eQuest Floor Multiplier vs System Multiplier

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Fellow eQuesters;
Am running into some confusion on the use of multipliers; and how the do/don't appear to cascade out to HVAC Systems. If I create a 10 story building in the DD Wizard with 'use multipliers' checked and 'HVAC System per Level', this creates a building with the area of the 10 story building, on 3 floors, with 3 HVAC systems. Granted the middle floor has a floor multiplier of 8, which is linked to the spaces and zones - but not the systems. Thus, it is really 3 AHU's - top, bottom, and a much larger AHU for the middle floor(s).

I have been unable to find anything in the documentation that say 'oh, by the way, this is floor multipliers don't multiple HVAC Systems' or 'Don't use this if you really do have multiple HVAC system." Which is both odd, but unsurprising all at the same time.

This approach could impact model performance, especially if performance curves do not scale in a multiplier fashion or if one is unaware of this behavior and looks up incorrect efficiencies based on the 'multiplied' unit's capacity. It also impacts reporting to LEED/Code if they see 3 systems (from my example) and not the 10 AHU's/RTU's scheduled.

Question is two part:

1. is this behavior correct with other's experience?
2. There is no means within eQuest to specify a Systems multiplier?

I see where multipliers could be used, but that isn't my applciation here.

Thanks,
DARIC R ADAIR PE, CEM, BEMP
Mechanical Engineer, Energy Analyst

Henderson Engineers
daric.adair at hendersonengineers.com

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Daric Adair's picture
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Hi Daric!

The behavior you've described in your first paragraph has me nodding - sounds expected. But I think you're in luck today!

If you want a 'middle,' multiplied shell representing 7 levels to be served by 7 equally sized systems, then you need to specify NUMBER-OF-UNITS (and not be using a zonal system type to enable this input).

Nicholas Caton2's picture
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Hi Daric,

I've struggled with this issue a lot too when I first started modeling;
what do you mean floor multipliers don't also apply to the HVAC systems?!

is this behavior correct with other?s experience?

Correct me if I'm wrong, but I believe HVAC system capacities should be
reflective of all respective zones *including *multipliers, rather than of
a single zone with no multipliers. For example, 30000 BTU/H should be
entered for the cooling capacity of an HVAC system with a zone of floor
multiplier 3, rather than 10000 BTU/H for the same zone.

There is no means within eQuest to specify a Systems multiplier?

I don't think there is a way to specify an HVAC system multiplier in
eQuest.

Hope this helps,
Calvin

On Tue, Aug 27, 2019 at 3:47 PM Daric Adair via Equest-users <

--
*Calvin Chu, MFBA, EIT*
Energy Modeler
646-780-5536 | cchu at brightpower.com
www.brightpower.com

11 Hanover Square, 21st Floor
New York, NY 10005

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To further clarify,

FLOOR and SPACE multipliers consistently will multiply whatever loads are associated before the assigned system(s) deal with those loads.

Where both SPACE and FLOOR multipliers co-exist, their effects are additive, which is to say they will multiply each other (i.e. a SPACE with a multiplier of 2 in a FLOOR with a multiplier of 3 will send the space?s loads times 6 to the SYSTEM assigned to that SPACE).

Small nitpick to correct some loose language, for any newer users following along: once we leave the wizard mode and get into detailed edits, FLOORs are not assigned to SYSTEMS. If you choose ?system per floor? or similar in wizards, the result is that a family of SPACEs/ZONEs representative of one floor together are assigned to a single system.

A SYSTEM, unless provided a multiplier, will auto-size (or else report unmet hours with specified capacities) commensurate with the loads being seen after considering all FLOOR and SPACE multipliers.

If however you also provide a multiplier to the SYSTEM, you will then divide the summed and multiplied loads from the SPACES. This again can be done with or without specifying system capacities. With Calvin?s example, if you specify a SYSTEM multiplier of 3, then you can specify the individual system @ 10,000 Btu/h (with other capacities such as airflow specified in kind to reflect an individual unit).

To go on the record WRT the topic of accuracy here, I think the average LEED/Code reviewer has enough on their plates to be catching/tracking nuances like this. It feels contingent on the energy modeler to make a decision, stick with it, and document accordingly ? make it plain whenever you do or don?t use multipliers, and be ready to demonstrate the intended effects in the outputs (for yourself or others). In some cases, representing many systems as one would represent a meaningful departure in terms of accuracy, but in others I would consider it a perfectly fine & justifiable simplification... that?s to say this sort of decision is pretty contextual, and I wouldn?t push someone to always err one way or the other.

~Nick

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