2.4 Building Mechanical Systems

A space-conditioning system (also referred to as HVAC system) is made up of the heating subsystem (also referred to as heating unit or heating equipment or heating system), cooling subsystem (also referred to as cooling unit or cooling equipment or cooling system) (if any), the distribution subsystem details and fan subsystem (if any). Ventilation cooling systems and indoor air quality ventilation systems are defined at the building level for single-family dwellings or as part of the dwelling unit information for multi-family buildings (see also Sections 2.4.9 and 2.4.10.

2.4.1 Heating Subsystems

The heating subsystem describes the equipment that supplies heat to a space conditioning system. Heating subsystems are categorized according to the types shown in Table 7.

Proposed Design

The user selects the type and supplies inputs for the heating subsystem in the heating system data screen shown in Figure 3. The user inputs the appropriate rated heating efficiency factor. Except for heat pumps, the rated heating capacity is not used as a compliance variable by the compliance software. For heat pumps the user inputs the rated heating capacity at 47°F and 17°F for the heat pump compressor to be installed and the software sizes the backup electric resistance heat for use in the simulation.

Until there is an approved compliance option for ductless heat pumps (ductless mini-split, multi-split, and VRF systems) these systems are simulated as a minimum efficiency split system equivalent to the standard design and with default duct conditions.

Figure 3: Heating System Data Screen

Standard design

When electricity is used for heating, the heating equipment for the standard design is an electric split system heat pump with default ducts in the attic and a heating seasonal performance factor (HSPF) meeting the Appliance Efficiency Regulations (CEC-400-2014-009) requirements for split systems with default ducts in the attic. The standard design heat pump compressor size is determined by the software as the larger of the compressor size calculated for air conditioning load, or the compressor with a 47 degree F rating that is 75 percent of the heating load (at the heating design temperature).

When electricity is not used for heating, the equipment used in the standard design building is a gas furnace (or propane if natural gas is not available) with default ducts in the attic and an annual fuel utilization efficiency (AFUE) meeting the Appliance Efficiency Regulations minimum efficiency for central systems. When a proposed design uses both electric and non-electric heat, the standard design is a gas furnace.

Verification and Reporting

The proposed heating system type and rated efficiency are reported in the compliance documentation. For heat pumps, which are supplemented by electric resistance back-up heating, the rated heating capacity of each proposed heat pump is reported on the CF1R to verify that installed capacity is equal or larger than the capacities modeled at 47° and 17°.

Table 7: HVAC Heating Equipment Types

2.4.2 Combined Hydronic Space/Water Heating

Combined hydronic space/water heating is a system whereby a water heater is used to provide both space heating and water heating. Dedicated hydronic space-heating systems are also a modeling capability. Space-heating terminals may include fan coils, baseboards, and radiant surfaces (floors, walls or ceilings).

For combined hydronic systems, the water-heating portion is modeled in the normal manner. For space heating, an effective AFUE is calculated for gas water heaters. For electric water heaters, an effective HSPF is calculated. The procedures for calculating the effective AFUE or HSPF are described below.

Combined hydronic space conditioning cannot be combined with zonal control credit.

Proposed Design

When a fan coil is used to distribute heat, the fan energy and the heat contribution of the fan motor must be considered. The algorithms for fans used in combined hydronic systems are the same as those used for gas furnaces and are described in Chapter 3.

If a large fan coil is used and air distribution ducts are located in the attic, crawlspace or other unconditioned space, the efficiency of the air-distribution system must be determined using methods consistent with those described in Section 2.4.6 Duct efficiency is accounted for when the distribution type is ducted.

2.4.2.1 Large or Small Storage Gas Water Heater

When storage gas water heaters are used in combined hydronic applications, the effective AFUE is given by the following equation:

                                                                                    Equation 5

Where:

AFUEeff  = The effective AFUE of the gas water heater in satisfying the space heating load.

RE = The recovery efficiency (or thermal efficiency) of the gas storage water heater. A default value of 0.70 may be assumed if the recovery efficiency is unknown. This value is generally available from the Energy Commission appliance directory.

PL = Pipe losses (kBtu/h). This can be assumed to be zero when less than 10 feet of piping between the water heater storage tank and the fan coil or other heating elements are located in unconditioned space.

RI=The rated input of the gas water heater (kBtu/h) available from the Energy Commission appliance directory.

2.4.2.2 Instantaneous Gas Water Heater

When instantaneous gas water heaters are used in combined hydronic applications, the effective AFUE is given by the following equation:

                                                                                                                  Equation 6

Where:

AFUEeff  = The effective AFUE of the gas water heater in satisfying the space heating load.

EF = The rated Energy Factor of the instantaneous gas water heater.

2.4.2.3 Storage Electric Water Heater

The HSPF of storage water heaters used for space heating in a combined hydronic system is given by the following equations.

                     Equation 7

Where:

HSPF_eff = The effective HSPF of the electric water heater in satisfying the space heating load.

PL=Pipe losses (kBtu/h). This can be assumed to be zero when less than 10 feet of piping between the water heater storage tank and the fan coil or other heating elements are located in unconditioned space

kWi =The kilowatts of input to the water heater available from the Energy Commission’s appliance directory.

Standard Design

When electricity is used for heating, the heating equipment for the standard design is an electric split system heat pump with an HSPF meeting the Appliance Efficiency Regulations requirements for split systems. The standard design heat pump compressor size is determined by the software based on the compressor size calculated for the air conditioning system.

When electricity is not used for heating, the equipment used in the standard design building is a gas furnace (or propane if natural gas is not available) with default ducts in the attic and an AFUE meeting the Appliance Efficiency Regulations minimum efficiency for central systems. When a proposed design uses both electric and non-electric heat, the standard design is a gas furnace.

2.4.3 Special Systems – Hydronic Distribution Systems and Terminals

[Not yet implemented]

Proposed Design

This listing is completed for hydronic systems that have more than 10 feet of piping (plan view) located in unconditioned space. As many rows as necessary may be used to describe the piping system.

Standard Design

The standard design is established for a hydronic system in the same way as for a central system, as described in Section 2.4.1.

Verification and Reporting

A hydronic or combined hydronic system is reported on the CF1R.

Other information reported includes:

• Piping Run Length (ft). The length (plan view) of distribution pipe located in unconditioned space, in feet, between the primary heating/cooling source and the point of distribution.

• Nominal Pipe Size (in.). The nominal (as opposed to true) pipe diameter in inches.

• Insulation Thickness (in.). The thickness of the insulation in inches. Enter "none" if the pipe is uninsulated.

• Insulation R-value (hr-ft²-°F/Btu). The installed R-value of the pipe insulation. Minimum pipe insulation for hydronic systems is as specified in §150.0(j)

2.4.4 Ground-Source Heat Pump

A ground-source heat pump system, which uses the earth as a source of energy for heating and as a heat sink for energy when cooling, is simulated as a minimum efficiency split system equivalent to the standard design with default duct conditions in place of the proposed system. The mandatory efficiencies for ground-source heat pumps are a minimum coefficient of performance (COP) for heating and EER for cooling.

2.4.5 Cooling Subsystems

The cooling subsystem describes the equipment that supplies cooling to a space-conditioning system.

Figure 4: Cooling System Data

Proposed Design

Cooling subsystems are categorized according to the types shown in Table 8. The user selects the type of cooling equipment and enters basic information to model the energy use of the equipment. Enter the cooling equipment type and additional information based on the equipment type and zoning, such as the SEER and EER. For some types of equipment, the user may also specify that the equipment has a multi-speed compressor and if the system is zoned or not via checkboxes. For ducted cooling systems the cooling air flow from the conditioned zone through the cooling coil is input as CFM per ton. The rated cooling capacity is not a compliance variable.

Until there is an approved compliance option for ductless heat pumps (ductless mini-split, multi-split, and variable refrigerant flow (VRF) systems) these systems are simulated as a minimum efficiency split system equivalent to the standard design with default duct conditions.

See sections below for the details of specific inputs.

Standard Design

The cooling system for the standard design building is a non-zonal control split system air conditioner or heat pump meeting the minimum requirements of the Appliance Efficiency Regulations. The standard design system shall assume verified refrigerant charge in climate zones 2 and 8 through 15 for all ducted split systems, ducted package systems, mini-split, multi-split, and VRF systems. Mandatory fan efficacy is assumed in all climate zones.

Table 8: HVAC Cooling Equipment Descriptors

Verification and Reporting

Information shown on the CF1R includes cooling equipment type and cooling efficiency (SEER and/or EER). Measures requiring verification are listed in the HERS verification section of the CF1R.

2.4.5.1 Verified Refrigerant Charge or Fault Indicator Display

Proper refrigerant charge is necessary for electrically driven compressor air conditioning systems to operate at full capacity and efficiency. Software calculations set the compressor efficiency multiplier to 0.90 to account for the effect of improper refrigerant charge or 0.96 for proper charge.

Proposed Design

The software allows the user to indicate if systems will have diagnostically tested refrigerant charge or a field-verified fault indicator display (FID). This applies only to ducted split systems and packaged air conditioners and heat pumps.

Standard Design

The standard design building is modeled with either diagnostically tested refrigerant charge or a field-verified FID if the building is in climate zone 2 or 8-15, and refrigerant charge verification is required by §150.1(c) and Table 150.1-A for the proposed cooling system type.

Verification and Reporting

These features require field verification or diagnostic testing and are reported in the HERS required verification listings on the CF1R. Details on refrigerant charge measurement are discussed in Reference Residential Appendix RA3.2. Information on the requirements for FIDs is located in Reference Joint Appendix JA6.1.

Table 9: Summary of Air Conditioning Measures Requiring Verification

2.4.5.2 Verified System Airflow

Adequate airflow from the conditioned space is required to allow ducted air conditioning systems to operate at their full efficiency and capacity. Efficiency is achieved by the air distribution system design, by improving the efficiency of motors or air distribution systems with less resistance to airflow. Software calculations account for the impact of airflow on sensible heat ratio and compressor efficiency.

A value less than 350 cfm/ton (minimum 150 cfm/ton) is a valid input only if zonally controlled equipment is selected and multi-speed compressor is not selected.

The mandatory requirement in Section 150.0(m)13 is for an air-handling unit with a verified airflow rate greater than or equal to 350cfm/ton. Credit for a higher airflow rate requires diagnostic testing using procedures in Reference Residential Appendix RA3.3.

For Single Zone Systems:

• Installers may elect to use an alternative to HERS verification of 350 cfm/ton: HERS verification of a return duct design that conforms to the specification given in Table 150.0-B or C.

• The return duct design alternative is not an input to the compliance software but must be documented on the certificate of installation.

• If a value greater than 350 cfm/ton is modeled for compliance credit, the alternative return duct design method using Table 150.0-B or C is not allowed for use in demonstrating compliance.

• Multispeed or variable-speed compressor systems must verify airflow rate (cfm/ton) for system operation at the maximum compressor speed and the maximum air handler fan speed.

For Zonally Controlled Systems:

• The Table 150.0-B or C return duct design alternative is not allowed for zonally controlled systems.

• Multispeed, variable-speed and single-speed compressor systems must all verify airflow rate (cfm/ton) by operating the system at maximum compressor capacity and maximum system fan speed with all zones calling for conditioning.

Single-speed compressor systems must also verify airflow rate (cfm/ton) in every zonal control mode.

Proposed Design

The default cooling airflow is 150 cfm/ton for a system with zonally controlled selected and multi-speed compressor not selected (single speed). The default cooling airflow is 350 cfm/ton for all other ducted cooling systems. Users may model a higher-than-default airflow and receive credit in the compliance calculation if greater verified system airflow is diagnostically tested using the procedures of Reference Residential Appendix RA3.

Standard Design

The standard design shall assume a system that complies with mandatory (Section 150.0) and prescriptive (Section 150.1) requirements for the applicable climate zone.

Verification and Reporting

The airflow rate verification compliance target (cfm or cfm/ton) is reported in the HERS required verification listings of the CF1R. When there is no cooling system it is reported on the CF1R as a special feature.

2.4.5.3 Verified Air-Handling Unit Fan Efficacy

The mandatory requirement in §150.0(m)13 is for an air-handling unit fan efficacy less than or equal to 0.58 Watts/cfm as verified by a HERS rater. Users may model a lower fan efficacy (W/cfm) and receive credit in the compliance calculation if the proposed fan efficacy value is diagnostically tested using the procedures in Reference Residential Appendix RA3.3.

For Single Zone Systems:

• Installers may elect to use an alternative to HERS verification of 0.58 Watts/cfm: HERS verification of a return duct design that conforms to the specification given in or C.

• The return duct design alternative is not an input to the compliance software, but must be documented on the Certificate of Installation.

• If a value less than 0.58 Watts/cfm is modeled by the software user for compliance credit, the alternative return duct design method using Table 150.0-B or C is not allowed for use in demonstrating compliance.

• Multispeed or variable-speed compressor systems must verify fan efficacy (Watt/cfm) for system operation at the maximum compressor speed and the maximum air handler fan speed.

For Zonally Controlled Systems:

• The Table 150.0-B or C return duct design alternative is not allowed for zonally controlled systems

• Multispeed, variable-speed and single-speed compressor systems must all verify fan efficacy (Watt/cfm) by operating the system at maximum compressor capacity and maximum system fan speed with all zones calling for conditioning.

• Single speed compressor systems must also verify fan efficacy in every zonal control mode.

Proposed Design

The software shall allow the user to enter the fan efficacy. The default mandatory value is 0.58 W/cfm. Users may, however, specify a lower value and receive credit in the compliance calculation if verified and diagnostically tested using the procedures of Reference Appendices, Residential Appendix RA3.3

If no cooling system is installed a default value of 0.58 W/cfm is assumed.

Standard Design

The standard design shall assume a verified fan efficacy complying with the mandatory requirement for less than or equal to 0.58 Watts/cfm.

Verification and Reporting

For user inputs lower than the default mandatory 0.58 Watts/cfm, fan efficacy is reported in the HERS required verification listings of the CF1R.

For default mandatory 0.58 Watts/cfm, the choice of either fan efficacy or alternative return duct design according to Table 150.0-B or C is reported in the HERS required verification listings of the CF1R.

When there is no cooling system it is reported on the CF1R as a special feature.

2.4.5.4 Verified Energy Efficiency Ratio (EER)

Proposed Design

Software shall allow the user the option to enter an EER rating for central cooling equipment. For equipment that is rated only with an EER (room air conditioners), the user will enter the EER. The Appliance Efficiency Regulations require a minimum SEER and EER for central cooling equipment. Only if a value higher than a default minimum EER is used is it reported as a HERS verified measure.

Standard Design

The standard design for central air-conditioning equipment is 11.7 EER.

Verification and Reporting

EER verification is only required if higher than 11.7 EER is modeled. The EER rating is verified using rating data from AHRI Directory of Certified Product Performance at www.ahridirectory.org or another directory of certified product performance ratings approved by the Energy Commission for determining compliance. Verified EER is reported in the HERS required verification listings on the CF1R.

2.4.5.5 Verified Seasonal Energy Efficiency Ratio (SEER)

Proposed Design

The software allows the user to specify the SEER value.

Standard Design

The standard design is based on the default minimum efficiency SEER for the type of cooling equipment modeled in the proposed design, based on the applicable Appliance Efficiency Regulations. For central cooling equipment, the minimum efficiency is 14 SEER and 11.7 EER.

Verification and Reporting

If a SEER higher than the default minimum efficiency is modeled in software, the SEER requires field verification. The higher than minimum SEER rating is verified using rating data from AHRI Directory of Certified Product Performance at www.ahridirectory.org or another directory of certified product performance ratings approved by the Commission for determining compliance.

Verified SEER is reported in the HERS required verification listings on the CF1R.

2.4.5.6 Verified Evaporatively-Cooled Condensers

Proposed Design

Software shall allow users to specify an evaporatively-cooled condensing unit. The installation must comply with the requirements of RA4.3.2 to ensure the predicted energy savings are achieved. This credit must be combined with verified refrigerant charge testing, EER, and duct leakage testing.

Standard Design

The standard design is based on a split system air conditioner meeting the requirements of Section 150.1(c) and Table 150.1-A.

Verification and Reporting

An evaporatively-cooled condensing unit, verified EER, and duct leakage testing are reported in the HERS required verification listings on the CF1R.

2.4.5.7 Evaporative Cooling

Evaporative cooling technology is best suited for dry climates where direct and/or indirect cooling of the supply air stream can occur without compromising indoor comfort. Direct evaporative coolers are the most common system type currently available, but provide less comfort and deliver more moisture to the indoor space. They are assumed to be equivalent to a minimum split system air conditioner. The evaporative cooling modeling methodology addresses two performance issues. The first performance issue is the increase in indoor relative humidity levels during periods with extended cooler operation. Since modeling of indoor air moisture levels is beyond the capability of simulation models, a simplified algorithm is used to prohibit evaporative cooler operation during load hours when operation is expected to contribute to uncomfortable indoor conditions. The algorithm disallows cooler operation when outdoor wet bulb temperatures are 70°F, or above. The second performance issue relates to evaporative cooler capacity limitations. Since evaporative coolers are 100 percent outdoor air systems, their capacity is limited by the outdoor wet bulb temperature. Each hour with calculated cooling load, the algorithm will verify that the cooling capacity is greater than the calculated cooling load.

Proposed Design

Software shall allow users to specify one of three types of evaporative cooling: (1) direct evaporative cooler is the most commonly available system type, (2) indirect, or (3) indirect-direct. Product specifications and other modeling details are found in the Energy Commission appliance directory for evaporative cooling. Direct system types are assigned an efficiency of 13 SEER (or minimum appliance efficiency standard for split system cooling). The default system type is evaporative direct. For indirect or indirect-direct, select the appropriate type, from the Energy Commission appliance directory and input a 14 EER as well as the air flow and media saturation effectiveness or cooling effectiveness from the Energy Commission appliance directory.

Standard Design

The standard design is based on a split system air conditioner meeting the requirements of Section 150.1(c) and Table 150.1-A.

Verification and Reporting

When a direct evaporative cooling system is modeled, the system type and minimum efficiency are shown in the appropriate section of the CF1R. When indirect or indirect-direct evaporative cooling is modeled, the EER verification is shown in the HERS verification section of the CF1R along with the system type, air flow and system effectiveness.

2.4.6 Distribution Subsystems

If multiple HVAC distribution systems serve a building each system and the conditioned space it serves may be modeled in detail separately or the systems may be aggregated together and modeled as one large system. If the systems are aggregated together they must be the same type and all meet the same minimum specifications.

For the purposes of duct efficiency calculations, the supply duct begins at the exit from the furnace or air handler cabinet.

Figure 5: Distribution System Data

2.4.6.1 Distribution Type

Fan-powered, ducted distribution systems that can be used with most heating or cooling systems. When ducted systems are used with furnaces, boilers, or combined hydronic/water heating systems the electricity used by the fan is calculated. R-value and duct location are specified when a ducted system is specified.

Proposed Design

The compliance software shall allow the user to select from the basic types of HVAC distribution systems and locations 'listed in Table 10. For ducted systems, the default location of the HVAC ducts and the air handler are in conditioned space for multi-family buildings and in the attic for all other buildings.

The software will allow users to select default assumptions or specify any of the verified or diagnostically tested HVAC distribution system conditions in the proposed design (see Figure 5 and Table 11), including duct leakage target, R-value, supply and return duct area, diameter and location.

Table 10: HVAC Distribution Type and Location Descriptors

Table 11: Summary of Verified Air Distribution Systems

Standard Design

The standard heating and cooling system for central systems is modeled with non-designed air distribution ducts located as described in Table 12, with duct leakage as specified in Table 15. The standard design duct insulation is determined by Package A (assuming attic option B) as R-6 in climate zones 3 and 5-7, and R-8 in climate zones 1-2, 4 and 8-16. The standard design building is assumed to have the same number of stories as the proposed design for purposes of determining the duct efficiency.

Table 12: Summary of Standard Design Duct Location

This table is applicable only when the standard design system has air distribution ducts as determined in Table 10.

Verification and Reporting

Distribution type, location, R-value, and whether tested and sealed will be shown on the CF1R. If there are no ducts, this is shown as a special feature on the CF1R. Any duct location other than attic (for example, crawl space) is shown as a special feature on the CF1R. Ducts in crawl space or basement shall include a special feature note if supply registers are located within 2 feet of the floor. Measures that require HERS verification will be shown in the HERS required verification section of the CF1R.

2.4.6.2 Duct Location

Duct location determines the external temperature for duct conduction losses, the temperature for return leaks, and the thermal regain of duct losses.

Proposed Design

If any part of the supply or return duct system is located in an unconditioned attic, that entire duct system is modeled with an attic location.  If no part of the supply or return duct system is located in the attic, but the duct system is not entirely in conditioned space, it is modeled in the unconditioned zone, which contains the largest fraction of its surface area. If the supply or return duct system is located entirely in conditioned space the duct system is modeled in conditioned space.

For ducted HVAC systems with some or all ducts in unconditioned space, the user specifies the R-value and surface area of supply and return ducts, and the duct location.

Duct location and areas other than the defaults shown in Table 13 may be used following the verification procedures in Reference Appendices, Residential Appendix RA3.1.4.1.

Standard Design

The standard design duct location is determined from the building conditions (see Table 12).

Verification and Reporting

Duct location is reported on the CF1R. Ducts in conditioned space in other than multi-family buildings or low leakage ducts in conditioned space are reported in the HERS Required Verification listing on the CF1R.

Default duct locations are as shown in Table 13. The duct surface area for crawl space and basement applies only to buildings or zones with all ducts installed in the crawl space or basement. If the duct is installed in locations other than crawl space or basement, the default duct location is “Other.” For houses with two or more stories 35 percent of the default duct area may be assumed to be in conditioned space as shown in Table 13.

The surface area of ducts located in conditioned space is ignored in calculating conduction losses.

Table 13: Location of Default Duct Area

2.4.6.3 Duct Surface Area

The supply-side and return-side duct surface areas are treated separately in distribution efficiency calculations. The duct surface area is determined using the following methods.

2.4.6.4 Default Return Duct Surface Area

Default return duct surface area is calculated using:

                                                             Equation 8

Where K_r (return duct surface area coefficient) is 0.05 for one-story buildings and 0.1 for two or more stories.

2.4.6.5 Default Supply Duct Surface Area

Standard Design

The standard design and default proposed design supply duct surface area is calculated using Equation 10.

                                                           Equation 9

Where K_s (supply duct surface area coefficient) is 1 for one-story buildings and 0.65 for two or more stories.

2.4.6.6 Supply Duct Surface Area for Less Than 12 feet of Duct In Unconditioned Space

Proposed Design

For proposed design HVAC systems with air handlers located outside the conditioned space but with less than 12 linear feet of duct located outside the conditioned space including air handler and plenum, the supply duct surface area outside the conditioned space is calculated using Equation 11. The return duct area remains the default for this case.

                                                               Equation 10

2.4.6.7 Diagnostic Duct Surface Area

Proposed designs may claim credit for reduced surface area using the procedures in Reference, Residential Appendix RA3.1.4.1

The surface area of each duct system segment shall be calculated based on its inside dimensions and length. The total supply surface area in each unconditioned location (attic, attic with radiant barrier, crawl space, basement, other) is the sum of the area of all duct segments in that location. The surface area of ducts completely inside conditioned space need not be input in the compliance software and is not included in the calculation of duct system efficiency. The area of ducts in floor cavities or vertical chases that are surrounded by conditioned space and separated from unconditioned space with draft stops are also not included.

2.4.6.8 Bypass Duct

Section 150.1(c)13 prohibits use of bypass ducts unless a bypass duct is otherwise specified on the certificate of compliance. A bypass duct may be needed for some single speed outdoor condensing unit systems. The software allows users to specify a bypass duct for the system. Selection of a bypass duct does not trigger changes in the ACM modeling defaults, but verification by a HERS rater is required utilizing the procedure in Reference Residential Appendix Section RA3.1.4.6.

Note: specification of a single-speed condensing unit for the system will trigger a default airflow rate value of 150 cfm/ton for the calculations which reduces the compliance margin as compared to systems that model 350 cfm/ton. Users may model airflow rates greater than 150 cfm/ton and receive credit in the calculations as described in Section 2.4.5.2.

Proposed Design

Software shall allow users to specify whether a bypass duct is or is not used for a zonally controlled forced air system.

Standard Design

The standard design is based on a split system air conditioner meeting the requirements of Section 150.1(c) and Table 150.1-A. The system is not a zonally-controlled system.

Verification and Reporting

An HVAC system with zonal control, and whether the system is assumed to have a bypass duct or have no bypass duct, is reported in the HERS required verification listings on the CF1R.

2.4.6.9 Duct System Insulation

For the purposes of conduction calculations in both the standard and proposed designs, 85 percent of the supply and return duct surface is assumed to be duct material at its specified R-value and 15 percent is assumed to be air handler, plenum, connectors and other components at the mandatory minimum R-value.

The area weighted effective R-value is calculated by the compliance software using Equation 12 and including each segment of the duct system that has a different R-value.

                                                                     Equation 11

Where:

R_eff = Area weighted effective R-value of duct system for use in calculating duct efficiency,
(h-ft²-°F/Btu)

A_N = Area of duct segment n, square feet

R_n = R-value of duct segment n including film resistance, (duct insulation rated R + 0.7),
(h-ft²-°F/Btu)

Proposed Design

The software user inputs the R-value of the proposed duct insulation and details. The default duct thermal resistance is based on Table 150.1-A, Attic Option B, which is R-6 in climate zones 3 and 5-7, R-8 in zones 1-2, 4, and 8-16.

Duct location and duct R-value are reported on the CF1R. Credit for systems with mixed insulation levels, non-standard supply and return duct surface areas, or ducts buried in the attic require the compliance and diagnostic procedures in Reference Residential Appendix RA3.1.4.1.

If a verified duct design is selected, non-standard values for the supply-duct surface area and the return-duct surface area may be input by the user. A verified duct design must be verified by a HERS rater according to the procedures in Reference Residential Appendix RA3.1.4.1.1. Supply and return duct R-values, location and areas are reported on the CF1R when non-standard values are specified.

Standard Design

Package A required duct insulation R-values for the attic option B, for applicable climate zone are used in the standard design.

Verification and Reporting

Duct location, duct R-value, supply, and return duct areas are reported on the CF1R.

2.4.6.10 Buried Attic Ducts

Ducts partly or completely buried in blown attic insulation in dwelling units meeting the requirements for verified quality insulation installation may take credit for increased effective duct insulation.

The duct design shall identify the segments of the duct that meet the requirements for being buried, and these are separately input into the computer software. Ducts to be buried shall have a minimum of R-6.0 duct insulation prior to being buried. The user shall calculate the correct R-value based on the modeled attic insulation R-value, insulation type, and duct size for ducts installed on the ceiling, and whether the installation meets the requirements for deeply buried ducts for duct segments buried in lowered areas of ceiling.

The portion of duct runs directly on or within 3.5 inches of the ceiling gypsum board and surrounded with blown attic insulation of R-30 or greater may take credit for increased effective duct insulation as shown in Table 14. Credit is allowed for buried ducts on the ceiling only in areas where the ceiling is level and there is at least 6 inches of space between the outer jacket of the installed duct and the roof sheathing above.

Duct segments deeply buried in lowered areas of ceiling and covered by at least 3.5 inches of insulation above the top of the duct insulation jacket may claim effective insulation of R-25 for fiberglass insulation and R-31 for cellulose insulation.

Proposed Design

The software shall allow the user to specify the effective R-value of buried ducts. This feature must be combined with duct sealing and verified quality insulation installation. The default is no buried ducts.

Standard Design

The standard design has no buried ducts

Verification and Reporting

Buried duct credit is reported in the HERS required verification listing on the CF1R.

Table 14: Buried Duct Effective R-values

2.4.6.11 Duct/Air Handler Leakage

The total duct/air handler leakage shown in Table 15 is used in simulating the duct system. The supply duct leakage for each case is the table value times 0.585 The return leakage is the table value times 0.415.

Proposed Design

For each ducted system the software user specifies one of the duct/air handler leakage cases shown in Table 15.

Standard Design

For ducted systems the standard design is sealed and tested duct systems in existing dwelling units or new duct systems.

Verification and Reporting

Sealed and tested duct systems are 'listed in the HERS verification section of the CF1R.  Duct leakage is measured in accordance with procedures and values specified in Reference Appendices, Residential Appendix RA3.

2.4.6.12 Low Leakage Air Handlers

A low leakage air handler may be specified as well as a lower duct leakage value (see Section 2.4.6.11). Installation requires installing one of the list of approved low leakage air handling units published by the Energy Commission. The manufacturer certifies that the appliance complies with the requirements of Reference Joint Appendices 9.2.1, 9.2.2, 9.2.3, and 9.2.4.

Table 15: Duct/Air Handler Leakage

Proposed Design

Credit can be taken for installation of a factory sealed air handling unit tested by the manufacturer and certified to the Energy Commission to meet the requirements for a low leakage air-handler. Field verification of the air handler model number is required.

Standard Design

The standard design has a normal air handler.

Verification and Reporting

A low leakage air handler is reported on the compliance report and field verified in accordance with the procedures specified in Reference Appendices, Residential Appendix RA3.1.4.3.9.

2.4.6.13 Verified Low-Leakage Ducts in Conditioned Space

Proposed Design

For ducted systems the user may specify that all ducts are entirely in conditioned space and the software will model the duct system with no leakage and no conduction losses.

Standard Design

The standard design has ducts in the default location.

Verification and Reporting

Systems that have all ducts entirely in conditioned space are reported on the compliance documents and this is verified by measurements showing duct leakage to outside conditions is equal to or less than 25 cfm when measured in accordance with Reference Appendices, Residential Appendix RA3.

2.4.7 Space Conditioning Fan Subsystems

Fan systems move air for air conditioning, heating and ventilation systems. The software allows the user to define fans to be used for space conditioning, indoor air quality and ventilation cooling.

Indoor air quality and ventilation cooling are discussed in Section 2.4.9 and 2.4.10.

Proposed Design

For the space conditioning fan system, the user selects the type of equipment and enters basic information to model the energy use of the equipment. For ducted central air conditioning and heating systems the fan efficacy default is the mandatory minimum verified efficacy of 0.58 W/cfm (also assumed when there is no cooling system).

Standard Design

The standard design fan shall meet the minimum Section 150.1(c) and Table 150.1-A requirements.

Verification and Reporting

Minimum verified fan efficacy is a mandatory requirement for all ducted cooling systems. Fan efficacy is reported in the HERS Required Verification listings on the CF1R.

2.4.8 Space Conditioning Systems

This section describes the general procedures for heating and cooling systems in low-rise residential buildings. The system includes the cooling system, the heating system, distribution system, and mechanical fans.

If multiple systems serve a building, each system and the conditioned space it serves may be modeled in detail separately or the systems may be aggregated together and modeled as one large system. If the systems are aggregated together they must be the same type and all meet the same minimum specifications.

2.4.8.1 Multiple System Types Within Dwelling

Proposed Design

For proposed designs using more than one heating system type, equipment type or fuel type, and the types do not serve the same floor area, the user shall zone the building by system type.

Standard Design

The standard design shall have the same zoning and heating system types as the proposed design.

Verification and Reporting

The heating system type of each zone is shown on the CF1R.

2.4.8.2 Multiple Systems Servings Same Area

If a space or a zone is served by more than one heating system, compliance is demonstrated with the most time-dependent valuation (TDV) energy-consuming system serving the space or the zone. For spaces or zones that are served by electric resistance heat 'in 'addition to other heating systems, the electric resistance heat is deemed to be the most TDV energy-consuming system unless the supplemental heating meets the Exception to Section 150.1(c)6.  See eligibility criteria in Residential Compliance Manual Section 4.2.2 for conditions under which the supplemental heat may be ignored.

For floor areas served by more than one cooling system, equipment, or fuel type, the system, equipment, and fuel type that satisfies the cooling load is modeled.

2.4.8.3 No Cooling

Proposed Design

When the proposed design has no cooling system, the proposed design is required to model the standard design cooling system defined in Section 150.1(c) and Table 150.1-A. Since the proposed design system is identical to the standard design system, there is no penalty or credit.

Standard Design

The standard design system is the specified in Section 150.1(c) and Table 150.1-A for the applicable climate zone.

Verification and Reporting

No cooling is reported as a special feature on the CF1R.

2.4.8.4 Zonally Controlled Forced-Air Cooling Systems

Zonally controlled central forced-air cooling systems must be able to deliver, in every zonal control mode, an airflow to the dwelling of > 350 CFM per ton of nominal cooling capacity, and operating at an air-handling unit fan efficacy of < 0.58 W/CFM. This is a HERS verified measure, complying with Residential Appendix RA3.3.

An exception allows multispeed or variable speed compressor systems, or single speed compressor systems to meet the mandatory airflow (cfm/ton) and fan efficacy (Watt/cfm) requirements by operating the system at maximum compressor capacity and system fan speed with all zones calling for conditioning, rather than in every zonal control mode.

Proposed Design

The user selects zonally controlled as a cooling system input.

Standard Design

The standard design building does not have zonally controlled cooling system.

Verification and Reporting

Zonally controlled forced air cooling systems are required to have the system bypass duct status verified by a HERS rater according to the procedures in Reference Residential Appendix RA3.1.4.6, and the fan efficacy and airflow rate are required to be verified according to the procedures in RA3.3.

2.4.9 Indoor Air Quality Ventilation

The standards require mechanical ventilation that complies with ASHRAE Standard 62.2 to provide acceptable indoor air quality for all newly constructed buildings and additions greater than 1,000 square feet. ASHRAE Standard 62.2 provides several ways to comply with the requirement for mechanical ventilation and these are described in the Residential Compliance Manual.

For the purposes of estimating the energy impact of this requirement in compliance software, the minimum ventilation rate is met either by a standalone indoor air quality (IAQ) fan system or a central air handler fan system that can introduce outdoor air. In many cases, this energy is substantially compliance neutral because the standard design is typically set equal to the proposed design.

The simplest IAQ fan system is an exhaust fan/bathroom fan that meets the criteria in ASHRAE Standard 62.2 for air delivery and low noise. More advanced IAQ fan systems that have a supply or both supply and exhaust fans are also possible. To calculate the energy use of standalone IAQ fan systems, the systems are assumed to be on continuously.

To calculate the energy use of central fan integrated ventilation, the systems are assumed to be on for at least 20 minutes each hour as described below. The fan flow rate and fan power ratio may be different than the values used when the system is on to provide for heating or cooling depending on the design or controls on the IAQ ventilation portion of the system.

The minimum ventilation rate for continuous ventilation of each single-family dwelling unit is given in Equation 12.

            Q_fan = 0.01A_floor + 7.5(N_br + 1)                                             Equation 12  

Where:

Q_fan = fan flow rate in cubic feet per minute (cfm),

A_floor =floor area in square feet (ft²),

N_br = number of bedrooms (not less than one).

The minimum ventilation rate for continuous ventilation of each multi-family dwelling unit is given in Equation 14.

Q_fan = 0.03A_floor + 7.5(N_br + 1)                                           Equation 13

Where:

Q_fan = fan flow rate in cubic feet per minute (cfm),

A_floor = floor area in square feet (ft²),

N_br = number of bedrooms (not less than one).

Proposed Design

The proposed design shall incorporate a mechanical ventilation system fan. This requirement is a mandatory measure. The compliance software allows the user to specify the IAQ ventilation type (see Table 16) and the cfm of outdoor ventilation air which must be equal to or greater than what is required by ASHRAE Standard 62.2. The default is a standalone exhaust system meeting standard 62.2.

Standard Design

The mechanical ventilation system in the standard design is the same as the proposed design. The air flow rate is equal to the proposed design. The sensible heat recovery effectiveness is 0.  For standalone IAQ fan systems, the fan power ratio is equal to the proposed design value or 1.2 W/cfm, whichever is smaller. For central air handler fans, the fan power ratio is 0.58 W/cfm of central system airflow in ventilation mode.

Verification and Reporting

The required ventilation rate to comply with ASHRAE Standard 62.2 and the means to achieve compliance are indicated on the CF1R. The IAQ system characteristics are reported in the HERS required verification listing on the CF1R. The diagnostic testing procedures are in RA3.7.

Table 16: IAQ Fans

Table 17: CF1R Report – Indoor Air Quality

2.4.10 Ventilation Cooling System

Ventilation cooling systems operate at the dwelling unit level using fans to bring in outside air to cool the house when this can reduce cooling loads and save cooling energy. Ventilation cooling systems such as whole house fans involve window operation and attic venting. Central fan ventilation cooling systems use the HVAC duct system to distribute ventilation air. Ventilation cooling systems operate according to the schedule and setpoints shown in Table 19. Ventilation cooling systems that exhaust air through the attic require a minimum the larger of 1 ft² of free attic ventilation area per 750 cfm of rated capacity for relief or the manufacturer specifications (see Section 150.1(c)12 of the standards).

Proposed Design

Software allows the user to specify whether a ventilation cooling system is included in conditioned and living zones (see Table 18). The user can specify the actual fan specifications or a default prescriptive whole house fan with a capacity of 1.5 CFM/ft² of conditioned floor area when there is a ventilated attic.

Standard Design

The standard design building for a newly constructed building or for an addition greater than 1,000 square feet has a whole house fan in climate zones 8 through 14 and no ventilation cooling in other climate zones (see Section150.1(c) and Table 150.1-A) The whole house fan has 1.5 CFM/ft² of conditioned floor area with 1 square foot of attic vent free area for each 750 CFM of rated whole house fan air-flow CFM.

Verification and Reporting

A ventilation cooling system is a special feature and the size and type is reported on the CF1R. A variable speed ventilation cooling system requires HERS verification of the make/model number and controls using the CF2R-MECH-30.

Table 18: Ventilation Cooling Fans