Shared Multifamily Mechanical Ventilation Systems (ANSI 301-2019)

According to endnote (k) of Table 4.2.2(1) of RESNET/ANSI 301-2019, mechanical ventilation systems serving more than one dwelling unit shall be handled in the following way:

(k) Where a shared mechanical Ventilation system serving more than one Dwelling Unit provides any Dwelling-Unit Mechanical Ventilation, the following shall be used to determine the Ventilation airflows in the Rated Home. 

1. 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. 
2. 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. 
3. 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.

What happens if the mechanical ventilation system also provides heating and cooling load? 

When considering centralized mechanical ventilation systems, it is common to find systems that offer integrated heating and cooling systems (i.e., Dedicated Outdoor Air Systems - DOAS). This article explains how to model mechanical ventilation systems with preconditioned air. First model the mechanical ventilation system as explained before. In addition, model a separate heating system that represents the heating provided by the ventilation system.

If the system is independent of other existing heating and cooling systems:

• % Heating Load = [Output Capacity Ventilation Heating]/[Sum of Output Capacities of all other heating systems].

• The rest is manufacturer data. 

If the DOAS heating and cooling is served by a central system (shared boiler or chiller/cooling tower), the design loads must be included in the total heating load of the central system. In this article, we explained how to model a heating system with a shared boiler and water-loop heat pump. The total heating load of a dwelling unit consisted of the shared boiler and the dwelling water-loop heat pump. However, in this case the DOAS ventilation system also contributes to the heating. 

• Model three separate heating systems that represent the heating provided by the shared boiler, the water-loop heat pump and the ventilation system.

• When calculating the load served by the system, consider two systems: heat delivered by shared boiler + water-loop heat pump, and heat delivered by shared boiler + DOAS ventilation system. 

• Model the shared boiler and the water-loop heat pump following this article. 
  

• Since the ventilation system acts as a heat distribution system, the heating load can be assigned directly to the boiler. Then model the heating ventilation system as another shared boiler with the appropriate heating load and boiler efficiency. Add a forced air distribution system to represent the DOAS. Model the heating load following this article.