@Jamespa I know it costs 30kwh per day as i monitored it over 3 days24/7 running. That was in colder weather. Its pretty uniform usage when temps similar within few degrees of each other. I never said setback saved me 35% usage. 3 big factors as you and i also highlighted many times. Ye also have not talked much about ufh and the slab retaining and emittingvheat as is my case. Weather stable here last few days. Im running 24/7 until 9pm tomorrow. I suspect i will use near 24kwh compared to 14 i used today. Sometimes things are over complicated.  This thread has not yet disproved cathode rays data of energy savings despite many efforts and changing queries. Im simply giving real world data. I  have no reason to convince people of anything.  Im v happy with improvements this winter with help of. this forum

Posted by: @newhouse87

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I never said setback saved me 35% usage

Noted and good and I apologise that I thought that you might have been implying that. 

Posted by: @newhouse87

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Ye also have not talked much about ufh and the slab retaining and emittingvheat as is my case.

I have when I talk about the effect of thermal mass.  As I say above its clear that,

• in a house with such a sufficiently high thermal mass that it effectively averages the energy input over >24hrs
• with a heat pump that can modulate down to the 24 average demand 
• which does not have any material standing loads
• and in the absence of overriding diurnal temperature variations which make it materially more efficient to generate heat during the daytime than at night 

setback can only result in an increase in flow temperature and thus decrease in COP and increase energy use. Such a house will therefore not benefit from setback in terms of energy input. 

However many circumstances don't meet these criteria, the interesting question is the boundaries.  The rationale for setback (or not) is very analogous to the rationale for zoning (or not), and just like zoning (or not) it isn't always a good idea.

Posted by: @newhouse87

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Sometimes things are over complicated.

Fully agreed.  Central heating is unfortunately one of those things by its very nature, and heat pumps (because, whilst they are good for the environment, they are non-linear in their response to energy demand) just make an already very complicated thing even more complicated.  Nobody on this forum can do much about that, however much they would wish to!  All we can do is try to focus on the material factors.

Posted by: @newhouse87

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I  have no reason to convince people of anything.  Im v happy with improvements this winter with help of. this forum

Great, and I think all of us can agree that whatever the explanation for the improvements, they are good news. 

Posted by: @sunandair

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Posted by: @derek-m

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I doubt whether anyone is going to post on the forum that setbacks are actually causing them to use more electrical energy, even if they knew that to be the case. It is human nature to brag about wins, and conveniently forget about defeats.

i am at a loss to know how to interpret your comments Derek,  You appear to be undermining everything anyone may post on these forums. I was about to post some interesting findings on a narrower setback temperature and trialling Weather Compensation instead of Auto Adapt and how that helps with morning recovery and improved, lower flow temperatures.

however, according to you nobody tells the truth apparently, so What’s is the point of posting anything here any more?

 

I am not against setbacks, in fact if Newhouse87 has discovered some way of reducing energy consumption by 35% or more, I would shout it from the roof tops.

What I am cautioning against is people making what may sound like claims, that have not been fully tested under more controlled conditions, with others then believing them as fact.

I have gradually been improving the spreadsheets, with invaluable help from CathodeRay, JamesPa, KevM and others, and would welcome any data that you can provide, since that is one of the important commodities that we are sorely lacking.

My comment listed above, was in relation to previous comments that stated that several forum members were achieving energy savings by using setbacks. I don't dispute that it may be possible to make energy reductions under certain circumstances, but in other circumstances a setback may end up using more energy. At the moment we don't know for certain what works and what does not for 100% of the time. My comment was not intended to put people off from posting, but merely to highlight the fact that people are more likely to post that they may have reduced energy consumption than post stating that they have actually increased energy consumption. Because it is almost impossible to repeat tests under exactly the same conditions, it is therefore very difficult, with any degree of certainty, to claim a certain percentage of energy reduction with reasonable accuracy.

If a spreadsheet can be developed that simulates how a home heating system reacts under varying weather conditions and different operating protocols, that can then be modified by changing a few parameters, such that it can represent most types of building, and further be enhanced with data for different types and sizes of heat pumps, then it may go some way to helping improve the way heat pumps are used within our homes.

So went to bed last night, house at 22 as usual, however kept heating on. House still@22 now, usually following morning it would be 21. I used 9kwh over the 10hoiur period i have off and normally wouldn't be back on until11am. I consider this needless heating. So i predict for the 24hour period i will use near 22kwh. Yesterday during same temp approx. i used just over 13kwh. The data to me can only be interpreted one way, i waste money on heat i do not need when running over night in mild conditions. All 42pages of this thread have yet to disprove the experimental data that set  backs save energy. Especially with ufh slab, it retains heat so is easier to heat up again as is usually still warm even after lengthy setback. Is this was a murder trial, it would be up to theorists to prove why this data is wrong, that so far has not happened. Again in older weather i will have to experiment when im not way in Scotland this time. My data is tested under my current conditions and this tells me i am wasting money keeping heat pump on all night for a bit more maybe too much comfort. This all done at fixed flow temp which may be of note.

Posted by: @newhouse87

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So went to bed last night, house at 22 as usual, however kept heating on. House still@22 now, usually following morning it would be 21. I used 9kwh over the 10hoiur period i have off and normally wouldn't be back on until11am. I consider this needless heating. So i predict for the 24hour period i will use near 22kwh. Yesterday during same temp approx. i used just over 13kwh. The data to me can only be interpreted one way, i waste money on heat i do not need when running over night in mild conditions. All 42pages of this thread have yet to disprove the experimental data that set  backs save energy. Especially with ufh slab, it retains heat so is easier to heat up again as is usually still warm even after lengthy setback. Is this was a murder trial, it would be up to theorists to prove why this data is wrong, that so far has not happened. Again in older weather i will have to experiment when im not way in Scotland this time. My data is tested under my current conditions and this tells me i am wasting money keeping heat pump on all night for a bit more maybe too much comfort.

What this is much more likely to indicate is indicate is that, at your current flow temperature, you are pumping in more energy than you need if you operate the heat pump 24*7.  The optimum way to save energy in this circumstance is to reduce flow temperature.  If you only need energy corresponding to an input of 13kWh per day, then your flow temperature should ideally be set to deliver only that much.  Currently it is apparently set to deliver energy corresponding to an input of 22kWh/day, so it could (apparently) be turned down quite a lot!

Obviously if there is a reason that the FT cannot be turned down to match the load then you are left with setback (ie time modulation) as your only option, but it is unlikely to be the optimum option particularly in a house such as yours with high thermal mass.

@jamespa dunno man, i tried lwt@27 and it cycled a lot as rwt gets up to23-25 easy enough. I get what you are saying but reckon the heatpump is restricting me. Even in cold snap@29 that flow was sufficient albeit longer running and may neccessiate24/7. I could try quiet mode sometime as it reduces output significantly. Even last night i had 13 compressor starts in the 10hour period. Was mild though.

Posted by: @newhouse87

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@jamespa dunno man, i tried lwt@27 and it cycled a lot as rwt gets up to23-25 easy enough. I get what you are saying but reckon the heatpump is restricting me. Even in cold snap@29 that flow was sufficient albeit longer running and may neccessiate24/7. I could try quiet mode sometime as it reduces output significantly. Even last night i had 13 compressor starts in the 10hour period. Was mild though.

"I get what you are saying but reckon the heatpump is restricting me"

Yes, I think so.  The case where a heat pump wont modulate down to the level necessary for 24x7 operation to work without cycling, and the house is high thermal mass, is an interesting one.  In this circumstance the options amount to: (i) allowing it to do its thing at the 'optimum' (ie lowest) possible flow temperature, resulting in frequent shortish shortish cycles, or (ii) imposing a long cycle by turning it off for a while.  In principle the former is probably the more efficient, however there are quite a few factors at play here so I wouldn't like to say for certain that this is the case.  Having said that I have yet to see an argument that deliberately increasing the flow temperature to avoid cycling (effectively what you are doing) is a good idea, but neither would I rule out the possibility that it might be with some heat pumps in some circumstances. 

What I would say for certain (based on the limited info I have) is that the most relevant comparison in your case (which would need to be done over quite an extended period given your apparent house thermal mass) is

a) consumption with the FT as low as possible to achieve the desired IAT with heat pump on 24x7, allowing the heat pump to cycle as it will

with

b) consumption with the FT turned up just sufficient to reduce or eliminate cycling, augmented by a period of setback tuned so that the desired IAT is maintained at the relevant times of day (ie your current mode of operation)

Whether you are interested in doing this is of course your decision; you seem to be happy now with your set up and there is always a strong argument for 'if it ain't broke don't fix it'!

Posted by: @jamespa

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Posted by: @newhouse87

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@jamespa dunno man, i tried lwt@27 and it cycled a lot as rwt gets up to23-25 easy enough. I get what you are saying but reckon the heatpump is restricting me. Even in cold snap@29 that flow was sufficient albeit longer running and may neccessiate24/7. I could try quiet mode sometime as it reduces output significantly. Even last night i had 13 compressor starts in the 10hour period. Was mild though.

"I get what you are saying but reckon the heatpump is restricting me"

 

Yes, I think so.  The case where a heat pump wont modulate down to the level necessary for 24x7 operation to work without cycling, and the house is high thermal mass, is an interesting one.  In this circumstance the options amount to: (i) allowing it to do its thing at the 'optimum' (ie lowest) possible flow temperature, resulting in frequent shortish shortish cycles, or (ii) imposing a long cycle by turning it off for a while.  In principle the former is probably the more efficient, however there are quite a few factors at play here so I wouldn't like to say for certain that this is the case.  Having said that I have yet to see an argument that deliberately increasing the flow temperature to avoid cycling (effectively what you are doing) is a good idea, but neither would I rule out the possibility that it might be with some heat pumps in some circumstances. 

 

What I would say for certain (based on the limited info I have) is that the most relevant comparison in your case (which would need to be done over quite an extended period given your apparent house thermal mass) is

a) consumption with the FT as low as possible to achieve the desired IAT with heat pump on 24x7, allowing the heat pump to cycle as it will

with

b) consumption with the FT turned up just sufficient to reduce or eliminate cycling, augmented by a period of setback tuned so that the desired IAT is maintained at the relevant times of day (ie your current mode of operation)

 

Whether you are interested in doing this is of course your decision; you seem to be happy now with your set up and there is always a strong argument for 'if it ain't broke don't fix it'!

Posted by: @newhouse87

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Happy enough with b scenario. major improvement on last winter. 

Fair enough!  As I have said many times in other contexts, good enough is good enough and the perfect is sometimes the enemy of the good

Posted by: @newhouse87

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If i spend anymore time in heatpump room, ill be sleeping alone.

Thats probably true of a fair few on this forum, me included!

Posted by: @jamespa

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Posted by: @newhouse87

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Happy enough with b scenario. major improvement on last winter. 

Fair enough!  As I have said many times in other contexts, good enough is good enough and the perfect is sometimes the enemy of the good

 

Posted by: @newhouse87

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If i spend anymore time in heatpump room, ill be sleeping alone.

Thats probably true of a fair few on this forum, me included!

Maybe we should consider cycling from a different angle.

Cycling is an overnight setback spread out throughout the day.

Posted by: @derek-m

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Maybe we should consider cycling from a different angle.

Cycling is an overnight setback spread out throughout the day.

It is indeed exactly that. 

There is a very plausible argument that fast cycling, at a rate sufficiently fast that the temperature of the circulating water doesn't cool too much between cycles, is better than slower cycling.  Having said that the same argument might well lead to the conclusion that cycling at an intermediate rate, not once a day but with sufficient gaps that the circulating water does cool between cycles, is quite possibly worse than cycling once per day.

Posted by: @jamespa

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Posted by: @derek-m

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Maybe we should consider cycling from a different angle.

Cycling is an overnight setback spread out throughout the day.

It is indeed exactly that. 

There is a very plausible argument that fast cycling, at a rate sufficiently fast that the temperature of the circulating water doesn't cool too much between cycles, is better than slower cycling.  Having said that the same argument might well lead to the conclusion that cycling at an intermediate rate, not once a day but with sufficient gaps that the circulating water does cool between cycles, is quite possibly worse than cycling once per day.

 

 

 

This is where the other components within a heating system, and the way the whole system is being operated, come into play.

Newhouse87 is in the very enviable position of having a well insulated home that also has a high thermal mass, so he can heat up the thermal mass using his heat pump, operating during the warmer, more efficient, parts of the day, and his home will maintain a comfortable temperature for lengthy periods of time overnight. He is actually doing something that I suggested quite some time ago, to heat up during the day using the heat pump and any available solar gain, so that less heating is required during the cooler, less efficient, overnight period. So maybe not a switch off for 6 hours setback, but a type of setback nonetheless.

Slow cycling, say once per hour, is another form of setback, whilst maintaining IAT within acceptable limits, and hopefully reducing energy consumption in the process. But this is where the other components within the system may cause problems.

If a heat pump were to run for a 1 hour period to warm up a home, so that it could then have a rest for 1 hour while the home gradually cools, there is a possibility for a reduction in energy consumption. But if during the 'off' period the water pumps are kept running, then some of the thermal energy that has just been put into the home, may then start to be removed merely by the action of the pump continuing to circulate the water.

Other factors such as the heat pump being operated when it is actually cooler outside, and then being 'off' during the warmer period. The variability of the UK weather therefore would make any form of meaningful scheduling rather difficult.

I suppose these considerations are why there is so much discussion around the benefit of setbacks.