New Home - "Upgrade" to Weather Comp or OpenTherm??

[Barnacles]

Hi All,

 

We have recently bought a newly built "dolly house" which is equipped with an Ideal Combi ESP1 35 boiler with 2 zones (upstairs and downstairs) managed by Honeywell T6R wireless thermostats.

 

I have been looking into heating controls for friend and got around to the learning a bit about OpenTherm and weather compensation. Then it dawned on me to check my own CH system and I was not entirely surprised to find that although both my boiler and thermostats support OpenTherm it wasn't being used! Clearly the plumbers weren't ready to embrace the new technology.

 

I then learned that my boiler also has the option of weather comp too and this got me thinking. As it would cost very little and take minimal effort to modify my system to use either OpenTherm or weather comp would one have any significant benefits over the other? If it were your house which would you choose?

 

The Honeywell control box is right next to the boiler so running a cable for OpenTherm would be a doddle and I can easily run a cable from the boiler to a north-facing wall for a temperature sensor for weather comp so either way would take no more than 30 minutes work.

[MrPotts]

Try both and see what works best. OT relies on interior temps reported by an indoors thermostat and WC relies on exterior temps and an thermostat outdoors.

[JohnMo]

If you have radiators then Opentherm is pretty easy to implement. Set desired temps on the thermostat and it will do the rest.

 

Not sure about Opentherm and UFH, that may be better WC.

 

But both options would reduce flow temp and keep house more comfortable.

[Barnacles]

Sorry, I forgot to say that the house has radiators all round. They seem to be specced about right for the room sizes given the fairly decent insulation.

[JohnMo]

Do the easy Opentherm first see how it goes.

 

Do you have any zone valves to open, if so you will need them open to get heat around. The Opentherm bit just modulates boiler output and flow temp. Doesn't deal with stuff in the system.

[Barnacles]

19 minutes ago, JohnMo said:

Do the easy Opentherm first see how it goes.

 

Do you have any zone valves to open, if so you will need them open to get heat around. The Opentherm bit just modulates boiler output and flow temp. Doesn't deal with stuff in the system.

Yes, there are two zone valves. I'll check the docs on the Honeywell control box to see if it has info about whether the valves should be disconnected (electrically) when using OT. I suppose I could disconnect them and use the levers on the valves to open them permanently.

[Barnacles]

And another thought. As most of my radiators have TRVs fitted, presumably I just set them to their maximum setting? Or remove the heads completely??

[marshian]

8 minutes ago, Barnacles said:

And another thought. As most of my radiators have TRVs fitted, presumably I just set them to their maximum setting? Or remove the heads completely??

 

Keep them as temp limiters is what I've done (set them fractionally above the desired room temp) - especially when you are in the getting the heat balance right stages

[marshian]

12 minutes ago, Barnacles said:

Yes, there are two zone valves. I'll check the docs on the Honeywell control box to see if it has info about whether the valves should be disconnected (electrically) when using OT. I suppose I could disconnect them and use the levers on the valves to open them permanently.

 

Careful here - you need a really good understanding of how your system is set up and wired

 

Manually opening the valves may not result in the micro switches sending the signal to the boiler

 

In my system the single CH zone valve is a normally open one (it only shuts when there is a demand for HW ie the tank needs re-charging and at the same time the HW zone valve opens) - the boiler isn't wired to fire on the confirmation of a CH zone valve opening ie microswitch made)

[LnP]

2 hours ago, MrPotts said:

Try both and see what works best. OT relies on interior temps reported by an indoors thermostat and WC relies on exterior temps and an thermostat outdoors.

My Worcester Bosch boiler is connected to the wifi and gets its outside air temp WC data from the internet. No thermostat outdoors. And the EasyControl app allows me to control it remotely.

[Barnacles]

1 hour ago, marshian said:

 

Careful here - you need a really good understanding of how your system is set up and wired

 

Manually opening the valves may not result in the micro switches sending the signal to the boiler

 

In my system the single CH zone valve is a normally open one (it only shuts when there is a demand for HW ie the tank needs re-charging and at the same time the HW zone valve opens) - the boiler isn't wired to fire on the confirmation of a CH zone valve opening ie microswitch made)

Good point, I'll be sure to know exactly what everything needs to do before I change anything.

 

My understanding of OT is that there are just a pair of wires from my Honeywell control box to the boiler and they do the "triggering" of the boiler and presumably some sort of PWM signal to tell the boiler what temp to heat the CH water to. If that's the case then I can't see zone valve microswitches have any purpose. Hmmm, I'm off to find the instruction book for the Honeywell kit. 😃

[Barnacles]

1 hour ago, LnP said:

My Worcester Bosch boiler is connected to the wifi and gets its outside air temp WC data from the internet. No thermostat outdoors. And the EasyControl app allows me to control it remotely.

Do you generally find the WC works well? Is your house usually at a comfortable temperature? Do you have radiators or UFH?

[Barnacles]

Looks like the zone valves do need to be connected:

 

 

To keep the valves open???

[LnP]

2 hours ago, Barnacles said:

Do you generally find the WC works well? Is your house usually at a comfortable temperature? Do you have radiators or UFH?

It's in a Victorian coach house in the garden which we refurbished as guest accommodation. Solid walls lined with insulated plasterboard. We don't use it very often so really can't comment on comfort levels except to say that the people who've used it said they were comfortable. It has radiators. I can select the Heat Curve parameters via the app. Right now, there's nobody there and I have it set on Away mode which has a room target of 10 degC. Outside is -2 degC and the flow temp it's chosen is 23 degC. If I turn off the Away mode it's targeting 20 degC room temp and it selects a flow temperature of 53 degC. Pretty straightforward and easy to make changes. It seems to work fine, though as I said, we don't have a lot of experience with it.

[MrPotts]

5 hours ago, LnP said:

My Worcester Bosch boiler is connected to the wifi and gets its outside air temp WC data from the internet. No thermostat outdoors. And the EasyControl app allows me to control it remotely.

How close are you to the local weather station where the control gets its information from? The further away you are the least accurate the information will be. Better than nothing but not as good as having an outside thermostat on the wall of your house.

Edited Saturday at 19:51 by MrPotts

[SteamyTea]

12 hours ago, MrPotts said:

How close are you to the local weather station where the control gets its information from

May be better to fit some outside temperature sensors to the exposed walls, then solar gain can be taken into account.

The difference between the NE and SW sides of my house is often over 3K depending on time of day.

[Barnacles]

I was going to launch into doing the switch to OpenTherm this morning but I got the look from my wife that says "it's really cold outside, if you mess this up and leave us without central heating....." 😄.

 

Perhaps I'll wait until the weather isn't so harsh.

[LnP]

23 hours ago, MrPotts said:

How close are you to the local weather station where the control gets its information from? The further away you are the least accurate the information will be. Better than nothing but not as good as having an outside thermostat on the wall of your house.

I don't know where the weather station is that the software in my boiler gets its temperature data from, but if it's a degree or two out, it won't matter. There are a host of other factors which a simple WC heat curve won't take into account, not least of which is that the "curve" in my boiler software is a straight line while the relationship between heat loss and flow temperature is non linear.