[Equest-users] Active Chilled Beam/Fan Coil System

[Bruce Easterbrook]

My main comment, indirectly, was that in my opinion chilled beams are a 
dry climate device as I noticed James was from Arlington VA.  You will 
be dealing with incoming air with a 57F dew point and James will have a 
66F DP.  You will have a latent load from the people in the room and 
their outside air requirement.  Phoenix for example would have a 49F 
DP.  Part of this will also depend on your chilled water temperature, 
that will set the dewpoint you have to control to in the room.  
Typically once you have to do any major dehumidification all the 
capacity you require is already in the DOAS.  You won't need a chilled 
beam.  You let the humidity float in a wider band to avoid having to 
reheat your air stream.  I would do it initially as a single zone air 
handler with an economizer for the economics, capacities and a check on 
air temperatures.  You could then manually split off the capacity of the 
chilled beam adding more fan energy and maybe pumping energy to run the 
beam.  The item to resolve is the tipping point for your area and system 
adding the increased cost, energy and complexity of the chilled beam 
system compared to its advantages. The main one being reducing the size 
of the DOAS.  One other item to consider is using your chilled water 
return flow for the beam, with it being a higher temperature it might be 
a more suitable flow for the chilled beam and allow an increase of the 
humidity in the room.
Bruce

On 09/04/2010 01:59 PM, Greg Collins wrote:
>
> Bruce,
>
> I agree with your theory and the justification, but the question is 
> ultimately "how to model it?"  I don't think you can put in negative 
> heat for a baseboard system, hook it up to a chilled water loop and 
> get results you can count on.
>
> Greg
>
> *From:* Bruce Easterbrook [mailto:bruce5 at bellnet.ca]
> *Sent:* Friday, April 09, 2010 8:59 AM
> *Cc:* equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] Active Chilled Beam/Fan Coil System
>
>     I'm not totally up on using DOAS with eQuest or with chilled beams 
> being in Canada but it would seem to me the OA will have to be used to 
> control humidity in the space.  The chilled beam should not be used 
> for latent cooling, sensible only, to prevent condensation issues.  
> The DOAS will need to control the dewpoint of the room air and 
> maintain it below the operating temperature of the coil in the chilled 
> beam.  The chilled beam would only be dealing with the sensible load 
> from the space.  The DOAS would do everything else.  The question 
> would be will eQuest allow a single zone AHU c/w economizer and a 
> baseboard system with negative heat?  I have never tried that with eQuest.
> Bruce Easterbrook
> Abode Engineering
>
> On 08/04/2010 04:46 PM, James Hansen wrote:
>
> I'm interested in this as well -- I know that in DOAS systems like 
> active chilled beams, the primary air often takes on a fairly large 
> chunk of space latent cooling, and if this can't be passed on from the 
> DOAS system to the space, then I don't see how we can believe the results.
>
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> *From:* equest-users-bounces at lists.onebuilding.org 
> <mailto:equest-users-bounces at lists.onebuilding.org> 
> [mailto:equest-users-bounces at lists.onebuilding.org] *On Behalf Of 
> *Greg Collins
> *Sent:* Thursday, April 08, 2010 4:39 PM
> *To:* equest-users at lists.onebuilding.org 
> <mailto:equest-users at lists.onebuilding.org>
> *Subject:* [Equest-users] Active Chilled Beam/Fan Coil System
>
> Hi all,
>
> I'm working on modeling an active chilled beam system.  It consists of 
> the chilled beams and a dedicated unit to provide primary air (mainly 
> ventilation air) to the beams at 55 degrees.  I've modeled the chilled 
> beam system as a fan coil system, but am wondering about my options 
> for modeling the primary air.
>
> My question is this:  If I attach the primary/ventilation air unit to 
> the fan coil system in the FC's Outdoor Air tab under "Outside Air 
> from System" will the temperature of the air coming from that unit 
> have an impact on the load in the space?  I have a ton of hours at 
> very low load during the winter months, and I want eQuest to use the 
> 55 degree primary air as the first stage of cooling for the space and 
> not "double up" the cooling energy by cooling the 55 degree air and 
> then not use that for cooling in the zones.
>
> If anybody has some input, it would be appreciated.
>
> *Greg Collins*
> Design Engineer / Energy Analyst
>
> Mechanical Department
> LEED® Accredited Professional
>
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