Why do something which isn't needed, is uneconomical and shortens the life of the ASHP/boiler?

We've had the tech to switch on the heating before we get home for a long time now, automatically.

Posted by: @deltona

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Why do something which isn't needed, is uneconomical and shortens the life of the ASHP/boiler?

Because there's situations where it is needed. You do want to get the house warm quickly when your plans change and you come home early or unexpectedly, or the heating has been off for some reason - maintenance, break-downs, power-cuts and you want to get the house warm. 

That isn't every day, or even every week, but having a heating system which can heat the house up reasonably quickly when needed is quite an important feature. 

Posted by: @temperature_gradient

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Is anyone doing this? Are the newer models more flexible if suitably sized, can they get a house warm quickly within several hours from cold?

Before I got a heat pump I turned down my gas boiler flow temperature from 70 to 50 which was the lowest it would go.  The result was a much more comfortable house because of reduced temperature gradients in both time and space and reduced gas bills because the boiler (just like a heat pump) operates more efficiently when run at a lower temperature for longer.  Getting a heat pump took the comfort improvement  to another level, why would I go back to the previous mode of operation when it involves spending more money for reduced comfort?  

Posted by: @temperature_gradient

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Because there's situations where it is needed. You do want to get the house warm quickly when your plans change and you come home early or unexpectedly, or the heating has been off for some reason - maintenance, break-downs, power-cuts and you want to get the house warm. 

If you go on holiday it of course makes sense to switch it off.  If you are out for the day it probably doesn't, unless your house gets cold very quickly.  What most people forget (and the heating aftermarket controls industry doesn't bother to remind us because it more or less invalidates their business model) is that  houses continue to lose heat at almost the same rate even if the heating is off, and that heat which was lost while the heating was switched off has to be replaced when you turn it back on. The amount saved therefore is actually quite small, unless you live in a house that has the characteristics of a tent (ie one that cools very quickly and has low thermal mass).  Turning the flow temperature down by a couple of degrees (a setback) may make sense, turning it off altogether is unlikely to do so.  If you are out during the daytime thats also generally the most efficient time to produce heat, because its warmer outside so COP will be higher.  Producing all your heat when its coldest outside usually doesn't make sense, unless of course you have an aggressive ToU tariff that fits with this model.  If you are out at night the argument for a setback is stronger.

Honestly when you get a heat pump you need to forget more less everything you learned about running a boiler.  Much of it was incorrect or overstated for boilers (but it suits the controls industry to tell us otherwise), even more of is incorrect for heat pumps.  

Feel free to explore further, as ever there are exceptions but in most cases there would be no sense at all in running short and hot.

Posted by: @jamespa

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Getting a heat pump took the comfort improvement  to another level, why would I go back when it involves spending more money for reduced comfort?  

But if you got home and found the house cold, for whatever reason, how long does it take for your heat pump to heat your house up to 20 deg C from cold, say +10 deg C, from 10 deg C upto 20 deg C ?

Posted by: @temperature_gradient

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Posted by: @jamespa

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Getting a heat pump took the comfort improvement  to another level, why would I go back when it involves spending more money for reduced comfort?  

But if you got home and found the house cold, for whatever reason, how long does it take for your heat pump to heat your house up to 20 deg C from cold, say +10 deg C, from 10 deg C upto 20 deg C ?

I dont, because I dont turn it off unless Im going away for several days, and in that case the technology to schedule a timed restart (and if necessary to change the time of the restart remotely) is built into the controller.

Also dont forget its not only flow temperature that matters its also capacity.  So if I wanted to be able to do what I dont actually need to do even when its very cold outside, I would need a heat pump that has a much higher capacity as well as a high maximum flow temperature, which would compromise its performance the rest of the time.

Posted by: @temperature_gradient

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Posted by: @deltona

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Why do something which isn't needed, is uneconomical and shortens the life of the ASHP/boiler?

Because there's situations where it is needed. You do want to get the house warm quickly when your plans change and you come home early or unexpectedly, or the heating has been off for some reason - maintenance, break-downs, power-cuts and you want to get the house warm. 

That isn't every day, or even every week, but having a heating system which can heat the house up reasonably quickly when needed is quite an important feature. 

No it isn't, these occasions are very rare, it's like buying a fire engine 'just in case'.

Is it such a trauma to arrive home to a cold house? Come on now, really?

You've been able to get Geofencing for a long time now, it automatically detects when you leave the house and lowers the temp, lifts it up when you're coming home. That and being able to turn the heating on manually, remotely mean those days of coming home to a cold house are a long time gone.

Posted by: @jamespa

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I dont, because I dont turn it off unless Im going away for several days, and in that case the technology to schedule a timed restart (and if necessary to change the time of the restart remotely) is built into the controller.

So how far in advance of returning home, do you need to turn it back on to recover the temperature - what sort of temperature rise can it achieve, what set-back do you use and how long does it take to recover if you were going away on holiday?

Posted by: @temperature_gradient

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Posted by: @jamespa

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I dont, because I dont turn it off unless Im going away for several days, and in that case the technology to schedule a timed restart (and if necessary to change the time of the restart remotely) is built into the controller.

So how far in advance of returning home, do you need to turn it back on to recover the temperature - what sort of temperature rise can it achieve, what set-back do you use and how long does it take to recover if you were going away on holiday?

 

I don't know exactly how long it takes to heat up (and to specify I would need to specify conditions) but in very general terms its 24 hours+ for the fabric (walls, floors) properly to heat if its got down to say 10C air temperature inside, although the inside air heats up in perhaps half that time or less.  I know that because my heat pump was fitted when it was pretty cold and, despite using a 4kW log burner as back up (my house needs 7kW at design temperature), the house got pretty chilly.  

If we go away for a couple of days I might turn the temperature down by 2-3 degrees and turn it back up half a day before we come home.  We typically don't do long winter holidays and obviously the question doesn't arise in summer.  But as I say the holiday function on the controller (which almost every heat pump and many boilers feature) allows you to schedule and remote control allows you to override the schedule.  Its just a non-problem and certainly not worth compromising performance the rest of the time for (which I think is the key point here).

That said nothing particularly wrong with accelerating the recovery after a holiday by increasing the flow temp above the normal value for whatever the OAT is, so long as you don't rely on being able to do that when its very cold outside and thus the heat pump may already be working at or near capacity.  This probably will cost the same or even more though as it would to raise it slowly.