• Oh dear! There are a lot of imponderables there! If OE can read your consumption - what are OVO playing at??? Perhaps an Ecodan user can assist with the DHW scheduling. I applaud your 10 kWp of PV (I only have 8.1 kWp. (in less than ideal orientation and with some shadowing problems)
• I have found Cosy to be a good deal as I do not have the option of an EV tariff - but I use 27 kWh of battery storage so I only use the lowest rate 8 hours each day. Our 97 sq. metres, well insulated semi is heated with a Daikin EDLA08 8 kW ASHP, as you say that you have your gas consumption figures, would your installer / surveyor not take that into account? Regards, Toodles.

@toodles I think the installer wanted to up sell / up size so gave me a rubbish EPC for MCS purposes (wrong wall spec, omitted panels, omitted LED etc. etc. ) and not interested in our actual consumption ! I think they are worried about a subsequent owner wanting to heat the property much higher than we do.

@carpenterstationhotmail-com, given the size of your property, the 17 kW system might not be oversized. Have you got two 8.5 kW units? Even if your property is well-insulated, a 17 kW system might not be oversized; it could actually be on the lower end of what’s required, especially during colder spells. Your historic LPG usage might be lower due to intermittent heating or higher indoor temperatures, but heat pumps need to cover the full heat loss of the property when running continuously.

Regarding monitoring, it is surprising that Melcloud and Ovo can’t track energy consumption for cascade systems. This is a notable limitation, particularly as cascade setups become more common. I’ll contact Mitsubishi about this to get their feedback. I’ll also ask Ovo.

The cost comparison between electricity and gas (even LPG) is a sore point for many of us. Electricity prices in the UK are significantly higher, which makes achieving cost parity a real challenge. The key is to maximise your system’s SCOP through careful design, weather compensation and making the most of your solar panels and battery storage.

Hi Carpenterstation,

Welcome to the forum.

17kW Heat loss on a 450sqm property is definitely on the lower side, that's a peak heat load of just over 37w per sqm.

What's the construction type- was it a major renovation and did you fit MVHR/triple glazing etc?

If your system does not support energy monitoring by default then you may wish to fit a heat meter on each unit to measure the flow/return temps, energy input in kW to allow you to monitor the COP of your system. Examples of this are OpenEnergyMonitor kits, Sontex Superstatic, Kamstrup etc. There are plenty available but they are generally aftermarket.

You can also do this with a flow meter in some circumstances.

You are correct in saying that cascades are notoriously difficuly to monitor usage on and often the manufacturer's controllers don't allow you to view this. Do you just have the one FTC controller (Mitsubishi one)?

Rob at Cirrus Energy

@rob_cirrus_energy Wall construction is 100mm kingspan between concrete block and thermalite block for half the house (all built 2018 to building regs), and 75mm insulated plasterboard on the other half. Ground floor is all heavily insulated UFH (250 m2). All windows double glazed. EPC conducted by installer lists walls as “solid/ poor” - which is just wrong. Why would they do that?

I just have one Mitsubishi controller - not the easiest thing to get to grips with - and the timed water heating doesn’t seem to work, as it kicks in when the water is already hot enough, and nothing is calling for heat (at a time when I have configured the system not to use the 300% tariff). Short of switching off both pumps at 4pm I am not sure how I can avoid this window?

Are you using the scheduler for hot water or is it on constant, if its the latter as soon as the tank drops by a few degrees which will happen when some uses a relatively small amount of water the reheat cycle will kick in.

Sorry not entirely sure what you mean by “scheduler” or “constant”, but I have used the standard Mitsubishi controller to schedule when the hot water should be heated including setting the water to the “timer” icon (rather than always on or always off)

I'm afraid I've forgotten how to do this with the Mitsi controller so I might have to do some digging. However....

I have a similar issue with not wanting to heat the hot water tank during peak expensive times but I also don't want to schedule and therefore potentially heat when no heating is needed. As a result, my DWH is set to heat to 50degC and to start heating if the water temperature drops below 45degC. I have then used the controller to prohibit heating between certain times each day; it's a bit like holiday mode for short times. Sounds like that's what you're after.

Oh, and as far as monitoring is concerned Melcloud has always been seen as OK but limited.

I don't know how technically confident you are but one option available to you - admittedly at an extra one-off cost - could be to fit the heat pumps with the optional modbus module that Mitsi sell, the idea being to allow a system of your choosing to talk directly with the heat pumps and therefore bypassing Melcloud altogether. There are several to choose from (BEMS Interfaces | Mitsubishi Electric) and I've only really looked into the mini one for a single unit so it might need a bit of research but either way going down the modbus route is definitely a more "hands-on" alternative which will require a bit of a learning curve on your part in exchange for far more flexibility and control.

Not a recommendation; just a thought.

@carpenterstation Here is a video that shows how to program the timer.  If you restrict it only to times when you want it to heat then it won't do anything outside of the those periods regardless of what the tank temperature is.

@gary thanks Gary. This is the video I used to set the timer. 

so the question remains - why are the units cycling when neither heat, nor hot water are being called?