[Bldg-sim] DOAS and chilled beam/radiator
Steven Savich
ssavich at systemswestengineers.com
Mon Aug 15 08:36:07 PDT 2011
One VAV approach that I've seen used successfully for larger chilled beam
spaces (open offices, conference rooms for instance) that have DVC is to
have VAV controls on the air handler supplying the chilled beams, and have
air valves that shut off primary air to a portion of the chilled beams in
the space when CO2, cooling, and heating needs for the space are all being
met, and throttle back the supply and return fans to match the reduction in
air volume. Modeling to account for the reduction in air volume was done
thru post-processing hourly reports.
Steven
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.
onebuilding.org] On Behalf Of Paul Erickson
Sent: Monday, August 15, 2011 6:34 AM
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
Eleanor,
I¡¯ll add to the conversation. I would agree with Vikram in that most
chilled beam projects tend to be designed with constant volume primary air.
It simplifies the design and helps to reduce first cost. If you do want to
pursue VAV primary air then you (or the project engineer) should speak with
the vendors you¡¯re considering to see how the beams perform at lower
airflows (especially if you¡¯re expecting to get capacity from the beam when
doing so).
Regarding 100% OA or RA, this decision has to consider a few things. First,
one has to acknowledge that the capacity of the beam per its given length
is, among other things, dependant on the amount of primary being supplied to
it. Often this primary air cfm is greater than the minimum ventilation air
needed, especially pronounced in perimeter spaces if loads are not minimized
well.
Second, as was discussed in this string, the primary air must be capable of
addressing the latent loads in the space. Depending on your method of
dehumidification (i.e. typical cooling coil, desiccant wheel, etc.), this
may be a challenge with minimum ventilation airflow. You¡¯ll need to
consider how much primary air is needed. If you find that more than the Min
OA is needed, then you¡¯ll need to increase accordingly.
After you consider these two aspects, the primary airflow needed for
achieving desired cooling capacity and the latent capacity of the primary
air, then you¡¯ll need to evaluate the energy implications of at 100% OA vs.
RA system. You may find that you need a volume of primary air 2-3 times the
OA needed, thus doubling or tripling the amount of OA that is being
conditioned if you choose the 100% OA approach. Depending on climate and
any airside energy recovery device, this can have a dramatic impact on
energy consumption.
You asked some good questions. I¡¯d encourage you to work closely with the
engineers doing the design so that you can talk through some of these items.
Good luck.
Paul
Paul Erickson LEED(r) AP BD+C
Sustainable
AEI | AFFILIATED ENGINEERS, INC.
5802 Research Park Boulevard | Madison, WI 53719
P: 608.236.1112 | F: 608.238.2614
<mailto:perickson at aeieng.com> perickson at aeieng.com | <http://www.aeieng.
com> www.aeieng.com
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.
onebuilding.org] On Behalf Of Sami, Vikram
Sent: Monday, August 15, 2011 7:57 AM
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
<http://www.perkinswill.com/> 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.
Sent from a mobile device
-----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
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
Fax: +8621-6469 2185
Email: eleanor.shen at erm.com <mailto:j at erm.com> <mailto:j at erm.com>
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