[Bldg-sim] Percent Energy Savings

[Todd Lagus]

I think that this issue has been brought up before, but in some cases, energy comparisons to ASHRAE 90.1 should also be looked at closely.  In particular, for a ground source heat pump, or any heat pump with electricity as its heating source, the ASHRAE baseline system calls for electric resistance heat.  This automatically makes the heat pump more attractive than it would, say, against a VAV system with hydronic heat and a high efficiency boiler, at least in terms of ASHRAE 90.1.  The heat pump will get you more LEED points, but will not necessarily be the most energy efficient system for your customer.

Todd Lagus, EIT
Mechanical Engineer
Sebesta Blomberg
sebesta.com | P  651.634.7236 | F  651.634.7400

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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 2:20 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<http://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
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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: 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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