hi @overeasy thanks for your reply, I’ll have to spend some time working your comments in btu, however here are some info regarding some statements you made:
Your approach requires a closed system. Heat pump water heaters usually
run a long time (compared to resistance heating). If there is any use
during that period, the results will be off.
That’s spon on and is the weak part of this method. The COP will get worse during those periods since energy is coming in and temperature will not increase as much.
However!!! it’s the price to pay to avoid inserting mechanical dongles to measure the water/liquid flow.
First, you don’t really say if you have PV solar panels or solar thermal panels. Big difference. I’m going to assume it’s PV, and that you mention it because you also heat the water with resistance.
Solar is vacuum tube heat pipes working in a closed circuit. I’m assuming that the energy-in of such a system is the water pump working to bring the heated fluid into the deposit. I also have a resistance and i am confident i will never have to use it lol!
I use something like this.
All said and done, it’s probably equal cost/effort to a temp sensor in a well (home-brew beer suppliers have nice stainless wells for DS18B type sensors). Added benefit - the best energy saving approach is to just use less hot water, so you get a metric on that.
So your energy-out is obtained by measuring the energy you extract from the system when you open your tap and then add some constants to account for losses? How do you scale your energy-in kWh? I mean, if the system is pumping energy into the tank for a long time, if you open your tap for 5 seconds how are you able to determine the COP of the system?
On my side, i’ve been experimenting and did the following:
Record the minimum and maximum values of the bottom temperature sensor.
create a new feed that subtracts these maximum and minimum values to obtain deltaT
multiply deltaT by the constant mentioned above and get energy-out
divide energy-out with the kWh/d recorded by the CT and get COP
Not only it does not account for the used energy on the heating period it also does not account for the fact that when the deposit is still during the night, heat is transferred to the top and the bottom temperature sensor becomes colder.
today i got a COP of 9 with this method, my heatpump has a rated COP of 4 and it worked only 2 hours to bring the temperature to a solid 47ºC. Of course the solar thermal worked all day, even though today was a very cloudy day.
I am assuming that the only energy-in of a solar thermal system is the small pump, that users about 40watt of power. The COP of such system is very very high, on pumpless systems the COP actually is infinite
Today with exclusive contribution from the heat pump (no sun), the result is a COP of 2.8.
The datasheet of my heatpump, for this outside temperature (11ºC) and heating cycle ( 15ºC-45ºC) reports a COP value of around 3.
I think that if the calculations are fundamentally correct, the error is not that important, what matters is how the COP behaves as the system gets older.
Slick! It’s interesting to see the efficiency drop as the tank temperature increases. The power into the heat pump increases, while the rate of rise decreases. COP probably is 3 at noon, and then down to 2.6 or so at 16:00
A new dark blue line indicates the output temperature of the thermostatic mixer valve fed by the tank’s hot water output and cold water feed. The COP remains very high, even with lot’s of energy going out the system for consumption. The numbers tell that with a bit less than 1kWh the system was able to generate almost 10kWh of energy, excluding consumption during that period!
I’m surprised with your website emoncms/ChabrosMaina/ and I’m searching information how to implement this, Recently I have bought a hpsu rotex 508 8KW and a solar system FV and I like how can I do this
At this moment I have collected information from my fronius primo values and recover from emconcms but now I like to obtain data from hpsu, can you give detail how to do this?
Also I liek to know if you implemented smartgrid, and for example if FV is generating more power than needed yu can increase hpsu usage to use this power?
