Multiple components for Air Distribution Unit

asked 2015-09-29 13:26:13 -0500

nfonner
616 ●2 ●8

updated 2017-05-08 15:53:26 -0500

I am nearly convinced that simply modeling the system (diagram below) with in-zone equipment for reheat will be easiest, but I would like to see if anyone has feedback on alternative methods for modeling branch in-duct HW heating coils upstream of chilled-beams. Some zones also have perimeter HW radiant heating.

There is no simultaneous heating and cooling amongst the various downstream heating equipment and the chilled-beams.

Original Diagram (there is an inconsistency with the upstream supply fan location, but that is not at question.) C:\fakepath\AHU-1 Diagram.jpg

Alternative (Simple) method - radiant in-zone reheating equipment. C:\fakepath\AHU-1 Diagram - Simple.jpg

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answered 2015-10-01 12:10:03 -0500

Archmage

7185 ●3 ●11

Version 8.4 added AirTerminal:SingleDuct:ConstantVolume:FourPipeBeam which should be thermodynamically equivalent. The hot water heating is by the beam rather than in the duct, but it will mix in the zone.

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Appreciate the suggestion. I am interested in 8.4 for other reasons. I was using DesignBuilder, but will have to head into EPlus anyway to model desiccant dehumidification.

Only concern (as commented below) is the difficulty in reverse engineering the heat beam to act as a generic HW coil in the air stream. That is why I like the concept of the FCU with fan energy zeroed out. I'll try both to see which is the best fit. Right now the FCU has massive unmet hours.

nfonner ( 2015-10-02 10:39:51 -0500 )edit

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answered 2015-10-01 07:22:26 -0500

Aaron Boranian

13830 ●76 ●24 http://bigladdersoftware.com/

In general, E+ doesn't allow placement of individual components (cooling coils, heating coils, fans, etc.) directly upstream from air terminal units. If you really wanted to have reheat of supply air from the air handler, you should place a central reheat coil as the final component of the air handling unit. As a result, if you use the AirTerminal:SingleDuct:ConstantVolume:CooledBeam object to model the chilled beam you should use your simple method.

If you wanted to model a terminal unit that can provide both heating and cooling, you can use the AirTerminal:SingleDuct:ConstantVolume:FourPipeInduction object. The Cooled Beam object only allows a chilled water connection, while the Four Pipe Induction object allows for a chilled water connection AND hot water connection.

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Thanks Aaron. I did look at the 4PipeInduction as an alternative since it is more fitting (over the central AHU reheat coil) with the zoning aspect of the branch reheat coil. My only concern there was whether or not it was a significant departure given the induction for both cooling and heating. Another solution was to zero out fan energy in a heating only FCU. I think I will try both and see what the outcome is. Thanks again.

nfonner ( 2015-10-01 09:19:55 -0500 )edit

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