[Bldg-sim] DOAS and chilled beam/radiator

Sami, Vikram Vikram.Sami at perkinswill.com
Sun Aug 14 19:25:11 PDT 2011

All chilled beam systems that I have worked on have 100% OA so there is no recirculation. Not sure I understand the point about needing to recirculate air back to balance the system and control RH. With the DOAS - you control dew point so there shouldn't be a problem. As far as I know the only condensation issues occur with passive beams (as opposed to the active beams that are really induction units).

Since the chilled water coils don't really see the supply air, but see room air (its only the induced air that flows over the coils) I would recommend checking the room functions before going to chilled beams. If there is a high latent load in the space, it might not be the best option.

From: Nearedge [near_ej at yahoo.com]
Sent: Saturday, August 13, 2011 5:11 AM
To: shenjie820730 at hotmail.com
Cc: Sami, Vikram; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] DOAS and chilled beam/radiator

Hello Eleanor,
Adding to Vikram's advice -- You may then also apply the heat recovery to the individual IU units instead of the DOAS.

But, an important question for experts who may be experienced with working real-life Chilled Beam systems is --

Whether or not the OA moved through the active chilled beams is completely (100%) Outside Air only OR Whether some of the supply air is still recirculated?
I presume it'll depend on latent loads but I understand that for most occupied zones some air is actually recirculated back to the AHU's to control the RH and balance the system!?
Please correct me if that is any different from anyone's real-life experience and what Vikram is referring to is the experience you all share? Vikram, your veiws?
We are modeling a couple of chilled beam and slab systems but with little live examples and experiences to corroborate on this aspect.

Your inputs would be valuable . . . .

Neeraj Kapoor
t: +91.99581.70018
Kalpakrit Sustainable Environments Pvt. Ltd.
New Delhi, India

On 12-08-2011 17:13, Sami, Vikram wrote:

If you are using an active chilled beam, then you don't need to model the doas - just use 100% OA for your ahu.

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 -----Original Message-----
From:   沈洁 [mailto:shenjie820730 at hotmail.com]
Sent:   Friday, August 12, 2011 04:25 AM Central Standard Time
To:     bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject:        [Bldg-sim] DOAS and chilled beam/radiator

Hi, all;

I’m simulating a project with chilled beam/radiator plus dedicated fresh air system, I search from archive, it seems most of you using DOAS (a dummy zone) and IU/FCU to simulate, DOAS provide the fresh air and IU/FCU use the “Outdoor air from” DOAS, the radiator use baseboard instead with zero fan energy power.

But the DOAS in my project is 1) variable speed to reduce the fresh air energy base on occupancy schedule; 2) wheel heat recovery with exhaust air; 3) during the transition period, the DOAS will bypass the wheel to provide maximum fresh air to offset all the heating and cooling demand and chilled beam and radiator will shut off.

Now, my method is :

1)  using VAV system to represent DOAS , enter the “ Design supply/return “ flow to show the DOAS fresh air and exhaust air volume;

2) Define the wheel heat recovery with fresh air and exhaust air, and operation control is “OA exhaust DT”

3) Define the dummy with the same maximum fresh air volume, and also control the cool and heat temperature (otherwise the heat recovery will not work at all).

It seems works very well. But when I reading hourly report, I found the fresh air volume keeps the maximum all the time, so the fan running at the rated power the whole year, which results in the large fan energy consumpation.

How can I make the DOAS’s fresh air volume variable and fan variable according to the acutal IU/FC’s fresh air volume ??

Any comments and suggestions will be appreciated.

Eleanor Shen (沈洁)
Environmental Resources Management

Tel: +8621-5385 3050, ext:158
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