Understanding HVAC Calculations: A Comprehensive Guide to Calculating Building Parameters for Efficient Heating and Cooling
Zone Floor Area: This parameter refers to the total floor area of the zone in square feet (sq ft). It is used to determine the heating and cooling loads for the space. The sample calculation for this parameter could be:
Assuming the zone floor area is 1000 sq ft, the value of this parameter would be:
Zone Floor Area = 1000 sq ft
Zone Population: This parameter refers to the number of people occupying the zone. It is used to determine the ventilation requirements for the space. The default value for this parameter is typically 1 person per 150 sq ft of floor area. The sample calculation for this parameter could be:
Assuming the zone floor area is 1000 sq ft, the default value for zone population would be:
Zone Population = 1000 sq ft / 150 sq ft/person = 6.67 people (rounded up to 7 people)
Zone Air Distribution Effectiveness: This parameter refers to the efficiency of the air distribution system in delivering conditioned air to the zone. It is used to calculate the amount of primary airflow needed to achieve the desired temperature and air quality in the zone. The value of this parameter ranges from 0 to 1, with higher values indicating more efficient air distribution. The sample calculation for this parameter could be:
Assuming the zone air distribution effectiveness is 0.8, the value of this parameter would be:
Zone Air Distribution Effectiveness = 0.8
Zone Outdoor Airflow: This parameter refers to the amount of outdoor air that needs to be supplied to the zone for ventilation purposes. It is calculated based on the occupancy and the ventilation rate required per person or per unit area of the zone. The sample calculation for this parameter could be:
Assuming the ventilation rate required is 20 cfm per person and there are 7 people in the zone, the zone outdoor airflow would be:
Zone Outdoor Airflow = 20 cfm/person x 7 people = 140 cfm
Zone Discharge Airflow: This parameter refers to the total airflow leaving the zone, including both the supply air and any return air. It is used to balance the airflow in the HVAC system. The sample calculation for this parameter could be:
Assuming the zone discharge airflow is 500 cfm, the value of this parameter would be:
Zone Discharge Airflow = 500 cfm
Zone Primary Airflow: This parameter refers to the amount of supply air needed to achieve the desired temperature and air quality in the zone. It is calculated based on the heating and cooling loads of the space and the zone air distribution effectiveness. The sample calculation for this parameter could be:
Assuming the heating load of the space is 20,000 BTU/hr, the cooling load is 30,000 BTU/hr, and the zone air distribution effectiveness is 0.8, the zone primary airflow would be:
Zone Primary Airflow = (20,000 BTU/hr + 30,000 BTU/hr) / (1.08 x 1.1 x 1.2 x 1.2 x 1.2) = 27,249 cfm
The conversion factor used to convert BTU/hr to cfm varies depending on the temperature and humidity conditions of the space.
Zone Secondary Recirculation Fraction: This parameter refers to the fraction of return air that is recirculated back into the zone after passing through a secondary air handling unit, such as a heat recovery ventilator. It is used to calculate the total amount of supply air needed for the space.