[Equest-users] Desiccant Wheel with Gas-fired Regeneration

[Eric Studer]

Hello Vikram,

 

This is how we modeled gas-fired desiccant units serving multiple AHUs in a
storage building with very tight conditioning tolerances.

 

1.	If you have a fresh air (FA) section to pre-cool the air, make a
single-zone AHU that is controlled to maintain the discharge temperatures
you want.  Note that the DAT has a lower limit of around 40°F or so.  Set
the design airflow rate to be whatever you need for ventilation air, force
the unit to be 100% OA.
2.	Create a “FA ghost zone”, and make the space temperature setpoints
be the desired FA discharge setpoints.  Don’t put any lights, people, etc in
the space. 
3.	Make a second single zone AHU that will be your desiccant section,
for now let’s call it DD system.  You need to set up the ‘outside air from
system’ as the FA system, set the ventilation airflow rate as what you need
to pass through the DD.
4.	Create a “DD ghost zone” that has temperature setpoints typical of
the discharge temperature from your desiccant section. 
5.	Create the AHUs that are actually in the design, include their
heating and cooling coils and any humidification equipment – this is
straightforward.  Outside air needs to come from the DD system.

 

This approach can accurately predict gas use for regeneration, cooling for
the FA and AHU units, and heating in the FA and AHU units when the DD
section is turned off.  The tricky thing about this approach is that you
need to select the DD discharge temperature to be representative of the
typical operating point during the dehumidification season since DD
discharge temp varies with the degree of dehumidification.  An alternate
approach (which we have not tried) would be to make 365 day schedules based
upon your weather file and use a user-defined function to calculate the DD
ghost zone space temp setpoints based on the humidity entering the DD unit.
This function would need to be based on detailed information from Munters.
Wouldn’t it be great if you could make user defined functions that directly
relate to hourly information in the weather file?  

 

Eric

 

Ph:   (781) 431-1100 ext 12
Fax:  (781) 431-1109

 

  _____  

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Vikram Sami
Sent: Monday, February 01, 2010 4:58 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Desiccant Wheel

 



 

I’m trying to model a Munters packaged  desiccant unit (diagram above) that
uses a heat pump to operate both sides of the wheel (heating side for the
desiccant recharge and cooling side for pre-cool). Is it possible to model
this in eQUEST? If so – how? 

 

Vikram Sami, LEED AP 
Direct Phone 404-253-1466 | Direct Fax 404-253-1366 

LORD, AECK & SARGENT ARCHITECTURE
1201 Peachtree Street NE, Suite 300, Atlanta, GA 30361 
Responsive Design * Technological Expertise * Exceptional Service 
Please visit our new website |  <file:///\\www.lordaecksargent.com\>
www.lordaecksargent.com

P Think GREEN before you print.

 

 

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