Posted by: @davispj3

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My system set up is a mitsubishi ashp and — Ecodan FTC6, two zones, evohome with 2 x BDR91, and Economy 7 tariff.  To work efficiently.
1. Which zone should be Zone 1 (UFH or radiators)?
2. How does the BDR91 evohome signal interact with their MELCloud commands — do they conflict?
3. How should I set evohome zone 2 (whichever they don't control) given the same flow temp limitation?

Lets step back.  Why do you need/want 2 zones?  The heat pump, just like a boiler, can only supply water at a single flow temperature at any one time and its generally best to operate 'low and slow' so that as much emitter area is active as possible thus allowing the minimum flow temperature for any given energy output (ie heat loss).  

If you could explain the rationale for two zones and say a bit about your house (floor area, any notable layout features - eg a house split into two etc) I or others will be able to give a more focussed response. 

In answer to the question - do the external controls conflict with the Mitsubishi controller, yes very likely unless the control strategy has been well thought through.  Its generally best to avid external controls altogether unless they are specifically designed to control the flow temperature of the heat pump.

Posted by: @jamespa

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In answer to the question - do the external controls conflict with the Mitsubishi controller, yes very likely unless the control strategy has been well thought through.  Its generally best to avid external controls altogether unless they are specifically designed to control the flow temperature of the heat pump.

This is what we are trying to avoid if we go Ecodan, multiple controls. We would have a single zone and Ecodan FTC Wireless Thermostat PAR-WT60R-E .

Hopefully it can work without internet.

Posted by: @jamespa

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The heat pump, just like a boiler, can only supply water at a single flow temperature at any one time

Just a caveat to this, while we are mostly located in the UK - if people are browsing from mainland Europe,  Ecodan systems with 2zones are commonly fitted with a mixing tank to allow different flow temperatures in different zones. Where Zone2 is usually the lower temperature UFH.

However, in this case, @jamespa is almost certainly correct

Posted by: @davispj3

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BDR91 evohome signal interact with their MELCloud

The BDR91 will control the demand from the heat pump, basic on/off when setpoint > actual
The "MELCloud" part is confusing, because MELCloud is supplementary

Posted by: @batpred

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We would have a single zone and Ecodan FTC Wireless Thermostat PAR-WT60R-E .

Hopefully it can work without internet.

 

Indeed this is the way to go, if your main controller screen is not located within the house in a sensible location for taking a room temperature measurement

Posted by: @batpred

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Hopefully it can work without internet.

It does, it uses it's own wireless 400mHz link.