Posted by: @ewan-costar

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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.

Electrical power diverters are excellent devices, we have had one connected to our system for quite a number of years.

Because they use electronic components to regulate the amount of power being diverted, I don't think that they would take too kindly to being reverse fed, that is having a 240v ac supply connected to the output terminals.

This prevents an immersion heater from being supplied from two different sources at the same time, one being the power diverter and the other being a separate 240v ac supply.

What is the size of your solar PV system?

If you have sufficient solar generation and don't use vast amounts of hot water, you may find that your solar system can provide the majority, if not all, of the hot water you use from Spring through to Autumn. To do this using the power diverter it would need to be connected directly to your electricity consumer unit, with the output from the power diverter wired directly to the immersion heater. By setting the immersion heater thermostat at 65C, it would periodically perform cylinder sanitization when there is sufficient solar generation. If there is an extended period when there is insufficient solar generation to perform legionella control, you would need to use the boost function. It may be possible to schedule the boost function either within the iboost itself, or if it can accept an external signal, from the heat pump controller. By heating the water using solar PV it should reduce the amount of water heating that your heat pump would need to perform.

I assume that for the heat pump controller to perform the legionella cycle, it will be energising the contactor that you mention, since a 3kW immersion heater will draw approximately 12.5 amps from the 240v ac supply.

Can you provide a closeup photo of your contactor and circuit breaker, so that they can be identified.

If the contactor has both Normally Open (NO) and Normally Closed (NC) contacts, and they are break before make, it may be possible to wire both the power diverter, and the alternative power supply, to the immersion heater via the contactor. It could operate in the following manner.

The electrical supply would be connected to the immersion heater via the NC connections during the majority of the time, and would provide solar energy to the immersion heater when it is available. It would also be possible to use the boost function if necessary.

If the heat pump controller is scheduled to perform the legionella cycle, it will energise the contactor. This will disconnect the immersion heater from the power diverter supply and connect the immersion heater to the alternative power supply. Simples. 😎 

Bit of an old thread but this is the way i am planning to use my iboost in case it helps anyone.

I have a Daikin Mono and third party cylinder.

I have three options

1) let the ASHP control the immersion for the boost periods such as the legionella cycle.

2) let the iboost control the immersion

3) Do some fancy stuff with additional relays/contactors so both are connected but only one live at a time.

WARNING!  The iboost powers the immersion via a DC output and not AC240v.  Therefore you CANNOT connect both the ASHP and Iboost at the SAME time without an interlock.

I'm going to keep it really simple based on wanting to use the spare solar energy I have as close to 100% of the time as i dont have a battery to take the excess.

I will wire only the iboost to the immersion so that the sun heats my water through the summer and assists through part autumn and spring.   I know when the once per week legionella cycle will run.   I do that at 1300hrs when my solar is generating max energy and i also do this on a Saturday as the hot 60c water is more likely to be used up earlier for going for an evening out.   As i know its Saturday at 1300hrs, i simply set the iboost "boost" schedule to come on at about 13:15 for 45 minutes.

I will choose 45 minutes as I will assume a starting water temp of 50c at the point the iboost schedule starts.  It takes 35 mins to heat 150 litres (my tank size) from 50c to 60c and i want it maintained for 5-10 mins at 60c.  I will monitor this to get an accurate amount of time needed to heat the delta 50c to 60c (Delta 10) and adjust to make it the most effective.

The iboost mains boost will only come on if there is something to do, which in the summer wont be much as the solar heats it to max most days anyway.