Fan power calculation for proposed model

11 posts / 0 new
Last post

Please comment on the following:

Based on Table G3.1.10.a, for an HVAC system in the proposed design, the system is determined by the following:

"Where a complete HVAC system exists, the model shall reflect the actual system type using actual component capacities and efficiencies."

In design of AHU systems, the scheduled or nameplate flow rate of the equipment is typically higher than the design flow rate of the system, as calculated by the simulation software. The system fan power calculation is based on the efficiency of the fan and ultimately the design flow rate of the fan. Also, in operation the fan typically does not operate at 60 Hz at peak flow rate, suggesting that the operating flow rate in this condition is more in line with the design flow rate calculated by the simulation software, rather than the nameplate flow rate of the equipment.

For these reasons, it is likely the case that the fan power calculation should be based on the design flow rate calculated by the software, rather than the nameplate flow rate.

Thanks,

Nick Blanton
____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses

Nicholas Blanton's picture
Joined: 2014-01-16
Reputation: 0

It is my understanding that the proposed model should always be the design values used in selecting the fan not what is calculated by the energy simulation. I agree the fan most likely will not operate at that flow rate, but that is what we have fan curves for.

Cory Duggin, PE, LEED AP BD+C
Associate/Energy Modeling Wizard, j.g.
[cid:image001.jpg at 01D0E4D0.829BE650]
TLC Engineering for Architecture
direct:

615-346-1939

crduggin's picture
Offline
Joined: 2013-04-16
Reputation: 0

I agree with Cory.
The ASHRAE 90.1 committee would be hard pressed to integrate the different
manners that all modeling software could be used to come up with specific
simulated flow rates using unspecified (for the model) operating schedules
and internal loads. The designer is already tasked with selecting the fan
using best available information, so I think that's a more reliable basis.

James V Dirkes II, PE's picture
Joined: 2011-10-02
Reputation: 203

Cory/Jim,

Because a fan selection only gives a single operating point for a specific system curve, I was interested in seeing if a proposed alternative, i.e. basing the system curve on a point produced by the simulation, could be a more accurate method of approximating fan energy consumption. But of course, the only known operating point for the fan is based on the fan selection.

Given that this is the case, would you agree with me that there is no industry standard for establishing a fan power curve, for the purpose of energy modeling? Also, would you agree that the modeler could claim false savings based on a fan curve that contains low part load input kW? I am not aware of any requirements on the curve itself, and that is really the root of the issue I was trying to bring up.

Thanks,

Nick Blanton

Nicholas Blanton's picture
Joined: 2014-01-16
Reputation: 0

When I?m really interested in making sure my fan power is accurate, such as in lab buildings or anytime the fan energy is the predominant end use, I use the system break horsepower curve from the fan selection to build my own custom fan curve in the energy model. I even look at my results to figure out what flow rates the fan operates at the most to specifically target those as points in my curve. As with many things, you could easily game the system.

Cory Duggin, PE, LEED AP BD+C
Associate/Energy Modeling Wizard, j.g.
[cid:image001.jpg at 01D0E596.0ABE8EA0]
TLC Engineering for Architecture
direct:

615-346-1939

crduggin's picture
Offline
Joined: 2013-04-16
Reputation: 0

The Venn diagram of individuals who are well enough versed in both energy
simulation AND the nuances of actual fan power consumption AND sufficiently
motivated to misrepresent energy consumption with their hard work is I
think relatively small. As such, the potential for deliberately skewing
performance by doctoring up part load curves doesn?t come up often for
discussion! It?s certainly a possibility, however?

To respond to the other Nick?s query: 90.1 Appendix G (and by its
relatively wide incorporation through LEED) does mandate part load fan
curves for baseline systems with VAV. I haven?t (honestly!) tried such
sneaky tactics before with LEED submissions, but based on recent review
commentary (in the past year) I would be surprised if an over-inflated fan
power consumption managed to slip through the cracks. GBCI?s reviewers have
proven eager to check ?full load equivalent? operation against annual
consumption, sometimes on more things than are usually appropriate ? fans
included.

Rounding back to the original query ? I think another perspective is that
it?s always ?safe? to reference design documentation when you have no
better information. If you are trying to evaluate relative savings with
existing systems, what?s measured/observed in the field or in ?as-built?
documentation should generally trump what?s on the original plans. Based
on the ultimate function/purpose of your simulation (informing actual
design decisions vs. quickly assembling a LEED-compliant submission), you
can make the call as to whether gathering the extra info from the field is
entirely necessary/appropriate.

If you?re looking to source fan curves ?accepted by industry? beyond the
Appendix G part load curve, there have been some truly interesting
discussions over these lists comparing notes!

~Nick

*NICK CATON, P.E.*
*Owner*

*Caton Energy Consulting*
306 N Ferrel

Olathe, KS 66061

office: 785.410.3317

www.catonenergy.com

*From:* Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf
Of *Duggin, Cory
*Sent:* Wednesday, September 02, 2015 3:43 PM
*To:* Nicholas Blanton; Jim Dirkes
*Cc:* bldg-sim at lists.onebuilding.org
*Subject:* Re: [Bldg-sim] Fan power calculation for proposed model

When I?m really interested in making sure my fan power is accurate, such as
in lab buildings or anytime the fan energy is the predominant end use, I
use the system break horsepower curve from the fan selection to build my
own custom fan curve in the energy model. I even look at my results to
figure out what flow rates the fan operates at the most to specifically
target those as points in my curve. As with many things, you could easily
game the system.

*Cory Duggin, PE, LEED AP BD+C *

*Associate/Energy Modeling Wizard, j.g.*

*[image: GreenWeek2015_FINAL-Email-Sig]*

*TLC Engineering for Architecture *

direct:

615-346-1939

*From:* Nicholas Blanton [mailto:nicholas.blanton at arup.com
]
*Sent:* Wednesday, September 02, 2015 3:34 PM
*To:* Jim Dirkes ; Duggin, Cory <
Cory.Duggin at tlc-eng.com>
*Cc:* bldg-sim at lists.onebuilding.org
*Subject:* RE: [Bldg-sim] Fan power calculation for proposed model

Cory/Jim,

Because a fan selection only gives a single operating point for a specific
system curve, I was interested in seeing if a proposed alternative, i.e.
basing the system curve on a point produced by the simulation, could be a
more accurate method of approximating fan energy consumption. But of
course, the only known operating point for the fan is based on the fan
selection.

Given that this is the case, would you agree with me that there is no
industry standard for establishing a fan power curve, for the purpose of
energy modeling? Also, would you agree that the modeler could claim false
savings based on a fan curve that contains low part load input kW? I am not
aware of any requirements on the curve itself, and that is really the root
of the issue I was trying to bring up.

Thanks,

Nick Blanton

*From:* Jim Dirkes [mailto:jim at buildingperformanceteam.com
]
*Sent:* Wednesday, September 02, 2015 6:04 AM
*To:* Duggin, Cory
*Cc:* Nicholas Blanton; bldg-sim at lists.onebuilding.org
*Subject:* Re: [Bldg-sim] Fan power calculation for proposed model

I agree with Cory.

The ASHRAE 90.1 committee would be hard pressed to integrate the different
manners that all modeling software could be used to come up with specific
simulated flow rates using unspecified (for the model) operating schedules
and internal loads. The designer is already tasked with selecting the fan
using best available information, so I think that's a more reliable basis.

Nicholas Caton's picture
Offline
Joined: 2014-12-09
Reputation: 0

It is my understanding that the proposed model should always be the design values used in selecting the fan not what is calculated by the energy simulation. I agree the fan most likely will not operate at that flow rate, but that is what we have fan curves for.

Cory Duggin, PE, LEED AP BD+C
Associate/Energy Modeling Wizard, j.g.
[cid:image001.jpg at 01D0E4D0.829BE650]
TLC Engineering for Architecture
direct:

615-346-1939

crduggin's picture
Offline
Joined: 2013-04-16
Reputation: 0

I agree with Cory.
The ASHRAE 90.1 committee would be hard pressed to integrate the different
manners that all modeling software could be used to come up with specific
simulated flow rates using unspecified (for the model) operating schedules
and internal loads. The designer is already tasked with selecting the fan
using best available information, so I think that's a more reliable basis.

James V Dirkes II, PE's picture
Joined: 2011-10-02
Reputation: 203

Cory/Jim,

Because a fan selection only gives a single operating point for a specific system curve, I was interested in seeing if a proposed alternative, i.e. basing the system curve on a point produced by the simulation, could be a more accurate method of approximating fan energy consumption. But of course, the only known operating point for the fan is based on the fan selection.

Given that this is the case, would you agree with me that there is no industry standard for establishing a fan power curve, for the purpose of energy modeling? Also, would you agree that the modeler could claim false savings based on a fan curve that contains low part load input kW? I am not aware of any requirements on the curve itself, and that is really the root of the issue I was trying to bring up.

Thanks,

Nick Blanton

Nicholas Blanton's picture
Joined: 2014-01-16
Reputation: 0

When I?m really interested in making sure my fan power is accurate, such as in lab buildings or anytime the fan energy is the predominant end use, I use the system break horsepower curve from the fan selection to build my own custom fan curve in the energy model. I even look at my results to figure out what flow rates the fan operates at the most to specifically target those as points in my curve. As with many things, you could easily game the system.

Cory Duggin, PE, LEED AP BD+C
Associate/Energy Modeling Wizard, j.g.
[cid:image001.jpg at 01D0E596.0ABE8EA0]
TLC Engineering for Architecture
direct:

615-346-1939

crduggin's picture
Offline
Joined: 2013-04-16
Reputation: 0

The Venn diagram of individuals who are well enough versed in both energy
simulation AND the nuances of actual fan power consumption AND sufficiently
motivated to misrepresent energy consumption with their hard work is I
think relatively small. As such, the potential for deliberately skewing
performance by doctoring up part load curves doesn?t come up often for
discussion! It?s certainly a possibility, however?

To respond to the other Nick?s query: 90.1 Appendix G (and by its
relatively wide incorporation through LEED) does mandate part load fan
curves for baseline systems with VAV. I haven?t (honestly!) tried such
sneaky tactics before with LEED submissions, but based on recent review
commentary (in the past year) I would be surprised if an over-inflated fan
power consumption managed to slip through the cracks. GBCI?s reviewers have
proven eager to check ?full load equivalent? operation against annual
consumption, sometimes on more things than are usually appropriate ? fans
included.

Rounding back to the original query ? I think another perspective is that
it?s always ?safe? to reference design documentation when you have no
better information. If you are trying to evaluate relative savings with
existing systems, what?s measured/observed in the field or in ?as-built?
documentation should generally trump what?s on the original plans. Based
on the ultimate function/purpose of your simulation (informing actual
design decisions vs. quickly assembling a LEED-compliant submission), you
can make the call as to whether gathering the extra info from the field is
entirely necessary/appropriate.

If you?re looking to source fan curves ?accepted by industry? beyond the
Appendix G part load curve, there have been some truly interesting
discussions over these lists comparing notes!

~Nick

*NICK CATON, P.E.*
*Owner*

*Caton Energy Consulting*
306 N Ferrel

Olathe, KS 66061

office: 785.410.3317

www.catonenergy.com

*From:* Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf
Of *Duggin, Cory
*Sent:* Wednesday, September 02, 2015 3:43 PM
*To:* Nicholas Blanton; Jim Dirkes
*Cc:* bldg-sim at lists.onebuilding.org
*Subject:* Re: [Bldg-sim] Fan power calculation for proposed model

When I?m really interested in making sure my fan power is accurate, such as
in lab buildings or anytime the fan energy is the predominant end use, I
use the system break horsepower curve from the fan selection to build my
own custom fan curve in the energy model. I even look at my results to
figure out what flow rates the fan operates at the most to specifically
target those as points in my curve. As with many things, you could easily
game the system.

*Cory Duggin, PE, LEED AP BD+C *

*Associate/Energy Modeling Wizard, j.g.*

*[image: GreenWeek2015_FINAL-Email-Sig]*

*TLC Engineering for Architecture *

direct:

615-346-1939

*From:* Nicholas Blanton [mailto:nicholas.blanton at arup.com
]
*Sent:* Wednesday, September 02, 2015 3:34 PM
*To:* Jim Dirkes ; Duggin, Cory <
Cory.Duggin at tlc-eng.com>
*Cc:* bldg-sim at lists.onebuilding.org
*Subject:* RE: [Bldg-sim] Fan power calculation for proposed model

Cory/Jim,

Because a fan selection only gives a single operating point for a specific
system curve, I was interested in seeing if a proposed alternative, i.e.
basing the system curve on a point produced by the simulation, could be a
more accurate method of approximating fan energy consumption. But of
course, the only known operating point for the fan is based on the fan
selection.

Given that this is the case, would you agree with me that there is no
industry standard for establishing a fan power curve, for the purpose of
energy modeling? Also, would you agree that the modeler could claim false
savings based on a fan curve that contains low part load input kW? I am not
aware of any requirements on the curve itself, and that is really the root
of the issue I was trying to bring up.

Thanks,

Nick Blanton

*From:* Jim Dirkes [mailto:jim at buildingperformanceteam.com
]
*Sent:* Wednesday, September 02, 2015 6:04 AM
*To:* Duggin, Cory
*Cc:* Nicholas Blanton; bldg-sim at lists.onebuilding.org
*Subject:* Re: [Bldg-sim] Fan power calculation for proposed model

I agree with Cory.

The ASHRAE 90.1 committee would be hard pressed to integrate the different
manners that all modeling software could be used to come up with specific
simulated flow rates using unspecified (for the model) operating schedules
and internal loads. The designer is already tasked with selecting the fan
using best available information, so I think that's a more reliable basis.

Nicholas Caton's picture
Offline
Joined: 2014-12-09
Reputation: 0