[Equest-users] 90.1 Supply Fan Energy
Joe Fleming
joe at thespinnakergroupinc.com
Thu Apr 7 08:11:08 PDT 2011
There it is, sorry, my outlook is a little slow.
-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Paul
Diglio
Sent: Thursday, April 07, 2011 10:54 AM
To: Brian Goldsmith; Jeremy Poling; Carol Gardner
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] 90.1 Supply Fan Energy
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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