Demand Controlled Ventilation

5 posts / 0 new
Last post

I have created a model with DCV as a parametric run and the results are
suspect. Comparing results for baseline and parametric run, there is
increased space cooling in the DCV model between November-March. Also,
ventilation fans are running much more during these same months than in the
summer. And, there are many hours where heating load is not being met.
Both models include economizer control limited by drybulb at 65 F.

I've attached .pd2 and .inp files.

I appreciate any help on this.

Thanks,

Colleen Nelson, LEED-AP

Colleen Nelson's picture
Offline
Joined: 2011-09-30
Reputation: 0

I would appreciate anyone's input on this as well. I have run 4 or 5
models recently with DCV, and the results have almost always been either
a wash, or INCREASED energy for DCV. Most of them are PIU systems with
either parallel or series VAV boxes. Have used both return air sensors,
zone sensors, as well as both options for calculating the OA quantities.
I think I'm missing something as well...and I get the same results with
increased space cooling in the winter, as well as increased heating
costs. I think it must be how I'm defining the zone / system outside
airflow rates, but I can't figure it out.

James Hansen, PE, LEED AP

James Hansen's picture
Offline
Joined: 2011-09-30
Reputation: 200

James,

In the past I've revised the minimum flow schedule within the thermal zones
and used a ratio of 0 during unoccupied hours to make sure no OSA is being
introduced and -999 ratio for hours of occupancy. I also do the same for
HVAC system. Then within the HVAC system I change the minimum OA Method to
DCV return or zonal sensors. I think the trick is making sure the thermal
zones and HVAC systems operate on the same minimum air schedule that you
specify. Hope this helps.

David Frank

David Frank's picture
Offline
Joined: 2011-09-30
Reputation: 0

Folks:

The question was put to me regarding campus chilled or hot water circulation loop looses or gains. The person contended that he always seemed to find campus central plants oversized because the designers were always sizing CHW piping for losses. He contends that, in reality, the ground is actually being cooled from the continuous flow and the normal 55?F ground temperature that exists 8 - 15 feet below the surface is actually helping maintain the CHW temperature.

Where in eQuest are we inputting the length of pipe run for such a system?

John R. Aulbach, PE, CEM

Aulbach, John's picture
Offline
Joined: 2011-09-30
Reputation: 0

John,

You can input the UA into the losses tab of a circulation loop ? a supply UA
and/or a return UA. You will, of course, need to do an outside calc of your
piping UA. You can then select where the circ loop is located (zone,
outdoor, tunnel, or underground). Losses are calculated based on UA and DT
between the delivery temperature and environment temperature. You can
specify a temperature or temperature schedule for tunnel. Underground just
uses the weather file ground temp, I believe.

Haven?t had time to try it out, but it would be interesting to see if
chilled water consumption is decreased in an eQuest model by locating it
underground with a favorable ground temperature difference.

Steven Savich

Steven Savich's picture
Offline
Joined: 2011-09-30
Reputation: 0