[BLDG-SIM] How to stimulate displacement ventilation in eQuest?

[Renee J. Azerbegi]

Brandon,

 

Displacement ventilation. Always some what of a mystery



 

This is a checklist I used for a recent project. I’d be curious to hear
other’s opinion on this subject.


System Type

Variable Air Volume 

Underfloor Distribution

Variable Air Volume         Overhead Distribution


TEMPERATURES

 

 


Supply air temp cooling

64 F from AHU

95 F from box heating coil


Supply air temp heating

67 F from box heating coil

55 F from AHU


ECONOMIZER

 

 


Economizer high limit

62 F 

53 F 


FANS

 

 


Supply/return fan static pressure 

0.9” ESP supply

0.6” ESP return

2.2” ESP supply

1.5” ESP return


LIGHTING

 

 


Light to conditioned space ratio

0%

100%


COOLING

 

 


Increase in cooling COP with higher supply air temp

10% increase in EER

9.8 EER


Reduced outside airflow due to higher ventilation effectiveness

20% reduction in outside air

Varies per air handling unit

Notes:  

1.	I could not find a place within eQuest to change the miscellaneous
loads such that a portion of the load went to the plenum instead.
2.	I lowered the plenum height as much as possible but not to the 6
foot level as eQuest does not allow windows in the plenum zones.
3.	I used a VAV system, not a CV system as suggested below since there
would be a heating coil with a damper to reduce the air flow at the zones.

 

 

Renée Azerbegi, CEM, LEED-AP

ambient energy – solar & sustainable design solutions

t 303.278.1532 | f 303.278.8533 | c 303.885.2695

renee at ambient-e.com

ambient-e.com  

 

  _____  

From: BLDG-SIM at GARD.COM [mailto:BLDG-SIM at GARD.COM] On Behalf Of Brandon
Nichols
Sent: Tuesday, August 29, 2006 5:12 PM
To: BLDG-SIM at GARD.COM
Subject: [BLDG-SIM] How to stimulate displacement ventilation in eQuest?

 

All,

 

Thanks for the responses on yesterday's question, 'simulating a VAV without
cooling coil'.  A reasonable result was obtained by using a DX coil and
setting the capacity to 1.  Believe I tried sending it to zero prior, but
this as I now understand invoked autosizing.

 

Today I'd like to take a conventional VAV system with cooling and model its
performance in a displacement ventilation (DV) configuration.  OUr 'typical
school' DV does not require underfloor air distribution, so were not worried
about accounting for any radiant effect.  I've read (well, skimmed) the
Addison-Nall paper and they seem to explain the issues sufficiently, but
didn't see anything in there I could explicitly apply to developing a DV
model with eQuest.

 

Here is what Trane has to say about modeling displacement ventilation
systems using Trace 700 (wherever they say 'underfloor' read
'displacement'):

*	The air in a space supplied by an underfloor system is stratified
and you only need enough airflow to handle the temperature (loads) in the
lower stratified region. Trace (as well as the rest of the simulation
programs) assumes well mixed spaces with the same temperature at all
locations.
*	The way to handle this is to model the lower portion (the bottom 6
ft or so) as the height in the space. The top portion is then modeled by
calling it a plenum space (plenum of about 5 or 6 feet). Then create custom
miscellaneous loads and assign a portion of them to the plenum. The same
thing can be done with the lights. 
*	As for the system side, choose a Constant Volume Variable
Temperature system. Go to the Temp/Humidity tab and assign a Leaving Cooling
Coil Min and Max temperature of 55°F. Under the Direct/Indirect
Humidification Controls, select "CV Mixed Air Bypass with Wild Coil Leaving
Temp". 
*	This will cause the temp off the coil to be low dewpoint, then air
will be bypassed around main cooling coil and reintroduced and mixed back in
after the main CC, which will allow the air to be supplied to the space with
a reasonable %RH at a higher temperature (60-65°F).

When everything is working right, for equivalent space loads and equipment
the DV model should allow a higher supply temperature (60-65°) and thus
perform with measurably greater number hours of economizer operation than
the conventional overhead distribution system.  

 

Does anyone have a similar checklist or reference to Trane's for doing a DV
model in eQuest?  After having attended a one-day eQuest seminar, I am
familiar with parameters.  But I'm not at all clear on how to assign say two
thirds of the lighting load to a parameter, and transfer it to the exhaust
air.

 

 

 

Thanks

 

Brandon Nichols, PE
Mechanical
HARGIS ENGINEERS
600 Stewart St
Suite 1000
Seattle, WA 98101
d | 206.436.0400 c | 206.228.8707
o | 206.448.3376 f | 206.448.4450
www.hargis.biz

 

  _____  

From: Brandon Nichols 
Sent: Monday, August 28, 2006 5:15 PM
To: 'bldg-sim at gard.com'
Subject: How to simulate VAV systems without cooling coils in eQuest

All,

 

 

In the northwest USA we often use VAV systems without cooling for schools --
100% outside air economizer cooling, and 'off' for three months in the
summer.  The particular system I want to model in eQuest is the standard VAV
with heat recovery, but I can't figure how to either define it without a
cooling coil, or render the cooling coil and chiller ineffective.

 

What is the best way to do this?

 

 

Thanks

 

Brandon Nichols, PE

Mechanical

HARGIS ENGINEERS

600 Stewart Street

Suite 1000

Seattle, WA 98101

www.hargis.biz

 

d | 206.436.0400  c | 206.228.8707

o | 206.448.3376  f  | 206.448.4450

 

 

 
 
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