Honeywell Evohome, Tado, Hive, Nest, Drayton - which Opentherm thermostat & system?

[SimonD]

As the title really. Anyone able to provide a view on these systems, their preference and why? But also, if you have any of the above, what's your experience been?

 

I'm also considering the 'smart' trv modules and wondering whether they're worth it over well set up manual trvs running with opentherm and system running hot water priority to avoid unwanted heating system temperature peaks.

 

Thanks.

[JohnMo]

Do you have the option of weather compensation?

 

Are you on a heat pump, gas boiler or something else?

 

What sort of house are looking to fit the system too, such as insulation standard, one bedroom flat, 20 bedroom mansion etc as it makes a difference.

 

[SimonD]

8 minutes ago, JohnMo said:

Do you have the option of weather compensation?

 

Are you on a heat pump, gas boiler or something else?

 

What sort of house are looking to fit the system too, such as insulation standard, one bedroom flat, 20 bedroom mansion etc as it makes a difference.

 

 

Ah, yes, weather compensation is in. Currently gas going in with upsized rads for 55 degree flow temps for future heatpump upgrade. Although technically a renovation & extension, it's got good insulation standard (better than BR newbuild), good airtighntess, 3g glazing, 5 bedrooms and a few other rooms - actually room numbers is fluid as we're probably now leaving a large portion of the house open plan. I'm currently also leaving my options open for additional insulation within service voids so may get even better.

 

Total heat loss calc inc 3kW for water is 8833 watts. 18kW boiler that can modulate down to 3.6kW which is the lowest I could find.

[JohnMo]

So the boiler is slightly oversized for the coldest day, so anything warmer outside will make the boiler feel more oversized.  You will probably need a buffer. If you look at my other posts under heat pumps, there is the calculations for buffer sizing.

 

If you are implementing weather compensation, whole system would be run 24/7 on a variable temp based on outside temp.  The heat geek website tells you how the set up weather compensation and how to balance the system. The room thermostats will only be there to limit room temp, so the sun is out and warming the room, the thermostat/trv in that room will turn off the heating in that room only.

 

For this type of system a simple dumb mechanical thermostat/trv is all you need one per radiator.

[SimonD]

So looking at the controls in more detail and from what you've said, it appears that it's either weather compensation or Opentherm load compensation rather than a combination of both. I wonder if there are any figures for which generally provides the best balance between energy efficiency and comfort?

[JohnMo]

Some systems allow you use both.  Generally I believe load compensation is a active in one room and applies a shift in temperature to the whole house.  So if you use the load compensation in your living room and it hotter than your setting, it will cool the CH flow temp to all rooms.

 

Weather compensation is a low and slow, long boiler run times at very load loads.  So possibly suits people that are home slot of the time.  Load compensation is run it hot and for short periods with some modulation. Possibly suit people out most the time.