Vaillant aroTherm ASHP & Stelrad radiators - how do they work together?

[Alex Carr]

I won't mention the name of the company but installing and set-up of a Vaillant ASHP to provide heat for ufh downstairs, vertical Stelrad radiators upstairs plus domestic hot water, has been a saga I would not like to live through twice. Here's my query: I understand how to programme the UFH & DHW, and they seem to be working ok, but operation of the rads seem only controllable by valves fitted to the base of each rad (there are 4 + an unprogrammable thermostat in each of three rooms). I don't get the relationship of the rads to the rest of the ASHP system - do they operate solely on the basis of their valve settings? (1 -5; the temperature range of these settings is not obvious; I have to corelate the valve setting to the temp settings on the wall-mounted thermostats to see what level of heat the rads are generating. Currently the UFH doesn't turn on until 6 a.m. each day but the rads are going during the night, and I sure as hell don't want that - is there a way of getting control of these beasts above and beyond the valve control on each rad? Enlightenment would be hugely appreciated.

[JohnMo]

Tell us more about the system.

 

UFH do have lots of thermostats (so plenty of zone on that also)

 

Do you have a buffer?

 

Do you run weather compensation?

 

I suspect you are running the system similar to a gas boiler, as in timed running slots for heating?

[Alex Carr]

Yes, have a buffer. Weather compensation? I may be wrong, but I presume you mean that when the outside temperature falls below a certain point the heating kicks in; yes, the system does this. Yes, timed running slots for heating. More Q's?

[JohnMo]

No more Q's

 

You need to have think about how you actually operate the system.  Timed heating slots will drive up your heating cost most likely as the heating system has to run hotter than ideal to play catch-up. more further down

8 hours ago, Alex Carr said:

I don't get the relationship of the rads to the rest of the ASHP system - do they operate solely on the basis of their valve settings? (1 -5; the temperature range of these settings is not obvious; I have to corelate the valve setting to the temp settings on the wall-mounted thermostats to see what level of heat the rads are generating.

I would suspect you have two control methods in each room - a radiator thermostatic valve, so this controls the radiator output based on room temp, plus what sounds like a room thermostat that possibly calls for heat from the heat pump.

 

Your UFH will also be calling for heat randomly, so the whole system is likely to run rubbish and cost huge amounts to run.

 

My advise

Bedroom wall thermostats set very high so they are unlikely to stop calling for heat. Set radiator valves fully open for now.

Set all UFH thermostats high, so they always call for heat. 

Remove all timers and set to run 24/7

Now you need to get access to your heat loss calculations and the weather compensation setting in you controller. Read your manual

At the warm weather end of the WC curve, set to 25 deg flow at 20 degs outside, the cold end set per your heat loss calculations, so design outside temp to max flow temp. If you have predefined curves to select check and adjust as required.

 

Now you need to adjust the WC curves to get the lowest flow temp and a stable comfortable house temp. Now adjust your bedroom radiator valves to get a comfortable bedroom temp. This will take a few days at least.

 

You are now at the cheapest running mode, then adjust slightly to get the comforts you need. Never switch off, just have small 1 to 2 deg setbacks.

 

[Alex Carr]

On 17/05/2024 at 19:12, nod said:

 

Thanks for that information John, but it will take a bit of time to get my head around what you are saying as it is not entirely comprehensibe to me. The installation company have been no help at all in helping me understand how to achieve the optimum running of the system. (There's a significant learning curve which I'm only just taking tentative steps to negotiate.) I would like to study the contents of your reply and, if it's agreeable to you, ask you some Q's. We'll get our first month's bill in a day or so and we'll see how our untutored use of the system pays out - if I can re-calibrate the workings as you are suggest the second month's bill should reflect a more economical set-up.

[JohnMo]

I would make a change take note of electric meter readings, with average daily temperature.

 

Ask as many questions as needed. 

[Blooda]

Morning @Alex Carr

 

We have Vaillant Aerotherm, With 3 circuits,  UFH, Rads, Towel Rail, and DHW.  When I ordered this [full on covid] I didn't have a clue. but now have a bit more understanding.

 

UFH is controlled by Emetti, Rooms Stats, [was 5 zones [7 loops] now rewired to 2] and wiring centre and Manifold.

Room Rads - are controlled by Vaillant Sensocomfort. 

Towel Rails are on a timer to come on 20 mins morning and night. 

 

The first thing you need is the Vaillant Schematic, to ensure the installer has installed it as Vaillant designed.