Posted by: @sunandair

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I seem to have most of that list but some extra work on existing thermal mass is needed. If I manage to get some energy data sorted I may come back with the above information. After which my bank account won’t be worth much at all...😉

The only way I have found of assessing Thermal Mass is to see how the IAT falls when the heat pimp stops operating. Obviously the longer the time period, probably the more accurate the result.

Also try to eliminate or reduce any additional heat source, otherwise it may affect the results.

@cathoderay

I think that the PHE was included within your system to provide separation between the water containing ant-freeze, and that going through the heating coil in the DHW cylinder. This would then allow the cheaper (toxic) anti-freeze to be used, without fear of contamination of the DHW.

You therefore possibly have the option of removing the PHE altogether and replacing the anti-freee with the non-toxic solution, or having your system re-piped so that the PHE secondary water only goes through the DHW cylinder heating coil, and the CH system heat emitters are fed directly from the heat pump.

This may also help with defrosting, since there will be a larger volume of water containing more thermal energy directly available to the heat pump, without having to depend upon heat transfer (in reverse) through the PHE.

Posted by: @sunandair

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I seem to have most of that list but some extra work on existing thermal mass is needed. If I manage to get some energy data sorted I may come back with the above information. After which my bank account won’t be worth much at all...😉

One further item I forgot to add to the list.

It would be useful to know the concentration of anti-freeze, if any is present.

What size of Ecodan do you have?

Posted by: @derek-m

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I think that the PHE was included within your system to provide separation between the water containing ant-freeze, and that going through the heating coil in the DHW cylinder. This would then allow the cheaper (toxic) anti-freeze to be used, without fear of contamination of the DHW.

Freedom, who made the installation of a PHE (or LLH) a warranty requirement at the time my heat pump was installed, have never given a reason that I know of for making this a requirement. As I have mentioned before, I had no idea it was to be installed until I saw it in place after it had been installed.

It only separates the radiator circuit from the primary circuit, the primary circuit also supplies the DHW cylinder coil. The flow from the heat pump arrives in the airing cupboard, where it goes to the three port/two way valve, the two ways being either to the PHE (and the rads) or to the DHW coil. I'm pretty sure the glycol in the system is the 'safe' variant, at least it jolly well should at the price charged for the last top up. 

Posted by: @cathoderay

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Posted by: @derek-m

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I think that the PHE was included within your system to provide separation between the water containing ant-freeze, and that going through the heating coil in the DHW cylinder. This would then allow the cheaper (toxic) anti-freeze to be used, without fear of contamination of the DHW.

Freedom, who made the installation of a PHE (or LLH) a warranty requirement at the time my heat pump was installed, have never given a reason that I know of for making this a requirement. As I have mentioned before, I had no idea it was to be installed until I saw it in place after it had been installed.

It only separates the radiator circuit from the primary circuit, the primary circuit also supplies the DHW cylinder coil. The flow from the heat pump arrives in the airing cupboard, where it goes to the three port/two way valve, the two ways being either to the PHE (and the rads) or to the DHW coil. I'm pretty sure the glycol in the system is the 'safe' variant, at least it jolly well should at the price charged for the last top up. 

Maybe you should ask Freedom why they installed a PHE.

Posted by: @derek-m

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Maybe you should ask Freedom why they installed a PHE.

You know full well, because I have said so many times, Freedom won't talk to end users. My installer, who of course I did ask, wasn't sure why it was there, it was in effect part of the standard Freedom installation kit, and he just fitted it because it was part of the kit, and Freedom said it was essential.

That said, the usual reason for installing it is hydraulic separation, which in turn means a lower volume of glycol used, with some small cost savings. Why Freedom elevated this to a warranty requirement is beyond me.

Posted by: @sunandair

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Posted by: @sunandair

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I seem to have most of that list but some extra work on existing thermal mass is needed. If I manage to get some energy data sorted I may come back with the above information. After which my bank account won’t be worth much at all...

 

 

The only way I have found of assessing Thermal Mass is to see how the IAT falls when the heat pimp stops operating. Obviously the longer the time period, probably the more accurate the result.

Also try to eliminate or reduce any additional heat source, otherwise it may affect the results.

My plot of IAT-OAT vs energy supplied to the emitters, the latter corrected for changes in energy stored in the fabric (ie thermal mass), would seem to be another way.  With the @cathoderay data that gave an extremely good correlation indeed (one of the best I have seen in the exercise so far).  In the process thermal mass was used as a parameter in the fitting of the results and simply adjusted to give best fit to the expected linear relationship.

So if you wish to supply a few weeks of data IAT, OAT, energy to emitters, I can see what that turns up as an estimate of thermal mass.  

I have been doing a rapid literature review of the energy saving benefits or otherwise of setbacks, which with hindsight I should have done right at the beginning, but back then I didn't know a simple question was going to turn into the mother of all heat pump investigations. As a related question, I looked for evidence for the one degree lower thermostat setting saves 10% of energy rule of thumb.

As an off the top of my head answer, literally, I haven't written copious notes, it is clear many have investigated the question, and just as many have failed to provide a convincing answer. There are some comedy papers, including the one that claims savings of 20-30% or more (50%), depending on local climate (the paper uses two locations, Detroit and Miami in the USA - do they really have central heating in Miami?), but contains no description of the methodology used (=> File 13), but the more serious attempts have all come unstuck on the same problem as we have, a complex system with too many variables, some of which are probably unknown unknowns. One fairly common theme is the role of occupant behaviour in determining energy use, something I don't think we have really considered explicitly, beyond that fact the bulk of the work has been done on my data, which carries implicit information about my (n=1) behaviour eg six hour overnight setback, and the general assumption, present from the very beginning, that what I do in my particular house may or may not predict the results others will get. The more others vary their behaviour from mine, and the more their building characteristics vary from mine, the less likely my results will directly apply to them.

Heating degree days in some shape or form come up fairly often as a way of controlling for varying demand caused by constantly changing weather, as does the use of OAT (and/or IAT-OAT) as generally the best gross predictor of energy use, all pretty much in line with what has gone on here. But the bottom line seems to be that no one has come up with the mother of all heating equations to give an answer to the mother of all heat pump investigations, having come up against the same brick walls that the theoretical approaches discussed here have done.

Likewise, the 10% energy saving for a one degree drop in thermostat setting may be something of an urban myth, it being surprisingly difficult to find a solid base on which it stands.   

What we really need is an easily assimilated output from a model that allows us - meaning all interested and generally intelligent parties but not necessarily engineers or physicists - to compare actual observed energy use with predicted energy from the model over a range of weather conditions. Graphics are almost always better that the underlying tables (which should also be available, along with methods, otherwise it will end up in File 13), and the more systems this can be done for, the better. In the meantime, I am trying to think of ways of dealing with the concerns that have been raised about my observations based approach.        

@cathoderay

A 1C reduction in IAT from 19.2C to 18.2C would provide a predicted 10.94% decrease in electrical energy consumption using the variables associated with your home, at an OAT of 5C.

At an OAT of 0C, the predicted electrical energy reduction was 11.8%.

I can test other values if you wish.

Posted by: @derek-m

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A 1C reduction in IAT from 19.2C to 18.2C would provide a predicted 10.94% decrease in electrical energy consumption using the variables associated with your home, at an OAT of 5C.

At an OAT of 0C, the predicted electrical energy reduction was 11.8%.

There's no shortage of predictions of what the effect of a one degree change in the thermostat setting is, though few are as precise as to give an answer to two decimal places. For example, a while back the US Dept of Energy claimed a 8 degree F lower thermostat setting for eight hours a day would save 8-10% of home heating costs. Hard to translate into degrees C for 24 hours a day, but however you do it, clearly nowhere near your figure. Who should I believe (possible answers include none), and why should I believe them?

The problem is, the estimates are all over the place, baseline assumptions are rarely given, and methods are opaque. Until I come across something that is clearly based preferably on sound observation, or failing that, on theory that can be understood by by someone with O level maths and above, I consider the question unanswered (= no one knows the answer). For example the "According to the U.S. Department of Energy..." I paraphrased above comes from a press release from the Iowa Energy Centre, and NPO, and no verifiable source is given for the 8 degree F / 8-10% costs claim. Unfortunately, that doesn't stop others from grabbing the claim and regurgitating it left right and centre. Why, even I regurgitated it!

Edit: added the link I forgot to add

Edit: another try: https://web.archive.org/web/20120330203912/http://www.energy.iastate.edu/news/pr/energysavingideas/setbacktherm.htm

Edit: Wordpunk still won't accept the url! Try this

https:web.archive.org/web/20120330203912/http:www.energy.iastate.edu/news/pr/energysavingideas/setbacktherm.htm 

with // added twice at the two obvious places

Posted by: @cathoderay

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There's no shortage of predictions of what the effect of a one degree change in the thermostat setting is, though few are as precise as to give an answer to two decimal places. For example, a while back the US Dept of Energy claimed a 8 degree F lower thermostat setting for eight hours a day would save 8-10% of home heating costs. Hard to translate into degrees C for 24 hours a day, but however you do it, clearly nowhere near your figure. Who should I believe (possible answers include none), and why should I believe them?

The problem is, the estimates are all over the place, baseline assumptions are rarely given, and methods are opaque. Until I come across something that is clearly based preferably on sound observation, or failing that, on theory that can be understood by by someone with O level maths and above, I consider the question unanswered (= no one knows the answer). For example the "According to the U.S. Department of Energy..." I paraphrased above comes from a press release from the Iowa Energy Centre, and NPO, and no verifiable source is given for the 8 degree F / 8-10% costs claim. Unfortunately, that doesn't stop others from grabbing the claim and regurgitating it left right and centre. Why, even I regurgitated it!

It looks like this forum has been the victim of dumbing down, a little way upthread you were prepared to accept an answer based on A level maths, now its O level.

Fortunately this rather simpler problem (a reduction in the thermostat setting on a 24*7 basis) only requires O level maths.  Here it is:

Simplest possible estimate

The heat lost by the house is proportional to IAT-OAT, thats a fact of the physics.  The average UK OAT is about 10C and we will assume IAT is set to 20C.  So a reduction  of 1C reduces the energy required by the house by 1/(20-10)=10%.

This ignores -

a) (for heat pumps only) the fact that COP varies with temperature so averages wont give exact results

b) (for all forms of heating) the fact that 10C is a UK average whereas local climates differ both up and down

c) (for all forms of heating) other energy sources which heat the house.  These are likely fairly insignificant in a large poorly insulated house but in a passivhaus will make a significant difference.

Since none of the above has the potential to turn the reduction into an increase then, unless we are actually interested in the exact figure, telling people that turning down the thermostat by a degree saves energy is a safe public message, correct qualitatively albeit an an approximation quantitatively.  We know for sure that a 24x7 reduction in the thermostat value will save something and the amount of the saving is very roughly 10 pc.  By very roughly I mean, to within a factor of 2 (because none of the above effects have a magnitude greater than that even at their extremes). 

If you want a more accurate estimate get the typical hourly temperature figures for your location and for each hour during the heating season do the above calculation and for each hour divide by COP at the OAT in question.  Sum the results.  Still O level maths. This takes out a) & b)

To take out c) you need to know (in addition) i) the house loss at some design temperature and ii) the sum of other heating sources.  If you have gas heating and everything else is electric, then ii is roughly equal to your average electricity consumption.  With this information you calculate the heat loss for each hour from IAT, OAT (O level maths) and design loss, subtract the other heating sources, then do the a variant of the calculation above.  All O level maths and all pretty deterministic.

Its really not that difficult to calculate with a fairly high degree of accuracy the saving from a 24x7 reduction in thermostat setting.  Anyone with O level maths can, in fact, do it!

Measuring it is of course more difficult because the outside temperature rarely stays constant for any length of time.  As it happens, where I am today, its 10C from midnight until 3am 27 hours later, a rather unusual event in the UK.  It would thus be a good day to do experiments on my heating system, but Im not at home and anyway am not interested in this particular experiment because the O level physics and maths tells me the answer with a high degree of certainty.

@cathoderay

A 8 degree F change in temperature is equivalent to a 4.44C temperature change, which for 8 hours would have the same affect as a 1.48C temperature change for 24 hours.

I can show the maths if you wish.

As James has shown, this would probably provide an approximately 10% reduction if heat loss from a building, whatever the heating system. A heat pump based system should actually provide an even greater saving, because of the improved efficiency of it not working so hard at higher LWT.