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[JohnMo]

51 minutes ago, DamonHD said:

But plain WC does not increase flow temperature in response to anything other than falling outside temperatures.  If you are saying that someone might shift the whole WC curve up then that is a different matter which I address as "fiddling with the settings".  Notionally that WC curve is *computed* from the heat loss calcs at installation time and left alone.

As I said you have missed the point - WC curve is set up with all zones opens. House gets to a steady state. Now YOU start closing zones off, so the zones cool down.  Additional heat transfer occurs as heat moves from heated room to unheated.  Radiators in heated room no longer give off enough energy to keep heated rooms at set temp.  YOU then adjust WC upwards to compensate.  CoP hit.

 

The WC will never likely to be correct out the box, you can never do a full accurate heat loss calc on a retrofit, even a new build there are so many assumptions, that it is near but never exact. So not sure where the left alone comes from - early you said your house was stuffy and hot when running WC, so curve obviously not correct.

[marshian]

48 minutes ago, JamesPa said:

@DamonHDHere is another real-world scenario where a more intelligent TRV designed for heat pumps would be useful:

 

In common with many, I like my bedroom to be a bit cooler at night than the parts of the house that I am in most of the day.  The standard design temperatures used to size radiators take this into account.  However I would ideally like it warmer just as I get up, so I don't have to get up to a cool room. 

 

Currently the only ways to achieve this are:

 

a. use a smart TRV with timer, but that involves on/off control of the radiator which is bad for the heat pump efficiency and defrost volume

b. set back the whole house at night and raise the temperature just before getting up - but I dont want to do this because I have a ToU tarrif that is cheapest at night, in fact I actually want to set the whole house forward.  

 

A TRV properly designed for heat pumps could enable me to do this.  To the best of my knowledge no such device is available.

 

I'm the same on bedroom temps - unfortunately my better half is not - she like to sleep in a warm bedroom so I compromise 19.5 deg bedroom temp - she's happy and I don't overheat at night

 

48 minutes ago, JamesPa said:

Another risk, incidentally, with TRVs is that they can deprive the system of volume for defrost.  As a minimum this means that defrost takes longer, in the worst case it could (possibly) lead to a 'freeze down' where there is insufficient volume of hot water to defrost the unit without taking the FT below the dew point, and so it never recovers or takes an extremely long time because it is reliant n heat from the fabric. 

 

In my real world scenario above the radiator in question is a not insignificant part of the total system volume and so having a TRV which takes it out of circulation for part of the time is a very bad idea on days like today, when defrosts are occurring about once per hour!  Again a TRV designed for heat pumps wouldn't do this.

 

Another very good reason why not to over zone and why a lot of TRV intervention means a hard life for the boiler.

 

I'm pretty confident I've got about 30 L in the CH circuit (I did a drain down a while back where I closed all the rads and just drained down the circuit - BTW it's not a good idea if your system has a tendency to air lock Oh well "experience is what you get when you don't want it" I always say)

 

 

Quick bit of maths shows 16% of my system volume is subject to set backs (ie TRV intervention) Reason for those rooms being on setback

 

Front Hall - North Facing 3 external walls and door and glazing

 

Study - As above and it is directly above the front hall - if I use it I just boost the rad temp as when the PC is in use it'll add to heat input

 

Utility - Fridge and Freezer contribute to stable temps with minimal additional heat needed

 

Toilet - tiny room - only heated morning and evening (when it's likely to be used) responds quickly to heat input

 

84% is therefore available all the time as the TRV's are set to act as limiters not temp controllers and it's a circuit size of 110 litres and with a pump pushing 0.5 m3/hr (8.5 Litres per min) and a boiler min heat input of 3.2 kW system is quite happy

[JamesPa]

1 hour ago, marshian said:

Another very good reason why not to over zone and why a lot of TRV intervention means a hard life for the boiler.

 

Even more so for a heat pump which, in weather such as we are currently having, must stop heating and run a defrost cycle periodically, to remove accumulated frost from the air to refrigerant heat exchanger.  This is done (in most but possibly not all heat pumps) by robbing the energy from the central heating water to provide the required heat.  That's one reason, possibly the principal one, for a minimum system volume and why a volumiser is sometimes required for the amount available to be sufficient.  

 

The cloud of vapour when a defrost cycle runs is quite impressive!

Edited Saturday at 12:41 by JamesPa

[DamonHD]

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Edited Saturday at 17:12 by DamonHD
dupe

[DamonHD]

7 hours ago, JamesPa said:

However I would ideally like it warmer just as I get up, so I don't have to get up to a cool room.

 

...

 

A TRV properly designed for heat pumps could enable me to do this.  To the best of my knowledge no such device is available.

 

I have been out all day so I may not get to respond to everything...

 

OpenTRV / Radbot are intended to just this where possible by bringing rooms up to temperature when occupancy is predicted.  And indeed my bedroom Radbot did so this morning.

 

Some of the other things that you mention are things that I have considered since handing over the Radbot IPR and there is space in my research plan to think about and maybe model or prototype some of them.

[joth]

9 hours ago, JamesPa said:

Currently the only ways to achieve this are:

 

a. use a smart TRV with timer, but that involves on/off control of the radiator which is bad for the heat pump efficiency and defrost volume

b. set back the whole house at night and raise the temperature just before getting up - but I dont want to do this because I have a ToU tarrif that is cheapest at night, in fact I actually want to set the whole house forward.  

 

A TRV properly designed for heat pumps could enable me to do this.  To the best of my knowledge no such device is available.

Fwiw in a conventional UK house (poor insulation, no active cooling) this is easy to do with Loxone TRVs: use an eco temperature setting for the room overnight and then a comfort target temperature at getting up time. It learns the typical room warmup rate and will start preheating the room at the appropriate time prior to wake up. (Or bed time, or home time, or whatever regular schedule timings is set for comfort).

It takes some more fiddling to have this play nicely with overnight cheap rate batch heating (which is of course in intrinsic contention with wanting cooler rooms at night) and  to deal with defrost cycles (but that's largely because heat pumps lack a clear instruction & signal output for "I'm doing defrost or freeze protect, please open all zones"), it's not out of the box ideal for heat pumps, but it's very configurable so technically doable.

 

Regarding a TRV designed for heat pumps, I know startup aiming at this 

https://www.adiathermal.co.uk/

 

(Disclaimers: i install Loxone systems. An ex colleague is cofounder of that startup)

 

Edited Saturday at 19:30 by joth

[JamesPa]

18 hours ago, joth said:

Fwiw in a conventional UK house (poor insulation, no active cooling) this is easy to do with Loxone TRVs: use an eco temperature setting for the room overnight and then a comfort target temperature at getting up time. It learns the typical room warmup rate and will start preheating the room at the appropriate time prior to wake up. (Or bed time, or home time, or whatever regular schedule timings is set for comfort).

I can do this with a standard 'smart TRV'.  The problem is that it will, so far as I can tell, periodically shut down altogether (ie it will achieve the objective by time modulating).  That's not what is required for an efficient heat pump implementation, it needs to partly shut down so that, over time, it achieves the lower temperature, but never completely shut down.  Do Loxone TRVs do this (learning, over a period of several days, the setting needed to achieve the setback temperature) or do they alternately shut down and open up?

 

Basically we need a trv that operates like an automatic LSV, alternating between states corresponding to different room temperatures (on the assumption that WC is in use) but never closing off and preferably learning in very slow time.

Edited Sunday at 13:53 by JamesPa

[JamesPa]

20 hours ago, DamonHD said:

OpenTRV / Radbot are intended to just this where possible by bringing rooms up to temperature when occupancy is predicted.  And indeed my bedroom Radbot did so this morning.

Same question as for Loxone.  Does it control temperature by alternately shutting down and opening up like mechanical TRVs, or does it act like an automated lockshield controlling temperature by throttling the water supply but never closing it down, learning the 'correct' position in slow time (days probably) on the assumption that WC is in operation. 

 

For heat pumps we need the equivalent of an automated lockshield that never closes down, not a smart equivalent of mechanical TRVS that control temp essentially by on/off modulation.

[MrPotts]

47 minutes ago, JamesPa said:

I can do this with a standard 'smart TRV'.  The problem is that it will, so far as I can tell, periodically shut down altogether (ie it will achieve the objective by time modulating).  That's not what is required for an efficient heat pump implementation, it needs to partly shut down so that, over time, it achieves the lower temperature, but never completely shut down.  Do Loxone TRVs do this (learning, over a period of several days, the setting needed to achieve the setback temperature) or do they alternately shut down and open up?

 

Basically we need a trv that operates like an automatic LSV, alternating between states corresponding to different room temperatures (on the assumption that WC is in use) but never closing off and preferably learning in very slow time.

I wonder if this can be done with a smart TRV during the initial calibration. Just place a thin spacer on the pin, attach the TRV, run through the calibration and then remove the spacer. I wonder if the TRV will then remember to stop just shy of closing completely.

[JamesPa]

39 minutes ago, MrPotts said:

I wonder if this can be done with a smart TRV during the initial calibration. Just place a thin spacer on the pin, attach the TRV, run through the calibration and then remove the spacer. I wonder if the TRV will then remember to stop just shy of closing completely.

Interesting thought.

 

It also occurs to me that, to be useful, a 'smart lockshield' for heat pumps doesn't have to learn.  It could simply switch between states (numbered say 1-10) based on time of day, and the user could just pick the states, much like they do with mechanical TRVs which have numbers not temperatures on.  Of course it would be better if they did learn, specifically for automating balancing (for which I think they would also have to be networked), but the simplest useful version need neither learn nor be networked

Edited Sunday at 15:06 by JamesPa

[DamonHD]

1 hour ago, JamesPa said:

Same question as for Loxone.  Does it control temperature by alternately shutting down and opening up like mechanical TRVs, or does it act like an automated lockshield controlling temperature by throttling the water supply but never closing it down, learning the 'correct' position in slow time (days probably) on the assumption that WC is in operation. 

 

For heat pumps we need the equivalent of an automated lockshield that never closes down, not a smart equivalent of mechanical TRVS that control temp essentially by on/off modulation.

See live-ish charts of TRV open %-age further up the thread.  To avoid various problems they open fairly fast but close as slowly as they can without temperature overshooting too far.  They do not close fully if temperature does not significantly overshoot.

[joth]

4 hours ago, JamesPa said:

I can do this with a standard 'smart TRV'.  The problem is that it will, so far as I can tell, periodically shut down altogether (ie it will achieve the objective by time modulating).  That's not what is required for an efficient heat pump implementation, it needs to partly shut down so that, over time, it achieves the lower temperature, but never completely shut down.  Do Loxone TRVs do this (learning, over a period of several days, the setting needed to achieve the setback temperature) or do they alternately shut down and open up?

 

Basically we need a trv that operates like an automatic LSV, alternating between states corresponding to different room temperatures (on the assumption that WC is in use) but never closing off and preferably learning in very slow time.

On the electromechanical side yes Loxone TRVs do support fine grain modulation, although I'm not convinced the software would do what you ask for out of the box. AFAIK the self learning is just about time to reach comfort, not keeping the eco setback temperature satisfied with a constant minimal valve opening. 

With enough patience the software can be configured to do this though.

Next disclaimer: for cost and reliability reasons I've always gone with conventional on/off actuators (or self-balancing actuators) on UFH zones, but I'll be using the modulating TRVs on an upcoming project using rads. It'll be interesting to see how they compare.