Systems and methods for ventilating a building

1. A method for providing ventilation to a building, the method comprising:

installing a rooftop heating ventilation and air conditioning system comprising:

an economizer comprising an outdoor damper, which is for receiving ambient air from outside the heating ventilation and air conditioning system, and having ventilation vents for receiving ambient air from outside, and having a return damper, and

a barometric relief damper for allowing air to exit the rooftop heating ventilation and cooling system when operating in an economizer mode and that allows at least some leakage of ambient air from outside into the heating ventilation and air conditioning system when not in the economizer mode;

determining a pressure differential proximate the barometric relief damper;

determining-a first outdoor airflow leaking into the rooftop heating ventilation and air conditioning system through the barometric relief damper when not in the economizer mode, wherein this step comprises:

determining a pressure differential across the barometric relief damper, and

determining the first outdoor airflow leaking into the rooftop heating ventilation and air conditioning system based on the pressure differential proximate the barometric relief damper and based on a relationship between the pressure differential proximate the barometric relief damper and outdoor air entering the barometric relief damper;

subtracting the first outdoor airflow from a minimum outdoor airflow for the building to determine a second outdoor airflow for the outdoor damper; and

introducing into the rooftop heating ventilation and air conditioning system through the outdoor damper ambient air from outside the second outdoor airflow.

2. The method of claim 1 , wherein the step of introducing into the rooftop heating ventilation and air conditioning system through the outdoor damper ambient air from outside in an amount of the second outdoor airflow comprises adjusting the outdoor damper to obtain the second outdoor airflow based on an established relationship between the pressure differential across the outdoor damper and the flow rate through the outdoor damper.

3. The method of claim 1 , wherein the step of determining a pressure differential across the barometric relief damper comprises: using a pressure sensor proximate the outdoor damper to approximate the pressure differential proximate the barometric relief damper.

4. The method of claim 1 , wherein the step of determining a pressure differential across the barometric relief damper comprises: determining with a pressure sensor proximate the outdoor damper a pressure across the outdoor damper, D POD , and further adjusting the pressure based on an established relationship of pressure proximate the outdoor damper and proximate the barometric relief damper.

5. The method of claim 4 , wherein the established relationship of pressure proximate the outdoor damper and proximate the barometric relief damper comprises: D PBaro =D POD +D Prd , where D Prd =DC 2 *ρ air *(SupplAir−VenAir) 2 , where DC is a damper coefficient for the outdoor damper and which is a function of damper position, ρ air is the density of air, SupplAir is the supply airflow rate in CFM, VenAir is the outdoor airflow through the outdoor damper and D PBaro is pressure differential across the barometric relief damper.

6. A rooftop heating ventilating and cooling system for providing conditioned air to a building comprising:

an economizer comprising an outdoor damper, which is for receiving outdoor air, and a return damper;

an actuator coupled to the outdoor damper and the return damper for positioning blades of the outdoor damper and the return damper;

a barometric relief damper for allowing air to exit the system when in an economizer mode and allowing at least some outdoor air to leak into the heating ventilating and cooling system through the barometric relief damper when not in an economizer mode;

at least one pressure sensor for measuring a pressure differential across a portion of the economizer;

an evaporator in a conditioning flow path;

a heating element in the conditioning flow path;

a return damper; and

a controller associated with the actuator for controlling the outdoor damper and the return damper, wherein the controller includes at least one processor and at least one memory and is configured to:

determine a pressure differential across the barometric relief damper based on data from at least one pressure sensor;

determine a first outdoor flow, which is leaking through the barometric relief damper, based on an established relationship between the pressure differential proximate the barometric relief damper and outdoor air entering the barometric relief damper;

subtract the first outdoor airflow from a minimum outdoor airflow to determine a second outdoor airflow for the outdoor damper;

determine a pressure differential across the outdoor damper based on data from at least one pressure sensor; and

adjusting the outdoor damper to obtain the second outdoor airflow based on an established relationship between the pressure differential across the outdoor damper and the flow rate through the outdoor damper to adjust the outdoor damper to obtain the second outdoor airflow.

7. The system of claim 6 , wherein the step of determining a pressure differential across the barometric relief damper comprises: using a pressure sensor proximate the barometric relief damper to directly measure the pressure differential proximate the barometric relief damper.

8. The system of claim 6 , wherein the step of determining a pressure differential across the barometric relief damper comprises: using a pressure sensor proximate the outdoor damper to approximate the pressure differential across the barometric relief damper.

9. The system of claim 6 , wherein the step of determining a pressure differential, D PBaro , across the barometric relief damper comprises: using a pressure sensor proximate the outdoor damper to determine a pressure across the outdoor damper, D POD , and further estimating the pressure across the barometric relief damper based on an established relationship between pressure proximate the outdoor damper and proximate the barometric relief damper.

10. The system of claim 9 , wherein the established relationship of pressure proximate the outdoor damper and proximate the barometric relief damper comprises: D PBaro =D POD +D Prd , where D Prd =DC 2 *ρ air *(SupplAir−VenAir) 2 , where DC is a damper coefficient for the outdoor damper and which is a function of damper position, ρ air is the density of air, SupplAir is the supply airflow rate in CFM, and VenAir is the outdoor airflow through the outdoor damper.