Dear Jeannie,
First, a qualifier: I am not familiar with modeling of naturally
ventilated buildings, so what I say below is my opinion based on what I know
about mechanically ventilated systems and may need more research. (That means
YOU may be more knowledgeable than I!)
Second, a few thoughts:
·
The baseline system is “imaginary”. It is used
as an efficiency reference and I suspect that it was not envisioned by its
ASHRAE authors to be a reference for a non-mechanical comfort control system.
·
Baseline systems share a few common aspects with the “real”
(proposed) system. These common aspects include schedules for occupancy,
lighting and equipment. They also include operating setpoints for
comfort.
·
You do not need to turn on a baseline cooling or heating system.
For example the Availability Schedule for the chiller or cooling coil could be “OFF”
continuously. If it is “OFF” for the Baseline, though, the
identical schedule must be used for the Proposed system.
·
Similarly, I think that you are not required to maintain the
building within, say, the ASHRAE comfort window, but the control setpoints must
be identical for Baseline and Proposed models. Of course, the design
engineer’s responsibility is to make sure the client’s comfort
requirements are met (whatever they may be). This means that you can, for
example, define the cooling setpoint at 40C for both systems, resulting in the
cooling system never operating.
·
You ARE required to meet the ventilation minimums of ASHRAE 62.1.
That’s fairly easily done for mechanically ventilated systems; I trust
that you have a good idea how to model and verify it for a naturally ventilated
system!
So far, I have not addressed your question about fan power! I
wanted to “set the stage” a bit, though. Now on to fan power:
·
I think that every Baseline system’s fans should be defined
with reasonable fan efficiency and pressure rise. The definition for “reasonable”
is not provided anywhere in ASHRAE 90.1. My own definition is that I will
be able to confidently explain and defend my choices in front of a group of my
peers.
·
In addition, as defined by 90.1 the fan system Delta T must be
20F / 11.1C (as mentioned in an earlier post)
·
Your (autosized) Baseline fan system probably provides both ventilation
air and space heating. Depending on the amount of heating that is required, the
flow rate may still be the same as the ventilation amount. Regardless, it’s
“autosized” and autosizing accounts for minimum ventilation,
heating and cooling loads, uses the 20F delta T and also uses “reasonable”
fan efficiency and Delta P. The purpose of Baseline autosizing in the
Standard is (I think) to minimize the “game-playing” and make sure
a Baseline represents a fairly constant standard.
·
I’m not quite sure what you mean by “These
air flow rates obviously don't also meet the heating and cooling loads…” .
A Baseline system MUST meet the heating and cooling loads defined by your heating
and cooling setpoints. So must the Proposed system. Both systems
must meet the “unmet load hours” requirements in G3.1.2.2.
·
The Proposed fan system does not need to meet the heating
loads on its own if the radiant floor provides enough heat to maintain the heating
setpoint. Similarly, the Proposed fans should not use the efficiencies
and unloading coefficients specified for Baseline systems; they should use the actual
efficiency and unloading coefficients.
E-mail discussion are difficult! Nonetheless, I hope I’ve
helped.
Here’s a summary:
BOTH BASELINE and PROPOESED:
·
Identical schedules for occupancy, lighting and equipment.
·
Identical comfort setpoints
·
Identical ventilation minimum requirements
BASELINE:
·
Autosized for 62.1 ventilation, 20F delta T, “reasonable”
efficiency and delta P, and providing all heating and cooling loads
PROPOSED:
·
Assure 62.1 ventilation minimums are met (however that’s
done for naturally ventilated systems)
·
Actual efficiency, delta P and delta T for all fans and pumps
The Building Performance Team
James V. Dirkes II, P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of jeannieboef
Sent: Monday, September 06, 2010 6:27 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: ASHRAE Compliant Fans and Pumps
Dear Mr. Dirkes,
I'm modelling a building with ventilation purely for ASHRAE 90.1 code
compliance as it is in reallity 100% Naturally ventilated with just heating
(radiant floor). As you know the mechanical system takes the shape of the
baseline model which I gave as design supply air flow rates as per the minimum
rates outdoor air rates of ASHRAE 62.1. These air flow rates obviously don't
also meet the heating and cooling loads when all the heating and cooling loads
are met with the AHU systems, meaning that e+ has sized the needed air flows
and fan flow rates larger than the fan flow rates that I have thus far used in
the fan power calculation as per ASHRAE G3.1.2.5 & G3.1.2.8.
I'm busy assigning deltaP to achieve the desired fan powers given in by the
ASHRAE fan power calcualtion in e+, and wanted to ask your oppinion if this
methodology is correct. Because the input in the fan power calculation uses the
air flow purely for minimum outdoor air rates and not also to meet the heating
cooling load.
I've not found anything in Appendix G that would make me think that I couldn't
make the design air flow rate for the fan power calculation ZERO. E+ would
still calcualte the larger rate to meet heating and cooling loads, but I could
leave all my fan deltaPs at zero.
What is the best approach here? What should I use for design Air Flow Rates for
the baseline building (as the naturally ventilated proposed design building
doesn't have any requirement)?
Regards,
Jean.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx,
"James V Dirkes II, PE" <jvd2pe@...> wrote:
>
> Dear Vinay,
>
>
>
> While .6 fan efficiency is within normal range, the goal is to define a
> combination of fan efficiency and pressure rise which results in the
> acceptable fan power. You start with known air flow, make a reasonable
> estimate of fan efficiency and then derive the pressure rise.
>
>
>
> For a "Proposed" system, the derivation is not needed; you use
the actual
> fan and motor efficiencies, actual airflow and actual pressure rise.
>
>
>
> For your information (just in case it's helpful), the derivation of fan
> power is shown below in IP units.
>
>
>
>
>
>
>
>
>
>
>
> The Building Performance Team
> James V. Dirkes II, P.E., LEED AP
> 1631 Acacia Drive NW
> Grand Rapids, MI 49504
> 616 450 8653
>
>
>
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
On Behalf Of Vinay Devanathan
> Sent: Wednesday, July 07, 2010 9:32 PM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: Re: [EnergyPlus_Support] ASHRAE Compliant Fans and Pumps
>
>
>
>
>
> Mr. Dirkes,
>
>
>
> Thanks for your reply. So, is 0.6 Fan Efficiency (including motor
> efficiency) acceptable? or does it depend on any other variable? I am
> assuming there are no set specifics for Fan Efficiency value. So, with
this
> procedure, we can calculate Fan Power from Appendix G formula and adjust
> Pressure difference. Am I right on this?
>
>
> Thank you.
>
> Regards,
>
> Vinay
>
>
>
> On Wed, Jul 7, 2010 at 9:25 PM, James V Dirkes II, PE <jvd2pe@...>
> wrote:
>
>
>
> Dear Vinay,
>
>
>
> ASHRAE 90.1-2007 specifies Baseline system fan power in Table G3.1.2.9.
For
> VAV systems, also use Table G3.1.3.15 for part load performance. A sample
> object for the VAV fan is shown below.
>
>
>
> For all baseline fans, I made a spreadsheet which, based on anticipated
> motor and fan efficiency, calculates the pressure rise which will result
in
> the correct ASHRAE 90.1 fan power. Remember that E+, when asking for
"fan
> efficiency", really wants (Fan mechanical efficiency x Motor
efficiency).
> For example, if the fan mechanical efficiency = .60 and motor efficiency =
> .90, the E+ "fan efficiency" = .54.
>
>
>
>
>
>
> Fan:VariableVolume
>
>
> Name
>
> SFan_MainBldg
>
>
> Availability Schedule Name
>
> SchCpct_FanOpern
>
>
> Fan Efficiency (incl. motor)
>
> 0.6
>
>
> Pressure Rise (Pa)
>
> 498
>
>
> Maximum Flow Rate
>
> Autosize
>
>
> Minimum Flow Rate
>
> 0
>
>
> Motor Efficiency
>
> MT
>
>
> Motor In Airstream Fraction
>
> 1
>
>
> Fan Coefficient 1
>
> 0.0013
>
>
> Fan Coefficient 2
>
> 0.147
>
>
> Fan Coefficient 3
>
> 0.9506
>
>
> Fan Coefficient 4
>
> -0.0988
>
>
> Fan Coefficient 5
>
> 0
>
>
> Air Inlet Node Name
>
> NodeOut_ClgCoilAir_MainBldg
>
>
> Air Outlet Node Name
>
> NodeOut_SFan_MainBldg
>
>
> End-Use Subcategory
>
>
>
>
>
>
>
> The Building Performance Team
> James V. Dirkes II, P.E., LEED AP
> 1631 Acacia Drive NW
> Grand Rapids, MI 49504
> 616 450 8653
>
>
>
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
On Behalf Of Vinay Devanathan
> Sent: Wednesday, July 07, 2010 5:53 PM
>
>
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
>
> Subject: Re: [EnergyPlus_Support] ASHRAE Compliant Fans and Pumps
>
>
>
>
>
> Alan,
>
> In regards to your reply,
>
> Does ASHRAE specify any efficiency value for the fans? If yes, could you
> please direct me to the same.
>
> Thank you.
>
> Regards,
> Vinay
>
> On Tue, Jun 29, 2010 at 11:33 AM, Jackson, Alan <ajackson@...>
> wrote:
>
>
>
> You're going to want to adjust your Static Pressure DeltaP. Once you
> have your Watts for the Baseline from auto sizing the flow you can use
> DeltaP[Pa] = Power[W]*Eff/Flow[m3/s]
>
> Since ASHRAE is telling you Flow and Power you have to solve for static.
>
> Alan Jackson, LEED AP
> KlingStubbins
>
>
>
> -----Original Message-----
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com> ] On Behalf Of
eddiecorwin
> Sent: Tuesday, June 29, 2010 11:13 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>
> Subject: [EnergyPlus_Support] ASHRAE Compliant Fans and Pumps
>
> I am curious as to how people have gone about modeling ASHRAE compliant
> pumps and fans.
>
> The pumps seem relatively strait forward, run the model, see what the
> flow is, then enter in a wattage that equates to 22W/GPM. The fans,
> however, do not have an input for the rated wattage. The only option I
> see is to alter the fan's Motor Efficiency until you get close to the
> correct W/CFM.
>
> Are these the same methods people have applied in the past, or is there
> a better way to the the correct W/GPM and W/CFM?
>
> ------------------------------------
>
>
>
> Primary EnergyPlus support is found at:
> http://energyplus.helpserve.com
or send a message to
> energyplus-support@... <mailto:energyplus-support%40gard.com>
>
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
>
> The group web site is:
> http://groups.yahoo.com/group/EnergyPlus_Support/
>
> Attachments are currently allowed but be mindful that not everyone has a
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>
> EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under
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>
> Yahoo! Groups Links
>
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