[Equest-users] EMS Control System Modeling
Jeremy Poling
Jeremy.Poling at transwestern.net
Fri Mar 11 12:03:34 PST 2011
Charles,
One more thought for your consideration: since the DCV is based on
occupancy, the occupancy schedule is also going to drive it in reality
and in the model (as you're aware - just stating for the record).
Because of that, the hourly people-schedule is going to drive the
results given by the model. It may make sense to go through and look at
that schedule in detail to be certain it reflects your best
understanding of how the spaces will be occupied. Following on that
thought, a very real example of where DCV can save energy is going to be
after hours or during non-peak occupancy times (for the large conference
room spaces, etc.). ASHRAE 62.1-2007 Section 6.2.6 and Section 6.2.7
both will tell you how low your minimum ventilation rate can go during
the unoccupied period.
A note for everyone who reads this: I've been told I take a very literal
read of the code so this may not agree with your understanding of it,
but in my literal view I see Section 6.2.7 allowing you to reduce the
value of Pz in your VRP calculations to 0 during unoccupied times but
since Az remains fixed you are not allowed to reduce the outdoor air
down to 0 during unoccupied times. Explanatory material behind the
development of the current procedures in the standard explains that the
VRP calculation has two components: one to deal with IAQ associated with
people-generated contaminants and one for building-generated
contaminants. Regardless of your view on that, you should be able to
arrive at a minimum OA number that is LESS than the amount specified
using peak occupancy or time-averaged occupancy (per 6.2.6).
So - in summary: I would double check your occupancy schedule to make
sure it reflects what you are expecting to see in the building and then
double check your minimum OA setting to make sure it will allow the
system to reduce OA when occupancy drops. Also, one possible
"exaggeration" may be viewing it from a system energy perspective or a
whole building perspective: if I leave one zone and go to another and
both zones have DCV, then the one I left will reduce OA and the one I
entered will increase OA but the net effect should be to balance each
other out (oversimplified, but the concept is what I was going for not
the math). So when you look at building-level energy consumption for
the ventilation system the individual unit savings will wash out. The
only savings you'll see are when people leave the building altogether.
Jeremy R. Poling, PE, LEED AP+BDC
Manager | Sustainability Services
TRANSWESTERN
234 W. Florida St.
Milwaukee, WI 53204
Phone 414.255.3322 | Fax 414.224.7780 | Mobile 414.426.7273
Jeremy.Poling at Transwestern.net
http://www.transwestern.net/Energy-Sustainability.asp
From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Charles
Welch
Sent: Friday, March 11, 2011 1:14 PM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] EMS Control System Modeling
Thank you very much to those who helped me out with this... Finally made
some good headway.
Quick question....
Modeling the DCV for my location (AZ) I shows only a very small
improvement in energy consumption for my HVAC, does this sound correct?
I have always been "led to believe" by the local control companies that
DCV is a huge improvement?
Myth, sales "exaggeration", or have some of them found a way to control
the DCV in a manner that I am not modeling correctly?
Opinions or pointers appreciated.
----- Original Message -----
From: Karen Walkerman <mailto:kwalkerman at gmail.com>
To: MatthewRLarson at eaton.com
Cc: GCollins at glumac.com ; cwelch at capitalreviewgroup.com ;
equest-users at lists.onebuilding.org
Sent: Wednesday, March 09, 2011 2:48 PM
Subject: Re: [Equest-users] EMS Control System Modeling
Regarding DCV there are a few things to know:
1. demand is based on the number of people in the space and the
outdoor air per person specified at the zone level. If your outdoor air
rate is not entered as a per person air rate, then DCV will not work
properly
2. If your fans are not constant volume, ie they can cycle or
they are variable speed, then you need to make sure that the proper
ventilation air is supplied in your base case. Usually, I set the fan
flow to 'variable'. If, in reality, the fans cycle on and off, I change
the fan curve to linear. Then, i set the minimum flow to be equal to
the outdoor air rate fraction. Otherwise, implementing DCV can actually
RAISE energy.
On Wed, Mar 9, 2011 at 10:59 AM, <MatthewRLarson at eaton.com>
wrote:
Charles,
Regarding the DCV, you need to specify the "Minimum OA Control
Method" under the Outdoor Air tab for the system to state whether the
CO2 sensor is in the return or in the space. Then at the zone level,
specify the "Minimum Flow Control" under the Air Flow tab to state if
the minimum OA resets up or down depending on occupancy level. To
ensure the amount of OA going into a space doesn't go below the ASHRAE
62.1 minimum, I always input the OA Flow per Person and/or Flow per Area
at the zone level as well. DCV has always been something I've been a
little dicey about so any additional suggestions/comments would be
great.
Thanks,
Matthew Larson, LEED AP BD+C
Project Engineer
Energy Solutions Group
E M C Engineers, Inc.
Eaton's Electrical Services & Systems
143 Union Blvd, Suite 350
Lakewood, CO 80228
tel: +1 303 328-3419
mobile: +1 303 668-2511
fax: +1 303 974-1239
MatthewRLarson at Eaton.com
www.eaton.com/energysolutions
Error! Filename not specified.
From: equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] On Behalf Of Greg Collins
Sent: Tuesday, March 08, 2011 5:53 PM
To: Charles Welch; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] EMS Control System Modeling
Charles - A quick suggestion for the setback is to try setting
your system fans to "cycle on any." Otherwise, your system might not
kick on to maintain setback temperatures.
Greg Collins
GLUMAC | (949) 833-8190
From: Charles Welch [mailto:cwelch at capitalreviewgroup.com]
Sent: Tuesday, March 08, 2011 4:24 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] EMS Control System Modeling
I am doing an quick estimate for adding EMS control to an
existing HVAC system (schools) which incorporate the following measures
1) Automatic thermostat setbacks for building occupation
2) Demand controlled ventilation
3) Economizers
Here are my "challenges"
1) Simulation with setback temperatures shows no reduction in
energy
2) I am unsure how to handle DCV
3) Simulation with economizers show very little reduction
I would appreciate any pointers, suggestions, etc. on what to do
here.
I would especially appreciate any example files to see how you
input the data to get proper results.
Thanks in advance for any help.
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