[Equest-users] Baseline Fan Energy Very High

Tue Jul 23 06:40:12 PDT 2019

To add to what David wrote below, in my experience one of the most common
reason for excessively high fan energy savings is a substantial reduction
in fan runtime due to change from continuously running fans in the baseline
to cycling fans in the proposed design. You wrote below that this is a
small commercial project, so the baseline is probably System 3 – PSZ and
has constant volume (CV) fans. You can calculate the Effective Full Load
Hours (EFLH) of the baseline fan as a ratio of the annual fan energy (kWh)
to fan peak load (kW) from SS-P report. For baseline System 3, EFLH should
be slightly higher than the number of hours per year that your building is
occupied since, following 90.1 App G, fans must run continuously when
building is occupied and cycle with load during unoccupied hours.

If proposed systems are also CV, they should have very similar EFLH unless
there is a DOAS in the proposed design. If there is no DOAS but you get
significantly different EFLH between baseline and proposed, double-check
that you haven’t accidentally changed the proposed Indoor Fan Mode from
continuous to intermittent. You can also figure it out by looking at SS-L
report – for continuously running CV systems, only the “100+” bin would
have hours listed in it. If you see hours in other bins, it means that your
CV system is modeled as cycling with load.

Maria

*From:* Equest-users <equest-users-bounces at lists.onebuilding.org> *On
Behalf Of *David Eldridge via Equest-users
*Sent:* Monday, July 22, 2019 12:49 PM
*To:* equest-users at onebuilding.org
*Subject:* Re: [Equest-users] Baseline Fan Energy Very High

What’s the ratio of the kW/cfm for the two cases, and the ratio of total
cfm?

i.e. as you are proposing, if the two systems run at the same sequence of
operation to get a 6x factor of reduction you’d have to be some combination
of 2x the cfm in the baseline and 3x the power use per CFM – if that’s not
accurate then the likely culprit is the sequence which may be allowing the
proposed case to run fewer hours or running much longer at part-load if the
proposed case has that capability – maybe add a report to see the load
profile for the two cases.

Another check is that unmet hours and temperature plots in the SS-O report
were consistent between the two cases providing equal comfort. Reviewing
the SS-O can help you find an instance where the temperature control
sequence isn’t equivalent resulting in more runtime for the baseline case.

A third check – were the two cases showing reasonable increase in
efficiency for the proposed case of the other end-uses for cooling,
heating, lighting, etc – verify there isn’t a stray heat gain causing
increased run-time in one case.

David

*David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP*

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*From:* Equest-users [mailto:equest-users-bounces at lists.onebuilding.org
<equest-users-bounces at lists.onebuilding.org>] *On Behalf Of *Jeff Ross-Bain
via Equest-users
*Sent:* Sunday, July 21, 2019 2:05 PM
*To:* equest-users at lists.onebuilding.org
*Subject:* [Equest-users] Baseline Fan Energy Very High

Hi All,

To those of you who regularly and graciously contribute your knowledge to
this site, we all owe you a huge debt of gratitude. Thank you.

I am stumped. Usually, in my experience, following the standard Baseline
process of establishing [ASHRAE max] fan power and applying that value to
eQuest in kW/cfm, the resulting difference between Baseline and Proposed is
evident but not super big.

In this case, on a small project with 6 x under 5-ton split HP systems, the
Baseline fan energy use is, like, over 6 times bigger than the Proposed. I
have exhausted every check and iteration I can think of and cannot find out
why or how this occurs. As-is, the energy savings is incredible on fan
power alone and I know it is not right.

Any thoughts or similar experiences with this circumstance?

Thanks!

*Jeff Ross-Bain, BCxP, BEMP, LEED Fellow, MSc*

President

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