[Bldg-sim] Percent Energy Savings

[Nathan Miller]

Of course this gets into the whole debate about the absolute accuracy of
energy modeling. Appendix G makes it clear that it does not predict actual
energy usage, which is what you would be trying to compare to if you use
energy use intensities (ie- kbtu/sf/yr). It is much more difficult and
intensive to set up an energy model intending to show you are better than
a real-world EUI value rather than trying to be X% better than ASHRAE
baseline. 

 

At this point, given the pressure to make energy modeling more affordable
(not to spend many extra hours trying to nail down absolutes), it seems
reasonable to me to use the percent better methodology. 

 

Of course we all look forward to the day when we have cheap, easy to use
tools that can actually predict total building energy consumption, but I'm
not holding my breath. 

 

Nathan Miller

Senior Energy Engineer/Mechanical Engineer

direct: 206.788.4577

fax: 206.285.7111 

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Andy hoover
Sent: Wednesday, March 04, 2009 12:20 PM
To: 'Varkie C Thomas'
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Percent Energy Savings

 

The highlighted yellow and that entire paragraph nail it for me.  It
results in showing/taking the most effective steps to decrease energy
usage which should be the objective, regardless of percentage.  Percent
savings is always very very subject to manipulation.

 

Andy  

 

Andy Hoover

Principal

The BEST Consultant, Inc.

Office: 678-200-7648

Fax:678-827-0574

Cell: 678-793-1159

 

www.thebestconsultant.com

 

 

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From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Varkie C
Thomas
Sent: Wednesday, March 04, 2009 11:04 AM
To: Varkie C Thomas
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Percent Energy Savings

 

I received a few responses to this message from outside the USA sent
directly to me.  Below is the message again with some additional points in
red.  The sections highlighted in yellow is from one of the responses


  _____  

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Varkie C
Thomas
Sent: 2009-03-03 18:26
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Percent Energy Savings

 

ASHRAE Std90 for the baseline is already stringent and specifies the
commonly used systems & plants based on building type and size.  Based on
the CCGT building, high percentage energy savings for LEED certification
can be achieved with low-rise buildings with a high exposure to floor
surface areas to locate PV panels, high but efficient glass to wall area
for day-lighting, the use of GSHP (which requires a large site area which
may not be available in city blocks), and low common energy consuming
systems in baseline and proposed which increases "percentage" energy
savings.  

 

A school building is low-rise, is low in process loads (increases %
savings) and is high in occupancy ventilation which allows for air-to-air
heat recovery. It operates only during the day increasing the impact of
day-lighting. It is closed in summer, reducing the annual cooling load and
increases the impact of solar heating during the rest of the year in cold
climates.  So it is possible to achieve zero energy usage.  

 

The choices are limited in the case of inner city high-rise buildings.
Today's high-rise office building design tries to maximize the glass
percentage which increases the impact of day-lighting.  The glass could
have PV properties with a very small overall efficiency of converting
light to 110V electricity.  The ASHRAE Std90 baseline for Systems and
Plants for such a building is considered normal design.  UFAD and other
options are not typical.  The proposed envelope has to offset the 40%
Window-Wall-Ratio specified by ASHRAE.  If the office building envelope is
used for a hospital or hotel, which operate 8760 hours/year, then the
percent energy savings will go down.  

 

High percent energy savings does not therefore necessarily mean a better
or optimized designed building in terms of the client's interests.
Percent energy savings should therefore not be the criteria for energy
efficient building design.  It should be based on Energy Conservation
Measures (ECM) used for the given building that are more energy efficient
compared to ASHRAE Std90 for the given building type and size which
usually results in increased first costs. The ECMs are going to be
different for different types of buildings in different locations.  If the
ECM used is inappropriate, then the client pays a price for the high
percent energy savings.

 

In my opinion the way to express energy efficiency would be energy per
unit area.  Occupancy per unit area has to be defined for different types
of buildings (office, hotel, retail, hospital, etc.) and energy efficiency
should also take into account location based on HDD & CDD.  Energy per
Person will account for overall energy efficiency of buildings &
transportation when designing sustainable townships.

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