This group of building descriptors applies to all cooling systems.
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Cooling Source |
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Applicability |
All systems |
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Definition |
The source of cooling for the system. The choices are:
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Units |
List (see above) |
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Input Restrictions |
As designed |
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Baseline Rules |
The baseline building cooling source is direct expansion for systems 1-6 and chilled water for systems 7-8 and 11-13. Systems 9 and 10 have no cooling capability. See Table 3.7-2. |
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Total Cooling Capacity |
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Applicability |
All cooling systems |
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Definition |
The total cooling capacity (both sensible and latent) of a cooling coil or packaged DX system at AHRI test conditions. The building descriptors defined in this chapter assume that the fan is modeled separately, including any heat it adds to the air stream. The cooling capacity specified by this building descriptor should not consider the heat of the fan. |
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Units |
kBtu/h |
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Input Restrictions |
As designed. Fan energy shall be modeled separately from cooling, unless the fan cycles, so for packaged equipment that has the fan motor in the air stream the Total Cooling Capacity shall be adjusted for the heat generated by the fan using the following procedure . (Equation 3.7.5.1-1) $$Q_{Net} = Q_{Rated} - Q_{Fan}$$ (Equation 3.7.5.1-2) $$Q_{Fan}=\frac{Q_{Rated}}{COP_{cooling}}-\frac{Q_{Rated}}{COP_{nfcooling}}$$
where
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Baseline Rules |
The total cooling capacity of the baseline building system is oversized by 15%. Sizing calculations shall be based on 1% dry-bulb and 1% wet-bulb design conditions. |
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Sensible Cooling Capacity |
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Applicability |
All cooling systems |
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Definition |
The sensible heat cooling capacity of the coil or packaged equipment at ARI conditions. The building descriptors defined in this chapter assume that the fan is modeled separately, including any heat it adds to the air stream. The cooling capacity specified by this building descriptor should not consider the heat of the fan. |
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Units |
kBtu/h |
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Input Restrictions |
As designed. For packaged equipment that has the fan motor located in the air stream such that it adds heat to the cooled air, the software shall adjust the sensible cooling capacity as follows: (Equation 3.7.5.1-3) $$Q_{s.adj} = Q_{s,rated} + BHP_{supply} \times 2.545$$ ==Where
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Baseline Rules |
The sensible cooling capacity of the baseline building is oversized by 15%. Sizing calculations shall be based on 1% dry-bulb and 1% wet-bulb design conditions. |
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Cooling Capacity Adjustment Curves |
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Applicability |
All cooling systems |
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Definition |
A curve that represents the available total cooling capacity as a function of cooling coil and/or condenser conditions. The common form of these curves is given as follows: (Equation 3.7.5.1-4) $$Q_{t,available}=CAP\_FT \times Q_{t,adj}$$ For air cooled direct expansion (Equation 3.7.5.1-5) $$CAP\_FT=a + b \cdot t_{wb}+ c \cdot t_{wb}^{2}+ d \cdot t_{odb}+ d \cdot t_{odb}^{2}+f\cdot t_{wb}\cdot t_{odb}$$ For water cooled direct expansion (Equation 3.7.5.1-6) $$CAP\_FT=a + b \cdot t_{wb}+ c \cdot t_{wb}^{2}+ d \cdot t_{wt}+ d \cdot t_{wt}^{2}+f\cdot t_{wb}\cdot t_{wt}$$ For chilled water coils (Equation 3.7.5.1-7) $$CAP\_FT=a + b \cdot t_{wb}+ c \cdot t_{wb}^{2}+ d \cdot t_{db}+ d \cdot t_{db}^{2}+f\cdot t_{wb}\cdot t_{db}$$ Where
Note: if an air-cooled unit employs an evaporative condenser, todb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit. |
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Units |
Data structure |
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Input Restrictions |
As designed. The equations and coefficients given above are the default. |
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Baseline Rules |
The default curves shall be used for the baseline HVAC system. |
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Coil Bypass Factor |
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Applicability |
All cooling systems |
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Definition |
The ratio of air that bypasses the cooling coil at design conditions to the total system airflow. |
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Units |
Ratio |
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Input Restrictions |
The rated building shall use the factors given below. Table 3.7.5.1-1: Default Coil Bypass Factors
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Baseline Rules |
Same as the rated building |
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Coil Bypass Factor Adjustment Curves |
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Applicability |
All DX cooling systems (optional input) |
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Definition |
Adjustments for the amount of coil bypass due to the following factors:
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Units |
Data structure |
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Input Restrictions |
Where applicable, the following default values shall be used for the coil bypass factor adjustment curve: (Equation 3.7.5.1-8) $$CBF_{adj}=CBF_{Rated} \times COIL\_BF\_FFLOW \times COIL\_BF\_FT \times COIL\_BF\_FPLR$$ (Equation 3.7.5.1-9) $$COIL\_BF\_FFLOW = a + b\cdot CFMR + c \cdot CFMR^{2} + d \cdot CFMR^{3}$$ (Equation 3.7.5.1-10) $$COIL\_BF\_FT = a + b\cdot T_{wb} + c \cdot T_{wb}^{2} + b\cdot T_{db} + c \cdot T_{db}^{2} +f\cdot T_{wb} \cdot T_{db}$$ Equation 3.7.5.1-11) $$COIL\_BF\_FPLR = a + b\cdot PLR$$ Where
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Baseline Rules |
The above default values shall be used when applicable. |
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This group of building descriptors applies to all cooling systems.
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Cooling Source |
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Applicability |
All systems |
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Definition |
The source of cooling for the system. The choices are:
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Units |
List (see above) |
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Input Restrictions |
As designed |
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Baseline Building |
The baseline building cooling source is shown in Table 58. See Section 3.1.2 of this document for HVAC system mapping. Table 58. Cooling Source for Baseline Building System
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Total Cooling Capacity |
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Applicability |
All cooling systems |
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Definition |
The total cooling capacity (both sensible and latent) of a cooling coil or packaged DX system at Air-Conditioning, Heating and Refrigeration Institute (AHRI) conditions. The building descriptors defined in this chapter assume that the fan is modeled separately, including any heat it adds to the air stream. The cooling capacity specified by this building descriptor should not consider the heat of the fan. Note that most CHW coils, and coils in custom DX equipment, particularly those serving high outside air fractions, will have capacities provided in HVAC schedules and submittals at entering air conditions very different from AHRI conditions. For these units, when entered in software using the following simulation methods, custom performance curves will generally be needed, or the capacities and efficiencies recalculated at the AHRI conditions. |
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Units |
kBtu/h |
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Input Restrictions |
As designed. For packaged equipment that has the fan motor in the air stream such that it adds heat to the cooled air, the software shall adjust the total cooling capacity as follows:
Where: Qt,net,rated = The net total cooling capacity of a packaged unit as rated by AHRI (Btu/h) Qt,gross,rated = The AHRI rated total cooling capacity of a packaged unit (Btu/h) Qt,fan, rated = The heat generated by the fan and fan motor (if fan motor is in airstream) at AHRI rated conditions If the gross and net total cooling capacities at AHRI conditions are known, the fan heat at rated conditions is the difference between the two values. If the either the gross or net total cooling capacity is unknown, the fan heat at rated conditions shall be accounted for by using equation below :
Source: Standard 90.1-2019 User’s Manual (unpublished) |
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Baseline Building |
The total cooling capacity of the systems in the baseline building is oversized by 15%. Sizing calculations shall be based on the heating design day and cooling design day conditions, as defined in Section 3.2.3 of this document. Oversizing would be carried out at zone level where the sizing parameters would be applied to the zone design cooling coil loads, but not the airflow rates. |
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Sensible Cooling Capacity |
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Applicability |
All cooling systems |
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Definition |
The sensible cooling capacity of the coil or packaged equipment at Air-conditioning and Refrigeration Institute (ARI) conditions. The building descriptors defined in this chapter assume that the fan is modeled separately, including any heat it adds to the air stream. The cooling capacity specified by this building descriptor should not consider the heat of the fan. Note that the sensible heat ratio (SHR) used by some energy simulation tools can be calculated from the sensible cooling capacity and total cooling capacity: SHR = Sensible Cooling Capacity / Total Cooling Capacity |
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Units |
kBtu/h |
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Input Restrictions |
As designed. For packaged equipment that has the fan motor located in the air stream such that it adds heat to the cooled air, the software shall adjust the sensible cooling capacity as follows:
Where: Qs,adj = The adjusted sensible cooling capacity of a packaged unit (kBtu/h) Qs,rated = The ARI rated sensible cooling capacity of a packaged unit (kBtu/h) BHPsupply = The supply fan brake horsepower (bhp) in the proposed building design. If the number of UMLH in the proposed design exceeds 300, the software shall warn the user to resize the equipment. |
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Baseline Building |
The sensible cooling capacity of the systems serving baseline building is oversized by 15%. Sizing calculations shall be based on the heating design day and cooling design day conditions, as defined in Section 3.2.3 of this document |
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Cooling Capacity Adjustment Curves |
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Applicability |
All cooling systems |
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Definition |
The sensible cooling capacity of the coil or packaged equipment at ARI conditions. The building descriptors defined in this chapter assume that the fan is modeled separately, including any heat it adds to the air stream. The cooling capacity specified by this building descriptor should not consider the heat of the fan. Note that the SHR used by some energy simulation tools can be calculated from the sensible cooling capacity and total cooling capacity: SHR = Sensible Cooling Capacity / Total Cooling Capacity A curve that represents the available total cooling capacity as a function of rated cooling coil capacity and/or condenser conditions. The common form of these curves is given as follows:
For air-cooled DX
For water-cooled DX
For chilled water coils
Where: Qt,available = Available cooling capacity at specified evaporator and/or condenser conditions (thousand British thermal units per hour [MBH]) Qt,adj = Adjusted capacity at ARI conditions (Btu/h) (see Equation 5) CAP_FT = A multiplier to adjust Qt,adj twb = The entering coil wet-bulb temperature (°F) tdb = The entering coil dry-bulb temperature (°F) twt = The water supply temperature (°F) todb = The outside-air dry-bulb temperature (°F) Note: If an air-cooled unit employs an evaporative condenser, todb is the effective dry-bulb temperature of the air leaving the evaporative cooling unit. Software may represent the relationship between cooling capacity and temperature in ways other than the equations given above. Table 59. Cooling Capacity Curve Coefficients
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Units |
Data structure |
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Input Restrictions |
As designed. The equations and coefficients given above are the defaults. |
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Baseline Building |
Default curves will be used for baseline building |
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Coil Latent Modeling Method |
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Applicability |
All DX cooling systems |
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Definition |
The method of modeling coil latent performance at part-load conditions |
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Units |
List |
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Input Restrictions |
One of the following values: Bypass factor – used by DOE-2 based programs NTU-effectiveness – used by EnergyPlus |
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Baseline Building |
Same as proposed |
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Coil Bypass Factor |
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Applicability |
All DX cooling systems (optional input) |
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Definition |
The ratio of air that bypasses the cooling coil at design conditions to the total system airflow |
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Units |
Ratio |
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Input Restrictions |
Prescribed values as shown in Table 60 Table 60. Default Coil Bypass Factors
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Baseline Building |
Defaults |
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Coil Bypass Factor Adjustment Curve |
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Applicability |
All DX cooling systems (optional input) |
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Definition |
Adjustments for the amount of coil bypass due to the following factors:
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Units |
Data structure |
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Input Restrictions |
Where applicable, prescribed (fixed) simulation engine defaults based on HVAC system type. The following default values shall be used for the adjustment curves:
Where: CBFrated = The coil bypass factor at ARI rating conditions CBFadj = The coil bypass factor adjusted for airflow and coil conditions CFMR = The ratio of airflow to design airflow COIL-BF-FFLOW = A multiplier on the rated coil bypass factor to account for variation in airflow across the coil (take coefficients from Table 61) COIL-BF-FT = A multiplier on the rated coil bypass factor to account for a variation in coil entering conditions (take coefficients from Table 62) COIL-BF-FPLR = A multiplier on the rated coil bypass factor to account for the part load ratio (take coefficients from Table 63) Twb = The entering coil wet-bulb temperature (°F) Tdb = The entering coil dry-bulb temperature (°F) PLR = Part load ratio And the coefficients are listed in the tables below. Table 61. Coil Bypass Factor Airflow Adjustment Factor
Table 62. Coil Bypass Factor Temperature Adjustment Factor
Table 63. Coil Bypass Factor Part Load Adjustment Factor
Source: (CEC 2013) |
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Baseline Building |
Use defaults as described above |
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