What's the issue? Help Please ?

[RomyD]

29 minutes ago, ProDave said:

By far the simplest solution is turn off the Ecodan legionairs function and connect the immersion heater only to the immersion heater.

 

do you mean connect the immersion heater directly and only to the iboost? 

tks

[ReedRichards]

10 hours ago, ProDave said:

The issue is the Ecodan controller wants to control the immersion heater and turn it on and off as it needs.  BUT so does the iboost.  If you simply connect the two in parallel it is likely to end in smoke somewhere if both should ever try and turn on at the same time.

 

 

Shoemakers.  I have the heat pump controller and an app controlled switch wired in parallel.  I have never had them both on at the same time but I see no reason why that would cause harm (and it's easy to avoid).  About a day after my heat pump was installed it went wrong and the error state prevented me from using it to control my immersion heater so I could not even get hot water.  This was unacceptable!  So I got the electrician back to wire a switch for the immersion heater in parallel so I could use it even if the heat pump was out of action.  Any rational installation should be done that way.  Now I have an app-controlled switch with a timer but which I override manually if the sun is not shining.

 

Edit: Just to be absolutely clear, my immersion heater is on its own dedicated circuit with its own dedicated circuit breaker in the consumer unit.  So parallel really does mean parallel.  When my heat pump turns my immersion heater on or off it must use some sort of logic controlled power switch, not power from its own supply circuit.   

Edited February 9, 2022 by ReedRichards

[PeterW]

10 hours ago, RomyD said:

 

do you mean connect the immersion heater directly and only to the iboost? 

tks

Would be my choice too. Not keen on the FTC and it’s methods of control on the tanks as I am never quite sure what they are doing (plus the pointless legionella cycle) and I reckon there is just as much opportunity for the FTC to use the immersion as a backup heater if the tank isn’t getting to temperature but none of this is documented by Mitsubishi and the only way to find out is a clamp meter on the immersion feed. 
 

It also puts all your eggs in one basket as @ReedRichards says - you need some element of bypass. 
 

 

[RomyD]

So if the legionella cycle is pointless, the only reason to have an iboost/pv diverter is to have a back up hot water heating method?

 

Is a diverter really that appropriate for a ASHP based HW system then? surely it would be better to simply use the PV generated power to drive the heat pump during the day instead of the immersion and take advantage of the ASHP efficiency?

 

In the event of an ASHP failure, presumably the immersion can be just manually switched on?

 

 

[dpmiller]

even with an inverter, there is a minimum current needed for the ASHP to run reliably, plus it takes time to start the unit up and begin producing hot water.  You'll miss short breaks in the cloud  at times and pay for the balance of the power requirement at others.

 

A diverter can instantaneously respond and change the amount of juice going to the immersion.

[jack]

Just now, dpmiller said:

even with an inverter, there is a minimum current needed for the ASHP to run reliably, plus it takes time to start the unit up and begin producing hot water.  You'll miss short breaks in the cloud  at times and pay for the balance of the power requirement at others.

 

A diverter can instantaneously respond and change the amount of juice going to the immersion.

 

You also don't want to short-cycle your ASHP.

 

Ideally, you'd have some battery storage and accumulate enough energy to power the ASHP for some minimum period, but that's complicated and expensive.

 

We have an immersion diverter and ASHP, and they play very well together.

 

The immersion diverter allows you to store more energy, because it can heat the water above the maximum temperature the ASHP can manage. In summer, I expect that on many days the ASHP will have delivered all it can manage by 9 or 10 am. Using an immersion diverter lets me put a lot more energy into the tank.

[ReedRichards]

1 hour ago, RomyD said:

Is a diverter really that appropriate for a ASHP based HW system then? surely it would be better to simply use the PV generated power to drive the heat pump during the day instead of the immersion and take advantage of the ASHP efficiency?

 

 

Yes and no.  An immersion heater requires 3 kW of power (maximum).  That is well within the capability of my solar panels when the sun is shining, even now just about.  So you can heat your water for free.  And I can make the water hotter than my heat pump can manage so it lasts longer.

 

When my heat pump is heating the hot water it works its way up to in excess of 6 kW (total load on the house) to get the water up to 50 C.  Even with my battery and panels working together I am unlikely to achieve 6 kW of output power.

 

So my choice is between completely free but inefficiently produced hot water using the immersion heater or efficiently produced but costing money hot water using the heat pump.    

[ProDave]

The MAIN purpose of a diverter is to ensure (as near as possible) 100% self use of your home generated PV power rather than let it get exported to the grid for little or no payment.

 

It is better to heat some hot water with it (and so reduce the power needed from the ASHP) than let it go to the grid.  On mine I also have a wireless switched 700W convector heater to dump some spare heat into the house when the PV is generating more than the immersion heater is able to absorb.

 

I find in general over a year, about 1/3 of my PV generation ends up in the immersion heater. Most of the rest is self used by other appliances and very little goes to the grid.

[RomyD]

Tks very much for the replies, its really helpful. Self use of free (well kind of.....) electricity and little to no export is EXACTLY what we are trying to achieve so the i-boost or another PV diverter is a must then and it saves the ASHP from short cycling too.

 

The idea really is to be as self sufficient as possible but its proving quite difficult to get consistent answers from various suppliers. For example we've had "MCS" accredited installers suggest ASHPs with capacities from 12kW down to 6kW. Our heat loss is about 5kW according to JH spreadsheet. 

 

We are currently planning on battery storage too, an 8.2kWh Givenergy system recommended by the electrician. A bit worried now you say its complicated Jack...8/ Complicated seems a bit of a problem right now...

 

ProDave, how is your system configured to work the wireless 700W heater? it sounds like you are doing exactly what we want to.

 

Our idea is to have the solar charge the battery first when there is excess, then the hot water. Maybe the other way round. If there is still excess after that a regular heater sounds sensible.

 

Confused I Am (CIA i am not). But getting there.

 

Tks.

 

 

[ReedRichards]

There may be difficulties combining  a solar diverter with a battery.  You probably don't want the diverter to drain the battery when the sun goes behind a cloud.  But if you, for example, boil a kettle and the battery contributes to the power required then when the kettle switches off the battery does not switch off its output instantaneously but ramps down its output.  To do this it briefly exports energy to the grid.  An over-zealous diverter can see this brief export as excess solar power, engage the divert and drain the battery.    

[RomyD]

I am now thinking the diverter should maybe wait until we have the battery etc installed and see how much we actually end up exporting...

[Christiano]

13 hours ago, ReedRichards said:

An over-zealous diverter can see this brief export as excess solar power, engage the divert and drain the battery. 

We have exactly this problem, even with the configurability of the iBoost+.

 

With an ASHP and battery storage my advice would be not to bother with the PV diversion, let the battery have it all. Maybe set up some automation so if the battery has capacity in daytime then pop the heat pump on for the water.

 

A few thoughts:

• Diverting PV to heat water is 100% efficient while I expect using your heat pump will be 200%+ efficient.
• You would get lovely hot water from diversion whereas using the heat pump it will probably be less warm.
• You’re probably not getting RHI but you get nothing for heating the water via diversion whereas you would get something back for using the heat pump.
• The actual kWh required to heat your water isn’t that much, according to our EPC it’s about 10% of the heating requirement.
• We had to replace our iBoost after 4 years so that cost us about £60/year where our annual water heating was probably only about £100 before the heat pump, I need to check what it’s costing now.
• Someone said keep it simple above, it’s a good idea!

[ReedRichards]

I use one of these https://www.timeguard.com/products/time/immersion-and-general-purpose-timeswitches/wi-fi-controlled-fused-spur for timed/remote control of my immersion heater.  But it's an all-or-nothing control, unlike the iBoost which can regulate its output.

[Christiano]

I’ve just had a look at our energy consumption for heating hot water via heat pump. Tank is 250l, 2 in the household.

 

It runs each morning at 2am to heat to 50c with a weekly legionella run.

2am is not the best time for efficiency as it’s pretty cold outside but we’re on Octopus Go so only 5p/kWh.

Typically it is heating from around 44c and stops between 50.5c and 51.0c.

On Sunday morning, legionella runs after this and takes just the top half of the tank from 50c to 68c.

The day after legionella it doesn’t heat because the tank is still hot enough.

 

For the last week of January it used 11.9kWh, so is about £31/year!

 

In warmer times we will get greater efficiency from the heat pump and may return to PV diversion in really sunny times.

Thinking about it though, perhaps it would be even better to heat water in the afternoon using the heat pump with either PV or stored energy.

Just harder to control and more expensive if I get it wrong because of using full-price kWh!

[ProDave]

17 hours ago, RomyD said:

 

ProDave, how is your system configured to work the wireless 700W heater? it sounds like you are doing exactly what we want to.

My PV diverter is home made based on an Arduino and programmed by me.  The heater is controlled by a 934Mhz transmitter module in the diverter and a 934Mhz receiver and relay mounted at the heater.  Both cheap Chinese modules from ebay.  It is currently programmed to turn the 700W heater on when immersion divert reaches about 90% and to turn the heater off when immersion divert goes under about 10%  so quite a big overlap, that those are figures I can experiment with, e.g. if I thought more space heating was beneficial I could make it turn the heater on sooner.

 

A few other points.

 

If I ever venture into battery storage, that will probably be via an addition to the Arduino system so the same processor with some additions to the software will determine when to charge and when to discharge the batteries.

 

I don't turn on my ASHP DHW heating until 11AM on the basis by then there should be reasonable PV generation so more likely to help with productive self use of PV energy.  As long as the HW tank is heated up the previous evening, there is still enough hot water for one morning shower and only one of us showers in the morning.

 

On a general point, the ASHP uses about 2/3 the amount of electricity heating DHW as it does heating the house.

 

My own PV diverter failed after about 2 years, the solid state relay failed.  I suspect not enough heat sink compound so it may have overheated.  I have also repaired a couple of commercial PV diverters, one in particular (I forget which make) I thought was very poorly made, it was in fact an interconnecting cable from the PCB to the SSR that had burned out.

[Christiano]

2 hours ago, RomyD said:

I am now thinking the diverter should maybe wait until we have the battery etc installed and see how much we actually end up exporting...

We always panic when we see we’re exporting but it’s partly because we’re the only supply off a transformer so we know it’s going to waste.

[severnside]

Eddie Diverter with relay module provide quite sophisticated control. You can set a threshold for triggering relay. e.g. when excess power is more than 4kWh then trigger relay which starts ASHP. Also you can set minimum time to run as gap between mutliple starts.

Also it's wiring support ASHP based immersion control. Check Eddie's manual for examples.

Edited February 10, 2022 by severnside

[RomyD]

I had a look at the Eddi manuals and examples. Far better documentation than i-boost and very informative. Tks.

Edited February 10, 2022 by RomyD

[canalsiderenovation]

On 09/02/2022 at 14:28, jack said:

We have an immersion diverter and ASHP, and they play very well together.

 

The immersion diverter allows you to store more energy, because it can heat the water above the maximum temperature the ASHP can manage. In summer, I expect that on many days the ASHP will have delivered all it can manage by 9 or 10 am. Using an immersion diverter lets me put a lot more energy into the tank.

 

Same here. We heat the hot water by ASHP to the set 48 degrees kicking in during the Octopus Go 5.5p cheap rates (8;30pm for an hour and half only). We have been fine with this even on days of very minimal solar but in the past week we have noticed with some spring sunny days in the day the water temperature has risen to 56 degrees so the ASHP hasn't kicked in to heat the water in the evening as it's hotter than the 48 degrees. Last summer I turned the ASHP controlling the hot water off completely for 4 months as we just didn't need it as the solar was doing it all.

 

[J1mbo]

On 10/02/2022 at 12:20, Christiano said:

• The actual kWh required to heat your water isn’t that much, according to our EPC it’s about 10% of the heating requirement.

 

You obviously haven't met my teenagers! 430kW a month...

[ToughButterCup]

19 minutes ago, J1mbo said:

 

You obviously haven't met my teenagers! 430kW a month...

 

You log your teens' hot water consumption ?  Honestly?

I remember being glad if ours used any hot water at all. But then they met members of the opposite persuasion ....  

[SteamyTea]

2 hours ago, J1mbo said:

You obviously haven't met my teenagers! 430kW a month

So assuming an electric shower, that is £100 a month.  A weeks rent as a lodger.

To get me to move out the house, my Mother charged me a third of my take home pay.

Was only there a few weeks.

[RobLe]

On 10/02/2022 at 14:36, Christiano said:

We always panic when we see we’re exporting but it’s partly because we’re the only supply off a transformer so we know it’s going to waste.

It won't be wasted.  AC power flows both ways through a transformer just fine, somebody else will end up using it - so excess PV is likely to ever so subtly reduce gas used by a turbine somewhere.