Posted by: @marzipan71

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Do you think our set up is capable of doing that? When you say its a TS that's just doing the DHW, how can that be since we've run it for two years as the presumed thermal store for the UFH and rads?

Provided the system is plumbed as per 6.1.1 then it works as follows:

When in DHW mode, the hot working fluid travels from the ASHP to 3 port valve 3UV2, which is set to allow flow to port B. The hot fluid travels through the coil at the bottom of the tank, returning to the input port of 3 port valve 3UV1, which is set to allow flow to port A. The cooler fluid passes through the second coil in the tank (higher up) whereby it gives up more of it's heat into the TS. The fluid then returns to the ASHP via the return line. In this mode the flow temperature is set to heat the TS to provide you with 52 degree water out of your DHW coil.

When is space heating mode, 3UV2 is set to divert flow to port A, and 3UV1 is set to divert flow to port B. The working fluid travels through the mini-buffer HYW and on to the distribution header via pipes C and D where the mixed and unmixed pump groups attach. In this mode the flow temp is weather and/or load compensation controlled.

There is no connection between the fluid in the ASHP and the storage fluid in the TS, hence the fluid in the TS stays in the TS - it could be open vented. It is always loaded with heat via the coils.

Posted by: @marzipan71

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That optimisation I'd taken to best attempted by using the weather compensation and having the LWT set as low as was practical.

Do you think our set up is capable of doing that?

Absolutely... Use the room stats as hi-limit stats only, set them a couple of degrees above what you find comfortable. Then adjust the weather compensation curve downwards until you are maintaining your indoor target temperature just on wc alone. 

@marzipan71

As Hugh has pointed out, your system is one of the more complex arrangements, but with the addition of a power diverter or solar thermal, it should be able to provide both CH and DHW in a more efficient and cost effective manner.

A quick test that I would suggest you perform, is to see what is controlling your two CH pumps. Whilst monitoring the two pumps, get your lady wife, or a friend if you have one, (I don't) to lower and raise the temperature setting of the various thermostats, to see which if any start and stop the pumps. There may be some LED's on the pumps to indicate what is happening, or just put your hand on the pump motor and feel for 'good vibrations'. 😎 Also note if the thermostats stop and start your heat pump.

If, as I suspect, the pumps are being controlled by the thermostats, you may be able to better utilise your TS, by following this operating philosophy.

In Summer use the solar PV to heat the water in your TS and hence provide your DHW. Solar PV can also be used for AC. You could run the heat pump or alternatively use a power diverter to provide your hot water via your TS. You may have to switch from WC mode to provide warmer DHW.

In Spring and Autumn use the solar PV to drive your heat pump during the day to heat the water in the TS, and then use this heat energy to supply your CH during the nighttime period as much as possible. You could try raising the indoor temperature slightly during the daytime so you need less heat energy during the nighttime. Again, it may be more beneficial to run your heat pump at a higher LWT during the sunny periods, to store as much energy as possible in your TS.

In Winter use your solar PV to power your heat pump as much as possible to directly supply your CH or to put heat energy into your TS. Running the heat pump in WC mode should prove the most efficient.

Once you have a better understanding of what is happening within your system, you will be in a much better position to try different scenarios to see which provides the best results.

Posted by: @derek-m

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@marzipan71

As Hugh has pointed out, your system is one of the more complex arrangements, but with the addition of a power diverter or solar thermal, it should be able to provide both CH and DHW in a more efficient and cost effective manner.

A quick test that I would suggest you perform, is to see what is controlling your two CH pumps. Whilst monitoring the two pumps, get your lady wife, or a friend if you have one, (I don't) to lower and raise the temperature setting of the various thermostats, to see which if any start and stop the pumps. There may be some LED's on the pumps to indicate what is happening, or just put your hand on the pump motor and feel for 'good vibrations'. 😎 Also note if the thermostats stop and start your heat pump.

If, as I suspect, the pumps are being controlled by the thermostats, you may be able to better utilise your TS, by following this operating philosophy.

In Summer use the solar PV to heat the water in your TS and hence provide your DHW. Solar PV can also be used for AC. You could run the heat pump or alternatively use a power diverter to provide your hot water via your TS. You may have to switch from WC mode to provide warmer DHW.

In Spring and Autumn use the solar PV to drive your heat pump during the day to heat the water in the TS, and then use this heat energy to supply your CH during the nighttime period as much as possible. You could try raising the indoor temperature slightly during the daytime so you need less heat energy during the nighttime. Again, it may be more beneficial to run your heat pump at a higher LWT during the sunny periods, to store as much energy as possible in your TS.

In Winter use your solar PV to power your heat pump as much as possible to directly supply your CH or to put heat energy into your TS. Running the heat pump in WC mode should prove the most efficient.

Once you have a better understanding of what is happening within your system, you will be in a much better position to try different scenarios to see which provides the best results.

Have you had a chance to look at hydraulic diagram 6.1.1 in the thermal store manual? The thermal store is not part of the CH loop at all, it’s sole purpose is to provide a massive energy store to deliver near endless DHW.

Some plumbing would need to be changed to run the CH from the TS water.

@hughf

You may be correct.

I will have a close look at the diagram tomorrow and get back to you.

@hughf

Hi Hugh,

The schematic 6.1 is generic, and does not relate to the installed model, so cannot be taken as to how the system has been installed. Having now read through the manual in detail, it would appear that the TS can be used solely for DHW, or can be used for both DHW and heating support. To provide heating support would require heat exchanger WT5 to be present, which according to the actual nameplate it does not have, but comparing the nameplate shown in the manual with the actual one, just creates further confusion.

The nameplate displayed in the manual shows details of heat exchanger WT1 in the lower left hand area, WT1 will always be present since it is the heat exchanger for DHW.

The details for heat exchangers WT2, WT3, WT4 and WT5 are shown in the lower right hand area, with a tick indicated that they are installed. The confusion occurs when comparing this information with that on the actual installed nameplate. What was described as WT1 in the manual is now not labelled, and the manual's WT2 to WT5 have now become WT1 to WT4, with no reference at all to WT5 which is the one that would be used for heating support.

I suspect that some 'empty suit' at Daikin may have changed the numbering details, such that the presently installed TS incorporates the DHW heat exchanger, the heat exchanger for the 1st heat source WT2, but now labelled WT1, the heat exchanger for a pressurised solar system WT4, but now labelled WT3, and the heat exchanger for heating support WT5, but now labelled WT4.

Obviously I cannot prove which is correct without tracing out the full system and checking which optional extras have been included.

Simon, could you please contact Daikin, and ask them to clarify which heat exchanger are incorporated within the TS, and any optional extras that have been installed.

Many thanks @derek-m and @hughf this is terrific advice and background on how this system works which has been bamboozling me for a while. I'll certainly try out those tests to understand better how its all working, and adopt the seasonal approaches suggested - so I guess my original post may be a bit simplistic in suggesting a single strategy to optimise the system; there are actually different approaches needed by season to optimise how we utilise the solar and how best to fine tune performance of the ASHP & TS.

@derek-m I had never noticed that discrepancy between the sticker on the unit and diagram 8.1. I took a look at the table 8.5 in the manual which I think is the one that applies to our system and it might be possible to infer the set up from the water volumes listed for the various exchangers? Our sticker says we have a W1 with 18.1l, a W3 with 8.7l, and a W4 with 3.9l. From the table 8.5, these could correspond to the storage tank charging heat exchanger (18.1l), a pressurised solar heat exchanger (8.7l), and a solar heating backup (3.9l). If so, this would be in line with the curious history of our install, whereby the geometra (project mgr) gave us an itemised list of kit he was going to install that included solar thermal panels. These somehow disappeared from the specification at some point. He was probably already committed (being generous) to the Altherma ST so despite nixing the solar panels, we still have a solar-capable heat store with functionality we'd paid for but is not being utilised.

Per my earlier wrestling with whether to install a solar diverter (which I think would cost 1000+ euros if we had to buy the Daikin OEM immersion heater and the diverter) or add in the solar thermal panels (which would probably be in the same ball park of 1000+ euros for the panels) then maybe the presumed built-in capability of the heat store to support solar thermal might suggest that as a good/ preferred option? Its possible of course the geometra dropped the solar thermal from the spec because the other elements (e.g., our indoor unit for the ASHP?) might not be compatible or some other complicating factor we are not aware of...there were many instances of decisions not being explained to us during the build or fanciful explanations given.

Thanks again for continued interest and help here - very, very much appreciated 👍 

@marzipan71

Well spotted Steve. I obviously failed my observancy test, by not reading through table 8.5 in sufficient detail.

It would appear that Hugh is correct, in that the primary function of the TS is to provide hot water. If the smaller 3.9l heat exchanger is actually piped into your heating system, then it may be possible for the TS to help support your heat pump with the CH. I would suggest that you check what pipework is actually installed, so that the best operating scheme can be decided upon.

I am once more making assumptions, but here are a few thoughts for consideration.

Even if the small backup heat exchanger is connected into your heating system, I suspect that the system will need to run the ASHP to be able to make use of the stored energy within the TS.

If the small heat exchanger is being utilised, then during the Winter period the addition of solar thermal energy would help assist the CH, and also leave any excess solar PV to help run your ASHP. The addition of battery storage could be used to capture any remaining excess solar PV, to help reduce electricity demand during nighttime hours.

If the small heat exchanger is not piped into your system, then either solar PV or solar thermal would not be able to assist with CH, but either could still assist in producing hot water and reduce the need for the heat pump to do so. Battery storage could again reduce overnight electricity demand.

The above methods should also work quite well during the Spring and Autumn periods.

In the Summer period you will no doubt have an abundance of solar PV generation, but will still need to import electrical energy during the nighttime period, particularly if you are running AC units. Battery storage would therefore be very useful to store energy during the daytime for use at night. Hot water can be produced by your heat pump, solar PV or solar thermal.

I don't wish to influence you in any way, but it is always useful to know the various options. I suppose in an ideal World, where cost was of no importance, we would have all the suitable options installed.

Do you have cheaper overnight electricity tariffs in Italy? Do you get paid for any power that you export?

Posted by: @derek-m

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@hughf

Hi Hugh,

The schematic 6.1 is generic, and does not relate to the installed model, so cannot be taken as to how the system has been installed.

I would argue that there is a ‘pretty good chance’ that the system is piped like this. It’s the recommended hydraulic diagram for a heat pump install, it’s from the user manual for that specific TS, and It features both the mixed and unmixed pump groups that we know are present in the system.

I don’t think that the original plumber would have made this all up, he would have followed a diagram and until one of us flies to Italy and verifies what’s actually installed, this is a good starting point.

I don't disagree that the system may have been piped up as shown in schematic 6.1, though the TS shown is the unpressurised version whereas the one installed is the pressurised type.

What we don't know at the moment is if the 3-way valves are installed, and the necessary pipework to the small backup heat exchanger.

Hi @hughf and @derek-m - below are some photos of the pipework (the insulation is awful and I'll be re-doing it this winter - promise!) and the top of the Altherma 3 with helpful little drawings imprinted on the top of the tank below the pipes to indicate their function. It looks to me like the only items not installed are the immersion heater - would this be 6? - and the solar thermal kit - 10 and 11. I can't comment on the three way valves as my plumbing knowledge is so poor I wouldn't be able to match up diagram 6.1 to what's been installed.

Since I'm not really sure how a 'regular' ASHP and thermal store set up would operate (assuming mine is somewhat complex, ick) - is the interpretation of my system that the ASHP (i.e., the outdoor and indoor units) would have to be running whenever heat is supplied to the UFH or rads, and that this is non-normal? Would a 'normal' system with a TS be able to supply hot water to the emitters without having to use the ASHP as (I guess) if the TS is sufficiently hot (like a heat battery almost) and that was sufficiently heating the heat exchanger then the pumps that push the water to the emitters could run the heating system without needing the ASHP to be running at the same time? And technically, that's per how @hughf described the DHW and CH modes in an earlier post? Apologies but I'm very much still learning how this system works.

I've also added the consumer-facing catalogue for the Altherma ST range which might also give some background as to how the range is meant to be employed. As I say, its somewhat peculiar to me that our project manager chose to use this kit then dropped the solar thermal panels. The only explanation I can give is that in our original discussions at the design stage we were intending to have a small holiday let built (connected to the main house and accommodating 4 people) and we'd asked to spec the system to allow for hot water and UFH to be run from the main house - thus the system was designed for maximum loading as it were when for 90% of the time, a 500L TS seems overkill for 2 adults and a child. Maybe the Altherma ST was the only range in which such a large TS was available. So we are probably partly responsible...but still, I don't know why the solar thermal panels were dropped from the design.

Thanks again to you both for your continued help here.

Posted by: @derek-m

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Do you have cheaper overnight electricity tariffs in Italy? Do you get paid for any power that you export?

@derek-m Electricity here is pretty pricey at the moment - 55c for daytime (F1 - Mon to Fri 8am to 7pm) use and 52c for all other times so there's a small advantage to using overnight or weekend electricity v the F1 times. Yes, we get paid for exporting energy - in 2021 we received 495.06 euros (before fees) for 2966 kWh exported - so 0.167 euros per kWh on average. Incidentally, during the design of the heating/ energy systems in 2018/19 the average price of grid electricity was 6 - 11c per kWh, which are the figures we used to determine the viability of the ASHP and ROI on solar etc. So there's only been a 650% increase in the cost of grid electricity since then - in common with everyone else of course!