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:
- 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.
- 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.
- 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@xxxxxxxxxxxxx
ambient-e.com
From:
BLDG-SIM@xxxxxxxx [mailto:BLDG-SIM@xxxxxxxx] On
Behalf Of Brandon Nichols
Sent: Tuesday, August 29, 2006
5:12 PM
To: BLDG-SIM@xxxxxxxx
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.
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@xxxxxxxx'
Subject: How to simulate VAV
systems without cooling coils in eQuest
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?
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
==================
You received this e-mail because you are subscribed
to the BLDG-SIM@xxxxxxxx mailing list. To unsubscribe
from this mailing list send a blank message to
BLDG-SIM-UNSUBSCRIBE@xxxxxxxx