Table 12.5.1 Modeling Requirements for Calculating Design Energy Cost and Energy Cost Budget(Continued)
Proposed Design (Column A) Design Energy Cost (DEC)
Budget Building Design (Column B) Energy Cost Budget (ECB)
8. Thermal Blocks—HVAC Zones not Designed
Where the HVAC zones and systems have not yet been designed, thermal blocks shall be defined based on similar internal load densities, occupancy, lighting, thermal and space temperature schedules, and in combination with the following:
Separate thermal blocks shall be assumed for interior and perimeter spaces. Interior spaces shall be those located more than 15 ft from an exterior wall or semiexterior wall. Perimeter spaces shall be those located closer than 15 ft from an exterior wall or semiexterior wall. A separate thermal zone does not need to be modeled for areas adjacent to semiexterior walls that separate semiheated space from conditioned space.
Separate thermal blocks shall be assumed for spaces adjacent to glazed exterior walls or glazed semiexterior walls; a separate zone shall be provided for each orientation, except that orientations that differ by less than 45 degrees may be considered to be the same orientation. Each zone shall include all floor area that is 15 ft or less from a glazed perimeter wall, except that floor area within 15 ft of glazed perimeter walls having more than one orientation shall be divided proportionately between zones.
Separate thermal blocks shall be assumed for spaces having floors that are in contact with the ground or exposed to ambient conditions from zones that do not share these features.
Separate thermal blocks shall be assumed for spaces having exterior ceiling or roof assemblies from zones that do not share these features.
Residential spaces shall be modeled using at least one HVAC zone per dwelling unit except for those units with the same orientations, which may be combined into one thermal block. Corner units and units with roof or floor loads shall only be combined with units sharing these features.
Same as proposed design.
10. HVAC Systems
The HVAC system type and all related performance parameters, such as equipment capacities and efficiencies, in the proposed design shall be determined as follows:
Where a complete HVAC system exists, the model shall reflect the actual system type using actual component capacities and efficiencies.
Where an HVAC system has been designed, the HVAC model shall be consistent with design documents. Mechanical equipment efficiencies shall be adjusted from actual design conditions to the standard rating conditions specified in Section 6.4.1 if required by the simulation model. Where efficiency ratings include supply fan energy, the efficiency rating shall be adjusted to remove the supply fan energy from the efficiency rating in the budget building design. The equations in Section 12.5.2 shall not be used in the proposed design. The proposed design HVAC system shall be modeled using manufacturers’ full- and part-load data for the HVAC system without fan power.
Exception to (a) and (b): Where part-load performance of chillers in the proposed design is not available, and design temperature across the condenser is 10°F, the performance curves in Normative Appendix J for the appropriate chiller type and capacity, as referenced in Table J-1 shall be modeled for the specified chiller. When using performance curves from Normative Appendix J, chiller minimum part-load ratio (ratio of load to available capacity at a given simulation time step) and minimum compressor unloading ratio (part-load ratio below which the chiller capacity cannot be reduced by unloading and chiller is false loaded) shall be equal to 0.25. Simulation programs that do not use performance curves are permitted to use an alternative simulation method that results in the same performance as the curves described in Normative Appendix J.
Where no heating system exists or no heating system has been specified, the heating system shall be modeled as fossil fuel. The system characteristics shall be identical to the system modeled in the budget building design.
Where no cooling system exists or no cooling system has been specified, the cooling system shall be modeled as an air-cooled single-zone system, one unit per thermal block. The system characteristics shall be identical to the system modeled in the budget building design.
The HVAC system type and related performance parameters for the budget building design shall be determined from Figure 12.5.2, the system descriptions in Table 12.5.2-1 and accompanying notes, and in accord with rules specified in Section 12.5.2(a) through 12.5.2(k).
