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savoc
25-07-2011, 11:37 AM
I have a question about heat pumps. In very cold ambients. When a unit is running on heating should the compressor suction pressure on r22 be around 0 degrees? ( coil clear of any ice) I know it may be silly question but my back ground is industrial/nh3. If the pressure drops below 0 degrees the coil will ice up. I understand about the de ice function, cycling of fans, etc. If your inside room is cold the discharge pressure will be lower but will your suction pressure be low aswell? what pressure ranges would you except for a day around -5> +5 ?

JoeAT50A
26-07-2011, 11:31 AM
For heatpump:
Heating:
Tc- condensing temperature around 0 C and Te- evaporating temperature around 40C
Cooing:
Opposite Tc=40C and Te=0C

***Carnot cycle are always rectangle shape in theoretically (not oval).***

Josip
26-07-2011, 04:54 PM
Hi, JoeAT50A :)


For heatpump:
Heating:
Tc- condensing temperature around 0 C and Te- evaporating temperature around 40C
Cooing:
Opposite Tc=40C and Te=0C

***Carnot cycle are always rectangle shape in theoretically (not oval).***

Are you sure? I am :confused:, how I can use heating mode to heat my home if condensing temperature is 0*C ....


Also for cooling mode isn't Te=0*C a little too low .... air coming out will be very cold, what about water droplets? .....


Best regards, Josip :)

Josip
26-07-2011, 06:04 PM
Hi, savoc :)


I have a question about heat pumps. In very cold ambients. When a unit is running on heating should the compressor suction pressure on r22 be around 0 degrees? ( coil clear of any ice) I know it may be silly question but my back ground is industrial/nh3. If the pressure drops below 0 degrees the coil will ice up. I understand about the de ice function, cycling of fans, etc. If your inside room is cold the discharge pressure will be lower but will your suction pressure be low aswell? what pressure ranges would you except for a day around -5> +5 ?

at air source heat pumps we can have outside air temperature down to -20*C with evaporator coil still clean of ice ... due to quite dry air at that temperature .... at outside air temperature around 0*C to 5*C with enough moisture you can have a frozen evaporator ... but then unit will go to defrost cycle by timer or some other controlling device depending do you have a smart or old one heat pump :)

in short .... heat pump efficiency i.e. COP and evaporating temperature is directly related to outside air temperature of course it is related also to refrigerant you have in your unit ... special units can work down to -30*C but refrigerant must be CO2 ...

please, search RE forums for heat pumps and you will find all answers you are looking for ;)

Best regards, Josip :)

JoeAT50A
28-07-2011, 05:34 AM
Hi, JoeAT50A :)
Are you sure? I am :confused:, how I can use heating mode to heat my home if condensing temperature is 0*C ....
Also for cooling mode isn't Te=0*C a little too low .... air coming out will be very cold, what about water droplets? .....
Best regards, Josip :)

Come on. I hope you are technical person, what I am saying is condensing temperature and evaporating temp which we use to design (calculated) value. It's not pipe temperature that you measured at fan coil unit.
For example R22 :Cooling mode with ambient 35C
Your high side pressure should be arround 220 psig (equivelant temperature is 42C)
You low side pressure should be aroung 60 psig (equivelant temperature is 1C)
Hope that will help.

mikeref
28-07-2011, 09:12 AM
I have a question about heat pumps. In very cold ambients. When a unit is running on heating should the compressor suction pressure on r22 be around 0 degrees? ( coil clear of any ice) I know it may be silly question but my back ground is industrial/nh3. If the pressure drops below 0 degrees the coil will ice up. I understand about the de ice function, cycling of fans, etc. If your inside room is cold the discharge pressure will be lower but will your suction pressure be low aswell? what pressure ranges would you except for a day around -5> +5 ?
I'd start with cooling cycle pressures after weighing in correct charge. When running reverse cycle, the condenser, now acting as the evaporator, is now oversized and pressures can fluctuate ( as condenser fan, now the evap. fan) cycles. In Australia, as far as i know, split a/c's are good to around -5C ambient but it's been a while since i've worked on one. I bought a Mistral about 7 years ago for the bedroom and now the condensate pipe and the cheap insulation on the refrigerant lines that was supplied with a/c, have perished, fallen off. Looks terrible but it still works:D..Mike.

Josip
28-07-2011, 08:16 PM
Hi, JoeAT50A :)


Come on. I hope you are technical person, what I am saying is condensing temperature and evaporating temp which we use to design (calculated) value. It's not pipe temperature that you measured at fan coil unit.
For example R22 :Cooling mode with ambient 35C
Your high side pressure should be arround 220 psig (equivelant temperature is 42C)
You low side pressure should be aroung 60 psig (equivelant temperature is 1C)
Hope that will help.

I do apologize if you feel hurt. It was not my intention. Just want to have a clear technical statement.

I think I'm a technical person and this is a technical forum, but here we have some people coming without technical background (willing to learn something) and for them we have to try to write down exactly what is what and not what we are thinking/meaning; if you agree?

Sometimes, meaning of the post is lost/ruin due to translation, because many of us are not speaking English as a mother tongue and for that reason it is very important to use a plain English language and full explanation.

Your design values for cooling mode are more or less OK, but explanation for heating mode is still unclear for me ....


Originally posted by JoeAT50A (http://www.refrigeration-engineer.com/forums/showthread.php?p=235106#post235106)

Re: Suction pressure
For heatpump:
Heating:
Tc- condensing temperature around 0 C and Te- evaporating temperature around 40C
Cooing:
Opposite Tc=40C and Te=0CIn your above example you reverse temperature, but within heat pump reverse is complete cycle and not temperature .... i.e. with cooling we remove heat from our room and transfer it to the mother nature through condenser, but with heating we cool down the mother nature and transfer that heat into our room again through evaporator now in reversed role as condenser, anyhow that heat must be always at higher temperature to be transferred to environment with lower temperature (either to the mother nature or to our room) ... is this OK?

For example, in my area, with outside air temperature in winter about -15*C, in summer about 35*C --- what will be your evaporating and condensing calculating temperature value for heating/cooling .... assuming to use air source heat pump ...

Thanks for answer.

Best regards, Josip :)

JoeAT50A
29-07-2011, 09:44 AM
Hi Josip,

Not at all, it's ok to debate, but we do not have much time to compose.
That's why instead of convincing you, I did confuse you. Sorry for that.

Thank you mod.
Joe

Josip
29-07-2011, 02:52 PM
Hi, JoeAT50A :),


Hi Josip,

Not at all, it's ok to debate, but we do not have much time to compose.
That's why instead of convincing you, I did confuse you. Sorry for that.

Thank you mod.
Joe

Good, even without having a time to compose, (what is really not necessary on this forum) .... but whatever we post here, we can try to not confuse just to explain and to convince ..... I was thinking that you made a small oversight what confused me .... maybe someone else too ...

Anyhow, when you find a time you can write down air source heat pump calculation values for Te/Tc ....

Thanks.

Best regards, Josip :)

JoeAT50A
01-08-2011, 03:38 AM
Hi Savoc,

Sorry for my so called a small oversight that confused you. (thanks you Mod-Josip)
Every manufacturers have different design to have better COP/EER and so on.
Theoretically or common sense or rule of thumb for R22 refrigerant heatpump should be more or less same as what I stated. We stayed in far east, my common sense slight favor to cooling te/tc (0/40).
Here, one of the Japanese brand's standard operating data.
Cooling
Discharge pressure: 250psig/47C (compressure discharged temperature 76C)
Suction pressure:62 psig/2C
Ambient temperature: 35C
Heating
Discharge pressure: 270psig/50C (compressure discharged temperature 84C)
Suction pressure:50psig/-2C
Ambient temperature: 7C
We could have judged based on manufacturer standard data or logical rule of thumb Te/Tc (-5 to 5/40 to 50).

Hope that will help to identify your issue.

Thank you.

Josip
01-08-2011, 10:47 AM
Hi, JoeAT50A :)


Hi Savoc,

Sorry for my so called a small oversight that confused you. (thanks you Mod-Josip)
Every manufacturers have different design to have better COP/EER and so on.
Theoretically or common sense or rule of thumb for R22 refrigerant heatpump should be more or less same as what I stated. We stayed in far east, my common sense slight favor to cooling te/tc (0/40).
Here, one of the Japanese brand's standard operating data.
Cooling
Discharge pressure: 250psig/47C (compressure discharged temperature 76C)
Suction pressure:62 psig/2C
Ambient temperature: 35C
Heating
Discharge pressure: 270psig/50C (compressure discharged temperature 84C)
Suction pressure:50psig/-2C
Ambient temperature: 7C
We could have judged based on manufacturer standard data or logical rule of thumb Te/Tc (-5 to 5/40 to 50).

Hope that will help to identify your issue.

Thank you.


Thanks for your time and effort. It will help to many to identify their own issues.

Sorry again for my slowness.

Best regards, Josip :)