J1mbo

The energy transferred from the pipes to the slab depends only on the temperature difference and thermal conductivity between them. Water speed within the pipe cannot alter the thermal loss across that boundary. If there is a higher average water temperature in the loop, more energy will be transferred (per unit time) all else being equal.

The average water temperature is halfway between flow and return temps. So the average energy transfer to the slab (or air if it's a radiator) is a function of the difference between the water and concrete (or air) temperatures. Higher pump speed = higher average temperature = greater energy transfer.

And also the backup heater, and also confirm that the ASHP fan is actually running.

Maybe there is a fault with it then. If the heat pump isn’t heating the water, something else (that is expensive to run) certainly is. Perhaps you can measure the dT across the backup heater.

Maybe the backup heater is doing all the work. Is the outdoor unit fan running?

The dT across the ASHP flow/return is dictated by flow rate (1800m3 per hour it seems) and energy applied. That’s the only two factors. The heat pump may not run continuously as it’s minimum output maybe higher than the heating system output - particular if there isn’t enough volume of water circulating, resulting in rapid swings. When the heat pump is resting between cycles, the return and flow temps will be the same as no energy is being provided. Is there a backup heater in the system?

I'm completely lost with DALI etc and hoping to find some help here! Current setup: Single room with 24V LED tape DALI triac driver DALI bus driver, and DALI 2-wire dimmer. Works OK (though driver is always very hot). I want to add this to HomeKit and have enough electronics, RaspberryPi and HomeBridge experience to glue the lot together once I figure out what's needed, and I want to retain a simple dimmer knob on the wall. I probably have too many questions to list but am looking for a general approach and pointers - even if this means replacing the DALI stuff. I do want to retain high-frequency drive for the LEDs (sensitive to flicker). Many thanks!

One thing I've noticed with the systems that support 'beam forming' is that they seem very good at creating packet loss as the end user moves, for example stuttering WhatsApp calls from a mobile as the user walks around the house. I still have the old UAP-AC-lite APs which over the years have got steadily better and better (especially with roaming between APs) with firmware updates and these don't suffer at all from that issue.

FWIW, I removed the UHF and FM aerials from my house is 2016 and haven't once thought 'that would be useful'.

You need to understand the building heat loss to draw any conclusions here. My advise (FWIW) would be to contact the installer and get that. Then set the system to run 24x7 for a week and start making measurements after that, as currently the consumption is feeding thermal loss and increasing the stored thermal energy of the structure each day (which is then dissipated outside of the heating period). Coupled with monitoring the outside temperature (e.g. degree days for the location), the energy supplied can then be compared to the calculated thermal loss of the structure and some conclusions drawn from that.

I don't see any particular problem with R32 here. But anyway, understanding what the property heat loss is supposed to be, seems key. Does the controller give any metrics indicating the total thermal output, or the environmental yield?

This doesn’t seem to make much sense from the point of view that the ASHP (when running) simply must be increasing the temperature of the water running through it otherwise it would not be 35* in the first place - and the property is warm. Does it ever achieve 40*? Are you able to compare the predicted heat loss at 8* outside temperature with the electrical consumption?

0,65, I think adaptive disabled and room temp mod enabled.

Degree minutes is the cumulative under or overshoot from target. I visualise it like this. Say the target is 40* and it’s producing 40* and as it happens the controller is reporting -30 degree minutes. Then the flow temperature creeps up and is 41* for a minute. The controller will now report -29 degree minutes. Say an additional zone was activated for heating. A load of cold water enters the heating circuit before the heat pump can respond and the flow temperature reduced to 30*. Now it’s subtracting 10* per minute that this condition holds, whilst increasing compressor output to restore the flow temperature to the target. Backing it off again is probably slow and likely it overshoots, adding to the degree minutes again until either 0 is reached or the flow returns to the set point. If you watch it (not the most interesting of activities) it tends to clock up the changes more quickly, but the above is the gist of it.

The Vaillant controller also uses degree-minutes (by default compressor starts at -60°, stops at 0°) to regulate flow temperature and really comes in to effect when the ASHP minimum output is greater than the demand, i.e. the set point cannot be maintained and the ASHP over-shoots. In this case, the heat pump cycles around the set point using the degree-minutes metric to average out the flow temperature to the set point over time. This is all done under the control of the heat pump interface, which is a box of electronics that also controls three-port valve, circulation pumps, immersions etc. Separately, the Vaillant system uses another device - VR700, VR700f, or SensoComfort - which is a room-stat and programmer which is cited somewhere in the living space because it includes a room temperature sensor. It computes the desired flow temperature based on outside temperature, inside temperature, set-point, configured curve, and min/max thresholds, and sends the required temperature to the heat pump controller, which deals with running the ASHP itself. In relation to the COPs, run-time and curves: the VR700 (etc) will reduce the flow temperature as the room temperature is exceeded (and vice-versa) by shifting the curve up and down (actually 45° according to the manual). It can also self-tune the curve over time but the curve needs to be approximately right in the first place for it to do so. The original point I was making is that the curve setting (or max/min temps on other controllers) aren't just dependent on the property but also on the number of hours per day that the heating is used and can be adjusted accordingly. Sorry for the confusion.

Automatically perhaps. But the settings can be adjusted to lower flow temperatures with longer runtime.

Shorter running hours obviously results in a lower average property temperature and hence lower total heat loss in any given 24-hour period. That the property isn't being actively heated however doesn't mean it is not losing stored heat to the surroundings (which needs to be 'charged up' again in a future heating cycle). Hence, the cost to run the system doesn't necessarily reduce proportionally as one might expect when containing run-hours because the total thermal demand is serviced in a shorter window, implying higher flow temperatures and hence lower COP. One of the Vaillant documents suggests (sorry I don't have the reference to hand) to avoid swings of more than 3 or 4°C IIRC. I will try and find that. Re pump/water noise. It might be worth rebalancing the system. Start by fully opening all valves - you want the water circulating as easily as possible - and increase the pump speed (at least 2 if it's a three-speed pump). Then balance down (especially smaller radiators and those closest to the pump) until everything is even and hopefully achieving 5°C drop across each radiator. At least one radiator should be fully open both ends, otherwise overall the flow is being unnecessarily restricted. A smaller drop across each radiator increases the panel average surface temperature and hence reduces the ASHP flow temperature by increasing the panel output at lower flow temperature.

If the radiator pump is running at significantly lower volume per hour than the ASHP circuit pump, water “short cuts” through the buffer and hence reaches (ands likely exceeds) the water leaving temperature target very quickly. What set-back temperature is configured?

RHI is paid to the homeowner directly, the installer doesn’t see any of it (directly)

that might indicate that it could be worth increasing the speed of your radiator circulation pump.

No looked at humidity yet. This is a good idea actually as there are some days there the COP is materially different to others despite similar profiles. I have tried to model solar heat gain.

Haha yes I’m the same on the battery. Solar just doesn’t make sense without one with the disparity between import and export rates atm. Whilst the Agile tariff has been pegged at 35p pretty much since October, it seems that we’ll all be paying that under the new cap in April anyway.

It’s an interesting project and credit where it’s due for getting it to work. I like Home Assistant and Home Bridge stuff. I wonder if the effort is worth it financially (this is not a criticism btw and I would be and still am tinkering with my system anyway, because it’s interesting). I’ve been modelling Heat loss and heat pump performance based on hourly temperature data from literally across the road which is seeming to indicate that the traditional turn off heating at night really saves 10% of cost for gas boilers. With heat pump the observed performance of my system interestingly is far more influenced by outside temperature than flow temperature. Therefore running at night on cheaper electricity (e7) is offset by the lower COP given the lower average temperature. Anyway, I’d be interested in your findings too.

Same with the Vaillant @Kevin - IMHO the installation of the systems with third party controls should be specifically banned as these are the cause of the public perception problem (obviously that is just MHO).

In 10 it regulating to the buffer temp, which means the flow temp from the heat pump itself will be slightly higher as there is always a drop across them. In 8 it works to water leaving the ASHP. How long are you running the heat pump each day?