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  1. #1
    Join Date
    Nov 2015
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    7
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    Refrigeration system in AHU's

    Hello everybody!

    From the start I want to apologise for my bad english skills. I'm new one here. I'm from Lithuania and I'm working in AHU's manufacturer company. My colleagues nominated me for this project. However, there are some points that I need to clear (I need your help, maybe you could provide me answers)!
    On the next year, we plan to present AHU's with refrigeration system block. Our refrigeration block will be able to cool in summer and heat in winter season. Refrigeration block will be combined with rotary heat exchanger. For example, on the first floor (supply air) after rotary heat exchanger will be evaporator coil. On the second floor (exhaust air) there will be compressor with additional equipment (like tubes, sight glass, filter drier and so on) and after rotary heat exchanger condenser coil. The whole block will look similar like SystemAir comapny DVU-HP unit (sorry I don't have enough posts to post a link here).

    Our planning refrigeration system will consist of evaporator, compressor, condenser, electronic expansion valve, filter drier, sight glass, liquid receiver, suction receiver, non-return valves, 4way valve, mechanical high-low pressure protection, temperature & pressure sensors, service valves. In attached files there is scheme ("cooling scheme.jpg" and same scheme for heating "heating scheme.jpg"), that we're thinking to use. As evaporator, condenser we will use evaporating/condensation coils. I have mentioned that our block will be able of cooling and heating. By that reason, both coils have 3 pipes connection (I have added picture "evaporating&condensation coil.jpg").

    My questions:
    what do you guys think of using such scheme? Is it ok, or is it bad? Looking forward for any coments.

    I'm actually confused of coils connection. On cooling mode, refrigerant enters top inlet and passes bottom outlet. When the heating mode is on (4way valve reverses), refrigerant should move from bottom outlet, to middle inlet. Is this correct? Why I'm asking this is that, that picture provided our coil supplier, and they said, that for both modes (cooling&heating) refrigerant should enter both inlets (for example on cooling top inlet and bottom outlet & for heating middle inlet and bottom outlet) and pass same outlet.

    I've been doing some calculations with Solkane of sizing pipes. Solkane software provides these lines diameters: suction line, discharge line, liquid line, suction riser, hot gas riser.
    In attached files there is construction of my block "piping.jpg". I understand that suction riser is the line from first floor to second floor, but I'm confused of till where that line continues and where I should use suction line? The same with hot gas riser/discharge line.

    Looking forward for any comments. If something is unclearly please write and I will try to explain it more detaily. Thanks guys!
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  2. #2
    Join Date
    Sep 2015
    Location
    Southern California
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    513
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    What is it your trying to accomplish? It's a heat pump I get it but what are you planning to do?
    Heat and cool at the same time?

  3. #3
    Join Date
    Nov 2015
    Posts
    7
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    Quote Originally Posted by Fan Curve View Post
    What is it your trying to accomplish? It's a heat pump I get it but what are you planning to do?
    Heat and cool at the same time?
    The main purpose is to satisfy client demand. For example client provides us his request with airflow, temperatures, humidities and so on. Such block main functions is cool/heat outdoor air according client demand. Sorry that I didn't presented other equipment. On both area I mean supply/exhaust air zones, there will be fans and filters.

    The block + other equipment (fans, filters) gonna cool summer outdoor air till client desired temperature and on winter mode, I mean when 4way valve reverses system, gonna heat winter outdoor air till desired temperature.

  4. #4
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    11,851
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    Quote Originally Posted by Ascorone View Post
    ...I'm actually confused of coils connection. On cooling mode, refrigerant enters top inlet and passes bottom outlet. When the heating mode is on (4way valve reverses), refrigerant should move from bottom outlet, to middle inlet. Is this correct? Why I'm asking this is that, that picture provided our coil supplier, and they said, that for both modes (cooling&heating) refrigerant should enter both inlets (for example on cooling top inlet and bottom outlet & for heating middle inlet and bottom outlet) and pass same outlet.
    I think I see where you may be confused about the coil connections, but then I also may be confused.

    The diagram indicates two separate inlets and one common outlet to each coil. One of the inlets is the distributor for the refrigerant from the expansion valve and is used when the coil is operating as an evaporator. The other inlet would be a manifold or header assembly for the discharge gas from the compressor when the coil is operating as a condenser. The outlet is used as either a suction or liquid outlet depending on which mode you are in.

    The problem exists with the two inlets. You cannot expect to have a set of distributor tubes to evenly feed each coil circuit and have a common inlet header feeding all of these same circuits as well...particularly if the coil is oriented vertically. If it's mounted vertically, during the cooling mode, gravity will come into play and cause some of the liquid feed from the expansion valve to drop to over-feed the bottom tubes. A better approach might be to use a side inlet distributor, such as those used with hot gas bypass systems. You introduce the hot gas through the side inlet of the distributor and through the distributor tubes. This may be similar to what you coil supplier is suggesting.

    I think the best way to do this is to reverse the coil flow in heating so the hot gas enters the suction header and the condensed liquid exits through the distributor tubes and distributor. Then it would bypass the expansion valve using a check valve loop. By reversing the flow you now have condensed liquid flow in the distributor tubes instead of hot gas, so the pressure drop is reduced...ie, smaller tubes and lower condensing pressure/temperature. Again you would use a side inlet distributor.

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