View Full Version : Calculationwith Evaporation Temp and A consumption

21-08-2015, 09:02 PM
I am trying to calculate how long a Danfoss BD compressor will be able to operate on a battery.
The battery says it has a Capacity of 15Ah.
the following numbers are given by danfoss:
I look at EN 12900 Household (CECOMAF) because i live in Europe and do everything in Celsius.
I dont seem to grasp how the Current consumption in A rises when the evaporation temperature rises. what does ''evaporation temperature'' mean in this case? i would think the lower the evap temperature, the higher the Amp consumption, because the compressor has to work harder for it. It is a Fixed speed Compressor BTW.

I hope someone is able to clear this up for me a bit.

21-08-2015, 10:04 PM
The rating on the battery means fully charged it can provide 15 amps for 1 hour

As the evaporation temperature drops it means that the system is removing less heat energy therefore it it doing less work. Less work equals less energy input

25-08-2015, 02:44 PM
okey that of the amp hours clears it up a bit
But the evaporation temperature means the evaporation temperature of the refrigerant? or is it the temperature inside the cooler ?

25-08-2015, 05:54 PM
It refers to the evaporation temperature of the refrigerant

25-08-2015, 09:43 PM
so does it mean the fisycal property of the refidgerant at which temperature it evaporates or does it means the temperature at which the refridgerant is cooled?
The power consumption rises when the evaporation temperature rises so that second statement would be strange i guess?

25-08-2015, 10:26 PM
Compressor capacity reduces a lot as evaporating temperature drops. Compressor energy also falls but not as quickly. So the heat removal rate decreases faster than the power input requirement and a compressor working at lower suction pressure has a lower efficiency but does draw less power.

30-08-2015, 03:53 PM
Is the most efficient speed full speed?

05-09-2015, 10:03 PM
Hi stijnijssel !
Usually if your compressor is part of refrigerator and the temp inside the cabinet is for example +2*c than the evaporating temperature will be around -8 to - 3 *c . Refering the table at -5*c evaporating the compressor will draw 3,37 Amps so the capacity of 15 Ah divided by 3,37 A equals 4 hours and 27 min . This is the point that the battery losses 20 % of its voltage or 9,6 volts

05-09-2015, 10:09 PM
Also test conditions are 55 c and ambient temp 32 c so if ambient temp is lower than condendensing temp will be lower and the compressor will draw less amps and for loner time .