Demand ventilation HVAC system comprising independently variable refrigerant flow (VRF) and variable air flow (VAF)

1. A dedicated outdoor air system (DOAS) comprising a plurality of evaporator coils each with independent refrigerant control configured to independently vary refrigerant flow for each of the evaporator coils to maintain a desired evaporator coil temperature; independent activation of evaporator coil surface for each of the plurality of evaporator coils; and, at least one block-off element disposed for independent adjustment of airflow for each of the plurality of evaporator coils, wherein the system is configured to obtain free cooling by positioning the block-off element to direct ventilation air to bypass active evaporator coil surface.

2. The dedicated outdoor air system (DOAS) of claim 1 wherein block-off element position is controlled by a demand volume of supply air, a cooling load of the demand air volume or an outdoor humidity level.

3. The dedicated outdoor air system (DOAS) of claim 1 wherein the system maintains an about 45° F. evaporator coil temperature.

4. The dedicated outdoor air system (DOAS) of claim 1 wherein the block-off element is a linearly positioned sliding block-off element disposed for independent adjustment of airflow and independent activation of evaporator coil surface.

5. The dedicated outdoor air system (DOAS) of claim 1 wherein the system comprises about 3 to 10 stacked evaporator coils.

6. The dedicated outdoor air system (DOAS) of claim 5 wherein the system comprises 5 stacked evaporator coils.

7. The dedicated outdoor air system (DOAS) of claim 6 wherein the system comprises at least one variable refrigerant flow compressor.

8. The dedicated outdoor air system (DOAS) of claim 1 wherein the system is configured such that a first portion of supply air is partly passed over an energized cold deck of an activated evaporator coil and a second portion of supply air by-passes the activated evaporator coil while maintaining a desired supply air dew point.

9. The dedicated outdoor air system (DOAS) of claim 1 wherein the system comprises a fixed capacity vapor compression system.

10. The dedicated outdoor air system (DOAS) of claim 1 wherein the system is structurally capable of providing constant dew point leaving air.

11. The dedicated outdoor air system (DOAS) of claim 10 wherein the system comprises a plurality of evaporators and the constant dew point leaving air is obtained by selectively controlling variable air flow and variable refrigerant flow based on the heat load presented to each active evaporator.

12. The dedicated outdoor air system (DOAS) of claim 1 wherein the system is located within a single housing and the block-off element is a shutter or damper disposed to move up and down a front side of the housing, wherein the front side of the housing receives air flow.

13. The dedicated outdoor air system (DOAS) of claim 12 wherein the shutter or damper is a motor driven shutter or damper with a linear positioner.

14. The dedicated outdoor air system (DOAS) of claim 1 wherein each evaporator coil is disposed within an independent compartment and each independent compartment comprises an intermediate drain pan.

15. The dedicated outdoor air system (DOAS) of claim 1 wherein heat transfer in each active evaporator coil is maintained with an electronic expansion valve operably connected to a system controller.

16. A method comprising manufacturing a system according to claim 1 .

17. The dedicated outdoor air system (DOAS) of claim 1 , wherein the system is located within a single housing and further comprises a directional air flow exposure valve comprising a plurality of dampers each configured to independently open and close as directed by a system controller.

18. The dedicated outdoor air system (DOAS) of claim 17 , wherein the system is located within a single housing, each evaporator coil is disposed within an independent compartment, and each of the plurality of dampers is configured to independently open and close as directed by the system controller to independently address a corresponding evaporator coil.

19. The dedicated outdoor air system (DOAS) of claim 18 , wherein each independent compartment comprises an intermediate drain pan.

20. The dedicated outdoor air system (DOAS) of claim 1 , wherein a system controller positions a directional air flow exposure valve to shunt bypass air to obtain a desired mixed leaving air temperature and relative humidity.

21. A method comprising using a system according to claim 1 .