[Bldg-sim] DOAS and chilled beam/radiator

Zhukovskiy, Sergey s.zhukovskiy at cundall.com.au
Mon Aug 15 20:06:55 PDT 2011


Dear Sami

Absolutely agree with you regarding some apparent advantages of the ACB technology. Just wanted to mention several issues that are extremely important.

Data regarding ACBs static pressure that is usually provided by the manufacturers and fan capacity needed are absolutely different things. 

Main difference between the full-air and ACB systems is that in the full-air system the dynamic pressure is mainly not converted (partially) to static pressure on the whole path up to the discharge grille (diffuser). This process is well understood by the designers and pressure drop in the ducts or on filters (index run), etc is accounted for to match capacity of the fan. 
ACB's technology needs the air being capable of doing ¡®entrainment¡¯ job. This requires application of some extra energy to this air (pressurising this air). 

Manufacturers of the ACB do not bother to consider how the whole system including ducts and plenums behave, assuming that the duct is ¡®working¡¯ as a regular duct and that the dynamic pressure is converted to static pressure in the plenum (and nowhere else). Usually ACB¡¯s ¡®plenums¡¯ are not working properly as plenums and the conversion of the static pressure does not happen in the ¡®plenums¡¯ (this is a desirable, but not achievable process). Being blocked by the ACB units the whole duct system starts working as a plenum (pressure vessel) itself. 

Probably customers who have installed the ACBs experienced increased static pressure in their duct system and some issues to achieve the required by pressure specified by the ACB's manufacture. 
This pressure increase results in the increased leaks through the tiny wholes and cracks in the ducts, ACB units, etc ¨C and this is extra noise, lost capacity and a number of other issues. The customers are trying to achieve the static pressure in the plenums and jump on the AHU¡¯s fan that is working on the full capacity and can not achieve the desired flow....

Just to summarise the provided information I would say that the ACB¡¯s technology is living technology, nothing here is with ¡®magic¡¯ as some of the manufacturers wish to present. It has a number of advantages, though many disadvantages must be also recognised when designing the ACB system. The main attention should be paid to the fan and the duct system and reasonable questions addressed to the manufacturers of the ACBs.

Cheers

Sergey
-----Original Message-----
From: Sami, Vikram [mailto:Vikram.Sami at perkinswill.com] 
Sent: Tuesday, 16 August 2011 11:06 AM
To: Zhukovskiy, Sergey; Éò½à; near_ej at yahoo.com
Cc: bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] DOAS and chilled beam/radiator

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

However


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; Éò½à; near_ej at yahoo.com
Cc: bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] DOAS and chilled beam/radiator

Colleagues

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.

Cheers

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: Éò½à; near_ej at yahoo.com
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] DOAS and chilled beam/radiator

Eleanor,


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 ¨C I would look up the manufacturers data. The typical range is around 3-6.

3.       Yes ¨C you can simulate a WSE now ¨C you need to add a chiller and select waterside economizer as chiller type. Not sure why your example is not working ¨C 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: Éò½à [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 . . . .
Thanks,
Neeraj

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:   Éò½à [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 (Éò½à£©

Consultant

Environmental Resources Management



Tel: +8621-5385 3050, ext:158

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