I bought a Heat Pump

QrizB

Reed_Richards said:

If anyone else keeps track of their monthly energy use for heating and hot water I would be interested to know if they have also seen a drop in the second half of December and January, compared to last year. 

Interesting statistics, R_R.

In January 2020 I used an average of 61kWh/day of gas. This January to date I've averaged 48kWh/day. That's a less dramatic fall than yours but still a reduction, and I can't claim it's all due to me turning down the flow temperature on my boiler.

Effician

It's been very mild this winter , never had the doors & windows opened so often at his time of year ( midlands), i'm suprised the reduction in usage  wasn't more if the weather in your region has been similar.

Playing devils advocate , maybe R-R's usage could have been less if he'd left things alone.

Reed_Richards

Effician said:

Playing devils advocate , maybe R-R's usage could have been less if he'd left things alone.

It's certainly possible but the effect of my not leaving things alone was to cause the heat pump to use lower Leaving Water Temperatures than hitherto and that ought to have caused it to run more efficiently.

Meatballs

Reed_Richards said:

After the first year of operation of my heat pump I was able to report that I had used 6930 kWh of electricity.  Now, about seven weeks later my consumption for 28/1/21 to 28/1/22 is 6026 kWh.  This means that I used far less electricity over the last seven weeks than in the corresponding period a year previously (about 900 kWh less).  This is very gratifying but I'm not sure how to account for it.  The possibilities I can think of are:

1. Commissioning and, perhaps, "bedding-in" of the heat pump caused it to use more power than in normal operation.
2. For the first few weeks of installation I kept the house about a degree warmer than normal (I cannot remember exactly how long for).
3. The corresponding period a year ago may have been much colder (I cannot remember).
4. I am now using more "aggressive" (but perfectly functional) weather compensation settings.

I continue to operate my heat pump as if it were a boiler, using a night-time set-back and using the "smart" feature of my third-party controller to try to ensure that the target temperature is reached at the start of the target period (so-called "comfort mode").

If anyone else keeps track of their monthly energy use for heating and hot water I would be interested to know if they have also seen a drop in the second half of December and January, compared to last year.  

   

Use degreedays.net to compare the two periods to account for the weather.

Reed_Richards

I have tried degreedays.net and it  makes very little sense to me.  Instead of giving you the basic information, which is the average temperature for any particular day, it obscures that information by telling you days that were warmer than some specified temperature.  I'm sure in some specialised contexts this is useful but I do not find it so.

Martyn1981

Reed_Richards said:

I have tried degreedays.net and it  makes very little sense to me.  Instead of giving you the basic information, which is the average temperature for any particular day, it obscures that information by telling you days that were warmer than some specified temperature.  I'm sure in some specialised contexts this is useful but I do not find it so.

I had a quick look at the anomaly maps on the Met Office site, and it seems to show Dec20 being average to below average depending on location, and Dec21 being fairly average. Then Jan21 quite a lot below average, but of course Jan22 is not yet available, but seems like a warm one to me. So both suggest a tad warmer which might account for some of the improvement, given it does seem like quite a lot, as you say.

Fascinating stuff, many thanks for all the details and updates.

shinytop

Reed_Richards said:

Effician said:

Playing devils advocate , maybe R-R's usage could have been less if he'd left things alone.

It's certainly possible but the effect of my not leaving things alone was to cause the heat pump to use lower Leaving Water Temperatures than hitherto and that ought to have caused it to run more efficiently.

I think that's the key.  (1) Lower LWT => higher COP and  (2) unless an ASHP is run 24/7, the circulating water cools down periodically and it takes less energy to heat it back up if the target temperature is lower.

Reed_Richards

I took readings and manually constructed this chart about a week ago.  I missed the start of the sequence but the heat pump had been heating the hot water immediately prior to this so the central heating water was probably unusually cool at the start.   The power measurement is taken from the monitor provided by my solar PV system and is the power to the entire house, not just the heat pump.  To use a single scale I have multiplied the power by 10 so, for example, 15 represents 1.5 kW.

Unlike @shinytop 's heat pump, mine starts off cautiously at somewhere about 1 kW used by the compressor and, seemingly, about 250 W used by the other mechanical parts.  Every so often it steps up the power by approximately 1 kW, presumably because the water temperature is too low or not increasing fast enough.  Eventually it gets to about 4 kW and holds that for 9 minutes until something decides enough is enough.

           

shinytop

Reed_Richards said:

I took readings and manually constructed this chart about a week ago.  I missed the start of the sequence but the heat pump had been heating the hot water immediately prior to this so the central heating water was probably unusually cool at the start.   The power measurement is taken from the monitor provided by my solar PV system and is the power to the entire house, not just the heat pump.  To use a single scale I have multiplied the power by 10 so, for example, 15 represents 1.5 kW.

Unlike @shinytop 's heat pump, mine starts off cautiously at somewhere about 1 kW used by the compressor and, seemingly, about 250 W used by the other mechanical parts.  Every so often it steps up the power by approximately 1 kW, presumably because the water temperature is too low or not increasing fast enough.  Eventually it gets to about 4 kW and holds that for 9 minutes until something decides enough is enough.

           

My ASHP behaves just like @Reed_Richards.  The graphs I posted before looked different because the time axis was a lot more compressed.  This is mine over a similar period showing a restart of heating after DHW.  It's the same shape after a longer pause, just more power for longer. I suspect the control software is very similar.
 

Reed_Richards

Ah, I see @shinytop .  The main difference that I can see is that my water temperature goes up about twice as fast with a similar amount of power supplied to the heat pump.  I'll have to think for a bit to work out what that means.  Perhaps it means that some of my rooms with TRVs were at temperature so not calling for heat?  I have noticed that the sun shining through a south-facing window is enough to raise the room temperature by a couple of degrees at the moment.