kW fur Heizung und AC

Re: kW fur Heizung und AC

Beitragvon kassiopeia » Do 6. Apr 2017, 19:03

umrath hat geschrieben:
I'm not sure if the heat loss rate is responsible or if it's just bad efficiency.

the heat loss rate is the reason for the neccessity of the heater, the efficiency of the heater determines the actual power consumption. both are connected, but on different levels

I also don't understand why the conventional heating and the heat pump are equal in energy consumption beyond -10 degrees.

if I understand Jan properly below -10 degree the heat pump stops working (due to bad cop) and only the conventional heater elements remain usable

edit: Jan already responded in between...
lg kassi

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Re: kW fur Heizung und AC

Beitragvon Jan Treur » Do 6. Apr 2017, 19:11

umrath hat geschrieben:
Hmm. I don't have any actual numbers for temperatures that low. But when driving the Premium (with heat pump) at -2 to -3 degree I was usually in the range of 0,6 kW while driving. A that sharp increase in energy consumption would astonish me because the heat pump had no problems to heat the car in no time. Why would it cease to work / be horribly inefficient just 7-8 degree lower?


The principle is that you calculate the heat loss by multiplying the loss rate by the temperature difference. Then the power used by the heat pump is the heat loss divided by the performance factor SPF. And this factor SPF becomes smaller and smaller for lower temperatures until it reaches 1, which corresponds to direct heating by a resistance heater. Because you divide through it it gives a nonlinear effect. Unfortunately winter has gone so we cannot test -10 anymore.

I made it so that the SPF 1 is reached exactly at -10. I also could make that at a lower temperature. Then a jump in the graph would occur at -10.
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Re: kW fur Heizung und AC

Beitragvon Roland81 » Do 6. Apr 2017, 20:09

Hey Jan,

the highest number for heating i saw was something around 4,6kW (Ioniq with heat pump). Unfortunately I do not have any data. From my memory the 4,6kW were for some minutes and were then stable around 2kW. (outside temp. -10°C)
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Re: kW fur Heizung und AC

Beitragvon Jan Treur » Do 6. Apr 2017, 20:15

OK, that is helpful. What was the temperature setting for the interior?
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Re: kW fur Heizung und AC

Beitragvon Roland81 » Do 6. Apr 2017, 20:40

21,5°or 22°C
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Re: kW fur Heizung und AC

Beitragvon Jan Treur » Sa 8. Apr 2017, 07:31

Based on these first reported experiences I adjusted some of the parameters a bit. For example, now I estimate the heat loss rate of a driving Ioniq at 80 Watt per °C temperature difference between inside and outside temperature. The graph below shows this update, assuming an interior temperature set at 22°C; the reported experiences are depicted as dots.

Still more experienced numbers are welcome!

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Re: kW fur Heizung und AC

Beitragvon KyRo » Sa 8. Apr 2017, 13:19

Just a word to efficienies of PTC (base principle Joule heating) and heat pumps:

Joule heating has an efficiency close to 100% especially where it can be used directly inside the medium / room to be heated, which is in general the case in vehicles where the elements are placed in the vehicles cabin and heats up an airflow.

The heat pump instead "pumps" heat/energy from a colder side to a warmer side (thus against natural temperature drop) by expanding a gas/coolant to cool it down, then heating up the coolant within the environment chiller, and compressing it again to heat it above the necessary temperature. The chiller is often referred to as the evapourator because the coolants normally are developed to change aggregate state to enable larger temperature differences. The heat pump gains more heat energy than it uses for mechanical gas compression (thus having an "efficiency" >100% compared to joule heat), but however, its clear that there is a limit on lowest environment temperature, respectively the temperature level of the expanded coolant flowing in the evapourator. Practically somewhere above that.
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Re: kW fur Heizung und AC

Beitragvon Jan Treur » Sa 8. Apr 2017, 14:29

Yes, for a given heat pump there is such a bound, which can be -10 °C or -20 °C, for example. The closer you come to this bound, the lower the performance factor will become. That is one of the reasons that the Ioniq only uses the heat pump for temperatures above -10 °C. Below that -10 °C a resistance heater is used.
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Re: kW fur Heizung und AC

Beitragvon Twizyflu » Mo 10. Apr 2017, 10:23

What about the consumption of the PTC battery heater. Can we measure it somehow?
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Re: kW fur Heizung und AC

Beitragvon Jan Treur » Di 18. Apr 2017, 06:14

I found another data point: an experience of @pmiddeld for +4 °C with temperature maintenance heating power level 0.5 kW, reported here: http://www.ioniqforum.com/forum/35281-post81.html. The graph was updated only by adding this data point, which turns out to fit well to the previously determined parameter values.

Maybe some more explanation is useful. An important entity for the above posts is how much heat is flowing out of the car each minute or hour, which is called the heat loss. This heat loss depends proportionally on the temperature difference between inside and outside, according to the so-called heat loss rate, which is a parameter that indicates heat loss for just 1 °C difference in temperature. The heat loss rate was now estimated at 80 Watt per °C difference in temperature between outside and inside. For example, when the outside temperature is +4 °C and the interior is at 22 °C, then this temperature difference is 18 °C, so the heat loss is 80*18 Watt = 1440 Watt. You can interpret this in the sense that the car heats the outside air as if it was a 1440 Watt heater.

To compensate for this heat loss, and thus maintaining the interior temperature at the same level, you need to add the same amount of heat by the car's heater. Fortunately, under these conditions a heat pump can produce 1440 Watt by only using a fraction of that amount of energy, in this case about 500 Watt. To know how much in kWh this will take from the battery you can just multiply this number by the duration of the trip in hours. For example, for a two hour trip it will cost your battery 2*500 = 1000 Wh = 1 kWh. This reduces the available full charge of 28 kWh by 1/28 = 0.036, which is almost 4%. You can expect a reduction in range by the same percentage due to having the heater on.

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Zuletzt geändert von Jan Treur am Di 18. Apr 2017, 06:36, insgesamt 2-mal geändert.
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