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

EDR has a document on their website,

http://www.energydesignresources.com/resource/200/

that discusses modeling displacement ventilation in eQuest.

Matt Dubrovich

EMC Engineers, Inc.

www.emcengineers.com

Making buildings work. Better.

Direct: (303) 974-1217

(303) 974-1200

(303) 974-1239 (fax)

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From: BLDG-SIM@xxxxxxxx [mailto:BLDG-SIM@xxxxxxxx] On Behalf Of Renee J. Azerbegi
Sent: Tuesday, August 29, 2006 7:31 PM
To: BLDG-SIM@xxxxxxxx
Subject: [BLDG-SIM] How to stimulate displacement ventilation in eQuest?

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.

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@xxxxxxxx'
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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