Calculate the COP of a heat pump to heat up a Jacuzzi

Hi Betel,

I tryd to understand your solution for the Energy meter.

As i understood you used some work arounds due to limitations of the Logo 0BA5.

I use a Logo 8.2 12/24RCE 6ED1 052-1MD08-0BA0, and i was wondering if there was a way to make the Energy meter more compact and easyer.

For my application i want to calculate the COP of a heat pump to heat up a Jacuzzi.

There fore i need the heat in kwh that the heat pump suply to the Jacuzi.

I have a flow sensor 1puls=0.084l and at in and output of the heatpump  2 PT100 4-20mA  0-100°C

At start up the water teperature is 7°C and the setpoint is 39°C

Via a bypass valve we try to maintain to have a delta T between the in and output of 2°C

The flow can varie very slow between 40 and 60l/min but does not fluctuate all the time.

Once the jaccuzi has reached the setpoint the heatpump works one ore 2 times/hour.

We mesure also the electrical consumption of the heatpump and we mesure the outside temperature.

Hope you can get me on the way to create a energy meter for this application

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Split from Energy meter (kWh).

Maybe this Link will help you. This seems to be exactly your application.

Regards, Scorp

Hi Betel,

I tryd to understand your solution for the Energy meter.

As i understood you used some work arounds due to limitations of the Logo 0BA5.

We use a Logo 8.2 12/24RCE 6ED1 052-1MD08-0BA0, with some aditional I/O modules.

I was wondering if there was a way to make the Energy meter application more compact and simplify .

For my application i want to calculate the COP of a heat pump to heat up a Jacuzzi.

There fore i need the heat in kwh that the heat pump suply to the Jacuzi.

I have a flow sensor 1puls=0.084l and at in and output of the heatpump  2 PT100 4-20mA  0-100°C

At start up the water teperature is 7°C and the setpoint is 39°C

Via a bypass valve we try to maintain to have a delta T between the in and output of 2°C

The flow can varie very slow between 40 and 60l/min but does not fluctuate all the time.

Once the jaccuzi has reached the setpoint the heatpump works one ore 2 times/hour.

We mesure also the electrical consumption of the heatpump and we mesure the outside temperature.

Hope you can get me on the way to create a energy meter for this application, especialy to adopt the parameters for the flow sensor and the 4-20mA sensors.

Hi Scorp,

ideed seems great, althow i have some questions 

Why is the flow limited to 30l/min in my aplication i go to a max of 60l/min

I have 11,78 pulses/liter rounding to 11 would be very drastic, is there another way to scale this ?

Wich temp sensor where you using ? I have PT100 4-20mA 0-100°C

How does this affect the calculation ?

There are different ways to optimize the calculation, this depends on your sensor and the application. The problem is the maximum integer of the Logo arithmetic (+32767) With 11-12 Impulses per Liter you will have a more inaccurate result for lower flowing.

Have you some values like typical flow, maximum flow, typical temperature difference and maximum temperature difference ? I think, you must have the same formula for your heat pump.

Q = m * c * dT, Q=Power [kW] m=Flow [l/s] c = 4.19 [kJ/l*K] dT=t2-t1 [K]

Maximum Q is 32767W=32.767kW or you lose the last digit, then Q=32767x10W=327.67kW and so on. If you have some values for me, i can make a base program with some comments simular to the program on the linked side.

Regards, Scorp

P.S. I have prepared a first version with your values, if i have understand correct.

Scorp,

Thanks for the effort, i will check your program.

For a good working, the Heatpump needs a flow of 3200 l/h, the water circulation pump of the jacuzi has 2 speeds and even at the lowest speed the flow is to high for the heatpump.

So we instaled a bypas valve that we can control in the PLC, but the flow is never exact the same.

The flow is between 40 & 60l/min, everything below does not count and the same for the value above.

It would be better to warn if the flow is out of those limits.

Because of the fact that the water circualtion pump can turn without the Heatpump is on, we also need to stop the heat mesuring when the heat pump is off

For the optimal working of the heatpump the optimal Delta T is 2°C, it never goes below 1 and if the flow stays around 53l/m it is 2°, if the flow is lower the Delta T is rising to 3 or max 4°C.

50 l/m seems to be 

The idea is to store the amount of kwh per day, per week and per month on a SD card or log it on a computer for further evaluation.

Want to do the same for the electric consumption an the outside temperature.

I integrated your program in mine but it is not clear where i can see the output in kwh, i would expect that it is in AM 4 but i stays at 0, i also see that AM3 and AM7 (translated to your blocks) varies between  -52 and 0

I can send you my program if you want.

With these values you can use power in W, because 60 l/min = 1 l/s and dT=2 K (°C) you have a maximum of 8400 W (< 32767). See next version with proper values for this and an additional datalog every day at the time 00:00. You can build the differences for each day and week in an excel sheet. If you want to display a historie on the Logo, then you must expand the counters for daily, weekly ... hours as you need.

Simulate first my program directly, e.g. type in 300 (30.0°C) for AI1, 290 (29.0°C) for AI2 and 12 (frequency 11.78 Hz = 1 l/s = 60 l/min) for I5 to see the power 4190 W in AM3 (Aq output of B004).

For display only use the blocks B004 for power, B005 for flow, B047,B069,B078 for temperatures and B011,B012 for energy.

Regards, Scorp