Has anyone tried comparing actual ASHP performance with their heat loss calcs?

[ReedRichards]

2 hours ago, JamesPa said:

...MCS doesn't, to the best of my knowledge, allow for body heat etc, unless someone can correct me.

 

MCS calculations are building-specific and do not take into account the occupancy.  Fill your house with enough people (or enough power-hungry appliances) and you don't need a heating system.    

Edited January 22, 2023 by ReedRichards

[IanR]

6 hours ago, DInwood said:

From your comment "50% greater" I am clearly missing something significant. 

 

Apologies for my blunt reply. Before you added this line, which came in an edit just after I had replied, it seemed you were burying your head and not considering you may have erred in your calcs. 

 

There's lot's of opportunity for the fabric of the building to not perform as intended as well as you own calcs missing losses and over estimating gains.

 

With regards to building fabric, for instance, you may be using theoretical U values, rather than ones that include the structural elements that cause pinch points with local reductions in insulation thicknesses, or allowing for correct timber fraction, and have you included allowances for thermal bridges. 

[JohnMo]

Let's simplify a little.

 

You are using more electric than you expected your CoP looks rubbish, except on one day where you got around 3.5 instead of 4.5. I think that sums it up.

 

Issues, you have a buffer, loose 1 from your CoP.

 

Way to many zones, merge most of them together ideally have one or two large zones.

 

DHW, this can be a huge consumer, assuming from ASHP. 

 

So how is it heated?

Cylinder set temp?

Flow temp to cylinder?

Does the ASHP see cylinder water temp or is it on/off signal from thermostat?

Do you have an immersion hooked up to ASHP controller?

 

[DInwood]

11 hours ago, JamesPa said:

In a low consumption house definitely, in a leaky house less so.  MCS doesn't, to the best of my knowledge, allow for body heat etc, unless someone can correct me.

You are right, the MCS pack doesn't explicitly allow for internal heat sources.  It does estimate annual demand & the document I've got doesn't say how this is calculated.  It isn't hard to work out how it's done though & I'm certain they use "heating degree days" times their estimated heat loss per degree.  I'm trying to emulate this "heating degree days" method by using actual outside temperature & estimated internal heat sources.  I was hoping others had tried this also and had some experience to share or correct my efforts.

[JohnMo]

They just use the nearest weather station to your post code, and use a historical average.  For us they would use Dyce airport (60 miles away), which can on average be 3 deg colder than where we live due to a micro climate.  But obviously close enough. They are only looking for magnitudes of heat loss.  Do they use a 3, 6, 9, 12... kW heat pump.

[DInwood]

8 hours ago, IanR said:

 

Apologies for my blunt reply. Before you added this line, which came in an edit just after I had replied, it seemed you were burying your head and not considering you may have erred in your calcs. 

 

There's lot's of opportunity for the fabric of the building to not perform as intended as well as you own calcs missing losses and over estimating gains.

 

With regards to building fabric, for instance, you may be using theoretical U values, rather than ones that include the structural elements that cause pinch points with local reductions in insulation thicknesses, or allowing for correct timber fraction, and have you included allowances for thermal bridges. 

No apologies needed.  In all humility I'm looking to gain from the wisdom of more experienced people.

So your feeling is that I'm underestimating fabric losses.  Any idea how I could estimate what to allow for?  I've tried some arithmetic modelling (eg looking at day-to-day variability and looking at empty periods) and if I increase the 88W/C by much then I couldn't make sense of the numbers (eg predicted negative heating days in winter).  I fully accept I'm making some mistakes & I'll go back to my modelling to explore again.

I'm very embarassed that I'm the only person who has tried doing this!

Edited January 23, 2023 by DInwood

[DInwood]

23 minutes ago, JohnMo said:

Let's simplify a little.

 

You are using more electric than you expected your CoP looks rubbish, except on one day where you got around 3.5 instead of 4.5. I think that sums it up.

 

Issues, you have a buffer, loose 1 from your CoP.

 

Way to many zones, merge most of them together ideally have one or two large zones.

 

DHW, this can be a huge consumer, assuming from ASHP. 

 

So how is it heated?

Cylinder set temp?

Flow temp to cylinder?

Does the ASHP see cylinder water temp or is it on/off signal from thermostat?

Do you have an immersion hooked up to ASHP controller?

 

Thanks JohnMo.  You are concentrating on the CoP side of my puzzle.  That's fine - but are you saying I really should be achieving over 4 as measured by the Ecodan?  If so, the installer needs re-educating as he thinks the current figures are realistic!

I allow the DHW separately in my analysis.  It is heated by ASHP with ASHP connected cylinder thermostat, there is an immersion but its never been needed as the ASHP gets the tank up tto 51C in about 45 mins.

[JohnMo]

So what flow temp is the ASHP using to achieve a cylinder temp of 51 in 45 mins.

 

Assume must have a big heating coil.

 

Flow temp 65, CoP close to 1.2

60, CoP close to 2.5

55 cop CoP close to 3

 

All the above are on a 5 deg day.  Depending how many times you heat the cylinder in a day, could have a marked influence on your electric consumption.

[DInwood]

2 minutes ago, JohnMo said:

So what flow temp is the ASHP using to achieve a cylinder temp of 51 in 45 mins.

 

Assume must have a big heating coil.

 

Flow temp 65, CoP close to 1.2

60, CoP close to 2.5

55 cop CoP close to 3

 

All the above are on a 5 deg day.  Depending how many times you heat the cylinder in a day, could have a marked influence on your electric consumption.

Peak flow temp was 53C yesterday, tank heated once per day, it took 51 mins to heat the tank from 42 to 51.  

As I say, I'm subtracting the estimated HW power from my calcs to arrive at my disspointment regarding heating power performance cf expectations.

[ReedRichards]

56 minutes ago, JohnMo said:

Issues, you have a buffer, loose 1 from your CoP.

 

 

I think  @JohnMo is citing a scientific study that was discussed here recently (but which I can't find at the moment). 

[akjos]

20 hours ago, DInwood said:

For comparison, on our coldest day so far (avg ext temp -0.7C) we used 23kWh of electrical power for heating (measured at the consumer unit supply to the Ecodan) and the Ecodan itself estimated 39kWh of heat output.  My method showed a net heat demand on that day of 34kWh & 10kWh power in. So one of the closest matches on heating but still poor electrical performance. 

 

It sounds like your calculation as to heat demand match those on the MCS as well as the Heat pump estimates. So there shouldn't be any issues there...

As for the electrical consumption and COP, that's a whole different story and depends fully on how your system is set up. As @JohnMo already mentioned: What system components do you have, how is it plumped, do you have enough system volume, defrosts, run times, flow temps, immersion etc etc etc. You could set up OpenEnergyMonitor to track a lot of this and then calculate the COP.

 

As far as the advertised COP from the manufacturers, I think that's a momentarily value. Meaning your heat pump has started up and is running a constant flow temp of 35'C at 7'C ambient for example. If you checked your COP at that specific time, it would probably match. But if you take it as a whole day it won't due to all the other factors mentioned above. Except maybe if you have a system which is set up to perfectly match your heat demand and run 24/7 with all being one zone, no buffers, no HW.
 

More realistically you need to compare to the SCOP (Seasonal COP) over a longer time period.

[PhilT]

If it helps you get an idea of whether or not your ASHP is performaing as it should, I have an Ecodan R32 11.2 and my installer calculated the following, but note - based on full occupancy. My house is a 30 year old self build of traditional construction.

Max heating design flow temp °C    50
Max DHW design flow temp °C    55    
EPC space heating kWh p.a.    13,374
EPC hot water demand figure kWh p.a.    2,839
Total   16,213    
Indoor average design temp. °C    19.2
House area sq metres    137
Peak power/heat loss kW    8.26
At design temperature °C    -2.4
Heat pump energy consumption kWh p.a.    4,971
SCOP    3.26

 

The FTC estimated data for 2022 gives heat output of 12,616 and input of 3,757 so SCOP of 3.36

My own measurements suggest the consumption is quite accurate - I know everything else except the heat pump averages 6kWh per day and my total annual consumption for 2022 was 6MWh. The output is much lower than the installer's estimate as there are only two of in the house for most of the year, and we generally heat our DHW to only 40 or 42degC.
 

[DInwood]

Thank you all for reading my post and your thoughtful responses.  It seems that nobody in this thread has tried do do this (predict daily heat requirements), but also nobody else is so dissapointed with their heating either.

The scientific part of me is hurting because I really feel this is capable of being modelled and I can't yet see where I'm going wrong.  Thanks to your comments I've gone back over my spreadsheet (which has data from before the heating started up and for a winter week it was off).  I find that if I use a higher rate of heat loss (say 120W/C) then to account for the periods the heating was off, no realistic amount of internal heat sources would account for the house temperature.  Conversely if I crank up my estimate of internal heating then the excess of Ecodan caimed heat output over predicted gets even worse.

FYI I'm not ready to give up yet.  Thanks also for the references which I shall now go away and study in more detail.

In parallel I will continue with the efforts to increase the CoP.  The MCS certificate used an sCoP of 4.1 - a long way from what I'm getting.

Edited January 23, 2023 by DInwood

[JohnMo]

Are your calculations allowing for glycol or no glycol in the water mix. This could 10-15% of energy meter reading.

[DInwood]

32 minutes ago, JohnMo said:

Are your calculations allowing for glycol or no glycol in the water mix. This could 10-15% of energy meter reading.

I asked the installer/ system commissioner this and he assured me the system knew it was the proper glycol mix.

[SteamyTea]

2 hours ago, DInwood said:

seems that nobody in this thread has tried do do this (predict daily heat requirements),

@TerryE does exactly this. And I do it manually with my basic storage heaters i.e. I adjust the input value according to the expected ambient temperature.

 

 

[DInwood]

16 hours ago, SteamyTea said:

@TerryE does exactly this. And I do it manually with my basic storage heaters i.e. I adjust the input value according to the expected ambient temperature.

 

 

Hi SteamTea I was hoping you might be able to help.  How well does your prediction/model match actual heat used?

[SteamyTea]

42 minutes ago, DInwood said:

Hi SteamTea I was hoping you might be able to help.  How well does your prediction/model match actual heat used?

Not sure yet, I am working on the last 4 years data.

It is not brilliant because I have to manually twiddle the input knob on the storage heaters (50p piece works a treat).

I have also had a peculiar last 15 months having been away for a couple of days most weekends in late 2021 and early 2022, then away again every 2 weeks or so since then, and there was lockdown in 2020.

I also have a nice 'problem' that my house is quite thermally stable, so need a lot of data points to start to find out what is actually making a difference, so just working on the 104,446 hourly data point for house power, internal temperature and external temperature.  It keep the data small enough to use Excel.

So far, what I can say, is that adding secondary glazing and heating just the top of the water cylinder (200lt, E7) has made a huge difference, and fixing the back door (I hardly use the fan heater now).  A mean power reduction of between 150W and 200W. 1.3 MWh.year^-1 to 1.7 MWh.year^-1, a saving not to be sniffed at with my low usage, previously between 4.4 MWh.^-1 and 4.8 MWh.year^-1, last year was 3 MWh,year^-1. And my house was warmer, between 0.6°C and 0.9°C, how brilliant is that.  Fixing the leaky back door will have helped a bit as the draught blew on my feet.

Here is a chart that shows the all year data for 2019 up to 2023.  Ignore anything below an internal temperature of 16°C as they seem to be corrupted data reading (or something else, not investigated yet, but they do only account for around 2% of reading.  Every thing about that internal temperature, is pretty linear, and it is including the non heating times as well.  I shall be looking at heating times only, later, and temperature slopes, which is what prompted me to get on and do it.

 

So hopefully, once I have digested all my data, I should be able to do as @TerryE does and simply vary the charge times for the storage heaters, rather than the input temperature controlling it.  Teasing out time data is often tricky as things like running the washing machine at night 3 times a week can throw it out a bit, but should be able to filter that out.

 

Edited January 24, 2023 by SteamyTea

[TerryE]

19 hours ago, DInwood said:

It seems that nobody in this thread has tried do this (predict daily heat requirements), but also nobody else is so disappointed with their heating either.

[My ital].  @DInwood you need to use the forum as a resource to get good benefit from it.  If you find the right consultant and pay the appropriate ££ then you might get VFM.  If you ask a complex and hard to read Q, then it will be discarded by many members as TL;DR, and other will reply on points.  I suggest that you treat the forum more as a knowledge base and do your research; expect to invest time and effort in finding content that is relevant and learn from it. Forum search and Uncle Google are good friends here.  The more karma you've earned in your content and responses, the more that old hands will be drawn to your topics.  Focused and interesting Qs tend to get more valuable answers.

 

I did my own near passive self-build roughly 2015-2017, and forum and community saved me a huge amount of grief, and we ended up with a far better living experience because of the advice given here, so I pay that back by visiting most days and contributing to interesting threads where I feel that I can add some value, if I am drawn to the thread in the first place.  I also confess to getting tired of answering another variation of the same Q that has been asked and answered many times before.  However, I have tried to documented my learnings and experience in my blog here and on various threads, so try reading these, and post any specific Qs related to these on the appropriate thread or topic, as keeping the discourse together helps other readers. 

 

I missed it if you mentioned your actual means of heating.  For example my main heating mechanism is a water UFH embedded in a warm slab, with the average output flow temp to the slab loops when heating under 30°C.  Most radiator based system use a circulation temperature of 60°C or more.  The actual ASHP CoP achieved for these two regimes can differ by perhaps 2× at current temperatures.

 

As @SteamyTea discusses, I heat my house using a very simple strategy: I dump enough heating into the fabric of the house during the 0-7AM off-peak to keep the average house temp stable, and accept the 1°C or so temperature ripple that I get over the day.  

 

I did design our heating system to use resistive heating in the first instance but facilitated the later addition of an ASHP.  However I have never installed because I can't make the RoI case given out estimated savings in running / maintenance / depreciation costs.  However if I did, then I would independently track input vs output power and feed this into my current heating control strategy: input power via power monitor on the ASHP spur; output by directly measuring flow rate and Δt of input vs return flow to ASHP. 

 

One of the issues that concerns me here is I don't want my own control to have to fight some smart ASHP control system doing its own thing.  I have this huge buffer tank (a ~70 tonne concrete slab) which I want to dump a chunk of X kWh into, so I want to be able to turn on an ASHP with a roughly fixed output temp of say 32°C or capped power (< 4kW say) and turn it off when my control system has measured its output as X kWh.  That's what I currently do with my restive heater, and it works well for me.

 

Like Nick, I have been instrumenting everything over this last 5 years, and I update my control strategies from time to time based on that empirical knowledge.

 

 

[TerryE]

On 22/01/2023 at 15:18, RobLe said:

While mvhr can be very efficient with ‘sensible heat’, it does not recover any of the latent heat of evaporation of water - so I believe every kg of water that evaporates indoors takes 0.68kWh of heat to get rid of, irrespective of the mvhr(anybody confirm?).

A good reference here is The Engineering Toolbox which gives the 0.68 kWh figure for evaporation at room temperatures. However, I suspect that modern near passive class houses have minimal evaporative cooling. 

 

Our kitchen probably has the highest AH and its RH hovers around 55% whereas my outside RH is typically around 90% in the winter months, which equates to an RH of 35% at room temperatures, so MVHR input will tend to drop the house RH.  On extract in these circumstances, the internal air will condense out about 40% of the absolute humidity in the heat exchanger (which is why MVHRs need an external drain) and thus this condensation latent heat will be covered into the input stream.  MVHRs are also typically ~85% efficient at recovery so heat losses in the other 15% are moot.  Given that extracts are typically placed in wet zones, I suspect that most moisture is pretty much immediately extracted and  I therefore suspect the effective net figure is therefore closer to 0.4 kWh/Kg.

 

We each shed maybe 3-400g moisture through respiration and evaporation, though the heat equivalent is a lot less that 2 kWh or so we radiate.  Cooking and misc drying probably add the remainder.  Even so from a heat efficiency perspective the best way to dump water is via the plug hole rather the MVHR, hence my other posts about "blading after showering" 🤣 as some regulars might recall. 

 

 

[Gone West]

3 hours ago, SteamyTea said:

Fixing the leaky back door will have helped a bit as the draught blew on my feet.

Not enough emphasis put on comfort I think. Feeling cold air near poor glazing or draughts around door, window frames or skirting. Sorting those out will help a lot with heating.

[DInwood]

I was vaguely aware of this issue but chose to ignore it in my modelling.  Perhaps I should look again. 

The Zehnder MVHR reports humidity as well as temperatures of the various airflows and Home Assistant logs 4 weeks of data.  Looking at this I see a relative constant ~85% outside RH & 55% inside (measured at the extracted airflow, so from the humid areas).  Here's the last 4 weeks daily averages for interest:

We too always blade after showering.

[SteamyTea]

4 minutes ago, DInwood said:

We too always blade after showering.

I always need another shower after.

Cleanliness is next to Godliness.