COMNET Commercial Buildings Energy Modeling Guidelines and Procedures
Comments Submitted
The following comments have been submitted:
Justification for Change:
As a minimum, COMNET needs to use the full fuel cycle, or source energy, (taking all energy forms to the point of extraction such as wellhead or minemouth) as the basis of its energy savings procedure and calculations. If an additional COMNET goal (not stated in the 3 shown above) is to shift loads, then and only then should it ADD a second requirement that incorporates time of use costs – as long as such strategies don’t increase annual source energy consumption associated with the building. If an additional goal is to reduce GHG emissions (not stated in the 3 shown above), an additional GHG compliance requirement can be added.
COMNET is also inherently flawed because it links directly to ASHRAE Standard 90.1-2001 and -2007, both of which are site energy based and permit tradeoffs only AFTER the fuel and technology choices are made.
As an example, when using ASHRAE Standard 90.1 criteria, a building design that includes an electric resistance water heater will comply, but will have much HIGHER full fuel cycle energy consumption and GHG emissions compared to a fully compliant gas, propane, or oil storage water heater (55% higher GHG emissions using national average values according to EPA http://www.aham.org/ht/a/GetDocumentAction/id/33223 ). This perversely incentivizes the designer to choose the less expensive qualifying technology, promoting fuel switching in the design decision away from more full fuel cycle energy efficient and lower GHG emitting technologies and providing an unfair and unearned market advantage to qualifying technologies such as electric resistance water heating that are lower cost/lower full fuel cycle efficient and higher GHG emitting. This is a key reason both ASHRAE in its Building Energy Labeling Program http://www.buildingeq.com/index.php/resources http://www.buildingeq.com/files/ABELFAQ.pdf and EPA in its full fuel cycle energy-based Energy Star Buildings rating system http://www.energystar.gov/ia/business/evaluate_performance/General_Overview_tech_methodology.pdf http://www.energystar.gov/ia/business/evaluate_performance/site_source.pdf http://www.energystar.gov/ia/business/tools_resources/new_bldg_design/2003_CBECSPerformanceTargetsTable.pdf http://www.energystar.gov/ia/business/evaluate_performance/Emissions_Supporting_Doc.pdf use a single statistically derived reference building by building category.
Until ASHRAE fixes its flawed standard, COMNET will be flawed unless it chooses to shift its approach slightly but meaningfully from the ASHRAE approach.
Proposed Change:
The following is offered as a way to address this flaw in an equitable manner by creating an efficient, achievable baseline building for source energy savings and GHG emission reduction comparisons in COMNET.
The heating system for the baseline building is as follows:
Fuel type: natural gas
Equipment type: System 11
Efficiency: Warm air furnaces, gas fired
The cooling system for the baseline building is as follows:
Fuel type: electricity
Equipment type: System 11
Efficiency: Air conditioners, Air cooled
The service water heating system for the baseline building is as follows:
Fuel type: natural gas
Efficiency: Storage water heaters, Gas
These 3 provisions effectively establish a single reference design building performance requirement for source energy calculations BEFORE making the technology and fuel choices for the proposed building. This then allows the designer to get the appropriate credit for putting innovative full fuel cycle energy efficient technologies that reduce GHG emissions into the proposed design (including equitable treatment of renewable energy options and waste heat recovery options).
The revised baseline building text is a rational approach to creating a “single reference building” concept for comparison of alternatives that is key to implementing both full fuel cycle energy and GHG emission savings calculations.
The revised baseline allows flexible technology and fuel choice decisions as well as an equitable full fuel cycle energy-based treatment of advanced renewable and multi-fuel technology options to improve the full fuel cycle energy efficiency and GHG emissions of the proposed design. It eliminates the technically unsupportable equivalency in the ASHRAE tables currently provided to less full fuel cycle energy efficient and higher GHG emitting technologies such as electric resistance heating and water heating technologies and fossil-fueled single effect absorption cooling technologies. It provides more equitable treatment of CHP, distributed generation, and waste heat recovery, and renewables. It is the most technically defensible methodology when using full fuel cycle energy and GHG emissions as compliance requirements. Otherwise full fuel cycle energy and GHG emissions calculations are only conversion factors with very limited design and societal impact.
If COMNET is concerned about inappropriate tradeoffs between envelopes and equipment (i.e., short life high efficiency equipment resulting in a less energy efficient long life envelope), consider adding the following:
The total annual energy loss from the building thermal envelope shall be less than or equal to the total annual energy loss from a building thermal envelope that meets the requirements of Table 11.3.1 of ASHRAE Standard 90.1.
The added text provides a minimum overall envelope loss requirement for all proposed designs that is at least equivalent to the ASHRAE budget building design requirements. The proposed text also eliminates tradeoffs between mechanical or lighting system options and envelope options while still permitting design flexibility across opaque elements and fenestration. As long as the combined total energy loss from the thermal envelope meets the stringency of the prescriptive envelope in Table 11.3.1 of ASHRAE Standard 90.1, the designer can still trade off individual envelope components such as fenestration and roofs to meet the overall requirement. It decouples the envelope from the mechanical and electrical systems, acknowledging the significantly different service lives of these major building components.
If GHG emissions are of interest, then the following additional requirement is offered for consideration:
GHG emissions associated with the proposed building design ≤ GHG emissions associated with the baseline building design.
The added text establishes a rational basis for GHG emissions compliance requirements to make sure a proposed design that focuses on innovative energy efficient technologies does not have the unintended consequence of increasing GHG emissions relative to a the baseline building.