[Bldg-sim] DOAS and chilled beam/radiator

Sami, Vikram Vikram.Sami at perkinswill.com
Mon Aug 15 18:35:48 PDT 2011

This is true - there is often an increase in static pressure with a chilled beam system.


in some cases - you more than make up for that by the reduced quantities of supply air. If you can drop your air change rate from 10-15 ACH down to 6ACH you come out ahead.

Like everything else - you have to do the analysis to make sure it makes sense. It often does.

From: Zhukovskiy, Sergey [s.zhukovskiy at cundall.com.au]
Sent: Monday, August 15, 2011 7:44 PM
To: Sami, Vikram; 沈洁; near_ej at yahoo.com
Cc: bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] DOAS and chilled beam/radiator


I wanted to mention another difference between ACBs and any other ‘conventional’ system.
Specific fan power (W/L/s) can be significantly higher that that for traditional systems as the process to create induction ratios depends on static pressure in the beam’s chamber.
This requires extra energy as the ACB does not just deliver OA to the room; it is supposed to entrain another 3-5 air volumes through heat exchanger....
Unfortunately, manufacturers of the ACBs do no like to mention this fact when list ACB’s advantages.


Sergey Zhukovskiy
ESD Consultant

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From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Sami, Vikram
Sent: Monday, 15 August 2011 10:27 PM
To: 沈洁; near_ej at yahoo.com
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] DOAS and chilled beam/radiator


1.       In my experience - active chilled beams typically operate at constant volume (set to the ventilation rate in the room) and you vary the cooling rate with a 3-way valve on the cooling coil to vary the cooling capacity of the beam.

2.       Different beam designs have different induction ratios – I would look up the manufacturers data. The typical range is around 3-6.

3.       Yes – you can simulate a WSE now – you need to add a chiller and select waterside economizer as chiller type. Not sure why your example is not working – if you attach an inp file I’m sure someone can shed some light no that.

Vikram Sami, LEED AP BD+C
Sustainable Design Analyst
1315 Peachtree St. NE, Atlanta, GA 30309
t: 404-443-7462    f: 404.892.5823       e: vikram.sami at perkinswill.com   www.perkinswill.com<http://www.perkinswill.com/>
Perkins+Will.  Ideas + buildings that honor the broader goals of society

From: 沈洁 [mailto:shenjie820730 at hotmail.com]
Sent: Sunday, August 14, 2011 10:36 PM
To: near_ej at yahoo.com; Sami, Vikram
Cc: bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] DOAS and chilled beam/radiator

Hi, Neeraj and Vikram:

Thanks for your promote advice. I'm reading DOE22Vol3-Topics.these days and found that IU's one application is just ceiling radiator .

Now, I have changed my system type to IU system with no separate MAU systems, but I still have two puzzles :
1) The fan control is gray which means you can't choose variable, so is it says that the fan is running the full power all the time?
2) How to define the induction ratio and make it reasonable? I'm not sure whether the recirculating air volume will affect the fan power. it seems not.

And another question is about water economizer? Can we simulate water economizer now?
For eQUEST 3.64, there are two methods, one is the water economizer in airside system, but the weakness of this water economizer is it will add the AHU fan power.
The other one is the water economizer chiller in waterside system, but it seems the function is not matural, I tried , but the hourly report shows the chillers still running in the winter for very low cooling load.

Thanks in advance.
Eleanor Shen

Date: Sat, 13 Aug 2011 02:11:07 -0700
From: near_ej at yahoo.com
Subject: Re: [Bldg-sim] DOAS and chilled beam/radiator
To: shenjie820730 at hotmail.com
CC: Vikram.Sami at perkinswill.com; bldg-sim at lists.onebuilding.org

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

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