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Packaged VAV system with water-cooled and elec heating

asked 2016-01-04 08:37:25 -0500

updated 2016-01-04 11:15:07 -0500

Can OS1.9 simulate a packaged VAV system with water-cooled units and elec heating?

DX units in the library are air-cooled since there is no place to link them to condenser water loop. I am thinking about using AirLoopHVAC Unitary System. However, the only water-cooled and VAV options are "Unitary - CW cooling - HW heating - VAV - HW reheat". But it is HW heating not elec heating&reheat. My system is elec heating. Also, it still uses cooling water coil for cooling and there is no place to input COP for this unit, which seems not a real "packaged" VAV for me.

Is there any method to simulate a water-cooled DX unit or a packaged VAV system with elec heating?

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answered 2016-01-04 11:18:14 -0500

The easiest way to create an HVAC system in OpenStudio is to select the system that best matches your intended system, then make the appropriate changes. For your system of DX cooling with electric central heating and electric reheat terminals, the best option may be the "Packaged Rootop VAV with Reheat" that creates two-speed DX cooling, HW central heat, and HW reheat terminals. To change the heating coils, it's fine to delete the default ones and replace them with electric coils (reference images below).

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Default Packaged Rooftop VAV with Reheat

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Delete the existing HW heating coils

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Replace with central electric heating coil

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Replace with electric reheat terminal

Once you assign a thermal zone to the HVAC loop, every new thermal zone assigned to the same HVAC loop will be connected to the same electric reheat terminal object.

To assign evaporative cooling condenser to DX cooling coils is a bit trickier in OpenStudio. In EnergyPlus, there is an input field where you can choose whether the DX cooling coil's condenser is Air-cooled or Evaporatively-cooled. This input field is not exposed in OpenStudio. However, according to the Input / Output Reference for DX cooling coils, you can model an evaporatively-cooled condenser if you have performance curve data for operation as a function of WET BULB air temperature entering the condenser instead of DRY BULB air temperature entering the condenser. The link is for the single-speed DX coil object, but the same is true for the two-speed DX coil object.

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The paragraph describing use of performance curves as a function of WB temperature only intends to show what should be done when curves are a function of WB temp. This should be rare. Use of normal DX cooling coil performance curves is acceptable.

rraustad gravatar image rraustad  ( 2016-01-04 11:47:06 -0500 )edit

Thanks for the quick response! The water-cooled units I would like to simulate is connected to condenster water loop and it is just water-cooled, not evaporately cooled. Does it matter if I don't link condenser loop to the DX units?

Yan gravatar image Yan  ( 2016-01-04 12:29:26 -0500 )edit

I even think about using Refrigeration system, not sure if it works. If I put the zone in "Suction Piping Zone Name", will the refrigeration system deal with all the cooling load of the zone?

Yan gravatar image Yan  ( 2016-01-04 15:33:50 -0500 )edit

Hmm,well according to @rraustad's comment above, as long as you have proper coil performance curve info you should enter it. To take the water pumping of the condenser into account in OpenStudio, you can either add an OtherEquipment object that consumes pump power whenever the DX cooling coil is available (simpler approach) or apply EnergyPlus EMS objects to have a sensor read cooling required, calculate water condenser flow required for that cooling, and calculate pump power required for that flow.

Aaron Boranian gravatar image Aaron Boranian  ( 2016-01-04 17:15:46 -0500 )edit

Q: If I put the zone in "Suction Piping Zone Name", will the refrigeration system deal with all the cooling load of the zone?

A: No, the Suction Piping Zone name is used to calculate piping losses and will not meet the load in that zone.

rraustad gravatar image rraustad  ( 2016-01-04 18:09:05 -0500 )edit

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Asked: 2016-01-04 08:37:25 -0500

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Last updated: Jan 04 '16