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How to model Zone DX Equipment

asked 2016-06-20 04:34:17 -0600

João Rodrigues's avatar

updated 2016-10-18 14:33:42 -0600

I have an air conditioning system using direct expansion of the type Wall Mounted (Daikin) that I would like to simulate in OpenStudio.

However, after exploring the existing area systems on OpenStudio as PTAC and PTHP I found that there aren’t devices which operation, for heating and cooling, is by direct expansion.

Is there any component that allows me to meet these requirements? (Basically acting as a reversible heat pump)

Or I have to make an assembly that resembles to my equipment? Thank you,

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answered 2016-06-20 04:53:47 -0600

updated 2016-06-20 04:56:20 -0600

Let's get back to the (real-world) basics:

  • A PTAC, or Packged Terminal Airconditioner, is a through-wall device where you have DX cooling and non-DX heating, typically via electric resistance (electric PTAC) or a hot-water coil[1] (hot water PTAC). There is a blower fan to blow air across the coils. The unit is inserted in a wall sleeve, on the inside you have the evaporator coil, the heating coil, and the fan. On the outside you have the condenser coil, a fan and the compressor. There's usually an outside air damper included in the unit too (which may or may not actually open)
  • A PTHP, or Packaged Terminal Heat Pump, is exactly like a PTAC except that it has DX heating too: it is a reversible system, the same coil is providing heating in winter and cooling in the summer. There is often backup electric resistance heating for cold climate operation (typically under 35°F/ 1°C, electric resistance is used either alone or in conjuction with the DX heating (mixed-mode))
  • Split system: I've covered that in How can I model a ductless split HVAC system? already.

As far as how to model this type of systems in openstudio (or energyplus in general for that matter), it's been covered before on the same question I just linked: you can either use a ZoneHVAC:PackagedTerminalHeatPump (or PTHP) or a VRF system: if your refrigerant flow is actually varying, it'll better capture the performance of your unit.

[1] There are also some PTAC units with steam coils, such as in the formerly Remington and now McQuay Type J and Type K, but I'm not sure you really encounter them much outside of NYC and maybe another couple of US cities in the North East that have a history of steam heating.

You also can encounter some PTAC with gas heating coils, but since that requires piping a gas line to each unit, I personally haven't seen them much.

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Thank you Julien by your answer, it sure helped me. HVAC is not my area of work or expertise, so your basics introduction were very helpful. Once again thank you.

João Rodrigues's avatar João Rodrigues  ( 2016-06-20 05:40:22 -0600 )edit

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Asked: 2016-06-20 04:34:17 -0600

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Last updated: Jun 20 '16