exposing the bypass passages 18 22 with perforated plate 34 thereacross in this position all of the volume of incoming air will pass through the bypass passages and none through the conditioning cores reference is now made to fig2 4 and 5 for a brief explanation of how the moveable panels 36 46 are positioned and moved it is evident that the panels may be slidably mounted and moved in any manner for example the panels could be mounted on rollers on either single or double tracks and moved by any desired mechanical or electrical means the panels could be manually driven gear driven pneumatically driven or electrically driven in a preferred embodiment the moveable panels 36 46 are slidably mounted on track assembly 48 which consists of upper 58 and lower 60 guide tracks see fig1 as well preferably the panels ride on v groove rollers 62 mounted to the upper and lower ends of each panel 36 48 which ride in v groove tracks 64 and 66 respectively on the upper guide rail 58 and lower guide rail 60 preferably a linear actuator 68 fig3 may be employed to move the moveable panels between the first and second positions although any type of actuator may be employed the position of moveable panels 36 46 can be determined in any convenient manner as will be evident to one of ordinary skill in the hvac art sensors not shown may be used to sense the temperature and humidity level of incoming air as well as air down stream of the air handling and conditioning unit which is to be distributed in the building a microprocessor not shown processes the data from the upstream and downstream sensors and issues a control signal to the linear actuator 68.