Economizer having damper modulation
A system having a mixed air box with inputs of return air from a space or spaces of a building, and of outside air. The mixed air box may have an output of discharge air to the space or spaces of the building. The air from the output may be return air that is conditioned with cooling, heat, or outside air. A damper may be situated at the input of outside air to the mixed air box. A temperature sensor may be positioned at the input for outside air and at the output of discharge air. A cooling mechanism may be at the output of the discharge air. The temperature sensor may be downstream from the cooling mechanism. An economizer may have connections with the damper, the temperature sensor and the cooling mechanism.
1. A heating, ventilation and air conditioning system comprising:
a mixed air box;
an outside air duct connected to the mixed air box;
a return air duct connected to the mixed air box;
a discharge air duct connected to the mixed air box;
an air mover situated in the discharge air duct;
a damper situated between the outside air duct and the mixed air box;
a cooling coil situated in the discharge air duct downstream from the mixed air box;
an outside air temperature sensor situated in the outside air duct;
a mixed air temperature sensor situated in the discharge air duct downstream from the cooling coil; and
an economizer connected to the damper, the cooling coil, the outside air temperature sensor and the mixed air temperature sensor; and
wherein:
the economizer compares an outside air temperature from the outside air temperature sensor with a mixed air temperature from the mixed air temperature sensor; and
if the mixed air temperature is lower than the outside air temperature, then modulation of the damper by the economizer is based on the outside air temperature.
2. The system of claim 1 , wherein the cooling coil can be activated only when the damper is open.
3. The system of claim 1 , wherein outside air is used for economizing when the outside air can be used for cooling return air.
4. The system of claim 3 , wherein when the outside air is used for economizing and the mixed air temperature is lower than the outside air temperature, then economizer can modulate the damper to be open even when the cooling coil is activated.
5. The system of claim 3 , wherein if the mixed air temperature is higher than the outside air temperature, then the economizer will modulate the damper according to the mixed air temperature whether or not the outside air is used for economizing.
6. The system of claim 5 , wherein if the cooling coil is activated, then the economizer will modulate the damper to stay open.
7. The system of claim 3 , wherein when the outside air is used for economizing, the mixed air temperature cannot be lower than the outside air temperature without activation of the cooling coil if in the mixer air box there is outside air mixed with return air from the return air duct that is warmer than the outside air.
8. The system of claim 7 , wherein the discharge air duct and the return air duct are connected to one or more spaces of a building.