[Equest-users] 90.1 Supply Fan Energy
Paul Diglio
paul.diglio at sbcglobal.net
Thu Apr 7 07:53:31 PDT 2011
Brian:
In detailed mode, right click the static and then choose "restore default".
Then you can enter the kW/CFM.
Paul Diglio
________________________________
From: Brian Goldsmith <Brian.Goldsmith at atce.com>
To: Jeremy Poling <Jeremy.Poling at transwestern.net>; Carol Gardner
<cmg750 at gmail.com>; Paul Diglio <paul.diglio at sbcglobal.net>
Cc: "equest-users at lists.onebuilding.org" <equest-users at lists.onebuilding.org>
Sent: Thu, April 7, 2011 10:46:48 AM
Subject: RE: [Equest-users] 90.1 Supply Fan Energy
I am trying to model a CAV 90.1 baseline system 4, but it won’t let me input
kW/cfm, just static and efficiency. The default static value is 1.25, but I’m
not sure if that’s correct because I obviously don’t know the external static of
the duct system. I would rather input the kW/cfm. Any advice?
Brian Goldsmith
Brian.Goldsmith at atce.com
direct 408.487.1217
________________________________
From:equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Jeremy Poling
Sent: Wednesday, April 06, 2011 8:47 PM
To: Carol Gardner; Paul Diglio
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] 90.1 Supply Fan Energy
Carol,
Here's my general thoughts on OA in the model, for what they're worth. The only
problem with using the OA-per keywords in eQuest is that they are not additive:
you can only use OA-flow-per-area or OA-flow-per-person but not both. Since
ASHRAE 62.1-2004 and later prescriptively defines both per-person and per-area
requirements in an additive fashion, eQuest is incapable of self-calculating the
amount of OA required to comply with ASHRAE 62.1. I'm more often in the role of
peer-reviewing models for engineers before they go to the LEED review teams and
this is one thing I find myself too often receiving a response of "this way
should work." The reviewers will compare the OA amounts specified in EQp1 and
EQc2 to the amounts used in the model in EAc1 and will more often than not kick
out a comment if they do not match.
I usually try to minimize the time for having to respond to comments, especially
knowing how many comments energy models receive. My recommendation to modelers
using eQuest is to always calculate your design CFM values (OA, supply, return,
exhaust) outside of the software using appropriate adjustment factors where
necessary or allowed by codes like ASHRAE 62.1 (elevation, etc.) and then use
the direct specification keywords for zone-level airflows in eQuest. As long as
you have elevation zero'd out you should be able to get eQuest to match the
airflow values you calculated, or else be able to easily identify where the
problem is (system sizing factor >1, etc.). An added benefit is that you do not
have to run the simulation and look at the results to know what CFM values you
have in the model: they are in the input file and can be accessed easily in the
summary tables in the user interface.
It would be great if eQuest was able to match the ASHRAE 62.1 calcs and even
provide an ASHRAE 62.1 summary report (like some other modeling software can),
but I know Hirsch's team was focused on the baseline compliance engine and the
soon-to-come Canadian version, so it is more than fair to be patient waiting for
that feature :) I also know that some really advanced users have ways to use
the customization features in eQuest to do this already and I encourage them to
share/teach...
In short - the Outside-air-flow keyword should be the preferred keyword and
indeed eQuest overrides all other OA keywords at the zone level if a value is
present for Outside-air-flow.
Separately, when you do calculate CFM values for the model, don't forget that
ASHRAE 90.1-2007 allows credit for pressure drop due to filters ;) Just one
more thing to have to worry about in the model...
Jeremy R. Poling, PE, LEED AP+BDC
________________________________
From:equest-users-bounces at lists.onebuilding.org on behalf of Carol Gardner
Sent: Wed 4/6/2011 7:03 PM
To: Paul Diglio
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] 90.1 Supply Fan Energy
The reason someone "thinks OA might cause a problem" is because of the way that
someone thinks it was entered. It sounds like it was entered using
outside-air-flow, and I may be wrong because Michael hasn't really said. Using
Outside-Air-Flow overrides any values eQUEST might otherwise calculate, and I
would suggest that might make a difference. If OA Flow-Per was used instead,
that's the one I use, it gives eQUEST the flexibility to calculate the OA cfm
itself. To my mind, that a good use of an energy model that is not only
interactive but uses 8760 hours of weather data.
Any other thoughts on this?
On Wed, Apr 6, 2011 at 4:07 PM, Paul Diglio <paul.diglio at sbcglobal.net> wrote:
Michael:
The kW/CFM you used seems reasonable.
I don't know if you are using a CV or VAV system, but lets assume VAV.
90.1-2007 G3.1.2.9 shows the formula CFMs *.0013+A for baseline BHP. A is
calculated per Section 6.5.3.1.1. Using Table 6.5.3.1.1A VAV, we have the
formula BHP<= CFMs*0013+A. The footnote defines A=sum of (PD*CFMd/4131). So
assuming you have a fully ducted return, the PD is .5 which should be multiplied
by (CFMd/4131). If there are various pressure drops throughout the system we
need to estimate the CFM flow at each pressure drop.
As an example, let's take a 20,000 CFM VAV system with 18,000 CFM of return air
through a ducted return.
A = (.5*(18000/4131) = 2.178
BHP =20000*.0013+2.178 = 28.17
pFan= 28.17*.746/ Fan Motor Efficiency. Note that since we need kW not watts
per CFM the 746 becomes .746. That is probably the reason you generated a large
kW number. Per Table 10.8 a 30 HP baseline motor needs to be 91% efficient.
The formula now becomes pFan =28.17*.746/.91 = 23.09 kW. Our kW per CFM is
.0011.
If I am modeling a proposed project with a defined supply and return CFM, I
would expect that the baseline would be approximately the same. The CFM/Ft2
required varies greatly between building and systems. In the real world I see
1.2 or so CFM/Ft2 much, much more than I see .5 CFM/Ft2. Check your CFM/Ton to
see if you are in the ballpark.
I don't know why someone would think that outside air would cause a problem.
Air is air. Too much outside air would raise energy costs though.
Paul Diglio
________________________________
From:M. Shields <mshields at fstrategies.com>
To: Paul Diglio <paul.diglio at sbcglobal.net>; Carol Gardner <cmg750 at gmail.com>
Cc: equest-users at lists.onebuilding.org
Sent:Wed, April 6, 2011 6:13:53 PM
Subject: RE: [Equest-users] 90.1 Supply Fan Energy
I’ll try OA as a per person number instead of a per space number and see what
happens. kW/CFM varied by space between ~ .0007 and .001, and when I look at
the SV-A reports the Fan Demand (kW) matches what I calculated using 90.1.
I found G3.1.2.9 could possibly be interpreted a couple different ways (for
example the denominator include X BHP instead of the whole fraction), but the
only one which produced a reasonable bhp for to me was . I guess this could
have been where I messed up but all the other possibilities generated kW numbers
which didn’t make sense (quite large or negative).
From:Paul Diglio [mailto:paul.diglio at sbcglobal.net]
Sent: Wednesday, April 06, 2011 5:51 PM
To: Carol Gardner; M. Shields
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] 90.1 Supply Fan Energy
Michael:
Just out of curiosity, what did you calculate for the kW/CFM?
I have modeled buildings where the ventilation fans use much more energy than
the heating and cooling energy combined.
Paul Diglio
________________________________
From:Carol Gardner <cmg750 at gmail.com>
To: M. Shields <mshields at fstrategies.com>
Cc: equest-users at lists.onebuilding.org
Sent: Wed, April 6, 2011 5:46:30 PM
Subject: Re: [Equest-users] 90.1 Supply Fan Energy
Yes, that is correct and obviously there isn't a large number in there. The
default is 0.5 cfm/sf. I really think it's your outdoor air. Try changing it to
cfm/person.
On Wed, Apr 6, 2011 at 1:47 PM, M. Shields <mshields at fstrategies.com> wrote:
Do you mean under the Systems->Fans->Flow Parameters Min Flow cfm/ft2? I left
this blank thinking that equest would then size the flow rate based on my design
parameters for supply air temp and zone temp as Appendix G requires, is that
incorrect?
From:Carol Gardner [mailto:cmg750 at gmail.com]
Sent: Wednesday, April 06, 2011 4:04 PM
To: M. Shields
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] 90.1 Supply Fan Energy
Under the HVAC systems tab, go to the Air Flow screen and look for the field
labeled cfm/sf. It usually defaults to 0.5 cfm/sf, something I've been going on
about a bit lately on this listserv. A better number is 1 or so, usually but it
depends on building type, exposure, etc. For you, make sure it is not too large.
I suspect, however, that this is not where your problem is. I suspect you have
accidentally entered too much OA. I suggest you go back and simply put in the
Standard 62 cfm/person rate and call it good. I have never specified it as a cfm
rate but that sounds like not such a good idea for energy modeling. See if that
helps.
On Wed, Apr 6, 2011 at 12:57 PM, M. Shields <mshields at fstrategies.com> wrote:
I looked at the ACH based on the SV-A system CFM and the volume of the zone and
it does seem high (2-5 ACH), but I let equest calculate the system CFM for me.
I have one system per zone so I specified OA in the zone tab as a overall CFM
rate based on the 62.1 calculations I did.
From:Carol Gardner [mailto:cmg750 at gmail.com]
Sent: Wednesday, April 06, 2011 3:37 PM
To: M. Shields
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] 90.1 Supply Fan Energy
Check your cfm/sf number in your systems, that would definitely cause this if
it's set too high. Also what field are you using for your OA ventilaton?
Carol
On Wed, Apr 6, 2011 at 12:22 PM, M. Shields <mshields at fstrategies.com> wrote:
Hi all,
I am in the process of breaking out the fan energy from my HVAC system per
ASHRAE 2004 G3.1.2.1, following G3.1.2.9. The amount of energy coming from my
fans seems massive and I’m not sure if that is typical, or if I’ve messed
something up. I started by setting the temperature difference of 20 degrees
between supply and desired temp (55/75 cooling and 90/70 for heating) and
specified 62.1-2004 ventilation for outside air. I then ran equest and used the
SV-A reports to get supply CFM for each system. From that number I then used
Table G3.1.2.9 to get BHP for each system, which I then converted to kW using
the formula in ASHRAE. I then took that number and divided by CFM to get kw/CFM
and entered this number on the system->fan tab. When I go to the SV-A report
the system kW is exactly what I calculated it to be, but the energy required for
my ventilation fans is about the same as my heating and cooling load combined,
which seems outrageous.
Is this typical? Have I entered it In the wrong way? I would think fan
consumption would typically be a fraction of the actually heating and cooling
energy. Thanks for any thoughts.
____________________________
Michael Shields
Facility Strategies Group, LLC
1012 Market Street, Suite 307
Fort Mill, SC 29708
Phone: 803-493-4507
Fax: 803-548-2511
Email: mshields at fstrategies.com
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Carol Gardner PE
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Carol Gardner PE
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