How to control an Ecodan with UFH manifolds?

[PhilT]

2 hours ago, JohnMo said:

With a heat pump, there is a slight disadvantage running rooms with heating off and others on, the internal heat loss between rooms, means a higher flow temp is required for the heated room, so you CoP goes down.  It actually becomes as cheap to heat the whole house.

I disagree. You use less energy to heat less volume, and that saving dwarfs any miniscule heat loss between a heated and a non-heated room.

[JohnMo]

Certainly not what heat geek states. And their calculations show.

 

But each to their own.

[joth]

There's so many free variables both answers can easily be right in some situation. In an extremely well insulated home you only need a teeny tiny heat emitter, and so long as the ASHP can modulate down to supply it at a low temperature without short cycling, then yeah a single room could conceivably easily provide all the heat for the house.

On a conventional/older home it's a completely different matter, where that room would have to be belting out heat to deal with all the losses everywhere else. But if the room it's in has sufficient drafts and losses it's moot as it's going to be blown out  before ever going to have chance to raise the temperature on any other room.

Many variables 

 

[ReedRichards]

I live in an old timber frame house.  The exterior walls have about 100 mm of rockwool insulation but so, it appears, do all the interior walls.  So in principle I could turn the heat off in some rooms and just reduce the effective volume of the house (provided I remember to keep the doors closed). 

[Jymmm]

On 20/10/2022 at 08:03, joth said:

@JohnMo solution is the most efficient one but takes a bit of setting up so installers often won't do that. Also some users will find it confusing that turning a roomstat up high won't cause the room to get any hotter.

 

For completeness the alternative is ditch the wireless stat and use the room stats to call for heat from the ASHP same as they normally would from a boiler. The requires an UFH wiring center at the manifold actuators with a "dry contact" relay output to call for heat, and wires this into the zone 1 or zone 2 call for heat inputs on the ecodan FTC

You can still use weather compensation. But the system can easily short cycle and run at low efficiency if rooms call for heat at different times to each other. (in my system I have logic controller manage the call for heat and it will only do so when a certain % of rooms need heating)

 

Do you have any details on the logic controller you have. Is it something you have DIY'd ? I'd be interested in one for my system.

[JohnMo]

I've been fiddling with my system, was on straight WC with a buffer in the system, seemed to work great at very low demands, but as demand went up the boiler started using a way higher rate of gas than it should.  So went for a thermostat on the buffer cylinder and used a relay to control the logic of when the boiler fires up.

 

So if the UFH has a heat demand, it sends 230v through the buffer thermostat.  If the thermostat is also calling for heat, the relay closes and gives a demand signal to the boiler.  The boiler only fires when both the cylinder thermostat and the UFH require heat, if only one requires heat the boiler does not fire up.  Set the buffer to 30 degrees and the thermostat has a hysteresis set to 2.  Have found that the buffer temp overshoots by a couple degrees, so the hysteresis is closer to 4 in reality.

 

Also I have installed a heat meter on the UFH, so this records kWh consumed, but what is really good, shows in real time the kW consumed by the floor, changing every second.  Slight changes in flow temp, show a change in kW being put in the floor.  You can make changes to set the ideal flow temp, based on heat loss calcs for the average monthly temp.

 

UFH heating is controlled by a simple thermostat, with a hysteresis of 0.25, but would be better if it was 0.1.

 

 

[joth]

10 hours ago, Jymmm said:

 

Do you have any details on the logic controller you have. Is it something you have DIY'd ? I'd be interested in one for my system.

 

I'm using a Loxone miniserver that I DIY installed. It would be  overkill for just this use case but it runs a lot of the house systems and easy to have it manage heating too.