Can evohome drive a boiler with a 3-way mixing valve using the HM80?

[courcirc8]

I replaced several month ago my single zone thermostat with the evohome system. In a first time I left the previous boiler control (3-way mixing valve with weather compensation) but I had to set the temp slope pretty high to have good regulation in the north room.
Now I want to upgrade the system because the high boiler output temp (65-70d) increases the losses in the walls, pipes (my installation is not well isolated and inside some rooms, the domestic COLD water becomes warm due to proximity with radiator pipes (!)).

All the "evohome proposals" I could read are based on a ON/OFF boiler control that does not sounds good to me. (Y plan, S plan or simple relay Wo domestic water).
I know that the mixing valve controller HM80 is compatible with the evohome system, but can it be used to adjust the boiler heat demand?
Did somebody tried it, or is there any doc available?

Best regards and many thanks for the help
Courcirc8

[SensibleHeatUK]

I've not tried the HM80 with Evo, but in Hometronic the HM80 registered as a zone device, not a boiler/demand relay, which meant it could not be used in the way you require.

I don't know if Evohomeshop has any experience with this and can confirm if it is any different.

[courcirc8]

I've not tried the HM80 with Evo, but in Hometronic the HM80 registered as a zone device, not a boiler/demand relay, which meant it could not be used in the way you require.

I don't know if Evohomeshop has any experience with this and can confirm if it is any different.

Many thanks for your reply.
I suspect you are right and that this is the same for evo, but it is hard to accept (as a customer) that a modern regulation system offers only ON/OFF control for heat production and advertises for cost savings... How does it works with modern condensing boilers that request a progressive control?
Maybe I will try to do it myself if I succeed spying the RF protocol to the HR92 valves.

Courcirc8

[top brake]

this is more of a continental Europe application and the HM80 isn't sold in the UK

[sharpener]

this is more of a continental Europe application and the HM80 isn't sold in the UK

Who said anything about the UK? courcirc8 is in Switzerland (the name is I think a play on the French for "short circuit") so it's a reasonable question. There are quite a few continental users who value this forum for the information it provides.

I wonder if the answer to the query about continuously variable boiler control lies in the OpenTherm bridge, can any of the experts enlighten us about this?

Incidentally my experience is that weather compensation is the single most effective measure in reducing energy consumption yet UK heating installers seem woefully ignorant about it. A shame that Danfoss stopped making their Boiler Energy Manager as a retrofit device.

[top brake]

Who said anything about the UK? courcirc8 is in Switzerland (the name is I think a play on the French for "short circuit") so it's a reasonable question. There are quite a few continental users who value this forum for the information it provides.

I wonder if the answer to the query about continuously variable boiler control lies in the OpenTherm bridge, can any of the experts enlighten us about this?

Incidentally my experience is that weather compensation is the single most effective measure in reducing energy consumption yet UK heating installers seem woefully ignorant about it. A shame that Danfoss stopped making their Boiler Energy Manager as a retrofit device.

Several boiler makers now offering weather compensated boilers, being driven by regulations
TPI and OpenTherm also widely unknown by installers, together with multi zoning becoming more accepted and recognised as the most effective measure

[sharpener]

Several boiler makers now offering weather compensated boilers, being driven by regulations

That's not really the point, weather compensation needs to be promoted by the installers to get widespread acceptance. I specified it when we had a new heating system installed in 2008 as part of a loft conversion but the heating subcontractor had never heard of it and then could not find any 12kW boiler that had it as an option (fortunately I discovered that the Vokera did).

I appreciate the technology is more common now on new boilers but that doesn't address the retrofit market. At our previous house I fitted the Danfoss BEM and two zone valves and immediately got a one-third saving on the gas bill (still not the 40% claimed in other threads though). New boiler had recently been fitted by previous owners but there were neither room stats nor any TRVs!

[top brake]

That's not really the point, weather compensation needs to be promoted by the installers to get widespread acceptance. I specified it when we had a new heating system installed in 2008 as part of a loft conversion but the heating subcontractor had never heard of it and then could not find any 12kW boiler that had it as an option (fortunately I discovered that the Vokera did).

I appreciate the technology is more common now on new boilers but that doesn't address the retrofit market. At our previous house I fitted the Danfoss BEM and two zone valves and immediately got a one-third saving on the gas bill (still not the 40% claimed in other threads though). New boiler had recently been fitted by previous owners but there were neither room stats nor any TRVs!

The retrofit market is covered very well with TPI thermostats that give you control over the cycle rate and minimum run time of the boiler; this achieves load compensation.
Add multi zone control and the potential savings are maximised.

[sharpener]

TPI thermostats ... give you control over the cycle rate and minimum run time of the boiler; this achieves load compensation.
Add multi zone control and the potential savings are maximised.

Well up to a point. But the boiler is still either firing or not firing. Modern boilers have modulating burners and their thermodynamic efficiency is better at low firing rates because the heat exchanger is in effect bigger in proportion to the heat input. TPI thermostats don't take advantage of this. And you have to have one for each zone unless there is a zone which is always on.

Additionally, weather compensation also seeks to keep the circulating water temperature as low as possible for a given heat demand. This keeps the boiler in condensing mode for as much of the time as it can. I don't think TPI thermostats can achieve this result either, because when it is fired up a low water content boiler will quickly achieve the maximum flow temperature set by its own thermostat, whereas with weather compensation this is automatically varied according to the OAT.

[top brake]

Well up to a point. But the boiler is still either firing or not firing. Modern boilers have modulating burners and their thermodynamic efficiency is better at low firing rates because the heat exchanger is in effect bigger in proportion to the heat input. TPI thermostats don't take advantage of this. And you have to have one for each zone unless there is a zone which is always on.

Additionally, weather compensation also seeks to keep the circulating water temperature as low as possible for a given heat demand. This keeps the boiler in condensing mode for as much of the time as it can. I don't think TPI thermostats can achieve this result either, because when it is fired up a low water content boiler will quickly achieve the maximum flow temperature set by its own thermostat, whereas with weather compensation this is automatically varied according to the OAT.

The efficiency ratings of boilers in conjunction with controls is about to be published and comes into effect in September, you may be suprised by some of the categories and overall efficiencies

[The EVOHOME Shop]

I don't know if Evohomeshop has any experience with this and can confirm if it is any different.

Sorry only just seen this but sadly I haven't used the HM80 with EVO.

Incidentally my experience is that weather compensation is the single most effective measure in reducing energy consumption yet UK heating installers seem woefully ignorant about it. A shame that Danfoss stopped making their Boiler Energy Manager as a retrofit device.

Weather Compensation is great - I agree it would maximise energy use but certainly not the single most effective measure for reducing energy consumption.

Having fitted weather compensated systems for some time (both commercial and domestic) and having my own weather compensated Ground Source Heat Pump - WC is something I do widely promote but certainly not a replacement for good controls.

Retrofitting WC to domestic systems (similar to commercial applications) is not necessarily the most efficient way of doing things. To have a boiler with a flow temperature of 75-82 degrees C to then mix it down to say 40 degrees C is the best a 'bolt on' kit will ever achieve and is in my opinion inefficient. A lot of the 'domestic energy management' systems I have seen really are just 'load compensated' and produce results not dissimilar to what evohome already achieves.

Much better to have a truly weather compensated domestic boiler (for instance a Worcester Bosch Greenstar CDi with FW100 controls) with zoned heating demand from evohome - this is a great application with the best of both worlds (heating zone control where you need it and accurate boiler flow temperature control) and something I have done many times with excellent results.

[Fursty Ferret]

True, but if you set the water temperature of the boiler fairly low it'll modulate its output to give the targeted temperature increase required.

[top brake]

True, but if you set the water temperature of the boiler fairly low it'll modulate its output to give the targeted temperature increase required.

The boiler temperature will be set during commissioning for example 70 degrees C
It will modulate down to suit the demand. For example our Vaillant with evohome is currently set to run at max of 70 and is actually at 59 right now, earlier today it was down to 45. Also remember if you want it to heat stored water to 60 it will need to be a bit hotter than that to allow for heat transfer losses.

If you set it too low it won't condense and will actually be less efficient!

[sharpener]

Lots of good stuff here!

Retrofitting WC to domestic systems (similar to commercial applications) is not necessarily the most efficient way of doing things. To have a boiler with a flow temperature of 75-82 degrees C to then mix it down to say 40 degrees C is the best a 'bolt on' kit will ever achieve and is in my opinion inefficient.

Agreed. If you do it with a mixing valve the mixing process results in an irrecoverable increase in entropy, much better to have the boiler running at the lower temperature to begin with. This is why combining radiators with underfloor heating does not achieve the energy savings it could if the boiler was in condensing mode all the time. Ideally you would use the return from the radiators as the flow to the UFH.

True, but if you set the water temperature of the boiler fairly low it'll modulate its output to give the targeted temperature increase required.

Then what happens in a cold snap? The beauty of WC is that once you have set the gradient you don't have to touch the boiler again.

The boiler temperature will be set during commissioning for example 70 degrees C
It will modulate down to suit the demand. For example our Vaillant with evohome is currently set to run at max of 70 and is actually at 59 right now, earlier today it was down to 45.

Is this demand management a feature of the boiler or of the evohome system?

Also remember if you want it to heat stored water to 60 it will need to be a bit hotter than that to allow for heat transfer losses.

Does the Vaillant do this automatically? I had to add a relay to cut out the WC when the DHW was calling for heat (though it would have been trivial for Vokera to do this in software).

If you set it too low it won't condense and will actually be less efficient!

Eh?

[top brake]

Lots of good stuff here!



Agreed. If you do it with a mixing valve the mixing process results in an irrecoverable increase in entropy, much better to have the boiler running at the lower temperature to begin with. This is why combining radiators with underfloor heating does not achieve the energy savings it could if the boiler was in condensing mode all the time. Ideally you would use the return from the radiators as the flow to the UFH.



Then what happens in a cold snap? The beauty of WC is that once you have set the gradient you don't have to touch the boiler again.



Is this demand management a feature of the boiler or of the evohome system?



Does the Vaillant do this automatically? I had to add a relay to cut out the WC when the DHW was calling for heat (though it would have been trivial for Vokera to do this in software).



Eh?

The TPI works with the boiler management (also Honeywell) to operate the boiler in condensing mode by achieving a return temperature differential of at least 20 deg C and below 55 deg C (dew point)

I have a really good faq on this i will share
Edit here it is:

http://www.honeywelluk.com/documents/All/pdf/TPI%20Functionality%20explained.pdf

Regarding the performance adjustment on a cold day this is where the optimum start helps, it knows to start the heating earlier to achieve temperature