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AndY1
25-10-2006, 11:01 PM
Hi!

I have Airwell Florida 12 DC Inverter AC.
COP at 7'C outside and 20'C inside is 3.82.
What is COP at 0'C or -5 or -10'C or -15'C?
How is COP falling with falling outside temperature? I can't seem to find that info anywhere. Is there a graph with outside temperature on the x axis and COP on the y axis?

Thanx for your replies.

nicolacozma
26-10-2006, 01:05 PM
Hi AndY1,


I don't have a chart or diagram with COP vs. outdoor temperature behavior, but around 0 degrees the heat pump will lose approx. 20% of nominal heating capacity. Also at -10 degrees the heat pump will return to have a high efficency around 95-97%. This happend because at 0 degrees the heat pump will heave many deicing cycle.
In some cases you have to apply a correction due to lengh of pipe and another correction due to deicing cycle.

Hope it's useful for you.
Nicola

NoNickName
26-10-2006, 02:28 PM
It depends on how much ambient temperature affects evaporating pressure, and this is not a constant figure across brands and models. I'm afraid that your question doesn't have a numeric answer, but a rule of thumb like nicola's.
Also it depends whether the heat pump performance is calculated with 7°C DB or WB, as some producers like Rhoss and RC declare as WB, others like us declare DB (which is more honest).

db= dry bulb
wb= wet bulb

Peter_1
26-10-2006, 04:57 PM
Also at -10 degrees the heat pump will return to have a high efficency around 95-97%. This happend because at 0 degrees the heat pump will heave many deicing cycle.


Why you think COP increases if temperature drops from 0°C to -10°C?
This sounds really magic for me :confused:

And why should you defrost less when it's outside -10°C instead of 0°C? What about outside humidity WB versus DB?

I don't follow you on this.

AndY1
26-10-2006, 05:01 PM
So what you're saying (Nicola) is that COP is higher at -10'C than at 0'C because the humidity at 0'C is usually much higher and thus demanding more deicing cycles?
Humidity at -10'C is usually at 20%-, right? So much less or almost no deicing cycles are needed.

But does the COP graph go something like this:
http://www.knut.si/nordic-tp.htm

TIA!

NoNickName
26-10-2006, 06:40 PM
Why you think COP increases if temperature drops from 0°C to -10°C?
This sounds really magic for me :confused:

And why should you defrost less when it's outside -10°C instead of 0°C? What about outside humidity WB versus DB?

I don't follow you on this.

I think he means that by 95-97% is a ratio of heat about 0.95 times the power input, because of defrosting.
So basically it draws more power than it releases.

AndY1
26-10-2006, 09:13 PM
I think he ment that at 0 - minus10 the COP gets back to the 95-97% of COP at 7'C whereas the actualy COP at 0'C+ is worse because of deicing necessary.

nicolacozma
27-10-2006, 12:59 PM
My observation was refered to heating capacity and not to COP. Obviously I am not agree that COP increse when outdoor temperature fall.
Therefore at -10 degree the moisture quantity is less then at 0 degree because a certain quantity of moisture becomes ice cristals, and AC system have to defrost less quantity of ice in a short period of time. This cause an increasing of heat quantity delivered into indoor ambient.

Peter_1
27-10-2006, 06:09 PM
Still don't follow you but don't pay attention on me.
Americans use COP, EER and SEER different then we do.

AndY1
27-10-2006, 08:02 PM
What Nicola means is, that air humidity is much higher at 0'C (50%-60%) than at -10'C(20% and below). That's why the outside unit doesn't need to defrost the ice on the external unit as many times at -10%, than at 0'C and thus not loosing that amount of energy for defrosting the external unit.

However COP is lower at -10'C than at 0'C. But because more defrosting is needed at 0'C than at -10'C, the energy for defrosting should be accounted as an enetgy loss and be substracted from COP factor at 0'C.

But, my original question is; if my A/C's COP at 7'C outside temperature is 3.82, how much is COP at 0'C and -10'C not accounting for humudity.

It's a shame, that these data are not included with the manual or the specs.

NoNickName
27-10-2006, 09:43 PM
Still not true: defrosting is started by time, temperature or pressure or a combination of these.
Temperature and pressure are lower at -10 than at 0, so disregarding whether the coil is frosted or not, the unit will defrost anyway.
I don't even believe the unit will be running at -10, as the evap temperature will be at -20 to -25°C, a temperature to which the corresponding pressure of R407c or R134a will stop the unit by LP switch cut out.

AndY1
28-10-2006, 11:36 AM
What if R-410A is used in A/C?

NoNickName
28-10-2006, 11:55 AM
What if R-410A is used in A/C?

Why not? The only problem I see is the pressure while producing warm water, but this can be addressed.

AndY1
28-10-2006, 12:49 PM
My A/C is Airwell Florida 12 DV Inverter and is already rated for -15'C. It is by default filled with R-410A so I should be fine.

But I still don't know my A/C's COP at 0'C and at -10'C.

Where can I find that info?

Andy P
28-10-2006, 01:36 PM
What Nicola means is, that air humidity is much higher at 0'C (50%-60%) than at -10'C(20% and below).
Confused of Glasgow here again. Who says that the RH will be 20% at -10C? It might be - but it might also be 100% depending on what the weather has been recently and where the temperature is heading. In fact the only way I can see the outdoor RH being as low as 20% at -10C is if the air temperature has been even colder (much colder!) and has warmed up rapidly - too quickly for much of the ice to sublime. At 0C the RH is likely to be nearer 80-90% - especially in Glasgow!

cheers

Andy P

NoNickName
28-10-2006, 03:37 PM
My A/C is Airwell Florida 12 DV Inverter and is already rated for -15'C. It is by default filled with R-410A so I should be fine.

But I still don't know my A/C's COP at 0'C and at -10'C.

Where can I find that info?

Either at Airwell's or I don't know.

Abby Normal
28-10-2006, 08:53 PM
Its COP drops with temperature as you are well aware. But what also drops is its heating capacity as the heat source is getting lower. Same time your heat demand is high.

They usually publish how cold before it hits 1

They will publish at freezing and below.17F seems to be a common number , -8C