@mattengineer, please do a write up; there will be a lot on here interested.

@mattengineer A write up would be great! I do like the sound of the ambisense, but as far as I can tell if i can get my drayton wiser system to play nice with the new setup, I already have the control it would offer (happy to be corrected though!) and then 0 additional outlay, cheapest I can find the ambisense trvs is ~£65 a pop, so would be the guts of £800 to do all the rads again! (not sure the good lady would be too happy!)

@mattengineer, if you’d like to publish a review or system set up article on the main site, please DM me. 

@dchilton, how's your system coming along now that temperatures are tumbling?

Hi @editor! So we finally had the system installed last week over the course of 2 days, with the boiler/heat pump installed on day 1 and day 2 taken up with the wiring installation for control of the pump etc.

So far it is probably too early to say how it is going as I am still trying to work my way through all the settings etc. but what I can say is that the house is toasty warm (possibly too warm at times!). On the concern raised by Brendon previously re: a new boiler would struggle as well, I was probably not clear enough on what I meant, the boiler was not struggling with the heating per say, but more the DHW, and that is definitely a non issue now, plenty hot and increased pressure as well.

The installers were unable to fit the heat meter on the day due to lack of stock and as such will need to revisit to install that and then drain and refill the system with glycol etc. so will be picking their brains on the setup upon their return.

In terms of upscaling radiators, we did not go down that route (at least not to K3s), but what I did do was add some additional rads in the coldest rooms and upscaled any type 11 or 21 rads so that all the rads are now type 22s (with the exception of some traditional column rads), which has definitely helped as well.

It was snowing earlier today, so I guess we will see how well the system will cope, but I would expect not to have too many issues as if the pump is not coping, or the trivalent system decides based on our gas/electric rates that gas is more efficient, the boiler will take over and the house should remain warm.

If I get a chance I will post some images and more detail as to exactly what has been installed as would be interested to see if anyone else has a similar system and what 'tweaks' should be applied to get the best overall performance out of it.

Will keep you updated as to how it proceeds!

Thanks

David

@dchilton 

Hi David,

I am pleased to hear that you have had your system installed and commissioned with what would appear to be little fuss.

I was conversing only yesterday with Adam, who has what sounds like a similar bivalent system to your own, so you may be able to exchange notes. One question that I would ask is 'is your heating being provided by your gas boiler or your ASHP at the moment'? The reason that I ask is that at the moment, Adam's heating is predominantly being provided by his gas boiler at the moment, because the controller has calculated that this is the most cost effective option.

My understanding from having studied Adam's system is that the gas boiler and ASHP do not both operate at the same time for heating, it is either the gas boiler or the ASHP that should be operating not both.

Adam's system is using the Vaillant controller that comes with the ASHP to make the decisions between gas boiler or ASHP, it does this based on the tariff rates for gas and electricity that have to be set in the controller. Is your system operating in a similar manner?

@derek-m

Hi Derek

Yes, sounds like the system is almost identical to that Adam has. Tariffs for both gas and electric are both entered on the system and it then makes the call as to the most (cost) efficient method of providing the heat, so at the minute, yes it seems to be predominantly be utilising the gas boiler, but the pump is also kicking in occasionally. Having had a dig through the settings I notice the installers have not activated Active weather comp, so would be interested to see what folks thoughts are on that and in terms of heat curve it is set to 1.5, so that may be something to tweak as time goes by.

For interest, the components I have installed are as follows (with some pictures - excuse the bombsite that is the kitchen - new one in January!)

• Vaillant Arotherm plus 5kW ASHP
• Vaillant Ecotech Plus 835 Combi boiler (all DHW provided by this)
• 45 L buffer tank
• Remote expansion vessel

   

• Vaillant VR71 wiring centre
• Vaillant VWZ AI Heat pump controller
• Vaillant Sensocomfort RF controller with outdoor weather sensor
• Vaillant VR921 internet gateway

• 

  

  

  

  

   

@dchilton 

Hi David,

I think that you will find that weather compensation does not work with the gas boiler, since the ASHP controller just switches the gas boiler on and off, so cannot set the required water flow temperature. I would suggest that you check the water flow temperature setting on the gas boiler, and if possible lower it to a low setting if possible.

You can still enable the weather compensation on the ASHP controller, and may find that the 1 or 0.8 curve may provide best results, but since it depends on the heat loss and heat emitter sizing, it may be necessary for you to try different curves to find the most appropriate one.

The changeover point from gas boiler to ASHP will obviously limit the ambient temperature range over which weather compensation will be functioning. I have just seen in the SensoComfort 720 instructions that it is capable of adaptive heat curve control, which should give better control of the indoor temperature.

One thing that I remember discussing with Adam, is that there are settings for the ambient air temperature range over which the bivalent point can operate, so this could be why your ASHP starts occasionally, or it could just be the fact that it is warmer outside and more economical to run the ASHP.

Have a look through the manuals and if you get stuck then give me a shout. 

@derek-m

Hi Derek, thanks for the feedback, I am digging through the mass of information in the manuals as we speak (so much for reducing carbon footprint, the amount of paper that comes with the system probably negates ANY saving! 🤣 )

A question if I may re: setting/selecting the heat curve. The installers had set the adaptive heat curve to Off, so would you suggest trying it activated?

Looking at the heat curve settings below, I think I agree (if I am reading it right!), as the setting of 1.5 it was on is targeting 40°C flow when it is ~12°C outside, so a setting of 0.8-1 seems more accurate for the current climate outside (5°C), and I have settings for manually adjusting the curve and also for activating the adaptive curve, so I suppose my questions is, does activating the adaptive automatically then adjust the curve based on outside temp (i.e. changes itself to be ~ 0.8), or should I set it to adaptive AND adjust the curve setting manually?

Obviously asking a question about a system you don't own, but you certainly know more than me!

@dchilton 

Hi David,

I have been monitoring our heating system for quite a number of years, and for our bungalow for each 1C that the ambient air temperature falls, the radiator temperature needs to be increased by approximately 1C. So starting with the 1 or 0.8 curve should not be too far from the ideal.

I'm afraid the description of adaptive heat curve is not very clear in the manual, so I am assuming that it is similar to that on the Ecodan controllers. I think that it will measure the indoor air temperature, probably within the SensoComfort VRC 720 and use this value to fine tune the water flow temperature. But don't quote me on this since I have not seen this description in black and white.

Actually, with your bivalent system it should not make that much difference, unless the ratio of gas to electricity tariffs change dramatically, since on your present tariffs, by the time the system switches over from gas boiler to ASHP, your energy consumption will be much reduced. I suppose if you are a perfectionist like me, you would aim to have the systems set so that the changeover from gas boiler to ASHP is as seamless as possible.

Thanks @derek-m!

Let the tweaking commence!

David

Posted by: @derek-m

@dchilton 

Hi David,

I think that you will find that weather compensation does not work with the gas boiler, since the ASHP controller just switches the gas boiler on and off, so cannot set the required water flow temperature. I would suggest that you check the water flow temperature setting on the gas boiler, and if possible lower it to a low setting if possible.

You can still enable the weather compensation on the ASHP controller, and may find that the 1 or 0.8 curve may provide best results, but since it depends on the heat loss and heat emitter sizing, it may be necessary for you to try different curves to find the most appropriate one.

The changeover point from gas boiler to ASHP will obviously limit the ambient temperature range over which weather compensation will be functioning. I have just seen in the SensoComfort 720 instructions that it is capable of adaptive heat curve control, which should give better control of the indoor temperature.

One thing that I remember discussing with Adam, is that there are settings for the ambient air temperature range over which the bivalent point can operate, so this could be why your ASHP starts occasionally, or it could just be the fact that it is warmer outside and more economical to run the ASHP.

Have a look through the manuals and if you get stuck then give me a shout. 

 

Given the Vaillant Ecotech Plus 835 Combi boiler itself is able to support weather compensation with the appropriate controller i do wonder what it is doing when it is actually turned on via the valiant ebus from the SensoCOMFORT. 

The SensoCOMFORT 720 can be used with just a standard Ecotech Plus 835 without an ashp. In this setup the controller can use weather compensation with the gas boiler.

I thought Valiant created the  SensoCOMFORT 720 to make it easier to configure bi valent systems and to provide a single controller.

Are we sure the ebus signal from  SensoCOMFORT is simply an on off control which seems like a missed opportunity from Valiant?