Hot Water Distribution Loops
In the development of the RESNET 301-2019 Standard, this situation is addressed to determine the pipe length for a dwelling unit that utilizes a central DHW recirculation loop.
When modeling the dwelling unit, the Pipe Length is the horizontal distance from the central recirculation loop to the farthest fixture in the dwelling unit. The 301-2019 Standard requires the central pump kW to calculate the pump energy of the recirculation loop.
Clothes Dryers
Clothes Dryer annual energy use for the Rated Home shall be based on the clothes dryer located within the Rated Home. If no clothes dryer is located within the Rated Home, a clothes dryer in the nearest shared laundry room on the project site shall be used, if available for daily use by the occupants of the Rated Home. If the shared laundry room has multiple clothes dryers, the clothes dryer with the lowest EF or CEF shall be used. If no laundry equipment is in the building, the RESNET default clothes dryer should be modeled.
Clothes Washers
Clothes Washer annual energy use and daily hot water use for the Rated Home shall be determined as follows, and shall be based on the clothes washer located within the Rated Home. If no clothes washer is located within the Rated Home, a clothes washer in the nearest shared laundry room on the project site shall be used, if available for daily use by the occupants of the Rated Home. If the shared laundry room has multiple clothes washers, the clothes washer with the highest LER shall be used. If no laundry equipment is in the building, the RESNET default clothes dryer should be modeled.
Ventilation
Where a shared mechanical ventilation system serving more than one Dwelling Unit provides Dwelling-Unit Mechanical Ventilation, the following shall be used to determine the ventilation airflows in the Rated Home.
- Where shared ventilation supply systems provide a mix of recirculated and outdoor air, the supply ventilation airflow shall be adjusted to reflect the percentage of air that is from outside.
- Where the Dwelling-Unit Mechanical Ventilation system is a Supply System or an Exhaust System, and not a Balanced System nor a combination of systems, the ventilation rate shall be the value measured in the Rated Home or adjusted in accordance with the previous step.
- Where the Dwelling-Unit Mechanical Ventilation system is a Balanced System or a combination of systems, the system airflows shall be analyzed separately, in accordance with the previous steps.
For Attached Dwelling Units, for the purpose of determining air exchange rate in the Rated Home, an Exhaust System (unpaired with one or more Supply Systems) shall be considered as drawing excessive ventilation air from adjacent Dwelling Units, if the value of reduction factor Aext < 0.5. This type of system is not considered adequate for ventilation air.
Where the ventilation system is designed to serve the ventilation needs of more than one Dwelling Unit, the Rated Home kWh/y fan energy shall be calculated as a proportion of the entire system fan energy, using the system airflow, ventilation type, fan run time and the rated fan power of the shared system. The Rated Home ventilation fan energy shall be calculated as the fan power of the entire system multiplied by the ratio of Dwelling Unit airflow to the system airflow. Where the system fan power cannot be determined, 1 Watt/cfm shall be used. Where the Dwelling Unit airflow cannot be measured, the Rated Home shall use the same fanCFM as the reference home when calculating fan energy.
Update (June 2021): we are in the process of releasing new inputs for shared heating, cooling and water heating equipment and some of the guidance below changes with these new inputs.
For modeling of a dwelling unit with shared heating, cooling and water heating :
| Equipment Type | Same as central equipment |
| Fuel Type | Same as central equipment |
| Distribution Type | Same as central equipment |
| Motor Type | Same as central equipment |
| Efficiency | Same as central equipment |
| Capacity | If you specify the number of dwelling units served by the system, then enter the full capacity of the central equipment. If you do not specify the number of dwelling units served by the system, then enter the nominal capacity of the terminal distribution equipment (fan coil, terminal heat pump, radiator/convectors, etc). |
| Auxiliary Electric Energy (EAE) | For some equipment types you will no longer see EAE for shared equipment, in this case you will actually enter the power of the auxiliary systems (e.g. pump and/or fan depending on the type of system). Refer to RESNET Multifamily guidelines or 301-2019 Standard for auxiliary equipment usage based on type. |
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