[Equest-users] Building area method ASHRAE 90.1

[David Eldridge]

Patrick, the space-by-space LPD aren't mandatory requirements, so you'd be able to trade lighting power through space-by-space or BAM. Someone will have to perform the take-off either way to calculate the BAM weighted LPD for the Proposed case, so you aren't saving much time on the Proposed model. (Only saving the time to actually assign the Watts to the zone in the model.)

There will be a small time savings in Baseline model creation by not determining and entering space-by-space power usage into the model.

I agree with Bill that 90.1's wording about "...if a lighting design exists..." points me towards space-by-space if at all possible. But GBCI seems to accept both, regardless of possible BAM inaccuracies which as Nick pointed out may or may not be significant, so the main result of this gigantic thread is:


1.       Use the same method in both cases.

2.       Several people think 90.1 suggests space-by-space if the lighting system is designed.



a.       Not always (ever?) enforced/requested by GBCI.


b.      When the model is being used to inform the design or calculate incentives, this is the more accurate approach if there is variance in the spaces for control types, LPD values, and occupancy schedules.



3.       Although BAM may not provide the most accurate predictions of energy usage, it may still be "legal" for EAC1 point calculation purposes.

David



David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates



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: Wednesday, May 23, 2012 2:41 PM
To: Bishop, Bill
Cc: eQuest Users; Oscar B.
Subject: Re: [Equest-users] Building area method ASHRAE 90.1

referencing this comment:  "The only obvious case for using the Building Area Method to determine modeled LPD is the case that Nick mentioned where lighting neither exists nor is specified."

or when the lighting designer/electrical engineer has higher lighting densities that exceed one (or more) of the space-by-space maximum allowable lpds but compensates for it by having lower lpds in other spaces such that the whole building lpd does not exceed the maximum allowable by the whole building method.




On 5/23/12 7:45 AM, Bishop, Bill wrote:
Building Area and Space-by-Space are not methods for designing lighting systems. They are prescriptive requirements for demonstrating lighting energy compliance in 90.1. The LPD allowances in Tables 9.5.1 and 9.6.1 do not need to be complied with if using energy modeling to demonstrate compliance for 90.1 and for LEED. (Only the Mandatory Provisions of 9.4 need to be met for the lighting design.) Energy modelers only need to know the lighting power and space use categorizations of the design as shown on the drawings (along with schedules and controls), not the process used to design it (which typically considers light levels in footcandles or lux).

I think that if a lighting system has been designed, a strong argument can be made that the space-by-space method needs to be used in both the proposed and baseline cases, and that lighting power needs to be entered individually for each space/zone.
                "If construction documents are complete, the proposed building lighting system power is modeled as shown on the design documents." (ASHRAE 90.1 User's Manual, p. G-17)
"The LPD for the proposed design is taken from the design documents for the building. The LPD specified in the models must correspond to the spaces within each thermal block." (ASHRAE 90.1 User's Manual, p. 11-14 and also p. G-18)
The only obvious case for using the Building Area Method to determine modeled LPD is the case that Nick mentioned where lighting neither exists nor is specified.

As Maria Karpman, Nick and Patrick have mentioned, you are likely to show higher energy savings using the Space-by-Space method. Beyond that, using Space-by-Space allows you to give valuable feedback to the design team, which I would argue is a responsibility of energy modelers. It is routine for me to point out areas of potential improvement of the lighting design in every project I model, based on the allowances in Table 9.6.1. "Yes, Ms. Architect, that is a lovely looking light fixture, but 2.6 W/ft2 of lounge lighting is more than twice the baseline allowance." I don't know how you give helpful feedback if you are just comparing two building-averaged lighting power densities.

Regards,
Bill



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