Posted by: @pie_eater

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In this case , better to use a portable small heater to provide heat on days she works there? Or still better to upgrade radiators?

Upgrading radiators is almost never a bad thing to do, what's the payback time and is there a requirement for it to be cooler at night (if so how do you plan to achieve that?)

Personally I would upgrade the radiator, you are talking about the loft so heating it will reduce the heat loss from the rooms immediately below.  You may even find you can knock back your WC a degree or two increasing overall efficiency. 

Posted by: @pie_eater

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one minor issue is that our loft /spare bedroom is around 0.5-1 degree cooler than the rest of the house (1 loop all on same temp). It was sort of expected, initially radiators we recommended to be replaced but we pushed back (all the other rooms are fine as expected).however the room is only used as a study 2 or 3 days a week and rest of the time empty. And as a bedroom the temp at 19.5 ish is totally fine. So to heat it to 21 the whole week feel totally wasteful.My wife uses it and feels the cold more than I do so would want to improve it.  

I think you've discovered why they wanted to upgrade the radiator - if it's a lived-in room, at least some of the time, you'd want it at a comfortable temperature.  You could always have turned the TRV down a bit when it's used as a bedroom.  It's not really wasteful to heat a room by an extra 1c as the heat is created regardless and it helps with the heat loss of any surrounding rooms.  I'd bite the bullet and upgrade the radiator.  Did you push back on ALL radiators they suggested to upgrade?  You may find as the weather gets colder that other rooms struggle too - you could adjust the WC upwards if that's the case (you're trading efficiency for install cost.)

Thanks both.

i hadnt really considered the heat loss reducing on the 1st floor. that makes sense.

Yes we pushed back on all radiators  - the ones they wanted to install were ugly an we suspected most rooms would be fine , as turned out to be the case (except for the loft). 
it’s alll quite marginal but to get the loft warm 20.5 or so it’ll be too warm on ground floor (UFH), 21-22.5. 1st floor hovering in the middle , that’s also where the thermostat is.

@pie_eater This may be the reason that the prospective installers had suggested replacing some radiators with higher output? Oversized emitters may be ‘throttled back’ via the LSV whereas an emitter that cannot provide sufficient oomph when fully open will not provide the level of comfort you may require. Regards, Toodles.

Posted by: @pie_eater

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i hadnt really considered the heat loss reducing on the 1st floor. that makes sense.

Its key to understand this, and it applies more generally.  'Unheated' rooms are in fact heated from adjacent rooms, which means that the rads in those rooms need a higher flow temperature than would otherwise be the case in order to increase their output, which reduces efficiency. 

Thus it doesn't necessarily save money to leave rooms unheated unless they settle at a very low temperature.  This is rarely the case because insulation between rooms is almost invariably much poorer than insulation between the house and the outside world.

Generally the most efficient and cheapest way to run a heat pump is 24*7 with all rooms heated to within 3C of each other, the latter adjusted on the lockshield valve not by fiddling with TRVs, which should (like thermostats) normally either be set to maximum or to 2C above target temperature if the room tends to overheat due to solar gain.

Posted by: @jamespa

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.... the latter adjusted on the lockshield valve not by fiddling with TRVs ...

Is this true even at the expense of DeltaT?  My bathrooms upstairs rooms are reaching 24-25c with TRVs fully open but were recently balanced to a DeltaT of 5c along with all other radiators.  I presume by closing down the LSV it will have an impact elsewhere in the system and other radiators would need to be re-balanced?  Is that still a better approach than turning down the TRV?

Posted by: @andrewj

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Is this true even at the expense of DeltaT?  My bathrooms upstairs rooms are reaching 24-25c with TRVs fully open but were recently balanced to a DeltaT of 5c along with all other radiators.  I presume by closing down the LSV it will have an impact elsewhere in the system and other radiators would need to be re-balanced?  Is that still a better approach than turning down the TRV?

 

Yes.  There is nothing sacrosanct about DT5 even on aggregate, and certainly not for any individual radiator.  Furthermore if all the rads have been balanced for DT5 then its possible that all have LSVs turned down, whereas at least one, preferably several, should be fully open.

Installers, if they balance at all, will usually balance for equal deltaT on the basis that this is how the system was designed, it can be done relatively quickly, and if all the calculations are correct this should result in the design room temperatures.   But design loss and actual loss are two different things so in practice a basic balance for deltaT may need to be tweaked to get the desired room temps.  Turning down one LSV is unlikely to have a major effect on others and yes its generally a better approach than turning down the TRV if only because it ensures that the volume of the radiator is always in circuit to help with cycling and defrost.

If all your upstairs rooms are reaching 24-25 then turning down all the LSVs may not be the thing to do (but neither is having them all switching on and off on TRVs).  More likely you could turn up some of the LSVs downstairs (reducing deltaT and thus raising output), perhaps turn them down a bit upstairs, and reduce the WC curve a tad.

@toodles has written an article on balancing for equal room temp/desired temp differences (as opposed to balancing for DeltaT); its worth a read.

That said one doesn't have to get obsessive about eliminating TRVs.  I have one out of ~14 rads on a TRV, its in the 'visitor' bedroom and I do it as a courtesy to visitors.  I started off with all the upstairs on TRVs and all the downstairs open loop, but gradually adjusted the LSVs until the TRVs became unnecessary.  Some installers will say TRVs upstairs, open downstairs.  That's not optimum but not completely silly, however it does risk roughly halving the system volume if they all shut down simultaneously, which will half cycle time (bad) at any given set of conditions and reduces the water available for defrost.

@andrewj The advantage of making the adjustment on the LSV is that the setting is a constant rather than a variable one and this ‘constant load’ is much better for the ‘low and slow’ operation of a heat pump. Gas boilers were frequently running dynamically but heat pumps benefit from a constant flow resistance from the emitters. Regards, Toodles.

Posted by: @toodles

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@andrewj The advantage of making the adjustment on the LSV is that the setting is a constant rather than a variable one and this ‘constant load’ is much better for the ‘low and slow’ operation of a heat pump. Gas boilers were frequently running dynamically but heat pumps benefit from a constant flow resistance from the emitters. Regards, Toodles.

I'm finding that the Octopus Cosy doesn't work like that but cycles around the thermostat temp.  Still trying to get a little more info out of Octopus before I look at the approach @jamespa has detailed in other posts.

Thanks both - I'll take a look at adjusting LSVs and read your article about balancing Toodles.

Posted by: @andrewj

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Posted by: @toodles

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@andrewj The advantage of making the adjustment on the LSV is that the setting is a constant rather than a variable one and this ‘constant load’ is much better for the ‘low and slow’ operation of a heat pump. Gas boilers were frequently running dynamically but heat pumps benefit from a constant flow resistance from the emitters. Regards, Toodles.

I'm finding that the Octopus Cosy doesn't work like that but cycles around the thermostat temp.  Still trying to get a little more info out of Octopus before I look at the approach @jamespa has detailed in other posts.

Thanks both - I'll take a look at adjusting LSVs and read your article about balancing Toodles.

 

I would personally be sceptical about reaching any conclusion that goes against the norm of heat pumps.  In the end the Cosy is a heat pump, subject to the same laws of thermodynamics  as every other heat pump, which are pretty dominant in both the way they work and the factors that affect efficiency.  Its true Octopus might have played games with the controller but if they were particularly clever games other manufacturers would likely do the same.  Most likely they behave in one of a small number of obvious ways.

The cycling around the thermostat temp is (almost certainly) because the thermostat the primary control for the heat pump rather than the weather comp curve.  Put another way the weather comp curve is set higher than it needs to be to maintain the desired temp.  As a result the room overheats, the heat pump is then is cut off by the thermostat, and once the temp has dropped the heat pump switches back on again.  Most if not all heat pumps can work like this and so long as the WC curve isnt too far out its not a bad way to operate.  However its generally best for comfort and cost first to get the C curve as close (ie as low) as possible.  If you do that its quite possible that you will conclude that the thermostat control isnt needed at all and so will set it above the desired temp so it has no effect.  Some heat pumps have a specific setting to disable it.

My Vaillant can operate in this mode.  At either end of the season I do operate it this way to deal with solar gain, which becomes significant.  However by now I have switched to pure weather compensation; the internal room temperature sensor is disabled from having any real time controlling effect.  This is more comfortable in my house, but of course that is house and person dependent.

One thing that isn't at all clear is whether the room temp setting on the Octopus also modifies the WC curve.  On the Vaillant and a few other heat pumps it does.   There are two ways this could work (both of which are available on the Vaillant ans some other heat pumps).  One is that the WC curve you set assumes a target room temperature of (say) 20C, and if you set the target temp to something else the WC curve is displaced but otherwise the room temp setting has no 'real time' effect.  Another way is that the room temp setting is used 'real time' to adapt the WC curve in an attempt to adjust to the house.  Generally the adaption is limited in extent only to a limited extent to prevent the control loop becoming unstable.

We dont know which (or which combination) of the above Octopus applies, unfortunately as the instruction manual is a bit dumbed down, but I think its likely its one or a combination of these, possibly selectable in the installer menu.

Posted by: @andrewj

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Posted by: @toodles

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@andrewj The advantage of making the adjustment on the LSV is that the setting is a constant rather than a variable one and this ‘constant load’ is much better for the ‘low and slow’ operation of a heat pump. Gas boilers were frequently running dynamically but heat pumps benefit from a constant flow resistance from the emitters. Regards, Toodles.

I'm finding that the Octopus Cosy doesn't work like that but cycles around the thermostat temp.  Still trying to get a little more info out of Octopus before I look at the approach @jamespa has detailed in other posts.

Thanks both - I'll take a look at adjusting LSVs and read your article about balancing Toodles.

Is that because it's putting out more heat than the property requires at this time of year? ASHPs can only modulate their output so low (typically to around a third to a quarter of full output) and achieving continuous running is not always possible this time of year as even at minimum output the heat pump may still be cycling or turning on/off by the thermostat (depending how it's been set up).