Boiler TRV's and weather compensation monitor

System

This discussion was created from comments split from: Boiler TRV's and weather compensation monitor.

legend99

Hi all,
Apologies for hijacking an older thread but it looks to have a lot of the questions I'm trying to understand asked already! 
We just got a new boiler, an Ideal Vogue Max System Boiler which I understand can handle both OpenTherm and Weather Compensation from an an external measure. 
The set up I have is 4 zones : 3 heating zones which are Ground Floor, First Floor and Second Floor and 1 hot water zone. In Ireland so we still tend to have a hot water cylinder in the hot press. All the radiators have Tado smart TRVs - each of these use a wired Tado thermostat on each of the 3 floors to make the call to the boiler to engage. One complication, by the way, is that the house came with the SL from the hot water cylinder and too floor thermostat wired together in a junction box in the hot press so only one wire actually goes back to the boiler. I.e. I can't distinguish, at the boiler side, whether the call for heat is from HW or second floor hearing zone. Note also that 2 towel rails on the first floor and 1 on the second floor do not have TRVs - they were left open to facilitate any bypass required if all the TRVs got stuck closed while somehow calling for heat. I should have got a bypass valve fitted at the boiler but never thought of it as I was away when the new boiler was installed. 

So now I've been googling TRVs versus Weather Compensation versus OpenTherm. Given the set up and the boiler I have, does anyone have any advice on what I should be doing? I think weather compensation maybe a problem as I won't be able to wire in a separate wire to the boiler so that it knows it is water calling for heat as I think the boiler needs to know it is a hot water call to increase the temperature? So does that mean weather compensation isn't really going to work? Should I consider OpenTherm from the wired Tado thermostats as I think they can be configured for it? And assume they can do is even if they are a slave to TRVs calling to them? 

This is more complicated than I thought. Or am I overthinking it - and do I just leave everything ad TRV set-up like was on the old boiler?!

Thanks for any advice or feedback!

MSE_Stephen

@legend99 We've spit this into a new thread for you.

FreeBear

Weather compensation is handled by the boiler. If you have priority hot water enabled, weather comp shouldn't affect DHW.

Got OpenTherm on my boiler, and I must admit, haven't bothered with weather compensation. My control system will dynamically vary the flow temperature depending on load.

tacpot12

The boiler needs to know whether the heating demand is from the house (for space heating) or the cylinder (for domestic water heating) if it is run at a higher temperature when heating the cylinder. 

The cylinder will usually need water that is a higher temperature than the house needs for efficient space heating. 

This idea is sometimes described as hot water priority - any demand for hot water is satisfied first and at a higher temperature. If the zone valves aren't set up to stop water going to the radaitiors when there is a priorty demand from the cylinder, then the TRVs stop the rooms becoming too warm.  

I don't know the TADO system well enough to know if it has a way to work out what heating load is being demanded from each of your zones and to add this up to create the one OpenTherm signal that would tell the boiler what temperature water is required to heat the house. I suspect that it cannot do that. If not, then the next best option is weather compensation using an outside sensor.

I have an Intergas system boiler that has an outdoor weather sensor that is connected to the boiler via a relay. The heating demand signal from the cylinder stat operates the relay. The effect of this is that if there is a heating demand from the cylinder, the relay disconnects the outdoor weather sensor, so the boiler just heats the water to the temperature set on the front panel (70C in my case). This ensures that the boiler can heat the cylinder to the point where the demand is satisfied - the cylinder stat is set for 55C. When there is no demand from the cylinder, the relay reconnects the weather sensor to the boiler so the water temperature is set according to the weather compensation curve. We also have TRVs on all the radiators except the one in the bathroom, so this stops the rooms from overheating when there is a demand from the cylinder and the boiler is producing water at 70C. 

This is not quite as efficient as having a proper priority hot water system where the water from the boiler can only go to the cylinder or to the space heating, but it works well enough for me. 

In your situation, I would consider consulting a heating engineer who says they are an expert with the TADO system, and ask them to suggest improvements.