[Equest-users] Supply Fan Power

Bishop, Bill wbishop at pathfinder-ea.com
Fri May 20 10:40:27 PDT 2011


Paul,

See my response in red italics, below.

Regards,

Bill

 

From: Paul Diglio [mailto:paul.diglio at sbcglobal.net] 
Sent: Friday, May 20, 2011 12:38 PM
To: Bishop, Bill; M. Shields; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Supply Fan Power

 

Bill:
For an apartment building with PTHP, the system cycles on temperature so there is not necessarily a load on the system for the infiltration load due to open windows or trickle vents.

For LEED and/or Appendix G., “fans shall operate continuously whenever spaces are occupied and shall be cycled to meet heating and cooling loads during unoccupied hours”, per G3.1.2.4. So there should be a FAN-SCHEDULE set to “1” during occupied hours, and fans should be set to “cycle on any” under NIGHT-CYCLE-CONTROL. Infiltration loads will at some point be handled by the system to meet the thermostat setpoint.


Per the eQuest Help menu, the zone exhaust fans are modeled with the exhaust air source as infiltration to simulate residential kitchen or bathroom exhaust and the exhaust fan will operate independently of the space conditioning system.

                My mistake. I was thinking of heat recovery systems, where the ERV-SCHEDULE “can lock out the ERV when it would otherwise be running, but cannot force the ERV to run when the HVAC fans are off”.


Without stirring up the controversy of Thermal Zones again, for an apartment, I have two zones in each zone group.  One is the main area including the bathroom and one is the kitchen.  This way I can add another exhaust fan in the kitchen with a separate fractional schedule.
The BEPS indicates a significant difference in energy use when adding the exhaust fans to the model.
How do you account for this energy if you do not model the fans?
            I model separate exhaust fans in the proposed model if they are present, including their fan power. I try to keep things simple, if justified, by modeling a constant ventilation rate (identically between baseline and proposed). Toilet exhaust is, at least in theory, a constant flow, even if in practice it may be intermittent, so I model it as constant and therefore there is no fan penalty between the baseline and proposed models. I usually address a large intermittent exhaust flow by creating a MIN-AIR-SCH to vary the ratio of min OA to supply air. The values in this schedule need to be different for the baseline and proposed models, since the system supply flow rates will be different. This equalizes heating and cooling loads associated with ventilation between the baseline and proposed models. If I wanted to account for the extra fan energy associated with arguably-process ventilation loads (such as kitchen exhaust, or a parking garage), I would add the fan power as an identical equipment load with its own fractional schedule in the baseline and proposed models.


Paul Diglio

 

________________________________

From: "Bishop, Bill" <wbishop at pathfinder-ea.com>
To: Paul Diglio <paul.diglio at sbcglobal.net>; M. Shields <mshields at fstrategies.com>; equest-users at lists.onebuilding.org
Sent: Fri, May 20, 2011 11:28:37 AM
Subject: RE: [Equest-users] Supply Fan Power

Paul,

True, makeup air can come from windows or infiltration, but it still constitutes a load that is met by heating and cooling coils if there is a thermostat. Are you going to model the baseline toilet-exhaust-only system and zone with those coils to handle the loads? If yes, use the same G3.2.1.9 system type as the rest of the project and be done with it. If no, you are either going to have a problem with unmet heating/cooling hours, or you’re considering the zone unconditioned and the toilet fan is a process load that should be modeled identically between the baseline and proposed models.

Bill

 

From: Paul Diglio [mailto:paul.diglio at sbcglobal.net] 
Sent: Friday, May 20, 2011 11:12 AM
To: Bishop, Bill; M. Shields; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Supply Fan Power

 

The makeup air can come from operable windows or infiltration and does not necessarily need to be conditioned.


Paul Diglio

 

________________________________

From: "Bishop, Bill" <wbishop at pathfinder-ea.com>
To: M. Shields <mshields at fstrategies.com>; Paul Diglio <paul.diglio at sbcglobal.net>; equest-users at lists.onebuilding.org
Sent: Fri, May 20, 2011 11:03:05 AM
Subject: RE: [Equest-users] Supply Fan Power

Maybe this is the source of the confusion. I disagree that toilet exhaust fans constitute independent HVAC systems that have to modeled separately in the baseline. To me, toilet exhaust, kitchen exhaust and clothes dryer exhaust are all components of the system that heats, cools and ventilates the zone(s). The air handlers, heating and cooling coils that serve these zones are designed to supply and condition the ventilation air that is exhausted, regardless of whether or not the exhaust is at the air handler or through a zonal exhaust fan. Yes, a toilet exhaust fan can operate with the HVAC system off, but the makeup air has to come from somewhere, and it needs to be heated/cooled (even if indirectly by mixing with the room air). I mentioned previously that I usually omit exhaust fans in baseline systems. Another reason I do this is because eQUEST zonal exhaust fans cannot operate when the system fan is off.

 

My personal interpretation of G3.2.1.9 is that if you choose to model separate supply and exhaust fans in the baseline system, the calculated baseline fan power is split up into supply and exhaust components so that their total power equals the calculated value. I do not think G3.2.1.9 requires you to model separate fans for any reason. It only adds complexity and modeling effort, not baseline fan energy.

 

Regards,

Bill

 

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of M. Shields
Sent: Friday, May 20, 2011 10:48 AM
To: 'Paul Diglio'; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Supply Fan Power

 

I agree the toilet exhaust system would be independent, but I guess I am having trouble coming up with an example of an exhaust system which is not independent other than an ERV which seems to be covered under G3.1.2.10.  Thus if everything other than ERVs are independent, why does G3.1.2.9 specify exhaust as one of the systems to be included in that calculation?

 

From: Paul Diglio [mailto:paul.diglio at sbcglobal.net] 
Sent: Friday, May 20, 2011 10:37 AM
To: M. Shields; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Supply Fan Power

 

Michael:

Would not the toilet exhaust be an independent system?  It does not return air to the HVAC system and can operate with the HVAC system off.

I am modeling a residential high rise and am modeling the kitchen exhaust hoods as an independent system.  In my case the toilet exhaust fans have been eliminated and the toilet/apartment exhaust air is returned to an ERV.  Each apartment is being supplied with ventilation air from a DOAS.  In my case, I will model the toilet exhaust as part of the HVAC system.

 

Paul Diglio

________________________________

From: M. Shields <mshields at fstrategies.com>
To: equest-users at lists.onebuilding.org
Sent: Fri, May 20, 2011 10:25:43 AM
Subject: Re: [Equest-users] Supply Fan Power

Thanks for all of the comments.  I think I may have figured out how the reviewer got confused.

 

As part of my documentation I provided a table which showed the supply and exhaust cfm, bhp, and kw as calculated from G3.2.1.9 for the baseline building.  I then showed the same for the proposed building using the actual equipment specified.  The building has stacks of apartment units, each stack has an exhaust riser which has a continuously running fan on the roof.  I am interpreting everything correctly now, the baseline building should only list the supply cfm, bhp, and kw as calculated from G3.2.1.9 which includes the fan power from this exhaust riser.  The proposed building would then use the actual supply fan and exhaust fans specified.

 

Does this seem like the correct path?  Alternatively the exhaust riser could be modeled separately in both buildings using the proposed equipment as a process load.

 

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bishop, Bill
Sent: Friday, May 20, 2011 9:51 AM
To: Nick Caton; Patrick J. O'Leary, Jr.; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Supply Fan Power

 

Michael,

 

I’m confused by your LEED reviewer’s comments. As Patrick mentioned, it would help to know what the reviewer means by “independent fan systems”. I can think of only two situations where you would need to model identical fan power in the baseline and proposed models. One is if you have no heating and/or cooling system in the proposed design, in which case the proposed system “shall be identical to the system modeled in the baseline building design” per Table G3.1(10.). Since you mention that you used the actual fan power in the proposed building, I’m assuming that heating and cooling systems have been specified for your proposed design.

The other situation is for process loads. If you have fan power associated with non-HVAC systems, it should be treated as a process load and modeled identically between the baseline and proposed designs. An example of this that has been discussed on this forum previously is parking garage exhaust.

 

I rarely model anything but supply fans in the baseline model unless there are process loads. I see no point in modeling return, exhaust or relief fans. The fan power calculated in G3.1.2.9 is for the sum of supply, return, exhaust and relief fans. The baseline systems have to move the same amount of air regardless of the combination of fan types, and the fan power is based on, and entered as, kW/cfm, so you will end up with the same fan energy in the baseline model regardless of how many fans you model for each baseline system.

 

I don’t know what the reviewer is trying to say with their comment about system types 1 through 8 and Table G3.1.1A.

 

Regards,

Bill

 

 

 

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Friday, May 20, 2011 9:50 AM
To: Patrick J. O'Leary, Jr.; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Supply Fan Power

 

Color me concerned… This reviewer may have an argument but I can’t reason it.  I think he/she may be leading us off the path regarding what the baseline fan power calculations apply to…

 

You’ve got exhaust fans in a proposed model matching the construction documents.  Sounds okay so far…  Going through this line by line:

 

·         I would start with directing the reviewer to the glossary.  The entry for “HVAC system” reads: the equipment, distribution systems, and terminals that provide, either collectively or individually, the processes of heating, ventilation, or air conditioning to a building or portion of a building.”

o   Clearly, an exhaust fan providing ventilation to a building independent of other systems is an HVAC system.  The reviewer’s phrasing of “..independent fan systems of the HVAC systems” is a misinterpretation.

o   Building on the understanding that an independent exhaust system is a complete HVAC system, Table G3.1.10.a is as far as you need to go for support of following the construction documents.

·         I’d again reject the reviewers’ choice of words:  Exhaust fans are not “independent fans of the HVAC systems.”

·         Sections G3.1.2.8 and G3.1.2.9 agreeably apply only to baseline systems.  They have no bearing on the topic at hand (what goes in the proposed model), unless your baseline fan capacities/efficiency calcs didn’t follow the instructions.

·         The request to document the independent fan systems’ energies separately is not new.  May as well do that after all’s said and done.

 

That’s my initial take.  Thoughts, anyone?

 

~Nick

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

Smith & Boucher Engineers

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

www.smithboucher.com 

 

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Patrick J. O'Leary, Jr.
Sent: Friday, May 20, 2011 8:35 AM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Supply Fan Power

 

it reads to me that your initial interpretation is what the reviewer is asking for.  on the other hand the question is what is constituting an "independent" exhaust fan here.  if the exhaust fan is part of the balance of the supply/return/exhaust system it probably should be modeled as such as it is not really different than having a return fan installed in the ductwork somewhere and not in a unit itself.  per hte 90.1 user's manual (page g-28 in 2004), "System fan electrical power for supply, return, exhaust and relief fans is calculated based on the following formula.  The power from this formula includes supply, return, relief, and exhaust fans ..."   if the exhaust fan is not part of the designed system supply/return/exhaust then i would think your initial interpretation of what the reviewer is asking is correct.  whichever situation applies make sure the response documents the purpose of the exhaust fans and how 90.1 applies (including section/user manual references).

On 5/20/11 6:15 AM, M. Shields wrote: 

The exact comment is this:

 

“The fan power spreadsheet for the Baseline and Proposed models indicate that the fan power of the exhaust fans have not been modeled identically in each model. All independent fan systems of the HVAC systems in the actual design must be modeled identically between the Proposed and Baseline models at actual equipment capacities (fan volume and fan power) as required by Table G3.1.10 in the Proposed building column, since the fan design air flow rates and fan power per Sections G3.1.2.8 and G3.1.2.9, respectively, only applies to system types 1 through 8 in Table G3.1.1A. If appealing this credit, revise the Proposed and Baseline models so all independent fan systems of the HVAC systems are modeled identically between the Proposed and Baseline models. In addition, separate the energy consumption and peak demand energy for independent fans in Table 1.8.1 and Table 1.8.2 of the template and provide revised SV-A reports for each model reflecting the changes.”

 

I initially interpreted this to be that for exhaust systems the bhp/kw needs to be identical in both buildings and based on the specified equipment from the mechanical designer, however, my supply fan energy was Ok.  After reading the comment and Appendix G I am not unsure if I also need to specify the fan power to be the same for both models, ie use table G3.1.2.9 to calculate fan power for both instead of just the baseline.

 

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Patrick J. O'Leary, Jr.
Sent: Friday, May 20, 2011 8:57 AM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Supply Fan Power

 

from your wording of "independent" it sounds like you may have an application where you have a unit in the proposed building that is required but not provided in the design?  or something similar.  is this the case?  if a unit is required in the proposed per the requirement all spaces be heated/cooled (per the definitions) they are required to be the same as the units in the baseline building.  if this is not the case if you post the exact comment it may shed some light on the subject.  otherwise i would argue the comment is in error - if all of your zones are served by units in the proposed and you have matching units in the baseline (regardless of system types) then your approach would be correct.  

On 5/20/11 5:31 AM, M. Shields wrote: 

Good Morning All,

 

I recently received comments back from LEED and one of them was about my fan power.  In the submission I calculated all of my fan power using G3.1.2.9 for the baseline building, and I used the actual fan power in the proposed building.  The reviewer has commented that all independent fan systems have to be modeled identically in both the baseline and the proposed building.  The supply fans use very high efficiency motors, and as such are substantially more efficient than the calculation that G3.1.2.9 provides.  Is there no way to take credit for using high efficiency supply fans?

 

Thanks,

 

____________________________
Michael Shields

Email: mshields at fstrategies.com

 

 
 
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