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Desiccant Wheel with both sides in the Supply Flow

asked 2016-07-13 14:35:48 -0500

updated 2017-05-05 09:19:18 -0500

I have a system I have not modelled before and thought that the clever unmethours people might be able to help, or at least point me to some papers / forum answers that have dealt with this topic before. I have a system which has a desiccant wheel in the middle of a unit and only within the supply air flow, moisture essentially moves from one side to the other on a continuous basis. I start with my outdoor air mixing with the return air, this then passes over a heating coil, which feds the top of the desiccant wheel (the regeneration air stream), the air is then passed over a fan, to a cooling coil and then back over the bottom of the desiccant wheel (process air stream) before being reheated. See image below:

image description

I have all my coils and fans in place but not quite sure how to model this desiccant wheel. I see there is the Dehumidifier:Desiccant:NoFans object, which looks like it might let me be able to do this. I will be feel like it won't be able to have the regeneration nodes and the process nodes in the same air stream. Also it says that the minimum regeneration temperature is 40C whereas my heating coil only goes to 21.1C. So whilst i am playing with this i thought i could ask on here as well. Here are my main questions

  1. For the Dehumidifier:Desiccant:NoFans object, can this wheel reject heat and humidity into the same air stream that is the process air stream, or will it always try to reject to the outside environment?
  2. If it can reject to the same air stream where does this object sit in the branch list?
  3. if it can't does anyone have work around suggestions. I can keep the desiccant wheel in place for the process air stream and remove the energy used by the coil and fan in the regeneration air stream, but how can I account for the additional humidity and reduction in temperature between the heating coil and fan in the actual unit?

Thank you all in advance!

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answered 2016-07-13 15:14:39 -0500

Look at the CoilSystem:Cooling:DX:HeatExchangerAssisted using the HeatExchanger:Desiccant:BalancedFlow. However, the fan is not between the coil and desiccant in this model.

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Fabulous, I think moving the fan shouldn't be too much of an issue. Is there any chance I can do this with a chilled water coil? A second issue I have is to look at the load on the chiller I have two units and both have had their DX coils replaced by chilled water coils. I think I can find a work around for this later on, but it would be great to do it in one fell swoop! Thanks again!

Annie Marston's avatar Annie Marston  ( 2016-07-13 15:22:43 -0500 )edit

Unfortunately, the HX used with water coils (CoilSystem:Cooling:Water:HeatExchangerAssisted) does not include the desiccant wheel as a "Heat Exchanger Object Type". No reason why not except that the original model development was for the Cromer Cycle DEAC model. It should be easy enough to add in.

rraustad's avatar rraustad  ( 2016-07-13 16:15:21 -0500 )edit

@Annie Marston@rraustad Have any of you been able to model a desiccant heat exchanger that uses the same air stream on both the regeneration and process side in Energyplus? When I tried to do what has been suggested in this question, I have problems specifying the inlet/outlet nodes of regeneration and process air in the HeatExchanger:Desiccant:BalancedFlow object. Apparently, Energyplus does not allow to specify the same air stream for regeneration and process sides. Any help on how to solve this issue would be greatly appreciated.

andresgallardo's avatar andresgallardo  ( 2019-03-26 09:58:26 -0500 )edit

The picture above is how this model is intended to be used. The air steam into the desiccant HX then passes through a coil (not the fan, directly to the coil). The coil outlet then passes through the desiccant HX. Is this what you mean by the "same air stream"?

rraustad's avatar rraustad  ( 2019-03-26 11:10:49 -0500 )edit

@rraustad thank you for your answer. What I want to model is basically a series desiccant wheel in a dedicated outdoor-air application (a separate regeneration air stream is not necessary). I think this model will help me to model what I want but I am getting Node connection errors. Can you please explain how to properly setup the inlet/outlet nodes of regeneration and process air in the HeatExchanger:Desiccant:BalancedFlow object? Also, I cannot find the CoilSystem:Cooling:DX:HeatExchangerAssisted object type when I tried to include this component in my air loop main branch.

andresgallardo's avatar andresgallardo  ( 2019-03-26 14:50:07 -0500 )edit

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Asked: 2016-07-13 14:35:48 -0500

Seen: 539 times

Last updated: Jul 13 '16