EMS Control System Modeling

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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.

Charles Welch2's picture
Joined: 2011-09-30
Reputation: 0

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

Greg Collins's picture
Joined: 2011-09-30
Reputation: 0


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.


Matthew Larson, LEED AP BD+C

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Joined: 2011-09-30
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Does anyone have a turbocor simulation (preferably the .INP file) that would
willing to share? I feel the explanation of the Keywords is not adequate.

Thanks in advance.

John R. Aulbach, PE, CEM

John Aulbach's picture
Joined: 2011-09-30
Reputation: 1

* Are your loads being met?

* You can model DCV sensors in your OA control tab

* Economizers aren't huge savers in all climates. How are you specifying them? Do you have a low limit?

Vikram Sami, LEED AP BD+C

Sami, Vikram's picture
Joined: 2011-09-30
Reputation: -1

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.

No Username provide's picture
Joined: 2011-09-30
Reputation: 200

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.

Charles Welch2's picture
Joined: 2011-09-30
Reputation: 0

I never heard of DCV implemented with cycling fans. Per 90.1 and our CT State
Code the fan needs to run continuously when the space is occupied. Most codes
require compliance with 90.1 whether we are modeling to that standard or not.

How can you provide the necessary ventilation air if you do not know how long
the fan will run each hour? Do you model the fan to run 3 times per hour and
bring in additional ventilation air so that the hourly average meets 62.1

My experience is with modeling DCV in both eQuest and using exceptional
calculations via Excel. I have verified the energy savings after the DCV
measure has been installed. You might expect a 6-8% savings in cooling and
heating energy attributed to the air handling units that have implemented this
measure. Often the simple payback is over 5 years because DDC CO2 sensors are
expensive. Of course, it depends on the unit size and the occupancy load.

Paul Diglio

Paul Diglio's picture
Joined: 2011-09-30
Reputation: 400


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

Jeremy Poling2's picture
Joined: 2011-09-30
Reputation: 0


Are you saying that one needs to provide the Az amount of ventilation air during
unoccupied hours? So you model the fans to run 24 X 7 to provide ventilation?

Paul Diglio

Paul Diglio's picture
Joined: 2011-09-30
Reputation: 400


I just have a literal viewpoint ? I think it is more me identifying a problem with equivalence in the codes: 90.1 allows cycling of fans during unoccupied hours but I haven?t seen anything in 62.1 that says you can turn off the area-based component of the ventilation calculation. I?m in the position most of the time of either modeling someone else?s design or reviewing a model built by someone else so this usually becomes a discussion I have if the model is attempting to take credit for DCV strategies. I mean, it is very literal, but the basic VRP equation is Ra*Az + Rp*Pz=Vbz and the only thing that changes over the short-term is Pz, right? The 62.1-2007 User?s Manual on page A-6 points to Section 5.4 and Section that state that ventilation is required whenever zones are occupied. That said, on page 6-2 the User?s Manual describes the two components of the VRP the way I mentioned earlier: one for the ?occupant-related component? and the other for the ?building area-based component? that is described as ?The building area-based component is intended to dilute sensory contaminants emitting from materials and furnishings within the space, and from non-occupant activities and processes taking place within the space.? From my reading, this agrees that there are sources of IAQ contamination that originate from the building itself that have nothing to do with the occupancy of the building. Since the building is present 24/7 it would make sense that it is generating IAQ contaminants 24/7 and therefore, those contaminants need dilution over that time. So the math says the answer to the equation cannot be 0, but in reality this will represent an energy penalty in most climate zones for a large portion of the year.

Thoughts? I?m definitely okay being proven wrong here, but I haven?t found anything in the text of the standard that overtly confirms that no outdoor airflow should be provided during unoccupied times.

Jeremy R. Poling, PE, LEED AP+BDC

Jeremy Poling2's picture
Joined: 2011-09-30
Reputation: 0


I don't see anything in 62.1 that implies ventilation is required during the
unoccupied mode.

I agree that there are off-gassing considerations to be taken into account.
62.1-2004 had a section that stated, in so many words, that if there was an
accumulation of contaminants during the unoccupied period, the fans shall be
started before occupancy to purge the contaminants. I did not see this in
62.1-2007, but I do not have a searchable copy, just a cut & paste from

Some designers specify a night purge mode to clear the air after the cleaning
crew has left the building in order to purge the air of the cleaning solution

62.1-2007, section states that the "Ventilation systems shall be
designed to be capable of providing the required ventilation rates in the
breathing zone whenever the zones served by the system are occupied". I take
the "required ventilation rates" to mean those defined in Table 6.1 which is
where the CFM per person and the CFM/Ft2 is defined.

I would be interested if anyone else on the forum shares your interpretation.

Paul Diglio

Paul Diglio's picture
Joined: 2011-09-30
Reputation: 400

My interpretation was that the Az part of the equation was your limiting factor during "occupied" periods. So if you are using CO2 based DCV then you shouldn't reduce the outside air quantity below your (Ra*Az)/(Ez).
And during unoccupied periods ventilation is not required, (if a tree falls in the........) Those contaminants being off gassed from the furniture and carpet will have to wait to be diluted when the occupants arrive and the fresh air intake damper opens up.
Interesting that there are so many interpretations.

Joe Fleming

Fleming, Joe's picture
Joined: 2011-09-30
Reputation: 0

In agreement and in extension of Jeremy/Paul?s thoughts:

62.1-2007 and 2004 define a ?breathing zone? as ?the region in an occupied space?? in the glossary.

Once a space is unoccupied, it ceases to have a breathing zone. When there?s no breathing zone, per, there?s little to discuss ;).

Do provide ventilation for off-gassing. Another good example from my short experience has been tire storage.



Nick-Caton's picture
Joined: 2011-09-30
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Michael.Hupel at jci.com's picture
Joined: 2011-09-30
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You brought up a good point - I have not yet had to apply the 2010
version of the standard so I was only looking into the issue in the 2007

There is a revision in ASHRAE 62.1-2010 that actually agrees with my
interpretation as it functions for DCV (not necessarily for the
building's unoccupied hours). ASHRAE 62.1-2010 Section 6.2.7 still
covers dynamic reset of OA and Section says: "The breathing
zone airflow (Vbz) shall be reset in response to current occupancy and
shall be no less than the building component (Ra*Az) of the DCV zone."

So during occupied hours at a minimum, your OA can go no less than Ra*Az
(under ASHRAE 62.1-2010).

I could not find an official interpretation on the issue of ventilation
during unoccupied hours but there are quite a few interpretations that
regularly unoccupied spaces (even if occupiable) are not required to be

So that is the place where I think I could use more input, since the
first part seems true: under the current version of the standard DCV
cannot reduce OA to 0, only to the minimum amount determined by Ra*Az.

Jeremy R. Poling, PE, LEED AP+BDC

Jeremy Poling2's picture
Joined: 2011-09-30
Reputation: 0

Quick contribution ? Section 5.4 - ?Mechanical Ventilation systems shall include controls, manual or automatic, that enable the fans system to operate whenever the spaces served are occupied.?

It may be reading into the statement, but I?ve thought this could provide justification for, say, turning off the fresh air supply system at night, and turning it back on automatically prior to the start of the next occupied period. And also possibly also tied into any occupied-over-ride buttons on space temperature sensors?

Aaron Dahlstrom , PE, LEED? AP

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