"Active Heat recovery unit"

[samux12]

Hello colleagues,
Currently I'm designing "active heat recovery" in other words air to air reversing heat pump.
The main components the system composes are:
2 x tandem Scroll type compressors (1 variable speed, 1 fixed),
2 coils, electronic expansion valve,
reverse valve,
suction line accumulator and
liquid receiver.
The problem is that I couldn't find the proper type of liquid receiver. Furthermore, can anybody explain me how liquid receiver is working in reverse cycle, when the inlet and outlet port changed its direction. How does the liquid manage to move back to compressor?
I found one scheme according which I think I could design my system10514
but I could understand how the Tank which I circled in red, works. Is it conventional receiver with one pipe at the bottom and one at the top, or both pipes are at the same level (bottom) and it works like expansion vessel?

I forgot to mention:
Unit type - Reversing vary capacity air to air heat pump
Heating capacity - 98 kW (evap. temp. +7C; condensing temp. 40C)

Thank you in advance guys.

[Brian_UK]

You state that you are using an accumulator but have not shown one on your schematic.

You do need one fitted to the compressor suction line to prevent liquid flood back after system change over.

The receiver is not really needed in this type of set up.

[samux12]

This scheme was just an example.
The real scheme of my HP is shown below:
10540

There is a sence in your words about liquid receiver. The system piping is short, furthermore coils are the same size and working conditions are almost constant.

But if the system would be different with the long piping and very different working condition. What type of liquid receiver I should use in reversing system unit. I don't think that conventional one (one pipe inside receiver is short and other is long) would fit in this kind of system.

[The MG Pony]

you don't, you use your coils as the reciever as in essence it acts like a critical charge system, so you charge enough to ensure the bottom row of the coil is flooded.

All so will an EEV work in either direction? I know they make a thermal static valve for heat pumps with built in check valve, one for each coil.

Personaly if I where you, I'd eliminate the sight glasses, and check valves and eev, I'd put two perallel bi directional flow filter driers and a standerd heat pump txv's on either coil, I'd use a VFD on my compressors for my fine tuning of capacity control based off the temp of in going and out going air.

If you are stuck on the EEV's you can add a check to them, unless they do not care about direction of flow in which case one will work as you have placed it!

I'll scetch out a schematic by hand in a while to show what I mean, I can't find any simple computer graphic programs <_<

[samux12]

The EEV is bi-flow, and it is highly recommended to use it in this system, because one of compressor is variable speed so the system capacity will change in wide range depending from heating demand.
So TXV wouldn't be capable to control the flow between 25-100%.

MG Pony, I'll waiting you scetch to see what you recommend for this scheme.

[The MG Pony]

well I have a high tech drawing on the back of an envelope for you, lol, now I just need to find the scanner cable! but now I know it works in either way it is yet simpler!

Air Coil > Bidirectional Filter drier > EEV < Bidirectional Filter Drier < Air Coil.

no check valves or sight glasses, only 8 to 10 braze joints so way less possibilities of leaks! (Sight glasses can leak ;) )