What is the purpose of this design?

[lana]

Dear all,

I attached a picture which schematically shows a split unit which can be a heat pump. I came across this design and I can not get the reason for two cap tubes.
As you can see, in cooling mode only one cap tube is in operation but in heating mode refrigerant goes through two cap tubes!!!
Would you please have a look and give me your opinion.

Thanks
LANA

[Aik]

May be it depends on different evaporating temperatures when cooling and when heating. When cooling evaporating temperature (in inside unit) higher than heating (in outside unit).
When heating two cap tubes work in series and pressure drop would be bigger...

[NoNickName]

Exactly. The evap temp is lower therefore longer equivalent cap is necessary.

[lana]

Thanks for the reply.

I was wondering why all heat pumps are not designed like this?
Cheers

[NoNickName]

Probably because nobody uses capillaries anymore?

[lana]

Almost all split air conditioners use cap tubes.

[desA]

Probably because nobody uses capillaries anymore?

LOL... You sure about that? :D

[NoNickName]

Well, no, I'm talking about high end split systems, VRVs and euro-japanese appliances.
I'm not much into chinese parafernalias.

[lana]

Guys, I am not convinced with this reasoning.
If in the heating mode, evaporating must be lower and so two cap tubes are used; why not always?

Any ideas?

[Below 0]

differant size coils?

[mad fridgie]

The actual reason is to keep the discharge pressure elevated, so that the air off is hot, to reduce wind chill factor.
More complex systems, use EEV, indoor fan speed control, to achieve similar effects.

[NoNickName]

If in the heating mode, evaporating must be lower and so two cap tubes are used; why not always?


Because in cooling mode, evaporating must be higher and so one cap is used.

[install monkey]

all wrong-in cooling mode 1 expansion device is on use then heating mode the other expansion device is used-the tip is to recognise the check valves!!

[mad fridgie]

all wrong-in cooling mode 1 expansion device is on use then heating mode the other expansion device is used-the tip is to recognise the check valves!!
Look at drawing again, the caps are in series, it is not an "either/or/both" expansion set up which is also a common method (then parralell)

[install monkey]

good point-no reversing valve neither!

[moideen]

what wiil be the evaporating temperature in heating mode?
moideen

[lana]

Thanks everybody for the replies.

Cheers