dont know exactly how the immersion heaters work, don't they have their own stat integrated on them? I'm sure mine has a little dial you can turn to set how hot it should go until it turns off? In which case it should be indepedant of the heat pump as long as the heat pump isnt connected to the same immersion on the cylinder?

ewan.costar · 18 Jan 2023 at 11:20

no, this is not my case as it's supposed to be fully controlled by the pump. there's a thermostat that is wired to the pump and it's lg that decides when you turn the heater on or off.

i've seen that there are cylinders (not mine) that have to heaters. it would then make sense that one is controlled by the pump and the other by the diverter when there's an excess.

this seems to me like the installer was trying to make some extra money out of me but didn't really understand my setup. the electricians that they sent were all subcontractors and when they came around kept scratching their heads trying to figure out if that would even work!

BUDFORCE · 18 Jan 2023 at 11:34

If your immersion heater element doesn't have its own independent thermostat than I cannot see how it would work either.

ewan.costar · 18 Jan 2023 at 13:16

agreed. no point in taking more of your time.
i really appreciate your feedback and i can finally put this behind. I will call them and tell them i'm not going through with this.

dirtychinchilla · 18 Jan 2023 at 14:21

Is there any reason why your PV isn't hooked up to the heat pump? Or am I misreading this?

ewan.costar · 18 Jan 2023 at 15:15

they are not hooked up and they never are if my understanding is correct.
the pv generates electricity that goes to the inverter and then it's consumed by whatever needs it (whether it's the pump or not is irrelevant, whatever needs it)

then, if i have excess, it goes to the batteries.

when the batteries are full and it starts exporting to the grid, the pv diverter could "send" it to the tank. not the commas, as "send" is a bit of a stretch. basically, what it means is that the diverter tells the heater to be on and consume energy so that it doesn't go back to the grid.

so, the systems are not really linked in any way that i know of, at least directly. we only have a clamp to mesure if anything goes out of the house and it turns on things to use that excess.

or maybe i'm not understanding what you mean by hooked up?

-Ad- · 18 Jan 2023 at 15:41

Just get a LAP Immersion timer from Screwfix. £20 Vs a £500-600 complicated (and maybe not properly working iboost type system) is the real thing to look at here.

From one calc a mod used on a Solar PV group on FB, it'll take 2500 full cycles of an iboost heating your cylinder for it to repay the additional cost. It'll be out of warranty and likely dead before it has paid back the initial investment.

You can configure that LAP timer to top-up your DHW to the 60degree zone to ensure legionella is killed off.

You may not have it coming on when you have PV excess, but that excess will be exported to the grid via SEG/FIT. Then I assume you have a cheaper tariff rate for overnight leccy, so just fire up the immersion at the end of the cheap leccy rate (e.g. 4.30am).

Sometimes keeping it simple is best and getting all these different systems to work together will just end up giving you a continual headache.

ewan.costar · 18 Jan 2023 at 18:18

well, in my case i don't have to do anything. lg already does both. i can tell it to heat up the tank from 3 to 4am and also schedule the sanitising cycle once a week.
very easy to program from the touch screen