What is that base??

The isolator looks like it’s in the restrictive zone.

The diverter valve has a very low value and shut off pressure for a double fan unit 

why the buffer as the pumps are big? 

@damon

What is that base??

               This is temporary and was last minute , we had to raise the unit to get the correct fall for the drain

The isolator looks like it’s in the restrictive zone.

                angle of the pic, it’s out of the zone

The diverter valve has a very low value and shut off pressure for a double fan unit 

                will inquire about this, what do you think it should be?

why the buffer as the pumps are big? 

                no idea!

Why the Tado controls? Get rid of them and use the native Vaillant controller, the Tado controls will only harm efficiency. 

@ectoplasmosis 

seems to split opinion this one, I want to try both ways and see the results , each room can call for heat and has a generous temp plus good living room / bedroom overlaps.

reality is the system is pretty much ‘on’ all the time anyway, heating pipe work only doesn’t sit well with me!

TADO isn’t just a simple on/off system , but as I said I want to trial both ways and see the results on efficiency 

@showi Tado very much is just a dumb ‘on/off’ system when used with your Vaillant ASHP.

It cannot interface with the heat pump in any way, except for calling for heat or not (on/off). 

Running my Arotherm Plus 24/7 via pure weather compensation with all TRVs open and the entire house constantly at my chosen set temperature turned out to be much more efficient and cheaper to run than using any kind of schedule or night time setback temp.

The heat pump just uses significantly more energy to recover from the house cooling down in between heating times than it does gently and constantly giving just the right amount of heat to maintain your chosen temp. 

@ectoplasmosis 

Appreciate ultimately it is on/off but what I meant is it is able to maintain the system on from 6am-10pm with each room at exactly the temp I want it to be, I don’t want every room to be the same temp , what is comfortable for one in a bedroom isn’t for another ?

 So where do you have your room stat? , is it on over night? Or do you set back? 

lots of talk about treating a heat pump as one big open loop constantly on system yet they have the controls to turn on/off on their own stat aswell as setting heating on/off periods.

as I said I will experiment and ultimately it’s which way ends up being the most efficient, don’t think one solution fits all however.

@showi I don’t have a room stat at all. My sensocomfort controller is set to pure weather compensation mode, and I’ve nailed down a heat curve setting which keeps the whole house at my chosen internal temperature automatically, the entire time. 

I can of course choose to schedule a setback temperature for example, but I find it more comfortable not to.

The thing to wrap your head around is 1. With pure weather compensation there is no longer the concept of a ‘thermostat’ at all, and 2. Trying to maintain different temperatures in various bits of the house is less efficient than maintaining a single temperature everywhere.

Unless all the rooms are hermetically sealed the whole time, you will only be running the heat pump at an unnecessarily higher flow temperature to service the warmer-set rooms, with the colder-set ones shutting off their TRVs and reducing system volume, with the heat from the warmer rooms leaking into the colder ones regardless and eventually achieving equilibrium whilst using more energy to do so than just heating the whole house with a lower flow temp in the first place. 

@showi, I had the same mindset as you when we initially chose our heat pump system. We set up smart TRVs on every radiator, but years later we realised this approach wasn’t ideal. We still use the smart TRVs, but they’re now all set to around 25°C, a temperature the rooms will never reach, which keeps the valves open all the time. We mainly use them now to track room temperatures over time.

When TRVs constantly turn on and off, it affects the circulation throughout the system. Many reputable installers now recommend using smart TRVs only in bedrooms, especially if you want a cooler sleeping environment at night. A set like the Eve Thermo Comfort is perfect in this scenario - it can regulate the bedroom temperature without calling for heat, so you can maintain a comfortable overnight temperature without disrupting overall system performance.

Eve Thermo Comfort Set: https://amzn.to/48q1LP2

PS - we found Tado customer to be arrogant, rude and dismissive.

@showi The other thing to consider is that Tado TRVs are notoriously poor at actually acting as TRVs. Their temp sensors are too close to the radiator, causing over-reading and premature shutdown. There are plenty of threads from frustrated customers online about this. 

This was the main reason I ditched my entire Tado system. The TRVs are useless, they just don’t work as intended, and the heating controller is also useless and a hindrance when used with a heat pump. 

It is of course your house to experiment with, but I’m just speaking from my own experience. 

@ectoplasmosis 

yes it’s certainly a different mindset from 40 years of gas boilers and a room stat!

so you don’t have any feedback of any room temp into the controller? , desired vs actual temp on the SensoComfort has no bearing at all? I thought this was used in the system flow calc? 

also curious how you run DHW?

haven’t searched yet but have you documented your system settings on here already ?  

@Mars

yes I watched your initial video on this recently and made a lot of sense , but as you say it’s a learning curve, would certainly need to keep the bedrooms cool overnight if we adopted this method 

There has indeed been a lot of discussion about whether setbacks save money and/or compromise comfort, including this mega-thread. The answer is not straight forward, with theory and empirical results seemingly at odds at times. 

All can agree that a long setback eg going on holiday for two weeks in winter and leaving the house with just frost protection on eg main thermostat set to 10 degrees (which is still a setback, albeit a big one) will save money, but doesn't compromise comfort, as you are not at home.

The same applies to a one week frost protection setback. The saving is more than large enough to offset any extra energy needed during the initial reheat, and a net saving is made.

The same applies to shorter and smaller setbacks until at some point, things start to get muddy, typically when we get to the most common setback, an over-night one of a few degrees. Rather curiously, no one has managed to work out when the obvious savings become less obvious, but suffice it to say we have got there when we get to over-night setbacks.

On the face of it, a setback should save money, because the heating is off for several hours and the average temperature of the house is lower over the 24 hour period. The problem is the house does use more energy during the recovery period, and the question becomes how much extra energy over and above what it would have used if on continuous running does the house use during this recovery boost? Is it enough to wipe out the known real gains during the setback itself?

I think it is fair to say the theory has failed to answer this one, except in the broadest brush terms, with high level statements about the conservation of energy etc. What happens at the individual house level is the theory fails because there are just too many variables, and the models can't cope with that level of complexity. Remember the real question we need to answer is how much extra energy did the house use during the reheat, and is this more or less than that saved during the setback?

The alternative to modelling the answer (an approach I have dubbed whatiffery, in fact whatiffery is any model that asks what if questions eg weather forecasts: what if the Atlantic low tracks east rather than north east?) is to measure the data, ie get an empirical answer. If you have a reasonably comprehensive verified monitoring system as I do, then I can plot the key parameter, hourly energy consumed, over time and see what actually happens. Here is a typical 7 day period from spring this year with over-night setbacks triggered by taking the main room stat down to 16 degrees for six hours between 2100 and 0300. For the rest of the time the heating is always on in weather compensation mode, crucially with a DIY script that boosts output when the actual room temp is below the desired room temp. This script is what achieves the recovery, without it, the house takes too long to recover, and comfort is compromised:       

This is my standard monitoring chart which includes a lot of variables. The ones we are interested in are the outside air temp, the OAT, which shows a fairly steady pattern over the period (which helps, less variation), with an average around 10 degrees, the indoor air temp, the IAT, which can be seen to vary as expected, and, in the green bars in the lower chart, the energy consumed in the previous hour. I can confirm that during this week, the house was comfortable to live in.

On most mornings, there is an increase in energy use immediately after the setback. I can easily determine how much energy I actually used during the period by summing the hourly energy use. Now comes the tricky bit: is that extra energy more or less than that saved during the setback? Here I have to do some whatiffery of my own: what if the setback hadn't happened? How much energy would I have used?

As it happens, my energy use in standard weather compensation mode is, unsurprisingly, very closely tied to the OAT. I can use that to determine what the energy use would have been with no setback, ie running continuously in weather compensation mode, by doing a regression of the hourly energy in on the OAT for the hours when the heating was on, and then use the regression equation to predict what the hourly energy use would have been for each and every hour during the whole period. As a sanity check, I have plotted the actual measured energy use with the setback against the predicted (by the regression equation) energy use without the setback: 

In a way, this chart really is the defining chart of this argument (it should really be a bar chart, but the result is too messy, so I used lines). It shows the setbacks and subsequent recovery peaks in the blue line, and the predicted hourly use without the setback in the orange line. We can see the predictions make sense: when away from the setback periods, the orange predicted line is very close to the blue actual line, with a bit of smoothing, which is to be expected because we used a single regression based equation throughout. The occasional middle of the day drops in the actual blue line use, if you are wondering, are the hours when the DHW heating was on, so less space heating that hour. 

And now for the answer to the question 'did the setback save money?'. The answer is that in my house, and in this week, yes it did, quite a bit in fact. The actual measured use (sum of the hourly values) for the week was 164kWh, while the predicted use (again, sum of the hourly values), had I not had a setback, came out at 227kWh. The setback saved me 63kWh that week, which is a saving of 28% for that week. 

Note the italics in the previous paragraph, because that is where the arguments start. This is a classic n=1 study, in this case in a small old leaky listed  building in southern England with a relatively high thermal mass for its size during a period of middle of the road OATs. To what extent, if any, can these findings be generalised to other buildings and other settings? Over to you...